Organic carbon deposition on the North Carolina continental slope off Cape Hatteras (USA) - Thomas, C. J.; Blair, N. E.; Alperin, M. J.; DeMaster, D. J.; Jahnke, R. A.; Martens, C. S.; Mayer, L. (Deep-Sea Research Part Ii-Topical Studies in Oceanography, 2002)
The continental slope off Cape Hatteras, NC is a region of high sediment accumulation and organic matter deposition. Sediment accumulation rates range from 3 to 151 cm kyr(-1). Organic carbon deposition rates are 5-13 moles C m(-2) yr(-1), the highest reported for the slope off the eastern US. Burial efficiencies are 3-40%. The organic matter deposited is marine in origin and a mix of old and young particles. High organic carbon deposition rates support remineralization throughout the upper 2-3 m of sediment. Deep bioirrigation to depths of 60-100 cm within the seabed affects the biogeochemistry of the sediments by extending the zone of sulfate reduction and by steepening DIC porewater gradients through the non-local exchange of porewater. Stable and radiocarbon isotope mixing curves for porewater dissolved inorganic carbon (DIC) indicate that the dominant source of DIC accumulating in the upper 2-3 m of the seabed is of nearly uniform delta(13)C (-21.10parts per thousand) and Delta(14)C (-546parts per thousand.). (C) 2002 Elsevier Science Ltd. All rights reserved.
607kxTimes Cited:31 Cited References Count:77
Keywords: anaerobic methane oxidation; early diagenesis; margin; marine-sediments; MATTER; middle-atlantic-bight; sea-floor; shelf; south; waters

Ostracoda and paleoceanography - Cronin, T. M.; Boomer, I.; Dwyer, G. S.; Rodriguez-Lazaro, J. (American Geophysical Union Monograph - The Ostracoda: Applications in Quaternay Research, 2002)
id: 1473

Paleoceanographic proxies in Long Island Sound, CT, USA - Thomas, E.; Lugolobi, F.; Varekamp, J. C. (Geochimica Et Cosmochimica Acta, 2002)
Suppl. 1583rx Times Cited:0 Cited References Count:0

Paleoenvironmental history of Long Island Sound - Varekamp, J. C.; Thomas, E.; Lugolobi, F.; Buchholtz ten Brink, M. R. (Long Island Sound/NEERS Research Conference AGU Fall Meeting, 2002)
id: 1177

Plans for expanded 14C analyses at the NOSAMS facility - a status and progress report - von Reden, K. F.; Donoghue, J.; Elder, K.; Gagnon, A.; Gerlach, D.; Griffin, V.; Healy, R.; Long, P.; McNichol, A.; Percy, D.; Roberts, M. L.; Schneider, R. J.; et al. (International Conference on Accelerator Mass Spectrometry, 2002)
id: 1685

Pleistocene chronology of continental margin sedimentation: New insights into traditional models, New Jersey - McHugh, C. M. G.; Olson, H. C. (Marine Geology, 2002)
Commonly accepted models for the evolution of continental margins link sediment erosion, transport and deposition to eustasy. To test these models, we constructed an oxygen isotope record from 520 m of Pleistocene sediment recovered by the Ocean Drilling Program Leg 174A from the New Jersey continental slope. The delta(18)O record was calibrated to SPECMAP oxygen isotope time scale [Imbrie et al. (1984), in: Berger et al. (Eds.), Milankovitch and Climate, 269-305] with radiocarbon ages, nannoplankton biostratigraphy, magnetostratigraphy, and opal and calcium carbonate stratigraphy. Sixteen glacial/interglacial fluctuations of global ice volume have been recorded in the Pleistocene: oxygen isotope stages (OIS) 1 (partial), 2-4, 5 (partial) and 8 throughout 18. Contrary to predicted sedimentation models, a classification of mass-wasting deposits, based on variations in the styles of soft-sediment deformation and grain size, shows that: (1) mass-wasting is not restricted to glacial times but is present during both glacial and interglacial stages; (2) glacial stages are dominated by fine-grained sediments some of which were deposited by gravity flows; and (3) the transitions from glacial to interglacial stages are characterized by the deposition of coarse sands. The sedimentary record shows large-scale trends that do not fit the traditional models of higher glacial sedimentation rates since there is no consistent variation in sediment accumulation between glacial and interglacial stages. Instead there are longer-term sedimentation patterns. Uniform sedimentation rates of 62 cm/kyr characterize the early middle Pleistocene (OIS 12-18), followed by varying rates from low to very high for three consecutive time periods: OIS 11 to 9 (98-560 cm/kyr), OIS 8 (52-560 cm/kyr), and OIS 5 to 2 (37-353 cm/kyr). Each of these depositional units is contained within one seismic-stratigraphic sequence and bounded by sequence boundaries. Their deposition was influenced by the supply of sediment rather than eustasy. Sediment supply was modulated by: (1) the transition from the dominance of obliquity to that of eccentricity (OIS 18-12 to OIS 11-1); and (2) the proximity of the ice sheet (located similar to 150 km away from the paleoshoreline during the last glacial maximum). (C) 2002 Elsevier Science B.V. All rights reserved.
582qnTimes Cited:33 Cited References Count:89
Keywords: baltimore canyon; coastal-plain; glacioeustasy; global sea-level; isotopes; late quaternary sedimentation; mass-wasting; new-york; north-atlantic; northwest atlantic; passive margin; Pleistocene; sedimentary processes; sequence stratigraphy; shelf; slope

Possible biological or physical explanations for decadal scale trends in North Pacific nutrient concentrations and oxygen utilization - Keller, K.; Slater, R. D.; Bender, M.; Key, R. M. (Deep-Sea Research Part Ii-Topical Studies in Oceanography, 2002)
We analyze North Pacific GEOSECS (1970s) and WOCE (1990s) observations to examine potential decadal trends of the marine biological carbon pump. Nitrate concentrations ([NO3]) and apparent oxygen utilization (AOU) decreased significantly in intermediate waters (by -0.6 and -2.9 mu mol kg(-1) respectively, at sigma (theta) = 27.4 kg m(-3), corresponding to approximate to 1050 m). In shallow waters (above roughly 750 m) [NO3-] and AOU increased, though the changes were not statistically significant. A sensitivity study with an ocean general circulation model indicates that reasonable perturbations of the biological carbon pump due to changes in export production or remineralization. efficiency are insufficient to account for the intermediate water tracer trends. However, changes in water ventilation rates could explain the intermediate water tracer trends and would be consistent with trends of water age derived from radiocarbon. Trends in AOU and [NO3-] provide relatively poor constraints on decadal scale trends in the marine biological carbon pump for two reasons. First, most of the expected changes due to decadal scale perturbations of the marine biota occur in shallow waters, where the available data are typically too sparse to account for the strong spatial and temporal variability. Second, alternative explanations for the observed tracer trends (e.g., changes in the water ventilation rates) cannot be firmly rejected. Our data analysis does not disprove the null-hypothesis of an unchanged biological carbon pump in the North Pacific. (C) 2001 Published by Elsevier Science Ltd.
507ceTimes Cited:24 Cited References Count:71
Keywords: anthropogenic co2 invasion; atmospheric co2; carbon-cycle; el-nino; hydrographic data; organic-matter; redfield ratios; sargasso-sea; subtropical gyre; vertical fluxes

Precambrian marine carbonate isotope database: Version 1.1 - Shields, G.; Veizer, J. (Geochemistry Geophysics Geosystems, 2002)
[1] We present a compilation of strontium, carbon, and oxygen isotope compositions of roughly 10,000 marine carbonate rocks of Archean - Ordovician age (3800 Ma - 450 Ma). The Precambrian Marine Carbonate Isotope Database (PMCID) has been compiled from 152 published and 3 unpublished articles and books of the past 40 years. Also included are 30 categories of relevant "metadata'' that allow detailed comparisons and quality assessments of the isotope data to be made. The PMCID will be updated periodically as new data and better age constraints come to light. Here we outline the structure of the first published version of the database and its inherent merits and limitations.
561enTimes Cited:103 Cited References Count:26
Keywords: 1010 geochemistry : chemical evolution; 1030 geochemistry : geochemical cycles (0330); 1040 geochemistry : isotopic composition/chemistry; 1050 geochemistry : marine geochemistry (4835,4850); calcite; carbonates; cycle; dolomite; evolution; Geochemistry; isotope stratigraphy; oceans; precambrian; SEAWATER; sediments; strontium; sulfur; time

Prehistoric cereamics in the upper James River region of the northeastern plains - Toom, Dennis L.; Schneider, Frederick E. (Conference on the ceramics of the northeastern plains and adjacent areas, 2002)
id: 1436

Prehistoric horticulture in the northeastern plains - Schneider, Frederick E. (Plains Anthropologist, 2002)
id: 1437

Radiocarbon analysis, calibration and applications - Kromer, B.; Hughen, K. (Current methods in geochronology: Temporal resolution in geology, palaeontology, archaeoloty, and anthropology, 2002)
id: 326

Radiocarbon as a tool to apportion the sources of polycyclic aromatic hydrocarbons and black carbon in environmental samples - Reddy, C. M.; Pearson, A.; Xu, L.; McNichol, A. P.; Benner, B. A.; Wise, S. A.; Klouda, G. A.; Currie, L. A.; Eglinton, T. I. (Environmental Science & Technology, 2002)
To determine the relative inputs of polycyclic aromatic hydrocarbons (PAHs) and black carbon (BC) in environmental samples from the combustion of fossil fuels and biomass we have developed two independent analytical methods for determining the C-14 abundance of PAHs and BC. The 5730 yr half-life of C-14 makes it an ideal tracer for identifying combustion products derived from fossil fuels (C-14-free) versus those stemming from modern biomass (contemporary C-14). The C-14 abundance of PAHs in several environmental Standard Reference Materials was measured by accelerator mass spectrometry after extraction and then purification by high-performance liquid chromatography and preparative capillary gas chromatography. This method yields pure compounds that allow for a high degree of confidence in the C-14 results. The PAHs data were then used to compare and evaluate results from an operationally defined thermal oxidation method used to isolate a BC fraction. The C-14 compositions of PAHs and BC were very similar and suggest that the thermal oxidation method employed for isolating BC is robust and free from interferences by non-BC components. In addition, these data indicate that both the PAHs and the BC species derive mostly from fossil fuels and/or their combustion products.
541gfTimes Cited:133Cited References Count:59

Radiocarbon content of synthetic and natural semi-volatile halogenated organic compounds - Reddy, C. M.; Xu, L.; Eglinton, T. I.; Boon, J. P.; Faulkner, D. J. (Environ Pollut, 2002)
Some halogenated organic compounds, such as polychlorinated biphenyls (PCBs), polychlorinated dibenzo-p-dioxins (PCDDs) and polybrominated diphenyl ethers (PBDEs), have been suggested to have natural sources but separating these compounds from their commercially synthesized counterparts is difficult. Molecular-level 14C analysis may be beneficial since most synthetic compounds are manufactured from petrochemicals (14C-free) and natural compounds should have "modern" or "contemporary" 14C levels. As a baseline study, we measured, for the first time, the 14C abundance in commercial PCB and PBDE mixtures, a number of organochlorine pesticides, as well as one natural product 2-(3',5'-dibromo-2'-methoxyphenoxy)-3,5-dibromoanisole. The latter compound was isolated from a marine sponge and is similar in structure to a PBDE. All of the synthetic compounds were 14C-free except for the pesticide toxaphene. which had a modern 14C abundance, as did the brominated natural compound. The result for toxaphene was not surprising since it was commercially synthesized by the chlorination of camphene derived from pine trees. These results suggest that measuring the 14C content of halogenated organic compounds may be quite useful in establishing whether organic compounds encountered in the environment have natural or synthetic origins (or both) provided that any synthetic counterparts derive from petrochemical feedstock.
Reddy, Christopher MXu, Li Eglinton, Timothy I Boon, Jan P Faulkner, D John eng Research Support, Non-U.S. Gov't Research Support, U.S. Gov't, Non-P.H.S. England 2002/10/25 04:00 Environ Pollut. 2002;120(2):163-8.
Keywords: Animals; Carbon Radioisotopes/*analysis; Environmental Pollutants/*analysis; Hydrocarbons, Halogenated/chemical synthesis/*chemistry; Insecticides/chemistry; Polychlorinated Biphenyls/chemistry; Porifera/*chemistry; Toxaphene/chemistry

Radiocarbon dates bason on organic matter in diatom frustules, Abstract - Donoghue, Joanne C.; Hayes, John M.; Manganini, Steven J.; Francois, Roger (EOS. Trans. AGU, 2002)
OS42E-156
id: 1720

Radiocarbon Dates of Corals, Gastropods and Forminifers from Saurashtra Peninsula, Gujarat and Their Implications for Sea-level Studies - Mathur, U. B.; Pandey, D. K. (Journal Geological Society of India, 2002)
id: 1219

Radiocarbon dating, chronologic framework, and changes in accumulation rates of Holocene estuarine sediments from Chesapeake Bay - Colman, S. M.; Baucom, P. C.; Bratton, J. F.; Cronin, T. M.; McGeehin, J. P.; Willard, D.; Zimmerman, A. R.; Vogt, P. R. (Quaternary Research, 2002)
Rapidly accumulating Holocene sediments in estuaries commonly are difficult to sample and date. In Chesapeake Bay, we obtained sediment cores as much as 20 m in length and used numerous radiocarbon ages measured by accelerator mass spectrometry methods to provide the first detailed chronologies of Holocene sediment accumulation in the bay. Carbon in these sediments is a complex mixture of materials from a variety of sources. Analyses of different components of the sediments show that total organic carbon ages are largely unreliable, because much of the carbon (including coal) has been transported to the bay from upstream sources and is older than sediments in which it was deposited. Mollusk shells (clams, oysters) and foraminifera appear to give reliable results, although reworking and burrowing are potential problems. Analyses of museum specimens collected alive before atmospheric nuclear testing suggest that the standard reservoir correction for marine samples is appropriate for middle to lower Chesapeake Bay. The biogenic carbonate radiocarbon ages are compatible with (210)Pb and (137)Cs data and pollen stratigraphy from the same sites.Post-settlement changes in sediment transport and accumulation is an important environmental issue in many estuaries, including the Chesapeake. Our data show that large variations in sediment mass accumulation rates occur among sites. At shallow water sites, local factors seem to control changes in accumulation rates with time. Our two relatively deep-water sites in the axial channel of the bay have different long-term average accumulation rates, but the history of sediment accumulation at these sites appears to reflect overall conditions in the bay. Mass accumulation rates at the two deep-water sites rapidly increased by about fourfold coincident with widespread land clearance for agriculture in the Chesapeake watershed.
517wpTimes Cited:57Cited References Count:33

Radiocarbon dating of alkenones in sediments from the Namibian continental margin - Mollenhauer, Gesine; Eglinton, Timothy I.; Ohkouchi, Nao; Grootes, Pieter M.; Muller, Peter J.; Rullkotter, Jurgen; Schneider, Ralph R. (European Geophysical Society, XXVII General Assembly, 2002)
id: 546

Radiocarbon in a Fanning Island coral: Inter-decadal variability in waters upwelling in the central equatorial Pacific from 1922-1955 - Grottoli, A. G.; Gille, S. T.; Druffel, E. R. M.; Dunbar, R. B. (ALSO/AGU Ocean Sciences Meeting, 2002)
id: 658

Radiochemical measurements from FOODBANCS: Examining carbon cycling and benth-pelagic coupling on the Antarctic continental shelf - DeMaster, D. J.; Thomas, J.; al, et (AGU/ASLO Ocean Sciences Meeting, 2002)
id: 1143

Rainwater as a Removal Mechanism for Fossil Fuel Derived Atmospheric Organic Carbon - Avery, Brooks (2002)

Rapid isolation of biomarkers for compound specific radiocarbon dating using high-performance liquid chromatography and flow injection analysis - atmoospheric pressure chemical ionisation mass spectrometry - Smittenberg, R. H.; Hopmans, E. C.; Schouten, S.; Sinninghe-Damste, J. S. (Journal of Chromatography A, 2002)
id: 669

Rate of plate creation and destruction: 180 Ma to present - Rowley, D. B. (Geological Society of America Bulletin, 2002)
One of the primary measures of plate tectonics is the history of production of new oceanic lithosphere. As shown by B. Parsons, a direct estimate of the rate of plate creation can be derived from the area/age versus age distribution of the modern oceanic lithosphere. Inversion of the most recent area versus age data (digital isochrons by R.D. Muller et al.) yields a result that the rate of oceanic plate production has not varied significantly since 180 Ma from a mean rate of 3.4 km(2)/yr. Reconstruction of the cumulative area of subducted lithosphere over the past 90 m.y. is in excellent agreement with a fixed rate of ridge production. The conclusion that the rate of ridge production has not varied significantly contrasts markedly with most existing estimates in which the rate is modeled as decreasing by 50% or more since ca. 100 Ma. A constant rate of ridge production has important implications for models of sea level and p(CO2), among other phenomena that have been linked to variations in global rates of seafloor spreading.
583daTimes Cited:142Cited References Count:20

Rates of evolution in ancient DNA from Adelie penguins - Lambert, D. M.; Ritchie, P. A.; Millar, C. D.; Holland, B.; Drummond, A. J.; Baroni, C. (Science, 2002)
Well-preserved subfossil bones of Adelie penguins, Pygoscelis adeliae, underlie existing and abandoned nesting colonies in Antarctica. These bones, dating back to more than 7000 years before the present, harbor some of the best-preserved ancient DNA yet discovered. From 96 radiocarbon-aged bones, we report large numbers of mitochondrial haplotypes, some of which appear to be extinct, given the 380 living birds sampled. We demonstrate DNA sequence evolution through time and estimate the rate of evolution of the hypervariable region I using a Markov chain Monte Carlo integration and a least-squares regression analysis. Our calculated rates of evolution are approximately two to seven times higher than previous indirect phylogenetic estimates.
Lambert, D MRitchie, P AMillar, C DHolland, BDrummond, A JBaroni, CengResearch Support, Non-U.S. Gov'tResearch Support, U.S. Gov't, P.H.S.2002/03/23 10:00Science. 2002 Mar 22;295(5563):2270-3.

Reassessment of Lake Victoria–Upper Nile River paleohydrology from oxygen isotope records of lake-sediment cellulose - Beuning, K. R. M.; Kelts, K. R.; Russell, J. M.; Wolfe, B. B. (Geology, 2002)
Reconstruction of lake-water δ18O from analysis of cellulose δ18O in two sediment cores from Lake Victoria, East Africa, shows a large shift to lower values during the terminal Pleistocene. This shift records the transition from closed- to open-basin conditions following desiccation at the Last Glacial Maximum. Although oxygen isotope analysis of cellulose from one core had placed this overflow at 8 ka (7200 14C yr B.P.), reevaluation of the age model for this core, in addition to new stratigraphic and chronological evidence from a second core, suggests that basin overflow was established much earlier, ca. 13 ka. Our refined view of the timing of Lake Victoria overflow inferred from the oxygen isotope records is consistent with other paleolimnological studies, indicating that lake-sediment cellulose is an effective and sensitive isotopic archive of major hydrologic events in this region.
id: 1011
Keywords: cellulose; East Africa; isotope; oxygen; paleohydrology

Sea level rise in Long Island Sound over the last millennium - Thomas, E.; Varekamp, J. C. (Long Island Sound/NEERS Research Conference AGU Fall meeting, 2002)
id: 728

Separating natural and bomb-produced radiocarbon in the ocean: The potential alkalinity method - Rubin, S. I.; Key, R. M. (Global Biogeochemical Cycles, 2002)
[1] The use of radiocarbon (Delta(14)C) as a tracer for oceanic processes generally requires differentiation of naturally occurring radiocarbon from the bomb component produced by atmospheric nuclear weapons testing. We present a new separation method based on the strong linear correlation between Delta(14)C and potential alkalinity. Unlike previous techniques the new algorithm is applicable at all latitudes. Additionally, the potential alkalinity method provides an estimate of surface ocean prebomb Delta(14)C concentrations. Predictions with the technique appear to be unbiased and have uncertainties which are less than previous techniques.
646xuTimes Cited:44 Cited References Count:35
Keywords: bomb-produced radiocarbon; CO2; indian-ocean; inventory; natural radiocarbon; pacific-ocean; potential alkalinity method; radiocarbon inventory; radiocarbon separation; silicate method; thermocline; ventilation; woce

The Shandong mud wedge and post-glacial sediment accumulation in the Yellow Sea - Liu, J. P.; Milliman, J. D.; Gao, S. (Geo-Marine Letters, 2002)
Two well-defined deltaic sequences in the Bohai Sea and in the South Yellow Sea represent post-glacial accumulation of Yellow River-derived sediments. Another prominent depocenter on this epicontinental shelf, a pronounced clinoform in the North Yellow Sea, wraps around the northeastern and southeastern end of the Shandong Peninsula, extending into the South Yellow Sea. This Shandong mud wedge is 20 to 40 m thick and contains an estimated 300 km(3) of sediment. Radiocarbon dating, shallow seismic profiles, and regional sea-level history suggest that the mud wedge formed when the rate of post-glacial sea-level rise slackened and the summer monsoon intensified, at about 11 ka. Geomorphic configuration and mineralogical data indicate that present-day sediment deposited on the Shandong mud wedge comes not only from the Yellow River but also from coastal erosion and local rivers. Basin-wide circulation in the North Yellow Sea may transport and redistribute fine sediments into and out of the mud wedge.
538tcTimes Cited:56Cited References Count:34

Shelf record of climatic changes in flood magnitude and frequency, north-coastal California - Sommerfield, C. K.; Drake, D. E.; Wheatcroft, R. A. (Geology, 2002)
Continental-shelf deposits off the Eel River, north-coastal California, document a recent increase in the magnitude and frequency of major hydrologic floods (greater than or equal to10 yr recurrence interval). The shelf record reveals a sudden, three-fold increase in sedimentation rate ca. 1954 and a concomitant increase in the frequency of preserved flood beds. Comparison of sedimentary and river-discharge records reveals that major floods after ca. 1950 had a more pronounced effect on coastal sediment delivery and accumulation offshore than previous recorded events of similar magnitude, and that stratigraphic preservation of flood events is highly dependent on flood frequency and net sedimentation rate. We contend that this change in marine sedimentation is a response to documented climatic phenomena that have increased the frequency of major floods throughout the western United States during the past half century, together with intrabasinal impacts of extreme floods in 1955 and 1964. Anthropogenic increase in watershed-sediment production is a probable secondary factor.
551ucTimes Cited:46Cited References Count:34

Slip rates of the Karakorum fault, Ladakh, India, determined using cosmic ray exposure dating of debris flows and moraines - Brown, E. T.; Bendick, R.; Bourles, D. L.; Gaur, V.; Molnar, P.; Raisbeck, G. M.; Yiou, F. (Journal of Geophysical Research-Solid Earth, 2002)
We measure an average slip rate of 4+/-1 mm yr(-1) along the Karakorum fault, heretofore considered one of Earth's greatest strike-slip faults and thought by many to play a key role in Asian deformation kinematics. Levees of a debris flow, and contours of the fan on which it was deposited, have been displaced 40+/-5 m. Concentrations of Be-10 in boulders from the debris flow yield ages of 11-14 ka, implying a slip rate of 4+/-1 mm yr(-1) during that period. A fresher debris flow has been offset 2-2.5 m since 1-2 ka, implying the occurrence of an earthquake with Msimilar to7 since that time. Concentrations of Be-10 in boulders on the crest of the most extensive moraine near Leh imply that the most recent major glacial advance occurred at 90+/-15 ka. This is consistent with the inference of others that alpine glaciers in this region have not necessarily expanded in concert with Northern Hemisphere continental ice sheets. If features, including lateral moraines, that Liu inferred to have been offset 300-350 m by the Karakorum fault date from the same period, they too imply a slip rate of 3-4 mm yr(-1). This slip rate is comparable to rates of extension across grabens within Tibet. With recent evidence that slip along the Altyn Tagh fault occurs at similar to10 mm yr(-1), our rate suggests that slip along the boundaries of Tibet is not significantly more rapid than extension within the plateau. Hence, plate tectonics, in the strictest sense, ought not be applied to Tibet, because Tibet does not behave as a rigid plate.
634wuTimes Cited:104Cited References Count:72

Spatial and temporal offsets between proxy records in a sediment drift - Ohkouchi, N.; Eglinton, T. I.; Keigwin, L. D.; Hayes, J. M. (Science, 2002)
Chronologies for Late Quaternary marine sediment records are usually based on radiocarbon ages of planktonic foraminifera. Signals carried by other sedimentary components measured in parallel can provide complementary paleoclimate information. A key premise is that microfossils and other indicators within a given sediment horizon are of equal age. We show here that haptophyte-derived alkenones isolated from Bermuda Rise drift sediments are up to 7000 years older than coexisting planktonic foraminifera. This temporal offset, which is apparently due to lateral transport of alkenones on fine-grained particles from the Nova Scotian margin, markedly influences molecular estimates of sea surface temperatures. More broadly, the observation raises questions about both the temporal and the geographic delity of paleoenvironmental records encoded by readily transported components of sediments.
612mqTimes Cited:147Cited References Count:38

Stable carbon isotope record in a Palau Sclerosponge - Grottoli, A. G. (Fall AGU, 2002)
id: 657

Stable chlorine and carbon isotopic compositions of selected semi-volatile organochlorine compounds - Drenzek, N. J.; Tarr, C. H.; Eglinton, T. I.; Heraty, L. J.; Sturchio, N. C.; Shiner, V. J.; Reddy, C. M. (Organic Geochemistry, 2002)
To assess whether the isotopic composition of semi-volatile organochlorine compounds (SVOCs) may be a useful tool, we measured the bulk delta(37)Cl and delta(13)C values of several pesticides and Aroclor mixtures from different suppliers. Overall, the delta(37)Cl and delta(13)C values ranged from -5.10 to + 1.22% and -31.63 to -22.39%, respectively. These values are narrower than the ranges observed previously for volatile organic contaminants (VOCs). In particular, the isotopic compositions of the Aroclor mixtures were very tightly constrained for both chlorine and carbon, We also observed that SVOCs synthesized from hexachlorocyclopentadiene had the most enriched delta(37)Cl values. These data provide a baseline for future work employing isotope ratios to study the environmental fate of SVOCs. (C) 2002 Elsevier Science Ltd. All rights reserved.
545bnTimes Cited:41 Cited References Count:25
Keywords: aroclors; fractionation; hydrocarbons; intrinsic bioremediation; samples; solvents; trichloroethene

Stable isotope composition of Littoridina australis from the coast of Buenos Aires province, Argentina, during Holocene climatic fluctuations - Aguirre, M. L.; Zanchetta, G.; Fallick, A. E. (Geobios, 2002)
Stable isotope (carbon and oxygen) analyses were performed on Littoridina australis shells collected from molluscan concentrations within Holocene littoral deposits along the Bonaerensian coastal area of Argentina (south-western Atlantic). Isotope data allow us to define two very different areas: the Samborombon Bay, where isotope composition of shells was mainly governed by mixing between marine and freshwater, and the Mar Chiquita lagoon, where the original brackish environment was dominated by evaporation of water that originated high isotope shell values. In both areas some isotope profiles show short and quite large oscillations in delta(18)O. Their origin may be tentatively explained as due to the changes in moisture regime that control freshwater supply. The results suggest that these deposits can represent natural archives potentially useful for palaeoclimate reconstruction. (C) 2002 Editions scientifiques et medicales Elsevier SAS. All rights reserved.
563lxTimes Cited:9Cited References Count:27
Keywords: Argentina; Holocene; Littoridina australis; Molluscs; Palaeoenvironments; Stable isotopes

Super ENSO and global climate oscillations at millennial time scales - Stott, L.; Poulsen, C.; Lund, S.; Thunell, R. (Science, 2002)
The late Pleistocene history of seawater temperature and salinity variability in the western tropical Pacific warm pool is reconstructed from oxygen isotope (delta18O) and magnesium/calcium composition of planktonic foraminifera. Differentiating the calcite delta18O record into components of temperature and local water delta18O reveals a dominant salinity signal that varied in accord with Dansgaard/Oeschger cycles over Greenland. Salinities were higher at times of high-latitude cooling and were lower during interstadials. The pattern and magnitude of the salinity variations imply shifts in the tropical Pacific ocean/atmosphere system analogous to modern El Nino-Southern Oscillation (ENSO). El Nino conditions correlate with stadials at high latitudes, whereas La Nina conditions correlate with interstadials. Millennial-scale shifts in atmospheric convection away from the western tropical Pacific may explain many paleo-observations, including lower atmospheric CO2, N2O, and CH4 during stadials and patterns of extratropical ocean variability that have tropical source functions that are negatively correlated with El Nino.
Stott, LowellPoulsen, ChristopherLund, SteveThunell, Roberteng2002/07/13 10:00Science. 2002 Jul 12;297(5579):222-6.

Tahuka Site (32SN121) 1998 Archeological Excavations. Anthropology Research, Department of Anthropology, University of North Dakota, Grand Forks (Report) - Toom, Dennis L. (Dakotas Area Office, U. S. Bureau of Reclamation, 2002)
id: 1363

Temporal and regional variability in sources and cycling of DOC and POC in the northwest Atlantic continental shelf and slope - Bauer, J. E.; Druffel, E. R. M.; Wolgast, D. M.; Griffin, S. (Deep-Sea Research II, 2002)
id: 685

Test of negative ion beams from a microwave ion source with a charge exchange canal for accelerator mass spectrometry applications - Kim, S. W.; Schneider, R. J.; von Reden, K. F.; Hayes, J. M.; Wills, J. S. C. (Review of Scientific Instruments, 2002)
A test facility has been constructed to evaluate negative ion beams from small gaseous samples for accelerator mass spectrometry applications. The positive ion beams from the microwave ion source are passed into a charge-exchange canal (CXC) where the ions exchange electrons with magnesium vapor and become negatively charged. Positive molecular ions were: either neutralized or broken up into atomic ions and neutral atoms and molecules by collision processes. Most of the resulting particles were suspected to be neutrals. In studies with injections of CO2 pulses, the resulting positive and negative C-12 current peaks gave a 0.09% yield of C- ions from CO2 molecules, which includes a charge-exchange efficiency of 10%. Since nitrogen does not form a stable negative ion, N-14 background is virtually eliminated after the beam goes through the CXC, which is necessary for radiocarbon measurements. (C) 2002 American Institute of Physics.
2522wyTimes Cited:8Cited References Count:7

U. S. WOCE Indian Ocean survey: Final report for radiocarbon, Ocean Tracer Laboratory Tech. Report #902-1 - Key, R. M.; Quay, P. D. (2002)
id: 528

Uncertainties and novel prospects in the study of the soil carbon dynamics - Wang, Y.; Hsieh, Y. P. (Chemosphere, 2002)
Establishment of the Kyoto Protocol has resulted in an effort to look towards living biomass and soils for carbon sequestration. In order for carbon credits to be meaningful, sustained carbon sequestration for decades or longer is required. It has been speculated that improved land management could result in sequestration of a substantial amount of carbon in soils within several decades and therefore can be an important option in reducing atmospheric CO2 concentration. However, evaluation of soil carbon sources and sinks is difficult because the dynamics of soil carbon storage and release is complex and still not well understood. There has been rapid development of quantitative techniques over the past two decades for measuring the component fluxes of the global carbon cycle and for studying the soil carbon cycle. Most significant development in the soil carbon cycle study is the application of accelerator mass spectrometry (AMS) in radiocarbon measurements. This has made it possible to unravel rates of carbon cycling in soils, by studying natural levels of radiocarbon in soil organic matter and soil CO2. Despite the advances in the study of the soil carbon cycle in the recent decades, tremendous uncertainties exist in the sizes and turnover times of soil carbon pools. The uncertainties result from lack of standard methods and incomplete understanding of soil organic carbon dynamics, compounded by natural variability in soil carbon and carbon isotopic content even within the same ecosystem. Many fundamental questions concerning the dynamics of the soil carbon cycle have yet to be answered. This paper reviews and synthesizes the isotopic approaches to the study of the soil carbon cycle. We will focus on uncertainties and limitations associated with these approaches and point out areas where more research is needed to improve our understanding of this important component of the global carbon cycle.
Wang, YangHsieh, Yuch-Ping eng England 2002/11/15 04:00 Chemosphere. 2002 Dec;49(8):791-804.
Keywords: Carbon Dioxide/chemistry/metabolism; Carbon Radioisotopes/analysis; Carbon/*chemistry/metabolism; Ecosystem; Kinetics; Models, Chemical; Plants/metabolism; Seasons; Soil/*analysis

An unexplored sedimentary record for the study of environmental change in Mediterranean environments: Posidonia oceanica (L.) Delile peats - Mateo, M. A.; Renom, P.; Julià, R.; Romero, J.; Michener, R. (The Study of Environmental Change Using Isotope Techniques. IAEA C&S Papers Series, 2002)
id: 351

The use of carbon isotopes to trace changes in biological oxygen demand in Long Island Sound - Lugolobi, F.; Varekamp, J. C.; Thomas, E. (Long Island Sound/NEERS Research Conference, 2002)
id: 730

Vapour undersaturation in primitive mid-ocean-ridge basalt and the volatile content of Earth's upper mantle - Saal, A. E.; Hauri, E. H.; Langmuir, C. H.; Perfit, M. R. (Nature, 2002)
The analysis of volatiles in magmatic systems can be used to constrain the volatile content of the Earth's mantle and the influence that magmatic degassing has on the chemistry of the oceans and the atmosphere. But most volatile elements have very low solubilities in magmas at atmospheric pressure, and therefore virtually all erupted lavas are degassed and do not retain their primary volatile signatures. Here we report the undersaturated pre-eruptive volatile content for a suite of mid-ocean-ridge basalts from the Siqueiros intra-transform spreading centre. The undersaturation leads to correlations between volatiles and refractory trace elements that provide new constraints on volatile abundances and their behaviour in the upper mantle. Our data generate improved limits on the abundances of carbon dioxide, water, fluorine, sulphur and chlorine in the source of normal mid-ocean-ridge basalt. The incompatible behaviour of carbon dioxide, together with the CO(2)/Nb and CO(2)/Cl ratios, permit estimates of primitive carbon dioxide and chlorine to be made for degassed and chlorine-contaminated mid-ocean-ridge basalt magmas, and hence constrain degassing and contamination histories of mid-ocean ridges.
Saal, Alberto EHauri, Erik HLangmuir, Charles HPerfit, Michael RengEngland2002/10/09 04:00Nature. 2002 Oct 3;419(6906):451-5.

Volcanic gases, black smokers, and the Great Oxidation Event - Holland, H. D. (Geochimica Et Cosmochimica Acta, 2002)
This paper proposes that gradual changes in the composition of volatiles that have been added to the atmosphere-ocean system are responsible for the Great Oxidation Event (G.O.E.) ca. 2.3 Ga. Before ca. 2.3 Ga, the composition of these volatiles was probably such that 20% of the carbon gases could be reduced to organic matter and all of the sulfur gases could be reduced to pyrite. Since 2.3 Ga, the composition of these volatiles has been such that 20% of the carbon gases could be reduced to organic matter, but only a fraction of the sulfur gases could be reduced to pyrite. This change led to the oxygenation of the atmosphere and to a large increase in the SO4-2 concentration of seawater. A considerable body of observational data supports these proposals. Copyright (C) 2002 Elsevier Science Ltd.
608ztTimes Cited:295 Cited References Count:57
Keywords: atmospheric oxygen; carbon; chemistry; east pacific rise; evolution; hydrothermal vent fluids; midocean ridges; precambrian cherts; south-africa; sulfur cycle

Were glacial iceberg surges in the North Atlantic triggered by global climatic warming? - Moros, M.; Kuijpers, A.; Snowball, I.; Lassen, S.; Backstrom, D.; Gingele, F.; McManus, J. F. (Marine Geology, 2002)
id: 712

The West Falmouth oil spill after thirty years: the persistence of petroleum hydrocarbons in marsh sediments - Reddy, C. M.; Eglinton, T. I.; Hounshell, A.; White, H. K.; Xu, L.; Gaines, R. B.; Frysinger, G. S. (Environ Sci Technol, 2002)
The long-term fate of petroleum hydrocarbons in marsh sediments (West Falmouth, MA) contaminated in 1969 by the spill of the barge Florida was investigated. A 36-cm-long sediment core was collected in August 2000, and sediment extracts were analyzed by gas chromatography (GC) and comprehensive two-dimensional gas chromatography (GC x GC). The latter technique is capable of separating 1 order of magnitude more compounds than the former and was used to observe whether any compositional changes in the unresolved complex mixture (UCM) occurred. No evidence of petroleum residues was detected in the top 6 cm (0-6 cm) and the lower 8 cm (28-36 cm) of the core. However, the central sections 16-28 cm) were dominated by a UCM in the boiling range of n-C13-n-C25 alkanes, consistent with a No. 2 fuel oil source. The 12-14- and 14-16-cm sections had the highest concentrations of UCM approximately 8 mg g(-1)). These values are similar to concentrations observed shortly after the spill. Initial GC x GC analysis revealed that only the n-alkanes were completely degraded, and contrary to previous studies, pristane and phytane as well as numerous other branched alkanes are still present in the sediments. These results suggestthatatthis site hydrocarbon contamination will persist indefinitely in the sedimentary record.
Reddy, Christopher MEglinton, Timothy I Hounshell, Aubrey White, Helen K Xu, Li Gaines, Richard B Frysinger, Glenn S eng Research Support, Non-U.S. Gov't Research Support, U.S. Gov't, Non-P.H.S. 2002/12/19 04:00 Environ Sci Technol. 2002 Nov 15;36(22):4754-60.
Keywords: *Accidents; Chromatography, Gas; Environmental Monitoring; Geologic Sediments/*chemistry; Hydrocarbons/*analysis; Massachusetts; Petroleum/*analysis; Ships; Time Factors; Water Pollutants, Chemical/*analysis

WOCE radiocarbon IV: Pacific Ocean results; P10, P13N, P14C, P18, P19 & S4P - Key, R. M.; Quay, P. D.; Schlosser, P.; McNichol, A. P.; von Reden, K. F.; Schneider, R. J.; Elder, K. L.; Stuiver, M.; Ostlund, H. G. (Radiocarbon, 2002)
The World Ocean Circulation Experiment, carried out between 1990 and 1997, provided the most comprehensive oceanic survey of radiocarbon to date. Approximately 10,000 samples were collected in the Pacific Ocean by U.S. investigators for both conventional large volume P counting and small volume accelerator mass spectrometry analysis techniques. Results from six cruises are presented. The data quality is as good or better than previous large-scale surveys. The C-14 distribution for the entire WOCE Pacific data set is graphically described using mean vertical profiles and sections, and property-property plots.
591keTimes Cited:33Cited References Count:56

Woodlands in ancient and modern times in the territory of Sagalassos - Vermoere, M.; Vanhecke, L.; Paulissen, E.; Waelkens, M.; Smets, E. (Sagalassos VI. Report on the survey and excavation campaigns of 1998, 1999 and 2000, 2002)
id: 346

14C-dead living biomass: evidence for microbial assimilation of ancient organic carbon during shale weathering - Petsch, S. T.; Eglington, T. I.; Edwards, K. J. (Science, 2001)
Prokaryotes have been cultured from a modern weathering profile developed on a approximately 365-million-year-old black shale that use macromolecular shale organic matter as their sole organic carbon source. Using natural-abundance carbon-14 analysis of membrane lipids, we show that 74 to 94% of lipid carbon in these cultures derives from assimilation of carbon-14-free organic carbon from the shale. These results reveal that microorganisms enriched from shale weathering profiles are able to use a macromolecular and putatively refractory pool of ancient organic matter. This activity may facilitate the oxidation of sedimentary organic matter to inorganic carbon when sedimentary rocks are exposed by erosion. Thus, microorganisms may play a more active role in the geochemical carbon cycle than previously recognized, with profound implications for controls on the abundance of oxygen and carbon dioxide in Earth's atmosphere over geologic time.
Petsch, S TEglington, T IEdwards, K JengHistorical ArticleResearch Support, Non-U.S. Gov'tResearch Support, U.S. Gov't, Non-P.H.S.2001/04/03 10:00Science. 2001 May 11;292(5519):1127-31. Epub 2001 Mar 29.

A 160,000-year record of tropical climate variability from Salar de Uyuni, Bolivia - Fritz, S. C.; Baker, P. A.; Dwyer, G. S. (EOS, Transactions, American Geophysical Union, 2001)
id: 1474

A 700 year sedimentary record of intense hurricane landfalls in southern New England - Donnelly, Jeffrey P.; Bryant, Sarah Smith; Butler, Jessica; Dowling, Jennifer; Fan, Linda; Hausmann, Neil; Newby, Paige; Shuman, Bryan; Stern, Jennifer; Westover, Karlyn; Webb, Thompson, III (GSA Bulletin, 2001)
id: 1343

Abrupt climate change and pre-Columbian cultural collapse - Brenner, M.; Hodell, D. A.; Curtis, J. H.; Rosenmeier, M.; Binford, M. W.; Abbott, M. B. (Interhemispheric Climate Linkages, 2001)
id: 1408

Accumulation rates and sources of sediments and organic carbon on the Palos Verdes shelf based on multiple radioisotopic tracers (137Cs, 239,240Pu, 210Pb, 234Th, 238U and 14C) - Santschi, P. H.; Guo, L.; Asbill, S.; Allison, M.; Kepple, B.; Wen, L. S. (Marine Chemistry, 2001)
We report here bioturbation and sediment accumulation rates determined from replicate sediment cores at four different sampling sites on the Palos Verdes shelf, Southern California, using bomb fallout and natural radionuclides (137Cs, 239,240Pu, 210Pb, 234Th, and 14C), along with supporting measurements of organic carbon (OC), porosity and granulometry. Present-day particle reworking, on time scales of several months, is restricted to the upper 3 cm, with rates ranging from 13 to 200 cm2/year, as deduced from 234Thxs profiles. There is little evidence that particle reworking reached depths significantly greater than 5 cm. Post-1963 (or post-1971) sediment accumulation rates ranged from 0.7 to 1.4 g/cm2/year (equivalent to 1.1–1.8 cm/year for surficial sediments), as calculated from Pu and Cs isotope profiles, with little change over time or distance from the outfall. Lateral transport of older sediment and multiple sediment sources on the Palos Verdes shelf is suggested from radiocarbon measurements on foraminifera and bulk sedimentary organic matter at two sampling sites, which showed variable, old and refractory sources of OC. Pre-1953 sediments accumulated at rates that were at least 0.4 g/cm2/year (≥0.3 cm/year), based on 210Pbxs dating. Given the abundance of sediment sources to the Palos Verdes shelf, the high sedimentation rates, and shallow particle mixed layers, contaminant-enriched layers should continue to move deeper into the sediments.
id: 1309

Across forests and savannas: Later Stone Age assemblages from Ituri and Semliki, Northeast Domacratic Republic of Congo - Mercader, J.; Brooks, A. (Journal of Antropological Research, 2001)
id: 1217

Algal and archaeal polyisoprenoids in a recent marine sediment: Molecular isotopic evidence for anaerobic oxidation of methane - Bian, L. Q.; Hinrichs, K. U.; Xie, T. M.; Brassell, S. C.; Iversen, H.; Fossing, H.; Jorgensen, B. B.; Hayes, J. M. (Geochemistry Geophysics Geosystems, 2001)
Analyses of C-13 contents of individual organic molecules in a marine sediment show that crocetane, 2,6,11,15-tetramethylhexadecane, an isomer of phytane, is produced by microorganisms that use methane as their main source of carbon. The sediments lie at a water depth of 68 m in the Kattegat, the strait between Denmark and Sweden. Crocetane appears first 185 cm below the sediment-water interface, in the zone marking the transition from sulfate reduction to methanogenesis. Its delta C-13 value is -90 +/- 10 parts per thousand versus Vienna Pee Dee Belemnite (VPDB). Its structure, which includes four isoprene units arranged symmetrically around a tail-to-tail linkage, suggests that it is produced by a member of the archaea. Growing at the intersection of the diffusion gradients for sulfate and methane in sedimentary pore waters, the source organism apparently function as a methane-consuming member of the microbial consortium responsible for the anaerobic oxidation of methane [Hoehler et al., 1994], in which, as first demonstrated quantitatively in these sediments [Iversen and Jorgensen, 1985], electrons are transferred from methane to sulfate. The presence of archaeal biomass throughout the sediment section is indicated by significant concentrations of 2,6,10,15,19-pentamethylicosane (PMI) and of ether-bound phytane and biphytane. The PMI reaches a minimum delta value of -47 parts per thousand well below the transition zone. Its isotopic depletion could reflect either methanogenic or methanotrophic sources. The ether-bound lipids are isotopically uniform throughout the section and are presumed to derive from archaea that utilize a carbon source unaffected by the oxidation of methane.
458jvTimes Cited:51Cited References Count:79

Amino acid composition and diagenesis in the shells of terebratulid brachiopod Bouchardia rosea (SW Atlantic) - Carroll, M.; Kowalewski, M.; Simeos, M. G.; Goodfriend, G. A. (Geological Society of America Abstracts with Programs, 2001)
id: 1417

AMS radiocarbon dating of a shell fishhook from Santa Rosa Island, California - Rick, T. C. (Radiocarbon, 2001)
Several single-piece shell fishhooks from CA-SRI-43 on Santa Rosa Island were dated by association to roughly 5500 cal BP and were argued to be among the oldest specimens in the region. Direct accelerator mass spectrometry (AMS) radiocarbon dating of one of these hooks provided a date of 560 cal BP, however, making it about 5000 yr younger than originally presumed. This younger date is more consistent with the regional shell fishhook chronology and demonstrates the importance of obtaining direct AMS C-14 dates to refine artifact and site chronologies.
458qxTimes Cited:7 Cited References Count:18

The Beadmaker Site: A plains village site at Heart Butte Reservoir, North Dakota - Jackson, Michael L. (2001 Fall meeting of the North Dakota Archeological Association, 2001)
id: 297

Benthic remineralization and burial of biogenic SiO2, CaCO3, organic carbon, and detrital material in the Southern Ocean along a transect at 170oW - Sayles, F. L.; Martin, W. R.; Chase, Z.; Anderson, R. F. (Deep-Sea Res., 2001)
id: 276

Biogenic silica and organic carbon in sediments from the Pacific Sector of the Southern Ocean - Giglio, F.; Langone, L.; Morigi, C.; Frignani, M.; Ravaioli, M. (Antarctic Earth Sciences at the close of a Millenium: Proceedings 8th International Symposium on Artarctic Earth Sciences, 2001)
id: 284

Bomb 14C versus anthropogenic CO2 in OCMIP ocean biogeochemical models - Matsumoto, K.; Sarmiento, J. L.; Key, R. M.; Slater, R. D.; Sabine, C. L. (Global Change Open Science Conference, 2001)
id: 1446

Brachiopod shell taphonomy in subtropical siliciclastic environments: preliminary field results - Simoes, M. G.; Kowalewski, M.; Carroll, M.; Rodland, D. L.; Mello, L. H. C. (Reuniao Anal de Sociedade Brasileira de Paleontologia, Paleo-2001, 2001)
id: 281

A budget of Holocene carbonate sediments, Kailua Bay, Oahu, Hawaiian Islands - Harney, Jodi N.; Fletcher, Charles H. (University of Hawaii, 2001)
id: 329

Carbon dioxide cycling and implications for climate on ancient Earth - Sleep, N. H.; Zahnle, K. (Journal of Geophysical Research-Planets, 2001)
The crustal Urey cycle of CO2 involving silicate weathering and metamorphism acts as a dynamic climate buffer. In this cycle, warmer temperatures speed silicate weathering and carbonate formation, reducing atmospheric CO2 and thereby inducing global cooling. Over long periods of time, cycling of CO2 into and out of the mantle also dynamically buffers CO2. In the mantle cycle, CO2 is outgassed at ridge axes and island arcs, while subduction of carbonatized oceanic basalt and pelagic sediments returns CO2 to the mantle. Negative feedback is provided because the amount of basalt carbonatization depends on CO2 in seawater and therefore on CO2 in the air. On the early Earth, processes involving tectonics were more vigorous than at present, and the dynamic mantle buffer dominated over the crustal one. The mantle cycle would have maintained atmospheric and oceanic CO2 reservoirs at levels where the climate was cold in the Archean unless another greenhouse gas was important. Reaction of CO2 with impact ejecta and its eventual subduction produce even lower levels of atmospheric CO2 and small crustal carbonate reservoirs in the Hadean. Despite its name, the Hadean climate would have been freezing unless tempered by other greenhouse gases.
395tjTimes Cited:185Cited References Count:101

Carbon isotope geochemistry of the Santa Clara River - Masiello, C. A.; Druffel, E. R. M. (Global Biogeochemical Cycles, 2001)
The Santa Clara River is a prototypical small mountainous river, with a headwater height greater than 1000 m and a basin area smaller than 10,000 m(2). Although individual small mountainous rivers export trivial amounts of sediment and carbon to the ocean, as a group these rivers may export a major fraction las much as 50%) of the total global river sediment flux [Milliman and Syvitski, 1992], making their geochemistry relevant the study of the ocean's carbon cycle. In addition, many small rivers export sediment in a few high flux events, causing massive, sporadic discharge of carbon onto coastal shelves, discharge conditions very different from those of large rivers. This class of rivers is an end-member of the river-ocean carbon exchange system, opposite the Earth's largest river, the Amazon. The carbon mass and isotopic properties of the Santa Clara River are significantly different from previously studied large rivers. During the 1997-1998 winter, all Santa Clara carbon pools were old, with flux-weighted average Delta (14)C values of -428 +/- 76 parts per thousand for particulate organic carbon, -73 +/- 31 parts per thousand for dissolved organic carbon, and -644 +/- 58 parts per thousand for black carbon. The age of exported carbon is primarily due to the deep erosion of old soils and not to inclusion of fossil fuel carbon. Additionally, the delta (13)C signatures of exported carbon pools were high relative to terrestrial carbon, bearing a signature quite similar to marine carbon (average particulate organic carbon (POC) delta (13)C = -22.2 +/- 0.8 parts per thousand). The Santa Clara's estuary is small and drains onto the narrow eastern Pacific coastal margin, exporting this old soil organic matter directly into the ocean. If the Santa Clara export patterns are representative of this class of rivers, they may be a significant source of refractory terrestrial carbon to the ocean.
441mbTimes Cited:116Cited References Count:34

Carbon Isotope Ratios of Organic Compound Fractions Separated From Sinking Particulate Organic Matter at a Deep Sea Station in the Northeast Pacific - Druffel, E. R.; Grottoli, A. G.; Gille, S. T.; Dunbar, R. B. (EOS, 2001)
id: 256

Carbonate 14C Background: Does it have Multiple Personalities? - Nadeau, Marie-Josee; Grootes, Pieter M.; Voelker, Antje; Bruhn, Frank; Duhr, Alexander; Oriwall, Angelika (Radiocarbon, 2001)
id: 1501

Chronology of the Palmer Deep Site, Antarctic Peninsula: A Holocene Paleoenvironmental reference for the circum-Antarctic - Domack, E. W.; Leventer, A.; Dunbar, R.; Taylory, R.; Brachfeld, S.; Sjunneskog, C. (The Holocene, 2001)
id: 119

Chronology of the Palmer Deep Site, Antarctic Peninsula: A Holocene Paleoenvironmental reference for the circum-Antarctic - Domack, E. W.; Leventer, A.; Dunbar, R.; Taylor, R.; Brachfeld, S.; Sjunneskog, C. (The Holocene, 2001)
Palmer Deep sediment cores are used to produce the first high-resolution, continuous late Pleistocene to Holocene time-series from the Antarctic marine system. The sedimentary record is dated using accelerator mass spectrometer radiocarbon methods on acid insoluble organic matter and foraminiferal calcite. Fifty-four radiocarbon analyses are utilized in the dating which provides a calibrated timescale back to 13 ka BP. Reliability of resultant ages on organic matter is assured because duplicates produce a standard deviation from the surface age of less than laboratory error (i.e., ±50 years). In addition, surface organic matter ages at the site are in excellent agreement with living calcite ages at the accepted reservoir age of 1260 years for the Antarctic Peninsula. Spectral analyses of the magnetic susceptibility record against the age model reveal unusually strong periodicity in the 400,–200 and 50-70 year frequency bands, similar to other high-resolution records from the Holocene but, so far, unique for the circum-Antarctic. Here we show that comparison to icecore records of specific climatic events (e.g., the ’Little Ice Age‘, Neoglacial, Hypsithermal, and the Bølling/Allerød to Younger Dryas transition) provides improved focus upon the relative timing of atmosphere/ocean changes between the northern anid southern high latitudes.
id: 1319

Climate change in the circum-Caribbean (late Pleistocene-to-Present) and implications for regional biogeography - Curtis, J. H.; Brenner, M.; Hodell, D. A. (Biogeography of the West Indies: Patterns and Perspectives, 2nd Edition, 2001)
id: 265

Climatic significance of large lakes on the Altiplano of South America - Baker, P. A.; Seltzer, G. O.; Fritz, S. C.; Rigsby, C. A.; Dwyer, G. S. (EOS, Transactions, American Geophysical Union, 2001)
id: 333

Comparative analysis of methane-oxidizing archaea and sulfate-reducing bacteria in anoxic marine sediments - Orphan, V. J.; Hinrichs, K. U.; Ussler, W.; Paull, C. K.; Taylor, L. T.; Sylva, S. P.; Hayes, J. M.; DeLong, E. F. (Appl Environ Microbiol, 2001)
The oxidation of methane in anoxic marine sediments is thought to be mediated by a consortium of methane-consuming archaea and sulfate-reducing bacteria. In this study, we compared results of rRNA gene (rDNA) surveys and lipid analyses of archaea and bacteria associated with methane seep sediments from several different sites on the Californian continental margin. Two distinct archaeal lineages (ANME-1 and ANME-2), peripherally related to the order Methanosarcinales, were consistently associated with methane seep marine sediments. The same sediments contained abundant (13)C-depleted archaeal lipids, indicating that one or both of these archaeal groups are members of anaerobic methane-oxidizing consortia. (13)C-depleted lipids and the signature 16S rDNAs for these archaeal groups were absent in nearby control sediments. Concurrent surveys of bacterial rDNAs revealed a predominance of delta-proteobacteria, in particular, close relatives of Desulfosarcina variabilis. Biomarker analyses of the same sediments showed bacterial fatty acids with strong (13)C depletion that are likely products of these sulfate-reducing bacteria. Consistent with these observations, whole-cell fluorescent in situ hybridization revealed aggregations of ANME-2 archaea and sulfate-reducing Desulfosarcina and Desulfococcus species. Additionally, the presence of abundant (13)C-depleted ether lipids, presumed to be of bacterial origin but unrelated to ether lipids of members of the order Desulfosarcinales, suggests the participation of additional bacterial groups in the methane-oxidizing process. Although the Desulfosarcinales and ANME-2 consortia appear to participate in the anaerobic oxidation of methane in marine sediments, our data suggest that other bacteria and archaea are also involved in methane oxidation in these environments.
Orphan, V JHinrichs, K UUssler, W 3rdPaull, C KTaylor, L TSylva, S PHayes, J MDelong, E FengComparative StudyResearch Support, Non-U.S. Gov'tResearch Support, U.S. Gov't, Non-P.H.S.2001/04/03 10:00Appl Environ Microbiol. 2001 Apr;67(4):1922-34.

Composition of hydrothermal vent microbial communities as revealed by analyses of signature lipids, stable carbon isotopes, and Aquificales cultures - Jahnke, Linda L.; Eder, Wolfgang; Huber, Robert; Hope, Janet M.; Hinrichs, Kai-Uwe; Hayes, John M.; Des Marais, David J.; Cady, Sherry L.; Summons, Roger E. (Applied and Environmental Microbiology, 2001)
id: 1783

Compound-specific D/H ratios of lipid biomarkers from sediments as a proxy for environmental and climatic conditions - Sauer, P. E.; Eglinton, T. I.; Hayes, J. M.; Schimmelmann, A.; Sessions, A. L. (Geochimica Et Cosmochimica Acta, 2001)
Hydrogen isotope ratios (D/H) of lipid biomarkers extracted from aquatic sediments were measured to determine whether they can be used as a proxy for D/H of environmental water. Values of deltaD were determined by using a recently developed isotope-ratio-monitoring gas chromatograph-mass spectrometer system (irmGCMS) and were confirmed by conventional hydrogen isotopic measurements (i.e., combustion followed by reduction) on individual compounds isolated by preparative capillary gas chromatography. Diverse lipids (alkanes, n-alkanols, sterols, and pentacyclic triterpenols) were analyzed to examine hydrogen-isotopic controls on lipids of varying origin and biosynthetic pathway. For algal sterols (24-methylcholest-3 beta -ol, 24-ethylcholest-5,22-dien-3 beta -ol, and 4,23,24-trimethylcholesterol, or dinosterol), the fractionation between sedimentary lipids and environmental water was -201 +/- 10 parts per thousand and was similar in both marine and freshwater sites. In a sediment from a small lake in a forested catchment, triterpenols from terrestrial sources were enriched in D by 30 parts per thousand relative to algal sterols. Apparent fractionation factors for n-alkyl lipids were smaller than those of triterpenols and were more variable, probably reflecting multiple sources for these compounds. We conclude that hydrogen-isotopic analyses of algal sterols provide a viable means of reconstructing D/H of environmental waters. Results are less ambiguous than reconstructions based on analyses of kerogen or other operationally defined organic matter fractions. Copyright (C) 2001 Elsevier Science Ltd.
395npTimes Cited:209Cited References Count:64

Contribution of "old" carbon from natural marine hydrocarbon seeps to sedimentary and dissolved organic carbon pools in the Gulf of Mexico - Wang, X. C.; Chen, R. F.; Whelan, J.; Eglinton, L. (Geophysical Research Letters, 2001)
Natural radiocarbon (C-14) abundances and stable carbon isotope (delta C-13) compositions were measured for sediment total organic carbon (TOC), and total lipid fractions of sediments, bottom water, and hydrate-water collected from two hydrocarbon seepage sites in Green Canyon, Northern Gulf of Mexico to determine the contribution of "old" carbon from seeps to sediment TOC and dissolved organic carbon (DOC) pools. Our results indicate that 40-60% of the organic carbon preserved in the sediments and 30% of the DOC in the deep water above the seeps were seep-derived C-14-depleted organic carbon. This new evidence along with our previous studies suggest that natural marine hydrocarbon seepage could be a significant source contributing "old" carbon to the marine environment. Our findings suggest that the global importance and the long-term impact of this contribution to biogeochemical carbon cycling in the ocean need to be more thoroughly investigated.
467jmTimes Cited:20Cited References Count:25

Converting AMS data to radiocarbon values: Considerations and conventions - McNichol, A. P.; Jull, A. J. T.; Burr, G. S. (Radiocarbon, 2001)
We summarize the basic operation of accelerator mass spectrometry (AMS) systems used to measure radiocarbon and discuss the calculations used to convert AMS output to C-14 data.
1531yc Times Cited:24 Cited References Count:19
Keywords: accelerator mass-spectrometry; NOSAMS; ratio

Correction of H3+ contributions in hydrogen isotope ratio monitoring mass spectrometry - Sessions, A. L.; Burgoyne, T. W.; Hayes, J. M. (Anal Chem, 2001)
Two fundamentally different approaches, termed "pointwise" and "peakwise," are currently used to correct hydrogen isotope ratio monitoring data for the presence of H3+ ion contributions. Consideration of the underlying assumptions shows that the peakwise approach is valid only for peaks with the same functional shape and only when background signals do not vary. The pointwise correction is much more versatile and can be used even when peak shapes and sizes, as well as background signals, vary significantly. It is not exact and is limited in accuracy by (1) the signal-broadening effects of electronic time constants, (2) the analog-to-digital conversion frequency, and (3) the highest frequency of the sample signal. To minimize errors for typical gas chromatographic signals, time constants of <500 ms and analog-to-digital sampling intervals of < or =250 ms are needed. Errors are further minimized by matching sample and standard peaks in both amplitude and D/H ratio. Using the pointwise algorithm, we demonstrate that a series of 14 homologous n-alkanes varying in concentration over a 5-fold range can be analyzed with a mean precision of 2.3 per thousand and no systematic errors.
Sessions, A LBurgoyne, T W Hayes, J M eng 2001/02/24 12:00 Anal Chem. 2001 Jan 15;73(2):192-9.

On the d13C:PO4 relationahip in the modern and glacial ocean - Toggweiler, J. R.; Key, R. M.; McNeil, B. (Fall AGU Meeting, 2001)
id: 1447

Dating modern deltas: progress, problems and prognostics - Stanley, D. J. (Annual Review of Earth and Atmospheric Sciences, 2001)
Radiocarbon dating is the method most frequently used to date Holocene deltaic sequences, but less than one quarter of 14C dates are within ±500 years of predicted age. Such dates tend to be unreliable, in other words, often too old and commonly inverted upsection, and core sample dates obtained near deltaic plain surfaces may be as old as mid- to late Holocene. Stratigraphic irregularities result primarily from downslope reworking of upland alluvial sediment, with displacement of “old carbon” in the sediment that accumulates in lower valleys and deltaic plains. Use of dates that are too old results in inaccurately calculated rates (most often too low) of relative sea-level rise and/or land subsidence. More reliable timing of deltaic sediment requires a multiple-method dating approach, including, where possible, identification of associated archaeological material. Developing an accurate dating strategy is a critical step for implementing reliable coastal protection measures needed for the rapidly increasing human populations in these low-lying, vulnerable nearshore settings.
id: 1378

Decadal record of climate variability spanning the last 700 years in the southern tropics of East Africa - Johnson, T. C.; Barry, S. L.; Chan, Y.; Wilkinson, P. (Geology, 2001)
id: 1477

The deglaciation of eastern Maine: in Deglacial history and relative sea-level changes, northern New England and adjacent Canada - Dorion, C. C.; Kaplan, M. R.; Kreutz, K. J.; Balco, G.; Wright, J.; Borns, H. W., Jr. (Deglacial history and relative sea-level changes, northern New England and adjacent Canada, 2001)
id: 1310

Deposition of Bomb C-14 in Continental Slope Sediments: Use of Radiocarbon in Understanding Benthic Food Web Dynamics - DeMaster, D. J.; Blair, N. E.; Smith, C. R.; Fornes, W. L.; Thomas, C. J.; Plaia, G. (Aquatic Sciences Meeting, ASLO, 2001)
id: 1368

Determination of the the H3 factor in hydrogen isotope ratio monitoring mass spectrometry - Sessions, A. L.; Burgoyne, T. W.; Hayes, J. M. (Anal Chem, 2001)
The H3 factor, K, is a parameter required in high-precision, mass spectrometric analyses of hydrogen isotopic abundances. When H2 is used as the sample gas, R* = R - Ki2, where R* is the true HD/H2 ratio, R is the observed (mass 3)/(mass 2) ion-current ratio, and i2 is the ion current at mass 2. Four different methods for the determination of K were defined and tested under conditions characteristic of isotope ratio monitoring systems. Three of these were peak-based. The fourth employed steady flows of H2 from a conventional inlet system. Results obtained using the latter method were more precise (standard deviation of K = 0.1 versus approximately 0.6 ppm mV(-1) for the peak-based methods). However, use of the resulting values of K for correction of isotope ratio monitoring GC/MS results led to systematic errors as large as 9 per thousand, whereas use of the peak-based values led to no systematic errors. Values of K were only weakly dependent on the pressure of He, declining approximately 5% for each 10-fold increase in P(He). Small variations in partial pressures of H2O and CH4, potential contaminants under isotope ratio monitoring conditions, had no significant effect on values of K.
Sessions, A LBurgoyne, T W Hayes, J M eng 2001/02/24 12:00 Anal Chem. 2001 Jan 15;73(2):200-7.

Development of a Carbon Isotope-Based Tracer of Groundwater Fluxes into Estuaries and the Coastal Ocean - McCorkle, D. C.; Gramling, C. M.; Mulligan, A. E.; Woods, T. L. (EOS, 2001)
id: 1409

Diastems and time-averaging: The limits of resolution in stratigraphy and paleontology - Kowalewski, M.; Bambach, R. K. (Geological Society of America Abstracts with Programs, 2001)
id: 282

Drainage of late Wisconsin glacial lakes and the morphology and late quaternary stratigraphy of the New Jersey-southern New England continental shelf and slope - Uchupi, E.; Driscoll, N.; Ballard, R. D.; Bolmer, S. T. (Marine Geology, 2001)
We propose that late Wisconsin deposition and erosion (Hudson Shelf and Block Island valleys) on the shelf and slope from New Jersey to southern New England were a consequence of the catastrophic drainage of glacial lakes behind terminal moraine systems and the huge volume of water stored beneath the Laurentian ice sheet and subsequent erosion of the lake sediments by flash floods. The morphology imparted by glaciation regulated the discharge associated with the ablation of the glaciers. Associated with the deposits west of Hudson Shelf Valley are the remains of mammoth and mastodon which were transported from their living habitats along the lake shores to their present burial sites on the shelf. The floods also triggered gravity flows on the upper continental slope which made possible the transportation of coarse debris over hundreds of km into the deep-sea. That these catastrophic hood morphologies can still be recognized on the middle to outer shelf suggest that much of its surface was little modified during the late Pleistocene/Holocene transgression. Thus the late Pleistocene/Holocene transgression may have been characterized by short periods when sea level rose rapidly allowing for the preservation of relict features. (C) 2001 Elsevier Science B.V. All rights reserved.
400trTimes Cited:50Cited References Count:115

The Effect of Different Acid Treatments on the Radiocarbon Age of Sedimentary Organic Matter - Batista, F; McNichol, A P; Gerlach, D S (EOS, Transactions, American Geophysical Union, 2001)
To date the bulk organic carbon in marine sediments it is necessary to first remove any inorganic carbon present by acidification. We tested three different acid treatments to see how the different methods affected the stable and radio-carbon isotopic values of the remaining organic matter. The standard NOSAMS method is to react the sediment with repeated aliquots of1.2N HCl until no visible dissolution reaction is present. The remaining sediment is then rinsed with distilled water. This method leaves a carbonate-free sediment that is easy to combust but suffers from the possible removal of acid-soluble organic matter. We compared this method to two methods that do not require rinsing of the sediments after acid treatment--a vapor phase acidification method using concentrated HCl (Hedges and Stern, 1984) and an in situ acidification with sulfurous acid (Verardo et al., 1990). Scaling these methods up to deal with the amount of sediment required for a radiocarbon date can present challenges that are not evident when dealing with the small quantities required for a percent organic carbon measurement. Vapor phase acidification of high carbonate sediments leaves hygroscopic salts that can impede sample combustion. Sulfurous acid is a weak acid and it is very difficult to determine when all the carbonate has been removed from a sediment sample. We tested sediments from 6 locations in (or near) the Atlantic Ocean that represented riverine, estuarine, and marine environments as well as a range of both organic and inorganic concentrations. We will present the isotopic results for these sediments and evaluate what is the most appropriate method to use. Hedges J.I. and J.H. Stern (1984) Limnol. Oceanogr. 29, 657-663. Verardo D.J., P.N. Froelich and A. McIntyre (1990) Deep-Sea Res. 37, 157-165.
Date revised - 2007-02-01SuppNotes - Session: OS41A 9 The Truth About Paleoceanographic Proxies - What Are They Really Telling Us III Posters.Last updated - 2016-05-27
Keywords: A, Atlantic; Acidification; Brackish; Brackishwater environment; carbon cycling; Chronostratigraphy; Estuarine sedimentation; organic carbon; organic matter; Palaeoceanography; Radioactivity and radioisotopes; Radiocarbon dating; Sediment chemistry; Stable isotopes

Effects of biosynthesis and physiology on relative abundances and isotopic compositions of alkenones - Gonzalez, E. L.; Riebesell, U.; Hayes, J. M.; Laws, E. A. (Geochemistry Geophysics Geosystems, 2001)
The number of double bonds in long-chain, unsaturated ketones (alkenones) produced by some members of the Haptophyceae is correlated with the ambient temperature at the time of synthesis. For these same organisms the depletion of carbon-13 in biosynthetic products relative to dissolved inorganic carbon is related directly to the specific growth rate and inversely to the concentration of dissolved carbon dioxide. This report summarizes issues relating to the physiology, metabolism, and biochemistry of alkenone producers and how they affect the abundances and isotopic compositions of alkenones. These considerations show that an understanding of cellular responses to parameters governing uptake of inorganic carbon (C-i), isotopic fractionation, growth under diverse nutrient conditions, and genetic variability, both in the field and in culture, is necessary for developing a conceptual understanding of the biological significance of the epsilonp and U-37(K') indices. Emiliana huxleyi is the best known alkenone producer and can serve as a model organism for these studies. This report identifies knowledge gaps and appropriate objectives for both field- and laboratory-based research.
458kdTimes Cited:6 Cited References Count:39
Keywords: algae; alkenones; anhydrase; biogeochemical processes; biosynthesis; calcification; carbon-13; emiliania-huxleyi prymnesiophyceae; fractionation; Haptophytes; inorganic carbon utilization; instruments and techniques; isoprenoid biosynthesis; marine diatom; paleoceanography; photosynthesis; physiology; phytoplankton; sea surface temperature

Estimates of anthropogenic carbon uptake from four three-dimensional global ocean models - Orr, J. C.; Maier-Reimer, E.; Mikolajewicz, U.; Monfray, P.; Sarmiento, J. L.; Toggweiler, J. R.; Taylor, N. K.; Palmer, J.; Gruber, N.; Sabine, C. L.; Le Quere, C.; Key, R. M.; et al. (Global Biogeochemical Cycles, 2001)
We have compared simulations of anthropogenic CO2 in the four three-dimensional ocean models that participated in the first phase of the Ocean Carbon-Cycle Model Intercomparison Project (OCMIP), as a means to identify their major differences. Simulated global uptake agrees to within +/- 19%, giving a range of 1.85 +/-0.35 Pg C yr(-1) for the 1980-1989 average, Regionally, the Southern Ocean dominates the present-day air-sea flux of anthropogenic CO2 in all models, with one third to one half of the global uptake occurring south of 30 degreesS. The highest simulated total uptake in the Southern Ocean was 70% larger than the lowest. Comparison with recent data-based estimates of anthropogenic CO2 suggest that most of the models substantially overestimate storage in the Southern Ocean; elsewhere they generally underestimate storage by less than 20%. Globally, the OCMIP models appear to bracket the real ocean's present uptake, based on comparison of regional data-based estimates of anthropogenic CO2 and bomb C-14. Column inventories of bomb C-14 have become more similar to those for anthropogenic CO2 with the time that has elapsed between the Geochemical Ocean Sections Study (1970s) and World Ocean Circulation Experiment (1990s) global sampling campaigns. Our ability to evaluate simulated anthropogenic CO2 would improve if systematic errors associated with the data-based estimates could be provided regionally.
417rwTimes Cited:187Cited References Count:64

Evaluation of a protocol for the quantification of black carbon in sediments, soils, and aquatic sediments - Gustafsson, O.; Bucheli, T. D.; Kululska, M.; Andersson, C.; Largeau, C.; Rouzard, J. N.; Reddy, C. M.; Eglinton, T. I. (Global Biogeochem. Cycles, 2001)
id: 1439

Fluttuazioni tardo quaternarie dei flussi sedimentari di componenti biogene nel settore pacifico dell'Oceano Meridionale--Thesis - Focaccia, P. (Universita di Balogna, 2001)

Fractionation of the isotopes of carbon and hydrogen in biosynthetic processes - Hayes, John M. (Stable Isotope Geochemistry, Reviews in Mineralogy and Geochemistry, 2001)
id: 1709

Geometry, numerical models and revised slip rates for the Reelfoot blind thrust and truishear fault-propagation fold, New Medrid Seismic zone - Champion, J.; Mueller, K.; Tate, A.; Guccione, M. J. (Engineering Geology, 2001)
The geometry and structural relief of late Holocene sediments folded across the Reelfoot scarp are characterized with trench excavations, shallow borings, a digital elevation model (DEM) of topography and Reelfoot Lake (RL) bathymetry. Results suggest the scarp forms by heterogeneous shear in the forelimb of a fault-propagation fold. Seismic data and the accompanying structural analysis support the argument that the Reelfoot fault does not offset the surface, and that the Reelfoot scarp is a fold limb. Structural relief measured across the Reelfoot scarp is slightly higher than previous determinations and varies from 7 to 11 m along the western shoreline of RL. Numerical models based on trishear kinematics constrain growth of the Reelfoot monocline and indicate that the underlying Reelfoot thrust fault is steeply dipping. The shallowest portion of the central Reelfoot thrust segment dips 75° where the fault tip has propagated upward from 911 m to its current location 465 m beneath the surface. The models indicate that the shallowest section of the southern thrust segment in the Reelfoot thrust system dips even more steeply at 80° but has propagated upward only a few tens of meters to its present location 1016 m beneath the surface. The thrust is flatter at deeper levels based on the location of earthquake hypocenters. Strain across the Reelfoot scarp is partitioned into two or three separate fold scarps that collectively record a late Holocene fault slip rate of 3.9±0.1 mm/yr. The slip rate is based on 9 m of structural relief, the 2290±60 ybp age of folded sediment and a 75° dip for the fault. This implies a rate of horizontal contraction in the seismic zone of ∼1.0 mm/yr. This rate is strongly dependent on the dip of the thrust calculated by the structural analysis. The numerical models argue for reactivation of faults that previously offset Paleozoic strata.
id: 1381

Greenhouse warming and the impact of sea level rise on water resources on the coastal plain of the gulf coast, U.S.A - Carey, Anne (Annual PIs meeting of the DOE National Institute for Global Environmental Change Southeast Regional Center, 2001)
id: 344

Heart Butte Reservoir 1998-2000 Archeological Investigations, Grant County, North Dakota - Jackson, Michael A.; Bales, Jennifer R. (Department of Anthropology, University of North Dakota, Grand Forks, 2001)
id: 200

High frequency dynamics of the East Asian Monsoon during the last 200,000 years - Garidel-Thoron, T. de; Beaaufort, L.; Linsley, B. K.; Dannenmann, S. (Paleoceanography, 2001)
id: 272

The history of South American tropical precipitation for the past 25,000 years - Baker, P. A.; Seltzer, G. O.; Fritz, S. C.; Dunbar, R. B.; Grove, M. J.; Tapia, P. M.; Cross, S. L.; Rowe, H. D.; Broda, J. P. (Science, 2001)
Long sediment cores recovered from the deep portions of Lake Titicaca are used to reconstruct the precipitation history of tropical South America for the past 25,000 years. Lake Titicaca was a deep, fresh, and continuously overflowing lake during the last glacial stage, from before 25,000 to 15,000 calibrated years before the present (cal yr B.P.), signifying that during the last glacial maximum (LGM), the Altiplano of Bolivia and Peru and much of the Amazon basin were wetter than today. The LGM in this part of the Andes is dated at 21,000 cal yr B.P., approximately coincident with the global LGM. Maximum aridity and lowest lake level occurred in the early and middle Holocene (8000 to 5500 cal yr B.P.) during a time of low summer insolation. Today, rising levels of Lake Titicaca and wet conditions in Amazonia are correlated with anomalously cold sea-surface temperatures in the northern equatorial Atlantic. Likewise, during the deglacial and Holocene periods, there were several millennial-scale wet phases on the Altiplano and in Amazonia that coincided with anomalously cold periods in the equatorial and high-latitude North Atlantic, such as the Younger Dryas.
id: 369; Baker, P A Seltzer, G O Fritz, S C Dunbar, R B Grove, M J Tapia, P M Cross, S L Rowe, H D Broda, J P New York, N.Y. Science. 2001 Jan 26;291(5504):640-3.

The Holocene paleolimnology of Lake Issyk-Kul, Kyrgystan: trace element and stable isotope composition of ostracods - Ricketts, R. D.; Johnson, T. C.; Brown, E. T.; Rasmussen, K. A.; Romanovsky, V. V. (Paleogeography, Palaeoclimatology, Palaeocecology, 2001)
The stable isotope and trace element geochemistry of ostracode shells from Lake Issyk-Kul, Kyrgyzstan, provide an important new paleoclimate record for central Asia. The δ18O, δ13C, Sr/Ca, Mg/Ca and U/Ca composition of shells from the species Candona neglecta found in two piston cores constrains the paleohydrology of the lake from 8700 to 1000 calendar yr before present. These data, combined with robust chronologies based on 16 AMS 14C dates, suggest that the region went from a relatively moist climate in the early Holocene to a more arid climate in the late Holocene. Intense freshwater input, presumably glacial runoff, flowed into the lake from 8700 to 8300 cal yr BP as evident from the δ18O and δ13C values. From 8300 to 6900 cal yr BP δ18O and Sr/Ca values indicate that the lake was relatively fresh and an open basin, and U/Ca values suggest that the lake was well-mixed with well-oxygenated bottom waters. There is a transition zone between 6900 and 4900 cal yr BP when δ18O and Sr/Ca values rapidly increase and Mg/Ca and U/Ca values rapidly decrease. During this period the lake evolved from an open, freshwater, well-mixed lake to a closed, more saline, less well-mixed lake. For the remainder of the record δ18O, Sr/Ca, Mg/Ca and U/Ca are relatively constant, implying conditions similar to modern conditions, although the slight increasing trend in Sr/Ca may suggest an increase in salinity over this period. The δ13C values were approximately in equilibrium with atmospheric CO2 in the early part of the record but became relatively negative in the later part of the record. This indicates that the dominant mechanism controlling the isotopic composition of dissolved inorganic carbon shifted from exchange with the atmosphere to variations in biological productivity.
id: 341

Holocene–late Pleistocene non-tropical carbonate sediments and tectonic history of the western rift basin margin of the southern Gulf of California - Halfar, J.; Godinez-Orta, L.; Goodfriend, G. A.; Mucciarone, D. A.; Ingle, J. C.; Holden, P. (Sedimentary Geology, 2001)
Using high-resolution seismic reflection profiling and dating of (1) shallow marine vibracores and (2) sediments collected from uplifted marine terraces we reconstruct the tectonic history and sediment accumulation patterns of Holocene to late Pleistocene warm-temperate to subtropical carbonates in the southern Gulf of California, Mexico. The study was conducted in the vicinity of La Paz where carbonates form along the fault bounded narrow western shelf of the tectonically active Gulf of California rift basin. The non-tropical nature of the setting is responsible for (1) poor cementation of the bioclastic carbonates, and (2) a composition which is dominated by rhodoliths (coralline red algae), corals and mollusks. Unrimmed carbonate flats forming in small pocket bays and a rhodolith bioherm, which has a surface area of more than 20 km2 and is up to 16 m thick, constitute the major carbonate factories. Holocene carbonate accumulation rates were deduced from seismic and core data and are highest on the rhodolith bioherm (260 cm/ka) and in subtidal zones of pocket bays (210 cm/ka), and lowest on the inner and middle shelf (100 cm/ka). Taken together, rates of carbonate accumulation are intermediate in magnitude between higher rates recorded in fully tropical carbonate settings and lower rates typical of cool-water carbonates. Seismic reflection profiles demonstrate that Isla Espiritu Santo in the center of the study area is a west dipping fault block, which is tectonically influenced by two distinct faults, the La Paz and Espiritu Santo faults. The latter fault accommodates at least 700 m of east-side down normal offset, and forms a steep eastern escarpment leading into the La Paz slope basin. Some of the sediments produced in the shallow carbonate factories of the narrow La Paz shelf are transported across this escarpment and are redeposited in the slope basin at a water depth of 750 m. Uranium-series dates of marine terraces exposed on Isla Espiritu Santo indicate that late Pleistocene uplift along the eastern side of the island could be as high as 310 mm/ka whereas downdropping along the western side of the island occurred at a rate of up to 15 mm/ka. Isla Espiritu Santo therefore constitutes part of the uplifted shoulder of the western margin of the Gulf of California rift basin. Patterns of vertical tectonic movements of Isla Espiritu Santo together with fault offsets on the surrounding seafloor and slump features on steep submarine slopes, point to continuous activity of the La Paz and Espiritu Santo faults. Results of this study will assist in recognizing and interpreting similar settings along ancient non-tropical rift basin margins worldwide and especially in the Neogene of the Gulf of California.
id: 1316

Hydrology, vegetation, and climate change in the southern Everglades during the Holocene - Winkler, M. G.; Sanford, P. R.; Kaplan, S. W. (Bulletin of American Paleontology, 2001)
Paleoecological study of 18 AMS-dated sediment cores from the southern Everglades provides evidence of a shifting mosaic of biotic communities in the past similar to those on the Everglades landscape today. Our results also indicate initiation of Everglades peatlands at 5900 yr B. P., the importance of fire (from charcoal analysis) as a structuring agent in the tropical Everglades, evidence of past plant communities (Isoetes marshes) not present in the modern landscape, and the introduction of exotic plants (Schinus, Casuarina, etc.) today. Past vegetation changes are documented by pollen and sclereid changes. Past water level changes are documented by plant community changes, diatom species and habitat changes, sponge spicule changes, and by intervals of peat (wet) or marl (dry) deposition in the sediment cores. Marl deposition dominates today at these sites in the southern Everglades, a long-term trend exacerbated by human impacts. The Everglades may become less complex in the near future as introduced plants outcompete native vegetation and decreased water levels result in decreased peat production. A rewatering plan must include both wet and dry seasonal cycles in order to preserve the shifting mosaic nature of the landscape and to maintain the Everglades as a functional habitat for both plants and animals.
id: 125

Hypothesized climate forcing time series for the last 500 years - Robertson, A.; Overpeck, J.; Rind, D.; Mosley-Thompson, E.; Zielinski, G.; Lean, J.; Koch, D.; Penner, J.; Tegen, I.; Healy, R. (Journal of Geophysical Research-Atmospheres, 2001)
A new compilation of annually resolved time series of atmospheric trace gas concentrations, solar irradiance, tropospheric aerosol optical depth, and stratospheric (volcanic) aerosol optical depth is presented for use in climate modeling studies of the period 1500 to 1999 A.D. Atmospheric CO2 CH4, and N2O concentrations over this period are well established on the basis of fossil air trapped in ice cores and instrumental measurements over the last few decades. Estimates of solar irradiance, ranging between 1364.2 and 1368.2 W/m(2), are presented using calibrated historical observations of the Sun back to 1610, along with cosmogenic isotope variations extending back to 1500. Tropospheric aerosol distributions are calculated by scaling the modern distribution of sulfate and carbonaceous aerosol optical depths back to 1860 using reconstructed regional CO2 emissions; prior to 1860 the anthropogenic tropospheric aerosol optical depths are assumed to be zero. Finally, the first continuous, annually dated record of zonally averaged stratospheric (volcanic) optical depths back to 1500 is constructed using sulfate flux data from multiple ice cores from both Greenland and Antarctica, in conjunction with historical and instrumental (satellite and pyrheliometric) observations. The climate forcings generated here are currently being used as input to a suite of transient (time dependent) paleoclimate model simulations of the past 500 years. These forcings are also available for comparison with instrumental and proxy paleoclimate data of the same period.
456yeTimes Cited:108Cited References Count:89

Identification of a novel alkenone in Black Sea sediments - Xu, L.; Reddy, C. M.; Farrington, J. W.; Frysinger, G. S.; Gaines, R. B.; Johnson, C. G.; Nelson, R. K.; Eglinton, T. I. (Organic Geochemistry, 2001)
We report the identification of a novel long-chain ketone in Holocene Black Sea sediments. Based on chemical properties, and chromatographic and mass spectrometric characteristics, this compound has been identified as a diunsaturated C-36 ethyl ketone. Further analyses indicated the position and configuration of the double bonds, and the novel alkenone was determined to be hexatriaconta-(16E,21E)-dien-3-one. While this compound is present in only trace quantities in Unit I sediments, it is the most abundant alkenone in portions of Unit II. Its presence thus apparently pre-dates the invasion of Emiliania huxleyi in the Black Sea. The down-core profiles and isotopic compositions suggest that the precursor for the C-36:2 alkenone may be distinct from that of the C37-39 alkenones, however the biological origin of this novel compound is presently unknown. (C) 2001 Elsevier Science Ltd. All rights reserved.
id: 1946; PT: J; UT: WOS:000168692100002

The impact of sea ice concentration accuracies on climate model simulations with the GISS GCM - Parkinson, C. L.; Rind, D.; Healy, R. J.; Martinson, D. G. (Journal of Climate, 2001)
The Goddard Institute for Space Studies global climate model (GISS GCM) is used to examine the sensitivity of the simulated climate to sea ice concentration specifications in the type of simulation done in the Atmospheric Model Intercomparison Project (AMIP), with specified oceanic boundary conditions. Results show that sea ice concentration uncertainties of +/-7% can affect simulated regional temperatures by more than 6 degreesC, and biases in sea ice concentrations of +7% and -7% alter simulated annually averaged global surface air temperatures by -0.10 degrees and +0.17 degreesC, respectively, over those in the control simulation. The resulting 0.27 degreesC difference in simulated annual global surface air temperatures is reduced by a third, to 0.18 degreesC, when considering instead biases of +4% and -4%. More broadly, least squares fits through the temperature results of 17 simulations with ice concentration input changes ranging from increases of 50% versus the control simulation to decreases of 50% yield a yearly average global impact of 0.0107 degreesC warming for every 1% ice concentration decrease, that is, 1.07 degreesC warming for the full +50% to -50% range. Regionally and on a monthly average basis, the differences can be far greater, especially in the polar regions, where wintertime contrasts between the +50% and -50% cases can exceed 30 degreesC. However, few statistically significant effects are found outside the polar latitudes, and temperature effects over the nonpolar oceans tend to be under 1 degreesC, due in part to the specification of an unvarying annual cycle of sea surface temperatures. The +/-7% and +/-4% results provide bounds on the impact (on GISS GCM simulations making use of satellite data) of satellite-derived ice concentration inaccuracies, +/-7% being the current estimated average accuracy of satellite retrievals and +/-4% being the anticipated improved average accuracy for upcoming satellite instruments. Results show that the impact on simulated temperatures of imposed ice concentration changes is least in summer, encouragingly the same season in which the satellite accuracies are thought to be worst. Hence, the impact of satellite inaccuracies is probably less than the use of an annually averaged satellite inaccuracy would suggest.
id: 1944; PT: J; UT: WOS:000169239100008

Implications of the carbon isotope and mineral inclusion record for the formation of diamonds in the mantle underlying a mobile belt: Venetia, South Africa - Deines, P.; Viljoen, F.; Harris, J. W. (Geochimica Et Cosmochimica Acta, 2001)
A total of 199 diamonds from the Venetia kimberlite, South Africa, whose mineral inclusion chemistry had already been measured, were analyzed for their carbon isotopic composition. Silicate inclusions in these diamonds either belong to a peridotitic (P-Type), an eclogitic (E-Type) or transitional, websteritic (W-Type), paragenesis.The carbon isotopic composition of 161 P-Type diamonds ranges from delta C-13 = -2.23 to - 18 parts per thousand vs. PDB. The large number of samples available and the wide range in delta C-13 permitted, for the first time, a detailed analysis of the relationships between P-Type inclusion chemistry and the carbon isotopic composition of the diamond host. The delta C-13 Sampling frequency distribution is multi-modal. Examination of the inclusion chemistry (chromite, olivine, garnet) as a function of the carbon isotope composition mode to which the host belongs, as well as multivariate regression analyses, revealed no correlation between inclusion chemistry and C-13 content. The inclusion compositions in diamonds of low C-13 content are not distinctive. For a given carbon isotopic composition the combination of Ni/Fe and Mg/(Mg + Fe) of olivine inclusions varies systematically along fractionation trends. The composition of the olivine inclusions and the C-13 content of their hosts can be interpreted as reflecting similar petrogenetic processes occurring in several mantle environments into which carbon of variable isotopic composition was introduced. The iron/magnesium distribution between coexisting garnets and olivines permits an estimate of their pressure/temperature equilibration conditions. Diamonds whose inclusions were equilibrated at lower temperatures and pressures tend to have, on average, lower C-13 contents. The compositions of coexisting olivines and chromites suggest oxygen fugacities between 2.9 and 5.8 log units below the quartz-fayalite-magnetite buffer at 50 kbar, and temperatures between 1280 and 1490 degreesC prevailed during diamond formation. Inclusions from diamonds of lower C-13 content do not indicate systematically lower fO(2) values during their formation. The fO(2)/T conditions determined suggest minimal (0.0 to -0.5 parts per thousand) isotope fractionation between a C-H-O vapor phase (carbon dioxide, carbon monoxide, methane, water, hydrogen) and diamond. The large C-13 depletion of some Venetia P-Type diamonds appears to be unrelated to the composition of their inclusions, igneous fractionation trends, oxygen fugacity, and vapor isotope fractionation processes. This conclusion is consistent with evidence deduced from more limited data sets from other kimberlites.
412wtTimes Cited:31Cited References Count:90

Initiation of the Australian summer monsoon 14,000 years ago - Wyrwoll, K. H.; Miller, G. H. (Quaternary International, 2001)
Definitive evidence for the onset of monsoon moisture in northern Australia following the and phase of the Last Glacial Maximum has been elusive, in large part due to the lack of long, continuous sediment records. Here we report new evidence from two separate drainage basins in the Kimberley region of monsoonal northwestern Australia. At both sites, radiocarbon ages on (basal) biogenic materials in flood deposits indicate stream flow, as high or higher than maximum historic levels, began about 14 cal ka BP. These results suggest that the Australian summer monsoon was fully active several millennia earlier than previously expected. The early onset of the monsoon and the widespread evidence for diminished monsoon activity in the late Holocene cannot be reconciled with primary forcing of the Australian monsoon by changes in low-latitude summer insolation over Australia. (C) 2001 Elsevier Science Ltd and INQUA. All rights reserved.
478pnTimes Cited:78Cited References Count:42

Installation of a 134-sample MC-SNICS at the NOSAMS facility and first results - Bellino, Mary; von Reden, Karl F.; Schneider, Robert J.; Long, Patricia Long; Healy, Richard (Symposium of NorthEastern Accelerator Personnel, Oak Ridge National Lab., USA, October 25-28, 1999, 2001)
id: 1718

Isotopes as tracers of the oceanic circulation: results from the world ocean circulation experiment - Schlosser, P.; Jenkins, W. J.; Key, R.; Lupton, J. (International Conference on the Study of Environmental Change Using Isotope Techniques, I.A.E.A., 2001)
id: 318

Isotopic Evolution of the Biogeochemical Carbon Cycle During the Precambrian - Des Marais, David J. (Reviews in Mineralogy & Geochemistry, Stable Isotope Geochemistry, 2001)
id: 1556

The last interglacial to glacial transition, Togiak Bay, Southwestern Alaska - Kaufman, D. S.; Manley, W. F.; Wolfe, A. P.; Hu, F. S.; Preece, S. J.; Westgate, J. A.; Forman, S. L. (Quaternary Research, 2001)
An 18-m-high coastal bluff at Togiak Bay (northwestern Bristol Bay, southwestern Alaska) exposes marine, lacustrine, fluvial, glacial, volcanic, and organic deposits that record the ∼50,000-year-long transition from the peak of the last interglaciation to the early Wisconsin glaciation. The base of the section is dominated by stratified sand and silt extending up to 4.3 m above sea level; marine diatoms are present, and pollen assemblages are characterized by relatively high percentages of Picea, Alnus, and Betula and low percentages of Poaceae and Cyperaceae. The marine sediment was probably deposited during the peak of marine oxygen-isotope stage (OIS) 5e. An infrared stimulated luminescence (IRSL) age of 151,000±13,000 yr from near the base of the exposure is permissive of this correlation. The marine sand and silt are overlain by 0.8 m of peaty silt with diatoms that record a transition from marine to lacustrine conditions. During this interval, Poaceae and Cyperaceae dominate the pollen assemblages, and Picea and shrubs are nearly absent, suggesting that herb tundra occupied the landscape. This interval probably encompasses OIS 5d on the basis of the herb tundra and an IRSL age of 119,000±10,000 yr from 60 cm below the marine/lacustrine transition. The organic mud is overlain by 3.1 m of stratified sand and organic silt that apparently record shallowing of the lake; reappearance of spruce and shrubs (=OIS 5c?); and subsequent deepening of the lake (=OIS 5b?); followed by aggradation of a floodplain (=OIS 5a?), which was dry at the time basaltic lava buried the site. Thermoluminescence analyses on lava-baked sediment indicate that the eruption occurred 70,000±10,000 yr ago. Sometime thereafter, but prior to 53,600 14C yr B.P. an outlet of the Ahklun Mountains ice cap advanced over the site and deposited ∼7 m of bouldery ice-contact drift. The sedimentary sequence contains at least four tephra beds. Major- and trace-element chemistry provide a basis for correlating two of the tephras with tephra beds at nearby sites. The tephras, luminescence ages, and correlations with marine isotope stages provide the geochronological control to place the Togiak Bay section into a global context. The site serves as an important new reference section for late Pleistocene paleoenvironmental change in eastern Beringia.
id: 1392

Late quaternary climate and hydrology of tropical South America inferred from an isotopic and chemical model of Lake Titicaca, Bolivia and Peru - Cross, S. L.; Baker, P. A.; Seltzer, G. O.; Fritz, S. C.; Dunbar, R. B. (Quaternary Research, 2001)
A simple mass balance model provides insight into the hydrologic, isotopic, and chemical responses of Lake Titicaca to past climatic changes. Latest Pleistocene climate of the Altiplano is assumed to have been 20% wetter and 5 degreesC colder than today, based on previous modeling. Our simulation of lacustrine change since 15,000 cal yr B.P. is forced by these modeled climate changes. The latest Pleistocene Lake Titicaca was deep, fresh, and overflowing. The latest Pleistocene riverine discharge from the lake was about 8 times greater than the modern average, sufficient to allow the expansion of the great paleolake Tauca on the central Altiplano. The lake delta O-18 value averaged about -13 parts per thousand SMOW (the modern value is about -4.2 parts per thousand). The early Holocene decrease in precipitation caused Lake Titicaca to fall below its outlet and contributed to a rapid desiccation of paleolake Tauca. Continued evaporation caused the 100-m drop in lake level, but only a slight(1-2 parts per thousand) increase (relative to modern) in delta O-18 Of early Holocene lake waters. This Holocene lowstand level of nearly 100 m was most likely produced by a precipitation decrease, relative to modern, of about 40%, The lake was saline as recently as 2000 cal yr B.P. The timing of these hydrologic changes is in general agreement with calculated changes of insolation forcing of the South American summer monsoon, (C) 2001 University of Washington.
452lzTimes Cited:50Cited References Count:46

Late Quaternary water-level variations and vegetation history at Crooked Pond, southeastern Massachusetts - Shuman, B.; Bravo, J.; Kaye, J.; Lynch, J. A.; Newby, P.; Webb, T. (Quaternary Research, 2001)
Sediment cores collected along a transect in Crooked Pond, southeastern Massachusetts, provide evidence of water-level changes between 15,000 cal yr B.P. and present. The extent of fine-grained, detrital, organic accumulation in the basin, inferred from sediment and pollen stratigraphies, varied over time and indicates low water levels between 11,200 and 8000 cal yr B.P. and from ca. 5300 to 3200 cal yr B.P. This history is consistent with the paleohydrology records from nearby Makepeace Cedar Swamp and other sites from New England and eastern Canada and with temporal patterns of regional changes in effective soil moisture inferred from pollen data. The similarities among these records indicate that (1) regional conditions were drier than today when white pine (Pinus strobus) grew abundantly in southern New England (11,200 to 9500 cal yr B.P.); (2) higher moisture levels existed between 8000 and 5500 cal yr B.P., possibly caused by increased meridonal circulation as the influence of the Laurentide ice sheet waned; and (3) drier conditions possibly contributed to the regional decline in hemlock (Tsuga) abundances at 5300 cal yr B.P. Although sea-level rise may have been an influence, moist climatic conditions during the late Holocene were the primary reason for a dramatic rise in water-table elevations. (C) 2001 University of Washington.
id: 1379; 493FU Times Cited:43 Cited References Count:41

A marine record of holocene climate events in tropical South America - Haug, G. H.; Hughen, K. A.; Sigman, D. M.; Peterson, L. C.; Rohl, U. (Science, 2001)
id: 1466

Metamorphic devolatilization of subducted oceanic metabasalts: implications for seismicity, arc magmatism and volatile recycling - Kerrick, D. M.; Connolly, J. A. D. (Earth and Planetary Science Letters, 2001)
Subducted oceanic metabasalts are believed to be a primary source of volatiles for are magmatism and fluid-induced seismicity. From phase equilibria computed for an average oceanic metabasalt we present a model for subduction zone devolatilization for pressures up to 6 GPa (similar to 180 km). Along high temperature geotherms complete dehydration occurs under forearcs, whereas dehydration does not occur along low temperature geotherms. For intermediate geotherms, major dehydration occurs under subarcs and provides a subjacent H2O source for are volcanism. Decarbonation is negligible along cold and intermediate geotherms and limited along high temperature geotherms. Because decarbonation is limited for all subducted carbonate-bearing lithologies, transfer of CO2 from subducted slabs to are magmas may be triggered by aqueous fluid infiltration. Metabasalt devolatilization could induce seismicity in forearcs (high temperature geotherms) and subarcs (intermediate geotherms); however, because of the lack of devolatilization, metabasalts would not be a fluid source for seismicity with low temperature geotherms. Along low temperature geotherms, limited devolatilization of subducted oceanic metabasalts and marine sediments in forearcs and subarcs provides a mechanism for return of volatiles to the deeper mantle. (C) 2001 Elsevier Science B.V. All rights reserved.
446xmTimes Cited:202Cited References Count:49

Millennial-scale dynamics of the East Asian winter monsoon during the last 200,000 years - de Garidel-Thoron, Thibault; Beaufort, Luc (Paleoceanography, 2001)
id: 251

Multiple anthropogenic tracer distributions in the ocean - Sabine, C. L.; Key, R. M.; Bullister, J. L.; Feely, R. A.; Lamb, M. F.; Millero, F. J.; Wanninkhof, R.; Peng, T. H.; Lee, K.; Kozyr, A.; Gruber, N. (Sixth International CO2 Conference, 2001)
id: 319

A new method for separating bomb-produced and natural D14C, Global Change - Key, R. M. (Open Science Conference, 2001)
id: 1445

New records show pronounced changes in Arctic Ocean circulation and climate (cover article) - Darby, D.; Bischof, J.; Cutter, G.; de Vernal, A.; Hillaire-Marcel, C.; Dwyer, G.; McManus, J.; Polyak, L.; Osterman, L.; Poore, R. (EOS, Transactions, American Geophysical Union, 2001)
id: 332

New techniques define combustion product signatures in sediments - Eglinton, T. I. (Woods Hole Oceanographic Institution 2000 annual report, 2001)
id: 1487

Ocean Circulation and Climate - Schlosser, P.; Bullister, J. L.; Fine, R.; Jenkins, W. J.; Key, R.; Lupton, J.; Roether, W.; Smethie, W. M., Jr. (Observing and Modelling the Global Ocean, 2001)
id: 309

Ocean process tracers: Radiocarbon - Key, R. M. (Encyclopedia of Ocean Sciences, 2001)
id: 310

Ocean Process Tracers: Single compound radiocarbon measurements - Eglinton, T. I.; Pearson, A. (Encyclopedia of Ocean Sciences, 2001)
id: 1420

Oceanic changes in the southern Pacific Ocean during the last deglaciation time, as recorded by planktic foraminifers and oxigen isotopes. --Extended abstract - Morigi, C.; Capotondi, L.; Giglio, F.; Langone, L.; Brilli, M.; Turi, B.; Ravaioli, M. (ANTOSTRAT Symposium on "The geologic record of the Antarctic ice sheet from drilling, coring and seismic studies", 2001)
id: 1428

Optical dating, ages, and scatter from tsunami-laid sands from Bradley Lake, Oregon - Ollerhead, Jeff; Huntley, David J.; Nelson, Alan R.; Kelsey, Harvey M. (Quaternary Science Reviews, 2001)
id: 1406

Optical dating of tsunami-laid sand from an Oregon coastal lake - Ollerhead, J.; Huntley, D. J.; Nelson, A. R.; Kelsey, H. M. (Quaternary Science Reviews, 2001)
Optical ages for five samples of tsunami-laid sand from an Oregon coastal lake were determined using an infrared optical-dating method on K-feldspar separates and, as a test of accuracy, compared to ages determined by AMS C-14 dating or detrital plant fragments found in the same beds. Two optical ages were about 20% younger than calibrated C-14 ages of about 3.1 and 4.3 ka. Correction of the optical ages using measured anomalous fading rates brings them into agreement with the C-14 ages. The approach used holds significant promise for improving the accuracy of infrared optical-dating methods.Luminescence data for the other three samples result in optical age limits much greater than the C-14 ages. These data provide a textbook demonstration of the correlation between scatter in the luminescence intensity of individual sample aliquots and their normalization values that is expected when the samples contain sand grains not adequately exposed to daylight just prior to or during deposition and burial. Thus, the data for these three samples suggest that the tsunamis eroded young and old sand deposits before dropping the sand in the lake. (C) 2001 Elsevier Science Ltd. All rights reserved.
500nqTimes Cited:24Cited References Count:39

Origins of lipid biomarkers in Santa Monica Basin surface sediment: A case study using compound-specific D14C analysis - Pearson, A.; McNichol, A. P.; Benitez-Nelson, B. C.; Hayes, J. M.; Eglinton, T. I. (Geochimica et Cosmochimica Acta, 2001)
id: 1419

Paleoceanographic changes in the Southern Ocean, during the last deglaciation time, as recorded by planktic foraminifers and oxygen isotopes--Poster - Morigi, C.; Capotondi, L.; Giglio, F.; Langone, L.; Turi, B.; Brilli, M.; Ravaioli, M. (ANTOSTRAT Symposium on "The geologic record of the Antarctic ice sheet from drilling, coring and seismic studies"--Poster, 2001)
id: 1424

Paleoclimate through the ages from the Cariaco Basin, Abstract - Hughen, K. A.; Peterson, L. C.; Black, D.; Haug, G.; Poore, R. (American Geophysical Union, 2001)
id: 1467

Paleoproterozoic Huronian basin: product of a Wilson cycle punctuarted by glaciations and a meteorite impact - Young, G. M.; Long, D. G. F.; Fedo, C. M.; Nesbitt, H. W. (Sedimentary Geology, 2001)
The Huronian Supergroup (∼2.4–2.2 Ga) comprises up to 12 km of mainly sedimentary supracrustal rocks. The oldest Huronian unit, the Livingstone Creek Formation, is chemically and mineralogically immature. Significant chemical weathering and deposition of U-rich quartz pebble conglomerates followed deposition of the Livingstone Creek Formation and extrusion of the overlying, rift-related lavas of the Thessalon Formation. Much of the succeeding Huronian comprises climatically(?)-controlled tripartite cycles, each of which begins with glaciogenic diamictites, followed by mudstones and cross bedded arenaceous units. Huronian deposition is interpreted as the result of a partial Wilson cycle, involving rifting and development of a southward-facing passive margin. The ∼2.4 Ga Murray and Creighton granites have been considered by others to be co-eval with an early orogenic episode (Blezardian). Expected unconformities are, however, lacking and these granites, together with co-eval volcanic rocks and abundant soft sediment deformation structures are considered to be due to anorogenic processes during Huronian basin subsidence. The main deformation of the Huronian is probably related to the Penokean orogeny (∼1.89–1.8 Ga). Geochemical investigations have contributed to paleoclimatic and provenance studies and have helped to define basin-wide metasomatic events. A large impact at ∼1.85 Ga likely played an important role in formation of the Sudbury Igneous Complex (SIC) and deposition of fallback breccias of the Onaping Formation (basal Whitewater Group in the Sudbury basin). Overlying sedimentary rocks of the Whitewater Group are considered to be a fortuitously-preserved portion of a widespread flysch apron that spread across the southern margin of the Superior Province as a foreland basin fill, in response to the closure phase of the Wilson cycle during the Penokean orogeny. Geochronological data suggest that these events occurred during the Penokean orogeny.
id: 1606
Keywords: Geochemistry; Glaciation; Impact; Paleoproterozoic; Wilson cycle

Persistent solar influence on North Atlantic climate during the Holocene - Bond, G.; Kromer, B.; Beer, J.; Muscheler, R.; Evans, M. N.; Showers, W.; Hoffmann, S.; Lotti-Bond, R.; Hajdas, I.; Bonani, G. (Science, 2001)
Surface winds and surface ocean hydrography in the subpolar North Atlantic appear to have been influenced by variations in solar output through the entire Holocene. The evidence comes from a close correlation between inferred changes in production rates of the cosmogenic nuclides carbon-14 and beryllium-10 and centennial to millennial time scale changes in proxies of drift ice measured in deep-sea sediment cores. A solar forcing mechanism therefore may underlie at least the Holocene segment of the North Atlantic's "1500-year" cycle. The surface hydrographic changes may have affected production of North Atlantic Deep Water, potentially providing an additional mechanism for amplifying the solar signals and transmitting them globally.
id: 1397; Bond, G Kromer, B Beer, J Muscheler, R Evans, M N Showers, W Hoffmann, S Lotti-Bond, R Hajdas, I Bonani, G New York, N.Y. Science. 2001 Dec 7;294(5549):2130-6. Epub 2001 Nov 15.

Pleistocene glacial history of the southern Ahklun Mountains, southwestern Alaska: Soil-development, morphometric, and radiocarbon constraints - Manley, W. F.; Kaufman, D. S.; Briner, J. P. (Quaternary Science Reviews, 2001)
Four new AMS ages, glacial mapping, and measurements of soil development, loess thickness, and moraine morphology constrain the age and extent of at least three Quaternary advances by outlet lobes of an ice cap over the Ahklun Mountains of southwestern Alaska. The relative-age data are from 107 sites correlated to 25 ice-marginal positions in the Kanektok, Goodnews, Togiak, and Kulukak River valleys and along the southeastern flank of the range. Radiocarbon ages provide minimum ages for six — and a maximum age for one — of the former ice margins. Soil and morphometric parameters subdivide the ice limits into three relative-age groups. One to three pre-Wisconsin advances, probably middle Pleistocene in age, are represented by drift with relatively thick B horizons (60±5 cm, with Bt horizons), thick loess caps (80±12 cm), and broad moraines (135±134 m) with gentle side slopes (7±5°). An extensive early Wisconsin (sensu lato, s.l.) advance, >39.9 ka, and three associated stillstands or readvances are characterized by intermediate soil and morphometric parameters (Bw and weak Bt horizons with thicknesses of 40±11 cm; loess thicknesses of 69±46 cm; crest widths of 38±13 m; and slope angles of 14±4°). The maximum late Wisconsin advance, >16.9 ka, and two readvances or stillstands are associated with thin (20±5 cm), weakly to moderately developed Bw horizons, thin loess caps (28±8 cm), narrow crest widths (28±9 m), and steep slope angles (18±3°). The data confirm that early-Wisconsin glaciers in southeast Beringia were much more extensive than late Wisconsin glaciers, which were apparently limited by availability of moisture.
id: 1204

Pollen record of the last 500 years from the Doninos coastal lagoon (NW Iberian Peninsula): Changes in the pollinic catchment size versus paleoecological interpretation - Santos, L.; Bao, R.; Goni, M. F. S. (Journal of Coastal Research, 2001)
Pollen, diatom, charcoal and sedimentological analyses of a 4.20-m long core collected in the margin of the Doninos coastal lagoon, northwest Iberian Peninsula, provide information about the environmental evolution of this lagoon during the last 530 yr BP. During this time period, local environmental changes, such as changes in the sand-barrier permeability, alluvial sedimentation and/or anthropogenic activity, played a major role in the evolution of this coastal system. This scenario allows us to test the degree the pollinic signal recorded in the sediments of coastal lagoons is reshaped by the influence of local processes.Diatom and sedimentological data as well as historical archives indicate the development of a lacustrine system at the bottom of the sequence. Therefore, the coring site might be included in the lagoon itself. Pollen data seems to reflect the regional vegetation as a consequence of the large pollinic catchment area. Local Castanea cultivation and anthropogenic deforestation are also recorded. At the top of the sequence, diatom facies suggest increased marine influence at this time as a consequence of the more common events of breaching of a retrograding barrier. This, plus natural silting up by alluvial sedimentation and man-induced drying up of the lagoonal margins, lead to a progressive decrease in the water body extension. The coring point is now outside of the lagoon, implying a reduction in the pollinic catchment area that gave rise to a gradual increase in the local pollinic rainfall of periphytic vegetation. From the pollen diagram of this coastal deposit signatures of regional vegetation are swamped by local pollen input. The fluctuations in the percentages of the different pollen taxa are related to the complex interaction between basin size, human activities and breaching of the barrier. Caution must therefore be taken with direct paleoclimatic inferences from pollinic studies in coastal lagoons as an alternative where other continental deposits are lacking.
479bdTimes Cited:6 Cited References Count:46
Keywords: charcoal; coastal lagoon; diatoms; human impact; Late Holocene; late-holocene; nw iberian peninsula; pollen; representation; source area; vegetation; vegetation history

Possible record of the yunger dryas event in sediments of the Southern Ocean (Pacific Sector)--Poster - Morigi, C.; Capotondi, L.; Langone, L.; Giglio, F.; Ravaioli, M. (AUG, 2001)
id: 1423

Possible record of the yunger dryas event in sediments of the southern ocean (Pacific sector)--abstract - Morigi, C.; Capotondi, L.; Langone, L.; Giglio, F.; Ravaioli, M. (AUG, 2001)
id: 1427

Post-glacial eruptive history of the western volcanic zone, Iceland - Sinton, John M.; Gronvold, Karl (EOS Trans. Amer. Geophys. Union, 2001)
id: 355

Pre-Columbian fish farming in the Amazon - Erickson, Clark L. (Expedition, 2001)
id: 1481

Pre-Columbian roads of the Amazon - Erickson, Clark L. (Expedition, 2001)
id: 1482

Pre-late Wisconsin glacial history, coastal Ahklun Mountains, southwestern Alaska-New amino acid, thermoluminescence, and 40Ar/30Ar results - Kaufman, D. S.; Manley, W. F.; Forman, S. L.; Layer, P. (Quaternary Science Reviews, 2001)
New stratigraphic and geochronologic data from the Togiak Bay area of southwestern Alaska indicate that glaciers advanced from the southern Ahklun Mountains at least three and as many as six times prior to the late Wisconsin. The oldest glaciations are represented by glacial–marine sediment in coastal exposures on Hagemeister Island. The extent of amino acid (isoleucine) epimerization in fossil molluscs indicates that at least one, and possibly four, older middle Pleistocene glacial intervals are represented, with age estimates spanning ∼500–280 ka and averaging ∼400±100 ka. The youngest glacial-marine drift on Hagemeister Island may correlate with the eruption of the Togiak tuya. A new 40Ar/39Ar age on basalt that overlies pillow lava indicates that the volcano erupted through glacial ice at least 300 m thick 263±22 ka. The youngest drift in the region overlies the Old Crow tephra (140±10 ka) and a 70±10 ka basaltic lava flow dated by thermoluminescence analysis of underlying baked sediment. The drift delimits flat piedmont lobes that spread out onto the continental shelf and terminated >100 km from their source areas during the early Wisconsin (sensu lato). The glacial-geologic evidence suggests that major expansions of glaciers were out of phase with global ice volume.
id: 1203

Proceedings of a Workshop on Alkenone-Based Paleoceanographic Indicators (Introduction to special issue of journal) - Eglinton, T. I.; Conte, M. H.; Eglinton, G.; Hayes, John M. (Geochem. Geophys. Geosyst., 2001)
id: 1739

Radiocarbon and stable carbon isotopic evidence for transport and transformation of DOC, DIC and CH4 in a northern Minnesota peatland - Chasar, L. S.; Chanton, J. P.; Glaser, P. H.; Siegel, D. I.; Rivers, J. S. (Global Biogeochemical Cycles, 2001)
id: 98

Radiocarbon Dating of Wood Samples and Plutonium Sediment Disturbance Studies at the Queen Anne's Revence Wreck Site - Martens, Christopher S.; McNichol, Ann P. (Southeastern Geology, 2001)
id: 1200

Radiocarbon in a Fanning Island Coral: Inter-decadal Variability in Waters Upwelling in the Central Equatorial Pacific from 1922 - 1955 - Grottoli, A. G.; Gille, S. T.; Druffel, E. R. M.; Dunbar, R. B. (EOS, 2001)
id: 1399

Rapid shoreward encroachment of salt marsh cordgrass in response to accelerated sea-level rise - Donnelly, J. P.; Bertness, M. D. (Proc Natl Acad Sci U S A, 2001)
The distribution of New England salt marsh communities is intrinsically linked to the magnitude, frequency, and duration of tidal inundation. Cordgrass (Spartina alterniflora) exclusively inhabits the frequently flooded lower elevations, whereas a mosaic of marsh hay (Spartina patens), spike grass (Distichlis spicata), and black rush (Juncus gerardi) typically dominate higher elevations. Monitoring plant zonal boundaries in two New England salt marshes revealed that low-marsh cordgrass rapidly moved landward at the expense of higher-marsh species between 1995 and 1998. Plant macrofossils from sediment cores across modern plant community boundaries provided a 2,500-year record of marsh community composition and documented the migration of cordgrass into the high marsh. Isotopic dating revealed that the initiation of cordgrass migration occurred in the late 19th century and continued through the 20th century. The timing of the initiation of cordgrass migration is coincident with an acceleration in the rate of sea-level rise recorded by the New York tide gauge. These results suggest that increased flooding associated with accelerating rates of sea-level rise has stressed high-marsh communities and promoted landward migration of cordgrass. If current rates of sea-level rise continue or increase slightly over the next century, New England salt marshes will be dominated by cordgrass. If climate warming causes sea-level rise rates to increase significantly over the next century, these cordgrass-dominated marshes will likely drown, resulting in extensive losses of coastal wetlands.
Donnelly, J PBertness, M DengResearch Support, Non-U.S. Gov't2001/11/29 10:00Proc Natl Acad Sci U S A. 2001 Dec 4;98(25):14218-23. Epub 2001 Nov 27.

Ricostruzioni paleoambientali nel Mare di Ross (Antartide) attraverso lo studio di associazioni di foraminiferi--Thesis - Orsini, G. (Universita di Bologna, 2001)

The search for early shell middens on San Miguel Island, California - Erlandson, Jon M. (University of Oregon, 2001)
id: 331

Sedimentary evidence of intense hurricane strikes from New Jersey - Donnelly, J. P.; Roll, S.; Wengren, M.; Butler, J.; Lederer, R.; Webb, T. (Geology, 2001)
Nine Vibracores from the backbarrier marsh at Whale Beach, New Jersey, reveal three large-scale overwash deposits associated with historic and prehistoric storms. The uppermost and smallest overwash fan was deposited in the Ash Wednesday northeaster of March 5-8, 1962, A second more substantial overwash fan between 100 and 35 cm depth dates to the late eighteenth or early nineteenth century. This fan was most likely deposited during the 1821 hurricane, the only intense hurricane to make landfall in New jersey in the past 350 yr, A third, larger overwash fan between 200 and 300 cm depth was deposited between A.D. 1278 and 1438 and is likely the result of a prehistoric intense hurricane strike. The combination of historical and stratigraphic evidence indicates that two intense hurricanes (winds > 50 m s(-1)) have likely made landfall on the southern New Jersey coast in the past 700 yr, resulting in an annual landfall probability of 0.3%.
449elTimes Cited:102Cited References Count:14

A Silent Tandetron AMS System - von Reden, K. F.; Schneider, R. J. (Proceedings of the 31st SNEAP, 2001)
id: 1680

A solid state 13C NMR study of kerogen degradation during black shale weathering - Petsch, S. T.; Smernik, R. J.; Eglinton, T. I.; Oades, J. M. (Geochim. Cosmochim. Acta, 2001)
id: 277

Stratigraphic Development of a Northeastern South Carolina Barrier Island: Waites Island - Wright, E.; Harris, M. S.; Sapp, A.; Lewis, K.; Kruse, S.; Edgar, T. (Geological Society of America National Meeting, Abstracts with Program, 2001)
id: 1410

Stratigraphy, paleoceanography, chronology, and paleoenvironment during deglaciation of eastern Maine, Report - Dorion, C. C.; Balco, G.; Kaplan, M. R.; Kreutz, K. J.; Wright, J.; Borns, H. W. (Deglacial History and Relative Sea Level Changes, Northern New England and adjacent Canada, 2001)
id: 1333

Studi paleoambientali nel settore Pacifico dell'Oceano Meridionale attraverso indagini geochimiche--thesis - Giuliana, Tino (Universita di Bologna, 2001)

Subdivision of glacial deposits in southeastern Peru based on pedogenic development and radiometric ages - Goodman, A. Y.; Rodbell, D. T.; Seltzer, G. O.; Mark, B. G. (Quaternary Research, 2001)
The Cordillera Vilcanota and Quelccaya Ice Cap region of southern Peru (13 degrees 30'-14 degrees 00'S; 70 degrees 40'-71 degrees 25'W) contains a detailed record of late Quaternary glaciation in the tropical Andes, Quantification of soil development on 19 moraine crests and radiocarbon ages are used to reconstruct the glacial history. Secondary iron and day increase linearly in Quelccaya soils and clay accumulates at a linear rate in Vilcanota soils, which may reflect the semicontinuous addition of eolian dust enriched in secondary iron to all soils. In contrast, logarithmic rates of iron buildup in soils in the Cordillera Vilcanota reflect chemical weathering; high concentrations of secondary iron in Vilcanota tills may mask the role of eolian input to these soils. Soil-age estimates from extrapolation of field and laboratory data suggest that the most extensive late Quaternary glaciation occurred >70,000 yr B.P. This provides one of the first semiquantitative age estimates for maximum ice extent in southern Peru and is supported by a minimum-limiting age of similar to 41,520 C-14 yr B.P. A late glacial readvance culminated similar to 16,650 cal yr B.P. in the Cordillera Vilcanota, Following rapid deglaciation of unknown extent, an advance of the Quelccaya Ice Cap occurred between similar to 13,090 and 12,800 cal yr B.P., which coincides approximately with the onset of the Younger Dryas cooling in the North Atlantic region. Moraines deposited <394 cal yr B.P. in the Cordillera Vilcanota and <300 cal yr B.P. on the west side of the Quelccaya Ice Cap correlate with Little Ice Age moraines of other regions. (C) 2001 University or Washington.
452lzTimes Cited:27Cited References Count:51

Thirty thousand year record of climate from the Galapagos Islands and links with high latitudes - Koutavas, A.; Lynch-Stieglitz, J.; Sachs, J. P.; Marchitto, T. M. (EOS, 2001)
Fall Meeting Supplement F737
id: 255

Time-averaged shell accumulations as records of past levels of marine benthic productivity: Implications for conservation biology and ecosystem restoration efforst - Kowalewski, M.; Avila-Serrano, G. A.; Flessa, K. W.; Goodfriend, A. G. (North American Paleontologial Convention, Programs and Abstracts, 2001)
id: 283

Time-Averaging in articulate brachiopod accumulations: A quantitative estimate of temporal resolution from a Holocene tropical shelf (Southern Brazil) - Carroll, M.; Kowalewski, M.; Simoes, M. G.; Goodfriend, G. A. (North American Paleontological Convention, Programs and Abstracts, 2001)
id: 1418

Tropical climate changes at millennial and orbital timescales on the Bolivian Altiplano - Baker, P. A.; Rigsby, C. A.; Seltzer, G. O.; Fritz, S. C.; Lowenstein, T. K.; Bacher, N. P.; Veliz, C. (Nature, 2001)
Tropical South America is one of the three main centres of the global, zonal overturning circulation of the equatorial atmosphere (generally termed the 'Walker' circulation1). Although this area plays a key role in global climate cycles, little is known about South American climate history. Here we describe sediment cores and down-hole logging results of deep drilling in the Salar de Uyuni, on the Bolivian Altiplano, located in the tropical Andes. We demonstrate that during the past 50,000 years the Altiplano underwent important changes in effective moisture at both orbital (20,000-year) and millennial timescales. Long-duration wet periods, such as the Last Glacial Maximum—marked in the drill core by continuous deposition of lacustrine sediments—appear to have occurred in phase with summer insolation maxima produced by the Earth's precessional cycle. Short-duration, millennial events correlate well with North Atlantic cold events, including Heinrich events 1 and 2, as well as the Younger Dryas episode. At both millennial and orbital timescales, cold sea surface temperatures in the high-latitude North Atlantic were coeval with wet conditions in tropical South America, suggesting a common forcing.
id: 388

Tropical cooling and the isotopic composition of precipitation in general circulation model simullations of the ice age climate - Charles, C. D.; Rind, D.; Healy, R.; Webb, R. (Climate Dynamics, 2001)
id: 1716

Use of 14C and 13C natural abundances for evaluating riverine, estuarine, and coastal DOC and POC sources and cycling: Review and Synthesis - Raymond, P. A.; Bauer, J. E. (Org. Geochem, 2001)
id: 278

Use of bomb radiocarbon to validate otolith section ages of red snapper Lutjanus campechanus from the northern Gulf of Mexico - Baker, M. S.; Wilson, C. A. (Limnology and Oceanography, 2001)
The red snapper Lutjanus campechanus is an important recreational and commercial fish species in the northern Gulf of Mexico. Management approaches have varied in part because of uncertainty of their longevity. Snapper ages have been based on presumed otolith annuli; however, this methodology has not been validated for all age classes. A recent technique to validate otolith age utilizes the increase in oceanic C-14 resulting from atmospheric testing of nuclear bombs during the 1950s and 1960s. Analyses of annuli from living corals and fish otoliths from 1900 to the present have documented that elevated C-14 input has occurred throughout the world's oceans. We validated otolith section age estimates through accelerator mass spectrometry analysis of bomb-produced C-14 in red snapper (otoliths) hatched before, during, and after the nuclear testing periods. Delta C-14 data from the otoliths of red snapper with presumed birth dates between 1960 and 1973 clearly reflect the sharp increase in oceanic radiocarbon attributable to previous nuclear testing. Similarities between the otolith and nearby coral Delta C-14 chronologies suggest that annulus-based age estimates of red snapper are valid on average to within 1-3 yr. In addition, this study provides the first carbonate bomb radiocarbon time series from the northern Gulf of Mexico.
491vzTimes Cited:36Cited References Count:22

U-Th dating of carbonate platform and slope sediments - Henderson, G. M.; Slowey, N. C.; Fleisher, M. Q. (Geochimica Et Cosmochimica Acta, 2001)
Absolute chronology of marine sediment beyond the C-14 age range provides a test for models of climate change and has many other applications. U-Th techniques have been used for such chronology by dating corals, but extending these techniques to marine sediment is complicated by the presence of significant initial Th-230-both in detrital material and scavenged from seawater. In this study, we investigate four methods of solving the initial Th-230 problem for a particular type of marine sediment-the aragonite-rich sediments of carbonate platforms and slopes. Bulk sediment U-Th analyses can be corrected for initial Th to yield ages with approximate to2 to 3 kyr precision for highstand periods when sediment aragonite contents are particularly high. Uncertainty on the corrections causes inadequate precision for sediment from other periods, however. Removal of scavenged Th before analysis would enable a dramatic increase in this precision but has not proved successful despite a range of chemical leach approaches. Using heavy liquids to separate the various carbonate minerals found in Bahamas sediment enables an isochron approach to correct for initial Th, but the presence of initial Th from two sources requires correction or removal of one source of initial Th before the other is deconvolved by the isochron. Quantitative removal of detrital material before isochron analysis proves a successful approach. Such isochron data demonstrate that, although sediment remains closed to U-Th on a centimetre scale, nuclides are moved from grain to grain by alpha -recoil. Such intergrain exchange is expected to be observed in all sediments containing mineral grains with different U concentrations. Measured U-234/U-238 allows the recoil movement to be corrected and results in isochron ages with precision sometimes as low as 3 kyr. The accuracy of this approach has been proved by dating samples within the 14C age range. Sediments spanning the penultimate deglaciation have also been dated. After a small correction for bioturbation, the age for this event is found to be 135.2 +/- 3.5 ka. TWs date is approximate to8 kyr before the peak in northern hemisphere insolation and suggests that deglaciation is initiated by a mechanism in the southern hemisphere or tropics. This isochron approach shows considerable promise for dating of sediments older than this event, which will provide further information about the timing and mechanisms of global climate change. Copyright (C) 2001 Elsevier Science Ltd.
462zlTimes Cited:49Cited References Count:44

Validation of compound-specific 14C dating using the varved sedimentary record of Saanich Inlet, Canada - Smittenberg, R. H.; Hopmans, E. C.; Eglinton, T. I.; Hayes, J. M.; Whiticar, M. J.; Schouten, S.; Sinninghe Damsté, J. S. (Proceedings of the 20th international meeting on organic geochemistry, 2001)
id: 270

Vegetation succession and carbon sequestration in a coastal wetland in northwestern Florida: evidence from carbon isotopes - Choi, Y.; Wang, Y.; Hsieh, Y. P.; Robinson, L. (Global Biogeochemical Cycles, 2001)
id: 267

Were Rhyolitic Glasses in the Vedde Ash and in the North Atlantic's Ash Zone 1 produced by the Same Volcanic Eruption? - Bond, G. C.; Mandeville, C.; Hoffmann, S. (Quaternary Science Reviews, 2001)
New evidence from North Atlantic deep-sea sediment cores suggests that rhyolitic glass shards in Ash Zone 1 and in the Vedde Ash may not have been produced by the same eruption as has been widely assumed. Our argument is based on (1) a marine ice-rafted deposit approximately 1000 years older than the Vedde Ash contains rhyolitic shards with the same major element chemistry as the Vedde Ash itself and (2) coincidence of Ash Zone 1 with an abrupt increase in discharge of glacial icebergs into the North Atlantic. Hence, we cannot rule out the possibility that Vedde-like rhyolitic glasses were erupted onto Icelandic glaciers before eruption of the Vedde Ash, stored in the glacial ice, then dispersed by icebergs into the North Atlantic and deposited partly or entirely as Ash Zone 1. While not disproving that Ash Zone 1 and the Vedde Ash came from the same eruption, our findings indicate that further study is needed to establish the exact relation between the two ash deposits.
id: 253

14C Dating of sediment of the Uppermost Cape Fear Slide Plain: Constraints on the timing of this massive submarine landslide (Book Section) - Rodriquez, N. M.; Paull, C. K. (Scientific Results of the Ocean Drilling Program, Leg 164, 2000)
id: 1342

Acceptance of the 1997 Alfred E. Treibs Award - Hayes, J. M. (Geochimica Et Cosmochimica Acta, 2000)
287naTimes Cited:0Cited References Count:0

Age and composition of carbonate shoreface sediments, Kailua Bay, Oahu, Hawaii - Harney, J. N.; Grossman, E. E.; Richmond, B. M.; Fletcher, C. H. (Coral Reefs, 2000)
The origin, age, and dynamics of carbonate sediments in Kailua Bay on Oahu, Hawaii, are described. The shoreface (from shoreline to 4 km offshore) consists of a broad (5 km(2)) fringing coral reef ecosystem bisected by a sinuous, shore-normal, sand-filled paleostream channel 200-300 m wide. The median grain diameter of surface sands is finest on the beach face (<0.3 mm) and increases offshore along the channel axis. Kailua sands are >90% biogenic carbonate, dominated by skeletal fragments of coralline algae (e.g. Porolithon, up to 50%) followed by the calcareous green alga Halimeda (up to 32%), coral fragments (1-24%), mollusc fragments (6-21%), and benthic foraminifera (1-10%). Sand composition and age across the shoreface are correlated to carbonate production. Corals and coralline algae, principal builders of the reef framework, are younger and more abundant in sands along the channel axis and in offshore reefal areas, while Halimeda, molluscs, and foraminifera are younger and more dominant in nearshore waters shoreward of the main region of framework building. Shoreface sediments are relatively old. Of 20 calibrated radiocarbon dates on skeletal constituents of sand, only three are younger than 500 years B.P.; six are 500-1000 years B.P.; six are 1000-2000 years B.P.; and five are 2000-5000 years B.P. Dated fine sands are older than medium to coarse sands and hence may constitute a reservoir of fossil carbonate that is distributed over the entire shoreface. Dominance of fossiliferous sand indicates long storage times for carbonate grains, which tend to decrease in size with age, such that the entire period of relative sea-level inundation (similar to 5000 years) is represented in the sediment. Despite an apparently healthy modern coral ecosystem, the surficial sand pool of Kailua Bay is dominated by sand reflecting an antecedent system, possibly one that existed under a + 1-2 m sea-level high stand during the mid- to late Holocene.
341wmTimes Cited:32Cited References Count:43

Amino acid racemization in ostracodes - Kaufman, D. S. (Perspectives in Amino Acid and Protein Geochemistry, 2000)
id: 1390

An artificial landscape-scale fishery in the Bolivian Amazon - Erickson, C. L. (Nature, 2000)
Historical ecologists working in the Neotropics argue that the present natural environment is an historical product of human intentionality and ingenuity, a creation that is imposed, built, managed and maintained by the collective multigenerational knowledge and experience of Native Americans. In the past 12,000 years, indigenous peoples transformed the environment, creating what we now recognize as the rich ecological mosaic of the Neotropics. The prehispanic savanna peoples of the Bolivian Amazon built an anthropogenic landscape through the construction of raised fields, large settlement mounds, and earthen causeways. I have studied a complex artificial network of hydraulic earthworks covering 525 km2 in the Baures region of Bolivia. Here I identify a particular form of earthwork, the zigzag structure, as a fish weir, on the basis of form, orientation, location, association with other hydraulic works and ethnographic analogy. The native peoples used this technology to harvest sufficient animal protein to sustain large and dense populations in a savanna environment.
Erickson, C LengHistorical ArticleResearch Support, Non-U.S. Gov'tResearch Support, U.S. Gov't, Non-P.H.S.England2000/11/23 11:00Nature. 2000 Nov 9;408(6809):190-3.

Black carbon in lacustrine and coastal marine sediments, Thesis - Muri, G. (University of Ljubljana, Slovenia, 2000)

Characterising the Namaqualand mudbelt of southern Africa: chronology, palynology and palaeoenvironments - Gray, C. E. D.; Meadows, M. E.; Lee-Thorp, J. A.; Rogers, J. (South African Geographical Journal, 2000)
id: 219

Chesapeake Bay sedimentary record of Holocene climatic variability and human ecosystem disturbance - Cronin, T.; Willard, D.; Karlsen, A.; Ishman, S.; Verardo, S.; McGeehin, J.; Kerhin, R.; Holmes, C.; Colman, S. M.; Zimmerman, A. (Geology, 2000)
id: 184

Chronostratigraphy of sediments in the southern Gulf of California, based on amino acid racemization analysis of mollusks and rhodolith (Book Section) - Goodfriend, G. A.; Halfar, J.; Godinez-Orta, L. (Perspectives in Amino Acid and Protein Geochemistry, 2000)
id: 174

Climate change in the northern American tropics since the last ice age: implications for environment and culture (Book Section) - Hodell, D. A.; Brenner, M.; Curtis, J. H. (Imperfect Balance: Landscape transformations in the Precolumbian Americas, 2000)
id: 198

Climate, fire, and vegetation between about 13,000 and 9,200 14C yr. B. P - Moreno, P. I. (Quaternary Research, 2000)
id: 237

A continuous high-resolution record of late Pleistocene climate variability from the Estacia basin, New Mexico - Allen, B. D.; Anderson, R. Y. (Geological Society of America Bulletin, 2000)
Lake sediments that accumulated in the Estancia basin, central New Mexico, provide a detailed record of submillennial latest Pleistocene climatic oscillations. Sedimentologic, biologic, and geochemical proxies for changes in salinity and lake level were used to identify episodes of wet and dry climate that occurred between 24 and 12 k.y. B.P., as dated by 14C by means of accelerator mass spectrometry from shoreline and basin-center deposits. These dates determine the timing and duration of the episodes of wet and dry climate. The lake expanded and contracted repeatedly during the last glacial maximum and fluctuated near its highest elevation several times during the interval ca. 20 to 15 k.y. B.P. A pronounced lowstand lasting ∼1 k.y. occurred between ca. 15 and 14 k.y. B.P., followed by two more highstands of the lake between ca. 14 and 12.5 k.y. B.P. Desiccation of the perennial lake after 12 k.y. B.P. was followed by a final, poorly dated highstand at ca. 10 k.y. B.P. The record of lake-level fluctuations from the Estancia basin provides a high-resolution record of changes in water budget in a basin, the comparatively simple physiography and hydrogeology of which ensured a direct response to the strong climatic fluctuations that occurred during the last glacial maximum and termination.
id: 239
Keywords: Lacustrine sediments; Last glacial maximum; ostracodes; Paleoclimate; trace metals

d13C values and radiocarbon dates of microbial biomarkers as tracers fro carbon recycling in peat deposits - Pancost, R. D.; van Geel, B.; Baas, M.; Damste Sinninghe, J. S. (Geology, 2000)
id: 1330

Deep Sea Sediments off Baja California Reflect Greenland Ice Core climate cycles - Ortiz, J.; O'Connell, S.; van Geen, A.; Party, Melville ' Shipboard Scientific (Geological Society of America, Annual meeting, 2000)
id: 110

Detecting holocene changes in thermohaline circulation - Keigwin, L. D.; Boyle, E. A. (Proc Natl Acad Sci U S A, 2000)
Throughout the last glacial cycle, reorganizations of deep ocean water masses were coincident with rapid millennial-scale changes in climate. Climate changes have been less severe during the present interglacial, but evidence for concurrent deep ocean circulation change is ambiguous.
Keigwin, L DBoyle, E A eng Research Support, U.S. Gov't, Non-P.H.S. 2000/03/04 09:00 Proc Natl Acad Sci U S A. 2000 Feb 15;97(4):1343-6.
Keywords: *Climate; *Plankton; Animals; Atlantic Ocean; carbon isotopes; ice; oxygen isotopes; time

Differences in great earthquake rupture extent inferred from tsunami-laid sand and foraminiferal assemblages at Alsea Bay, central Oregon coast - Nelson, A. R.; Jennings, A. E. (Geological Society of America Abstracts with Programs, 2000)
id: 257

Ecosystem development and response to climatic change: a comparative study of forest-lake ecosystems on different substrates - Ewing, Holly A. (Evolution and Behavior, 2000)
id: 1384

Enormous Ganges-Brahmaputra sediment discharge during strengthened early Holocene monsoon - Goodbred, S. L., Jr.; Kuehl, S. A. (Geology, 2000)
Rivers are the main source of terrigenous sediment delivered to continental margins and thus exert a major control on coastal evolution and sequence development. However, little is known about past changes in fluvial sediment loads despite the recognition of significant variation under changing climatic regimes. In this study we present the first quantified estimate of sediment discharge for a major river system under conditions of an intensified early Holocene monsoon. Development of the Ganges-Brahmaputra River delta began ca. 11000 yr B.P., when rising sea level flooded the Bengal basin, thereby trapping most of the river's discharge on the inner margin. Chronostratigraphic data from these deltaic deposits are used to calculate the rates of sediment storage on the margin, which provide a minimum estimate of the river's past sediment load. Results reveal that ∼5 × 1012 m3 of sediment was stored in the Bengal basin from ca. 11000 to 7000 yr B.P., which corresponds to a mean load of 2.3 × 109 t/yr. In comparison, modern sediment load of the Ganges-Brahmaputra is ∼1 × 109 t/yr, ranking it first among the world's rivers and underscoring the significance of a two-fold increase sustained over 4 k.y. Furthermore, the timing of immense discharge in the early Holocene strongly suggests its relation to a stronger than present southwest monsoon in South Asia. Similar patterns of high monsoon-related sediment discharge have been noted throughout the tropics and subtropics, suggesting a widespread fluviosedimentary response, the potential magnitude of which is showcased by the Ganges-Brahmaputra system.
id: 147

Environmental changes in the last centure in Little Trout Lake, Inkspot Bay, Great Corn and Little Corn Lakes, Lac du Flambeau Tribal Lands, Wisconsin. Report - Winkler, M. G.; Sanford, P. R. (2000)
id: 128

Erosional scour and geologic evolution of Croatan Sound, northeastern North Caroline: N.C - Riggs, S. R.; Rudolph, G. L.; Ames, D. V. (Department of Transportation, 2000)
id: 243

An estimate of the anthropogenic offset of oceanic d13CDIC based on the ventilation of the California Current at 42N - Ortiz, J. D.; Mix, A. C.; Wheeler, P.; Key, R. M. (Global Biogeochem. Cycles, 2000)
id: 307

Evidence from U-Th dating against Northern Hemisphere forcing of the penultimate deglaciation - Henderson, G. M.; Slowey, N. C. (Nature, 2000)
Milankovitch proposed that summer insolation at mid-latitudes in the Northern Hemisphere directly causes the ice-age climate cycles. This would imply that times of ice-sheet collapse should correspond to peaks in Northern Hemisphere June insolation. But the penultimate deglaciation has proved controversial because June insolation peaks 127 kyr ago whereas several records of past climate suggest that change may have occurred up to 15 kyr earlier. There is a clear signature of the penultimate deglaciation in marine oxygen-isotope records. But dating this event, which is significantly before the 14C age range, has not been possible. Here we date the penultimate deglaciation in a record from the Bahamas using a new U-Th isochron technique. After the necessary corrections for alpha-recoil mobility of 234U and 230Th and a small age correction for sediment mixing, the midpoint age for the penultimate deglaciation is determined to be 135 +/- 2.5 kyr ago. This age is consistent with some coral-based sea-level estimates, but it is difficult to reconcile with June Northern Hemisphere insolation as the trigger for the ice-age cycles. Potential alternative driving mechanisms for the ice-age cycles that are consistent with such an early date for the penultimate deglaciation are either the variability of the tropical ocean-atmosphere system or changes in atmospheric CO2 concentration controlled by a process in the Southern Hemisphere.
HendersonSloweyengEngland2000/03/15 09:00Nature. 2000 Mar 2;404(6773):61-6.

Further evidence of abrupt Holocene drowning of the Black Sea shelf - Ballard, R. D.; Coleman, D. F.; Rosenberg, G. D. (Marine Geology, 2000)
A 1999 survey of the Black Sea continental shelf off the north central Turkish seaport of Sinop using a side-scan sonar, small remotely operated vehicles, and a series of dredge lowerings located, inspected and sampled an exposed high-energy paleoshoreline at a depth of 155 m. Radiocarbon dating of mollusk shells collected from this ancient beach revealed that the marine flooding of the Black Sea took place between 7460 and 6820 yr B.P. tall ages are reported in radiocarbon years, not calendar years, without correction for reservoir age or dendro-calibration) changing it from a lacustrine to marine environment. This relic surface remained in contact with the bottom waters of the Black Sea for a long period of time before being draped by a thin layer of sapropel mud. Wood samples recovered from this same location were very well preserved and yielded dates as old as 3580 yr B.P. (C) 2000 Elsevier Science B.V. All rights reserved.
380xeTimes Cited:71Cited References Count:8

Geochemical and Lithological Records of the Hypsithermal and Nipissing Flood Event from Lake Erie--Thesis - Kempthorne, Rebecca (University of Akron, 2000)

A giant vampire (Mammalia, Chiroptera) in the Late Holocene from the Argentinean pampas: paleoenvironmental significance - Pardinas, U. F. J.; Tonni, E. P. (Palaeogeography Palaeoclimatology Palaeoecology, 2000)
The first fossil desmodontine record and the only well documented chiropteran fossil record from Argentina is described. A complete left upper canine was collected at Centinela del Mar (38 degrees 21'S58 degrees W, General Alvarado County, Buenos Aires Province) from fossil-bearing sediments referred to the Late Holocene. The tooth size is 25% larger than that of the modern vampire bat. Desmodus rotundus. We assign this tooth to Desmodus cf. D. draculae, an extinct species recorded in the Pleistocene-Holocene of South America (Brazil and Venezuela). The southernmost distribution of present-day Desmodus extends to northeast Buenos Aires province (35 degrees S). The presence of Desmodus some 600 km south of this present-day limit (July minimal isotherm of 10 degrees C) indicates that around 300 years BP the southeastern Buenos Aires province was at least 2 degrees C higher than modern July isotherm. The Desmodus tooth is associated with sigmodontine rodents characteristic of subtropical and temperate-warm areas (e.g., Pseudoryzomys simplex, Bibimys cf. B. torresi), and provides additional evidence to support this hypothesis. A correlation with a global warming phase is discussed. (C) 2000 Elsevier Science B.V. All rights reserved.
330jhTimes Cited:12Cited References Count:40

Glacial deep water geometry: South Atlantic Benthic foraminiferal Cd/Ca and delta13C evidence - Oppo, Delia W.; Horowitz, Michael (Paleoceanography, 2000)
id: 13050883-8305/00/1999PA000436

Glacial-Interglacial variations in the accumulation rates of major biogenic components in the Southern Pacific Ocean sediments--Abstract - Giglio, F.; Langone, L.; Ravaioli, M.; Frignani, M.; Mangini, A.; Fonti, P. (Third International SO-JGOFS Symposium, 2000)
id: 287

Global Distribution of Total Inorganic Carbon and Total Alkalinity Below the Deepest Winter Mixed Layer Depths - Goyet, C.; Healy, R.; Ryan, J. (Carbon Dioxide Information Analysis Center, Oak Ridge National Laboratory, 2000)
Modeling the global ocean-atmosphere carbon dioxide system is becoming increasingly important to greenhouse gas policy. These models require initialization with realistic three- dimensional (3-D) oceanic carbon fields. This report presents an approach to establishing these initial conditions from an extensive global database of ocean carbon dioxide (CO2) system measurements and well-developed interpolation methods. These methods are limited to waters below the deepest mixed layer. The data used for these interpolations include the recent high-quality data sets from the World Ocean Circulation Experiment (WOCE), Joint Global Ocean Flux Study (JGOFS), and Ocean-Atmosphere Carbon Exchange Study (OACES) programs. Prior to analysis, all carbon data were adjusted to established reference material listed in http://andrew.ucsd.edu/co2qc/. The interpolation methodology employs correlation between CO2 system properties and other more widely measured properties: potential temperature, salinity, and apparent oxygen utilization. The correlations are computed for each profile, and the coefficients are interpolated to the 1°×1°×32 vertical-layer grid at a monthly temporal resolution. Finally, the gridded coefficients are applied to a global monthly climatology of ocean temperature, salinity, and oxygen to compute total CO2 (TCO2) and total alkalinity (TALK) for the 3-D grid. This approach offers advantages over spin up of a single profile in defining spatial variation in CO2 system properties because it reduces initialization time and provides a more accurate carbon field. The results provide an unprecedented "view" of the global distribution of TALK and TCO2 in the ocean. These results as well as those from the monthly mixed layer depths can be used in diagnostic and prognostic global ocean models. The data set of the gridded climatological fields of TCO2, TALK, and mixed layer depths is available free of charge as a numeric data package from the Carbon Dioxide Information Analysis Center (CDIAC). The interpolated data set includes seasonal TCO2 and TALK fields as well as the coefficients used to estimate these concentrations and the monthly mixed layer depths.
id: 1970

Gulf of Mexico Intraslope Basins (BIB) Phase 1 Project Atlas - Damuth, J. E.; Olson, H. C.; Moss, G. (Institute for Geophysics, University of Texas at Austin Department of Geology and Geophysics, University of Texas at Arlington, 2000)
id: 354

High resolution proxy record of late Quaternary climate change from Soledad Basis, northwest Mexico, Abstract - Pike, J.; van Geen, A.; Beaufort, L.; Party, Shipboard Scientific (UK Pages, 2000)
id: 111

Holocene and recent rates of sediment accumulation in southern Lake Michigan - Colman, S. M.; King, J. W.; Jones, G. A.; Reynolds, R. L.; Bothner, M. H. (Quaternary Science Reviews, 2000)
id: 183

Holocene cirque glacier activity in Western Spitsbergen, Svalbard: sediment records from pro-glacial Linnevatnet - Snyder, J. A.; Werner, A.; Miller, G. H. (The Holocene, 2000)
id: 234

Holocene climate in the western Great Lakes national parks and lakeshores: Implications for future climate change - Davis, M.; Douglas, C.; Calcote, R.; Cole, K. L.; Winkler, M. G.; Flakne, R. (Conservation Biology, 2000)
We reconstruct Holocene climate history (last 10,000 years) for each of the U.S. National Park Service units in the western Great Lakes region in order to evaluate their sensitivity to global warming. Annual precipitation, annual temperature, and July and January temperatures were reconstructed by comparing fossil pollen in lake sediment with pollen in surface samples, assuming that ancient climates were similar to modern climate near analogous surface samples. In the early Holocene, most of the parks experienced colder winters, warmer summers, and lower precipitation than today. An exception is Voyageurs National Park in northern Minnesota where, by 8000 years ago, January temperatures were higher than today. The combination of high mean annual temperature and lower precipitation at Voyageurs resulted in a dry period between 8000 and 5000 years ago, similar to the Prairie Period in regions to the south and west. A mid-Holocene warm-dry period also occurred at other northern and central parks but was much less strongly developed. In southern parks there was no clear evidence of a mid-Holocene warm-dry period. These differences suggest that global model predictions of a warm, dry climate in the northern Great Plains under doubled atmospheric CO2 may be more applicable to Voyageurs than to the other parks. The contrast in reconstructed temperatures at Voyageurs and Isle Royale indicates that the ameliorating effect of the Great Lakes on temperatures has been in effect throughout the Holocene and presumably will continue in the future, thus reducing the potential for species loss caused by future temperature extremes. Increased numbers of mesic trees at all of the parks in the late Holocene reflect increasing annual precipitation. This trend toward more mesic conditions began 6000 years ago in the south and 4000 years ago in the north and increased sharply in recent millennia at parks located today in lake-effect snow belts. This suggests that lake-effect snowfall is sensitive to continental-scale changes in climate and could be affected by future climate change. Plant and animal species sensitive to changes in the moisture regime could thus be endangered within the Great Lakes parks.
338uvTimes Cited:47Cited References Count:46

The Holocene history of Lake Victoria, East Africa - Johnson, T. C.; Kelts, K.; Odada, E. O. (Ambio, 2000)
id: 340

Holocene hydrological reconstructions from stable isotopes and paleolimnology, Cordillera Real, Bolivia - Abbott, M. B.; Wolfe, A. P.; Aravena, R.; Wolfe, A. P.; Seltzer, G. O. (Quarternary Science Reviews, 2000)
Multiproxy analyses of sediment cores from Lago Taypi Chaka Kkota (LTCK) Cordillera Real, Bolivia, provide a record of drier conditions following late Pleistocene deglaciation culminating in pronounced aridity between 6.2 and 2.3 ka B.P. Today LTCK is a glacial-fed lake that is relatively insensitive to changes in P–E because it is largely buffered from dry season draw-down through the year-round supply of glacial meltwater. This was not the case during the middle to late Holocene when glaciers were absent from the watershed. Lake-water δFull-size image (<1 K) values inferred from δFull-size image (<1 K) analysis of sediment cellulose range from −12.9 to −5.3‰ and average −8.7‰ between 6.2 and 2.3 ka B.P. Modern lake-water δFull-size image (<1 K) from LTCK averages −14.8‰ which is compatible with the δFull-size image (<1 K) value of −14.3‰ for the surface sediment cellulose. Analyses of δFull-size image (<1 K) from modern surface waters in 23 lakes that span the range from glacial-fed to closed basin vary from −16.6 to −2.5‰. This approximates the magnitude of the down-core shift in δFull-size image (<1 K) values in LTCK during the middle to late Holocene from −12.9 to −5.3‰. Strong paleohydrologic change during the middle Holocene is also evident in diatom assemblages that consist of shallow-water, non-glacial periphytic taxa and bulk organic δFull-size image (<1 K) and δFull-size image (<1 K) that show increases likely resulting from degradation of lacustrine organic matter periodically exposed to subaerial conditions. Neoglaciation began after 2.3 ka B.P. as indicated by changes in the composition of the sediments, lower δFull-size image (<1 K) values, and a return to diatom assemblages characteristic of the glacial sediments that formed during the Late Pleistocene. Collectively, these data indicate that the past 2.3 ka B.P. have been the wettest interval during the Holocene. Millennial-scale shifts in the paleohydrologic record of LTCK during the early to middle Holocene conform to other regional paleoclimatic time-series, including Lake Titicaca and Nevado Sajama, and may be driven by insolation and resultant changes in atmospheric circulation and moisture supply. In contrast, an apparent 1200-year lag in the onset of wetter conditions at LTCK (2.3 ka B.P.) compared to Lake Titicaca (3.5 ka B.P.) provides evidence for variable sub-regional hydrologic response to climate change during the middle to late Holocene.
id: 1206

Holocene lake sediment records of Arctic hydrology - MacDonald, G. M.; Felzer, B.; Finney, B. P.; Forman, S. L. (Journal of Paleolimnology, 2000)
Although paleoclimatic research in the Arctic has most often focused on variations in temperature, the Arctic has also experienced changes in hydrologic balance. Changes in Arctic precipitation and evaporation rates affects soils, permafrost, lakes, wetlands, rivers, ice and vegetation. Changes in Arctic soils, permafrost, runoff, and vegetation can influence global climate by changing atmospheric methane and carbon dioxide concentrations, thermohaline circulation, and high latitude albedo. Documenting past variations in Arctic hydrological conditions is important for understanding Arctic climate and the potential response and role of the Arctic in regards to future climate change. Methods for reconstructing past changes in Arctic hydrology from the stratigraphic, isotopic, geochemical and fossil records of lake sediments are being developed, refined and applied in a number of regions. These records suggest that hydrological variations in the Arctic have been regionally asynchronous, reflecting the impacts of different forcing factors including orbitally controlled insolation changes, changes in geography related to coastal emergence, ocean currents, sea ice extent, and atmospheric circulation. Despite considerable progress, much work remains to be done on the development of paleohydrological proxies and their application to the Arctic.
id: 375
Keywords: Arctic; Climate change; Holocene; paleohydrology; paleolimnology

Ice core evidence for climate change in the Tropics: implications for our future - Thompson, L. G. (Quaternary Science Reviews, 2000)
Reliable meteorological observations for climate reconstruction are limited or absent prior to A.D. 1850 for much of the Earth and particularly in both tropical South America and the Tibetan Plateau region of central Asia. Over 50% of the Earth's surface lies between 30 degrees N and 30 degrees S and 75% of the world's inhabitants live and conduct their activities in these tropical regions. Thus, much of the climatic activity of significance to humanity, such as variations in the occurrence and intensity of the El Nino-Southern Oscillation and monsoons, are largely confined to lower latitudes. Moreover, the variability of these tropical systems and particularly that of the tropical hydrological system in response to regional and global climate forcing are not well understood. Fortunately, ice core records are also available from selected high altitude, low and mid-latitude ice caps. The ice core studies described here were undertaken as part of a long-term program to acquire the global-scale, high-resolution climatic and environmental history essential for understanding more fully the linkages between the low and the high latitudes. Two ice core records, one covering the last full glacial cycle from the Guliya Ice Cap, China (35 degrees N; 6200 m asl) and one from Huascaran, Peru, which reveal significant cooling during the Last Glacial Cycle Maximum (LGM similar to 20,000 yr BP) are compared with preliminary data coming from the new Sajama, Bolivia (18 degrees S, 6550 m asl) and the Dasuopu, Himalaya (China, 28 degrees N, 7200 m asl) cores. Lower delta(18)O values (equivalent to cooling of similar to 8 degrees C) contribute to the growing body of evidence that the tropical climate was cooler and more variable during the last glacial cycle and has renewed current interest in the tropical water vapor cycle. The new tropical ice core records raise additional questions about our understanding of the role of the tropics in global climate. Unfortunately, as a result of recent warming, all known tropical glaciers and ice caps are retreating and soon will no longer continue to preserve viable paleoclimatic records. The characteristics of the current warming will be examined and compared to earlier periods of climatic warming such as the transition form the last glacial into the current interglacial as well as other periods within the Holocene. It is important to distinguish natural variation in the climate system from the anthropogenic influences superimposed during the: last century. These tropical ice cores offer long-term perspectives of accumulation, temperature, atmospheric dust and "greenhouse" gas concentrations against which recent variations may be assessed, with particular relevance for lower latitude regions where most people live. (C) 1999 Elsevier Science Ltd. All rights reserved.
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Ice Core Paleoclimate Records in Tropical South America Since the Last Glacial Maximum - Thompson, L. G.; Mosley-Thompson, E.; Henderson, K. A. (Journal of Quaternary Science, 2000)
id: 245

Identification of a novel alkenone in Black Sea sediments - Xu, L.; Reddy, C. M.; Farrington, J. W.; Frysinger, G. S.; Gaines, R. B.; Johnson, C. G.; Nelson, R. K.; Eglinton, T. I. (Organic Geochemistry, 2000)
We report the identification of a novel long-chain ketone in Holocene Black Sea sediments. Based on chemical properties, and chromatographic and mass spectrometric characteristics, this compound has been identified as a di-unsaturated C36 ethyl ketone. Further analyses indicated the position and configuration of the double bonds, and the novel alkenone was determined to be hexatriaconta-(16E,21E)-dien-3-one. While this compound is present in only trace quantities in Unit I sediments, it is the most abundant alkenone in portions of Unit II. Its presence thus apparently pre-dates the invasion of Emiliania huxleyi in the Black Sea. The down-core profiles and isotopic compositions suggest that the precursor for the C36:2 alkenone may be distinct from that of the C37-39 alkenones, however the biological origin of this novel compound is presently unknown.
id: 1719
Keywords: Alkenone; Black Sea; Haptophytes; Holocene; Sediment; Structure characterization