Freeman K H, Wakeham S G, Hayes J M
Department of Geosciences, Pennsylvania State University, State College 16802, USA.
Org Geochem. 1994;21(6-7):629-44. doi: 10.1016/0146-6380(94)90009-4.
Carbon isotopic compositions were determined for individual hydrocarbons in water column and sediment samples from the Cariaco Trench and Black Sea. In order to identify hydrocarbons derived from phytoplankton, the isotopic compositions expected for biomass of autotrophic organisms living in surface waters of both localities were calculated based on the concentrations of CO2(aq) and the isotopic compositions of dissolved inorganic carbon. These calculated values are compared to measured delta values for particulate organic carbon and for individual hydrocarbon compounds. Specifically, we find that lycopane is probably derived from phytoplankton and that diploptene is derived from the lipids of chemoautotrophs living above the oxic/anoxic boundary. Three acyclic isoprenoids that have been considered markers for methanogens, pentamethyleicosane and two hydrogenated squalenes, have different delta values and apparently do not derive from a common source. Based on the concentration profiles and isotopic compositions, the C31 and C33 n-alkanes and n-alkenes have a similar source, and both may have a planktonic origin. If so, previously assigned terrestrial origins of organic matter in some Black Sea sediments may be erroneous.
测定了来自卡里亚科海沟和黑海的水柱及沉积物样品中各烃类的碳同位素组成。为了识别源自浮游植物的烃类，根据二氧化碳（aq）的浓度和溶解无机碳的同位素组成，计算了这两个地区表层水中自养生物量预期的同位素组成。将这些计算值与颗粒有机碳和各烃类化合物的实测δ值进行比较。具体而言，我们发现番茄烃可能源自浮游植物，而双萜烯源自生活在有氧/缺氧边界上方的化学自养生物的脂质。三种一直被视为产甲烷菌标志物的无环类异戊二烯、五甲基二十烷和两种氢化角鲨烯，具有不同的δ值，显然并非源自同一来源。根据浓度分布和同位素组成，C31和C33正构烷烃及正构烯烃具有相似的来源，两者可能都有浮游生物起源。如果是这样，先前确定的一些黑海沉积物中有机质的陆源可能是错误的。
