Beschreibung: Dissolved organic matter (DOM) in marine sediment pore waters derives largely from decomposition of particulate organic matter and its composition is influenced by various biogeochemical and oceanographic processes in yet undetermined ways. Here, we determine the molecular inventory of pore water DOM in marine sediments of contrasting depositional regimes with ultrahigh-resolution mass spectrometry and complementary bulk chemical analyses in order to elucidate the factors that shape DOM composition. Our sample sets from the Mediterranean, Marmara and Black Seas covered different sediment depths, ages and a range of marine environments with different (i) organic matter sources, (ii) balances of organic matter production and preservation, and (iii) geochemical conditions in sediment and water column including anoxic, sulfidic and hypersaline conditions. Pore water DOM had a higher molecular formula richness than overlying water with up to 11,295 vs. 2114 different molecular formulas in the mass range of 299–600 Da and covered a broader range of element ratios (H/C = 0.35–2.19, O/C = 0.03–1.19 vs. H/C = 0.56–2.13, O/C = 0.15–1.14). Formula richness was independent of concentrations of DOC and TOC. Near-surface pore water DOM was more similar to water column DOM than to deep pore water DOM from the same core with respect to formula richness and the molecular composition, suggesting exchange at the sediment–water interface. The DOM composition in the deeper sediments was controlled by organic matter source, selective decomposition of specific DOM fractions and early diagenetic molecule transformations. Compounds in pelagic sediment pore waters were predominantly highly unsaturated and N-bearing formulas, whereas oxygen-rich CHO-formulas and aromatic compounds were more abundant in pore water DOM from terrigenous sediments. The increase of S-bearing molecular formulas in the water column and pore waters of the Black Sea and the Mediterranean Discovery Basin was consistent with elevated HS- concentrations reflecting the incorporation of sulfur into biomolecules during early diagenesis. Sulfurization resulted in an increased average molecular mass of DOM and higher formula richness (up to 5899 formulas per sample). In sediments from the methanogenic zone in the Black Sea, the DOM pool was distinctly more reduced than overlying sediments from the sulfate-reducing zone. Bottom and pore water DOM from the Discovery Basin contained the highest abundances of aliphatic compounds in the entire dataset; a large fraction of abundant N-bearing formulas possibly represented peptide and nucleotide formulas suggesting preservation of these molecules in the life inhibiting environment of the Discovery Basin. Our unique data set provides the basis for a comprehensive understanding of the molecular signatures in pore water DOM and the turnover of sedimentary organic matter in marine sediments.

Beschreibung: We have investigated the delivery of terrestrial organic carbon (OC) to the Amazon shelf and deep sea fan based on soil marker bacteriohopanepolyols (BHPs; adenosylhopane and related compounds) and branched glycerol dialkyl glycerol tetraethers (GDGTs), as well as on 14C dating of bulk organic matter. The microbial biomarker records show persistent burial of terrestrial OC, evidenced by almost constant and high BIT values (0.6) and soil marker BHP concentration [80–230 μg/g TOC (total OC)] on the late Holocene shelf and even higher BIT values (0.8–0.9), but lower and more variable soil-marker BHP concentration (40–100 μg/g TOC), on the past glacial deep sea fan. Radiocarbon data show that OC on the shelf is 3–4 kyr older than corresponding bivalve shells, emphasizing the presence of old carbon in this setting. We observe comparable and unexpectedly invariant BHP composition in both marine sediment records, with a remarkably high relative abundance of C-35 amino BHPs including compounds specific for aerobic methane oxidation on the shelf (avg. 50% of all BHPs) and the fan (avg. 40%). Notably, these marine BHP signatures are strikingly similar to those of a methane-producing floodplain area in one of the Amazonian wetland (várzea) regions. The observation indicates that BHPs in the marine sediments may have initially been produced within wetland regions of the Amazon basin and may therefore document persistent export from terrestrial wetland regions, with subsequent re-working in the marine environment, both during recent and past glacial climate conditions.