SHIFTS IN THE δ13C OF SERRIPES GROENLANDICUS SHELL ORGANIC MATTER: A PROXY FOR INTRA- AND INTERANNUAL CHANGES IN PRIMARY PRODUCTION IN THE ARCTIC?
Samples of live Serripes were collected from Kongsfjord on the west coast of Svalbard during July of 2004 and June of 2006. Winter and summer shell material from duplicate animals were sampled for the years 1996, 1997, 2000, and 2001 and entire growth bands were sampled from multiple organisms for each year between 1991 and 2002, except 1999, for carbon isotope composition of the shell organic fraction. Isotopic values of amino acids in bivalves can vary by as much as 28; thus, the amino acid composition of these shell layers was also determined.
Preliminary results suggest that there were statistically significant seasonal isotopic differences in 1997, 2000, and 2001. Shell organic matter from the winter growth layers was enriched in 13C relative to the summer layers. These isotopic shifts can not be attributed to seasonal differences in amino acid composition alone, and may reflect seasonal changes in the available food supply. The Serripes may have consumed more ice algae during the winter months, and more phytoplankton during the summer months. Additional isotopic and amino acid analyses are needed to confirm this interpretation. Between 1991 and 2000, the δ13C values of the annual growth bands were relatively consistent (avg δ13C = -18.6 ± 0.2). The years 2001 and 2002 were enriched in 13C by 1 relative to the rest of the time series, indicating that an environmental shift occurred in Kongsfjord after 2000, the nature of which is currently under investigation.