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Carbon isotopic fractionation (epsilon p) of C37-alkenones in deep sea sediments: Its potential as a paleonutrient proxy

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Schulte, S. , Benthien, A. , Müller, P. and Rühlemann, C. (2004): Carbon isotopic fractionation (epsilon p) of C37-alkenones in deep sea sediments: Its potential as a paleonutrient proxy , Paleoceanography, 19, PA1011 . doi: 10.1029/2002PA000811
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Abstract:

We compared ocean atlas values of surface water [PO4] and [CO2(aq)] against the carbon isotopic fractionation (epsilon p) of alkenones obtained from surface sediments of the South Atlantic and the central Pacific (Pacific data are from Pagani et al. [2002]). We observed a positive correlation between epsilon p and 1/[CO2(aq)], which is opposite of what would be expected if the concentration of CO2(aq) were the major factor controlling the carbon isotopic fractionation of C37:2 alkenones. Instead, we found inverse relationships between ep and [PO4] for the two ocean basins (for the Atlantic, epsilon p = -4.6*[PO4] + 15.1, R = 0.76; for the Pacific, epsilon p = -4.1*[PO4] + 13.7, R = 0.64), suggesting that epsilon p is predominantly controlled by growth rate, which in turn is related to nutrient concentration. The similarity of the slopes implies that a general relationship between both parameters may exist. Using the relationship obtained from the South Atlantic, we estimated surface water nutrient concentrations for the past 200,000 years from a deep-sea sediment core recovered off Angola. Low epsilon p values, indicating high nutrient concentrations, coincide with high contents of total organic carbon and C37 alkenones, low surface water temperatures, and decreased bulk d15N values, suggesting an increased upwelling of nutrient-rich cool subsurface waters as the main cause for the observed epsilon p decrease.

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