Inorganic geochemistry of Pliocene-Pleistocene sediments from the Bering Sea (IODP Expedition 323) - Studying feedbacks of productivity, nutrient availability, and redox conditions in the northernmost Pacific
Final Report Abstract
The DFG/IODP Research Fellowship carried out at Newcastle University was very successful. We created the first inorganic geochemical record for the Pliocene-Pleistocene of the Bering Sea, highlighting the development of primary productivity and nutrient cycling in this marginal sub-Arctic basin. For the first time, we could show that, in contrast to the open North Pacific, the onset of the NHG around 2.75 million years ago did not result in a dramatic decrease in biogenic opal productivity in the Bering Sea. In fact, by combining sediment and pore water geochemical data and reaction-transport modelling, we reconstructed that the onset of the NHG was followed by a drastic increase in opal productivity and associated carbon burial in the Bering Sea, most probably as a result of nutrient leakage from the increasingly stratified open North Pacific. This pulse of reactive organic material to the sea floor resulted in intense diagenetic processes, and in the overprint of various paleoceanographic proxy records (e.g., biogenic barite, magnetic susceptibility). Our study also revealed surprising new insights into the biogeochemical cycling and burial of phosphorus in the Bering Sea. Most notably, we identified a substantial terrigenous component of the supposedly authigenic carbonate fluorapatite record, and showed that biogenic opal-bound P is a significant component of the sedimentary P pool in this setting. These findings have important implications for our understanding of the marine P cycle on a global scale. Vast areas of the global ocean recieve carbonate fluorapatite from detrital sources by wind or rivers, and/or biogenic opal-bound P from diatom-dominated ocean regions. Further studies into these P fractions will definitely be required to get an improved understanding of the biogeochemical cycling of P in the oceans, and its burial into marine sediments, on glacial-interglacial timescales.
Publications
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Coupled organic and inorganic carbon cycling in the deep subseafloor sediment of the northeastern Bering Sea slope (lODP Exp. 323). Chemical Geology 284, 251-261
L.M. Wehrmann, N. Risgaard-Petersen, H.N. Schrum, E.A. Walsh, Y. Huh, M. Ikehara, C. Pierre, S. D'Hondt, T.G. Ferdelman, A.C. Ravelo, K. Takahashi, C. Alvaerz Zarikian, lODP Expedition 323 Scientific Party (including C. März)
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(2013): Nutrient leakage from the North Pacific to the Bering Sea (lODP Site U1341) following the onset of Northern Hemispheric Glaciation? Paleoceanography 28, 1-11
C. März, B. Schnetger, H.-J. Brumsack
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(2013): The evolution of early diagenetic signals in Bering Sea subseafloor sediments in response to varying organic carbon deposition over the last 4.3 Ma. Geochimica et Cosmochimia Acta 109, 175-196
L.M. Wehrmann, S. Arndt, C. März, T.G. Ferdelman, B. Brunner
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Phosphorus burial and diagenesis in the Bering Sea (Bowers Ridge, lODP Site U1341): Perspectives on the marine P cycle. Chemical Geology, Vol. 363. 2014, pp. 270–282.
C. März, S.W. Poulton, T. Wagner, B. Schnetger, H.-J. Brumsack
