Stable carbon isotope compositions and concentrations of biphytanes from IODP Hole 311-U1327C and 311-U1328B@en

We have investigated the distributions and carbon isotopic compositions of archaeal membrane lipids in gas-hydrate-bearing sediments collected from the northern Cascadia Margin offshore from Vancouver Island (Sites U1327 and U1328) by the R/V JOIDES Resolution during IODP Expedition 311. Archaeal lipid biomarkers, including glycerol dialkyl glycerol tetraethers (GDGTs), tend to become abundant below 100 mbsf (meters below sea floor). Tricyclic biphytane (BP[3]; which is a robust biomarker derived from GDGT), crenarchaeol, and other BPs exhibit d13C values of ca. -20 per mil, and become abundant between 130 and 230 mbsf at Site U1328. In this depth range, concentrations of ammonium and phosphate in interstitial waters also increase, suggesting that a larger population and higher activity of heterotrophic community consisting of crenarchaeota and other archaea decompose the sedimentary organic matter, thereby liberating ammonium and phosphate. Such crenarchaeotic activity can produce other metabolic products such as molecular hydrogen by fermentation of organic matter during diagenesis. Furthermore, near the organic matter decomposition zone (130 to 230 mbsf), a probable methanogen biomarker (13C-depleted BP[1] with d13C values as low as -48.8 per mil) becomes abundant, indicating that methanogens utilize these diagenetic products. The molecular and isotopic distributions of archaeal lipid biomarkers indicate that the archaeal community plays an important role in the biogeochemical cycles of deep-sea sediments, including both methanogenesis and nutrient recycling.本研究针对温哥华岛近海卡斯卡迪亚北部边缘（站位U1327与U1328）的含天然气水合物沉积物中的古菌膜脂分布与碳同位素组成展开分析，样品由R/V JOIDES Resolution号科考船在国际大洋发现计划（IODP）311航次中采集获取。包括甘油二烷基甘油四醚（glycerol dialkyl glycerol tetraethers, GDGTs）在内的古菌脂类生物标志物，在海底以下100米（meters below sea floor, 简称mbsf）深度以深的沉积物中丰度通常显著升高。三环植烷（BP[3]，一种源自GDGTs的稳定生物标志物）、古菌醇（crenarchaeol）以及其他BPs的δ¹³C值约为-20‰，在U1328站位130至230 mbsf深度区间内丰度明显提升。该深度区间内，间隙水中的铵盐与磷酸盐浓度同样升高，表明由泉古菌（crenarchaeota）与其他古菌组成的异养群落种群规模更大、活性更强，可降解沉积物中的有机质并释放铵盐与磷酸盐。此类泉古菌代谢活动可在成岩作用过程中通过有机质发酵产生分子氢等其他代谢产物。此外，在有机质降解带（130至230 mbsf）附近，一种潜在的产甲烷菌生物标志物（δ¹³C值低至-48.8‰的¹³C贫化BP[1]）丰度显著升高，表明产甲烷菌可利用这些成岩作用产物。古菌脂类生物标志物的分子与同位素分布特征表明，古菌群落在深海沉积物的生物地球化学循环中发挥着关键作用，涵盖产甲烷作用与营养盐循环两大过程。