Oral Session 10 | Thursday, October 6, 15:20–15:40 | Abstract 601

Pore-water dissolved organic matter in the oxygen limited Baltic Sea zones: Accessing diagenetic changes and release by means of optical properties and size exclusion chromatography

Around 10 % of remineralized organic carbon in sediments may accumulate in dissolved form (DOC). The efflux of dissolved organic matter (DOM) into overlying waters may serve as an important escape mechanism for carbon from sediments. Although DOM in sediments is commonly assumed to be recalcitrant a few recent studies suggested that sediment pore waters may serve as a source of bioavailable DOM to the overlying water column, which may stimulate microbial activity in the near-bottom waters. In this study, we combine the measurements of DOC and DOM optical properties, such as chromophoric (CDOM) and fluorescent (FDOM) DOM, with size exclusion chromatography to trace diagenetic changes of DOM in the sediment pore waters and to evaluate the DOM release to the overlying bottom water in three southern Baltic Sea Deeps: Bornholm, Gdansk, and Gotland, affected by sub- and anoxia. We found strong spatial differences in DOM efflux to the water column, as well as in optical properties accumulation with sediment depth among the three deeps, caused by different diagenetic stages of the organic matter in the Deeps. Interestingly, the molecular weight of DOM was not altered significantly with sediment depth (i.e. during later diagenetic stages) and among the three Deeps. Our results suggest that DOM is likely to undergo structural recombination rather than molecular decomposition during aging.

Alexandra Loginova, Institute of Oceanology of Polish Academy of Sciences, 0000-0003-2805-7386

Urban Wünsch, Technical University of Denmark

Piotr Kowalczuk, Institute of Oceanology Polish Academy of Sciences

Monika Zablocka, Institute of Oceanology Polish Academy of Sciences

Marta Borecka, Institute of Oceanology Polish Academy of Sciences

Aleksandra Winogradow, Institute of Oceanology Polish Academy of Sciences

Colin Stedmon, Technical University of Denmark

Beata Szymszycha, Institute of Oceanology Polish Academy of Sciences

Karol Kulinski, Institute of Oceanology Polish Academy of Sciences

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