Logatchev热液场附近表层沉积物中有机质的组成特征、来源及其影响因素

Characteristics of organic composition and source of organic matter in surface sediments near the Logatchev hydrothermal field

利用2005年"大洋一号"科学考察船电视抓斗采样器采集的表层沉积物样品,对大西洋洋中脊Logatchev热液场附近7个站位表层沉积物样品中的烷烃组分进行了定量分析,并结合总有机碳(TOC)及C稳定同位素(δ13C值)分析,探讨了表层沉积物中有机质的组成及可能的来源和影响因素。结果表明:表层沉积物中正构烷烃组分以低碳数化合物为主,nC16、nC18以及nC11(仅在部分样品中)的含量较高,姥鲛烷与植烷的比值(Pr/Ph)普遍较低;表层沉积物中的有机质以细菌来源为主,浮游植物和浮游动物也有一定的贡献,而陆源有机质的贡献极小;另外,表层沉积物中的有机质可能遭受了一定程度的热液蚀变作用。

Surface sediments collected from the Logatchev hydrothermal field of Mid-Atlantic Ridge have been analyzed for element C of total organic matter（TOC）,stable isotopes（δ13C） and alkanes.The compositions and distributions of alkanes are studied and the possible sources of the organic matter of the sediments have preliminary been discussed.The contents of total organic carbon vary from 0.12% to 0.30%.And δ13C ranges from-23.5‰ to-20.1‰.The contents of n-alkanes vary from 0.78×10-6 to 10.29×10-6.The carbon number ranges from nC11~nC31.The low carbon number compounds of n-alkanes of the sediments are the main compounds,and the contents of nC16 or nC18 in most samples and nC11 in some samples are relatively high.The Pr/Ph ratios are generally very low.Unresolved complex mixture（UCM） exists in almost every sample of studying area.The contents of total organic carbon of some samples near the hydrothermal vents may indicate the productivity of chemosynthetic-based communities.The contents of nC11 in some samples are relatively high may show that the organic matter have been influenced by thermal cracking.And UCM may indicate that the organic matter have been influenced by biodegradation and hydrothermal alteration.δ13C and the distribution of n-alkanes indicate that the bacteria are the main source of organic matter in the surface sediments from the Logatchev hydrothermal field of Mid-Atlantic Ridge.Phytoplankton and zooplankton also have some contribution to the source of organic matter while the contribution of terrestrial organic matter is minimal.The higher contents of Pr and Ph may be related to the archaebacteria of hydrothermal field.