Sources Of Terrestrial Organic Carbon In Surface Sediments Across The Bering And Chukchi Seas In The Arctic,Insights From Lignin Phenols

Organic carbon(OC)buried in the marine sediment is a net sink of atmospheric carbon dioxide,and the burial process occurs mainly in the continental shelf.In the marine environment,the sediments contain 700 Gt OC,and can store for millions of years,in turn,affecting the entire carbon geochemical cycle.Although 33%?54%POC input to the ocean is terrigenous organic carbon,only 10%is buried in sediments,which rises the "the missing carbon".Despite all kinds of hypotheses try to explain this puzzle,it is still far away from completely explaining the fate of terrigenous organic carbon in the ocean.As a result,scientists have been concerned about the fate of terrigenous organic carbon in the ocean,in order to better understand the global carbon cycle.This study selected series of surface sediments from the Bering Sea and Chukchi Sea,and used lignin phenols as the biomarker,in combination with grain size,specific surface area,organic carbon content(OC%),total nitrogen(TN%),carbon stable isotope(?13C),to analysis the distribution,source,vegetation types and the degradation mechanism of OC in the surface sediments of the Bering and Chukchi Seas.The distribution of OC in the surface sediment of the Bering Sea is the result of hydrodynamic sorting.Lignin contents-A8 in the east sediments are higher than the west,cutin acids,fatty acids have positive correlations with ?8.The distribution of ?13C is similar to carbon nitrogen ratio(C/N),decreasing from east to west.C/V and S/V indicate that angiosperms and gymnosperms tissue have the similar contribution,while non-woody tissue is more dominant than woody tissue.(Ad/AI)v and(Ad/Al)s have no obvious relationship with the water depth,but 3,5-Bd showed an obvious decreasing trend,showing 3,5-Bd compared with lower reactivity of lignin.There is a negative correlation between ?8 and ?13C in the sediments of the Bering Sea,and it means the percentage of terrestrial OC can be calculated using a two end-member model.Based on the model,the percentage of terrestrial OC varied from 18.6%-99.6%.As to the Chukchi Sea,the samples are divided into two groups with a depth of 100 m.The shelf group is shallower than 100 m while the slop group is deeper than 100 m.The results show that the OC contents vary along the grain size,angiosperm tissue is relatively more dominant than gymnosperm tissue,whereas there is an equal contribution from woody and non-woody tissue to the surface sediments of the Chukchi Sea,according to the C/V and S/V ratios.The wide PON/V ratio proves that Sphagnum moss is a negligible influence with other multi-sourced contribution of plants like shrubs,grasses,and conifers.In addition,the evidence that the concentration of C9DA is relatively high among DAs,which is obtained from the CuO oxidation of aliphatic-rich kerogen,we firmly believe that kerogen can play a pregnant role in the sources of the OM.In this thesis,the sources of organic carbon in the surface sediments of the Bering Sea and Chukchi Sea are studied by using lignin.The understanding of the source,content and distribution characteristics of organic carbon in the typical high latitude sea area is the first step to understand the mechanism and influencing factors of the trend of lignin in the sediments from nearshore to deep sea,providing important data for the transport and burial of organic matter in shelf regions in polar regions.