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

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 (C27, C28, and C29 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.