Stable isotope profiles ofSerripes groenlandicus shells. I. Seasonal and interannual variations of Alaskan Coastal Water in the Bering and Chukchi Seas

Abstract

Serripes groenlandicus shells were collected alive from the eastern regions of the Bering and Chukchi seas where Alaskan Coastal Water occupies dominantly. High-resolution stable isotope profiles of the shell carbonates exhibit distinct, apparently annual, cycles caused by seasonal variations of temperature, seawater isotopic composition and other factors. The shell σ18O profiles show a moderately high-amplitude seasonal temperature cycle with considerable interannual variability. Superimposed on the temperature-controlled cycles are periodic excursions which are associated with reduced salinity, and more negative seawater σ18O, related presumably to an increased freshwater flux to the Alaskan Coastal Current during the summer: Comparison between two oxygen isotope profiles supports the occurrence of seasonal and interannual variability of Alaskan Coastal Water in the eastern part of the Bering and Chukchi Shelf. The cycles in the σ13C profiles are interpreted as being controlled primarily by phytoplankton productivity and seasonal temperature. In addition, a trend of more negative σ13C values towards the later stage of growth may reflect physiological changes associated with sexual maturity, gametogenesis, and slower growth rate. The oxygen and carbon isotope profiles as a biorecorder of bivalve shells are substantiated in the subarctic environments, probing the seasonal and internanual variation of Alaskan Coastal Water.