Production and sequestration of dissolved organic carbon in the Weddel Sea: Tracing deep-water formation with molecular methods

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Dissolved organic matter (DOM) in the deep oceans contains about the same amount of carbon as the global biomass or atmospheric CO2. Sources and preservation mechanisms of DOM remain a missing link in models of global elemental cycles. We hypothesize that the Weddell Sea is a primary source of DOM in the deep ocean because sea-ice derived DOM from surface waters can efficiently convect down to the oceans’ bottom. The molecular characteristics of DOM in sea ice are widely unknown, and it is not clear whether sea-icederived DOM is persistent enough to survive downward transport. Based on preliminary data we roughly estimate that ~50-75 Tg of dissolved organic carbon (DOC) may be exported annually into the deep Weddell Sea. The main objective of this project is to investigate the formation of persistent DOM, to chemically characterize this DOM and to quantify its transport to the deep Weddell Sea. In the third year of our project the analytical results will be evaluated using multivariate statistical methods and related to results from oceanographic models for bottom-water formation in the Weddell Sea and from the distribution of persistent chlorofuorocarbon (CFC) markers. Since the first results support the biogeochemical process of a “DOM-pump” we aim at a first quantitative estimate of this CO² sink as a central aim of the third year of this project.