Major events in the geological development of the Precambrian Earth - Lowe, D. R. (The Proterozoic Biosphere, 1992)
id: 1584

The National Ocean Sciences Accelerator Mass Spectrometer for Precision C-14 at Woods Hole Oceanographic Institution -- Status and new results - von Reden, K. F.; Jones, G. A.; Schneider, R. J.; McNichol, A. P.; Cohen, G. J. (EOS, Transactions of the American Geophysical Union, 1992)
id: 926

The new National Ocean Sciences Accelerator Mass Spectrometer Facility at Woods Hole Oceanographic Institution-Progress and first results (Proceedings of the 14th International Radiocarbon Conference, 1991) - von Reden, K. F.; Jones, G. A.; Schneider, R. J.; McNichol, A. P.; Cohen, G. J.; Purser, K. H. (Radiocarbon, 1992)
id: 1787

The new National Ocean Sciences Accelerator Mass Spectrometer Facility at Woods Hole Oceanographic Institution - Progress and First Results - von Reden, K. F.; Jones, G. A.; Schneider, R. J.; McNichol, A. P.; Cohen, G. J.; Purser, K. H. (14th International Radiocarbon Conference 1991, 1992)
id: 1618

The occurrence of extralimital boreal mollusks in West Greenland during the Holocene (abstract) - Jones, G. A.; Elder, K. L. (EOS, Transactions, American Geophysical Union, 1992)
id: 1758

Oceanic Crustal Thickness from Seismic Measurements and Rare-Earth Element Inversions - White, R. S.; Mckenzie, D.; Onions, R. K. (Journal of Geophysical Research-Solid Earth, 1992)
Seismic refraction results show that the igneous section of oceanic crust averages 7.1 +/- 0.8 km thick away from anomalous regions such as fracture zones and hot-spots, with extremal bounds of 5.0-8.5 km. Rare earth element inversions of the melt distribution in the mantle source region suggest that sufficient melt is generated under normal oceanic spreading centers to produce an 8.3 +/- 1.5 km thick igneous crust. The difference between the thickness estimates from seismics and from rare earth element inversions is not significant given the uncertainties in the mantle source composition, though it is of the magnitude that would be expected if partial melt fractions of about 1% remain in the mantle and are not extracted to the overlying crust. The inferred igneous thickness increases to 10.3 +/- 1.7 km (seismic measurements) and 10.7 +/- 1.6 km (rare earth element inversions) where spreading centers intersect the regions of hotter than normal mantle surrounding mantle plumes. This is consistent with melt generation by decompression of the hotter mantle as it rises beneath spreading centers. Maximum inferred melt volumes are found on aseismic ridges directly above the central rising cores of mantle plumes, and average 20 +/- 1 and 18 +/- 1 km for seismic profiles and rare earth element inversions respectively. Both seismic measurements and rare earth element inversions show evidence for variable local crustal thinning beneath fracture zones, though some basalts recovered from fracture zones are indistinguishable geochemically from those generated on normal ridge segments away from fracture zones. This is consistent with a model where the melt generated beneath spreading ridges is redistributed to intrusive centers along the ridge axis, from where it may flow laterally along the axis at crustal or surface levels. The melt may sometimes flow into the bathymetric lows associated with fracture zones. Oceanic crust created at very slow-spreading ridges, and in regions adjacent to some continental margins where rifting was initially very slow, exhibits anomalously thin crust from seismic measurements and unusually small amounts of melt generation from rare earth element inversions. We attribute the decreased mantle melting on very slow-spreading ridges to the conductive heat loss that enables the mantle to cool as it rises beneath the rift.
Kd951Times Cited:645Cited References Count:119

Operation of the Woods Hole AMS System - Schneider, R. J. (12th International Conference on the Application of Accelerators in Research and Industry, 1992)
id: 963

Planung, Aufbau und Betrieb der Woods Hole AMS Anlage - von Reden, K. F. (AMS Symposium at Christian-Ausust University, 1992)
id: 1668

Rapid Analysis of Seawater Inorganic Carbon at the National Ocean Sciences AMS Facility: Progress and Preliminary Results (abstract) - McNichol, A. P.; Jones, G. A.; Schneider, R. J.; von Reden, K. F.; Key, R. M. (EOS, Transactions of the American Geophysical Union Meeting, 1992)
id: 1655

Sedimentary Cycling and Environmental-Change in the Late Proterozoic - Evidence from Stable and Radiogenic Isotopes - Derry, L. A.; Kaufman, A. J.; Jacobsen, S. B. (Geochimica Et Cosmochimica Acta, 1992)
We report C, Sr, and O isotopic as well as selected major and trace element data from Late Proterozoic (ca. 900-540 Ma) marine carbonates in three widely separated basins. The isotopic and elemental data are used to evaluate effects of post-depositional alteration of Sr-87/Sr-86 and delta-C-13. Using our present best estimates for unaltered samples, we construct a new delta-C-13-curve for 850 500 Ma marine carbonates using data in this paper and from literature sources. Delta-C-13 values are high (+4 to +8 parts per thousand) during most of the late Riphean (ca. 900-600 Ma) with brief negative excursions likely associated with glacial periods. Similarly, in the Vendian delta-C-13 falls sharply (from late Riphean highs) to < -3 parts per thousand around the Varanger glaciation (ca. 600 Ma), and then returns to high values (+4 to +2 parts per thousand) remaining until the Precambrian-Cambrian boundary where the curve drops to a value of about -1 parts per thousand in Lower Cambrian carbonates. Coupling of the Sr and C isotopic data is used to develop a simple model for evaluating organic carbon (C(org)) burial in Late Proterozoic oceans. These calculations indicate that C(org) burial rates were lower than present-day values during much of the late Riphean, at the same time that erosion rates were low. Excess O2 produced by the burial of C(org) was likely balanced by oxidation of reduced hydrothermal fluids and weathering reactions. Near the time of the Varanger glaciation, C(org) burial rates dropped but quickly recovered and reached a maximum (a factor of 2-4 greater than present day) in Vendian sediments. High C(org) burial rates were probably driven by high sedimentation rates, and possibly high productivity. The high C(org) burial rate likely gave rise to a large flux of O2; high values of delta-S-34 in Late Proterozoic marine sulfates suggest that this O2 flux was not balanced by increased sulfate formation. Further, the Sr-isotopic record indicates that excess O2 was not balanced by oxidation of submarine hydrothermal fluids. Increased oxidative weathering was probably an important sink for O2; nonetheless, we conclude that a significant and rapid increase in atmospheric O2 occurred in the Vendian. These results have important implications for environmental changes during the first appearance of an Ediacaran metazoan fauna.
Hj963Times Cited:357Cited References Count:100

Variability of the delta13C of dissolved inorganic carbon at a site in the North Pacific Ocean - McNichol, A. P.; Druffel, E. R. M. (Geochimica et Cosmochimica Acta, 1992)
id: 1746

AMS radiocarbon results obtained from graphite targets produced at the Woods Hole Oceanographic Institution between 1986 and 1991 - Gagnon, A. R.; Jones, G. A. (14th Internation Radiocarbon Conference, 1991)
id: 957

Carbon cycling in coastal sediments: 2. An investigation of the sources of CO2 to pore water using carbon isotopes - McNichol, A. P.; Druffel, E. R. M.; Lee, C. (Organic Substances and Sediments in Water, Processes and Analytical, 1991)
id: 1743

Carbon cycling in coastal sediments: 2. Estimating remineralization in Buzzards Bay, MA--A comment - Rowe, G. T.; McNichol, A. P. (Geochimica et Cosmochimica, 1991)
id: 1786

Carbon isotope anomalies in carbonates of the Karelian Complex - Yudovich, Y. E.; Makarikhin, V. V.; Medvedev, P. V.; Sukhanov, N. V. (Geochemistry International, 1991)
id: 1607

The compressibility of silicate liquids containing Fe2O3 and the effect of composition, temperature, oxygen fugacity and pressure on their redox states - Kress, V. C.; Carmichael, I. S. E. (Contributions to Mineralogy and Petrology, 1991)
id: 1582

Illumination of a black box: Gas composition changes during graphite target preparation for AMS (Proceedings of the 14th International Radiocarbon Conference, 1991) - McNichol, A. P.; Gagnon, A. R.; Jones, G. A.; Osborne, E. A. (Radiocarbon, 1991)
id: 1745

Measuring 14C in seawater by Accelerator Mass Spectrometry - McNichol, A. P.; Jones, G. A. (WOCE Hydrographic Programme Office/Woods Hole Oceanographic Institution, 1991)
id: 1610

A Model for Atmospheric Co2 over Phanerozoic Time - Berner, R. A. (American Journal of Science, 1991)
A new model has been constructed for calculating the level of atmospheric CO2 over Phanerozoic time which is much simpler mathematically than the BLAG model, but more complex geologically and biologically. Mathematical simplification comes about by following the cycle of carbon only, lumping all carbonate minerals together, combining the ocean and atmosphere into one reservoir, and calculating atmospheric CO2 level as a series of successive ocean-atmosphere steady states. The isotope mass balance model of Garrels and Lerman (1984) is expanded to include the effect of changing area, elevation, and position of the continents as well as the evolution of land plants as they affect weathering rate, and changes in seafloor area generation rate and the relative importance of deep sea versus shallow platform carbonate deposition as they affect global degassing. Atmospheric CO2 level is calculated from a weathering feedback function for silicates which varies with time as vascular land plants arise and evolve.Results suggest that there has been a notable pattern of varying atmospheric CO2 level over the past 570 my with high levels during the Mesozoic and early Paleozoic and low levels during the Permo-Carboniferous and late Cenozoic. Sensitivity analysis shows that, within reasonable limits of the principal governing parameters, this qualitative trend of varying CO2 is relatively insensitive to the actual values chosen for these parameters. Causes of the CO2 variation are multiple, and no single geological or biological process can be called upon to explain all CO2 variation for all time.The calculated trend of CO2 over time agrees well with independent estimations of paleoclimates. Thus, the greenhouse theory of paleoclimate on a long geological time scale is supported by the results of the present study.
Ff648Times Cited:412Cited References Count:61

The optimization of target production for AMS - McNichol, A. P.; Gagnon, A. R.; Jones, G. A.; Schneider, R. J.; von Reden, K. F. (14th International Radiocarbon Conference, 1991)
id: 922

Quantification and characterization of porewater organic colloids - Chin, Y. P.; McNichol, A. P.; Gschwend, P. M. (Organic Substances and Sediments in Water. Processes and Analytical, 1991)
id: 1744

Radiocarbon - Key, R. M. (WOCE Hydrographic Operations and Methods Manual, 1991)
id: 321

Response of G. quinqueloba to Hypsithermal warming in the Norwegian-Greenland Sea (abstract) - Jones, G. A.; Elder, K. L. (EOS, Transactions, American Geophysical Union, 1991)
id: 1759

Response of the Norwegian-Greenland Sea to Mid-Holocen warming (abstract) - Jones, G. A.; Elder, K. L. (20th Arctic Workshoip, INSTAAR, 1991)
id: 1760

A triple-isotope injector for Accelerator Mass Spectrometry: Conference Record of the 1991 IEEE Particle Accelerator Conference - Schneider, R. J.; von Reden, K. F.; Purser, K. H. (IEEE Particle Accelerator Conference, 1991)
id: 923