Variation Of Marine Productivity In The Bering Sea Shelf Under Global Warming And Its Implication For The Formation Of Source Rocks

Sediment organic matter is the source of the initial organic matter of source rocks and is also the basis for the formation of source rocks.In marine environment,marine productivity has a significant impact on the input of organic matter in sediments,meanwhile,it is effected by different environmental conditions with different effects.So it is important to find out the influence of various environmental conditions on marine productivity,and an important part of the study of marine high-quality source rocks formation.During the last century,there is an evident increase in the global temperature,which facilitates the study of changes in marine productivity at elevated temperatures and provides a modern process reference for exploring the effects of temperature changes on the source rocks formation.In this paper,three types of biomarkers including saturated hydrocarbons,fatty acids and alcohols from sediment core BL16 were detected,which was collected during the Fifth Chinese National Arctic Research Expedition from the Bering Sea shelf.Combined with previous studies,we analyzed the source of these lipid compounds and discussed variation of marine productivity in this area over the past 70 years in the context of climate change.The distribution of lipids in sediment core indicates that organic matter in sediments has a mixed source from terrigenous and marine,while the terrigenous organic matter is mainly derived from terrestrial higher plants and the marine organic matter mainly originates from marine phytoplankton and microbes.It is showed that there was no significant correlation between the sediment grain size and the concentration of each component compound,indicating the sediment did not selectively adsorb these lipids and there is no significant effect on the burial of these lipids in sediment.Although there is a fluctuation of the concentrations of long-chain n-alkanes and long-chain fatty alcohols in sediment core,on obvious up or down trend has been observed,indicating that there is no significant change on the terrigenous input in the Bering Sea during the last 70 years.The variation of compositional characteristics and content changes of marine lipid compounds in the sediment core are consistent with total organic carbon(TOC)and total nitrogen(TN),together showing an apparent increase trend since the 1970 s,indicating a significant increase of marine productivity.By comparing the annual global surface temperature,the average annual sea-ice coverage of the Bering Sea during 70 years and the variations of characteristics and content of marine lipids in the sediment core,we can assume that the increase in marine productivity in the Bering Sea shelf may be due to the reduction in sea-ice under the influence of global warming.The reduction in sea-ice has resulted in an increase in photic zone and an extension of the ice-free period,which in combination with high nutrient has led to an improvement in marine productivity.The improvement in marine productivity together with the development of high-quality source rocks under climate warming during the geological history indicates that climate warming could favor the formation of source rocks.