Abstract：
The Black Sea is a permanently anoxic, marine basin serving as model system for the deposition of organic-rich sediments in a highly stratified ocean. In such systems, archaeal lipids are widely used as paleoceanographic and biogeochemical proxies; however, the diverse planktonic and benthic sources as well as their potentially distinct diagenetic fate may complicate their application. To track the flux of archaeal lipids and to constrain their sources and turnover, we quantitatively examined the distributions and stable carbon isotopic compositions (δ13 C) of intact polar lipids (IPLs) and core lipids (CLs) from the upper oxic water column into the underlying sediments, reaching deposits from the last glacial. The distribution of IPLs responded more sensitively to the geochemical zonation than the CLs, with the latter being governed by the deposition from the chemocline. The isotopic composition of archaeal lipids indicates CLs and IPLs in the deep anoxic water column have negligible influence on the sedimentary pool. Archaeol substitutes tetraether lipids as the most abundant IPL in the deep anoxic water column and the lacustrine methanic zone. Its elevated IPL/CL ratios and negative δ13 C values indicate active methane metabolism. Sedimentary CL- and IPL-crenarchaeol were exclusively derived from the water column, as indicated by non-variable δ13 C values that are identical to those in the chemocline and by the low BIT (branched isoprenoid tetraether index). By contrast, in situ production accounts on average for 22% of the sedimentary IPL-GDGT-0 (glycerol dibiphytanyl glycerol tetraether) based on isotopic mass balance using the fermentation product lactate as an endmember for the dissolved substrate pool. Despite the structural similarity, glycosidic crenarchaeol appears to be more recalcitrant in comparison to its non-cycloalkylated counterpart GDGT-0, as indicated by its consistently higher IPL/CL ratio in sediments. The higher TEX86 , CCaT, and GDGT-2/-3 values in glacial sediments could plausibly result from selective turnover of archaeal lipids and/or an archaeal ecology shift during the transition from the glacial lacustrine to the Holocene marine setting. Our in-depth molecular-isotopic examination of archaeal core and intact polar lipids provided new constraints on the sources and fate of archaeal lipids and their applicability in paleoceanographic and biogeochemical studies.
摘要：
黑海是永久缺氧的地方，海洋盆地是在高度分层的海洋中沉积富含有机物的沉积物的模型系统。在这样的系统中,古细菌脂质被广泛用作古海洋学和生物地球化学代理；然而，不同的浮游和底栖来源以及它们潜在的独特成岩命运可能会使它们的应用复杂化。为了跟踪古细菌脂质的流动并限制其来源和周转，我们定量检查了完整的极性脂质（IPL）和核心脂质（CLs）的分布和稳定的碳同位素组成（δ13C）从上含氧水柱进入下面的沉积物，到达最后冰川的沉积物。IPL的分布对地球化学分区的响应比CLs更敏感，后者受化学跃层沉积的控制。古细菌脂质的同位素组成表明，深缺氧水柱中的CLs和IPL对沉积池的影响可以忽略不计。古菌醇取代四醚脂质成为深缺氧水柱和湖相甲烷带中最丰富的IPL。其升高的IPL/CL比率和负的δ13C值表明活跃的甲烷代谢。沉积的CL-和IPL-古菌完全来自水柱，如与chemocline中相同的非可变δ13C值和低BIT（支链类异戊二烯四醚指数）所示。相比之下,基于同位素质量平衡，原位生产平均占沉积的IPL-GDGT-0（甘油二二二联苯酰甘油四醚）的22％，使用发酵产物乳酸作为溶解底物池的末端成员。尽管结构相似,与非环烷基化的对应物GDGT-0相比，糖苷类cr古醇似乎更顽固，其在沉积物中始终较高的IPL/CL比表明了这一点。TEX86越高,CCaT,冰川沉积物中的GDGT-2/-3值可能是由于从冰川湖相到全新世海洋环境过渡期间古细菌脂质的选择性周转和/或古细菌生态转变所致。我们对古细菌核心和完整极性脂质的深入分子同位素检查为古细菌脂质的来源和命运及其在古海洋学和生物地球化学研究中的适用性提供了新的限制。
