UC San Diego

High resolution archives of environmental conditions determined from the chemistry and growth increments of bivalves provide a unique opportunity to examine relationships between climate-induced environmental change and biological productivity in the Southern California Bight. However, before bivalves can be used as high resolution biorecorders of environmental change, the record of interest (e.g. [delta]¹⁸O, [delta]¹³C, Sr/Ca, Ba /Ca or growth increments) must first be calibrated to known environmental conditions. For Donax gouldii this was accomplished by comparing [delta]¹⁸O, [delta]¹³C and Sr/Ca to well-constrained environmental records. D. gouldii Ba/ Ca was investigated by assigning an exact date to each laser ablation Ba/Ca determination by cross-dating tidal growth increments and then comparing the dated Ba/Ca values to local biological and physical parameters. The timing of growth increments and temperature of thermally induced growth shut down in Chione undatella was determined by a mark-recapture study. To obtain historic context, C. undatella from over 6,000 years were analyzed for growth, age, and size at harvest. Calibrations of D. gouldii provide the context necessary to utilize D. gouldii as a paleothermometer and Ba/Ca may have utility as an upwelling indictor. Additionally, the technique of cross-dating was applied to tidal growth increments, providing a new level of accuracy to shell dating. C. undatella have a lower thermal limit for growth of 17 °C and form winter growth increments with decreasing growth with age. Archaeological C. undatella show a remarkably stable growth rate and size at harvest through the Middle and Late Holocene. This research presents a greater understanding of how environmental variables are recorded in bivalves and the utility of these proxies for paleoecological and paleoclimite studies