Trace Element Proxies of Carbon Flux and Bottom Water Oxygen Concentration

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9401138 ARCHER Uranium is removed from the ocean by precipitation in chemically- reducing sediments. Here, we present preliminary results from the subantarctic South Atlantic showing high rates of authigenic U deposition in glacial-age sediments. There is no analog for such high rates of authigenic U deposition in modern pelagic sediments. The observed burial of uranium implies that one of two conditions existed in the glacial ocean: either greatly-reduced oxygen content of Circumpolar Deep Water (compared to modern levels in excess of 200 micromolar), or greatly-enhanced biological productivity of subantarctic surface waters. Either condition would represent a significant feature of the carbon cycle in the glacial ocean. Our hypothesis is that subantarctic sediments hold the key record which will lead to the long-sought explanation for lower atmospheric CO2 concentrations during the ice ages. Our goals are not only to test this hypothesis, but to derive quantitative information about ice-age ocean productivity and deep- sea O2 content.