Published pore water and solid phase data from cores GeoB15105-1, GeoB15105-2, GeoB15105-4@en

An understanding of how the coupled cycles of carbon, iron and sulfur in sediments respond to environmental change throughout Earth history requires the reconstruction of biogeochemical processes over a range of spatial and temporal scales. In this study, sediment cores from the southwestern Black Sea were analyzed to gain insight into past changes in biogeochemical processes with particular focus on the cycling of dissolved organic carbon (DOC). The sediment consists of Late Pleistocene deposits of iron oxide-rich and organic-poor lacustrine sediments, a Holocene sapropel layer deposited after the inflow of saline Mediterranean seawater about 9300 yr BP, and overlying recent marine sediments. The porewaters displayed high concentrations of DOC, acetate, dissolved iron and an extended depth interval over which sulfate and methane were both present. The historical fluctuations of the fluxes of carbon, sulfur and iron species at the seafloor that led to these present-day geochemical profiles, and which cannot be easily interpreted from the measured data alone, were hindcasted with a reaction-transport model. The model suggests that the inflow of Mediterranean seawater impacted the rain rate and reactivity of organic matter reaching the sediments, which shifted the sedimentary redox regimes throughout the Holocene that now are reflected on different lithology units. Organic matter in the sapropel layer is apparently the main source of modern-day accumulations of DOC and acetate, both of which probably sustained subsurface microbial activity throughout the post-glacial period. The ratio between DOC and dissolved inorganic carbon (DIC) flux to the bottom water decreased from ∼40 % before the inflow of Mediterranean water to ∼2 % at the present day. We suggest that the coexistence of methanogenesis and sulfate reduction was associated with sulfate-reducing bacteria and methanogens sharing common substrates of acetate and lactate and utilizing non-competitive substrates such as methylated compounds in the sapropel layer and in the bottom of modern marine deposits. Intense sulfur and iron cycling mainly took place in the organic-poor freshwater deposits, today characterized by high concentrations of dissolved iron and methane. In contrast to previous studies in similar environments, anaerobic oxidation of methane coupled to the reduction of ferric iron was negligible. […]若要阐明沉积物中碳、铁与硫的耦合循环如何响应地球历史全周期的环境变化，需在多时空尺度下重建其生物地球化学过程。本研究对黑海西南部的沉积物岩芯进行分析，以揭示过去生物地球化学过程的演化规律，重点聚焦溶解有机碳（dissolved organic carbon, DOC）的循环过程。该沉积物序列包含三类沉积单元：富含氧化铁且贫有机质的晚更新世湖相沉积物；约9300年前（yr BP）地中海咸水入侵后形成的全新世腐泥层；以及上覆的近代海相沉积物。孔隙水中DOC、乙酸盐、溶解铁浓度较高，且存在硫酸盐与甲烷共存的延伸深度区间。造就现今地球化学剖面的海底碳、硫、铁物种通量历史波动，仅依靠实测数据难以直接阐释，本研究借助反应-输运模型（reaction-transport model）开展了回算模拟。模型结果显示，地中海海水的入侵改变了抵达沉积物的有机质沉降通量与反应活性，进而重塑了整个全新世的沉积物氧化还原环境，这一环境变化如今可通过不同岩性单元体现出来。腐泥层中的有机质显然是现今DOC与乙酸盐富集的主要来源，二者或为冰期后阶段的地下微生物活动提供了能量支撑。输入到底层水体的DOC与溶解无机碳（dissolved inorganic carbon, DIC）通量之比，已从地中海海水入侵前的约40%降至现今的约2%。我们认为，产甲烷作用与硫酸盐还原作用的共存，与两类微生物的代谢活动密切相关：硫酸盐还原菌与产甲烷菌共享乙酸盐、乳酸盐等共同底物，同时可利用腐泥层及近代海相沉积物底部的甲基化化合物等非竞争性底物。强烈的硫、铁循环主要发生在贫有机质的淡水沉积物中，这类沉积物现今以高浓度溶解铁与甲烷为典型特征。与同类环境的既往研究不同，耦合三价铁还原的厌氧甲烷氧化（anaerobic oxidation of methane）作用可忽略不计。[…]