Paleoenvironmental implications of Holocene long-chain n-alkanes on the northern Bering Sea Slope

The records of high-resolution terrestrial biological markers(biomarkers) from Core B2-9 from the northern Bering Sea Slope over the last 9.6 ka BP were presented in the study.Variations in input of terrestrial long-chain nalkanes(referred to as n-alkanes) and vegetation structure in their source regions were investigated.The results show that the nC27is the main carbon peak and has the greatest contribution rate of the total n-alkane content;this might be related to the abundance of woody plants and their spatial distribution in the source region.nC23is another n-alkane having a relatively high content;this was mainly derived from submerged plants widespread along the coastal areas in the northern hemisphere.Total n-alkane content dropped quickly at ca.7.8 ka BP,ca.6.7 ka BP and ca.5.4 ka BP,and was followed by four relatively stable stages mostly controlled by sea-level rise,climate change and vegetation distribution in the source region.Variation in carbon preference index(CPI)indicates that the n-alkanes primarily originated from higher land plants,and the average chain length(ACL) and nC31/nC27ratio reveal the relatively stable presence of woody/herbaceous plants during the Holocene,and dominate woody plants in most of the time.Simultaneous variation in total n-alkane content,nC27content and its contribution,CPI,ACL and nC31/nC27ratio over several short periods suggest that the growth rate of the woody plant n-alkane contribution was lower than that of herbaceous plants and fossil n-alkanes under the particular climatic conditions of the source region.