Identification of seasonal-to-decadal timescale variations in the zonal currents of the central equatorial Pacific - Grottoli, A. G.; Druffel, E. R. M.; Gille, S. T.; Dunbar, R. B. (International Coral Reef Symposium, 2000)
id: 1401

Identification of Seasonal-to-Decadal Timescale Variations in the Zonal Currents of the Central Equatorial Pacific Prior to 1955 Using A14C in Coral - Grottoli, A. G.; Druffel, E. R. M.; Gille, S. T.; Dunbar, R. B. (EOS, 2000)
F767
id: 254

Implementazione di sistemi di datazione con il 14C ed estensione all 'impiego di piccole quantita di materiale, Thesis - Salvatore, Improta (Universita degli studi di Roma La Sapienza, 2000)

The Indian Ocean 13C Suess effect - Sonnerup, R. E.; Quay, P. D.; McNichol, A. P. (Global Biogeochemical Cycles, 2000)
id: 1816

Installation of a 134-sample MC-SNICS ion source at NOSAMS and first results - von Reden, K. F.; Bellino, M.; Long, P.; Schneider, R. J.; Loger, R. (Nuclear Instruments & Methods in Physics Research Section B-Beam Interactions with Materials and Atoms, 2000)
In April 1999, the National Ocean Sciences AMS (NOSAMS) facility received the shipment of a 134-sample MC-SNICS ion source from the National Electrostatics Corporation (NEC). It replaced one of the two 59-sample spherical ionizer sources (US-AMS Model 3090A, HVEE Model 846). In this paper, we will describe the adaptation of the NEC ion source to the US-AMS/HVEE recombinator injector at NOSAMS. This is the first lime that the two leading sputter ion source designs are directly comparable on the same system. We will present ion beam optics calculations for both in comparison with measured results. Once fully operational, the new ion source will assume all of the sputter sample measurements at NOSAMS, while the remaining 59-sample source will be replaced by the newly developed microwave gas ion source. One of the most desirable features of the MC-SNICS design is the smaller cathode geometry. At comparable extracted currents, the surface diameter of the pressed samples is reduced from 1.5 to 1 mm. A new, automatic sample pressing procedure is being developed for this design. This will improve the capability for preparing and analyzing smaller sputter samples (carbon weight <100 <mu>g). Our US-AMS cathodes showed considerable reduction in the extracted currents when the sample diameter was reduced to 1 mm, even with samples of normal size (>200 mug C). (C) 2000 Elsevier Science B.V. All rights reserved.
8th International Conference on Accelerator Mass SpectrometrySEP 06-10, 1999 VIENNA, AUSTRIA
Keywords: AMS; beam extraction/injection; C-14; ion sources; ocean; pacific

Isotopic evidence for Late Glacial and Holocene climatic change in the tropical Andes - Seltzer, G.; Rodbell, D.; Burns, S. (Geology, 2000)
id: 1338

Lake Erie: The Impact of Mid-Holocene Flooding by Upper Great Lake Waters - Kempthorne, R. A.; Barrera, E.; Coakley, J. P.; Palmer, D. F. (EOS, Transactions, American Geophysical Union, 2000)
id: 248

Late glacial paleohydrology and vegetational change in Salada Medinana, Central Ebro Basin, Spain - Valero-Garces, B. L. (Quarternary International, 2000)
id: 382

A late Holocene pollen record from Torrey Pine State Reserve, California - Cole, K. L.; Wahl, Eugene (Quaternary Research, 2000)
id: 214

Late Pleistocene and Holocene geological evolution of the central Penobscot River Valley: Surficial geology, geoarchaeology, and water supply (Book Section) - Kelly, A. R.; Dorion, C. C.; Balco, G.; Dieffenbacher-Krall, A.; Garrett, P.; Locke, D.; Tolman, A. (Guidebook for Field Trips in Coastal and East-Central Maine: NEIGC 92nd Annual Meeting, 2000)
id: 152

Late Quaternary sedimentary fluctuations of biogenic fluxes driven by climatic changes in the Southern Ocean--abstract - Langone, L.; Giglio, F.; Ravaioli, M.; Frignani, M.; Marozzi, G.; Rovatti, G. (XXV General Assembly of European Geophysical Society, 2000)
id: 288

Lipids as a Common Interest of Microorganisms and Geochemists (Commentary) - Hayes, John M. (Proc. National Academy Sciences USE, 2000)
id: 1778

Lomas de ocupacion en los Llanos de Moxos (Book Section) - Erickson, Clark L. (La Arqueologia de las Tierras Bajas, 2000)
id: 180

Los caminos prehispanicos de la amazonia boliviana (Book Section) - Erickson, Clark L. (Vias Precolombinas: los caminos, los ingenieros y los viajeros, 2000)
id: 179

Low-level (submicromole) environmental 14C metrology - Currie, L. A.; Kessler, J. D.; Marolf, J. V.; McNichol, A. P.; Stuart, D. R.; Donoghue, J. C. (Nucl. Instr. and Meth. in Phys. Res., 2000)
id: 1713

Mapping of C4 plant input from North West Africa into North East Atlantic Sediments - Huang, Yongsong; Dupont, Lydie; Sarnthein, Michael; Hayes, John M.; Eglinton, Geoffrey (Geochimica et Cosmochima Acta, 2000)
id: 1777

Mass spectra of sn-2hydroxyarchaeol, a Polar-lipid Biomarker for Anaerobic Methanotrophy - Hinrichs, Kai-Uwe; Pancost, Richard D.; Summons, Roger E.; Sprott, G. Dennis; Sylva, Sean P.; Sinninghe-Damste, Jaap S.; Hayes, John M. (Geochem. Geophys. Geosyst., 2000)
id: 1735

Memorial to Henry G. Thode, 1910-1997 - Shaw, Denis M.; Epstein, Sam; Hayes, John M. (Geological Society of America Memorials, 2000)
id: 1737

Molecular and isotopic analysis of anaerobic methane-oxidizing communities in marine sediments - Hinrichs, K. U.; Summons, R. E.; Orphan, V.; Sylva, S. P.; Hayes, J. M. (Organic Geochemistry, 2000)
Convergent lines of molecular, carbon-isotopic, and phylogenetic evidence have previously indicated (Hinrichs, K.U., Hayes, J.M., Sylva, S.P., Brewer. P.G.. DeLong, E.F., 1999. Methane-consuming archaebacteria in marine sediments. Nature 398, 802-805.) that archaea are involved in the anaerobic oxidation of methane in sediments from the Eel River Basin. offshore northern California. Now, further studies of those same sediments and of sediments from a methane seep in the Santa Barbara Basin have confirmed and extended those results. Mass spectrometric and chromatographic analyses of an authentic standard of sn-2-hydroxyarchaeol (hydroxylated at C-3 in the sn-2 phytanyl moiety) have confirmed our previous, tentative identification of this compound but shown that the previously examined product was the mono-TMS, rather than di-TMS, derivative. Further analyses of C-13-depleted lipids, appreciably more abundant in samples from the Santa Barbara Basin, have shown that the archaeal lipids are accompanied by two sets of products that are only slightly less depleted in C-13. These are additional glycerol ethers and fatty acids. The alkyl substituents in the ethers (mostly monoethers, with some diethers) are non-isoprenoidal. The carbon-number distributions and isotopic compositions of the alkyl substituents and of the fatty acids are similar, suggesting strongly that they are produced by the same organisms. Their structures, n-alkyl and methyl-branched n-alkyl, require a bacterial rather than archaeal source. The non-isoprenoidal glycerol ethers are novel constituents in marine sediments but have been previously reported in thermophilic, sulfate- and nitrate-reducing organisms which lie near the base of the rRNA-based phylogenetic tree. Based on previous observations that the anaerobic oxidation of methane involves a net transfer of electrons from methane to sulfate, it appears likely that the non-archaeal, C-13-depleted lipids are products of one or more previously unknown sulfate-reducing bacteria which grow syntrophically with the methane-utilizing archaea. Their products account for 50% of the fatty acids in the sample from the Santa Barbara Basin. At all methane-seep sites examined, the preservation of aquatic products is apparently enhanced because the methane-oxidizing consortium utilizes much of the sulfate that would otherwise be available for remineralization of materials from the water column. Crown Copyright (C) 2000 Published by Elsevier Science Ltd. All rights reserved.
384quTimes Cited:204Cited References Count:49

The N and W Iceland Shelf: insights into Last Glacial Maximum ice extent and deglaciation based on acoustic stratigraphy and basal radiocarbon AMS dates - Andrews, J. T.; Hardardottir, J.; Helgadottir, G.; Jennings, A. E.; Geirsdottir, A.; Sveinbjornsdottir, A. E.; Schoolfield, S.; Kristjansdottir, G. B.; Smith, L. M.; Thors, K.; Syvitski, J. P. M. (Quaternary Science Reviews, 2000)
We present 32 AMS radiocarbon dates collected from sediments obtained during cruises of CSS Hudson (1993, RV Jan Mayen (1996), and Bjarni Saemundsson (1997). The radiocarbon dates were obtained on samples from the basal part of sediment cores collected across an area between 64 and 67 degrees N and 18-29 degrees W. Core sites were based on 3.5 kHz acoustic subbottom surveys. The 3.5 kHz subbottom profiles indicate that several of the troughs contain greater than or equal to 30 m of Quaternary sediment. At many sites, the acoustic surveys suggest the presence of one or more strong reflectors which can be traced over extended areas ( > 100 km) of the seafloor. These may represent large-scale volcanic ash falls, such as the Vedde ash and its correlatives, as well as other regionally significant tephras. We report dates from seven areas; (1) Northern troughs - Eyjafjardarall, Hunafloadjup, and Reykjafjardarall: (2) Hunafloi area and inner shelf and fjords; (3) Djupall area; (4) Isafjardardjup area; (5) Kolluall; (6) western shelf break and slope; and 7) Jokuldjup. The dates range in age from Marine Isotope Stages 3-1. Five cores have basal dates greater than or equal to 16 ka and thus provide information on the timing and environments during the deglaciation, Several dates of similar to 12 ka indicate that the inner shelf may have been largely ice-free by that time. Estimates of average sediment accumulation rates vary between 4 and 90 cm/kyr, with modal estimates of 30-30 cm/kyr, (C) 2000 Elsevier Science Ltd. All rights reserved.
298udTimes Cited:71Cited References Count:75

A New Estimate of the Holocene Lowstand Level of Lake Titicaca and Implications for Tropical Paleohydrology - Cross, S. C.; Baker, P. A.; Seltzer, G. O.; Fritz, S. C. (The Holocene, 2000)
id: 1339

The NOSAMS sample preparation laboratory in the next millenium: Progress after the WOCE program - Gagnon, A. R.; McNichol, A. P.; Donoghue, J. C.; Stuart, D. R.; von Reden, K. (Nuclear Instruments & Methods in Physics Research Section B-Beam Interactions with Materials and Atoms, 2000)
Since 1991, the primary charge of the National Ocean Sciences AMS (NOSAMS) facility at the Woods Hole Oceanographic Institution has been to supply high throughput, high precision AMS C-14 analyses for seawater samples collected as part of the World Ocean Circulation Experiment (WOCE). Approximately 13,000 samples taken as part of WOCE should be fully analyzed by the end of Y2K. Additional sample sources and techniques must be identified and incorporated if NOSAMS is to continue in its present operation mode.A trend in AMS today is the ability to routinely process and analyze radiocarbon samples that contain tiny amounts (<100 <mu>g) of carbon. The capability to mass-produce small samples for C-14 analysis has been recognized as a major facility goal. The installation of a new 134-position MC-SNICS ion source, which utilizes a smaller graphite target cartridge than presently used, is one step towards realizing this goal. New preparation systems constructed in the sample preparation laboratory (SPL) include an automated bank of 10 small-volume graphite reactors, an automated system to process organic carbon samples, and a multi-dimensional preparative capillary gas chromatograph (PCGC). (C) 2000 Elsevier Science B.V. All rights reserved.
372jrTimes Cited:20Cited References Count:12

Oceanic uptake of CO2 re-estimated through d13C in WOCE samples - Lerperger, M.; McNichol, A. P.; Peden, J.; Gagnon, A. R.; Elder, K. L.; Kutschera, W.; Rom, W.; Steier, P. (Nuclear Instruments and Methods in Physics Research, 2000)
id: 1817

An ocean-wide DIC-13 data set - McNichol, A. P.; Quay, P. D.; Stuart, D. R.; Sonnerup, R. E.; Key, R. M. (AGU Ocean Sciences Meeting, 2000)
id: 1444

An Ocean-Wide DIC-13 Data Set - McNichol, A P; Quay, P D; Stuart, D R; Sonnerup, R E; Key, R M (2000 Ocean Sciences Meeting, San Antonio, TX (USA), 24-28 Jan 2000, 2000)
High quality DIC-13 measurements were made throughout the world's oceans at the University of Washington (UW) and the National Ocean Sciences Accelerator Mass Spectrometry (NOSAMS) Facility during both the OACES and WOCE programs. We are currently merging these two data sets which represent 25000 individual DIC- 13 measurements from 1260 stations. We will present the inter-laboratory calibration and standardization data. Based on 135 measurements on CO2 gas extracted at UW, the mean offset between the two labs is 0.01 o/oo, similar to the offset observed from an exchange of DIC standards (0.012 o/oo). Stations measured by both laboratories will also be examined for offsets, although one comparison in the Indian Ocean shows no significant differences. We will present our progress towards a global atlas of DIC-13, primarily maps of the merged data sets in the Pacific, Southern, and Indian Oceans. In this poster we will concentrate on regions that have been under-sampled in the past, e.g. the Southern Ocean. Additionally, we will examine the relationship of DIC-13 to PO4 and to DIC-14. A preliminary analysis of DIC-13 and PO4 from three WOCE lines in the Pacific indicates that the expected relationship is observed in the deep waters and that the data from different water masses occupy well-defined regions of the graph. We are examining the potential for using the relationship between DIC-14 and DIC-13 to improve our understanding of the penetration of bomb radiocarbon into the ocean as well as fundamental processes in the deep ocean. The relationship is complex yet the data from shallow to intermediate depths (100 to 1000m) follow two distinct parallel lines that are related to the hemisphere in which
Date revised - 2007-04-01SuppNotes - Abstracts available.Last updated - 2016-12-21
Keywords: carbon cycling; Carbon dioxide; Deep water; dissolved inorganic carbon; ISW, Indian Ocean; Marine; Mass Spectrometry; Ocean circulation; Phosphates; PS, Antarctic Ocean; Q2 09146:TSD distribution, water masses and circulation; Stable isotopes; Standardization; Water masses; World Ocean; World Ocean Circulation Experiment (WOCE)

An organic tracer for surface ocean radiocarbon - Pearson, A.; Eglinton, T. I.; McNichol, A. P. (Paleoceanography, 2000)
The Delta(14)C of surface water dissolved inorganic carbon (DIC) in the Southern California Eight was compared to Delta(14)C as recorded by the sterols in Santa Monica and Santa Barbara Basin sediments. All of the C-26, C-27, C-28, and C-29 sterols as well as dinosterol had C-14 concentrations equal to surface water DIG, indicating that all of the major sterols were derived from phytoplanktonic production. There is no detectable terrestrial component. Their tracer capability was confirmed by comparing the "bomb C-14"-derived change in surface water Delta(14)C(DIC) With the change in Delta(14)C(sterol). The "prebomb" Delta(14)C(DIC) was similar to 82 parts per thousand, and prebomb sterols averaged -75 +/- 19 parts per thousand. The Delta(14)C value in 1996 was +71 parts per thousand, Eighteen measurements representing eight different sterols from the sediment-water interface of both Santa Monica and Santa Barbara Basins averaged +62 +/- 23 parts per thousand. When three of these values were eliminated because of suspected contamination, the remaining data averaged +71 +/- 12 parts per thousand. The entire compound class could serve as an excellent proxy for the C-14 concentration of ocean surface waters.
358wyTimes Cited:37Cited References Count:58

Organogenic dolomitization in peritidal to deep-sea sediments - Mazzullo, S. J. (Journal of Sedimentary Research, 2000)
Presumed barriers to early dolomitization in normal seawater-derived pore fluids at earth-surface temperatures appear to be overcome within some anoxic, organic-rich sediments as a result of bacterial sulfate reduction and methanogenesis, These processes may promote early dolomitization, particularly during methanogenesis and late stages of sulfate reduction, by concurrently raising and sustaining high pH and high total alkalinity and CO32- concentrations in pore fluids, and by simultaneously either decreasing Mg and Ca hydration or by promoting crystal surface reactions with less hydrated Mg-Ca neutral ion pairs. Volumetrically significant quantities of dolomite are associated with sulfate reduction and/or methanogenesis within peritidal, shallow-marine, and deep-sea deposits. Average concentrations of organogenic dolomite are as much as 70% in some Holocene peritidal deposits, and 28% in Mesozoic to Quaternary deep-sea sediments.Organogenic dolomites are mainly cements, and contain relatively low concentrations of Sr and Mn, Sulfate-reduction dolomites generally are Fe-deficient because of concurrent pyrite precipitation, whereas methanogenetic dolomites may be somewhat more ferroan as Fe substitutes for depleting Mg. Sources of Mg and Ca for dolomite are diffusion from overlying seawater and/or dissolution of precursor carbonate sediments. Dolomites are characterized by a wide range in delta(13)C values wherein those of sulfate reduction versus methanogenetic origin typically are C-13-depleted and C-13-enriched, respectively. The extent of C-13 depletion or enrichment, however, depends on the extent of organodiagenetic reactions and amount of C-13 contributed by seawater diffusion, and commonly results in overlap of delta(13)C(dolomite) values. The range of delta(18)O(dolomite) values is somewhat more restricted, and generally reflects differences in pore-fluid temperature and salinity. Some of the unresolved issues in organogenic dolomitization are: the relative efficiencies of sulfate reduction versus methanogenesis in promoting dolomitization, depths of dolomite formation inferred on the basis of delta(18)O(dolomite) values and probable sources of Mg and Ca, and the mode of dolomitization with progressive burial into methanogenetic zones.
A287nxTimes Cited:125Cited References Count:106

The origin of Antarctic precipitation: a modelling approach - Delaygue, G.; Masson, V.; Jouzel, J.; Koster, R. D.; Healy, R. J. (Tellus Series B-Chemical and Physical Meteorology, 2000)
The contribution of different moisture sources to Antarctic precipitation for present-day and glacial conditions is estimated with the NASA/GISS Atmospheric General Circulation Model. Despite its low horizontal resolution (8 degrees x 10 degrees), this model simulates reasonably well the broad features of the observed present-day hydrological cycle. Simulated present-day Antarctic precipitation is dominated throughout the year by moisture from a subtropical/midlatitude band (30 degrees S-60 degrees S). The moisture supplied to a given coastal area of Antarctica originates mostly in the adjacent oceanic basin; closer to the pole, other oceanic basins can also contribute significantly. Replacing the present-day sea surface temperatures (SSTs) and sea ice cover in the GCM with those from the CLIMAP oceanic reconstruction for the last glacial maximum (LGM), greatly increases the simulated latitudinal temperature gradient, with the consequence of slightly enhancing the contribution of low latitude moisture to Antarctic precipitation. It also changes the seasonality of the different contributions and thus their budget, particularly in coastal regions. Because the nature of LGM tropical SSTs is still under debate, Ne performed an additional LGM simulation in which the tropical SSTs are reduced relative to those of CLIMAP. The resulting decrease in the latitudinal gradient brings the relative contributions to Antarctic precipitation more in line with those of the present-day simulation.
id: 1942; PT: J; UT: WOS:000085432600002

The origin of n-alkanes in Santa Monica Basin surface sediment: A model based on compount-specific Delta14C and delta13C data - Pearson, A.; Eglinton, T. I. (Org. Geochem, 2000)
id: 364

Osmium isotopes demonstrate distal trnasport of contaminated sediments in Chesapeake Bay - Helz, G. R.; Adelson, J. M.; Miller, C. V.; Cornwell, J. C.; Hill, J. M.; Horan, M.; Walker, R. J. (Environmental Science Technology, 2000)
id: 1371

Ostracode Mg/Ca ratios suggest warmer-than-present early and middle Holocene in the western Arctic Ocean - Dwyer, G. S. (EOS, Transactions, American Geophysical Union, 2000)
id: 1475

OxCal analyses and varve-based sedimentation rates constrain the times of 14C-dated tsunamis in southern Oregon - Nelson, A. R.; Kelsey, H. M.; Hemphill-Haley, Eileen; Witter, R. C. (Abstract for Geological Society of America Penbrose Conference on Great Cascadia Earthquake Tricentennial Seaside, 2000)
id: 1405

Paleoceanographic changes in the Southern Ocean (Pacific sector) during the last 14 Ka.--Poster - Morigi, C.; Capotondi, L.; Ravaioli, M.; Giglio, F.; Turi, B.; Brilli, M.; Langone, L. (Third International SO-JGOFS Symposium, 2000)
id: 1422

Paleoclimate signals in a speleothem from Belize, Senior Thesis - Gaines, Sarah M. (Princeton University, 2000)

Palynlogical evidence for human occupation between 2550 and 1270 years BP recorded in two mountain wetlands (near Sagalassos, western Taurus range, SW Turkey) - Vermoere, M.; Waelkens, M.; E, Smets (International Symposium on High Mountain Lakes and Streams, 2000)
id: 1370

Particle mixing and sediment accumulation rates of Peconic Estuary sediments: A sediment accretion study in support of the Peconic Estuary Program (Report) - Cochran, J. K.; Hirschberg, D. J.; Amiel, D. (2000)
id: 1344

Postglacial and Late Holocene earthquakes on the Toe Jam strand of the Seattle fault, Bainbridge Island Washington - Nelson, A. R.; Johnson, S. Y.; Pezzopane, S. K.; Wells, R. E.; Kelsey, H. M.; Sherrod, B. L.; Koehler, R. D.; Bradley, L. A.; Bucknam, R. C.; LaPrade, W. T.; Cox, J. W.; Narwold, C. F. (Geological Society of America Abstracts with Programs, 2000)
id: 258

Postglacial climate and vegetation history, north-central Kola Peninsula, Russia: pollen and diatom records from Lake Yarnyshnoe-3 - Snyder, J. A.; MacDonald, G. M.; Forman, S. L.; Tarasov, G. A.; Mode, W. N. (Boreas, 2000)
A sediment core from Lake Yamyshnoe-3 (69 degrees 04'N; 36 degrees 04'E), an emerged coastal lake from the tundra of the north-central Kola Peninsula, has been analyzed for fossil pollen and diatoms. The pollen record shows the Younger Dryas event marked by increasing Artemisia coupled with decreases in Poaceae, Cyperaceae and Salix at c. 10 700 to 10 000 BP. This core provides the first well-defined palynological record of the Younger Dryas event on the Kola Peninsula. Stomates from Pinus were recovered from the core interval between 8000 and 6000 BP. The stomates, coupled with elevated values of pine pollen, indicate that Pinus sylvestris grew near the arctic coastline of the central Kola Peninsula in the middle Holocene. However, the small number of stomates suggests that pines were not plentiful. The diatom record from the core reflects basin isolation from the sea and indicates additional limnological changes during the climate transition between c. 5000 and 4000 BP. The broadly similar climate and vegetation history on the north-central Kola Peninsula and in Fennoscandia demonstrates the propagation of late glacial and Holocene climate events from the North Atlantic region into the Eurasian Arctic.
378dxTimes Cited:28 Cited References Count:82
Keywords: atlantic; finnish lapland; Holocene; late pleistocene; norway; sea; sediments; varanger-peninsula; western part; younger-dryas

Procesos y formas periglaciares en la montana mediterranea - Garcia-Ruiz, J. M. (Instituto de Estudios Turolenses, Teruel, 2000)
id: 371

Processes and rates of Holocene sedimentation in Santa Monica Bay, CA - Sommerfield, C. K.; Lee, H. J. (EOS, 2000)
id: 139

Quantitative estimates of time-averaging in articulate brachiopod accumulations from a Holocene tropical shelf (Southern Brazil) - Carroll, M.; Kowalewski, M.; Simoes, M. G.; Goodfriend, G. A. (Geological Society of America Abstracts with Programs, 2000)
id: 124

Quaternary Geology of Central Sheboygan County, Wisconsin, Thesis - Chapel, Dawn (University of Wisconsin, 2000)

Quaternary palaeohydrological evolution of a playa lake: Salada Mediana, central Ebro Basin, Spain - Valero-Garces, B. L.; Delgado-Huertas, A.; Navas, A.; Machin, J.; Gonzalez-Samperiz, P.; Kelts, K. (Sedimentology, 2000)
Sedimentary features, mineralogy, bulk geochemical composition, stable isotope analyses and pollen data from sediment cores were used to reconstruct the Late Quaternary depositional evolution of the Salada Mediana playa lake (central Ebro Basin, northeastern Spain). The 150-cm-long sediment core sequence is composed of gypsum- and dolomite-rich muds (Lower and Middle sections) and black, laminated, calcite-bearing sediments (Upper section). The Salada Mediana formed as a karstic depression in the Miocene gypsum substratum during the Late Pleistocene. The Lower section was deposited in a sulphate-carbonate saline lake that ended with a period of desiccation and basin floor deflation. Subsequent deposition (Middle section) took place in a playa-lake system. Two cycles of lower water table and expanded saline mud flats occurred. The Holocene sequence is missing, probably as a result of aeolian erosion. Sedimentation resumed only a few centuries ago, and saline pan environments dominated until modern times. The Salada Mediana facies succession was mainly governed by fluctuations in the hydrological balance, brine composition, and salinity; however, aeolian processes (detrital input and deflation) and recycling of previously precipitated salts also played a significant role.
383xwTimes Cited:31Cited References Count:76

The radiocarbon age of calcite dissolving at the sea floor: Estimates from pore water data - Martin, W. R.; McNichol, A. P.; McCorkle, D. C. (Geochimica Et Cosmochimica Acta, 2000)
We measured the radiocarbon content and stable isotopic composition of pore water and bottom water Sigma CO2, sedimentary organic carbon, and CaCO3 at two sites on the Ceara Rise, one underlying bottom water that is supersaturated with respect to calcite (Site B), the other underlying undersaturated bottom water (Site G). The results were combined with pore water O-2, Sigma CO2, and Ca2+ profiles (Martin and Sayles, 1996) to estimate the radiocarbon content of the CaCO3 that is dissolving in the sediment mixed layer. At Site G, the CaCO3 that is dissolving in the upper 2 cm of the sediments is clearly younger (richer in C-14) than the bulk sedimentary CaCO3, indicating that nonhomogeneous CaCO3 dissolution occurs there. The case for nonhomogeneous dissolution is much weaker at the site underlying supersaturated bottom water. The results indicate that nonhomogeneous dissolution occurs in sediments underlying undersaturated bottom water, that the dissolution is rapid relative to the rate of homogenization of the CaCO3 in the mixed layer by bioturbation, and that the dissolution rate of CaCO3 decreases as it ages in the sediment mixed layer. The results support the hypothesis, based on solid phase analyses, that the preferential dissolution of young (i.e., radiocarbon-rich) CaCO3 leads to a pattern of increasing radiocarbon age of mixed-layer CaCO3 as the degree of undersaturation of bottom water increases (Keir, 1984; Broecker et al., 1991). Copyright (C) 2000 Elsevier Science Ltd.
303ueTimes Cited:26Cited References Count:31

Radiocarbon calibration and abruptchanges in atmospheric 14Cconcentration during Marine Isotope Stage 3 - Hughen, K. A.; Southon, J.; Lehman, S. J.; Peterson, L. C.; Overpeck, J. T. (American Geophysical Union, 2000)
id: 327

The radiocarbon content of individual lignin-derived phenols: Technique and initial results - McNichol, A. P.; Ertel, J. R.; Eglinton, T. I. (Radiocarbon, 2000)
We present a method for the isolation of phenolic compounds derived from lignin for radiocarbon analysis. These phenols are generated by chemical oxidation of polymeric materials and derivatized for separation and recovery by preparative capillary gas chromatography (PCGC). This technique yields tens of micrograms of pure, stable compounds that can he converted to graphite and analyzed by accelerator mass spectrometry (AMS). Analysis of model flavor compounds and dated woods indicates that, in most cases, the radiocarbon (C-14) contents of the individual compounds, corrected for the contribution of the derivative, agree with that of the bulk material to within 20 parts per thousand.
365vkTimes Cited:19 Cited References Count:17
Keywords: AMS; isotope-ratio; NOSAMS; oxidation-products

Radiocarbon dated Pinus sylvertis L. wood from beyond treeline on the Kola Peninsula, Russia - MacDonald, G. M.; Gervalis, B.; Snyder, J. A.; Tarasov, G. A.; Borisova, O. A. (The Holocene, 2000)
Radiocarbon dates were obtained from 24 samples of Pinus sylvestris L. (Scots pine) wood recovered from sites beyond the modern conifer tree-line on the Kola Peninsula of Russia. Twenty-one of the samples came from the shallow waters and eroding peats at the edges of two small lakes at 68°439N, 35°109E, located north of the modern conifer tree-line. Three samples came from a small pond located above the modern elevational limits of Pinus sylvestris at 68°259N, 35°199E. The radiocarbon dates indicate that pine trees grew approximately 20 km north of the mapped modern limits of the species from 6680 BP to 3830 BP. Pine trees were also growing some 40 m above their modern elevational limits between 5890 BP and 3450 BP. Nineteen of the samples date from 6680 BP to 5070 BP, suggesting that the density of trees north of the modern tree-line was greatest between 7000 and 5000 BP. The timing of tree-line advance and greatest density on the Kola Peninsula are in agreement with the results of similar studies from northern Fennoscandia which indicate that maximum northern and elevational extension of tree-line occurred between 7000 BP and 4000 BP. The general agreement between tree-line reconstructions suggests that the climatic changes that promoted mid-Holocene tree-line extension along the North Atlantic margins in northern Fennoscandia propagated eastward to the Kola Peninsula. The late timing of initial pine expansion on the Kola and in adjacent northern Fennoscandia remains problematic and may relate to lower winter insolation, temperature regimes in the adjacent oceans or slow rates of migration.
id: 376

Radiocarbon dates in China's Holocene Yangtze delta: record of sediment storage and reworking, not timing of deposition - Stanley, D. J.; Chen, Z. (Journal Coastal Res., 2000)
id: 230

Radiocarbon dating of Marion-Dufresne cores MD99-2204, 2207, and 2209, Chesapeake Bay - Colman, S. M.; Bratton, J. F.; Baucom, P. C. (Initial Report on IMAGES V Cruise of the Marion-Dufresne to the Chesapeake Bay June 20-22, 1999, 2000)
id: 1414

Radiocarbon dating the artifically contained surfaces of the Rhone deltaic plain, southern France - Stanley, D. J. (Journal Coastal Res., 2000)
id: 1377

The radiocarbon gradient at the Antarctic Polar Front - Schneider, R. J.; McNichol, A. P.; von Reden, K. F.; Elder, K. L.; Gagnon, A. R.; Key, R. M.; Quay, P. D.; Schlosser, P. M. (AGU Ocean Sciences Meeting, 2000)
id: 317

Radiocarbon-Based Estimates of the Groundwater Contribution to Estuarine Freshwater Budgets: An Example from Pages Creek, North Carolina - McCorkle, D. C.; Gramling, C. M.; Mulligan, A. E.; Woods, T. L.; Lott, D. E. (EOS, 2000)
id: 1315

Rapid ice margin fluctuations during the Bolling/Allerod and Younger Dryas intervals in the Peruvian Andes - Rodbell, D. T.; Seltzer, G. O. (Quaternary Research, 2000)
id: 392

Rapid ice margin fluctuations during the Younger Dryas in the tropical Andes - Rodbell, D. T.; Seltzer, G. O. (Quaternary Research, 2000)
Radiocarbon dated lacustrine sequences in Peru show that the chronology of glaciation during the late glacial in the tropical Andes was significantly out-of-phase with the record of climate change in the North Atlantic region. Fluvial incision of glacial-lake deposits in the Cordillera Blanca, central Peru, has exposed a glacial outwash gravel; radiocarbon dates from peat stratigraphically bounding the gravel imply that a glacier advance culminated between similar to 11,280 and 10,990 C-14 yr B.P.; rapid ice recession followed. Similarly, in southern Peru, ice readvanced between similar to 11,500 and 10,900 C-14 yr B.P. as shown by a basal radiocarbon date of similar to 10,870 C-14 yr B.P. from a lake within 1 ion of the Quelccaya Ice Cap. By 10,900 C-14 yr B.P, the ice front had retreated to nearly within its modern limits. Thus, glaciers in central and southern Peru advanced and retreated in near lockstep with one another. The Younger Dryas in the Peruvian Andes was apparently marked by retreating ice fronts in spite of the cool conditions that are inferred from the partial derivative O-18 record of Sajama ice. This retreat was apparently driven by reduced precipitation, which is consistent with interpretations of other paleoclimatic indicators from the region and which may have been a nonlinear response to steadily decreasing summer insolation. (C) 2000 University of Washington.
388erTimes Cited:61Cited References Count:66

Responces of a saline lake ecosystems in semi-arid regions to irrigation and climate variability. The history of Salada Chiprana, Central Ebro Basin, Spain - Valero-Garces, B. L.; Navas, A.; Machin, J.; Stevenson, T.; Davis, B. (Ambio, 2000)
id: 385

Shared Technologies: Later Stone Age Forager-Farmer Interaction and Metallurgy in the Ituri Rainforest, Democratic Republic of Congo - Mercader, J.; Rovira, S.; Gomez, P. (Azania, 2000)
id: 396

The significance of large sediment supply, active tectonism, and eustasy on margin sequence development: Late Quaternary stratigraphy and evolution of the Ganges-Brahmaputra delta - Goodbred, S. L.; Kuehl, S. A. (Sedimentary Geology, 2000)
Borehole data from the Ganges-Brahmaputra delta system unveil an intriguing Late Quaternary history controlled by immense sediment discharge, tectonics, and eustasy. Sea level first intersected a major portion of the lowstand surface similar to 10,000-11,000 cal yr BP, marking the onset of sediment trapping and delta growth. Despite rapid sea-level rise (>1 cm/yr), sediment load was sufficient to maintain relative shoreline stability during this time. By similar to 7000 cal yr BP, accommodation was quickly infilled with slowed sea-level rise, leading to upstream channel migration and widespread dispersal of sands. This forced coastal progradation along the western delta front where the Ganges was situated, and much of the river's fine-grained discharge bypassed the subaerial delta and formed a prograding deltaic clinoform on the shelf. Concurrently, Brahmaputra sediments were sequestered to an inland tectonic basin, thus starving the adjacent shoreline and leading to transgression along the eastern delta. By similar to 5000 cal yr BP, the two rivers had migated or changed course to discharge along the eastern delta shoreline which began to prograde into what is now the modern river-mouth estuary. Present delta configuration appears to have developed by similar to 3000 cal yr BP. Evolution of the tectonically active Ganges-Brahmaputra (G-B) system reveals important similarities and differences with other deltas. Overall facies succession follows that of basic models, progressing from an alluvial valley to coastal marine delta front to a prograding subaerial delta plain. However, the timing, thickness, and controls of these deposits differ. Immense sediment discharge from the Ganges and Brahmaputra rivers allowed initial delta growth 2000-3000 yr earlier than the global average, despite debouching onto a canyon-incised, high-energy margin. Subsequently, a thick (similar to 50 m) transgressive systems tract was formed during the early Holocene phase of delta aggradation, contrasting with extensive shoreline retreat documented along most margins. Highstand progradation of coastal and shelf sequences ensued by the middle Holocene, but subsiding inland basins also favored accumulation of a thick (to 40 m) highstand sequence in the: lower floodplains. Unlike many other delta systems, subsidence in the subaerial G-B delta is not dominated by compaction, but rather by plate-driven tectonic processes that generate rates up to 4 mm/year. Overall, the huge sediment load, tectonic subsidence, major seismic events, and a nearshore canyon system have led to widespread sediment dispersal and sequence formation across the subaerial delta, shelf, and deep-sea Bengal Fan throughout the Late Quaternary. (C) 2000 Elsevier Science B.V. All rights reserved.
337jeTimes Cited:203Cited References Count:63

Sonota Complex Sites in Eastern North Dakota - Toom, Dennis L.; Jackson, Michael A. (2000 Plains Conference, 58th Annual Meeting of the Plains Anthropological Society, 2000)
id: 205

Sources, distribution and transformations of PAH in the Gulf of Triests (northern Adriatic), Thesis - Notar, M. (University of Ljubljana, Slovenia, 2000)

Stable- and radio-carbon isotopic composition of porewater DOC in an organic-rich marine sediment - Alperin, M. J.; Hee, C. A.; Albert, D. A.; Martens, C. S. (EOS, 2000)
id: 1438

Stable carbon isotope record of middle to late Holocene climate changes from land snail shells at HInds Cave, Texas (Book Section) - Goodfriend, G. A.; Ellis, G. L. (Holocene Environmental Change on the Great Plains of North America, 2000)
id: 175

Stable chlorine isotopic compositions of aroclors and aroclor-contaminated sediments - Reddy, C. M.; Heraty, L. J.; Holt, B. D.; Sturchio, N. C.; Eglinton, T. I.; Drenzek, N. J.; Xu, L.; Lake, J. L.; Maruya, K. A. (Environmental Science & Technology, 2000)
An exploratory investigation was conducted to evaluate if stable chlorine isotopic ratios of polychlorinated biphenyls (PCBs) could be useful in studying the processes that determine their transport and fate in the environment First, we determined the variability of delta(37)Cl in the source materials for PCBs. Second, we determined if the delta(37)Cl values of contaminated environmental samples fell outside the range in source variability. The isotopic variability among the source materials (Aroclors) was rather small; delta(37)- Cl values ranged from -3.37 to -2.11% (mean and standard deviation, -2.78 +/- 0.39%, n = 12). There was no correlation between the delta(37)Cl values and percentages of chlorine in the mixtures. We also found very similar values in several Clophen mixtures and one Phenoclor. The delta(37)Cl values in the total PCBs isolated from Aroclor-contaminated sediments from the Hudson River, New Bedford Harbor, and Turtle River Estuary ranged from -4.54 to -2.25% (n = 19). While most of the delta(37)Cl values were within 2 standard deviations of the mean Aroclor value (our assumed estimate for overall source variability), two of the PCB contaminated sediment samples from New Bedford Harbor did appear to be isotopically distinct. The PCBs in these sediments had lower amounts of less chlorinated congeners (when compared to the source material) and were likely isotopically affected by alteration processes that preferentially removed these congeners. Compound specific measurements of two congeners in Aroclor 1268 suggest that there are no large congener-specific differences in the stable chlorine isotope ratios in Aroclors. This study shows that the delta(37)Cl Values of PCBs may be a potentially useful diagnostic tool in studying the transport and fate of PCBs and indicates that additional research is warranted.
330rcTimes Cited:39Cited References Count:16

Status of the WOCE tracer synthesis effort, Invited presentation - Key, R. M. (WOCE Data Products Committee Meeting 13, 2000)
id: 1457

Systematics, distributional and palaeoenvironmental aspects of Littoridina australis(D'Orbigny, 1835) (Mesogastropoda) in the Marine Quaternary of Argentina (South America) - Aguirre, M. L.; Farinati, E. A. (Geobios, 2000)
LittoridinaSouleyet, 1852 (Mesogastropoda, Hydrobiidae) is the best represented genus among themolluscan taxa recorded in the marine late Quaternary from Argentina. It is distinguished by its ubiquity and high abundance along the coastal area from Río de La Plata down to southern Buenos Aires Province, both in beach ridge and coastal lagoon and estuarine facies and tidal flats. It is practically absent in Holocene littoral depositis from Patagonia and a very scarce component of the Pleistocene deposits from the whole Argentine coast. At present it is not recorded along the Argentine Sea or occurs only rarely in scarce quantities and restricted distribution, always associated to marginal marine environments. Most specimens collected from the marine Quaternary are assignable to Littoridina australis (D'Orbigny, 1835), a dominant species (50-> 80%) in the Holocene from La Plata down to Bahía San Blas (Buenos Aires Province). Due to the similarity of the original illustrations and of the type material of L. australis crassa, L. isabelleana, L. australis nana and L. conexa with L. australis, these taxa are considered synonyms. L. australis is proposed as a polytipic species with three main morphs (ecomorphs) which represent adaptations to different environmental conditions, mostly of salinty: ‘A’ (wide and short, very scarce, similar to L. charruana and L. conexa), ‘B’ (identical to the lectotypo de L. australis, similar to L. australis crassa; predominant) and ‘C’ (strongly elongated, similar to L. isabelleana and L. australis nana, with variations according to size; scarce). At present ‘B’ is dominant in mixohaline conditions, ‘C’ in polyhaline environments and ‘A’ in oligo-mixohaline sites. The morphological variations observed within the abundant material (fossil and modern), geographically and through time, would be a consequence of the influence over the littoral benthonic communities of environmental and climatic changes occurred during the late Quaternary: A trend was observed towards a major abundance of the morph ‘C’ (polyhaline) in the northern sector of the distribution, Samborombón Bay, and before ca. 5 ka A.P., whilst the morph ‘B’ (mixohaline) predominates in the central and southern sectors of the distribution, Mar Chiquita and Bahía Blanca, and is dominant after ca. 4.5 ka. This in turn would be a response to a progressive decrease of salinity along the littoral zone following the Climatic Optimum (Holocene ‘Hypsithermal’, >7-5 ka A.P.), in coincidence with the sea-level (and temperature) decreasing trend until the present.
id: 1372
Keywords: Hydrobiidae; Late Quaternary; Littoridina australis; Palaeoecology; Southwestern Atlantic; Systematics

Ten years after - the WOCE AMS radiocarbon program - McNichol, A. P.; Schneider, R. J.; von Reden, K. F.; Gagnon, A. R.; Elder, K. L.; Key, R. M.; Quay, P. D. (Accelerator Mass Spectrometer Conference, 2000)
id: 316

Ten years after - The WOCE AMS radiocarbon program - McNichol, A. P.; Schneider, R. J.; von Reden, K. F.; Gagnon, A. R.; Elder, K. L.; Key, R. M.; Quay, P. D. (Nuclear Instruments & Methods in Physics Research Section B-Beam Interactions with Materials and Atoms, 2000)
The National Ocean Sciences Accelerator Mass Spectrometry (NOSAMS) Facility is measuring all of the samples collected as part of the US WOCE Program - over 13,000 samples. We designed our extraction lines so that we also measure precise, oceanographically useful delta C-13-Sigma CO2 values. We have completed the analysis of samples from the Pacific and Southern Oceans and are processing those from the Indian Ocean now. At present, this constitutes the world's largest AMS data set. Reviews of the Pacific radiocarbon data are available and demonstrate the increased penetration of the "bomb signal" into the water column since the 1970s. Stable isotope data are being combined with those collected as part of NOAA's Ocean-Atmosphere Carbon Exchange Study to study the ocean's role in the anthropogenic CO2 cycle. The relationship of delta C-13 to other chemical tracers, e.g., PO4, O-2 and chlorofluorocarbons, will further our understanding of basic oceanographic processes. We present preliminary results from these studies as well as investigate the relationship of C-14 to C-13 in the ocean. (C) 2000 Elsevier Science B.V. All rights reserved.
372jrTimes Cited:14Cited References Count:12

Tests of positive ion beams from a microwave ion source for AMS - Schneider, R. J.; von Reden, K. F.; Hayes, J. M.; Wills, J. S. C.; Kern, W. G. E.; Kim, S. W. (Nuclear Instruments & Methods in Physics Research Section B-Beam Interactions with Materials and Atoms, 2000)
A test facility has been constructed to evaluate high-current positive ion beams from small gaseous samples for AMS applications. The major components include a compact permanent magnet microwave ion source built at the AECL Chalk River Laboratory and now on loan from the University of Toronto, and a double-focusing spectrometer magnet on loan from Argonne National Laboratory. Samples are introduced by means of a silica capillary injection system. Loop injection into a carrier gas provides a stable feed for the microwave driven plasma. The magnetic analysis system is utilized to isolate carbon ions derived from CO? samples from other products of the plasma discharge, including argon ions of the carrier gas. With a smaller discharge chamber, we hope to exceed a conversion efficiency of 14% for carbon ions produced per atom, which we reported at AMS-7. The next step will be to construct an efficient charge-exchange cell, to produce negative ions for injection into the WHOI recombinator injector. (C) 2000 Elsevier Science B.V. All rights reserved.
372jrTimes Cited:16Cited References Count:4

The tie-in of a varve-count chronology and radiocarbon dates: a method for addressing 14C-reservoir age - Schimmelmann, A.; Lange, Carina B. (Climate Conference, LDGO, 2000)
id: 199

Trophic Transfer of Anthropogenic Contaminants to Salt-Marsh Bacteria: A Molecular Radiocarbon Approach (Poster) - Pease, Tamara; Wakeham, Stuart (Skidaway Institute of Oceanography, Savannah, GA 31411, 2000)
id: 222; Presented at the Gordon Research Conference in Organic Geochemistry

Turbidite Megabeds in an Oceanic Rift Valley Recording Jokulhlaups of Late Pleistocene Glacial Lakes of the Western United States - Zuffa, G. G.; Normark, W. R.; Serra, F.; Brunner, C. A. (Journal of Geology, 2000)
Escanaba Trough is the southernmost segment of the Gorda Ridge and is filled by sandy turbidites locally exceeding 500 m in thickness. New results from Ocean Drilling Program (ODP) Sites 1037 and 1038 that include accelerator mass spectrometry (AMS) 14C dates and revised petrographic evaluation of the sediment provenance, combined with high-resolution seismic-reflection profiles, provide a lithostratigraphic framework for the turbidite deposits. Three fining-upward units of sandy turbidites from the upper 365 m at ODP Site 1037 can be correlated with sediment recovered at ODP Site 1038 and Deep Sea Drilling Program (DSDP) Site 35. Six AMS 14C ages in the upper 317 m of the sequence at Site 1037 indicate that average deposition rates exceeded 10 m/k.yr. between 32 and 11 ka, with nearly instantaneous deposition of one approximately 60-m interval of sand. Petrography of the sand beds is consistent with a Columbia River source for the entire sedimentary sequence in Escanaba Trough. High-resolution acoustic stratigraphy shows that the turbidites in the upper 60 m at Site 1037 provide a characteristic sequence of key reflectors that occurs across the floor of the entire Escanaba Trough. Recent mapping of turbidite systems in the northeast Pacific Ocean suggests that the turbidity currents reached the Escanaba Trough along an 1100-km-long pathway from the Columbia River to the west flank of the Gorda Ridge. The age of the upper fining-upward unit of sandy turbidites appears to correspond to the latest Wisconsinan outburst of glacial Lake Missoula. Many of the outbursts, or jokulhlaups, from the glacial lakes probably continued flowing as hyperpycnally generated turbidity currents on entering the sea at the mouth of the Columbia River.
id: 162; J Geol. 2000 May;108(3):253-274.

Un registro de 8,000 anos del paleoclima del noroeste de Yucatan, Mexico - Brenner, M.; Leyden, B. W.; Curtis, J. H.; Medina-Gonzalez, R. M.; Dahlin, B. H. (Revista de la Universidad Autonoma de Yucatan, 2000)
id: 264
Keywords: Ciencias de la atmósfera; Geología; México; Paleoclima; Península de Yucatán; Yucatán

Use of bomb produced C-14 to validate otolith section age estimates of red snapper Lutjanus compechanus from the northern Gulf of Mexico, Artwork - Baker, M. Scott; Wilson, Charles A. (53rd Annual Gulf and Carribbean Fisheries Institute Meeting, 2000)

Use of Natural C-14 Measurements to Examine Benthic Food Webs - DeMaster, D. J.; Fornes, W. L.; Smith, C. R.; Plaia, G.; Blair, N. E.; Levin, L. A. (National AGU/ASLO Meeting, 2000)
id: 1367

Ventilation of the deep Pacific Ocean, invited talk - Key, R. M. (AGU Ocean Sciences Meeting, 2000)
id: 315

Was it melt-water outflor or ice-sheet discharge? A high-resolution study of ice-sheet discharge from the high-latitude sector of the LIS during the LGM - Rashid, H.; Hesse, R.; Piper, D. J. W. (EOS, 2000)
id: 138

What can paired measurements of foraminifera d13C and sedimentary 231 Pa/230Th tell us about the link between thermohaline circulation and rapid climate oscillations? - McManus, J. F.; Francois, R.; Marchal, O. (EOS, 2000)
id: 169

Years of Sediment, Vegetation, and Water-Level Changes at the Makepeace Cedar Swamp, Southern Massachusetts - Newby, P. E.; Killoran, P.; Waldorf, M. R.; Shuman, B. N.; Webb, R. S.; Webb, T., III (Quaternary Research, 2000)
id: 231

A 0.5-million-year record of millennial-scale climate variability in the north atlantic - McManus, J. F.; Oppo, D. W.; Cullen, J. L. (Science, 1999)
Long, continuous, marine sediment records from the subpolar North Atlantic document the glacial modulation of regional climate instability throughout the past 0.5 million years. Whenever ice sheet size surpasses a critical threshold indicated by the benthic oxygen isotope (delta18O) value of 3.5 per mil during each of the past five glaciation cycles, indicators of iceberg discharge and sea-surface temperature display dramatically larger amplitudes of millennial-scale variability than when ice sheets are small. Sea-surface temperature oscillations of 1 degrees to 2 degreesC increase in size to approximately 4 degrees to 6 degreesC, and catastrophic iceberg discharges begin alternating repeatedly with brief quiescent intervals. The glacial growth associated with this amplification threshold represents a relatively small departure from the modern ice sheet configuration and sea level. Instability characterizes nearly all observed climate states, with the exception of a limited range of baseline conditions that includes the current Holocene interglacial.
McManusOppo Cullen eng 1999/02/12 03:03 Science. 1999 Feb 12;283(5404):971-5.

2-Methylhopanoids as biomarkers for cyanobacterial oxygenic photosynthesis - Summons, R. E.; Jahnke, L. L.; Hope, J. M.; Logan, G. A. (Nature, 1999)
Oxygenic photosynthesis is widely accepted as the most important bioenergetic process happening in Earth's surface environment(1). It is thought to have evolved within the cyanobacterial lineage, but it has been difficult to determine when it began. Evidence based on the occurrence and appearance of stromatolites(2) and microfossils' indicates that phototrophy occurred as long ago as 3,465 Myr although no definite physiological inferences can be he made from these objects. Carbon isotopes and other geological phenomena(4,5) provide clues but are also equivocal, Biomarkers are potentially useful because the three domains of extant life-Bacteria, Archaea and Eukarya-have signature membrane lipids with recalcitrant carbon skeletons. These lipids turn into hydrocarbons in sediments and can be found wherever the record is sufficiently well preserved. Here we show that 2-methylbacteriohopanepolyols occur in a high proportion of cultured cyanobacteria and cyanobacterial mats, Their 2-methylhopane hydrocarbon derivatives are abundant in organic-rich sediments as old as 2,500 Myr. These biomarkers may help constrain the age of the oldest cyanobacteria and the advent of oxygenic photosynthesis. They could also be used to quantify the ecological importance of cyanobacteria through geological time.
223rtTimes Cited:510Cited References Count:28

87Sr/86Sr, delta 18O evolution of Phanerozoic seawater - Veizer, Jan; Davin, Ala; Azmy, Karem; Bruckschen, Peter; Buhl, Dieter; Bruhn, Frank; Carden, Giles A. F.; Diener, Andreas; Ebneth, Stefan; Godderis, Yves; Jasper, Torsten; Korte, Christoph; et al. (Chemical Geology, 1999)
id: 1603

The abundance of 13C in marine organic matter and isotopic fractionation in the global biogeochemical cycle of carbon during the past 800 Ma - Hayes, John M.; Strauss, Harald; Kaufman, Alan J. (Chemical Geology, 1999)
id: 1547

The Antarctic Radiocarbon Storage Ring - Schneider, Robert J.; McNichol, Ann P.; von Reden, Karl F.; Elder, Kathryn L.; Gagnon, Alan R.; Key, Robert M.; Quay, Paul D. (8th International Conference on Accelerator Mass Spectrometry, 1999)
id: 1791

Application of a compact microwave ion source to radiocarbon analysis - Schneider, R. J.; von Reden, K. F.; Hayes, J. M.; Wills, J. S. C. (The eighth international conference on heavy-ion accelerator technology, 1999)
The compact, high current, 2.45 GHz microwave-driven plasma ion source which was built for the Chalk River TASCC facility is presently being adapted for testing as a gas ion source for accelerator mass spectrometry, at the Woods Hole Oceanographic Institution accelerator mass spectrometer. The special requirements for producing carbon-ion beams from micromole quantities of carbon dioxide produced from environmental samples will be discussed. These samples will be introduced into the ion source by means of argon carrier gas and a silicon capillary injection system. Following the extraction of positive ions from the source, negative ion formation in a charge exchange vapor will effectively remove the argon from the carbon beam. Simultaneous injection of the three carbon isotopes into the accelerator is planned.
id: 1977
Keywords: carbon; ion sources; mass spectroscopy; spectrochemical analysis; tandem accelerators

Application of Compact Microwave Ion Source to Radiocarbon Analysis - Schneider, R. J.; von Reden, K. F.; Hayes, J. M.; Wills, J. S. C. (8th International Conference on Heavy Ion Accelerator Technology, 1999)
id: 1824

An Archaeological Investigation of Late Archaic Cerros de Trincheras Sites in Chihuahua, Mexico - Hard, R.; Roney, J. (University of Texas, Center for Archaeological Research, 1999)
id: 1389

Assessing the importance of subtropical waters in ventilating the Equatorial Pacific thermocline: A combined transient-tracer approach - Peacock, S.; Jenkins, W.; Key, R.; Broecker, W. (International WOCE Newsletter, 1999)
id: 1465

Assessment of a hard water dating problem in Wonder Lake, Denali National Park, Alaska - Child, J. C.; Werner, A. (Geographie Physique et Quatenaire, 1999)
id: 1383

Biogenic silica and organic carbon in sediments from the Pacific sector of the Southern Ocean.--Abstract - Giglio, F.; Frignani, M.; Langone, L.; Morigi, C.; Pianosi, G.; Ravaioli, M. (8th International Symposium on Antarctic Earch Sciences, 1999)
id: 286

Biogenic silica records from the BDP-93 drill site and adjacent areas of the Selenga Delta, Lake Baikal, Siberia - Colman, S. M.; Peck, J. A.; Hatton, J.; Karabanov, E. B.; King, J. W. (Journal of Paleolimnology, 1999)
id: 186

Carbon isotopes as tracers of groundwater discharge into the coastal ocean: A preliminary study of saltmarsh groundwater from North Inlet, SC - Gramling, C. M.; McCorkle, D. C. (EOS, 1999)
id: 1314

Carbon sequestration and vegetation succession in a coastal wetland in northwest Florida (abstract) - Choi, Y.; Wang, Y.; Hsieh, Y.; Robinson, L. (Spring meeting of American Geophysical Union, 1999)
id: 164

Climate and fisheries on the south east Australian continental shelf and slope (final report) - Koslow, J. A.; Thresher, R. (Fisheries Research and Development Corporation, 1999)
id: 109

Climate and lake-level history of the northern Altiplano Bolivia, as recorded in Holocene sediments of the Rio Desaguadero - Baucom, P. C.; Rigsby, C. A. (Journal of Sedimentary Research, 1999)
Strata exposed in terraces and modern cutbanks along the Rio Desaguadero contain a variety of lithofacies that were deposited in four distinct facies associations. These facies associations document a history of aggradation and downcutting that is Linked to Holocene climate change on the Altiplano.Braided stream, meandering stream, deltaic and shoreline, and la custrine sediments preserved in multi-level terraces in the northern Rio Desaguadero valley record two high-water intervals: one between 4500 and 3900 yr BP and another between 2000 and 2200 yr BP. These wet periods were interrupted by three periods of fluvial downcutting, centered at approximately 4000 yr BP, 3600 Sr BP, and after 2000 yr BP. Braided-river sediments preserved in a single terrace level in the southern Rio Desaguadero valley record a history of nearly continuous fluvial sedimentation from at least 7000 yr BP until approximately 3200 yr BP that was followed by a single episode (post-3210 ST BP) of down cutting and lateral migration.The deposition and subsequent fluvial downcutting of the northern strata was controlled by changes in effective moisture that can he correlated to Holocene water level fluctuations of Lake Titicaca, The deposition and dissection of braided-stream sediments to the south are more likely controlled by a combination of base-level change and sediment input from the Rio Mauri.
A197atTimes Cited:30Cited References Count:61

Climate change in the Lake Valencia Basin, Venezuela, approximately 12,600 yr BP to present - Curtis, J. H.; Brenner, M.; Hodell, D. A. (The Holocene, 1999)
id: 197

Combined use of bomb radiocarbon and tritium to place constraints on the relative importance of northern- and southern- derived waters in ventilating the equatorial Pacific thermocline - Peacock, S.; Key, R.; Jenkins, W.; Broecker, W. (WOCE-AIMS Tracer Workshop, 1999)
id: 314

A continuous Holocene glacial record inferred from proglacial lake sediments in Banff National Park, Albert, Canada - Leonard, Eric M.; Reasoner, Mel A. (Quaternary Research, 1999)
Sediment cores from three proglacial lakes in northern Banff National Park, Alberta, preserve a record of Holocene glacial activity upvalley which is more continuous and better dated than available surficial records. Dating of the cores is based on tephrochronology and 16 AMS14C ages of terrestrial macrofossils. All cores contain a threefold sequence of lacustrine sediments overlying a late Pleistocene diamicton. Basal lacustrine sediments >10,10014C yr old contain little organic matter. Sediment composition indicates a large glacigenic contribution. A sharp increase in organic content marks the beginning of the Altithermal interval at all three lakes. This transition occurred abruptly at about 10,10014C yr B.P. at Crowfoot Lake and possibly more gradually at the other lakes. Altithermal sediments contain relatively little glacigenic material, and during most of the Altithermal, glaciers may have been absent above Crowfoot and Bow Lakes. Glaciers draining into Hector Lake appear to have persisted through the Altithermal. A subsequent decrease in organic content in each lake, reflecting increased clastic sedimentation, marks the end of the Altithermal and the onset of Neoglacial ice advances. The transition took place between about 5800 and 400014C yr B.P. and may be time-transgressive, beginning earlier in Hector Lake than in Crowfoot Lake. Changing Neoglacial clastic sedimentation rates through the Neoglacial interval indicate two main periods of increased glacier extent, between ca. 3000 and 1800 varve yr ago (ca. 2900–190014C yr B.P.) and during the last several hundred years. During the intervening period glaciers were less extensive, but much more extensive than during the recessions of the Altithermal interval.
id: 48; illus. incl. 4 tables, sketch maps, 42 refs.
Keywords: Canadian Rocky Mountains; glacial history; glaciolacustrine sedimentation; Holocene; Altithermal

Cool surface waters of the subtropical North Pacific Ocean during the last glacial - Lee, K. E.; Slowey, N. C. (Nature, 1999)
One of the most controversial results of the CLIMAP(1,2) project's reconstruction of past sea surface temperature (SST) is that large areas of the subtropical Pacific Ocean were warmer during the last glacial period than they are today. This finding has important implications because SST patterns at low to subtropical latitudes strongly influence climate, and SST changes are closely linked with climate fluctuations(3-5). Until now, a lack of well-preserved, high-resolution marine sediment cores from the region has hindered efforts to confirm these unexpectedly high ice-age SST estimates. Here we use both the oxygen-isotope compositions and species assemblages of planktonic foraminifera in a shallow-water core with high deposition rates near Hawaii to estimate glacial SST of the subtropical North Pacific Ocean, Contrary to the CLIMAP results(2), our data indicate that the annual average SST in this region was similar to 2 degrees C cooler during the last glaciation than it is today, These results help to reconcile the marine SST record with inferences drawn from snowline depressions on Hawaii during the last glacial(3,6), and should ultimately yield improved estimates of global climate sensitivity by providing important new constraints on climate model simulations of ice-age cycles.
166knTimes Cited:31Cited References Count:29

Coupled inner shelf--shoreline sediment responses to small-scale Holocene sea-level fluctuations; North Carolina coastal zone - Riggs, S. R. (The non-steady state of the inner shelf and shoreline: coastal change on the time scale of decades to millennia in the late Quaternary, 1999)
id: 1393

Deep-sea sedimentary record of the late Wisconsin cataclysmic floods from the Columbia River - Brunner, C. A.; Normark, W. R.; Zuffa, G. G.; Serra, F. (Geology, 1999)
New results from Ocean Drilling Program Site 1037 and U.S. Geological Survey high-resolution seismic-reflection profiles confirm the great thickness, fast deposition rate, distant source, and convolute path of turbidites that fill the Escanaba Trough, the rift valley of the southernmost segment of the Gorda Ridge. Accelerator mass spectrometry C-14 measurements provide the first direct dating of the Escanaba Trough turbidites, demonstrating an average deposition rate faster than 10 m/k.y. between 32 and 11 ka and as fast as 15 m/k.y. during the oxygen isotope stage 2 lowstand, In the upper 60 m of sediment, the petrology of turbidite sand beds, which are as much as 12 m thick, show that the dominant source for the turbidites is from the Columbia River, which is more than 800 km to the north, rather than from the much closer rivers of northern California. New high-resolution seismic-reflection profiles show that, except for areas of very recent volcanism, the entire Escanaba Trough below 3200 m water depth is floored by the turbidite sequence that was cored in the upper 60 m at Site 1037B, The ages of the upper 120 m of turbidites correspond with the ages of channeled scabland deposits associated with latest Quaternary jokulhlaups from glacial Lake Missoula, The age and source characteristics suggest that these megaturbidite beds in Escanaba Trough are most likely deposits formed by hyperpycnally generated turbidity currents as the largest of the Lake Missoula floods entered the sea.
193qfTimes Cited:40Cited References Count:19

Deglaciation of the northwestern White Mountains, New Hampshire - Thompson, W. B.; Fowler, B. K.; Dorion, C. C. (Geographie Physique Et Quaternaire, 1999)
The mode of deglaciation in the northwestern White Mountains of New Hampshire has been controversial since the mid 1800's. Early workers believed that active ice deposited the Bethlehem Moraine complex in the Ammonoosuc River basin during recession of the last ice sheet. In the 1930's this deglaciation model was replaced by the concept of widespread simultaneous stagnation and downwastage of Late Wisconsinan ice. The present authors reexamined the Bethlehem Moraine complex and support the original interpretation of a series of moraines deposited by active ice. We found other moraine clusters of similar age to the northeast in the Johns River and lsrael River basins. lce-marginal deposits that probably correlate with the Bethlehem Moraine also occur west of Littleton. The Bethlehem Moraine complex and equivalent deposits in adjacent areas were formed by readvance and oscillatory retreat of the Connecticut Valley lobe of the Laurentide Ice Sheet. This event is called the Littleton-Bethlehem Readvance. Throughout the study area, sequences of glaciolacustrine deposits and meltwater drainage channels indicate progressive northward recession of the glacier margin. Radiocarbon dates from nearby New England and Quebec suggest that the ice sheet withdrew from this part of the White Mountains between about 12,500 and 12,000 (14)C yr BP. We attribute the Littleton-Bethlehem Readvance to a brief climatic cooling during Older Dyas time, close to 12,000 BP.
218kbTimes Cited:18 Cited References Count:56
Keywords: canada; chronology; climate; last termination; new-england; record; tills

Deltas, radiocarbon dating, and measurements of sediment storage and subsidence - Stanley, D. J.; Hait, A. K. (Geology, 1999)
id: 1376

Diagenetic Zonation and Authigenic Carbonate Formation within Methane- and Gas Hydrate-Bearing Sedimentary Sections, Offshore, Southeastern North America, Thesis - Rodriques, N. M. (University of North Carolina, 1999)

The distribution and carbon isotopic composition of dissolved organic matter in Florida Everglades (abstract) - Wang, Y.; Hsieh, Y. P.; Landing, W. M.; Salters, V.; Cooper, W.; Proctor, L. (The Sixth Symposium on Biogeochemistry of Wetlands, 1999)
id: 165

Environmental changes in the last centure in Little Trout Lake and Inkspot Bay, Lac du Flambeau Tribal Lands, Wisconsin. Preliminary Results Report - Winkler, M. G.; Sanford, P. R. (Water Resources Division, Lac du Flambeau Tribe, 1999)
id: 1320

Evidence for Late Pleistocene-Holocene Intermediate-Water variability in the North Atlantic - McManus, J. F.; Oppo, D. W.; Curry, W.; Marchitto, T.; Cullen, J. L. (EOS, 1999)
id: 172

Extreme 13C carb enrichment in ca. 2.0 Ga magnesite-stromatolite--dolomite--"red beds" association in a global context: a case for the world-wide signal enhanced by a local environment - Melezhik, Victor A.; Fallick, Anthony E.; Medvedev, Pavel V.; Makarikhin, Vladimir V. (Earth-Science Reviews, 1999)
id: 1567

Fault slip rates in the modern new madrid seismic zone - Mueller, K.; Champion, J.; Guccione, M.; Kelson, K. (Science, 1999)
Structural and geomorphic analysis of late Holocene sediments in the Lake County region of the New Madrid seismic zone indicates that they are deformed by fault-related folding above the blind Reelfoot thrust fault. The widths of narrow kink bands exposed in trenches were used to model the Reelfoot scarp as a forelimb on a fault-bend fold; this, coupled with the age of folded sediment, yields a slip rate on the blind thrust of 6.1 +/- 0.7 mm/year for the past 2300 +/- 100 years. An alternative method used structural relief across the scarp and the estimated dip of the underlying blind thrust to calculate a slip rate of 4.8 +/- 0.2 mm/year. Geometric relations suggest that the right lateral slip rate on the New Madrid seismic zone is 1.8 to 2.0 mm/year.
MuellerChampion Guccione Kelson eng 1999/11/05 Science. 1999 Nov 5;286(5442):1135-8.

Fluttuazioni tardo quaternarie dei flussi sedimentari di carbonio organico e silice biogena nel settore pacifico dell'Oceano Meridionale--Thesis - Pianosi, G. (Universita di Bologna, 1999)

Fractionation of hydrogen isotopes in lipid biosynthesis - Sessions, A. L.; Burgoyne, T. W.; Schimmelmann, A.; Hayes, J. M. (Organic Geochemistry, 1999)
Isotopic compositions of carbon-bound hydrogen in individual compounds from eight different organisms were measured using isotope-ratio-monitoring gas chromatography-mass spectrometry. This technique is capable of measuring D/H ratios at natural abundance in individual lipids yielding as little as 20 nmol of H-2, and is applicable to a wide range of compounds including hydrocarbons, sterols, and fatty acids. The hydrogen isotopic compositions of lipids are controlled by three factors: isotopic compositions of biosynthetic precursors, fractionation and exchange accompanying biosynthesis, and hydrogenation during biosynthesis. delta D values of lipids from the eight organisms examined here suggest that all three processes are important for controlling natural variations in isotopic abundance. n-Alkyl lipids are depleted in D relative to growth water by 113-262 parts per thousand, while polyisoprenoid lipids are depleted in D relative to growth water by 142-376 parts per thousand. Isotopic variations within compound classes (e.g., n-alkanes) are usually less than similar to 50 parts per thousand, but variations as large as 150 parts per thousand are observed among isoprenoid lipids from a single organism. Phytol is consistently depleted in D by up to 50 parts per thousand relative to other isoprenoid lipids. Inferred isotopic fractionations between cellular water and lipids are greater than those indicated by previous studies. (C) 1999 Elsevier Science Ltd. All rights reserved.
254efTimes Cited:281Cited References Count:26

The geochemistry of redox sensitive trace metals in sediments - Morford, J. L.; Emerson, S. (Geochimica Et Cosmochimica Acta, 1999)
We analyzed the redox sensitive elements V, Mo, U, Re and Cd in surface sediments from the Northwest African margin, the U.S. Northwest margin and the Arabian Sea to determine their response under a range of redox conditions. Where oxygen penetrates 1 cm or less into the sediments, Mo and V diffuse to the overlying water as Mn is reduced and remobilized. Authigenic enrichments of U, Re and Cd are evident under these redox conditions. With the onset of sulfate reduction, all of the metals accumulate authigenically with Re being by far the most enriched. General trends in authigenic metal accumulation are described by calculating authigenic fluxes for the 3 main redox regimes: oxic, reducing where oxygen penetrates less than or equal to 1 cm, and anoxic conditions. Using a simple diagenesis model and global estimates of organic carbon rain rate and bottom water oxygen concentrations, we calculate the area of sediments below 1000 m water depth in which oxygen penetration is less than or equal to 1 cm to be 4% of the ocean floor. We conclude that sediments where oxygen penetrates less than or equal to 1 cm release Mn, V and Mo to seawater at rates of 140%-260%, 60%-150% and 5%-10% of their respective riverine fluxes, using the authigenic metal concentrations and accumulation rates from this work and other literature. These sediments are sinks for Re, Cd and U, with burial fluxes of 70%-140%, 30%-80% and 20%-40%, respectively, of their dissolved riverine inputs. We modeled the sensitivity of the response of seawater Re, Cd and V concentrations to changes in the area of reducing sediments where oxygen penetrates less than or equal to 1 cm. Our analysis suggests a negligible change in seawater Re concentration, whereas seawater concentrations of Cd and V could have decreased and increased, respectively, by 5%-10% over 20 kyr if the area of reducing sediments increased by a factor of 2 and by 10%-20% if the area increased by a factor of 3. The concentration variations for a factor of 2 increase in the area of reducing sediments are at about the level of uncertainty of Cd/Ca and V/Ca ratios observed in foraminifera shells over the last 40 kyr. This implies that the area of reducing sediments in the ocean deeper than 1000 m (4%) has not been greater than twice the present value in the recent past. Copyright (C) 1999 Elsevier Science Ltd.
227ktTimes Cited:455Cited References Count:92

The Geochemistry of Redox Sensitive Trace Metals: Thesis - Morford, J. L. (University of Washington, 1999)

A geostrophic transport estimate for the Florida Current from the oxygen isotope composition of benthic foraminifera - Lynch-Stieglitz, J.; Curry, W. B.; Slowey, N. (Paleoceanography, 1999)
We present a new method for the quantitative reconstruction of upper ocean flows for during times in the past. For the warm (T>5 degrees C) surface ocean, density can be accurately reconstructed from calcite precipitated in equilibrium with seawater, as both of these properties increase with decreasing temperature and increasing salinity. Vertical density profiles can be reconstructed from the oxygen isotopic composition of benthic foraminifera. The net volume transport between two vertical density profiles can be calculated using the geostrophic method. Using benthic foraminifera from surface sediment samples from either side of the Florida Straits (Florida Keys and Little Bahama Bank), we reconstruct two vertical density profiles and calculate a volume transport of 32 Sv using this method. This agrees well with estimates from physical oceanographic methods of 30-32 Sv for the mean annual volume transport. We explore the sensitivity of this technique to various changes in the relationship between temperature and salinity as well as salinity and the oxygen isotopic composition of seawater.
198xcTimes Cited:81Cited References Count:45

Glacial modulation of rapid climate change during the last 0.5 million years - McManus, J. F.; Oppo, D. W.; Cullen, J. L. (PAGES newsletter, 1999)
id: 168

High Molecular Weight Dissolved Organic Matter in Seawater: Chemical Structure, Sources, and Cycling, Thesis - Aluwihare, Lihini I. (High Molecular Weight Dissolved Organic Matter in Seawater: Chemical Structure, Sources, and Cycling, Thesis, 1999)
id: 150; Chemical Oceanography

A high resolution ~15,000 year record of El-Nino driven alluviation in southwestern Ecuador - Rodbell, D. T.; Seltzer, G. O.; Anderson, D. M.; Abbott, M. B.; Enfield, D. B.; Newman, J. H. (Science, 1999)
id: 393

Holocene and modern sediment budgets for the Ganges-Brahmaputra River: Evidence for highstand dispersal to floodplain, shelf, and deep-sea depocenters - Goodbred, S. L.; Kuehl, S. A. (Geology, 1999)
id: 149

Holocene depositional patterns, neotectonics and Sundarban Mangroves in the western Ganges-Brahmaputra delta - Stanley, D. J.; Hait, A. (Jour. Coastal Res., 1999)
id: 229

Holocene Environmental changes in the Lake Erie Basis - Kepthorne, R. A.; Barrera, E.; Coakley, J. P.; Tevesz, M. J. S.; Miller, B. B. (International Association for Great Lakes Research Program and Abstract, 1999)
id: 249

Holocene surface faulting in the Seattle fault zone, Bainbridge Island, Washington - Nelson, A. R.; Pezzopane, S. K.; Bucknam, R. C.; Koehler, R. D.; Narwold, C. F.; Kelsey, H. M.; Sherrod, B. L.; LaPrade, W. T.; Wells, R. E.; Johnson, S. Y. (Seismological Research Letters, 1999)
id: 1404

Installation and First Results of a 134-Sample MC-SNICS Ion Source at NOSAMS - von Reden, K. F.; Schneider, R. J.; McNichol, A. P.; Elder, K. F.; Gagnon, A. R. (8th International Conference on Accelerator Mass Spectrometry, 1999)
id: 1802

Installation of a 134-Sample MC-SNICS Ion Source at NOSAMS and first results - von Reden, Karl F.; Bellino, Mary; Long, Patricia; Schneider, Robert J.; Loger, Roger (Accelerator Mass Spectrometry, Proceedings of the Eighth International Conference on Accelerator Mass Spectrometry, 1999)
id: 1724

Interdisciplinary environmental project probes Chesapeake Bay down to the core - Cronin, T.; Colman, S. M.; Willard, D.; Kerhin, R.; Holmes, C.; Karlsen, A.; Ishman, S.; Bratton, J. (EOS, 1999)
id: 185

Interpreting carbon-isotope excursions: carbonates and organic matter - Kump, L. R.; Arthur, M. A. (Chemical Geology, 1999)
Variations in the carbon isotopic compositions of marine carbonate and organic carbon provide a record of changes in the fraction of organic carbon buried through time and may provide clues to changes in rates of weathering and sources of organic carbon. Paired carbonate and organic carbon isotope determinations provide a possibility of interpreting not only changes in the global carbon cycle through time, but changes in atmospheric pCO(2) as well. Interpretations of these types of data are typically rather qualitative; a quantitative basis is required to develop a better understanding of changes in the carbon cycle. For this purpose, we employ a simple model of the global carbon cycle which is subjected to a number of different perturbations, each lasting 500 ky, i.e., much longer than the residence times of carbon and phosphorus in the ocean-atmosphere system. In addition to standard considerations of carbon mass and isotopic fluxes to the ocean-atmosphere system from weathering and volcanism and fluxes of organic carbon and carbonate-carbon to sediments, the model ;incorporates sensitivity of the photosynthetic carbon isotope effect to changes in pCO(2). The inclusion of this parameter leads to unexpected carbon isotope responses to forcing that causes increased rates of organic carbon burial. A series of simple to more complex simulations illustrates the significant effects of varying differences between the carbon isotopic composition of sedimented carbonate and organic carbon (Delta(B)). With constant Delta(B) a 50% increase in organic carbon burial produces a parallel increase in carbonate and organic carbon isotopic compositions. However, the same simulation with Delta(B) responsive to pCO(2) changes produces an initial parallel delta(13)C increase, but this is followed by an even greater C-13-enrichment in organic carbon because pCO(2) falls in response to increased organic carbon burial. The counterintuitive overall result of the enhanced organic carbon burial event is that the carbonate carbon isotopic composition actually decreases because of the more substantial increase in delta(13)C(org). In addition, we illustrate the effects on carbon isotopic compositions of the oceanic inorganic carbon reservoir and buried organic matter of a 50% increase in volcanic CO2 outgassing, a 50% increase in weathering rate (with coupled phosphate and riverine carbon flux responses), a 50% decrease in shale-associated organic carbon weathering, a 50% decrease in silicate weathering rate, and the possible effects of the rise in abundance of C-4 plants in the late Miocene to Recent. We compare the model simulated carbon isotopic responses for some of these experiments to paired carbonate- and organic-carbon records to illustrate how these records might be interpreted in light of the model response. (C) 1999 Elsevier Science B.V. All rights reserved.
243xyTimes Cited:398Cited References Count:64

An investigation of a transition in glacial landforms in southeastern Main. Thesis - Lurvey, L. Kirk (University of Maine, 1999)

Isotopic and molecular fractionation in combustion; three routes to molecular marker validation, including direct molecular 'dating' (GC/AMS) - Currie, L. A.; Klouda, G. A.; Benner, B. A.; Garrity, K.; Eglinton, T. I. (Atmospheric Environment, 1999)
The identification of unique isotopic, elemental, and molecular markers for sources of combustion aerosol has growing practical importance because of the potential effects of fine particle aerosol on health, visibility and global climate. It is urgent, therefore, that substantial efforts be directed toward the validation of assumptions involving the use of such tracers for source apportionment. We describe here three independent routes toward carbonaceous aerosol molecular marker identification and validation: (1) tracer regression and multivariate statistical techniques applied to field measurements of mixed source, carbonaceous aerosols; (2) a new development in aerosol (14)C metrology: direct, pure compound accelerator mass spectrometry (AMS) by off-line GC/AMS ('molecular dating'); and (3) direct observation of isotopic and molecular source emissions during controlled laboratory combustion of specific fuels. Findings from the combined studies include. independent support for benzo(ghi)perylene as a motor vehicle tracer from the first (statistical) and second (direct 'dating') studies; a new indication, from the third (controlled combustion) study, of a relation between (13)C isotopic fractionation and PAH molecular fractionation, also linked with fuel and stage of combustion; and quantitative data showing the influence of both fuel type and combustion conditions on the yields of such species as elemental carbon and PAH, reinforcing the importance of exercising caution when applying presumed conservative elemental or organic tracers to fossil or biomass burning field data as in the first study. Published by Elsevier Science Ltd.
208duTimes Cited:38Cited References Count:31

The Last Deglaciation in Southern Chile - Anderson, D. M.; Archer, R. B. (Development of Paleoceanography as a New Field of Science, 1999)
id: 145

Late Pleistocene-Holocene sea-level change and the New Jersey coastline - Miller, K. G.; Sugarman, P. J.; Sheridan, R. E.; Ashley, G. M. (Trans. Am. Geophys. Un., 1999)
id: 163

Late Quaternary stratigraphy of Marresale, Yamal Peninsula, Russia: new constraints on the footprint of the Eurasian ice sheet - Forman, S. L.; Ingolfsson, O.; Manley, W. F.; Lokrantz, H. (Geology, 1999)
id: 370

Late Quaternary stratigraphy, Paleoclimate and neotectonism of the Persian (Arabian) Gulf region - Uchupi, E.; Swift, S. A.; Ross, D. A. (Marine Geology, 1999)
The last glacial deposits in the Persian (Arabian) Gulf consist of a > 22,000 year old paralic terrigenous sequence in the Mesopotamia Shelf, the foredeep in front of the Iranian Zagros Mountains and the northern side of the Biaban Shelf. Elsewhere, the Gulf, and probably the Biaban Shelf, were mantled by > 30,000 year old carbonates. Comparison of C-14 data from foraminifera from the last glacial terrigenous unit in the foredeep off Iran with curves published by Hopley [Hopley, D., 1982. The Geomorphology of the Great Barrier Reef: Quaternary Development of Coral Reefs. Wiley, New York, 453 pp.] and Chapell et al. [Chapell, J., Omura, A., Tezer, E., McCulloch, M., Pandolfi, J., Ota, Y., Pillans, B., 1996. Reconciliation of late Quaternary sea levels derived from coral terraces at Huon Peninsula with deep sea oxygen isotope records. Earth Planet. Sci. Lett. 141, 227-236.] indicates that the region may have experienced uplift during the last glacial, whereas other geologic data indicate that the foredeep has had a history of continuous subsidence during the Cenozoic. A possible explanation for this discrepancy is that the foraminifera analyzed are not in place, but were reworked into shallower water during the Holocene transgression. However, the foraminifera analyzed do not display any evidence of wear, indicating that such transport was limited. A third alternative is that sea level during the last glacial was much higher than indicated by the curves of Hopley and Chapell et al.At the peak of the last glaciation 21,000 to 20,000 years ago, when sea level was 120 m lower than now, the Gulf was a waterless basin and deposition was negligible. On the Biaban Shelf, the Holocene transgressive sequence resting unconformably on last glacial sediments consists of 14,000 year old carbonates, a > 11,000 year old terrigenous delta on the northern end of the Biaban Shelf and 11,000-10,000 year old intertidal-tidal aragonite deposited in a dry climate. On the northeast side of the Gulf, the last glacial sediments are covered by 10,000 to 7000 year old aragonite muds (younging toward the northwest). Resting on the aragonites on the Biaban Shelf and on the northeast and northwest sides of the Gulf are marls deposited under the present humid climate. The southwest side of the Gulf continued to be a site of carbonate deposition throughout the Holocene. Comparison of AMS C-14 measurements of the late Holocene marls with the sea level curve of Fairbanks [Fairbanks, R.G., 1989. A 17,000 year glacio-eustatic sea level record; influence of glacial melting rates and the Younger Dryas event and deep-ocean circulation. Nature 342, 637-642.] indicates that the axial zone of the Gulf off Iran experienced subsidence during the Holocene. This subsidence coupled with a rapid rise in sea level during a major glacial melt 9500 to 8500 years ago, when global sea level rose from -50 to -28 m, led to the replacement of marl with a shallow (8-25 m) water fauna by a 'deep' (> 50 m) water one. Similar measurements and other geologic data indicate that the Mesopotamia Shelf and the mouth of the Mesopotamian Depression on the northwest side of the Gulf underwent both subsidence and uplift during the Cenozoic. These vertical oscillations, however, were more subdued than these in the foredeep off iran. The Arabian Shelf along the Gulfs southwest side appears to have experienced minor uplift during the Cenozoic. (C) 1999 Elsevier Science B.V. All rights reserved.
214vaTimes Cited:31Cited References Count:58

Late Wisconsian deep-sea sedimentary record from convulsive geologic events, Northeast Pacific - Serra, Francesca; Normark, William R.; Zuffa, Gian Gaspare; Brunner, Charlotte A. (IAS 19 Regional Meeting of Sedimentology, 1999)
id: 1471

Linking the 10Be continental record of Lake Baikal to marine and ice archives for the last 50 ka: Implication for the global dust-aerosol input - Aldahan, A.; Possnert, G.; Peck, J.; King, J.; Colman, S. (Geophysical Research Letters, 1999)
We present here a 10Be profile from the continental sediments of Lake Baikal (the world's largest fresh water lake), which, for the first time, shows the ≈ 40 ka 10Be enhancement and a pattern that strongly matches those from the marine and ice records for the last 50 ka. This finding provides a new horizon for global and regional correlation of continental archives. Additionally, our VADM-predicted 10Be production confirms and further strengthens a common global cause (geomagnetic field intensity) for the change in atmospheric 10Be over the last 50 ka. We also show that most of the 10Be inventory to the lake has been provided by riverine input, but with a significant addition from direct precipitation and dust-aerosol fallout. We estimate a higher dust-aerosol contribution of 10Be during the Holocene and interstadial stage 3 (22–50 ka) as compared with the glacial period (12–22 ka).
id: 1353

Long-term fluxes and budget of ferric iron: implication for the redox states of the Earth's mantle and atmosphere - Lecuyer, C.; Ricard, Y. (Earth and Planetary Science Letters, 1999)
Net flux of ferric iron from the subducted oceanic crust to the mantle has been estimated to constrain the evolution of the redox state of the Earth's mantle. The main mechanism responsible for the transfer of ferric iron towards the mantle is the production of magnetite during the hydrothermal alteration of the oceanic crust. Both modeling and compilation of chemical data lead to a flux of 21 x 10(3) kg s(-1) of ferric iron transported by the subducted oceanic crust. The net flux of ferric iron towards the deep mantle is estimated to be 12 x 10(3) kg s(-1) when corrected from the production rates of basic magmas at oceanic ridges, island arcs, and hot spots. We discuss several hypotheses. Ferric iron could react at depth with reduced species that buffer the redox state of the mantle to its present-day value. One possible mechanism could be the reaction of this ferric iron with the core that would have been reduced by only 500 m since 2 Ga. At the opposite, we may also consider that ferric iron accumulates in the deep mantle, being possibly accepted by the structure of spinel, garnet, and perovskite. The transfer of ferric iron from subducted slabs to the mantle contributes from 10 to 25% in the global budget of the ferric iron component of the mantle. The long-term loss of ferric iron from the Earth's surface may be considered as a plausible mechanism to regulate the photosynthetic production of molecular oxygen. (C) 1999 Elsevier Science B.V. All rights reserved.
160gtTimes Cited:87Cited References Count:66

Marine and meteoric diagenesis of Pleistocene carbonates from a nearshore submarine terrace, Oahu, Hawaii - Sherman, C. E.; Fletcher, C. H.; Rubin, K. H. (Journal of Sedimentary Research, 1999)
The nearshore slope of Oahu consists of a shallowly dipping shelf extending from the shoreline out to the similar to -20 m contour, where there is a sharp break in slope down to similar to -30 m, Limestones recovered in a series of short cores taken from this nearshore terrace are typical of shallow-marine reef environments and comprise either a branching-coral or massive-coral facies, The composition as well as shoreward zonation of facies suggests that the terrace represents an in situ fossil reef complex. Th-U ages of in situ corals are all Pleistocene and suggest that the bulk of the feature formed during marine oxygen isotope stage 7. Later accretion along the seaward front of the terrace occurred during marine oxygen isotope substages 5a and/or 5c. Deposition during these interglacial highstands has not previously been documented in the sea-level record on Oahu,Although the diagenetic record in the cored samples is incomplete, three periods of diagenesis are identified: early shallow marine, meteoric, and post-meteoric shallow marine. Early shallow-marine diagenesis includes cementation by aragonite and Mg calcite in an active marine phreatic zone and predominantly micritization in a stagnant marine phreatic zone. Meteoric processes occurred in the vadose zone and include precipitation of calcite (needle fibers, meniscus cements, micritic networks), neomorphism, and dissolution. All limestones are now in an active marine phreatic zone. Evidence of post-meteoric shallow-marine diagenesis is found in last-generation Mg calcite cements and internal sediments occurring directly on limestone substrates that have otherwise been stabilized to calcite. The present seafloor is undergoing extensive biological and physical erosion. No Holocene limestones were recovered. Petrographic and geochemical signatures of subaerial exposure and meteoric diagenesis are recognized within the upper several centimeters of all cores. Thus, the present seafloor in the study area is a flooded Pleistocene subaerial exposure surface.
A237cq Times Cited:42 Cited References Count:79
Keywords: barrier-reef; calcite; corals; fringing-reef; Holocene; oxygen isotopes; platform; recrystallization; sea-level; stabilization

Marine and meteoric diagenesis of pleistocene carbonates from a nearshore submarine terrace, Ohau, Hawaii - Sherman, C. E.; Fletcher, C. H.; Rubin, K. H. (Journal of Sedimentary Research, 1999)
id: 298

Measured and predicted sediment yield from a subtropical, heavy rainfall, steep-sided river basin: Hanalei, Kauai, Hawaiian Islands - Calhoun, R. S.; Fletcher, C. H. (Geomorphology, 1999)
To determine the sediment yield of the 54.4 km(2) Hanalei River basin, we employ three methods: (1) the Universal Soil Loss Equation (USLE), which uses natural characteristics of the basin such as the amount of rain, slope steepness and length values, and soil types to predict sediment erosion in a basin; (2) the thickness and calibrated radiocarbon age of fluvial deposits cored from the coastal plain; and (3) field measurements of suspended sediment in the river. Method 1 (USLE) provides a model prediction of sediment yield that we test with observational data of methods 2 and 3. Several curves, including one by the US Soil Conservation Service, predict a sediment delivery ratio (measured sediment yield: gross erosion) between approximately 15% and 50%. With 5260 +/- 2210 Mg (metric tons) yr(-1) of suspended sediment in the Hanalei River and 2300 +/- 700 Mg yr(-1) deposited on the coastal plain, however, the delivery of sediment in the Hanalei basin ranged between 45% and 101% of the maximum predicted USLE value (88 +/- 103 Mg km(-2) yr(-1)). This higher than predicted yield may be the result of mass movement. We are not able to differentiate, however, between erosion and mass movement as the principle agent of denudation. Our measurements indicate a total sediment yield of 140 +/- 55 Mg km(-2) yr(-1) for the Hanalei Valley. (C) 1999 Elsevier Science B.V. All rights reserved.
267flTimes Cited:14Cited References Count:37

Methane-consuming archaebacteria in marine sediments - Hinrichs, K. U.; Hayes, J. M.; Sylva, S. P.; Brewer, P. G.; DeLong, E. F. (Nature, 1999)
Large amounts of methane are produced in marine sediments but are then consumed before contacting aerobic waters or the atmosphere. Although no organism that can consume methane anaerobically has ever been isolated, biogeochemical evidence indicates that the overall process involves a transfer of electrons from methane to sulphate and is probably mediated by several organisms, including a methanogen (operating in reverse) and a sulphate-reducer (using an unknown intermediate substrate). Here we describe studies of sediments related to a decomposing methane hydrate. These provide strong evidence that methane is being consumed by archaebacteria that are phylogenetically distinct from known methanogens. Specifically, lipid biomarkers that are commonly characteristic of archaea are so strongly depleted in carbon-13 that methane must be the carbon source, rather than the metabolic product, for the organisms that have produced them. Parallel gene surveys of small-subunit ribosomal RNA (16S rRNA) indicate the predominance of a new archael group which is peripherally related to the methanogenic orders Methanomicrobiales and Methanosarcinales.
Hinrichs, K UHayes, J MSylva, S PBrewer, P GDeLong, E FengResearch Support, Non-U.S. Gov'tResearch Support, U.S. Gov't, Non-P.H.S.England1999/05/11 02:03Nature. 1999 Apr 29;398(6730):802-5.

Millennial-scale climate changes in ventilation of the thermocline, intermediate and deep waters of the glacial North Atlantic - Curry, W. B.; Marchitto, T. M.; McManus, J. F.; Oppo, D. W.; L, Laarkamp K. (Geophysical Monograph series, 1999)
id: 207

New Developments at the NOSAMS Facility - von Reden, K. F.; Schneider, R. J.; McNichol, A. P.; Hayes, J. M.; Pearson, A.; Eglinton, T. I. (Proceeding of the International Workshop on Frontiers in Accelerator Mass Spectrometry, 1999)
id: 1723(JISTEC)

New Developments at the NOSAMS Facility - von Reden, K. F.; Schneider, R. J.; McNichol, A. P.; Hayes, J. M.; Pearson, A.; Eglinton, T. I. (International Workshop on Frontiers in Accelerator Mass Spectrometry, 1999)
id: 1679

The North Atlantic's 1-2 kyr climate rhythm: Relation to Heinrich events, Dansgaard/Oeschger cycles and the Little Ice Age (Book Section) - Bond, G. C.; Showers, W.; Elliot, M.; Evans, M.; Lotti, R.; Hajdas, I.; Bonani, G.; Johnson, S. (Mechanisms of global climate change at mellennial time scales, 1999)
id: 216

The overturning circulation of the glacial Atlantic: A view from the top - Lynch-Stieglitz, J.; Curry, W. B.; Slowey, N. C. (Sixth International Conference on Paleoceanography, 1999)
id: 1337

The overturning circulation of the glacial Atlantic: A view from the top - Lynch-Stieglitz, J.; Curry, W. B.; Slowey, N.; Schmidt, G. A. (Reconstructing Ocean History: A Window into the Future, 1999)
id: 1364

Paleoceanographic changes in the Southern Ocean (Pacific Sector) during the last 14 ka.- -Abstract - Morigo, C.; Capotondi, L.; Ravaioli, M.; Giglio, F.; Turi, B.; Brilli, M.; Langone, L. (Third International SO-JGOFS Symposium, 1999)
id: 1426

Paleoclimate of Southwestern China for the past 50,000 yr inferred from lake sediment records - Hodell, D. A.; Brenner, M.; Kanfoush, S. L.; Curtis, J. H.; Stoner, J. S.; Song, X. L.; Yuan, W.; Whitmore, T. J. (Quaternary Research, 1999)
Long sediment cores (12.5 and 13.5 m) from two lakes in Yunnan Province were used to infer the paleoclimate of southwest China over the past 50,000 yr, During the Holocene and marine isotope stage (MIS 3), bio-induced carbonate precipitation and organic matter (OM) production was high, suggesting warm temperatures and high primary productivity. In contrast, sediment inorganic carbon (IC) and organic carbon (OC) concentrations were low in last glacial deposits from 38,000 to 12,000 cal yr B.P., indicating cool temperatures and low productivity. The 50,000-yr record has alternating peaks of carbonate and coarse-grain (>38 mu m) quartz that reflect warm, moist interglacial or interstadial conditions alternating with cold, dry glacial or stadial conditions, respectively. Spectral analysis of the carbonate and quartz signals reveals power concentrated at periods of 7200 and 8900 cal yr, respectively, that may reflect a nonlinear climate response to precessional forcing at a time of reduced eccentricity modulation (McIntyre and Molfino, 1996). Oxygen isotope values of calcite from Yunnan lake cores indicate the summer monsoon was weak during the last glaciation from 50,000 to 12,000 cal yr B.P. The summer monsoon intensified between 12,000 and 8000 cal yr B.P., but weakened gradually in response to insolation forcing during the mid-to-late Holocene. Our results support the Overpeck ef al. (1996) model that posits a weak summer monsoon during the last glaciation that responded nonlinearly to insolation forcing when its intensity was affected by Eurasian snow cover and ice-sheet extent. The summer monsoon intensified and responded linearly to seasonal insolation forcing in the Holocene when ice volume diminished. (C) 1999 University of Washington.
255ltTimes Cited:85Cited References Count:58

Paleoenvironmental changes during the last 17,000 years in western Patagonia - Markgraf, V.; Bianchi, M. M. (Bamberger Geographische Schriften, 1999)
id: 1382

Paleoenvironments of Capitol Reef National Park reconstructed from fossil packrate middens - Cole, K. L.; Murray, L. K. (4th biennial Conference on Research on the Colorado Plateau, 1999)
id: 1369

Peat accumulation and succession following permafrost thaw in the boreal peatlands of Manitoba, Canada - Camill, P. (Ecoscience, 1999)
Permafrost thaw in boreal peatlands may be widespread as climate warms over the next century. Thaw will lead to dramatic changes in vegetation, and an understanding of the patterns and rates of succession following thaw is important for assessing future ecosystem changes, such as carbon accumulation and the likelihood of permafrost formation during climate warming. This paper describes the autogenic processes of peat accumulation and succession from recently thawed, aquatic Sphagnum communities to lawn and hummock Sphagnum communities favorable for permafrost formation. Peat cores were used to construct bulk density profiles in aquatic, lawn, and hummock habitats. Soil bulk density increased over time from the edges to the centers of thawed bogs. These changes corresponded to changes from aquatic to lawn/hummock communities. Macrofossils from Pb-210-dated peat cores were used to document historical changes to hummock communities. Succession to hummock communities capable of forming permafrost was less than 80 years. Picea mariana seedlings colonized emergent Sphagnum hummocks in collapse scars, which may lead to permafrost formation. However, permafrost formation in today's discontinuous permafrost landscape is unlikely during future climate warming because of limited tree establishment and shifting mean annual temperature isotherms.
299bzTimes Cited:22Cited References Count:55

Planktic foraminifera and oxygen isotope as proxies for paleoceanographic reconstruction in the Southern Ocean during the last deglacial time--Abstract - Morigi, C.; Capotondi, L.; Ravaioli, M.; Giglio, F.; Turi, B.; Brilli, M.; Frignani, M.; Langone, L. (Convegno Glaciologia e Paleoclima, 1999)
id: 1425

Preliminary evidence of early deglaciation in southern Chile - Anderson, D. M.; Archer, R. B. (Palaeogeography Palaeoclimatology Palaeoecology, 1999)
The end of the last ice age in the channels of southern Chile is recorded by resumed sedimentation in formerly ice-filled basins. To identify the timing of initial ice retreat in Southern Chile, we examined ice-proximal sediments from a proglacial lake along the eastern margin of the Magallanes ice sheet, an environment thought to be sensitive to initial melting (Porter, S.C,, Clapperton, C.M., Sugden, D.E., 1992. Chronology and dynamics of deglaciation along and near the Strait of Magellan, southernmost South America. Sver. Geol. Unders. 81, 233-239). AMS-radiocarbon dates of the supra-till deposits in two cores indicate that sedimentation resumed 18 radiocarbon kyr. Deposition in kettle-holes and bogs on the adjacent land surfaces began at the same time or earlier (17-25 radiocarbon kyr) (Clapperton, C.M., Sugden, D.E., Kaufman, D.S., McCulloch, R.D., 1995. The last glaciation in central Magellan Strait, Southernmost Chile. Quat. Res. 44, 133-148). Our preliminary interpretation is that these events indicate initial deglaciation in the region and the formation of a large proglacial lake, followed several thousand years later by the invasion of salt water as sea level rose. Deglaciation in southers Chile occurred too early to be forced by the resumption of North Atlantic Deep Water formation, sea level rise, or northern hemisphere summer insolation, and we suggest instead that southern insolation played a role. The time of initial deglaciation in southern Chile (21-27 calendar kyr) occurred as southern hemisphere annual insolation increased from a minimum at 29 calendar kyr (6 W/m(2) less than today at 80 degrees S). (C) 1999 Elsevier Science B.V. All rights reserved.
160wbTimes Cited:13Cited References Count:25

A preliminary model-data comparison for bomb-14C in the Pacific thermocline - Rogers, K.; Peacock, S.; Latif, M.; Key, R. M. (WOCE-AIMS Tracer Workshop, 1999)
id: 313

Radiocarbon age anomalies in land snail shells from Texas: Ontogenetic, individual, and geographic patterns of variation - Goodfriend, G. A.; Ellis, G. L.; Toolin, L. J. (Radiocarbon, 1999)
Accelerator mass spectrometric (AMS) radiocarbon analyses of live-collected, prebomb samples of shell carbonates of the land snails Rabdotus dealbatus and R. alternatus from Texas were carried out to quantify the characteristic age anomalies of land snails from limestone areas. Age anomalies are similar for the two species; they average +700 yr and vary by +/-180 yr (1 sigma) among samples. Serial analysis of I shell reveals a significant ontogenetic trend in C-14 age anomalies, with older apparent ages (up to 1200 yr) in the apical part of the shell and younger and uniform ages in the last whorl. No trend in age anomalies was found across a broad range of rainfall conditions (from 300 to 1000 mm mean annual rainfall).
228qgTimes Cited:28 Cited References Count:18
Keywords: Carbonate

Radiocarbon analysis of Pinus lagunae tree rings: Implications for tropical dendrochronology - Biondi, F. (Radiocarbon, 1999)
A promising species for tropical dendrochronology is Pinus lagunae, a pine tree found in Baja California Sur (Mexico) around lat 23.5 degrees N. In 1995, we sampled a total of 27 wood cores from 13 Pinus lagunae trees in Sierra La Victoria (23 degrees 36'N, 109 degrees 56'W),just north of Sierra La Laguna, at an elevation of 1500-1600 m. Selected trees were locally dominant, but their ring-width patterns could not be crossdated. To test the hypothesis that visible growth layers in Pinus lagunae are formed annually, we measured radiocarbon amounts in individual rings by means of accelerator mass spectrometry (AMS). Twenty-three C-14 measurements were used to trace the location of the 1963-64 "bomb spike" in 3 wood increment cores. By comparing the location of that Delta(14)C extreme with the number of visible radial wood increments, it was possible to conclude that 2 cores had a number of locally absent rings, while the 3rd one included a few years with more than one growth layer. Therefore, ring-width patterns of sampled Pinus lagunae were not consistent from one tree to another, most likely because of climatic regime in combination with microsite features. While the possibility of generating Pinus lagunae tree-ring chronologies cannot entirely be ruled out, the development of dendrochronological proxy records of climate from coniferous species in tropical North America should focus on species and sites that experience a more pronounced seasonality.
289tcTimes Cited:16Cited References Count:31

Rapid strand-plain accretion in the northeastern Nile Delta in the 9th century A. D. and the demise of the port of Pelusium - Goodfriend, G. A.; Stanley, D. J. (Geology, 1999)
id: 177

Reconstructing the oceanic 13C Suess effect - Sonnerup, R. E.; Quay, P. D.; McNichol, A. P.; Bullister, J. L.; Westby, T. A.; Anderson, H. L. (Global Biogeochemical Cycles, 1999)
id: 1710

Records of Heinrich Events at the confluence of the distal Northwest Atlantic Mid-Ocean Channel, and the Immarssauk Mid-Ocean Channel of the North Atlantic, Europ. Union - Rashid, H.; Hesse, R.; Piper, D. J. W. (Geoscience 10th Annual Meeting, 1999)
id: 137; 1

Registro micropaleontologico de los cambios naturales y antropicos (500 anos BP-presente) en us ecosistema de lagoon (Doninos, NO Peninsula Iberica) - Bao, R.; Santos, L.; Sanchez-Goni, M. F. (Actas XV Jornadas Sociedad Espanola de Paleontologia, 1999)
id: 151

Relative Sea-Level Rise and the Development of Channel-Fill and Shallow-Water Sequences on Cape Cod, Massachusetts - Gutierrez, B. T.; Aubrey, D. G.; Driscoll, N. W.; Uchupi, E. (American Geophysical Union, Spring Meeting, 1999)
id: 120

Research of natural processes taking place in Issyk-Kul Lake and Issyk-Kul Hollow by means of isotopic methods - Johnson, T. J.; Rasmussen, K. A.; Romanovsky, V. V. (Science and New Technologies, 1999)
id: 210

Retreat of a tidewater margin of the Laurentide ice sheet in eastern coastal Maine ca. 14 to 13,000 14C yrs BP - Kaplan, M. F. (Geological Society of America Bulletin, 1999)
id: 104

The role of oceanic forcing in mid-Holocene Northern Hemisphere climatic change - Kerwin, M. W.; Overpeck, J. T.; Webb, R. S.; DeVernal, A.; Rind, D. H.; Healy, R. J. (Paleoceanography, 1999)
Previous model investigations suggested that changes in orbital forcing and feedbacks associated with northward expansion of the boreal forest were both required to explain the full magnitude of enhanced high-latitude Northern Hemisphere summer warming at 6 ka, thus implying that biospheric feedbacks (decreased planetary albedo associated with forest expansion) may be large in the future [Foley ct at., 1994; TEMPO (Testing Earth System Models with Paleo-Observations), 1996]. Before the magnitude of past biospheric and other feedbacks can be estimated with confidence, however, the role of realistic high-latitude oceanic forcing (i.e., sea surface temperature (SST) increases and sea ice reductions) should also be considered. Here we review existing paleoceanographic observations that suggest portions of the North Atlantic were up to 4 degrees C warmer than today at 6 ka. We then combine our estimates of mid-Holocene North Atlantic SST and sea ice conditions with new climate model simulations to suggest that a significant portion of high-latitude summer warming at 6 ka in the Northern Hemisphere can be accounted for by altered orbital forcing, SSTs, and sea ice relative to today. Our results underscore the importance of incorporating realistic boundary conditions when using paleoenvironmental data to evaluate the climate system's sensitivity to altered forcing and suggest that high-latitude oceanic feedbacks were major contributors to enhanced high-latitude summer warming in the Northern Hemisphere at 6 ka.
id: 1943; PT: J; UT: WOS:000079325100009

S4I Final report for AMS 14C samples - Key, R. M. (Ocean Tracer Laboratory Tech. Rep., 1999)
id: 325

Sedimentary facies analyses as paleohydrological proxies for saline alkes, Central Ebro Basin, Spain. Fourth workshop of the European Lake Drilling Programme - Valero-Garces, B. L. (Terra Nostra, 1999)
id: 383

Sedimentary organic matter preservation: A test for selective degradation under oxic conditions - Hedges, J. I.; Hu, F. S.; Devol, A. H.; Hartnett, H. E.; Tsamakis, E.; Keil, R. G. (American Journal of Science, 1999)
We report here a test of the hypothesis that the extent of organic matter preservation in continental margin sediments is controlled by the average period accumulating particles reside in oxic porewater immediately beneath the water/sediment interface. Oxygen penetration depths, organic element compositions, and mineral surface areas were determined for 16 sediment cores collected along an offshore transect across the Washington continental shelf, slope, and adjacent Cascadia Basin. Individual amino acid, sugar, and pollen distributions were analyzed for a 11 to 12 cm horizon from each core, and (14)C-based sediment accumulation rates and stable carbon isotope compositions were determined from depth profiles within a subset of six cores from representative sites. Sediment accumulation rates decreased, and dissolved O(2) penetration depths increased offshore along the sampling transect. As a result, oxygen exposure times (OET) increased seaward from decades (mid-shelf and upper slope) to more than a thousand years (outer Cascadia Basin). Organic contents and compositions were essentially constant within individual sediment cores but varied consistently with location. In particular, organic carbon/surface area ratios decreased progressively offshore and with increasing OET. Three independent compositional parameters demonstrated that the remnant organic matter in farther offshore sediments is more degraded. Both concentration and compositional patterns indicated that sedimentary organic matter exhibits a distinct and reproducible "oxic effect" OET helps integrate and explain organic matter preservation in accumulating continental margin sediments and hence provides a useful tool for assessing transfer of organic matter from the biosphere to the geosphere.
263rmTimes Cited:194Cited References Count:104

Sedimentological and carbon-isotopic record of late Holocene climate in the sediments of Soda Lake Carrizo Plain, California. Abstracts - Eigenbrode, J. L.; Pratt, L. M.; Rhodes, D. D.; Arrowsmith, J. R.; Mora, G. (Geological Society of America, Annual Meeting, 1999)
id: 224

Sedimentological, carbon-isotopic, and molecular records of late Holocene climate in the sediments of Soda Lake, Carrizo Plain, California. Thesis - Eigenbrode, J.L.; Pratt, L.M.; Rhodes, D.D.; Arrowsmith, J.R.; Mora, G. (Indiana University, 1999)

A Silent Tandetron AMS System - von Reden, Karl F.; Schneider, Robert J. (Symposium of North Eastern Accelerator Personnel, October 13-15, 1997, SNEAP XXXI, 1999)
id: 1722

Similar glacial and Holocene deep water circulation inferred from southeast Pacific benthic foraminiferal carbon isotope composition - Matsumoto, K.; Lynch-Stieglitz, J. (Paleoceanography, 1999)
We present Holocene and last glacial maximum (LGM) oxygen and carbon isotope measurements on Planulina wuellerstorfi in six southeast Pacific cores. Sedimentation rates are low in this part of the ocean, acid measurements were made on individual foraminiferal shells in order to identify the Holocene and glacial individuals on the basis of their extreme delta(18)O. The new delta(13)C data were combined with previous P. wuellerstorfi data for interpretation of global thermohaline circulation. Data from the Southern Ocean were examined closely for regional coherency and a few anomalous delta(13)C values suspected of having productivity overprint were removed. The resulting global delta(13)C distributions and gradients indicate that the deep water circulation was similar during the Holocene and LGM. This interpretation brings delta(13)C data to a better agreement with Cd/Ca data and marks a sharp contrast with a widely held view based on delta(13)C measurements that the glacial Southern Ocean was the terminus of the thermohaline circulation. The proposed presence of glacial North Atlantic Deep Water does not necessarily contradict the postulated presence of Glacial North Atlantic Intermediate Water.
179kdTimes Cited:61Cited References Count:90

Simulated time-dependent climate response to solar radiative forcing since 1600 - Rind, D.; Lean, J.; Healy, R. (Journal of Geophysical Research-Atmospheres, 1999)
Estimated solar irradiance variations since 1500 have been used to force the GISS atmospheric GCM coupled to a mixed layer "q-flux" ocean with heat diffusion through the bottom of the mixed layer. The goal is to assess solar-induced climate change in preindustrial and postindustrial epochs. Six simulations and control runs were made to test the effects of different initial conditions, estimates of initial solar forcing conditions, and ocean heat uptake. The results show that an estimated solar forcing increase of 0.25% accounts for a 0.45 degrees C temperature increase since 1600 and an increase of about 0.2 degrees C over the past 100 years. Global surface temperatures lag solar fluctuations by up to 10 years; the lag is greater over the oceans and so is the correlation due to reduced noise. With only a mixed layer ocean the phase lag is 5 years less. Solar forcing and water vapor feedback each directly account for 35% of the temperature response, with cloud cover changes contributing 20% and sea ice/snow cover 10%. Uncertainty in the initial radiation imbalance or solar forcing affects the surface temperatures for 60-90 years. Modeled and observed periodicities show dominance of long-period forcing (>50 years), as provided by the solar input in these experiments. Tropical temperatures correlate best with solar forcing, due to the influence of water vapor feedback, especially at these multidecadal periods. Sea ice and extratropical temperatures have less long-period power, while high-frequency fluctuations dominate simulated cloud cover variations, which are relatively independent of solar forcing changes. Global and extratropical precipitation increase as the climate warms, but not low and subtropical precipitation, due to conflicting influences of absolute temperature and temperature gradient changes. Solar forcing by itself was not sufficient to produce the rapid warming during the last several decades. A comparison experiment varying trace gas forcing suggests that if the solar estimate is correct, then negative forcing by tropospheric aerosols (and perhaps volcanoes, ozone, and land use changes) has been about -1.2 W m(-)2 since 1700, implying approximately equal contribution from direct and indirect tropospheric aerosol effects.
id: 1945; PT: J; UT: WOS:000078242200003

The slope water current over the Laurentian Fan on interunnual to millennial timescales - Keigwin, L. D.; Pickart, R. S. (Science, 1999)
id: 113

Spatial distribution of carbon and oxygen isotopes in laterally extensive carbonate-cemented layers: Implications for mode of growth and subsurface identification - Klein, J. S.; Mozley, P.; Campbell, A.; Cole, R. (Journal of Sedimentary Research, 1999)
Carbonate concretions and laterally extensive cemented layers are common features in the Prairie Canyon Member of the Mancos Shale at its type locality in western Colorado. Stable-isotope and petrographic data were obtained from these cemented zones in an attempt to determine: (1) how the cemented layers form, (2) whether or not they can be chemically correlated, and (3) if it is possible to differentiate them from concretions in the subsurface. The cement in both the layers and concretions consists of ferroan dolomite and lesser amounts of stoichiometric dolomite and ankerite. Samples for stable-isotope analysis were drilled from 10 grids, with a typical grid spacing of 10 cm x 10 cm, Gridded samples were obtained from two continuous cemented layers at several locations along the layers (2.3 m to 1.5 km apart on the same layer), and from isolated and stratabound concretions,Taken together, all the cements (regardless of spatial position) show a remarkably linear correlation (R-2 = 0.98) between delta(13)C and delta(18)O, Systematic center-to-edge decreases in both delta(13)C and delta(18)O occur in each of the cemented zones and are persistent over lateral intervals of at least 1.5 km, The cores of the cemented zones have positive delta(13)C values (up to > 10 parts per thousand PDB), which result from incorporation of C-13-enriched carbon during methanogenesis. The edges of the cemented zones have negative delta(13)C values (down to < -9 parts per thousand PDB), which suggests incorporation of C-13-depleted carbon from thermocatalytic decarboxylation reactions. Oxygen isotope paleothermometry indicates that precipitation may have started at moderate temperatures (similar to 25 degrees C) and ended at temperatures as high as 92 degrees C,The spatial distribution of the isotopic data in the cemented layers can be explained as resulting from the coalescence of stratabound concretions, followed by growth above and below the coalesced concretions. Such growth may have occurred in a complex: manner, in which early cements precipitated throughout the thickness of the layer but were more abundant in the core zone. Given the lateral persistence of the pattern of isotopic variation in the cemented layers, geochemical correlation of the layers may be possible in the subsurface. In addition, because laterally persistent cemented layers in the Prairie Canyon Member exhibit patterns of isotopic variation different from concretions (layers have a more asymmetrical vertical distribution), it should be possible to distinguish between the two styles of cementation from subsurface core data alone.
A157gxTimes Cited:36Cited References Count:39

The speciation and sources of dissolved phosphorus in the Everglades (Report) - Copper, W.; Hsieh, Y. P.; Landing, W. M.; Proctor, L.; Salters, V.; Wang, Y. (1999)
id: 1348

Stable isotope and trace element composition of ostracodes from Lake Issyk Kul, Kyrgyzstan - Ricketts, R. D.; Rasmussen, K. A.; Brown, E. T.; Johnson, T. J. (American Geophysical Union Fall Meeting, 1999)
id: 1366

Ten Years After--The WOCE AMS Radiocarbon Program - McNichol, A.; Schneider, R.; von Reden, K.; Gagnon, A.; Elder, K.; Key, R.; Quay, P. (8th International Conference on Accelerator Mass Spectrometry, 1999)
id: 1757

Terminal Proterozoic Mid-Shelf Benthic Microbial Mats in the Centralian Supervasin and their Environmental Significance - Logan, Graham A.; Calver, Clive R.; Gorjan, Paul; Summons, Roger E.; Hayes, John M.; Walter, Malcolm R. (Geochimica et Cosmochimica Acta, 1999)
id: 1734

Terrace Construction in Northern Chihuahua, Mexico at 1150 B.C. and the Present - Hard, R.; Roney, J.; Zapata, J.; Moses, B. (Journal of Field Archaeology, 1999)
id: 238

The uptake of carbon during alteration of ocean crust - Alt, J. C.; Teagle, D. A. H. (Geochimica Et Cosmochimica Acta, 1999)
The distributions and abundances of alteration types and carbonate minerals in sections of upper ocean crust have been measured in order to determine the carbon budget in altered ocean crust. Our results show that the ocean crust is a sink for carbon, with an annual storage rate of 3.4 x 10(12) mol C y(-1), in close agreement with a previous estimate by Staudigel et al. (1989). This surpasses the total production rate of carbon in new oceanic crust and, besides accounting for uptake of all CO2 lost via degassing at MOR, results in a net sink in the oceanic crust of 1.5-2.4 x 10(12) mol C y(-1). This sink is significant for global carbon budgets, and subduction of altered ocean crust may be an important source of CO2 to the atmosphere and/or recycling into the mantle. The bulk CO2 content of the crust decreases with depth, with most of the carbon taken up in the permeable upper few hundred meters of the volcanic section at low temperatures (0-60 degrees C) during aging of crust away from spreading ridges. The abundances of carbonate veins and the bulk CO2 contents of the upper crust are greater in older (110-165 Ma) than younger (6Ma) crust, suggesting progressive uptake of carbon by the upper ocean crust. Precipitation of carbonates within the crust is essentially complete within 100 Ma, and perhaps as soon as a few tens of million years after formation of the crust. Copyright (C) 1999 Elsevier Science Ltd.
221egTimes Cited:188Cited References Count:45

Use of Hydrogen and Carbon Stable Isotopes in the Characterization of Oils from the Potiguar Basin (onshore), Northeastern Brazil - Neto, Eugenio Vaz dos Santos; Hayes, John M. (Bulletin of the American Association of Petroleum Geologists, 1999)
id: 1732

Variability in shallow- and intermediate-water hydrography during the last climate cycle of the Quaternary - McManus, J. F.; Healey, S. L.; Oppo, D. W.; Curry, W. B. (EOS, 1999)
id: 170

Warm-temperate to subtropical shallow water carbonates of the southern Gulf of California and geochemistry of rhodoliths (Thesis) - Halfar, J. (Stanford University, 1999)

Weaker Gulf Stream in the Florida straits during the last glacial maximum - Lynch-Stieglitz, J.; Curry, W. B.; Slowey, N. (Nature, 1999)
As it passes through the Florida Straits, the Gulf Stream consists of two main components: the western boundary flow of the wind-driven subtropical gyre and the northward-flowing surface and intermediate waters which are part of the 'global conveyor belt' compensating for the deep water that is exported from the North Atlantic Ocean(1), The mean flow through the Straits is largely in geostrophic balance and is thus reflected in the contrast in seawater density across the Straits(2). Here we use oxygen-isotope ratios of benthic foraminifera which lived along the ocean margins on the boundaries of the Florida Current during the Last Glacial Maximum to determine the density structure in the water and thereby reconstruct transport through the Straits using the geostrophic method-a technique which has been used successfully for estimating present-day flow(3). Our data suggest that during the Last Glacial Maximum, the density contrast across the Florida Straits was reduced, with the geostrophic flow, referenced to the bottom of the channel, at only about two-thirds of the modern value. If the wind-driven western boundary flow was not lower during the Last Glacial Maximum than today, these results indicate a significantly weaker conveyor-belt component of the Gulf Stream compared to present-day values. Whereas previous studies based on tracers suggested that deep waters of North Atlantic origin were not widespread during glacial times, indicating either a relatively weak or a shallow overturning cell, our results provide evidence that the overturning cell was indeed weaker during glacial times.
264pcTimes Cited:122Cited References Count:31

A Younger Dryas Temperature Reversal in the Eastern Equatorial Pacific, EOS, Transactions - Koutavas, A.; Lynch-Stieglitz, J. (AGU, 1999 Fall Meeting, 1999)
id: 167; 46

A 25,000-year tropical climate history from bolivian ice cores - Thompson, L. G.; Davis, M. E.; Mosley-Thompson, E.; Sowers, T. A.; Henderson, K. A.; Zagorodnov, V. S.; Lin, P.; Mikhalenko, V. N.; Campen, R. K.; Bolzan, J. F.; Cole-Dai, J.; Francou, B. (Science, 1998)
Ice cores that were recovered from the summit of Sajama mountain in Bolivia provide carbon-14-dated tropical records and extend to the Late Glacial Stage (LGS). Oxygen isotopic ratios of the ice decreased 5.4 per mil between the early Holocene and the Last Glacial Maximum, which is consistent with values from other ice cores. The abrupt onset and termination of a Younger Dryas-type event suggest atmospheric processes as the probable drivers. Regional accumulation increased during the LGS, during deglaciation, and over the past 3000 years, which is concurrent with higher water levels in regional paleolakes. Unlike polar cores, Sajama glacial ice contains eight times less dust than the Holocene ice, which reflects wetter conditions and extensive snow cover.
ThompsonDavis Mosley-Thompson Sowers Henderson Zagorodnov Lin Mikhalenko Campen Bolzan Cole-Dai Francou eng 1998/12/04 03:02 Science. 1998 Dec 4;282(5395):1858-64.

AMS measurement of - von Reden, K. F.; McNichol, A. P.; Pearson, A.; Schneider, R. J. (Sixteenth International Radiocarbon Conference, 1998)
id: 1643

AMS Measurement of small samples with high-current system: (Proceedings of the 16th International Radiocarbon Conference, 1997) - von Reden, K. F.; McNichol, A.; Pearson, A.; Schneider, R. (Radiocarbon, 1998)
id: 1815

Arid phases in the western Mediterranean region during the last glacial cycle reconstructed from Lacustrine records - Valerol-Garces, B. L.; Zeroual, E.; Kelts, K. (Paleohydrology and Environmental Change, 1998)
id: 1211

Carbon cycling in sediments from the western equatorial Atlantic: Stable and radiocarbon isotopes in pore waters on the Ceara Rise - McNichol, A. P.; McCorkle, D. C.; Martin, W. R.; Berry, J. N. (EOS, 1998)
id: 108

Challenges in application of radiocarbon dating of organic carbon phases in opal-rich marine sediments from the Southern Ocean - Zheng, Y.; Anderson, R. F.; Froelich, P. N.; Beck, W.; McNichol, A. P.; Guilderson, T. (Trans. AGU 79, 1998)
id: 266

The chemical composition of subducting sediment and its consequences for the crust and mantle - Plank, T.; Langmuir, C. H. (Chemical Geology, 1998)
Subducted sediments play an important role in are magmatism and crust-mantle recycling. Models of continental growth, continental composition, convergent margin magmatism and mantle heterogeneity all require a better understanding of the mass and chemical fluxes associated with subducting sediments. We have evaluated subducting sediments on a global basis in order to better define their chemical systematics and to determine both regional and global average compositions. We then use these compositions to assess the importance of sediments to are volcanism and crust-mantle recycling, and to re-evaluate the chemical composition of the continental crust. The large variations in the chemical composition of marine sediments are for the most part linked to the main lithological constituents. The alkali elements (K, Rb and Cs) and high field strength elements (Ti, Nb, Hf, Zr) an closely linked to the detrital phase in marine sediments; Th is largely detrital but may be enriched in the hydrogenous Fe-Mn component of sediments; REE patterns are largely continental, but abundances are closely linked to fish debris phosphate; U is mostly detrital, but also dependent on the supply and burial rate of organic matter; Ba is linked to both biogenic barite and hydrothermal components; Sr is linked to carbonate phases. Thus, the important geochemical tracers follow the lithology of the sediments. Sediment lithologies are controlled in turn by a small number of factors: proximity of detrital sources (volcanic and continental); biological productivity and preservation of carbonate and opal; and sedimentation rate. Because of the link with lithology and the wealth of lithological data routinely collected for ODP and DSDP drill cores, bulk geochemical averages can be calculated to better than 30% for most elements from fewer than ten chemical analyses for a typical drill core (100-1000 m). Combining the geochemical systematics with convergence rate and other parameters permits calculation of regional compositional fluxes for subducting sediment. These regional fluxes can be compared to the compositions of are volcanics to asses the importance of sediment subduction to are volcanism. For the 70% of the trenches worldwide where estimates can be made, the regional fluxes also provide the basis for a global subducting sediment (GLOSS) composition and flux. GLOSS is dominated by terrigenous material (76 wt% terrigenous, 7 wt% calcium carbonate, 10 wt% opal, 7 wt% mineral-bound H2O+), and therefore similar to upper continental crust (UCC) in composition. Exceptions include enrichment in Ba, Mn and the middle and heavy REE, and depletions in detrital elements diluted by biogenic material (alkalis, Th, Zr, Hf). Sr and Pb are identical in GLOSS and UCC as a result of a balance between dilution and enrichment by marine phases. GLOSS and the systematics of marine sediments provide an independent approach to the composition of the upper continental crust for detrital elements. Significant discrepancies of up to a factor of two exist between the marine sediment data and current upper crustal estimates for Cs, Nb, Ta and Ti. Suggested revisions to UCC include Cs (7.3 ppm), Nb (13.7 ppm), Ta (0.96 ppm) and TiO2 (0.76 wt%). These revisions affect recent bulk continental crust estimates for La/Nb and U/Nb, and lead to an even greater contrast between the continents and mantle for these important trace element ratios. GLOSS and the regional sediment data also provide new insights into the mantle sources of oceanic basalts.The classical geochemical distinction between 'pelagic' and 'terrigenous' sediment sources is not valid and needs to be replaced by a more comprehensive understanding of the compositional variations in complete sedimentary columns. In addition, isotopic arguments based on surface sediments alone can lead to erroneous conclusions. Specifically, the Nd/Hf ratio of GLOSS relaxes considerably the severe constraints on the amount of sediment recycling into the mantle based on earlier estimates from surface sediment compositions. (C) 1998 Elsevier Science B.V. All rights reserved.
Zv404Times Cited:1407Cited References Count:173

CO2 fluxes from mid-ocean ridges, arcs and plumes - Marty, B.; Tolstikhin, I. N. (Chemical Geology, 1998)
Estimates of CO2 emissions at spreading centres, convergent margins, and plumes have been reviewed and upgraded using observed CO2/He-3 ratios in magmatic volatiles, He-3 content estimates in the magmatic sources, and magma emplacement rates in the different tectonic settings. The effect of volatile fractionation during magma degassing, investigated using new rare gas and CO2 abundances determined simultaneously for a suite of Mid-Ocean Ridge (MOR) basalt glasses, is not the major factor controlling the spread of data, which mainly result from volatile heterogeneity in the mantle source. The computed C flux at ridges (2.2 +/- 0.9) x 10(12) mol/a, is essentially similar to previous estimates based on a mon restricted data base. Variation of the C flux in the past can be simply scaled to that of spreading rate since the computed C depends mainly on the volatile content of the mantle source, which can be considered constant during the last 10(8) a. The flux of CO2 from arcs may be approximated using the CO2/He-3 ratios of volcanic gases at arcs and the magma emplacement rate, assuming that the He-3 content of the mantle end-member is that of the MORE source. The resulting flux is similar to 2.5 x 10(12) mol/a, with approx. 80% of carbon being derived from the subducting plate. The flux of CO2 from plumes, based on time-averaged magma production rates and on estimated contributions of geochemical sources to plume magmatism, is less than or equal to 3 x 10(12) mol/a. Significant enhancements of the CO2 flux from plumes might have occurred in the past during giant magma emplacements, depending on the duration of these events, although the time-integrated effect does not appear important. The global magmatic flux of CO2 into the atmosphere and the hydrosphere is found to be 6 x 10(12) mol/a, with a range of (4-10) x 10(12) mol/a. Improvement on the precision of this estimate is linked to a better understanding of the volatile inventory at arcs on one hand, and on the dynamics of plumes and their mantle source contribution on the other hand. (C) 1998 Elsevier Science B.V. All rights reserved.
Zv404Times Cited:212Cited References Count:109

The concentration and isotopic composition of dissolved inorganic carbon in ground water and submarine ground water discharge: Preliminary results from Onslow Bay, NC and North Inlet, SC - McCorkle, D. C.; Gramling, C. (Conference on Southeast Coastal Ocean Research, 1998)
id: 1313

Controls of chemical and isotopic composition of Lake water, Peten, Guatemala and implications for Holocene climatic variability in Central America. Abstracts with Programs - Martin, J. B.; Rosenmeier, M. F.; Hodell, D. A.; Brenner, M.; Curtis, J. H. (Geological Society of America Annual Meeting, 1998)
id: 140

A Correction for Aberrations in the Woods Hole Recombinator - Schneider, R. J.; von Reden, K. F. (Symposium of North-Eastern Accelerator Personnel, SNEAP 1996, 1998)
id: 1823

A Correction for Aberrations in the Woods Hole Recombinator. Symposium of North-Eastern Accelerator Personnel - Schneider, R. J.; von Reden, K. F. (World Scientific, 1998)
id: 1793

A Correction for Aberrations in the Woods Hole Recombinator. Symposium of North-Eastern Accelerator Personnel - Schneider, Robert J.; McNichol, Ann P.; von Reden, Karl F.; Elder, Kathryn L.; Gagnon, Allan R.; Key, Robert M.; Quay, Paul D. (World Scientific, 1998)
id: 1664

Cultural and climatic history of Coba, a lowland Maya city in Quintana Roo, Mexico - Leyden, B. W.; Brenner, M.; Dahlin, B. H. (Quaternary Research, 1998)
Lake Coba, within the archaeological site of Coba, provides evidence bearing on lowland Maya development, Palynological and geochemical data record multidecadal precipitation cycles from a 8.80-m, >8370-yr lake-sediment sequence terminating on bedrock. Late Classic sedimentation rates are rapid, but an anthropogenically derived colluvium layer is lacking, Initial vegetation was medium semi-deciduous and swamp forest. Forest clearance began 1650 B.C. (Early Preclassic) and maize first occurred at 850 B.C. (Middle Preclassic). Lakeside milpas existed until A.D. 720 (Late Classic) and then were moved from the city center as urbanization intensified and Lake Coba was diked as a reservoir. Coba was at most briefly vacated during the Classic Collapse and was abandoned after A.D. 1240, although some habitation persisted. The paleoecological record matches the archaeological history for Coba, but pervasive disturbance muted the climatic signal, as the Late Classic drought is barely evident. The question whether economic trees were maintained within the city is unresolved, Maize cultivation allowed the Maya to develop a complex society and support a large population, but dependence on maize was ultimately doomed by variable rainfall. Precipitation in extreme years was insufficient to support crops, while native vegetation was not directly affected by drought that devastated Maya agriculture, (C) 1998 University of Washington.
Yz880Times Cited:59Cited References Count:46

Decadal to millennial variability of fluviomarine sedimentation on the northern California continental shelf - Sommerfield, C. K. (EOS, 1998)
id: 1328

Early diagenetic minerals and variables influencing their distributions in two long cores (>40m), Mississippi River delta plain - Bailey, A. M.; Roberts, H. H.; Blackson, J. M. (Journal of Sedimentary Research, 1998)
Two long (>40 m) continuous push cores of sediments from the Mississippi Delta Plain, one at a northern freshwater site and one at a southern marine-influenced site, have provided samples of individual concretions and homogenized bulk samples for a study of early diagenesis. Early (<10,000 y) diagenetic minerals are abundant and include: siderite>pyrite>calcite nearly equal dolomite>vivianite approximately hematite. Siderite formed postburial and contains bands of clastic minerals and accessory diagenetic calcite and dolomite, as well as Ca, Mg, and Mn substituted in the lattice. Values for delta 13 C increase with increasing depth to +11 per mil (PDB) at a depth of 40 m, reflecting the increasing role of methanogenesis with depth. From analyses of bulk samples, pyrite concentrations are higher in organic-rich horizons, do not vary appreciably with depth below one meter when adjusted for organic-carbon control, and are generally higher in the marine-influenced core than at the freshwater site. Conversely, concentrations of siderite are higher in fine-grained siliciclastic horizons, increase with depth to about 20 m, and do not vary with the extent of marine influence in these cores. To a first approximation, distributions of pyrite appear to be controlled by variations in organic carbon concentration in sulfate-sufficient systems that formed through marine incursion into organic-rich layers that cap sediment packages in the deltaic system. Residual pyritic S is sulfate-controlled and lower in the northern, more freshwater organic-rich sediments. Siderite formation appears to be focused in sulfate-deficient systems that formed when siliciclastic wedges that constitute the central parts of sediment packages prograded into lacustrine or bay environments. Low sulfate levels in these horizons in both cores facilitated similar levels of siderite. A juxtaposition of marine versus freshwater diagenetic mineral suites in adjacent horizons resulted from these interactions between physical and geochemical processes.
id: 5

Early results from the WOCE radiocarbon program - Key, Robert M. (TYKKI workshop invited talk, 1998)
id: 312

Early to middle Holocene climatic variability in Central America: evidence from lacustrine sediments in the Peten, Guatemala - Rosenmeier, M. F.; Hodel, D. A.; Martin, J. B.; Brenner, M.; Curtis, J. H. (EOS: Transactions American Geophysical Union, 1998)
id: 1209

Environmental changes since deglaciation in Voyageurs National Park: A summary for park personnel in Holocene Paleoenvironnments in Western Great Lakes Park. Report - Winkler, M. G.; Sanford, P. R. (National Park Service, 1998)
id: 129