Bacteriohopanepolyols in the Yenisei River and its outflow in the Kara Sea, SPM and sediments

Bacteriohopanepolyols (BHPs) are ubiquitous bacterial membrane lipids, encountered in soils, river and marine suspended particulate matter (SPM) and sediments. Their abundance and distribution provides a direct means to identify bacterial inputs and can be used to trace soil-derived bacterial organic matter (OM) and in some cases the presence of bacterial groups and their activities in aquatic systems. We have studied the BHP distribution in the SPM of a major Siberian River (Yenisei River) that crosses a large latitudinal gradient, draining a large part of Mongolia and Siberian Russia. The Yenisei River is the main river to flow into the Kara Sea, a shelf sea of the Arctic Ocean. We show that the BHP distribution and concentration of SPM and surface sediments of the Yenisei Outflow in the Kara Sea allow to trace soil-marker BHPs and evaluate the performance of the R'soil index, a proxy developed to trace bacterial soil-derived OM. Soil-marker BHPs are present in the Yenisei River, and their concentration decreases from the Yenisei River Outflow into the offshore marine sediments. The R'soil correlates well with an independent proxy for bacterial OM, the BIT-index (r**2 = 0.82) and has a moderate correlation with the d13Corg values, a bulk OM proxy for terrigenous input (r**2 = 0.44). Consequently, the R'soil index performs well in the Kara Sea, strengthening its application for tracing bacterial OM in the Arctic Ocean, both in modern and downcore sediments. Furthermore, a suite of BHPs that are characteristic for methanotrophic bacteria, i.e. 35-aminobacteriohopane-30,31,32,33,34-pentol (aminopentol) and 35-aminobacteriohopane-31,32,33,34-tetrol (aminotetrol), is encountered in the Yenisei Outflow sediments. These components are partly sourced from terrigenous sources, but are likely also produced in-situ in the marine sediments. The distribution of the pentafunctionalized cyclitol ether BHP in the marine systems is noteworthy, and indicates that it can possibly be applied as a marker for cyanobacterial biomass in marine sediments.

细菌藿烷多醇（Bacteriohopanepolyols, BHPs）是一类广泛分布的细菌细胞膜脂质，见于土壤、河流与海洋悬浮颗粒物（suspended particulate matter, SPM）及沉积物中。其丰度与分布特征可为识别细菌输入来源提供直接手段，可用于示踪土壤来源的细菌有机质（organic matter, OM），在部分情形下还可指示水生系统中的细菌类群及其活动。我们针对横跨巨大纬度梯度、流域覆盖蒙古国与俄罗斯西伯利亚大部的西伯利亚大型河流——叶尼塞河的悬浮颗粒物中BHP的分布开展了研究。叶尼塞河是注入北冰洋陆架海喀拉海的主要入海河流。研究表明，喀拉海叶尼塞河入海口区域的悬浮颗粒物与表层沉积物的BHP分布及浓度特征，可用于示踪土壤标志性BHP，并评估R'soil指数的示踪效能——该指数是专为追踪土壤来源细菌有机质而开发的地球化学代用指标。土壤标志性BHP在叶尼塞河水体中广泛存在，其浓度从叶尼塞河入海口向远海沉积物逐渐降低。R'soil指数与独立的细菌有机质代用指标BIT指数相关性良好（决定系数r²=0.82），与表征陆源输入的总有机质代用指标有机碳稳定同位素δ¹³C_org也存在中等程度相关性（r²=0.44）。综上，R'soil指数在喀拉海区域表现优异，进一步支撑了其在北冰洋现代沉积物与岩芯沉积物中示踪细菌有机质的应用潜力。此外，在叶尼塞河入海口沉积物中检出了一类以甲烷氧化细菌为特征的BHP组分，即35-氨基细菌藿烷-30,31,32,33,34-五醇（aminopentol，氨基五醇）与35-氨基细菌藿烷-31,32,33,34-四醇（aminotetrol，氨基四醇），这些组分部分来源于陆源输入，但也可能在海洋沉积物中原位生成。五官能团化环醇醚类BHP在海洋系统中的分布特征值得关注，这表明其有望作为海洋沉积物中蓝细菌生物量的标志性标志物。