Composition and sources of sedimentary organic matter in the deep eastern Mediterranean Sea

[摘要] Surface sediments collected from deep slopes and basins (1018–4087 m depth)of the oligotrophic eastern Mediterranean Sea have been analysed for bulkelemental and isotopic composition of organic carbon, total nitrogen andselected lipid biomarkers, jointly with grain size distribution and othergeochemical proxies. The distribution and sources of sedimentary organicmatter (OM) have been subsequently assessed and general environmentalvariables, such as water column depth and physical circulation patterns, havebeen examined as causative factors of deep-sea sediment characteristics.Lithogenic and biogenic carbonates are the dominant sedimentary fractions,accounting for up to 85.4 and 66.5 % of the total weight respectively.The low OC and TN contents in the surface sediments of the study area, whichranged from 0.15 to 1.15 % and 0.06 to 0.11 % respectively, reflectthe oligotrophic character of the eastern Mediterranean Sea. Both bulk andmolecular organic tracers reflect a mixed contribution from autochthonous andallochthonous sources for the sedimentary OM, as indicated by relativelydegraded marine OM, terrestrial plant waxes and anthropogenic OM (e.g.degraded petroleum by-products) respectively. Wide regional variations havebeen observed amongst the studied proxies, which reflect the multiple factorscontrolling sedimentation in the deep eastern Mediterranean Sea. Our findingshighlight the role of deep eastern Mediterranean basins as depocentres oforganic-rich fine-grained sediments (mean 5.4 ± 2.4 μm), with OMaccumulation and burial being attributed to aggregation mechanisms andhydrodynamic sorting. A multi-proxy approach is applied aiming to investigatethe biogeochemical composition of sediment samples, which sheds new light onthe sources and transport mechanisms along with the impact of preservationvs. diagenetic processes on the composition of sedimentary OM in the deepbasins of the oligotrophic eastern Mediterranean Sea.

[学科分类] 地球化学与岩石