Production and sequestration of dissolved organic carbon in Antarctic areas with deep-water formation

Dissolved organic matter (DOM) in the oceans contains about the same amount of carbon as the global biomass or atmospheric CO₂. Although it is clear that DOM exhibits an average age of several thousand years, sources and preservation mechanisms of DOM remain a missing link in models of global elemental cycles. The polar oceans are a primary source of DOM to the deep ocean because surface waters efficiently convect down to the oceans’ bottom. Deepwater formation is directly linked to sea-ice formation, when salt is rejected and dense brine enriched waters penetrate the deep ocean. Sea ice is one of the most productive marine environments, and DOM concentrations in the brine are among the highest measured in marine waters. The molecular characteristics of DOM in sea ice are widely unknown, and it is not clear whether sea-ice-derived DOM is persistent enough to survive downward transport. Based on preliminary data we roughly estimate that ~50 Tg of dissolved organic carbon (DOC) may be exported annually from the surface Weddell Sea into the abyssal ocean.



Figure 1.'Green ice'

The main objective of this project is to investigate the formation of persistent DOM in sea ice, to chemically characterize this DOM and to quantify its transport to the deep Weddell Sea. Molecular characterization of refractory DOM will be carried out using ultrahigh resolution mass spectrometry. Our results will be integrated into physical models of regional ocean circulation, in order to obtain a detailed and quantitative biogeochemical model for DOC cycling in the Weddell Sea.



Figure 2. Conceptual model of water and dissolved organic carbon circulation in the Southern Ocean. Labile ice-algal derived DOC is mineralized in ventilated surface waters. Semi-labile and refractory compounds can be exported via deep- and bottom water formation into the abyssal ocean. Mineralization products and refractory compounds are trapped there for hundreds to thousands of years, respectively. Adapted after SPEER et al., 2000.

Scientists

Boris Koch
Gerhard Kattner
Oliver Lechtenfeld

Alfred Wegener Institute for Polar and Marine Research

Research areas

Circum antarctic

Publications

Lechtenfeld OJ, Koch BP, Geibert W, Kattner G, (submitted). Inorganics in organics: quantitative speciation of organic phosphorus, organic sufur and uranium in natural organic matter. Analytical Chemistry.

Koch BP, Ludwichowski KU, Kattner G, Dittmar T, Witt M, 2008. Advanced characterization of marine dissolved organic matter by combining reversed-phase liquid chromatography and FT-ICR-MS. Marine Chemistry 111, 233-241.

Koch BP, Witt M, Engbrodt R, Dittmar T, Kattner G, 2005. Molecular formulae of marine and terrigenous dissolved organic matter detected by Electrospray Ionisation Fourier Transform Ion Cyclotron Resonance Mass Spectrometry. Geochimica et Cosmochimica Acta 69, 3299-3308.

Koch BP, Witt M, Kattner, G, Dittmar T, 2007. Fundamentals of molecular formula assignment to ultrahigh resolution mass data of natural organic matter. Analytical Chemistry 79, 1758-1763.

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Research funding organisation

German Research Foundation

Project number: KO 2164/8-1
Funding period: 01.09.2008 - 31.08.2010