80 research outputs found

    Honorable Chief Judge Harold Barefoot Sanders, N.D. Tex., The

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    Southwest Atlantic water mass evolution during the last deglaciation

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    The rise in atmospheric CO2 during Heinrich Stadial 1 (HS1; 14.5–17.5 kyr B.P.) may have been driven by the release of carbon from the abyssal ocean. Model simulations suggest that wind‐driven upwelling in the Southern Ocean can liberate 13C‐depleted carbon from the abyss, causing atmospheric CO2 to increase and the δ13C of CO2 to decrease. One prediction of the Southern Ocean hypothesis is that water mass tracers in the deep South Atlantic should register a circulation response early in the deglaciation. Here we test this idea using a depth transect of 12 cores from the Brazil Margin. We show that records below 2300 m remained 13C‐depleted until 15 kyr B.P. or later, indicating that the abyssal South Atlantic was an unlikely source of light carbon to the atmosphere during HS1. Benthic δ18O results are consistent with abyssal South Atlantic isolation until 15 kyr B.P., in contrast to shallower sites. The depth dependent timing of the δ18O signal suggests that correcting δ18O for ice volume is problematic on glacial terminations. New data from 2700 to 3000 m show that the deep SW Atlantic was isotopically distinct from the abyss during HS1. As a result, we find that mid‐depth δ13C minima were most likely driven by an abrupt drop in δ13C of northern component water. Low δ13C at the Brazil Margin also coincided with an ~80‰ decrease in Δ14C. Our results are consistent with a weakening of the Atlantic meridional overturning circulation and point toward a northern hemisphere trigger for the initial rise in atmospheric CO2 during HS1.Key PointsDeep SW Atlantic was unlikely source of light carbon to atmosphere during HS1Mid‐depth isotopic anomalies due to change in northern component waterNorthern component water had robust influence in South Atlantic during HS1Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/111970/1/palo20190.pd

    Does sea level influence mid-ocean ridge magmatism on Milankovitch timescales?

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    Magma production at mid-ocean ridges is driven by seafloor spreading and decompression melting of the upper mantle. In the special case of Iceland, mantle melting may have been amplified by ice sheet retreat during the last deglaciation, yielding anomalously high rates of subaerial volcanism. For the remainder of the global mid-ocean ridge system, the ocean may play an analogous role, with lowering of sea level during glacial maxima producing greater magma flux to ridge crests. Here we show that the mantle decompression rate associated with changes in sea level is a substantial fraction of that from plate spreading. Modeled peaks in magma flux occur after sea level drops rapidly, including the Marine Isotope Stage (MIS) 5/4 and 3/2 transitions. The minimum in simulated flux occurs during the mid-Holocene, due to the rapid sea level rise at the MIS 2/1 boundary. The model results are highly sensitive to melt migration rate; rates of ~1 m/yr produce small signals, while those >5 m/yr yield substantial anomalies. In the latter case, sea level-driven magma flux varies by 15–100% relative to the long-term average, with the largest effect occurring at slow-spreading ridges. We suggest that sedimentary time series of hydrothermal particle flux, oceanic Os isotopic ratio, and oceanic radiocarbon may serve as proxies for magma-flux variations at mid-ocean ridges. Although well-dated records are rare, preliminary data from the Pacific and Atlantic suggest hydrothermal metal flux was elevated during MIS 2 and 4, broadly consistent with our modeling results

    Intravenous Iron as an Alternative to Blood Transfusion in Late Pregnancy

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    Vehicle Cost Reduction Through Cooling System Optimization

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