Evaluating reproducibility of seawater, inorganic and organic carbon 14C results at the National Ocean Sciences AMS Facility (NOSAMS) - Elder, K. L.; McNichol, A. P.; Gagnon, A. R. (Radiocarbon, 1998)

Evidence for episodic calcium-carbonate dissolution in the subpolar North Atlantic during the last glaciation - McManus, J. F.; Lohmann, G. P. (EOS, 1998)
id: 171

Geoforma Ediciones, Logrono, Barcelona - Valero-Garces, B. L.; Matri Bono, C.; Kelts, K. (Investigaciones recientes de la Geomorfologia esponola, 1998)
id: 384

Glacial-age hydrography of the far northwest Pacific Ocean - Keigwin, L. D. (Paleoceanography, 1998)
Stable isotope data on benthic foraminifera from more than 30 cores on the northern Emperor Seamounts and in the Okhotsk Sea are synthesized in paleohydrographic profiles spanning the depth range 1000-4000 m. Holocene (core-top) benthic foraminiferal delta(18)O and delta(13)C data are calibrated to modern hydrographic properties through measurements of delta(13)C of Sigma CO2 and delta(18)O of seawater. Cibicidoides stable isotope ratios are close to the delta(13)C and equilibrium delta(18)O of seawater, whereas Uvigerina delta(18)O and delta(13)C are variably offset from Cibicidoides. Glacial maximum delta(13)C of Cibicidoides displays a different vertical profile than that of the Holocene. When results are adjusted by +0.32 parts per thousand to account for the secular change in delta(13)C during the last glacial maximum, the data coincide with the modern seawater and foraminiferal curves deeper than similar to 2 km. However, at shallower depths delta(13)C gradually increases by as much as 1 parts per thousand above the modern value. Furthermore, above 2 km the benthic delta(18)O decreases by similar to 0.5 parts per thousand. These results are consistent with a benthic front at similar to 2 km in the North Pacific [see Herguera et al., 1992], but they differ from interpretations based on trace metal data which indicate a source of nutrient-depleted deep water during glaciation. The isotopic data suggest that during glaciation there was a better ventilated watermass at intermediate depths in the far northwestern Pacific, it was relatively fresher than deep waters there, and deep waters were as nutrient-rich as today.
105bqTimes Cited:192Cited References Count:61

Glacioisostasy and lake-level change at Moosehead lake, Maine - Balco, G.; Belknap, D. F.; Kelley, J. T. (Quaternary Research, 1998)
Reconstructions of glacioisostatic rebound based on relative sea level in Maine and adjacent Canada do not agree well with existing geophysical models. In order to understand these discrepancies better, we investigated the lake-level history of 40-km-long Moosehead Lake in northwestern Maine. Glacioisostasy has affected the level of Moosehead Lake since deglaciation ca. 12,500 C-14 yr B.P. Lowstand features at the southeastern end and an abandoned outlet at the northwestern end of the lake indicate that the lake basin was tilted down to the northwest, toward the retreating ice sheet, by 0.7 m/km at 10,000 C-14 yr B.P. Water level then rose rapidly in the southeastern end of the lake, and the northwestern outlet was abandoned, indicating rapid relaxation of landscape tilt. Lowstand features at the northwestern end of the lake suggest that the lake basin was tilted to the southeast at ca. 8750 C-14 yr B.P., possibly as the result of a migrating isostatic forebulge. After 8000 C-14 yr B.P., water level at the southeastern end was again below present lake level and rose gradually thereafter. We found no evidence suggesting that postglacial climate change significantly affected lake level. The rebound history inferred from lake-level data is consistent with previous interpretations of nearby relative sealevel data, which indicate a significantly steeper and faster-moving ice-proximal depression and ice-distal forebulge than geophysical models predict. (C) 1998 University of Washington.
Zm315Times Cited:9Cited References Count:46

High-precision Measurements of 14C as a Circulation Tracer in the Pacific, Indian, and Southern Oceans with Accelerator Mass Spectrometry (AMS) - von Reden, K. F.; Peden, J. C.; Schneider, R. J.; Bellino, M.; Donoghue, J.; Elder, K. L.; Gagnon, A. R.; Long, P.; McNichol, A. P.; Morin, T.; Stuart, D.; Hayes, J. M.; et al. (8th International Conference on Heavy Ion Accelerator Technology, 1998)
id: 1636

High-precision radiocarbon age calibration for terrestrial and marine samples - Stuiver, M.; Reimer, P. J.; Braziunas, T. F. (Radiocarbon, 1998)
Single-year and decadal radiocarbon tree-ring ages are tabulated and discussed in terms of C-14 age calibration. The single-year data form the basis of a detailed 14C age calibration curve for the cal AD 1510-1954 interval ("cal" denotes calibrated). The Seattle decadal data set (back to 11,617 cal sp, with 0 sp = AD 1950) is a component of the integrated decadal INTCAL98 C-14 age curve (Stuiver et al. 1998). Atmospheric C-14 ages can be transformed into C-14 ages of the global ocean using a carbon reservoir model. INTCAL98 C-14 ages, used for these calculations, yield global ocean C-14 ages differing slightly from previously published ones (Stuiver and Braziunas 1993b). We include discussions of offsets, error multipliers, regional C-14 age differences and marine C-14 age response to oceanic and atmospheric forcing.
155qrTimes Cited:705 Cited References Count:31
Keywords: ad 1950-500 bc; c-14 data; decadal calibration; reservoir ages; time scale

Historical geomorphic processes and human activities in the Central Spanish Pyrenees - Garcia-Ruiz, J. M.; Valero-Garces, B. L. (Mountain Research and Development, 1998)
In the Central Spanish Pyrenees there is a great diversity of geomorphic processes due to topographic and climatic heterogeneity and altitudinal gradient. Human activity during the last 4,000 years has contributed to the disturbance of the original landscape and its hydro-morphological dynamics. The upper forest belt was destroyed by fire during the Middle Ages in order to provide summer pastures to transhumant livestock. The hillslopes below 1,600 m were cultivated and frequently burnt to improve the soil and pasture quality, even on steep slopes. The most evident consequence of this has been the increase in the sources of sediment. In the subalpine belt, mass movements and dense rill networks have caused severe soil erosion and the expansion of gelifluxion terracettes; in the middle mountain belt overland flow has resulted in stoniness of the soil surface, and debris flows have occurred on hillslopes and along river channels. This paper discusses the effects of human activity on the geomorphic processes in the study area.
142mnTimes Cited:49Cited References Count:62

Holocene Evolution of Lake Erie Environments: inferrences from stable isotopes of cored sediments offshore Fairport Harbor, Ohio--Thesis - McCambridge, Constance (University of Akron, 1998)

How much deep water is formed in the Southern Ocean? - Broecker, W. S.; Peacock, S. L.; Walker, S.; Weiss, R.; Fahrbach, E.; Schroeder, M.; Mikolajewicz, U.; Heinze, C.; Key, R.; Peng, T. H.; Rubin, S. (Journal of Geophysical Research-Oceans, 1998)
Three tracers are used to place constraints on the production rate of ventilated deep water in the Southern Ocean. The distribution of the water mass tracer PO4* ("phosphate star") in the deep sea suggests that the amount of ventilated deep water produced in the Southern Ocean is equal to or greater than the outflow of North Atlantic Deep Water from the Atlantic. Radiocarbon distributions yield an export flux of water from the North Atlantic which has averaged about 15 Sv over the last several hundred years. CFC inventories are used as a direct indicator of the current production rate of ventilated deep water in the Southern Ocean. Although coverage is as yet sparse, it appears that the CFC inventory is not inconsistent with the deep water production rate required by the distributions of PO4* and radiocarbon. It has been widely accepted that the major part of the deep water production in the Southern Ocean takes place in the Weddell Sea. However, our estimate of the Southern Ocean ventilated deep water flux is in conflict with previous estimates of the flux of ventilated deep water from the Weddell Sea, which lie in the range 1-5 Sv. Possible reasons for this difference are discussed.
Zz547Times Cited:115Cited References Count:44

Impact of human activity on regional forest composition and dynamics in central New England - Fuller, T. L.; Foster, D. R.; McLachlan, T. S.; Drake, N. (Ecosystems, 1998)
Historical and ecological data from north-central Massachusetts suggest that widespread and intensive human disturbance after European settlement led to a shift in forest composition and obscured regional patterns of species abundance. A paleoecological approach was required to place recent forest dynamics in a long-term context. Pollen and charcoal data from 11 small lakes in north-central Massachusetts were used to reconstruct local vegetation dynamics and fire histories across the region over the past 1000 years. The sites are located across an environmental gradient. Paleoecological data indicate that prior to European settlement, there was regional variation in forest composition corresponding to differences in climate, substrate, and fire regime. Oak, chestnut, and hickory were abundant at low elevations, whereas hemlock, beech, sugar maple, and yellow birch were common at high elevations. Fire appears to have been more frequent and/or intense at lower elevations, maintaining high abundances of oak, and archaeological data suggest Native American populations were greater in these areas. A change in forest composition at higher elevations, around 550 years before present, may be related to the Little Ice Age (a period of variable climate), fire, and/or activity by Native Americans, and led to regional convergence in forest composition. After European settlement, forest composition changed markedly in response to human disturbance and there was a sharp increase in rates of vegetation change. Regional patterns were obscured further, leading to homogenization of broad-scale forest composition. There is no indication from the pollen data that forests are returning to pre-European settlement forest composition, and rates of vegetation change remain high, reflecting continuing disturbance on the landscape, despite regional reforestation.
Keywords: awenda provincial park; eastern north-america; european settlement; forest dynamics; history; human disturbance; lake sediment; land-use; new england; paleoecology; patterns; rates of change; united-states; vegetation dynamics

Influence of oxygen exposure time on organic carbon preservation in continental margin sediments - Hartnett, H. E.; Keil, R. G.; Hedges, J. I.; Devol, A. H. (Nature, 1998)
Today, over 90% of all organic carbon burial in the ocean occurs in continental margin sediments(1). This burial is intrinsically linked to the cycling of biogeochemically important elements (such as N, P, S, Fe and Mn) and, on geological timescales, largely controls the oxygen content of the atmosphere(2-4). Currently there is a volatile debate over which processes govern sedimentary organic carbon preservation(5-8). In spite of numerous studies demonstrating empirical relationships between organic carbon burial and such factors as primary productivity(9), the flux of organic carbon through the water column(10), sedimentation rate(11,12), organic carbon degradation rate(13), and bottom-water oxygen concentration(8,14), the mechanisms directly controlling sedimentary organic carbon preservation remain unclear. Furthermore, as organic carbon burial is the process that, along with pyrite burial(15), balances O-2 concentrations in the atmosphere, it is desirable that any mechanism proposed to control organic carbon preservation include a feedback buffering atmospheric oxygen concentrations over geological time. Here we compare analyses of sediments underlying two regions of the eastern North Pacific Ocean, one which has oxygen-depleted bottom waters and one with typical oxygen distributions. Organic carbon burial efficiency is strongly correlated with the length of time accumulating particles are exposed to molecular oxygen in sediment pore waters. Oxygen exposure time effectively incorporates other proposed environmental variables(8-14), and may exert a direct control on sedimentary organic carbon preservation and atmospheric oxygen concentrations.
Yv594Times Cited:355Cited References Count:27

Isotopic Biogeochemistry of the Neocomian Lacustrine and Upper Aptian Marine-Evaporitic Sediments of the Potiguar Basin, Northeastern Brazil - Neto, Eugenio Vaz dos Santos; Hayes, John M.; Takaki, Tikae (Organic Geochemistry, 1998)
id: 1729

Late Holocene climatic variability in Central America: evidence from lacustrine sediments in the Peten, Guatemala and implications for Maya cultural evolution; Procedings of the PEP 1 - Rosenmeier, M. F.; Hodell, D. A.; Martin, J. B.; Brenner, M.; Curtis, J. H. (PEP 1 (Pole-Equator-Pole, Paleoclimate of the Americas), 1998)
id: 141

Late Pleistocene Mammuthus primigenious from coastal mMaine - Hoyle, B. G.; Fisher, D. C.; Dorion, C. C.; Churchill, L. L.; W, Borns H., Jr.; Nelson, R. E. (33rd annual meeting, Geological Society of America, Northeastern Section, 1998)
id: 21

Le torbiditi dell'Escanaba Trough (Juan de Fuca Plate, Pacifico nordorientale): registrazione sedimentaria di piene fluviali catastrofiche del Fiume Columbia durante le fasi di deglaciazione tardo quaternaria - Brunner, C. A.; Normark, W. R.; Zuffa, G. G.; Serra, F. (Giornale di Geologia, 1998)
id: 1470

Manzala lagoon, Nile delta, Egypt: modern sediment accumulation based on radioactive tracers - Benninger, L. K.; Suayah, I. B.; Stanley, D. J. (Environmental Geology, 1998)
This study was undertaken to determine whether recent anthropogenic changes in the Nile basin have affected the modern rate of sediment accumulation in the Nile delta. Excess (210)pb, Cs-137, and Pu-239,Pu-240 were used to develop a sediment chronology for a core from central Manzala lagoon, the delta sector which has had the highest average rate of sediment accumulation during the Holocene (to about 0.7 cm year(-1)). Excess Pb-210 was detected in the top 32 cm of the core, yielding an accumulation rate of 1.2 cm year(-1), higher than the mean rate for the Holocene. A high Cs-137/Pu-239,Pu-240 ratio requires a reactor source (possibly Chernobyl) for these nuclides. Low concentrations of excess (210)pb and weapons-fallout nuclides precluded recognition of changes in sediment accumulation rate in Manzala lagoon during this century and may limit the use of tracer radionuclides for modern sediment chronology in the Nile delta.
id: 1283; Zq055 Times Cited:9 Cited References Count:37

A massive terraced village complex in Chihuahua, Mexico, 3000 years before present - Hard, R. J.; Roney, J. R. (Science, 1998)
Cerro Juanaquena is a residential complex with 8 kilometers of terrace walls in northwestern Mexico that was occupied at similar to 3000 calendar years before present based on radiocarbon dates on maize (Zea mays L.), Most other similar sized terrace complex sites that have been found date to similar to 1000 years before present, Cerro Juanaquena was contemporaneous with 10 other sites in the southwestern United States that have yielded 18 of the earliest maize or squash radiocarbon dates yet, and it is by far the largest and most complex site, The archaeological evidence from this site, combined with other recent data, implies that highly variable combinations of population aggregation, agricultural dependence, and degrees of sedentism were present during the time maize was being introduced into the American Southwest.
Zb612Times Cited:32Cited References Count:59

Method and Technology of AMS - von Reden, K. F. (University of Mass., Dartmouth, 1998)
id: 1677

Microscale AMS 14C Measurement at NOSAMS - Pearson, Ann; McNichol, Ann P.; Schneider, Robert J.; von Reden, Karl F. (16th International 14C Conference, 1998)
id: 1502

Microscale AMS 14C measurements at NOSAMS - Pearson, A.; McNichol, A. P.; Schneider, R. J.; von Reden, K. F.; Zheng, Y. (Radiocarbon, 1998)
id: 1621

Microscale AMS 14C measurements at NOSAMS: (Proceedings of the 16th International Radiocarbon Conference, 1997) - Pearson, A.; McNichol, A. P.; Schneider, R. J.; von Reden, K. F.; Zheng, Y. (Radiocarbon, 1998)
id: 1814

Microscale AMS (super 14) C measurement at NOSAMS - Pearson, Ann; McNichol, Ann P.; Schneider, Robert J.; von Reden, Karl F.; Zheng, Yan (University of Arizona, Department of Geosciences, Tucson, AZ, United States (USA), 1998)
Techniques for making precise and accurate radiocarbon accelerator mass spectrometry (AMS) measurements on samples containing less than a few hundred micrograms of carbon are being developed at the NOSAMS facility. A detailed examination of all aspects of the sample preparation and data analysis process shows encouraging results. Small quantities of CO (sub 2) are reduced to graphite over cobalt catalyst at an optimal temperature of 605 degrees C. Measured (super 14) C/ (super 12) C ratios of the resulting targets are affected by machine-induced isotopic fractionation, which appears directly related to the decrease in ion current generated by the smaller sample sizes. It is possible to compensate effectively for this fractionation by measuring samples relative to small standards of identical size. Examination of the various potential sources of background (super 14) C contamination indicates that the sample combustion process is the largest contributor, adding ca. 1 mu g of carbon with a less-than-modern (super 14) C concentration.
id: 2237; Source type: conferencepapers&proceedings; Object type: Article; Object type: Conference Paper; Copyright: GeoRef, Copyright 2007, American Geological Institute.; CSAUnique: 1999-044438; AccNum: 1999-044438; ISSN: 0033-8222; CODEN: RACAAT
Keywords: 03; absolute age; accelerator mass spectroscopy; accuracy; C-14; C-14/C-12; carbon; Carbon dioxide; combustion; data processing; Geochronology; graphite; isotope fractionation; isotopes; mass spectroscopy; mathematical methods; methods; native elements; radioactive isotopes; sample preparation; size; spectroscopy; Stable isotopes

Millennial-scale changes in North Atlantic circulation since the last glaciation - Marchitto, T. M.; Curry, W. B.; Oppo, D. W. (Nature, 1998)
Ocean circulation is closely linked to climate change on glacial-interglacial and shorter timescales. Extensive reorganizations in the circulation of deep and intermediate-depth waters in the Atlantic Ocean have been hypothesized for both the last glaciation(1-6) and the subsequent Younger Dryas cold interval(3,6-10), but there has been little palaeoceanographic study of the subtropical gyres(11-13). These gyres are the dominant oceanic features of wind-driven circulation, and as such they reflect changes in climate and are a significant control on nutrient cycling and, possible, atmospheric CO2 concentrations. Here we present Cd/Ca ratios in the shells of benthic foraminifera from the Bahama banks that confirm previous suggestions(11,12) that nutrient concentrations in the North Atlantic subtropical gyre were much lower during the Last Glacial Maximum than they are today (up to 50% lower according to our data). These contrasting nutrient burdens imply much shorter residence times for waters within the thermocline of the Last Glacial Maximum. Below the glacial thermocline, nutrient concentrations were reduced owing to the presence of Glacial North Atlantic Intermediate Water. A high-resolution Cd/Ca record from an intermediate depth indicates decreased nutrient concentrations during the Younger Dryas interval as well, mirroring opposite changes at a nearby deep site(3,9). Together, these observations suggest that the formation of deep and intermediate waters-North Atlantic Deep Water and Glacial North Atlantic Intermediate Water, respectively-wax and wane alternately on both orbital and millennial timescales.
Zt988Times Cited:106Cited References Count:30

A multi-proxy study of Holocene environmental change in the Maya lowlands of Peten, Guatemala - Curtis, J. H.; Brenner, M.; Hodell, D. A.; Balser, R. A.; Islebe, G. A.; Hooghiemstra, H. (Journal of Paleolimnology, 1998)
We used multiple variables in a sediment core from Lake Peten-Itza, Peten, Guatemala, to infer Holocene climate change and human influence on the regional environment. Multiple proxies including pollen, stable isotope geochemistry, elemental composition, and magnetic susceptibility in samples from the same core allow differentiation of natural versus anthropogenic environmental changes. Core chronology is based on AMS (14)C measurement of terrestrial wood and charcoal and thus avoids the vagaries of hard-water-lake error. During the earliest Holocene, prior to similar to 9000 (14)C yr BP, the coring site was not covered by water and all proxies suggest that climatic conditions were relatively dry. Water covered the coring site by similar to 9000 (14)C yr BP, coinciding with filling of other lakes in Peten and farther north on the Yucatan Peninsula. During the early Holocene (similar to 9000 to similar to 6800 (14)C yr BP), pollen data suggest moist conditions, but high delta(18)O values are indicative of relatively high E/P. This apparent discrepancy may be due to a greater fractional loss of the lake's water budget to evaporation during the early stages of lake filling. Nonetheless, conditions were moist enough to support semi-deciduous lowland forest. Decrease in delta(18)O values and associated change in ostracod species at similar to 6800 (14)C yr BP suggest a transition to even moister conditions. Decline in lowland forest taxa beginning similar to 5780 (14)C yr BP may indicate early human disturbance. By similar to 2800 (14)C yr BP, Maya impact on the environment is documented by accelerated forest clearance and associated soil erosion. Multiple proxies indicate forest recovery and soil stabilization beginning similar to 1100 to 1000 (14)C yr BP, following the collapse of Classic Maya civilization.
Zj856Times Cited:92Cited References Count:96

A new model for Proterozoic ocean chemistry - Canfield, D. E. (Nature, 1998)
There was a significant oxidation of the Earth's surface around 2 billion years ago (2 Gyr)(1-4). Direct evidence for this oxidation comes, mostly, from geological records of the redox-sensitive elements Fe and U reflecting the conditions prevailing during weathering(1-3). The oxidation event was probably driven by an increased input of oxygen to the atmosphere arising from an increased sedimentary burial of organic matter between 2.3 and 2.0 Gyr(5). This episode was postdated by the final large precipitation of banded iron formations around 1.8 Gyr(1,2). It is generally believed that banded iron formations precipitated from an ocean whose bottom waters contained significant concentrations of dissolved ferrous iron, and that this sedimentation process terminated when aerobic bottom waters developed, oxidizing the iron and thus removing it from solution(1,2). In contrast, I argue here that anoxic bottom waters probably persisted until well after the deposition of banded iron formations ceased; I also propose that sulphide, rather than oxygen, was responsible for removing iron from deep ocean water. The sulphur-isotope record supports this hypothesis as it indicates increasing concentrations of oceanic sulphate, starting around 2.3 Gyr(6), leading to increasing rates of sulphide production by sulphate reduction. The increase in sulphide production became sufficient, around 1.8 Gyr,to precipitate the total flux of iron into the oceans. I suggest that aerobic deep-ocean waters did not develop until the Neoproterozoic era (1.0 to similar to 0.54 Gyr), in association with a second large oxidation of the Earth's surface. This new model is consistent with the emerging view of Precambrian sulphur geochemistry and the chemical events leading to the evolution of animals, and it is fully testable by detailed geochemical analyses of preserved deep-water marine sediments.
145klTimes Cited:530Cited References Count:29

North Atlantic gyre ventilation and intermediate water formation during the last glaciation and Younger Dryas - Marchitto, T. M.; Curry, W. B.; W, Oppo D. (Nature, 1998)
id: 208

NOSAMS Controls with LabView - von Reden, K. F. (Proceedings of the 30th Symposium of Northeastern Accelerator Personnel - Woods Hole, 1996, 1998)
id: 1764

NOSAMS Controls with LabView - von Reden, K. F. (World Scientific, 1998)
id: 1675

NOSAMS Controls with LabView - von Reden, K. F. (Symposium of North-Eastern Accelerator Personnel, Woods Hole Oceanographic Institution, Woods Hole, USE, October 27-30, 1996, SNEAP XXX, 1998)
id: 1721

The NOSAMS Sample Preparation Laboratory: Systems and graphite performance analysis - Gagnon, A. R.; McNichol, A. P.; Donaghue, J. C.; Morin, T. J.; Peden, J. C. (16th International 14C Conference, 1998)
id: 1628

Overview of the eruption of Soufriere Hills volcano, Montserrat, 18 July 1995 to December 1997 - Young, S. R.; Sparks, R. S. J.; Aspinall, W. P.; Lynch, L. L.; Miller, A. D.; Robertson, R. E. A.; Shepherd, J. B. (Geophysical Research Letters, 1998)
The onset of phreatic volcanic activity at the Soufriere Hills volcano, Montserrat on 18 July 1995 followed a three-year period of heightened volcano-seismic activity beneath the island. Phreatic explosions gave way to continuous eruption of juvenile andesitic magma in the form of a lava dome on or around 15 November 1995. Magma production rate has varied, leading to changes in eruptive style. An explosive eruption on 17 September 1996 followed a period of enhanced dome growth and large-scale gravitational collapses from its eastern flank. Increasing dome volume led to stressing and overtopping of the confining crater walls to the southwest, north and west during early 1997. Sustained high magma production rate since June 1997 has led to three periods of major gravitational dome collapses followed by vulcanian explosive eruptions. Dome growth re-started immediately after the cessation of the latest of these explosive phases in October 1997 and continues as of December 1997.
119mkTimes Cited:102Cited References Count:7

P10 Final report for AMS 14C samples - Key, R. M. (Ocean Tracer Laboratory Tech. Rep., 1998)
id: 1463

P10 Final report for large volume 14C samples - Key, R. M. (Ocean Tracer Laboratory Tech. Rep., 1998)
id: 1462

P17N Final report for AMS 14C samples - Key, R. M. (Ocean Tracer Laboratory Tech. Rep., 1998)
id: 1460

P18 Final report for AMS 14C samples - Key, R. M.; D, Quay P. (Ocean Tracer Laboratory Technical Report, 1998)
id: 1464

P19C Final report for AMS 14C samples - Key, R. M. (Ocean Tracer Laboratory Tech. Rep., 1998)
id: 1461

Paleoclimatic Assessment of Cretaceous Lacustrine and Marine-Evaporitic Sequences from the Potiguar Basin Based on the Hydrogen Isotopic Compositions of Saturated Hydrocarbons - Neto, Eugenio Vaz dos Santos; Hayes, John M.; Takaki, Tikae (Revista Latino Americana de Geoquimica Ogranica, 1998)
id: 1776

Physical controls on dissolved inorganic radiocarbon variability in the California Current - Masiello, C. A.; Druffel, E. R. M.; Bauer, J. E. (Deep-Sea Research Part Ii-Topical Studies in Oceanography, 1998)
We present depth profiles of Delta(14)C and delta(13)C Of dissolved inorganic carbon (DIC) at Station M in the Eastern North Pacific. Several seasonal profiles are presented for the time period between 1991 and 1996. Comparison with GEOSECS data clearly shows changes in ocean radiocarbon profiles since 1973. The Delta(14)C Of DIC shows the most variability at depths of 450, 85, and 25 m, and the lowest variability at depths of 1600 and 2500 m. The largest variability in DIC Delta(14)C occurs at 450 m, a depth marked by large fluctuations in the radiocarbon signatures of the source waters. The likely controls of DIC Delta(14)C variability are physical changes in the circulation of the California Current System. A simple two-box model is used to show the importance of wind driven mixing at the surface. We discuss the likely effects of mesoscale eddies and ENSO on the DIC Delta(14)C values at this site. We also show that remineralization of organic carbon (dissolved or particulate) is not responsible for the variability in the Delta(14)C Of DIC observed at Station M. (C) 1998 Elsevier Science Ltd. All rights reserved.
102ttTimes Cited:21Cited References Count:43

Preparation for continuous flow accelerator mass spectrometry Radiocarbon - Schneider, R. J.; Hayes, J. M.; von Reden, K. F.; McNichol, A. P.; Eglinton, T.; Wills, J. S. C. (Radiocarbon, 1998)
id: 1623

Proceedings of the 30th Symposium of Northeastern Accelerator Personnel - Woods Hole, 1996 - von Reden, K. F.; Schneider, R. J. (World Scientific, 1998)
id: 1674

The Proceedings of the 30th Symposium of North-Eastern Accelerator Personnel - von Reden, K. F.; Schneider, R. J. (30th Symposium of North-Eastern Accelerator Personnel, 1998)

Proceedings of the 8th International Conference on Heavy Ion Accelerator Technology - Schneider, R. J.; von Reden, K. F.; Hayes, J. M.; Wills, J. S. C. (American Institute of Physics, Conference Proceeding Series, 1998)
id: 1624; submitted

Pyroclastic stratigraphy of the Soufriere Hills volcano, Montserrat - Implications for the present eruption - Roobol, M. J.; Smith, A. L. (Geophysical Research Letters, 1998)
The stratigraphy of the Soufriere Hills volcano is dominated by dense-andesite block and ash flow deposits. Forty-one radiocarbon ages permit a reconstruction of the eruptive history over the past 31,000 years. A single stratigraphic member yielding radiocarbon ages of 22,000 to 20,000 years B.P. is composed of block and ash flow deposits with semi-vesiculated clasts concentrated in the upper third of each deposit. The present eruption is also producing block and ash flow deposits with both dense and semi-vesiculated clasts. It marks a return to a more explosive driven type of activity as occurred 22,000 to 20,000 years ago. Deposits of this member have a broad sheet-like form and volumes in excess of any produced so far by the present eruption.
119mkTimes Cited:24Cited References Count:9

Quantitative Production of H2 by Pyrolysis of Gas Chromatographic Effluents - Burgoyne, Thomas W.; Hayes, John M. (Analytical Chemistry, 1998)
id: 1731

Radiocarbon in the North Pacific: What we have learned since GEOSECS - Key, Robert M. (Seventh Annual PICES Meeting, 1998)
id: 311

Radiometrically determined sedimentary fluxes in the sub-polar North Atlantic during the last 140,000 years - McManus, J. F.; Anderson, R. F.; Broecker, W. S.; Fleisher, M. Q.; Higgins, S. M. (Earth and Planetary Science Letters, 1998)
We have examined the record of sediment input during the last 140000 years in a deep-sea core from 49 degrees 27'N, 22 degrees 16'W in the eastern North Atlantic. Using uranium-series disequilibria to constrain time, we have calculated mass fluxes of total sediment, as well as mass and particle fluxes of major sedimentary components. Sediment accumulation rates were generally lower and relatively constant during broadly defined interglacial intervals, driven primarily by the burial of biogenic material. Accumulation rates were higher and more variable during glacial intervals, and were influenced primarily by terrigenous material. Peaks in bulk mass fluxes were associated with particular episodes (Heinrich events) within the last glacial and during each of the last two deglaciations. The flux of ice-rafted debris, as uniquely identified by coarse detrital fragments, was higher during layers representing each of the glacial Heinrich events, with modest increases during events H3 and H6 and dramatic increases during the others, confirming the widespread interpretation of these layers as episodes of enhanced iceberg delivery. The burial flux of foraminifera was markedly lower during each of the glacial Heinrich events, also confirming the original identification of these layers as barren intervals. Ice-rafting events within marine isotope stage 5 left neither a large detrital nor biogenic flux imprint at our study site. Variations in the burial rates of non-carbonate sediments were largely responsible for overall changes in sediment accumulation throughout the last climate cycle. Ice-rafting was apparently an important delivery mechanism for this terrigenous material. The instantaneous chronometer established here for the last 140000 years in the subpolar North Atlantic allows the transformation of existing and subsequent data from relative values to absolute burial fluxes. (C) 1998 Elsevier Science B.V.
Ze160Times Cited:70Cited References Count:55

A reassessment of the sources and importance of land-derived organic matter in surface sediments from the Gulf of Mexico - Goñi, M. A.; Ruttenberg, K. C.; Eglinton, T. I. (Geochimica Et Cosmochimica Acta, 1998)
Organic matter in surface sediments from two onshore-offshore transects in the northwestern Gulf of Mexico was characterized by a variety of techniques, including elemental, stable carbon, radiocarbon, and molecular-level analyses. In spite of the importance of the Mississippi River as a sediment source, there is little evidence for a significant terrigenous input based on the low carbon:nitrogen ratios (8-5) and the enriched delta(13)C values of bulk sedimentary organic carbon (-19.7 parts per thousand to -21.7 parts per thousand). Radiocarbon analyses, on the other hand, yield depleted Delta(14)C values (-277 parts per thousand to -572 parts per thousand) which indicate that a significant fraction of the sedimentary organic carbon (OC) in all these surface sediments must be relatively old and most likely of allochthonous origin. CuO oxidations yield relatively low quantities of lignin products (0.4-1.4 mg/100 mg OC) along with compounds derived from proteins, polysaccharides, and lipids. Syringyl:vanillyl and cinnamyl:vanillyl ratios (averaging 1.6 and 0.5, respectively) and acid:aldehyde ratios for both vanillyl and syringyl phenols (averaging 0.8 and 1.2, respectively) indicate that the lignin present in sediments originates from nonwoody angiosperm sources and is highly degraded. The delta(13)C values of lignin phenols in shelf sediments are relatively depleted in (13)C (averaging -26.3 parts per thousand) but are increasingly enriched in (13)C at the slope sites (averaging -17.5 parts per thousand for the two deepest stations). We interpret these molecular and isotopic compositions to indicate that a significant fraction (greater than or equal to 50%) of the lignin and, by inference, the land-derived organic carbon in northwestern Gulf of Mexico sediments ultimately originated from C(4) plants. The source of this material is likely to be soil organic matter eroded from the extensive grasslands of the Mississippi River drainage basin. Notably, the mixed C(4) and C(3) source and the highly degraded state of this material hampers its recognition and quantification in shelf and slope sediments. Our data are consistent with higher than previously estimated inputs of land-derived organic carbon to regions of the ocean, such as the Gulf of Mexico, with significant sources of terrigenous C(4)-derived organic matter. Copyright (C) 1998 Elsevier Science Ltd.
156xvTimes Cited:251Cited References Count:133

Reproducibility of seawater, inorganic and organic 14C results at NOSAMS - Elder, K. L.; McNichol, A. P.; Gagnon, A. R. (Sixteenth International 14C Conference, 1998)
id: 1625

Ritual, Power, and the Development of a Complex Society: The Island of the Sun and the Tiwanaku State, Thesis - Seddon, Matthew T. (University of Chicago, 1998)

Sea level higher than present 3500 years ago on the northern main Hawaiian Islands - Grossman, E. E.; Fletcher, C. H. (Geology, 1998)
New data from an emerged coastal bench and associated fossil beach on Kapapa Island (Oahu), Hawaii, preserve a detailed history of middle to late Holocene sea level. These include 29 new calibrated radiocarbon ages and elevations indicating mean sea level reached a maximum position of 2.00 +/- 0.35 m ca. 3500 yr B.P. These results correlate with additional evidence from Hawaii and other Pacific islands and provide constraints on Oahu's long-term uplift rate (0.03-0.07 mm/yr), previously based solely on Pleistocene age shorelines. Our sea-level reconstruction is consistent with geophysical model predictions of Earth's geoid response to the last deglaciation and with observations of increased Antarctic ice volume during the late Holocene.
Zg996Times Cited:34Cited References Count:25

Sea-level rise on eastern China's Yangtze delta - Chen, Z. Y.; Stanley, D. J. (Journal of Coastal Research, 1998)
The Yangtze delta is a densely populated, low-lying region highly vulnerable to flooding, high tides and typhoons. All previous studies indicated that relative sea level was higher from similar to 7500-4000 yrs. BP, then lowered and stabilized at about present msl during the past 3000 yrs. To the contrary, we find that sea level has been rising relative to the southern Yangtze delta plain based on new sea-level data derived from dated peats, reassessment of earlier sea-level curves and measurement of delta plain subsidence and analysis of prehistoric habitat bases from similar to 7000 to 3000 yrs. BP. Consequences of this relative rise include difficulty in expelling water from the low-lying delta plain to the coast and associated flood damage. Emplacement of the 3-Gorges Dam on the Yangtze will control flooding of the Yangtze river but decrease sediment accumulation on the delta plain that, in turn, is likely to accelerate saline inundation of this vital breadbasket.
Yt592Times Cited:46 Cited References Count:27
Keywords: delta flooding; Holocene; neolithic sites; peat; radiocarbon dates; relative sea level; sea-level curve; subsidence; taihu lake; yangtze delta

Status Report of the National Ocean Sciences AMS Facility at Woods Hole Oceanographic Institution: Operations and Recent Developments - Bellino, M.; von Reden, K. F.; Schneider, R. J.; Peden, J. C.; Donoghue, J.; Elder, K. L.; Gagnon, A. R.; Long, P.; McNichol, A. P.; Odegaard, A. P.; Stuart, D.; Handwork, S.; et al. (15th International Conference on the Applications of Accelerators in Research and Industry, 1998)
id: 1647

(super 14) C AMS measurements of - von Reden, Karl F.; McNichol, Ann P.; Pearson, Ann; Schneider, Robert J. (University of Arizona, Department of Geosciences, Tucson, AZ, United States (USA), 1998)
The NOSAMS facility at Woods Hole Oceanographic Institution has started to develop and apply techniques for measuring very small samples on a standard Tandetron accelerator mass spectrometry (AMS) system with high-current hemispherical Cs sputter ion sources. Over the past year, results on samples ranging from 7 to 160 mu g C showed both the feasibility of such analyses and the present limitations on reducing the size of solid carbon samples. One of the main factors affecting the AMS results is the dependence of a number of the beam optics parameters on the extracted ion beam current. The extracted currents range from 0.5 to 10 mu A of (super 12) C (super -) for the sample sizes given above. We here discuss the setup of the AMS system and methods for reliable small-sample measurements and give the AMS-related limits to sample size and the measurement uncertainties.
id: 2239; Source type: conferencepapers&proceedings; Object type: Article; Object type: Conference Paper; Copyright: GeoRef, Copyright 2007, American Geological Institute.; CSAUnique: 1999-044459; AccNum: 1999-044459; ISSN: 0033-8222; CODEN: RACAAT
Keywords: 03; absolute age; accelerator mass spectroscopy; C-14; carbon; dilution; Geochronology; ions; isotopes; mass spectroscopy; precision; radioactive isotopes; sample preparation; spectroscopy; volume

Synthesis and modeling of the WOCE radiocarbon data set - Key, Robert M. (WOCE Conference, 1998)
id: 1443

Target preparation for continuous flow accelerator mass spectrometry - Schneider, R. J.; Hayes, J. M.; von Reden, K. F.; McNichol, A. P.; Eglinton, T. I.; Wills, J. S. C. (Radiocarbon, 1998)
For very small samples, it is difficult to prepare graphitic targets that will yield a useful and steady sputtered ion beam. Working with materials separated by preparative capillary gas chromatography, we have succeeded with amounts as small as 20 mu g C. This seems to be a practical limit, as it involves 1) multiple chromatographic runs with trapping of effluent fractions, 2) recovery and combustion of the fractions, 3) graphitization and 4) compression of the resultant graphite/cobalt matrix into a good sputter target. Through such slow and intricate work, radiocarbon ages of lignin derivatives and hydrocarbons from coastal sediments have been determined. If this could be accomplished as an "online" measurement by flowing the analytes directly into a microwave gas ion source, with a carrier gas, then the number of processing steps could be minimized. Such a system would be useful not just for chromatographic effluents, but for any gaseous material, such as CO2 produced from carbonates. We describe tests using such an ion source.
1 Sp. Iss. SI113kt Times Cited:11 Cited References Count:10
Keywords: gas; ion-source

Technology revolutionizes tracer oceanography during WOCE - Key, R. M.; McNichol, A. (International WOCE Newsletter, 1998)
id: 324

Temporal variations of bomb radiocarbon inventory in the Pacific Ocean - Peng, T. H.; Key, R. M.; Ostlund, H. G. (Marine Chemistry, 1998)
The natural and anthropogenic components of the radiocarbon measurements from seawater samples can be successfully separated by an improved method, which is based on a very well-defined relationship between natural radiocarbon and dissolved silica observed mainly during the GEOSECS survey for waters beneath 1000 m depth. This relationship is further reconfirmed by the C-14 measurements from large volume samples taken in the deep waters in the Pacific Ocean during the recent WOCE survey program. Analysis of upper ocean C-14 measurements made along 152 degrees W, and north of 20 degrees N, in the northeastern Pacific Ocean during the NOAA's CGC91 cruise, which is a part of the WOCE survey program, indicates that the bomb C-14 inventory in this part of the ocean has increased by 22% since the GEOSECS measurements made in 1974, This increase is consistent with the model prediction of 25% for the northern hemisphere ocean. Change of the surface water bomb Delta(14)C values during this period is insignificant, This feature is also consistent with the model simulation. Results of this new analysis will provide useful information of the temporal variations of bomb C-14 inventory in the ocean, in addition to the spatial distribution, which can be used as powerful constraints in calibrating the global ocean carbon cycle models, especially those based on three-dimensional ocean general circulation models, for estimating the uptake of CO2 by the ocean. (C) 1998 Elsevier Science B.V.
Zm128Times Cited:22Cited References Count:18

Three Holocene tephras identified in lacustrine sediment cores from the Wonder Lake area, Denali National Park and Preserve AK - Child, J. C.; Beget, J.; Werner, A. (Arctic and Alpine Research, 1998)
id: 235

Un registro de 6,000 anos de manifestaciones intensas del fenomeno de El Nino en sedimentos de lagunas de las Islas Galapagos - Steinitz-Kannan, M.; Riedinger, M. A.; Last, W. M.; Brenner, M.; Miller, M. C. (Bulletin de l'Institut Francais d'Etudes Andines, 1998)
id: 196

Una Investigacion Arqueologica de los Sitios Cerros con Trincheras del Arcaico Tardio en Chihuahua, Mexico: Las Investigaciones de Campo de 1997 - Hard, R.; Roney, J. (University of Texas, Center for Archaeological Research, 1998)
id: 242

Water-induced errors in continuous-flow carbon isotope ratio mass spectrometry - Leckrone, K. J.; Hayes, J. M. (Anal Chem, 1998)
Formation of HCO2+ from CO2 and background H2O in isotope ratio mass spectrometers has been examined in detail. The process is troublesome because its product is not resolved from 13C16O2+. The resulting, artifactual enhancement of the mass 45 ion current (and analogous enhancement of the mass 46 ion current by transfer of hydrogen to mass 45 species) can cause systematic errors in analyses of 13C based on measurement of ion current ratios in the mass spectrum of CO2. Such errors are neutralized when isotopic analyses are based on differential comparisons in which ion currents and background water levels are precisely equal during admission and ionization of both sample and standard gases. In continuous-flow systems, however, that requirement is generally not met. The resulting systematic error is proportional to the 18/44 ion current ratio. When the widely used MAT252 mass spectrometer is tuned to yield maximum sensitivity, the constant of proportionality is 26 +/- 2/1000 (i.e., the error will be 0.26/1000 if the mass 18 ion current is 100 times smaller than that at mass 44). Errors can be reduced 5-fold when the ion-source residence time of CO2+ is decreased by use of stronger ion-extraction potential gradients. Under those same conditions, sensitivity is decreased by 60%. For operation at highest sensitivity, carrier gas dew points on the order of -70 degrees C are required to obtain errors < or = 0.1/1000 for samples yielding mass 44 ion currents of 10 nA. Carrier gas dew points < or = -80 degrees C are conveniently reached by use of a Nafion dryer operated at approximately 0 degree C.
Leckrone, K JHayes, J MengResearch Support, Non-U.S. Gov'tResearch Support, U.S. Gov't, Non-P.H.S.1998/07/17Anal Chem. 1998 Jul 1;70(13):2737-44.

Water-level changes in Lake Baikal, Siberia: Tectonics versus climate - Colman, S. M. (Geology, 1998)
id: 187

Western Great Lakes paleoecology study, global climate change initiative. In Holocene Paleoenvironments in Western Great Lakes Parks. Report - Winkler, M. G.; Sanford, P. R. (National Park Service & USGS Biological Resources Div., Northern Prairie Wildlife Research Center, 1998)
id: 130

Yangtze delta inundation and the discontinuity between Neolithic and younger cultures, China - Stanley, D. J.; Chen, Z.; Song, J. (Geoarchaeology, 1998)
id: 228

14C AMS measurement of C AMS measurement of C AMS measurement of - von Reden, K.; McNichol, A.; Pearson, A.; Schneider, R. (16th International Radiocarbon Conference, Groningen, 1997)
id: 952

A 3,500 14C yr. high-resolution record of lake level changes in Lake Titicaca, South America - Abbott, M. B.; Binford, M. W.; Brenner, M.; Kelts, K. R. (Quaternary Research, 1997)
Sediment cores collected from the southern basin of Lake Titicaca (Bolivia/Peru) on a transect from 4.6 m above overflow level to 15.1 m below overflow level are used to identify a new century-scale chronology of Holocene lake-level variations. The results indicate that lithologic and geochemical analyses on a transect of cores can be used to identify and date century-scale lake-level changes. Detailed sedimentary analyses of subfacies and radiocarbon dating were conducted on four representative cores. A chronology based on 60 accelerator mass spectrometer radiocarbon measurements constrains the timing of water-level fluctuations. Two methods were used to estimate the14C reservoir age. Both indicate that it has remained nearly constant at ∼25014C yr during the late Holocene. Core studies based on lithology and geochemistry establish the timing and magnitude of five periods of low lake level, implying negative moisture balance for the northern Andean altiplano over the last 3500 cal yr. Between 3500 and 3350 cal yr B.P., a transition from massive, inorganic-clay facies to laminated organic-matter-rich silts in each of the four cores signals a water-level rise after a prolonged mid-Holocene dry phase. Evidence of other significant low lake levels occurs 2900–2800, 2400–2200, 2000–1700, and 900–500 cal yr B.P. Several of the low lake levels coincided with cultural changes in the region, including the collapse of the Tiwanaku civilization.
id: 173; jpc

An abrupt drowning of the Black Sea shelf - Ryan, W. B. F.; Pitman, W. C.; Major, C. O.; Shimkus, K.; Moskalenko, V.; Jones, G. A.; Dimitrov, P.; Gorur, N.; Sakinc, M.; Yuce, H. (Marine Geology, 1997)
During latest Quaternary glaciation, the Black Sea became a giant freshwater lake. The surface of this lake drew down to levels more than 100 m below its outlet. When the Mediterranean rose to the Bosporus sill at 7,150 yr BP1, saltwater poured through this spillway to refill the lake and submerge, catastrophically, more than 100,000 km(2) of its exposed continental shelf. The permanent drowning of a vast terrestrial landscape may possibly have accelerated the dispersal of early neolithic foragers and farmers into the interior of Europe at that time. (C) 1997 Elsevier Science B.V.
Xj245Times Cited:283Cited References Count:35

AMS measurements of the 14C distribution in the Pacific Ocean - von Reden, K. F.; McNichol, A. P.; Peden, J. C.; Elder, K. L.; Gagnon, A. R.; Schneider, R. J. (Nuclear Instruments and Methods in Physics Research, 1997)
id: 1673

AMS measurements of the 14C distribution in the Pacific Ocean - von Reden, K. F.; McNichol, A. P.; Peden, J. C.; Elder, K. L.; Gagnon, A. R.; Schneider, R. J. (Proceedings of the Seventh International Conference on Accelerator Mass Spectrometry, 1997)
id: 1644; B123

Biostratigraphy and sedimentation rates of the Amazon Deep Sea Fan - Mikkelsen, N.; Maslin, M.; Firaudeau, J.; Showers, W. J. (Proceedings of the Ocean Drilling Program: Scientific Results, 1997)
id: 71

Carbon isotopic fractionation associated with lipid biosynthesis by a cyanobacterium: relevance for interpretation of biomarker records - Sakata, S.; Hayes, J. M.; McTaggart, A. R.; Evans, R. A.; Leckrone, K. J.; Togasaki, R. K. (Geochim Cosmochim Acta, 1997)
For the cyanobacterium Synechocystis UTEX 2470, grown photoautotrophically to a logarithmic stage of growth, the total lipid extract is depleted in 13C by 4.8% relative to average biomass. Depletions observed for acetogenic (straight-chain) lipids range from 7.6 (hexadecanoic acid) to 9.9% (a C16 n-alkyl chain bound in a polar-lipid fraction), with a mass-weighted average of 9.1%. Polyisoprenoid lipids fall into two isotopic groups, with phytol, diplopterol, and diploptene depleted by 6.4-6.9% and bishomohopanol (produced from the extracts by the preparative degradation of bacteriohopanepolyol) depleted by 8.4%. Analysis of the pattern of depletions indicates that two carbon positions in each C5 biomonomer leading to polyisoprenoid products are probably depleted in 13C relative to average biomass. The depletion of bacteriohopanepolyol relative to other polyisoprenoids can be ascribed to changes that occur over the life of each cell: (1) the 13C content of carbon flowing to lipid biosynthesis decreases as the cell size increases and (2) a greater proportion of the bacteriohopanepolyol which, unlike other polyisoprenoids, is present mainly in the cytoplasm rather than in membranes and is synthesized when cells are larger. Chlorophyll a is depleted relative to average biomass by O.7%. Given the observed depletion of 13C in phytol, the heteroaromatic, chlorophyllide portion of chlorophyll must be enriched in 13C by 2.7%. This enrichment is large relative to that in chlorophyllides produced by eukaryotes and may be related to a parallel enrichment of 13C in cyanobacterial glutamic acid. As in many previous investigations of cyanobacterial lipids, long-chain n-alkanes (C22-C29) are found in the extracts. They are, however, enriched in 13C relative to biomass and have isotopic compositions suggesting that they are contaminants of petrochemical origin. Available results indicate that cyanobacterial lipids will be depleted relative to dissolved CO2 that has served as a carbon source by 22-30% and that a wider range of depletions will be characteristic of eukaryotic products. The absence of long-chain n-alkanes in cyanobacteria reduces the possibility that petroleum ever formed from pre-eukaryotic sedimentary debris.
Sakata, SHayes, J M McTaggart, A R Evans, R A Leckrone, K J Togasaki, R K eng Research Support, U.S. Gov't, Non-P.H.S. 1997/01/01 00:00 Geochim Cosmochim Acta. 1997;61(24):5379-89.
Keywords: *Biomass; Acetic Acid/metabolism; Alkanes/*analysis/chemistry; Biomarkers/chemistry; carbon isotopes; Carbon/*chemistry; Chlorophyll/metabolism; Cyanobacteria/chemistry/*metabolism; Geologic Sediments/*chemistry; Lipids/*biosynthesis; NASA Discipline Exobiology; Non-NASA Center; Palmitic Acid/metabolism; Phytol/metabolism; Pigments, Biological/metabolism

Changes in the Pacific Ocean distribution of radiocarbon since GEOSECS, 1997 - Key, R. M. (U. S. WOCE Office, 1997)
id: 323

Climate variation and the rise and fall of an Andean civilization - Binford, M. W.; Kolata, A. L.; Brenner, M.; Janusek, J. W.; Seddon, M. T.; Abbott, M.; Curtis, J. H. (Quaternary Research, 1997)
Paleolimnological and archaeological records that span 3500 years from Lake Titicaca and the surrounding Bolivian-Peruvian altiplano demonstrate that the emergence of agriculture (ca. 1500 B.C.) and the collapse of the Tiwanaku civilization (ca. A.D. 1100) coincided with periods of abrupt, profound climate change, The timing and magnitude of climate changes are inferred from stratigraphic evidence of lake-level variation recorded in C-14-dated lake-sediment cores. Paleolake levels provide estimates of drainage basin water balance. Archaeological evidence establishes spatial and temporal patterns of agricultural field use and abandonment. Prior to 1500 B.C., aridity in the altiplano precluded intensive agriculture. During a wetter period from 1500 B.C. to A.D. 1100, the Tiwanaku civilization and its immediate predecessors developed specialized agricultural methods that stimulated population growth and sustained large human settlements, A prolonged drier period (ca. A.D. 1100-1400) caused declining agricultural production, field abandonment, and cultural collapse. (C) 1997 University of Washington.
Wu887Times Cited:148Cited References Count:53

Consistent Fractionation of 13C in Nature and in the Laboratory: Growth-rate Effects in Some Haptophyte Algae - Bidigare, Robert R.; Fluegge, Arnim; Freeman, Katherine H.; Hanson, Kristi L.; Hayes, John M.; Hollander, David; Jasper, John P.; King, Linda L.; Laws, Edward A.; Milder, Jeffrey; Millero, Frank J.; Pancost, Richard; et al. (Global Biogeochemical Cycles, 1997)
The carbon isotopic fractionation accompanying formation of biomass by alkenone-producing algae in natural marine environments varies systematically with the concentration of dissolved phosphate. Specifically, if the fractionation is expressed by єP ≈ δe − δp, where δe and δp are the δ13C values for dissolved CO2 and for algal biomass (determined by isotopic analysis of C37 alkadienones), respectively, and if Ce is the concentration of dissolved CO2, μmol kg−1, then b = 38 + 160*[PO4], where [PO4] is the concentration of dissolved phosphate, μM, and b = (25 − єp)Ce. The correlation found between b and [PO4] is due to effects linking nutrient levels to growth rates and cellular carbon budgets for alkenone-containing algae, most likely by trace-metal limitations on algal growth. The relationship reported here is characteristic of 39 samples (r2 = 0.95) from the Santa Monica Basin (six different times during the annual cycle), the equatorial Pacific (boreal spring and fall cruises as well as during an iron-enrichment experiment), and the Peru upwelling zone. Points representative of samples from the Sargasso Sea ([PO4] ≤ 0.1 μM) fall above the b = f[PO4] line. Analysis of correlations expected between μ (growth rate), єp, and Ce shows that, for our entire data set, most variations in єp result from variations in μ rather than Ce. Accordingly, before concentrations of dissolved CO2 can be estimated from isotopic fractionations, some means of accounting for variations in growth rate must be found, perhaps by drawing on relationships between [PO4] and Cd/Ca ratios in shells of planktonic foraminifera.
id: 1727

A correction for aberrations in the WHOI Recombinator Injector - von Reden, K. F.; Schneider, R. J. (Symposium of North Eastern Accelerator Personnel, 1997)

Corrections for contamination background in AMS 14C measurements - Brown, T. A.; Southon, J. R. (Nuclear Instruments and Methods in Physics Research B, 1997)
Measurements of ratios were made on samples of Oxalic Acid and 14C “dead” materials spanning the mass range from 10 μg to ∼1 mg. These measurements have allowed the determination of both the amount, and the 14C content, of the contaminant carbon introduced during sample processing in our laboratory. These data were used to correct measured ratios obtained from ANU Sucrose and “∼ one-half-life old” test samples for the influence of the contaminant. The test samples spanned the 10 μg to ∼1 mg mass range and the corrections were made using three different formulae. The results obtained from these calculations allow the accuracy of these background correction formulae to be evaluated.
id: 1493

Determination of the radiocarbon ages of individual PAH extracted from urban aerosol and marine sediment - Pearson, A.; Eglinton, T. I.; McNichol, A. P.; Currie, L. A.; Schneider, R. J.; von Reden, K. F.; Benner, B. A.; Wise, S. A. (16th International Radiocarbon Conference, 1997)
id: 951

Detritus dynamics in the seagrass Posidonia oceanica: Elements for an ecosystem carbon and nutrient budget - Mateo, M. A.; Romero, J. (Marine Ecology-Progress Series, 1997)
Leaf decay, leaf Litter export, burial in belowground sinks, and respiratory consumption of detritus were examined at 2 different depths in a Posidonia oceanica (L.) Delile meadow off the Medes Islands, NW Mediterranean. At 5 m, the amount of exported leaf Litter represented carbon, nitrogen and phosphorus losses of 7, 9 and 6 % of the plant primary production, respectively. About 26 % of the carbon produced by the plant in 1 yr was immobilized by burial in the belowground compartment, i.e. as roots and rhizomes. Annual nitrogen and phosphorus burial in the sediment was 8 and 5 % of total N and P needs, respectively. Respiratory consumption (aerobic) of carbon leaf detritus represented 17% of the annual production. An additional, but very substantial, loss of carbon as very fine particulate organic matter has been estimated at ca 48%. At 13 m the pattern of carbon losses was similar, but the lesser effect of wave action (relative to that at 5 m) reduced exportation, hence increasing the role of respiratory consumption. Data on carbon losses indicated that only a small part of the plant production was actually available to fuel the food web of this ecosystem. Total nutrient losses were in the range of 21 to 47 % of annual needs. From differences found in N and P concentrations between living and dead tissues, it is suggested that important nutrient recycling (50 to 70%) may be due either to reclamation or to leaching immediately after plant death.
id: 2004; PT: J; UT: WOS:A1997XE68700005

Dynamic changes of the Holocene Mississippi River delta plain: The delta cycle - Roberts, H. H. (Journal of Coastal Research, 1997)
Previous geologic research on Holocene Mississippi River deltaic deposits has verified that the present delta plain and associated nearshore barrier islands and submarine shoals are either direct or indirect products of cyclic delta-building events that have operated on a variety of temporal and spatial scales. A major depositional element of the modern delta plain is the delta complex, of which there are six: (1) Maringouin, (2) Teche, (3) St. Bernard, (4) Lafourche, (5) Balize, and (6) Atchafalaya. Major delta-building events have occurred at a frequency of one every 1-2 kyr. Deposits associated with the six major delta complexes are fundamental constructional units of the delta plain, which collectively covers an area of similar to 30,000 km(2). Sedimentary deposits associated with these delta-building events range in thickness from about 10 to 100 m. Their construction is modulated by stream capture, which develops a new delta complex by way of a new river course. Delta complexes may be comprised of one or more delta lobes. As a product of this delta switching, the depositional architecture of the delta plain consists of laterally offset and stacked delta lobes. Within delta lobes are subdeltas and even smaller crevasse-splays. These smaller scale deltas sedimentologically and geomorphically mimic their larger delta lobe counterparts, but they are considerably thinner, cover less area, and have a shorter period of development and abandonment. Subdeltas are usually < 10 m thick and may fill shallow bays that cover over 300 km(2). They build and deteriorate on time-scales of 150-200 years. Crevasse-splays or overbank splays are < 5 m thick, cover only a few square kilometers, and are abandoned after several decades of active growth.Each delta evolves through a rapid regressional phase as water and sediment are captured from an antecedent river course. If highstand conditions persist long enough, deltas may prograde to the outer shelf to form wedges of deltaic sediment much thicker than their inner shelf counterparts. The delta-building process starts with the filling of interior lakes (lacustrine deltas), which is followed by bayhead delta-building at the coast, and finally by progradation across the marine shelf(shelf delta). Delta complexes and delta lobes, as well as their smaller counterparts, experience three phases of growth and abandonment: (1) rapid growth with increasing-to-stable discharge, (2) relative stability during initial stages of waning discharge, when sediment input balances the collective effects of subsidence, and (3) abandonment, followed by rapid subsidence-driven subaerial delta deterioration. In the rapid growth stage, formerly eroding-subsiding coastal environments experience delta plain accretion and coastal progradation from renewed sediment input. On the abandonment side of the cycle, marine processes overwhelm fluvial processes and rework the delta perimeter. Forced by the combined processes of subsidence, the delta surface undergoes progressive submergence. Transgressive sand bodies created by wave reworking of the delta evolve from headland beaches and spits, to barrier islands, and finally to submarine shoals as the abandonment phase is completed.
Xq326Times Cited:167 Cited References Count:74
Keywords: barrier; delta cycle; lacustrine deltas; progradation; shoreline change; subsidence

Eastern Mississippi Delta; late Wisconsin unconformity, overlying transgressive facies, sea level and subsidence - Stanley, D. J.; Warne, A. G.; Dunbar, J. B. (Engineering Geology, 1997)
id: 79

Efficiency and temperature dependence of water removal by membrane dryers - Leckrone, K. J.; Hayes, J. M. (Anal Chem, 1997)
The vapor pressure of water in equilibrium with sorption sites within a Nafion membrane is given by log P(WN) = -3580/T + 10.01, where P(WN) is expressed in Torr and T is the membrane temperature, in kelvin. The efficiency of dryers based on selective permeation of water through Nafion can thus be enhanced by cooling the membrane. Residual water in effluents exceeds equilibrium levels if insufficient time is allowed for water to diffuse to the membrane surface as gas passes through the dryer. For tubular configurations, this limitation can be avoided if L > or = Fc(10(3.8)/120 pi D), where L is the length of the tubular membrane, in centimeters, Fc is the gas flow rate, in mL/ min, and D is the diffusion coefficient for water in the carrier gas at the operating temperature of the dryer, in cm2/s. An efficient dryer that at room temperature dries gas to a dew point of -61 degrees C is described; the same dryer maintained at 0 degrees C yields a dew point of -80 degrees C and removes water as effectively as Mg(ClO4)2 or a dry ice/acetone slush. The use of Nafion membranes to construct devices capable of delivering gas streams with low but precisely controlled humidities is discussed.
Leckrone, K JHayes, J MengComparative StudyResearch Support, U.S. Gov't, Non-P.H.S.1997/03/01 00:00Anal Chem. 1997 Mar 1;69(5):911-8.

Eruption of Soufriere Hills Volcano in Montserrat - Young, S. R.; Sparks, S.; Robertson, R.; Lynch, L.; Aspinall, W. (EOS, 1997)
On July 18,1995, the Soufriere Hills volcano in Montserrat erupted for the first time in recorded history. The eruption began with intense fumarolic venting and phreatic explosions following 3 years of elevated seismicity. An andesite lava dome emerged on November 15, 1995, and continued to grow, with several periods of copious pyroclastic flow generation and an explosive eruption on September 17, 1996. The largest pyroclastic flows to date (on June 25, 1997) and a period of vulcanian explosions with fountain collapse (during early August 1997) indicate continued escalation of the eruption.
id: 99

Evaluating reproducibility of seawater, inorganic and organic carbon 14C results at the National Ocean Sciences AMS Facility (NOSAMS) - Elder, K. L.; McNichol, A. P.; Gagnon, A. R. (16th International Radiocarbon Conference, 1997)
id: 956

The evaluation of geochemical indicators of anoxia in the Chesapeak Bay. Report - Adelson, Jordan Michael (1997)
id: 1374; rpc

Evidence for earliest olive oil production in submerged settlements off the Carmel coast, Israel - Galili, E.; Stanley, D. J.; Sharvit, Y.; Weinstein, E. M. (Journal of Archaeological Science, 1997)
Thousands of crushed olive stones with olive pulp are concentrated in pits at the Kfar Samir prehistoric settlement off the Carmel coast south of Haifa. Observations at this site, and at other Late Neolithic to Early Chalcolithic offshore settlements in this region, record an olive-oil technology that began along the Carmel coastal plain as early as 6500 years ago. This is about 500 years earlier than previously held. These new finds help define the technology of olive-oil production and refine the chronological definition of cultural units along the southern Levant coast during the 7th millenniumbp, a time of major transition between the end of the Neolithic and beginning of the Chalcolithic.
id: 81

The first trans-Arctic 14C section: comparison of the mean ages of the deep waters in the Eurasian and Canadian Basins of the Arctic Ocean; in Proceedings of the 7th International Conference on Accelerator Mass Spectrometry - Schlosser, P.; Kromer, B.; Ekwurzel, B.; Bonisch, G.; McNichol, A.; Schneider, R.; von Reden, K.; Ostlund, H.; Swift, J. (Nuclear Instruments and Methods, 1997)
id: 1751

The first trans-Arctic 14C section: comparison of the mean ages of the deep waters in the Eurasian and Canadian basins fo the Arctic Ocean - Schlosser, Peter; Kromer, Bernd; Ekwurzel, Brenda; Bonisch, Gerhard; McNichol, Ann; Schneider, Robert; von Reden, Karl; Ostlund, H. G.; Swift, J. H. (Nuclear Instruments and Methods in Physics Research, 1997)
id: 67

Foraminiferal constraints on very high-resolution seismic stratigraphy and late Quaternary glacial history, New Jersey continental shelf - Lagoe, M. B.; Davies, T. A.; Austin, J. K.; Olson, H. C. (Palaios, 1997)
Internal stratigraphy of a Late Quaternary sediment wedge on the New Jersey outer continental shelf has been investigated using regional and 3-D seismic surveys, sediment cores and foraminiferal biofacies analysis. Results from the study help constrain Late Wisconsinan glacial/deglacial history in this area. Three major reflectors (channels, S and R) define 5 stratigraphic units: S1-modern sediments; S2-sands overlying a channelized surface (Channels reflector); S3-muds, clays and sandy muds below the channelized surface and above reflector S; S4-an unsampled unit between reflectors S and R; and S5-sands underlying reflector R, the fatter surface defining the base of the sediment wedge. Multivariate quantitative analysis delineates four major faunal groups characterizing these stratigraphic units. Faunal patterns are interpreted in terms of modern foraminiferal distributions, planktonic/benthic ratios and faunal abundance patterns. Group A dominates units S2 and S5 and is characterized by Cibicides lobatulus and Cassidulina islandica. The fauna indicates middle neritic water depths, moderate to high current energy, and moderate accumulation rates. Group B dominates unit S3 (muddy unit) and is characterized by Elphidium excavatum s.l., Buccella frigida, Fursenkoina fusiformis and miliolid spp. This fauna represents an environment with no modern analogue on the New Jersey continental shelf reflecting middle neritic, low-energy conditions and the accumulation of predominantly muddy sediments. Group C dominates the modern sediment veneer (unit S1), and its diverse fauna is consistent with modern faunal distributions and environmental conditions. Group D consists of a low-diversity fauna dominated by Fursenkoina fusiformis and Nonionella sp., which characterizes a few samples in unit S3. Environmental conditions are probably similar to those described for faunal group B. The distribution and interpretation of these faunas, combined with preliminary C-14 AMS dates, indicate that the Quaternary history of the outer-shelf sediment wedge involves a middle Wisconsinan unconformity (R), overlain by an unsampled unit (S4) and several meters of mud (S3). This relationship may represent a middle Wisconsinan outwash event. The muddy deposit was later incised by the ''Channels'' horizon, possibly reflecting the Late Wisconsinan maximum lowering of sea level. This horizon is overlain by sandy transgressive deposits associated with rising sea level, presumably during the Holocene.
Xf026Times Cited:19Cited References Count:39

A high-resolution paleoenvironmental record from Bainbridge Crater Lake, Galapagos Islands - Reidinger, M.; Steinitz-Kannan, M.; Last, W.; Brenner, M. (Wurzburger Geographische Manuscripte, Heft, 1997)
id: 356

Hold-up and memory effect for carbon in a compact microwave ion source - Schneider, R. J.; vonReden, K. F.; Wills, J. S. C.; Diamond, W. T.; Lewis, R.; Savard, G.; Schmeing, H. (Nuclear Instruments & Methods in Physics Research Section B-Beam Interactions with Materials and Atoms, 1997)
The production of C+ in a microwave ion source injected with a gaseous CO2 sample has been investigated as an alternative to sample graphitization, A continuous flow of argon gas maintained the discharge, and 20 mu L Of CO2 gas at approximately 1 atm was pulsed into the source through a sample valve closely coupled to the plasma chamber, The C+ component of the beam fell to 1% of its original intensity less than 10 s after the valve was operated. in a separate experiment, the microwave ion source was operated with pure CO2 feed gas and the extracted beam was magnetically analyzed. Efficient breakup of the molecules was observed. These results are considered promising for such applications as accelerator mass spectrometry of C isotopes in gaseous samples.
Wt653Times Cited:13Cited References Count:7

Holocene Evolution of Lake Erie Environments - McCambridge, C.; Barrera, E.; Tevesz, M.; Fuller, J. (Geological Society of America, Abstracts with Programs, 1997)
id: 250

An isotopic biogeochemical study of Neoproterozoic and Early Cambrian sediments from the Centralian Superbasin, Australia - Logan, G. A.; Summons, R. E.; Hayes, J. M. (Geochim Cosmochim Acta, 1997)
Organic matter from Neoproterozoic and Early Cambrian sediments of the Amadeus and Officer basins of the Centralian Superbasin, Australia, has been studied for biomarker distributions and the carbon isotopic compositions of kerogen and individual hydrocarbons. These sediments represent both shallow and deep water marine facies in the older sections and marine and saline lacustrine carbonate deposits in the Cambrian. Hydrocarbon biomarker patterns were found to be quite consistent with the known sedimentary environments and provide valuable insights into the biogeochemical changes which accompanied the transition from a microbially-dominated ocean to the early stages of metazoan radiation. In particular, carbon isotopic data for n-alkyl and isoprenoid lipids presented here, and in earlier studies, showed a reversal in carbon isotopic ordering between the Proterozoic and Phanerozoic. By comparison with the delta 13C of kerogen, n-alkyl lipids from deep-water Proterozoic sediments were enriched in 13C and appear to be derived mainly from heterotrophs whilst open marine Phanerozoic counterparts are 13C depleted and evidently derived mainly from autotrophs. Data from the samples studied here are consistent with a model invoking a change in the redox structure of the ocean, possibly aided by the innovation of faecal pellets.
Logan, G ASummons, R E Hayes, J M eng Research Support, U.S. Gov't, Non-P.H.S. 1997/01/01 00:00 Geochim Cosmochim Acta. 1997;61(24):5391-409.
Keywords: Alkanes/analysis/chemistry; Animals; australia; biomarkers; carbon isotopes; Carbon/analysis/*chemistry; Cyanobacteria; Eukaryota; Feces; Fossils; Geologic Sediments/*analysis/chemistry; Hydrocarbons/analysis; NASA Discipline Exobiology; Non-NASA Center; Paleontology; phytoplankton; SEAWATER; Terpenes/analysis; Zooplankton

Isotopic stratigraphy of Amazon Fan sediments - Showers, W. J.; Schneider, R.; Mikkelsen, N.; Maslin, M. (Proceedings of the Ocean Drilling Program: Scientific Results, 1997)
id: 1277

Late Plains Woodland Occupation of the Kirschenman III Site in the James River Valley, North Dakota - Toom, Dennis L. (1997 Plains Conference, 55th Annual Meeting of the Plains Anthropological Society, 1997)
id: 204

Late Quaternary climate, fire, and vegetation dynamics (Book Section) - Winkler, M. G. (Sediment Records of Biomass Burning and Global Change, 1997)
id: 134

Late quaternary evolution of the Central Texas shelf: Sequence Stratigraphic Implications, Thesis - Eckles, Brenda (1997)
This study documents the evolution of the interdeltaic central Texas continental shelf over the last 350,000 years. The dataset consists of high-resolution seismic data, platform boring descriptions, oxygen isotope analyses, and radiocarbon dates. A strong correlation exists between seismic facies and lithofacies enabling seven stages of evolution to be mapped. The distribution of these facies is primarily controlled by fourth-order glacio-eustatic cycles. Seismic stratigraphy, oxygen isotope analyses, and radiocarbon dating were integrated to develop an independent sea-level curve for the area. Longshore and surface currents transport large volumes of sand into the area which is deposited as widespread, thick $(>$10 meters) barrier-bar highstand sand bodies on the inner shelf. Sediments are deposited and preserved in a repetitive manner during each glacio-eustatic cycle. This implies a predictable pattern of deposition, therefore, allowing for the development of depositional models that can be applied to ancient deposits in the exploration for hydrocarbons.

Late Quaternary Western Atlantic Paleoceanography and terrigenous sedimentation on the Amazon Fan: a view from delta d180 and d13C of planktonic foraminifera and bulk organic matter d13C - Schneider, R. R.; Muller, P. J.; Schlunz, B.; Segl, M.; Showers, W. J.; Wefer, G. (Proceedings of the Ocean Drilling Program: Scientific Results, 1997)
id: 1278

Lignin phenols in sediments of Lake Baikal, Siberia: application to paleoenvironmental studies - Orem, W. H.; Colman, S. M.; Lerch, H. E. (Organic Geochemistry, 1997)
Sediments from three cores obtained from distinct depositional environments in Lake Baikal, Siberia were analyzed for organic carbon, total nitrogen and lignin phenol concentration and composition. Results were used to examine changes in paleoenvironmental conditions during climatic cycles of the late Quaternary (<125 ka). Average organic carbon, and total nitrogen concentrations, atomic C/N ratios and organic carbon accumulation rates were significantly higher in the Holocene compared with the late Pleistocene, reflecting overall warmer temperatures and increased runoff during the Holocene. A Holocene maximum in organic carbon was observed at about 6 ka, and may represent the warmest/wettest period of the Holocene. At one site (Academician Ridge) pronounced late Pleistocene maxima in organic carbon and biogenic silica were observed at about 80-85 ka, probably indicative of an interstadial period with enhanced aquatic productivity. Total sedimentary lignin phenol contents were generally lower in the late Pleistocene compared to the Holocene, but with several peaks in concentration during the late Pleistocene. These late Pleistocene peaks in total sedimentary lignin content (dated at about 80, 50 and 30 ka) directly precede or occur during peaks in sedimentary biogenic silica contents. These periods likely represent relatively warm interstadial times, with increased precipitation producing the observed increase in terrestrial runoff and aquatic productivity. Lignin phenol ratios (S/V, C/V and P/V) were used to examine changes in terrestrial vegetation type resulting from changes in paleoenvironmental conditions during the late Pleistocene. A degree of caution must be used in the interpretation of these ratios with regard to vegetation sources and paleoenvironmental conditions, because of potential compositional changes in lignin resulting from biodegradation. Nevertheless, results show that long glacial periods were characterized by terrestrial vegetation composed of a mix of non-woody angiosperm vegetation and minor gymnosperm forest. Shorter interstadial periods are defined by a change to dominant gymnosperm forest and were observed at about 80, 75, 63, 50 and 30 ka, ranging from about 2-6 kyr in duration. These interstadial periods of the late Pleistocene defined by lignin phenol ratios generally occur during longer periods of enhanced sedimentary biogenic silica content (about 10-15 ka in duration), providing corroborative evidence of these warm interstadial periods. (C) 1997 Elsevier Science Ltd.
Yq252Times Cited:29Cited References Count:61

Mass transport deposits of Amazon Fans - Piper, D. J.; Pirmez, C.; Flood, R.; Long, D.; Manely, P.; Normark, W.; Showers, W. (Proceedings of the Ocean Drilling Program: Scientific Results, 1997)
id: 1279

Mediterranean deltas: subsidence as a major control of relative sea-level rise - Stanley, D. J. (Bulletin de l'Institut oceanographique(Monaco), 1997)
id: 1284

Molecular radiocarbon dating of archeological artifacts and marine muds - Eglinton, T. I. (Woods Hole Oceanographic Institution 1996 Annual Report, 1997)
id: 368

The National Ocean Sciences AMS (NOSAMS) Sample Preparation Laboratory: Systems and Graphite Performance Analysis - Gagnon, A. R.; McNichol, A. P.; Donoghue, J. C.; Morin, T. J.; Peden, J. C. (International Radiocarbon Conference, 1997)
id: 962

The NOSAMS sample preparation laboratory: overview of systems and techniques - Gagnon, A. R.; McNichol, A.; Donoghue, J. C.; Merkle, K. M.; Morin, T. J. (16th International Radiocarbon Conference, 1997)
id: 955

P13N final report for AMS 14C samples - Key, R. M.; Quay, P. D. (Ocean Tracer Laboratory Technical Report, 1997)
id: 1254

P14C final report for AMS 14C samples - Key, R. M. (Ocean Tracer Laboratory Tech. Report, 1997)
id: 1255

P16A17A final report for AMS 14C samples - Key, R. M. (Ocean Tracer Laboratory Tech. Report, 1997)
id: 1253

Paleoceanographic Variability on a Millennial Scale: A High Resolution Record of the Latest Deglaciation from the Blake Outer Ridge, Western North Atlantic, Thesis - Schlegel, Mary Ann (1997)

Paleoclimatic implications of Holocene lake-level fluctuations, Owasco Lake, New York: Comment - Balco, G.; Belknap, D. F.; Kelley, J. T. (Geology, 1997)
Wu319Times Cited:0Cited References Count:7

Paleoclimatic implications of silicieous microfossil succession in late Quaternary sediments in Lake Baikal, Siberia - Julius, M. L.; Stoermer, E. F.; Colman, S. M.; Moore, T. C. (Journal of Paleolimnology, 1997)
id: 1354

Paleocology research in Great Lakes (U.S.A.)National Parks - Winkler, M. G. (Abstracts for American Society of Limnology and Oceanography, 1997)
id: 1300

Paleoecological research at Isle Royale, Apostle Islands, and Voyageurs National Parks. Report - Winkler, M. G.; Sanford, P. R. (1997)
id: 1321

Paleogeography and sedimentary evolution of Nauset Marsh estuary, Cape Cod, MA. Final Report to the National Park Service - Allen, J. R.; Boothroyd, J. (1997)
id: 1311

Paleolimnology research at Isle Royale, Apostle Island, and Voyageurs National Parks - Winkler, M. G.; Sanford, P. R. (USGS Biological Resources Division, Global Change Research Program, 1997)
id: 1299

Possible role of climate in the collapse of the Akkadian Empire: evidence from Gulf of Oman marine sediments - Cullen, H. (AGU Fall Meeting, 1997)
id: 1235

Postglacial relative sea level history from sediment and diatom rcords of emerged coastal lakes, north-central Kola Peninsula, Russia - Snyder, J. A.; Forman, S. L.; Mode, W. N.; Tarasov, G. A. (Boreas, 1997)
id: 379

Precise temporal correlation of Holocene mollusc shells using sclerochronology - Marchitto, T. M.; Jones, G. A.; Goodfriend, G. A.; Weidman, C. R.; Jirikowic, J. (Palaeogeography, Paleoclimatology, Paleoecology, 1997)
id: 1293

Preliminary paleoecology study of Salt Pond and Nauset Lagoon, Cape Cod National Seashore (Report) - Cole, K.; Winkler, M. G.; Sanford, P. R. (National Park Service, North Atlantic Region, 1997)
id: 131

Preliminary results of the first drilling on Lake Baikal, Buguldeika site, southeastern Siberia - Baikal Members, B. D. Drilling Project (Quaternary International, 1997)
The Baikal Drilling Project (BDP) is a multinational effort to investigate the paleoclimatic history and tectonic evolution of the Baikal sedimentary basin during the Late Neogene. In March 1993 the Baikal drilling system was successfuly deployed from a barge frozen into position over a topographic high, termed the Buguldeika saddle, in the southern basin of Lake Baikal. The BDP-93 scientific team, made up of Russian, American and Japanese scientists, successfully recovered the first long (>100 m) hydraulic piston cores from two holes in 354 m of water. High quality cores of 98 m (Hole 1) and 102 m (Hole 2), representing sedimentation over the last 500,000 years, were collected in 78 mm diameter plastic liners with an average recovery of 72% and 90%, respectively. Magnetic susceptibility logging reveals an excellent hole-to-hole correlation. In this report the scientific team describes the preliminary analytical results from BDP-93 hole 1 cores. Radiocarbon dating by accelerator mass spectrometry provides an accurate chronology for the upper portion of Hole 1. Detailed lithologic characteristics, rock magnetic properties and inorganic element distributions show a significant change to the depositional environment occuring at 50 m subbottom depth, approximately 250,000 BP. This change may be due to uplift and rotation of the horst block in the Buguldeika saddle. The sedimentary section above 50 m is pelitic with varve-like laminae, whereas the section below 50 m contains a high proportion of sand and gravel horizons often organized into turbidite sequences. Accordingly, high resolution seismic records reveal a change in sonic velocity at this depth. It is inferred that sedimentation prior to 250 ka BP was from the west via the Buguldeika river system. After 250 ka BP the Buguldeika saddle reflects an increase in hemipelagic sediments admixed with fine-grained material from the Selenga River drainage basin, east of Lake Baikal. Variations in the spore-pollen assemblage, diatoms, biogenic silica content, rock magnetic properties, clay mineralogy and organic carbon in the upper 50 m of BDP-93-1 reveal a detailed record of climate change over approximately the last 250,000 years. These variables alternate in a pattern characteristic of glacial/interglacial climatic fluctuations. The present age model suggests that the climate signal recorded in Lake Baikal sediments is similar to Late Quaternary signals recorded in Chinese loess sections and in marine sediments.
id: 188

Preliminary results of the first scientific drilling on Lake Baikal, Buguldeika site, southeastern Siberia - Colman, S.; Grachev, M.; Hearn, P.; Horie, S.; Kawai, T.; Kuzmin, M.; Logachov, N.; Fialkov, V.; Gorigljad, A.; Tomilov, B.; Khakhaev, B.; Kochikov, S.; et al. (Quaternary International, 1997)
The Baikal Drilling Project (BDP) is a multinational effort to investigate the paleoclimatic history and tectonic evolution of the Baikal sedimentary basin during the Late Neogene. In March 1993 the Baikal drilling system was successfuly deployed from a barge frozen into position over a topographic high, termed the Buguldeika saddle, in the southern basin of Lake Baikal. The BDP-93 scientific team, made up of Russian, American and Japanese scientists, successfully recovered the first long (>100 m) hydraulic piston cores from two holes in 354 m of water. High quality cores of 98 m (Hole 1) and 102 m (Hole 2), representing sedimentation over the last 500,000 years, were collected in 78 mm diameter plastic liners with an average recovery of 72% and 90%, respectively. Magnetic susceptibility logging reveals an excellent hole-to-hole correlation. In this report the scientific team describes the preliminary analytical results from BDP-93 hole 1 cores. Radiocarbon dating by accelerator mass spectrometry provides an accurate chronology for the upper portion of Hole 1. Detailed lithologic characteristics, rock magnetic properties and inorganic element distributions show a significant change to the depositional environment occuring at 50 m subbottom depth, approximately 250,000 BP. This change may be due to uplift and rotation of the horst block in the Buguldeika saddle. The sedimentary section above 50 m is pelitic with varve-like laminae, whereas the section below 50 m contains a high proportion of sand and gravel horizons often organized into turbidite sequences. Accordingly, high resolution seismic records reveal a change in sonic velocity at this depth. It is inferred that sedimentation prior to 250 ka BP was from the west via the Buguldeika river system. After 250 ka BP the Buguldeika saddle reflects an increase in hemipelagic sediments admired with fine-grained material from the Selenga River drainage basin, east of Lake Baikal. Variations in the spore-pollen assemblage, diatoms, biogenic silica content, rock magnetic properties, clay mineralogy and organic carbon in the upper 50 m of BDP-93-1 reveal a detailed record of climate change over approximately the last 250,000 years. These variables alternate in a pattern characteristic of glacial/interglacial climatic fluctuations. The present age model suggests that the climate signal recorded in Lake Baikal sediments is similar to Late Quaternary signals recorded in Chinese loess sections and in marine sediments. Copyright (C) 1996 INQUA/Elsevier Science Ltd
Vq100Times Cited:44 Cited References Count:29
Keywords: asia; tectonics

Productivity-induced sulphur enrichment of hydrocarbon-rich sediments from the Kimmeridge Clay Formation - Lallier-Verges, E.; Hayes, J. M.; Boussafir, M.; Zaback, D. A.; Tribovillard, N. P.; Connan, J.; Bertrand, P. (Chem Geol, 1997)
This work aims to highlight the relationship between primary productivity, sulphate reduction and organic carbon preservation in cyclic marine sediments from the Kimmeridge Clay Formation. A concomitant increase of the total sulphur content with the preserved organic content (TOC), shows the progressive supply of both metabolisable organic matter and resistant organic matter is linked to primary productivity. However, variations in sulphate reduction efficiency, based on elemental abundance and isotopic composition of sulphur, reveal that the proportion of metabolisable vs. resistant organic matter has varied along the cycles. This is interpreted in terms of the variation in organic delivery. Organic sulphur content is found to be proportional to the organic matter content, whereas concentrations of pyritic sulphur are constant at very high (> 10% TOC) values. This result is explained by a limitation of available iron for pyritisation at times of very high organic flux. Under such conditions, HS- in excess could be responsible for the early formation of organo-sulphur compounds and thus for the preservation of highly aliphatic (i.e. lipid-rich) organic matter.
Lallier-Verges, EHayes, J MBoussafir, MZaback, D ATribovillard, N PConnan, JBertrand, PengResearch Support, Non-U.S. Gov'tNetherlands1997/01/01 00:00Chem Geol. 1997;134:277-88.

Radiocarbon chronology of Namaqualand mudbelt sediments: problems and prospects - Meadows, M. E.; Dingle, R. V.; Rogers, J.; Mills, E. G. (South African Journal of Science, 1997)
This paper presents the first radiocarbon-dated chronology of the mudbelt which occupies the continental shelf around southern Africa. The results confirm the Holocene age of the superficial deposits and suggest that laminations in the sediments of the mudbelt off the Orange River mouth are recent and terrestrially derived. Two anomalies are, however, apparent in the chronology. First, the surface sediments do not provide recent or contemporary radiocarbon ages, as would be expected. Second, the laminated sediments yield ages which are not in stratigraphic sequence and appear to be clustered around the period 1000 to 1700 sri Possible reasons for these anomalies are discussed together with alternative means of deriving a more accurate and reliable chronology for the mudbelt sediments.
Yb537Times Cited:7 Cited References Count:18
Keywords: accumulation rates; ages; Marine

Radiolarian Population Changes in the Glacial-Deglacial North Atlantic Ocean: Evidence for Changes in Ocean Circulation, Thesis - French, P. L. (University of Maine, 1997)

Recent subsidence of the northern Suez canal - Stanley, D. J.; Goodfriend, G. A. (Nature, 1997)
Xm528Times Cited:16Cited References Count:10

Regional, Holocene records of the human dimension of global change: Sea-level and land-use change in prehistoric Mexico - Sluyter, A. (Global and Planetary Change, 1997)
Regional, Holocene records hold particular relevance for understanding the reciprocal nature of global environmental change and one of its major human dimensions: ''sustainable agriculture'', i.e., food production strategies which entail fewer causes of and are less susceptible to environmental change. In an epoch of accelerating anthropogenic transformation, those records reveal the protracted regional causes and consequences of change (often agricultural) in the global system as well as informing models of prehistoric, intensive agriculture which, because of long tenures and high productivities, suggest strategies for sustainable agricultural in the present. This study employs physiographic analysis and the palynological, geochemical record from cores of basin fill to understand the reciprocal relation between environmental and land-use change in the Gulf of Mexico tropical lowland, focusing on a coastal basin sensitive to sea-level change and containing vestiges of prehistoric settlement and wetland agriculture. Fossil pollen reveals that the debut of maize cultivation in the Laguna Catarina watershed dates to ca. 4100 BC, predating the earliest evidence for that cultivar anywhere else in the lowlands of Middle America. Such an early date for a cultivar so central to Neotropical agroecology and environmental change, suggests the urgency of further research in the study region. Moreover, the longest period of continuous agriculture in the basin lasted nearly three millennia (ca. 2400 BC-AD 550) despite eustatic sea-level rise. Geochemical fluxes reveal the reciprocity between land-use and environmental change: slope destabilization, basin aggradation, and eutrophication. The consequent theoretical implications pertain to both applied and basic research. Redeploying ancient agroecologies in dynamic environments necessitates reconstructing the changing operational contexts of putative high productivity and sustainability. Adjusting land use in the face of global warming and eustatic sea-level rise necessitates understanding sediment influxes to coastal basins which, in turn, depend on vegetation, climate, and land use in watersheds.
Wk148Times Cited:17Cited References Count:116

Reproducibility of 14C AMS analyses at NOSAMS - Elder, K. L.; Gagnon, A. R.; McNichol, A. P. (16th International Radiocarbon Conference, 1997)
id: 961

Sedimentology of terrigenous mud from the Orange River delta and the inner shelf off Namaqualand, South Africa - Mabote, M.; Rogers, J.; Meadows, M. E. (South African Geographical Journal, 1997)
Sediment cores, from the inner shelf off the Namaqualand continental shelf have been examined using radiographic and grain-size techniques. Size-frequency distributions reveal that the sediments are poly modal, with a dominant very fine-silt mode being between 8-4μm, and suggest that the weak, poleward-flowing De Decker Current causes southward dispersal of terrigenous mud off the Orange River mouth. It appears that this current is not strong enough to transport material coarser than very fine silt. Material >63μm in size is rare, but may be indicative of storm events. Quartz and mica in the sediments are related to the semi-arid climate of Namaqualand, where they are entrained by adiabatic Berg winds moving offshore from the interior. Sponge spicules indicate the presence of filter-feeding animals (epifauna). Planktonic foraminifera may be indicative of relatively high productivity associated with nutrient-rich upwelling waters, which support an enormous population of plankton. The presence of faecal pellets is associated with the presence of burrowing infauna. Authigenic gypsum is associated with the presence of anaerobic conditions in the sediments. Two of the lithofacies identified in these fine-grained deposits are: (a) laminated mud and (b) homogeneous mud. Primary sedimentary structures are present, particularly in the portion of the mudbelt closest to the Orange Delta, where the mud is well laminated. Laminations decrease in abundance southward from the delta, where the muddy sediment is increasingly bioturbated (burrowed) by infauna, probably by polychaete worms.
id: 218

Source and contribution of terrigenous organic carbon to surface sediments in the Gulf of Mexico - Goñi, M. A.; Ruttenberg, K. C.; Eglinton, T. I. (Nature, 1997)
The sources and burial professes of organic matter in marine sediments are not well understood, yet they are important if we are to have a better understanding of the global carbon cycle(1). In particular, the nature and fraction of the terrestrial organic carbon preserved in marine sediments is poorly constrained. Here we use the chemical and stable carbon isotope signatures of oxidation products from a macromolecular component (lignin)(2) of the terrigenous organic matter preserved in offshore surface sediments in the Gulf of Mexico to complement similar data from an existing onshore transect(3) in this region. The complete onshore-offshore data set, along with radiocarbon dates of the bulk organic material at the same sites, allows the differentiation of material originating from plants that photosynthesize using the C-4 mechanism from those that undergo C-3 photosynthesis. We conclude that the offshore lignins derive from erosion of the extensive grassland (C-4) soils Of the Mississippi River drainage basin, and that the nearshore lignins originate largely from C-3 plant detritus from coastal forests and swamps, This distribution is probably due to the hydrodynamic sorting of the different source materials(4) during their seaward transport, These results suggest that previous studies(3,5) have significantly underestimated the terrigenous fraction of organic matter in offshore sediments by not recognizing the contribution of C-4 vegetation to the carbon-isotope composition. Such an underestimate may force revisions in the assessment of past marine primary productivity and associated organic carbon fluxes(6), and of organic matter preservation/remineralization(7) and nutrient cycling(8) in marine sediments.
Xw772Times Cited:194Cited References Count:30

Stratigraphic evolution of the inner continental shelf in response to late Quaternary relative sea-level change, northwestern Gulf of Maine - Barnhardt, W. A.; Belknap, D. F.; Kelley, J. T. (Geological Society of America Bulletin, 1997)
Accumulations of deltaic and littoral sediments on the inner continental shelf of Maine, Gulf of Maine, preserve a record of postglacial sea-level changes and shoreline migrations, The depositional response of coastal environments to a cycle of regression, lowstand, and transgression was examined with seismic-reflection profiles, vibracores, and radiocarbon dates collected from sediments at the mouths of the Kennebec and Penobscot Rivers, Sequence-stratigraphic analysis of these data reveals two distinctly different successions of late Quaternary deposits that represent end members in an evolutionary model for this glaciated coast. Seaward of the Kennebec River, coarse-grained shorelines with foreset beds occur at depths of 20-60 m and outline the lobate margin of the Kennebec River paleodelta, a complex, rock-framed accumulation of glaciomarine and deltaic sediments capped by estuarine and marine deposits, Sand derived from this system today supports large barrier spits and extensive salt marshes, In contrast, the mouth of the Penobscot River is characterized by thick deposits of glaciomarine mud overlain by marine mud of Holocene age, including gas-charged zones that have locally evolved into fields of pockmarks, The distinct lark of sand and gravel seaward of the Penobscot River and its abundance seaward of the Kennebec River probably reflect differences in sediment som ces and the physiography of the two watersheds, The contrasting stratigraphic framework of the se systems demonstrates the importance of understanding local and regional differences in sediment supply, sea-level change, bedrock structure, and exposure to waves and tides in older to model river-mouth deposition on glaciated coasts.Evolution of shelf deposits was largely controlled by relative sea level, which locally fell from a highstand (+60 to +70 m at 14 ka) contemporary with deglaciation to a lowstand (-55 m at 10.8 ka), The sea-level lowering was accompanied by fluvial incision of older deposits, producing a regressive, basal unconformity, Major rivers deposited abundant sediment over this surface, Sea level then rose at varying rates, extensively reworking formerly emergent parts of the shelf and producing a shoreface ravinement surface in areas exposed to waves, A tidal ravinement surface has developed in sheltered embayments where erosion is due mainly to tidal currents. Incised valleys in both settings preserve transgressive estuarine deposits that contain lagoonal bivalves and salt-marsh foraminifera at depths of 15-30 m, These deposits accumulated ca, 9.2-7.3 ka, locally a period of relatively slow sea-level rise.
Wy671Times Cited:38Cited References Count:65

Synchronous, high-frequency oscillations in tropical sea surface temperatures and North Atlantic Deep Water production during the last glacial cycle - Curry, W. B.; Oppo, D. W. (Paleoceanography, 1997)
Stable isotopic measurements of G. sacculifer and C. wuellerstorfi in a core from the western equatorial Atlantic imply that there are parallel, suborbital oscillations in surface water hydrography and deep water circulation occurring during oxygen isotope stages 2 and 3. Low values of G. sacculifer delta(18)O accompany high values of C. wuellerstorfi delta(13)C, linking warmer sea surface temperatures (SSTs) in the tropics with increased production of lower North Atlantic Deep Water (NADW). The amplitude of the delta(18)O oscillations is 0.6 parts per thousand (or 2 degrees-3 degrees C), which is superimposed on a glacial/interglacial amplitude of about 2.1 parts per thousand,. Using the G. sacculifer delta(18)O data, we calculate that surface waters were colder during stage 2 than calculated by CLIMAP [1976, 1981]. The longer-period (> 2 kyr) oscillations in air temperature recorded in the Greenland and Antarctic ice cores appear to correlate with oscillations in sea surface temperature in the equatorial Atlantic. The magnitude of these oscillations in tropical SST is too large to have resulted from changes in meridional heat transport caused by the global conveyor alone. The apparent synchroneity of equatorial SST and polar air temperature changes, as well as the amplitude of the SST changes at the equator, are consistent with the climate effects expected from changes in the atmosphere's greenhouse gas content (H(2)0(vapor), CO2, and CH4).
Wd891Times Cited:109Cited References Count:63

Target preparation for continuous flow accelerator mass spectrometry - Schneider, R. J.; Hayes, J. M.; Eglinton, T. I.; McNichol, A. P.; von Reden, K. F. (16th International Radiocarbon Conference, 1997)
id: 953

Target preparation for continuous flow accelerator mass spectrometry: (Proceedings of the 16th International Radiocarbon Conference, 1997) - Schneider, R. J.; Hayes, J. M.; von Reden, K. F.; McNichol, A. P.; Eglinton, T. (Radiocarbon, 1997)
id: 1752

Target preparation for continuous flow accelerator mass spectrometry - Schneider, R. J.; Hayes, J. M.; von Reden, K. F.; McNichol, A. P.; Eglinton, T. I. (Radiocarbon, 1997)
id: 1661

An updated high resolution chronology of deglaciation and accompanying marine transgression in Maine, Thesis - Dorion, C. C. (University of Maine, 1997)

Variability in radiocarbon ages of individual organic compounds from marine sediments - Eglinton, T. I.; BenitezNelson, B. C.; Pearson, A.; McNichol, A. P.; Bauer, J. E.; Druffel, E. R. M. (Science, 1997)
Organic carbon (OC) from multiple sources can be delivered contemporaneously to aquatic sediments. The influence of different OC inputs on carbon-14-based sediment chronologies is illustrated in the carbon-14 ages of purified, source-specific (biomarker) organic compounds from near-surface sediments underlying two contrasting marine systems, the Black Sea and the Arabian Sea, In the Black Sea, isotopic heterogeneity of n-alkanes indicated that OC was contributed from both fossil and contemporary sources. Compounds reflecting different source inputs to the Arabian Sea exhibit a 10,000-year range in conventional carbon-14 ages. Radiocarbon measurements of biomarkers of marine photoautotrophy enable sediment chronologies to be constructed independent of detrital OC influences.
Xq247Times Cited:175Cited References Count:37

Western Great Lakes Paleoecology Study. Report - Winkler, M. G.; Sanford, P. R. (National Biological Service Global Climate Change Initiative, 1997)
id: 1322

Western Great Lakes regional paleoenvironmental changes: island and inland contrasts - Winkler, M. G.; Sanford, P. R.; Cole, K. L.; Flakne, R. L. (Ecological Society of America Bulletin, 1997)
id: 1301

Western South Atlantic deepwater hydrography derived from benthic Cd/Ca and stable isotope data - Horowitz, M.; Oppo, D. W. (Supplement to EOS, 1997)
id: 1269

A 27,000 year record of Red Sea Outflow: Implication for timing of post-glacial monsoon intensification - Naqvi, W. A.; Fairbanks, R. G. (Geophysical Research Letters, 1996)
We reconstruct here the history of the Red Sea Outflow (RSO) over the past 27,000 years from an AMS C-14-dated high-resolution delta(13)C record of benthic foraminifera from the inner Gulf of Aden assuming the dominance of circulation over productivity in regulating benthic delta(13)C. The results reveal that, following a period of suppressed RSO due to shallow sill 24,000-18,000 yr BP, the Red Sea was vigorously flushed for similar to 2,000 years before a major monsoon intensification caused the cessation of deep water formation from 15,500 to 7,300 yr BP. It appears that the monsoon intensification did lag behind insolation until 15,500 yr BP. Between 15,500 and the present, however, there was no lag in conflict with the previous reports, implying a negligible dampening effect of continental albedo during this period. However, since our analysis is confined to a single depth horizon and our record is sensitive to sea level, it has some limitations as an indicator of monsoon intensity.
Up857Times Cited:16Cited References Count:27

An 84-kyr paleomagnetic record from the sediments of Lake Baikal, Siberia - Peck, J. A.; King, J. W.; Colman, S. M.; Kravchinsky, V. A. (Journal of Geophysical Research-Solid Earth, 1996)
We have conducted a paleomagnetic study of sediment cores obtained from the Selenga prodelta region of Lake Baikal, Russia. This record, which spans approximately the last 84 kyr, contributes to a better understanding of the nature of geomagnetic field behavior in Siberia and is a useful correlation and dating tool. We demonstrate that the Lake Baikal sediments are recording variations in the geomagnetic field. The directional record displays secular variation behavior with a geomagnetic excursion at 20 ka and additional excursions appearing as large-amplitude secular variation at 41, 61, and 67 ka. Smoothing of the geomagnetic excursion behavior occurs in Lake Baikal sediments owing to the intermediate sedimentation rate (13 cm kyr(-1)). The Lake Baikal relative paleointensity record correlates to absolute paleointensity data for the last 10 kyr and to relative paleointensity records from the Mediterranean Sea and Indian Ocean for the last 84 kyr. This correlation suggests a strong global (i.e., dipole) component to these records and further supports the reliability of sediments as recorders of relative geomagnetic paleointensity. We show that a relative geomagnetic intensity stratigraphy has a potential resolution of 7 kyr by correlating continental and marine records. The geomagnetic intensity stratigraphy helps constrain the age of the difficult to date Lake Baikal sediments.
Ul090Times Cited:76Cited References Count:48

Agroecological perspectives on the decline of the Tiwanaku State (Book Section) - Kolata, Alan L.; Ortloff, Charles R. (Tiwanaku and its Hinterland: Archaeology and Paleoecology of an Andean Civilization, 1996)
id: 1258

Altithermal of the Canadian Rockies; timing and internal structure; evidence from lake sediments - Leonard, Eric; Resoner, Mel (14th biennial meeting of the American Quaternary Association, 1996)
id: 1262

AMS measurements of the 14C distribution in the Pacific Ocean - von Reden, K. F.; McNichol, A. P.; Schneider, R. J. (7th International Conference on Accelerator Mass Spectrometry, 1996)
id: 950; 1

AMS radiocarbon analyses from Lake Baikal, Siberia: Challenges of dating sediments from a large, oligotrophic lake - Colman, S. M.; Jones, G. A.; Rubin, M.; King, J. W.; Peck, J. A.; Orem, W. H. (Quaternary Science Reviews, 1996)
A suite of 146 new accelerator-mass spectrometer (AMS) radiocarbon ages provides the first reliable chronology for late Quaternary sediments in Lake Baikal. In this large, highly oligotrophic lake, biogenic and authigenic carbonate are absent, and plant macrofossils are extremely rare. Total organic carbon is therefore the primary material available for dating. Several problems are associated with the TOC ages. One is the mixture of carbon sources in TOC, not all of which are syndepositional in age. This problem manifests itself in apparent ages for the sediment surface that are greater than zero. However, because most of the organic carbon in Lake Baikal sediments is algal (autochthonous) in origin, this effect is limited to about 1000+/-500 years, which can be corrected, at least for young deposits. The other major problem with dating Lake Baikal sediments is the very low carbon contents of glacial-age deposits, which makes them extremely susceptible to contamination with modern carbon. This problem can be minimized by careful sampling and handling procedures.The ages show almost an order of magnitude difference in sediment-accumulation rates among different sedimentary environments in Lake Baikal, from about 0.04 mm/year on isolated banks such as Academician Ridge, to nearly 0.3 mm/year in the turbidite depositional areas beneath the deep basin floors, such as the Central Basin. The new AMS ages clearly indicate that the dramatic increase in diatom productivity in the lake, as evidenced by increases in biogenic silica and organic carbon, began about 13 ka, in contrast to previous estimates of 7 ka for the age of this transition. Holocene net sedimentation rates may be less than, equal to, or greater than those in the late Pleistocene, depending on the site. This variability reflects the balance between variable terrigenous sedimentation and increased biogenic sedimentation during interglaciations. The ages reported here, and the temporal and spatial variation in sedimentation rates that they imply, provide opportunities for paleoenvironmental reconstructions at different time scales and resolutions. Published by Elsevier Science Ltd
Vp609Times Cited:112Cited References Count:29

Automated systems and techniques utilized at the NOSAMS sample preparation laboratory: An update of productivity and quality issues - Gagnon, A. R.; McNichol, A. P.; Hutton, D. L.; Osborne, E. A.; Donoghue, J. C. (Radiocarbon, 1996)
id: 959

Cape May site report - Miller, K. G.; Liu, C.; Browning, J. V.; Pekar, S.; Sugarman, P.; Van Fossen, M. C.; Mullikin, L.; Queen, D.; Feigenson, M. D.; Aubry, M. P.; Burckle, L. D.; Powars, D.; et al. (Proc. ODP, Init. Repts, 1996)
id: 55

Carbon isotopes and the rise of atmospheric oxygen - Karhu, J. A.; Holland, H. D. (Geology, 1996)
New data for the isotopic composition of carbon in carbonate sediments deposited between 2.6 and 1.6 Ga indicate that the value of delta(13)C in these sediments underwent a very large positive excursion between 2.22 and 2.06 Ga. A reassessment of the earlier delta(13)C data for carbonate sediments shows that this excursion was probably worldwide, and that it was preceded and followed by several hundred million years during which the delta(13)C of carbonate sediments differed little from that of modern carbonates. The large delta(13)C excursion between 2.22 and 2.06 Ga was probably related to an abnormally high rate of organic carbon deposition, which generated an abnormally high rate of O-2 production, We estimate that the total excess O-2 produced during the excursion was between 12 and 22 times the present atmospheric O-2 inventory. The delta(13)C data therefore suggest that the O-2 content of the atmosphere increased very significantly between 2.22 and 2.06 Ga. This inference is supported strongly by several other lines of evidence.
Vm224Times Cited:257Cited References Count:44

Catastrophic discharge of fluvial sediment to the ocean; evidence of jokulhlaups events in the Alsek Sea Valley, Southeast Alaska (USA) - Milliman, J. D.; Snow, J.; Jaeger, J.; Nittrouer, C. A. (International symposium on Erosion and sediment yield; global and regional perspectives, 1996)
id: 28

Character, paleoenvironment, rate of accumulation, and evidence for seismic triggering of Holocene turbidites, Canada Abyssal Plain, Arctic Ocean - Grantz, A.; Phillips, R. L.; Mullen, M. W.; Starratt, S. W.; Jones, G. A.; Naidu, A. S.; Finney, B. P. (Marine Geology, 1996)
Four box cores and one piston core show that Holocene sedimentation on the southern Canada Abyssal Plain for the last 8010 +/- 120 yr has consisted of a continuing rain of pelagic organic and ice-rafted elastic sediment with a net accumulation rate during the late Holocene of less than or equal to 10 mm/1000 yr, and episodically emplaced turbidites 1-5 m thick deposited at intervals of 830 to 3450 yr (average 2000 yr). The average net accumulation rate of the mixed sequence of turbidites and thin pelagite interbeds in the cores is about 1.2 m/1000 yr.Physiography suggests that the turbidites originated on the Mackenzie Delta or its clinoform, and delta(13)C values of -27 to -25 parts per thousand in the turbidites are compatible with a provenance on a delta. Extant displaced neritic and lower slope to basin plain calcareous benthic foraminifers coexist in the turbidite units. Their joint occurence indicates that the turbidites originated on the modern continental shelf and entrained sediment from the slope and rise enroute to their final resting place on the Canada Abyssal Plain. The presence of Middle Pleistocene diatoms in the turbidites suggests, in addition, that the turbidites may have originated in shallow submarine slides beneath the upper slope or outer shelf. Small but consistent differences in organic carbon content and delta(13)C values between the turbidite units suggest that they did not share an identical provenance, which is at least compatible with an origin in slope failures.The primary provenance of the ice-rafted component of the pelagic beds was the glaciated terrane of northwestern Canada; and the provenance of the turbidite units was Pleistocene and Holocene sedimentary deposits on the outer continental shelf and upper slope of the Mackenzie Delta. Largely local derivation of the sediment of the Canada Abyssal Plain indicates that sediment accumulation rates in the Arctic Ocean are valid only for regions with similar depositional sources and processes, and that these rates cannot be extrapolated regionally. The location of an elliptical zone of active seismicity over the inferred provenance of the turbidites suggests that they were triggered by large earthquakes.Distal turbidite sediment accumulation rates were more than two orders of magnitude greater than pelagic sediment accumulation rates on the Canada Abyssal Plain during the last 8000 years. This disparity reconciles the discrepancy between the high accumulation rates assumed by some for the Arctic Ocean because of the numerous major rivers and large ice sheets that discharge into this small mediterranean basin and the low pelagic sedimentation rates that have been reported from the Arctic Ocean.
Uy014Times Cited:36Cited References Count:46

Chemical Composition of Volcanic Gases - Giggenbach, W. F. (Monitoring and Mitigation of Volcano Hazards, 1996)
id: 1590

Chemical weathering and controls on atmospheric O2 and CO2: Fundamental principles were enunciated by J. J. Ebelmen in 1845 - Berner, Robert A.; Maasch, Kirk A. (Geochimica et Cosmochimica Acta, 1996)
id: 1533

Climate connections between the hemisphere revealed by deep sea sediment core ice core correlations - Charles, C. D.; LynchStieglitz, J.; Ninnemann, U. S.; Fairbanks, R. G. (Earth and Planetary Science Letters, 1996)
Correlation of Southern Ocean deep sea sediment core records with ice core records of polar climate delineates with unprecedented detail the relationship between high latitude climate and the ocean's thermohaline circulation over the last 80,000 years. Our observations suggest that, while North Atlantic Deep Water variability manifests itself clearly in Southern Ocean nutrient proxy records over periods as short as 500 yr, this deep water variability did not promote a direct link between climate variability in the high latitudes of the two hemispheres on millennial timescales. In particular, the proxy records indicate that, on average, northern hemisphere climate fluctuations lagged those of the southern hemisphere by 1500 yr.
Uz230Times Cited:201Cited References Count:33

A comparison of methods for the measurement of dissolved organic carbon in natural waters - Peltzer, E. T.; Fry, B.; Doering, P. H.; McKenna, J. H.; Norrman, B.; Zweifel, U. L. (Marine Chemistry, 1996)
A small suite of natural samples spanning a wide range of DOC concentrations and salinities were analyzed by three high-temperature combustion (HTC) techniques and persulfate oxidation, One of the HTC techniques, sealed-tube combustion (STC), served as a referee method, Using this method, it was possible to obtain absolute DOC concentrations for the natural samples free of any analytical blank offset, Prior to the comparison of samples, an exchange of carbon-free water and calibration standards showed that all methods were equally well calibrated, Linear correlation analysis was used to differentiate whether the differences observed between methods was due to variable oxidation yields or to an artifact of the instrument blank, Agreement among the various methods was quite good, but yields for all methods decreased compared to the STC technique at concentrations of > 400 mu M C. Persulfate results were found to be very similar to HTC results. Finally, carbon-free distilled water prepared by UV/H2O2 oxidation or Milli-Q systems had near-zero DOC concentrations and was adequate for blank correction of all the various techniques yielding DOC concentrations in excellent agreement with the referee method.
Vj296Times Cited:50Cited References Count:49

Compound specific radiocarbon analysis as a tool to quantitatively apportion modern and fossil sources of polycyclic aromatic hydrocarbons in environmental matrices. - Eglinton, T. I.; Pearson, A.; McNichol, A. P.; Currie, L. A.; Benner, B. A.; Wise, S. A. (Abstracts of Papers of the American Chemical Society, 1996)
1Va915 Times Cited:0 Cited References Count:0

Concentrations of carbonyl compounds and the carbon isotopy of formaldehyde at a coastal site in Nova Scotia during the NARE summer intensive - Tanner, Roger L.; Zielinska, Barbara; Uberna, Ewa; Harshfield, Gregory; McNichol, Ann P. (Journal of Geophysical Research: AtmospheresJ. Geophys. Res., 1996)
Keywords: 0315 Biosphere/atmosphere interactions; 0345 Pollution: urban and regional; 0365 Troposphere: composition and chemistry; 0394 Instruments and techniques

Concentrations of carbonyl compounds and the carbon isotopy of formaldehyde at a coastal site in Nova Scotia during the NARE summer intensive - Tanner, R. L.; Zielinska, B.; Uberna, E.; Harshfield, G.; McNichol, A. P. (Journal of Geophysical Research-Atmospheres, 1996)
The concentrations of gaseous atmospheric carbonyl compounds have been measured at a coastal site on the southern tip of Nova Scotia during August 1993 as part of the National Oceanic and Atmospheric Administration's North Atlantic Regional Experiment (NARE) summer intensive. The DNPH-cartridge technique was used for sampling, with analysis by HPLC with UV absorbance detection. The carbon isotopic content of formaldehyde was measured using a novel collection technique on bisulfite-coated fillers followed by accelerator mass spectrometric determination of C-14 content and C-13/C-12 isotopic ratios. Results from this study indicate that quantifiable levels above about 100 parts per trillion by volume were found at the Chebogue Point, Nova Scotia, site for several carbonyls, formaldehyde, acetaldehyde, acetone, propionaldehyde, methyl ethyl ketone, and benzaldehyde, for most 6-hour sampling periods. Six-hour averaged formaldehyde levels of <0.5 to about 3.5 parts per billion were found during periods of local influence and during influence of continental air masses crossing eastern Canada and northeastern US. In contrast, background levels of formaldehyde of 200-400 pptv were found under conditions of predominantly marine back trajectories. Large fractions of contemporary carbon (of the order of 80%) were found in collected formaldehyde samples for all transport regimes and formaldehyde concentrations, suggesting that biogenic sources of hydrocarbon precursors to formaldehyde predominated during the summer season.
Vz788Times Cited:38Cited References Count:42

Correlated temperature and icerafting records, early deglacial warming, and meltwater signals in V29-191, eastern North Atlantic Ocean - Lagerklint, I. Marianne (American Quaternary Association Conference, 1996)
id: 1260

Dating of explosive volcanic events associated with dome growth at Soufriere Hills volcano, Montserrat - Young, S. R.; Hoblitt, R. P.; Smith, A. L.; Devine, J. D.; Wadge, G.; Shepherd, J. B. (Proceedings of the Special Symposium on Volcanism in Montserrat, Second Caribbean Conference on Natural Hazards and Hazard Management, 1996)
id: 1306

Deep water formation and exchange rates in the Arctic Ocean: Implications from the distribution of 14C - Schlosser, P.; Kromer, B.; Ekwurzel, B.; Boenisch, G.; McNichol, A.; Schneider, R.; von Reden, K.; Oestlund, G. (7th International Conference on Accelerator Mass Spectrometry, 1996)
id: 947; 1

The development of Ryder Pond in the Cape Cod National Seashore and determination of the causes of recent Ryder Pondwater chemistry changes. Report - Winkler, Marjorie G. (University of Wisconsin Center for Climatic Research, 1996)
id: 92

Diatom and sediment evidence for late Holocene hydrologic changes, Everglades National Park - Winkler, M. G.; Kaplan, S. (ASLO Meeting, 1996)
id: 1303

Direct U-Th dating of marine sediments from the two most recent interglacial periods - Slowey, N. C.; Henderson, G. M.; Curry, W. B. (Nature, 1996)
A KNOWLEDGE of the age of marine sediments is necessary to determine the timing of events and rates of processes in the marine realm, and the relationships among marine and other climatically sensitive records. The establishment of an accurate chronology for Pleistocene marine sediments beyond the range of radiocarbon dating (approximately the past 45 kyr) has therefore been a goal of palaeoceanographers for decades. Early attempts(1,2) based on measurements of the radionuclides Th-230 and Pa-231 mere beset with problems, and subsequent studies focused on tying fluctuations in marine sediment oxygen-isotope records to events such as the formation of col al reef terraces and changes in the Earth's magnetic polarity(3,4), and tuning the resultant chronologies to the Earth's orbitally driven insolation variations(5-8). But these chronologies (especially the age and duration of the last interglacial period) have been challenged by several studies(9-12), raising questions about the fundamental cause of Pleistocene climate fluctuations. Here we report the direct U-Th dating of aragonite-rich marine sediments from the Bahamas, and present an accurately dated marine oxygen-isotope record for the last two interglacials. We obtain dates of 120-127 kyr BP for the last interglacial and 189-190 kyr np for the late stage 7 interglacial. These dates are in accord with the general theory of orbitally forced climate fluctuations and demonstrate the potential of our direct-dating approach for developing an absolute chronology for the Pleistocene marine oxygen-isotope record.
Vh315Times Cited:39Cited References Count:40

Distribution of otoliths in surficial sediments of the U. S. Atlantic continental shelf and slope and potential for reconstructing Holocene fish stocks - Elder, K. L.; Jones, G. A.; Bolz, G. (Paleoceanography, 1996)
id: 1755

The early and middle Weichselian interstadials in the central area of the Scandinavian glaciations - Donner, J. (Quaternary Science Reviews, 1996)
In the central parts of the Scandinavian glaciations, in Norway, Sweden and Finland, there are a number of Early Weichselian sites with fresh-water sediments, which, by comparison with sites further south, can be correlated with either the Brorup or Odderade interstadials. Few of these sites can with any certainty be correlated with just one of the two. In northern Jutland and at the coast of south-western Norway there are Early Weichselian marine sediments, some of those in Norway having been interpreted as interstadial.Middle Weichselian fresh-water sediments have only been found in Denmark and southern Sweden, whereas marine sediments occur in northern Jutland and at the coast in Norway, in the same areas as the Early Weichselian marine sediments. Most of the Middle Weichselian sites must be referred to as representing an interstadial complex, as a close correlation with the five interstadials identified in northwest Germany and The Netherlands is not possible.A close correlation has been made between the fluctuations in the deep-sea oxygen-isotope curve and the Weichselian history in Scandinavia, the justification for which is discussed. Copyright (C) 1996 Elsevier Science Ltd
Vl592Times Cited:10Cited References Count:56

East Asian monsoon variations; linkage to northern hemisphere millenniallll-scale climate oscillations - Oppo, D. W.; Deiner, L.; Curry, W. B.; Norris, R. D. (Supplement to EOS, 1996)
id: 56

Effects of turbidity flows on organic matter accumulation, sulfate reduction, and methane generation in deep-sea sediments on the Iberia Abyssal Plain - Meyers, P. A.; Silliman, J. E.; Shaw, T. J. (Organic Geochemistry, 1996)
Non-steady-state sedimentation has affected preservation of organic matter in a Pliocene-Pleistocene turbidite sequence sampled by the Ocean Drilling Program at four closely spaced drill sites on the Iberia Abyssal Plain. Organic carbon concentrations average ca. 0.7% in sediments from Sites 897 and 898 and ca. 0.4% at Sites 899 and 900. Headspace concentrations of interstitial methane exceed 100,000 ppm in sediments from Sites 897 and 898 but are essentially zero in those from Sites 899 and 900. Methane concentrations do not rise until interstitial sulfate concentrations are virtually depleted, suggesting the presence of deep in situ methanogenic bacterial activity at Sites 897 and 898 and its absence at Sites 899 and 900. Two factors associated with the turbidity flows that created the sedimentary sequence evidently influenced post-depositional diagenesis at these sites. The principal factor is that the rapidly deposited turbidite sequences at Sites 897 and 898 protected organic matter from early oxic degradation and thereby permitted subsequent anoxic degradation to proceed. In contrast, organic matter in the more slowly deposited turbidites at Sites 899 and 900 was oxidized soon after deposition and was therefore not available for later microbial utilization. A lesser factor is that the turbidity flows may have obtained their entrained organic matter from different environments and consequently delivered organic matter with different characteristics. Both factors contributed to heterogeneity of the types and amounts of organic matter that accumulated in these deep-sea sediments, and this variability has influenced subsequent sulfate reduction and methanogenesis. Copyright (C) 1996 Elsevier Science Ltd.
Wd943Times Cited:22Cited References Count:33

Evolution of the 14C signal in the surface North Atlantic Ocean - Weidman, C. R.; Jones, G. A. (7th International Conference on Accelerator Mass Spectrometry Abstract Radiocarbon, 1996)
id: 89; 1

Expanded Small Sample Capabilities at NOSAMS: Preparation and Analysis of Conventional Graphite Targets Containing 0.15 mg Carbon - Pearson, A.; McNichol, A. P.; Schneider, R. J.; von Reden, K. F. (7th International Conference on Accelerator Mass Spectrometry, 1996)
id: 946; 1

Fluxes of mantle and subducted carbon along convergent plate boundaries - Sano, Y.; Williams, S. N. (Geophysical Research Letters, 1996)
The potential impact of increases in atmospheric CO2 is a topic of considerable controversy. Even though volcanic emission of CO2 may be very small as compared to anthropogenic emissions, evaluation of natural degassing of CO2 is important for any model of the geochemical C cycle and evolution of the Earth's atmosphere. We report here the mantle C flux in subduction zones based on He and C isotopes and CO2/He-3 ratios of high-temperature volcanic gases and medium- and low-temperature fumaroles in circum-Pacific volcanic regions. The calculated volcanic C flux of 3.1x10(12) mol/a from subduction zones is larger than the flux of 1.5x10(12) mol/a from mid-ocean ridges, while contributions from the mantle in subduction zone is only 0.30x10(12) mol/a, equivalent to about 20% of the C flux in mid-ocean ridges. Since the estimated mantle C flux in hot spot regions is insignificant, 0.029x10(12) mol/a, we propose that the global mantle C flux is 1.8x10(12) mol/a in total. The flux, if accumulated over 4.5 billion year of geological time, amounts to 8.3x10(21) mol which agrees well with 9x10(21) mol of the present inventory of C at the Earth's surface. This may support a continuous degassing model of C or the idea that subducted C is recycled into the lower mantle.
Vl370Times Cited:137Cited References Count:39

Forcing of Atlantic Equatorial and Subpolar Millennial Cycles by Precession - McIntyre, A.; Molfino, B. (Science, 1996)
Abundance cycles of the marine alga Florisphaera profunda centered on a period of 7600 carbon-14 years (8400 calendar years) are present in high-resolution records from the equatorial Atlantic spanning 0 to 45,000 years ago. These cycles correlate with Heinrich events 1 through 5, which document rapid changes in continental ice melting around the subpolar North Atlantic. These variations in F. profunda are a direct response to modulation in zonal wind-driven divergence produced by a precessional component of orbital variation during a time of reduced eccentricity modulation.
McIntyreMolfino eng 1996/12/13 Science. 1996 Dec 13;274(5294):1867-70.

Gas chromatographic isolation of individual compounds from complex matrices for radiocarbon dating - Eglinton, T. I.; Aluwihare, L. I.; Bauer, J. E.; Druffel, E. R.; McNichol, A. P. (Anal Chem, 1996)
This paper describes the application of a novel, practical approach for isolation of individual compounds from complex organic matrices for natural abundance radiocarbon measurement. This is achieved through the use of automated preparative capillary gas chromatography (PCGC) to separate and recover sufficient quantities of individual target compounds for (14)C analysis by accelerator mass spectrometry (AMS). We developed and tested this approach using a suite of samples (plant lipids, petroleums) whose ages spanned the (14)C time scale and which contained a variety of compound types (fatty acids, sterols, hydrocarbons). Comparison of individual compound and bulk radiocarbon signatures for the isotopically homogeneous samples studied revealed that Delta(14)C values generally agreed well (+/-10%). Background contamination was assessed at each stage of the isolation procedure, and incomplete solvent removal prior to combustion was the only significant source of additional carbon. Isotope fractionation was addressed through compound-specific stable carbon isotopic analyses. Fractionation of isotopes during isolation of individual compounds was minimal (<5 per thousand for delta(13)C), provided the entire peak was collected during PCGC. Trapping of partially coeluting peaks did cause errors, and these results highlight the importance of conducting stable carbon isotopic measurements of each trapped compound in concert with AMS for reliable radiocarbon measurements. The addition of carbon accompanying derivatization of functionalized compounds (e.g., fatty acids and sterols) prior to chromatographic separation represents a further source of potential error. This contribution can be removed using a simple isotopic mass balance approach. Based on these preliminary results, the PCGC-based approach holds promise for accurately determining (14)C ages on compounds specific to a given source within complex, heterogeneous samples.
Eglinton, T IAluwihare, L IBauer, J EDruffel, E RMcNichol, A Peng1996/03/01 00:00Anal Chem. 1996 Mar 1;68(5):904-12. doi: 10.1021/ac9508513.

Gas venting and late Quaternary sedimentation in the Persian (Arabian) Gulf - Uchupi, E.; Swift, S. A.; Ross, D. A. (Marine Geology, 1996)
High resolution 3.5 kHz echo sounding profiles and piston cores were used to reconstruct the microtopography and late Quaternary depositional history of the Persian Gulf. Perversive throughout the seafloor of the Gulf is an extensive network of pockmarks formed by seepages of thermogenic gas. These gas seeps and bottom water exiting the Gulf via the Strait of Hormuz are the most significant processes controlling present-day sedimentation in the region. Erosion by these seeps has been so intense in the Baiban Shelf in the Strait of Hormuz as to create a ''hoodoo'' like terrain on the outer shelf. The surfical geology of the Gulf documents a short lived transgression 29,400 to 22,800 years ago during the Wisconsin regression which began 125,000 years ago, the Wisconsin regressive maxima when sea level dropped to -120/-130 m about 21,000/20,000 years ago and the climate was dry and eolian and paralic sedimentation characterized the Gulf, the Holocene transgression 18,000 to 12,000 years ago when the climate was more humid than during the climax of the Wisconsin regression, a dry phase 12,000 to 9000 years ago when the Persian Gulf was a site of eolian and carbonate deposition, and the present sediment cycle during the last 9000 years under a more humid regime. It was during the present cycle that southeast trending marl lobes were deposited off Iran, Arabia acquired its hyper-arid climate about 3000 years ago and the Gulf attained its present configuration about 1000 years ago as a result of the construction of the Tigris Euphrates Delta at its head and tectonism and aggradation along its Arabian and Iranian flanks.
Tv774Times Cited:49Cited References Count:82

Highly Variable Late Pleistocene and Holocene Sedimentation Rates In AMS C14-Dated Boxcores From the Central Arctic Ocean - Darby, D. A. Bischof J. F. Jones G. A. (EOS, 1996)
id: 906

A history of Pacific Northwest earthquakes recorded in Holocene sediments from Lake Washington - Karlin, R. E.; Abella, S. E. B. (Journal of Geophysical Research-Solid Earth, 1996)
Large earthquakes can trigger slumping of the steep walls of lake basins and landslides in the drainage area, resulting in turbidite deposition in the lake and increased detrital flux from inlets. Holocene sediments in piston cores from Lake Washington contain a series of terrigenous layers that were episodically deposited in the lake. Sedimentological, geochemical, and paleomagnetic analyses on nine piston cores show that the detrital layers are temporally and areally correlatable, indicating basinwide disruptions. These layers are opaque on X-radiographs, are coincident with magnetic susceptibility peaks, have abundant aluminosilicate minerals, are relatively coarse grained, and have low organic carbon and biogenic silica contents. The thicknesses and geographic distributions of the layers suggest that they are not due to floods or delta destabilization. Side scan swath imagery and subbottom profiling show that large slumps, subaqueous landslides, and debris flows are common along the margins of the lake. A detailed chronology, established from 21 radiocarbon ages on five cores, show that a prominent turbidite was deposited about 1000-1100 years ago. This turbidite apparently was triggered by a large earthquake that probably occurred on the Seattle fault. Other depositional events in the sediment record at 1500-1700, 2400-2500, and 2800-3200 years ago coincide with periods of landsliding that have been previously inferred from the dating of drowned trees in the lake. More than 30 depositional events have occurred in the last 12,000 years and 21 disturbances have occurred since the deposition of the Mazama ash about 7,600 years ago. If all the events are due to earthquakes, the Puget Sound region has been subject to major shaking every 300 to 400 years. The strong intensities needed to trigger subaqueous slides may not be generated by just local sources such as the Seattle fault but could also be caused by great subduction earthquakes occurring along the coast.
Ua372Times Cited:19Cited References Count:57

Holocene climatic and human influences on lakes of the Yucatan Peninsula, Mexico: An interdisciplinary, palaeolimnological approach - Whitmore, T. J.; Brenner, M.; Curtis, J. H.; Dahlin, B. H.; Leyden, B. W. (Holocene, 1996)
We used palaeolimnological techniques to examine effects of Holocene climate change and human influence on lakes of the Yucatan Peninsula, Mexico. The three study lakes are located along a west-east transect that represents a gradient of increasing modern precipitation and density of former Maya settlement. At Lake Coba, an 880-cm sediment core yields a complete record of lacustrine sedimentation that began when the lake first filled similar to 8000 BP as groundwater level rose in response to rising sea level and increased precipitation. Diatom, ostracod, and delta(18)O evidence indicate that Lake Coba was initially shallow and saline. Coba, presently in the region of greatest rainfall, showed more episodic water-level changes than Lake San Jose Chulchaca or Lake Sayaucil. High lake level and fresh water were evident at 440 cm (similar to 2600 BP), followed by a decline in water levels and an increase in total ionic salinity to the present time. In a 613-cm core from Sayaucil, in the intermediate precipitation zone, total salinity was high between 600 and 400 cm (similar to 3050 and 2000 BP), followed by consistently higher water levels. Salinity was high in the lower portion of a 110-cm San Jose Chulchaca core (beginning similar to 1860 BP), followed by a gradual and consistent freshening of water to the present time.Trophic state changes and human influence on lakes were evaluated using diatom, delta(18)O, total P, sedimentary organic matter, and preliminary pollen data. Maximal human disturbance at Lake Coba, a densely settled Maya urban site, occurred during a deep-water event at 440 cm, followed by a decline in human influence and trophic state to the present time. Trophic state and linear sedimentation rates in Sayaucil increased significantly above 400 cm (after similar to 2000 BP), probably associated with initial Maya settlement near Xtojil and subsequent small-scale farming. Limnological disturbance may have preceded the period of maximal human occupation because initial land clearance and consequent soil erosion probably affected water quality substantially. San Jose Chulchaca lacks archaeological evidence of human occupation in the drainage, and shows gradual changes in trophic state not caused by human disturbance. With the exception of a C-14 date on wood from the base of the Coba core, C-14 dates and chronologies may be artificially old as a consequence of hard-water-lake error. Trophic state changes in the study lakes were generally consistent with known patterns of human settlement and population change. Late-Holocene water-level fluctuations were most pronounced in Lake Coba in eastern Yucatan, where modern rainfall is currently greatest, but lake level is generally lower than during much of the past. Lake level was relatively constant in Sayaucil in the central peninsula, whereas lake level in San Jose Chulchaca in the arid western portion of the peninsula increased gradually over time.
Vh189Times Cited:56Cited References Count:65

Holocene paleoclimatic changes in the Lake Winnebago basin, east-central Wisconsin - Haase, Alisa A.; Smith, G. L.; Hardacker, E. P. (Abstracts with Programs - Geological Society of America, 1996)
id: 77

Holocene sea-level rise recorded by a radiocarbon-dated mussel in a submerged speleothem beneath the Mediterranean Sea - Fabrizio, A.; Oliverio, M. (Quaternary Research, 1996)
id: 1241

A Holocene vegetation history from lowland Guatemala - Islebe, G. A.; Hooghiemstra, H.; Brenner, M.; Curtis, J. H.; Hodell, D. A. (Holocene, 1996)
A 5.45-m core from Lake Peten-Irza, lowland Guatemala, contains a near-complete record of Holocene sedimentation. The age-depth relationship for the core is based on AMS C-14 dating of terrestrial wood fragments and provides a reliable chronology in this karst region where hard-water lake error has typically confounded sediment geochronology. In the basal part of the sequence, pollen of the Moraceae-Urticaceae group dominate, indicating the presence of widespread tropical forest during the early Holocene (c. 8600-5600 yr BP). Relative abundance of pollen of high forest taxa declined beginning as early as 5600 yr BP, indicating climatic drying or perhaps initial land clearance. Deforestation by prehistoric Mayan inhabitants is documented clearly in the pollen record beginning about 2000 pr BP (106 cal BC-122 cal Ao, 95.4%, 2 sigmas) by the appearance of disturbance taxa (e.g. Ambrosia and Poaceae) and presence of Zea. Forest regrowth occurred following the Classic Maya collapse, c. AD 900, as reflected by a relative increase in Moraceae-Urticaceae pollen.
Vh189Times Cited:103Cited References Count:44

Increased continental-margin slumping frequency during sea-level lowstands above gas hydrate-bearing sediments - Paull, C. K.; Buelow, W. J.; Ussler, W.; Borowski, W. S. (Geology, 1996)
We present C-14 data on sediment samples from cores of the upper 7 m of the sediment column overlying a major continental-rise gas hydrate field on the southern Carolina Rise and inner Blake Ridge offshore the southeastern United States. The data show that glacial-age sediments are underrepresented in the cores. The observation is consistent with a previously predicted association between sea-level lowstands and increased frequency of sea-floor slumping on continental margins containing gas hydrates.
Tt580Times Cited:86Cited References Count:26

Informe Final: Geocronologia de las aquas subterraneas del Salar Punta Negra, Antofagasta, II Region. Preparado para Minera Escondida Ltda. (Report) - Salamanca, Marco (Minera Escondid Ltda, 1996)
id: 181

Initial results from paleoclimatic drilling and geophysical studies of Washoe Lake, Nevada - Karlin, R.; Trexler, J.; Petersen, R. (USGS Circular 1119, Water Resources Division, 1996)
id: 1245

Inorganic radiocarbon in time-series trap samples: implication of seasonal variation of 14C in the upper ocean - Honda, Makio C. (Radiocarbon, 1996)
id: 27

Isolation of Individual Organic Compounds for AMS Radiocarbon Analysis -- A Novel Approach - Eglinton, T. I.; McNichol, A. P.; Benitez-Nelson, B. C.; Pearson, A.; von Reden, K. F.; Schneider, R. J.; Bauer, J. E.; Druffel, E. R. M. (7th International Conference on Accelerator Mass Spectrometry, 1996)
id: 1800; 1

Isolation of Individual Organic Compounds for AMS Radiocarbon Analysis--A Novel Approach - Eglinton, T. I.; McNichol, A. P.; Benitez-Nelson, B. C.; Pearson, A.; von Reden, K. F.; Schneider, R. J.; Bauer, J. E.; Druffel, E. R. M. (Radiocarbon, 1996)
id: 1650

Kinematic Effects in the Sputtering of Carbon Isotopes - Schneider, R. J.; Hartman, J.; von Reden, K. F.; McNichol, A. P. (Radiocarbon, 1996)
id: 1660

Kinematic Effects in the Sputtering of Carbon Isotopes - Schneider, R. J.; Hartman, J.; von Reden, K. F.; McNichol, A. P. (7th International Conference on Accelerator Mass Spectrometry, 1996)
id: 1801; 1

The "Lake" of Mayran: Reconstructing an Environmental History from Alluvial, Lacustrine, and Soils Records in Northern Mexico - Butzer, K. W. Frederick C. D. Cordova C. E. Butzer E. K. Abbott y J. T. (Annual Meeting, Sociedad Mexicana de Antropologia, 1996)
id: 903; Symposium: "El Hombre y el Lago: Ayer y Hoy"

Large-volume WOCE radiocarbon sampling in the Pacific Ocean - Stuiver, M.; Ostlund, H. G.; Key, R. M.; Reimer, P. J. (Radiocarbon, 1996)
At the University of Miami Tritium Laboratory and the University of Washington Quaternary Isotope Laboratory, more than 1000 large-volume Pacific Ocean radiocarbon samples were measured for the WOCE program. Here we present a comprehensive data set, and a brief discussion of our findings.
Xd080Times Cited:12 Cited References Count:8
Keywords: geosecs

Late holocene coastal plain stratigraphy and sea-level history at Hanalei, Kauai, Hawaiian islands - Calhoun, R. S.; Fletcher, C. H. (Quaternary Research, 1996)
Fluvial, marine, and mixed fluvial-marine deposition on the coastal plain of Hanalei Bay on the north shore of Kauai, Hawaii, records a middle- to late-Holocene fall of relative sea level. Radiocarbon dating of the regression boundary preserved in the stratigraphy of the coastal plain documents a seaward shift of the shoreline beginning at least 4800-4580 cal yr B.P. and continuing until at least 2160-1940 cal yr B.P. Marine sands stranded in the backshore and coastal plain environment are buried by fluvial floodplain and channel sands, silts, and muds. In places, erosion at the regression contact exposed older marine sands thus increasing the hiatus at the regression disconformity, The shoreline regression is best explained as the result of a fall in relative sea level. The age and elevation of the cored regression boundary at sites that have not been influenced by erosion are consistent with a middle-to late-Holocene highstand of relative sea level as predicted by geophysical models of whole Earth deformation related to deglaciation. (C) 1996 University of Washington.
Uf728Times Cited:21Cited References Count:35

Late Quaternary deep circulation in the western equatorial Atlantic (Book Section) - Curry, W. B. (The South Atlantic: Present and Past Circulation, 1996)
id: 1336

Late Quaternary stratigraphy, sea-level history and paleoclimatology of the southeast Florida outer continental shelf, Thesis - Toscano, M. A. (University of South Florida, 1996)

The Little Ice Age and Medieval Warm Period in the Sargasso Sea - Keigwin, L. D. (Science, 1996)
Sea surface temperature (SST), salinity, and flux of terrigenous material oscillated on millennial time scales in the Pleistocene North Atlantic, but there are few records of Holocene variability. Because of high rates of sediment accumulation, Holocene oscillations are well documented in the northern Sargasso Sea. Results from a radiocarbon-dated box core show that SST was approximately 1°C cooler than today approximately 400 years ago (the Little Ice Age) and 1700 years ago, and approximately 1°C warmer than today 1000 years ago (the Medieval Warm Period). Thus, at least some of the warming since the Little Ice Age appears to be part of a natural oscillation.
Keigwineng 1996/11/29 Science. 1996 Nov 29;274(5292):1504-8.

A long pollen record from lowland Amazonia: Forest and cooling in glacial times - Colinvaux, P. A.; DeOliveira, P. E.; Moreno, J. E.; Miller, M. C.; Bush, M. B. (Science, 1996)
A continuous pollen history of more than 40,000 years was obtained from a lake in the lowland Amazon rain forest. Pollen spectra demonstrate that tropical rain forest occupied the region continuously and that savannas or grasslands were not present during the last glacial maximum. The data suggest that the western Amazon forest was not fragmented into refugia in glacial times and that the lowlands were not a source of dust. Glacial age forests were comparable to modern forests but also included species now restricted to higher elevations by temperature, suggesting a cooling of the order of 5 degrees to 6 degrees C.
Vk748Times Cited:350Cited References Count:42

Molecular breakup of CO2 and hold-up time in a microwave ion source - Wills, J. S. C.; Diamond, W. T.; Lewis, R. A.; Schmeing, H.; von Reden, K. F.; Schneider, R. J. (1996)
id: 949

Neolithic migrations as a function of sea level-controlled topography in the Yangtze Delta, China - Stanley, D. J.; Chen, Zhongyuan (Geology, 1996)
id: 1282

Ocean Tracer Laboratory Tech. Report - Key, R. M. (P17E19S final report for AMS 14C samples, 1996)
id: 1252

ODP drilling on the Amazon Fan; initial results on growth pattern and timing of fan sedimentation - Flood, R. D.; Piper, D. J. W. (Annual Meeting Abstracts--American Association of Petroleum Geologists and Society of Economic Paleontologists and Mineralogists, 1996)
id: 23

One thousand years of change in the Great Lakes Region. A pilot project of the NBS Landscape Use History of North America (LUHNA) publ. electronically on the World Wide Web - Cole, K. L.; Davis, M. B.; Winkler, M. G. (1996)
id: 1323; http://www.nbs.gov/luhna/cole

P16 S17S TUNES-2 final report for AMS 14C samples (Report) - Key, R. M. (Ocean Tracer Laboratory Tech. Report, 1996)
id: 1250

P16A17A Final report for large volume samples and D14C measurements - Key, R. M. (Ocean Tracer Laboratory Tech. Rep., 1996)
id: 1454