Oceanic environmental changes of subarctic Bering Sea in recent 100 years: Evidence from molecular fossils

Abstract

The core sample B2-9 from the seafloor of the subarctic Bering Sea was dated with 210Pb to obtain a consecutive sequence of oceanic sedimentary environments at an interval of a decade during 1890—1999. A variety of molecular fossils were detected, including n-alkanes, isoprenoids, fatty acids, sterols, etc. By the characteristics of these fine molecules (C 27 , C 28 , and C 29 sterols) and their molecular indices (Pr/Ph, ∑C + 22 /∑C - 21 , CPI and C18∶2/C18∶0) and in consideration of the variation of organic carbon content, the 100-year evolution history of subarctic sea paleoenvironment was reestablished. It is indicated that during the past 100 years in the Arctic, there were two events of strong climate warming (1920—1950 and 1980—1999), which resulted in an oxidated sediment environment owing to decreasing terrigenous organic matters and increasing marine-derived organic matters, and two events of transitory climate cooling (1910 and 1970—1980), which resulted in a slightly reduced sediment environment owing to increasing terrigenous organic matters and decreasing marine-derived organic matters. It is revealed that the processes of warming/cooling alternated climate are directly related to the Arctic and global climate variations.