Processes controlling the stanol/stenol ratio in Black Sea seawater and sediments
Processes controlling the stanol/stenol ratio in Black Sea seawater and sediments
复制标题
控制黑海海水和沉积物中甾烷醇/甾烷醇比例的过程
作者：
R. Gagosian;Cindy Lee;F. Heinzer
甾体醇s1 - 10、酮类11和碳氢化合物12,13已被用作近代沉积物中生物有机质转化过程的示踪剂。这些研究中有几项涉及甾体醇的沉积转化反应之一，将甾体醇还原为甾体醇。然而，对上覆水柱在控制沉积中甾体/甾体分布中的作用的研究却很少。来自地表水生物的甾醇的输入加上相对不同的甾醇和甾醇降解率9,14也可能有助于观察到的沉积物分布。为了进一步评估这些过程在控制缺氧水和地表沉积物中甾醇/甾醇分布方面的相对重要性，我们进行了一次黑海巡航。由于黑海中部两个海拔2000米的盆地中125米以下的水是缺氧的，因此它是观察水柱或表面沉积物中任何微生物或化学媒介的还原反应的理想环境15,16。此外，由于表层沉积物是缺氧的，大型底栖动物对这些反应的影响很小。事实上，在沉积物（1,2,7 - 9,11,13）和海水（17）中，固醇转化反应被假定是由微生物介导的。然而，很少，如果有的话，细菌被认为是生物合成去甲基狭窄醇17,18。如果烯醇还原反应是化学介导的，它们也应该在这种高度还原（低EH）的环境中观察。我们在此讨论了控制一类生物源性有机化合物的特定转化反应（甾醇到甾醇转化）的主要过程。这些结论是根据对黑海两个站点的沉积物和上覆水柱取样所得的结果得出的。
STEROIDAL ALCOHOLS1–10, ketones11 and hydrocarbons12,13 have been used as tracers for the transformation processes of biogenic organic matter in Recent sediments. Several of these studies have been concerned with one of the sedimentary transformation reactions of steroidal alcohols, the reduction of stenols to stanols. However, little attention has been directed towards the role of the overlying water column in controlling sedimentary stenol/stanol distributions. The input of stanols from surface-water organisms coupled with relatively different degradation rates of stenols and stanols9,14 could also contribute to observed sediment distributions. To evaluate further the relative importance of these processes in controlling stanol/stenol distributions in anoxic water and surface sediments, we undertook a cruise to the Black Sea. Because water below 125 m is anoxic in the two central 2,000-m basins of the Black Sea, it is an ideal environment for observing any microbially or chemically mediated reduction reactions in the water column or surface sediments15,16. In addition, since the surface sediments are anoxic, the effects of macrobenthos on these reactions are minimal. Indeed, sterol transformation reactions have been postulated to be microbially mediated in sediments1,2,7–9,11,13, and in seawater17. However, very few, if any, bacteria are thought to biosynthesise desmethyl stenols17,18. If stenol reduction reactions are chemically mediated, they should also be observed in this highly reducing (low EH) environment. We discuss here the major processes controlling a specific transformation reaction (stenol to stanol conversion) of a class of biogenic organic compounds. These conclusions are based on results obtained by sampling both the sediments and the overlying water column from two stations in the Black Sea.