Source Sink Processes And Burial Records Of Modern Sedimentary Organic Carbon In The Arctic Laptev Sea

With the intensification of global warming,the Arctic,as the"amplifier"and"barometer"of global climate change,has attracted much attention in the study of the global carbon cycle.The Laptev Sea is a typical shelf margin sea in the Arctic Ocean,under the control of environmental factors such as the input from the Arctic Lena River,seasonal sea ice processes,marine primary productivity and coastal erosion,the source,transport and burial processes of sedimentary organic carbon in this area are unique.To further understand the source-sink processes of modern sedimentary organic carbon in the context of rapid changes in the Arctic,based on the sample data of suspended particulate matter,surface sediments and multi-tube sediment core samples obtained from the second joint Russian-Chinese Arctic scientific research in 2018,this paper evaluates the effects of sedimentary environment,marine primary productivity,river input and coastal erosion on the transport and burial of different types of organic carbon,and initially reveals the record of organic carbon burial evolution and its response to climate and environmental changes in the past 100 years,which provides an important basis for in-depth understanding of the sedimentary organic carbon source-sink processes and evolutionary characteristics of the region.The main insights are as follows.Particulate organic carbon(POC)concentrations in the Laptev Sea in late summer and early autumn ranged from 35.27 to 1,185.58?g/L,the distribution of surface POC concentrations showed a trend of high near-shore and low far-shore due to riverine input,coastal erosion and marine primary productivity;the distribution of bottom POC concentrations was mainly controlled by sediment resuspension,with high POC The distribution of bottom POC concentration is mainly controlled by sediment resuspension,with high POC content in the eastern part of the Lena River delta.Total suspended solids(TSS)concentrations showed a significant positive correlation with POC concentrations in general,showing its direct influence on the spatial distribution of POC,and the correlation between the two parameters was higher in the bottom layer than in the surface layer,which may indicate the source differences of POC in different layers.The?¹³C values of POC in the study area ranged from-31.03‰to-25.79‰,the?¹³C values in the surface layer were significantly more negative than those in the bottom layer,and the?¹³C values in some stations were even lower than the end members of organic carbon from surrounding terrestrial sources,which may reflect that in addition to the contribution of terrestrial source input,the production process of dissolved inorganic carbon(DIC)generated from the degradation of large amounts of terrestrial organic matter directly used by offshore phytoplankton also has important implications for the supply and source resolution of POC in the region.The total organic carbon(TOC)content of surface sediments ranged from 0.07%to 2%,which shows an overall distribution characteristic of high nearshore and low distant shore due to the influence of terrigenous input.The sediments were classified and found that the most widely distributed was clayey silt;and with finer sediment particles,the TOC%in the sediments was higher,indicating that the fine-grained sediments in this area are more likely to be enriched with organic matter such as organic carbon.The C/N values of surface sediments ranged from 7.37 to 17.46,and the C/N values were higher in the areas significantly influenced by land-based sources.The?¹³C values ranged from-27.47‰to-23.41‰,showing the characteristics of negative near-shore and positive far-shore,which combined with the comprehensive analysis of C/N,indicated that sedimentary organic carbon was contributed by both land and sea-based sources,and the spatial distribution showed that near-shore areas were influenced by land-based sources,the spatial distribution of sedimentary organic carbon is mainly influenced by terrestrial sources,reflecting the direct influence of runoff input and coastal erosion processes;the organic carbon in deep water areas such as the outer shelf and land slope is mainly contributed by marine sources.A high-resolution chronostratigraphic framework for the LV83-28 sedimentary column in the offshore shelf area based on ²¹⁰Pb reconstructs the depositional record of organic carbon on the Laptev Sea shelf since 1950s.Preliminary results indicate that the sedimente flux and organic carbon burial flux in this area are increasing year by year,which is consistent with the trend of increasing runoff of the Lena River and increasing intensity of permafrost erosion in the context of rapid Arctic changes,reflecting the increasing supply of terrestrial-sourced particulate matter to the sea in the context of warming.The TOC%of sedimentary core ranges from 1.75%to 2.11%,and shows a gradual increase from bottom to top in the vertical direction,especially starting in the late 1980s,the TOC burial flux increased significantly,which is consistent with the strengthening of permafrost erosion,the?¹³C value ranges from-26.09‰to-25.66‰,and the vertical direction shows a gradual negative bias toward the upper part,which also indicates the increasing influence of land-based sources.