Cross-calibration of daily growth increments, stable isotope variation, and temperature in the Gulf of California bivalve mollusk Chione cortezi: Implications for paleoenvironmental analysis

Annual-oxygen isotope profiles from two live-collected specimens of Chione cortezi Carpenter were analyzed in conjunction with daily growth -increment width profiles and high-resolution temperature records from the same site in the northern Gulf of California. The daily growth-increment profiles ser ve to date the deposition of the delta O-18 samples. Then the delta O-18 va lues were compared with high-resolution temperature records from the same s ite. Shell deposition began in late March or early April and ended in late November or early December. delta O-18-derived estimates of the maximum and minimum temperature thresholds of growth agree well with those obtained fr om the dated increment width profile. Shell deposition in these two specime ns of C. cortezi from the northern Gulf began when temperature warmed above similar to 17 degreesC and slowed or halted when temperature rose above si milar to 31 degreesC. The temporal resolution of stable isotope samples var ies throughout the year. Samples with the coarsest resolution (>3 weeks) we re taken from parts of the shell deposited near the minimum and maximum tem perature thresholds of growth. Higher resolution samples have intermediate delta O-18 values and most represent less than five days of growth. Calcula ted temperatures from the dated oxygen-isotope samples are similar to obser ved temperatures. Differences reflect the effects of daily temperature vari ation, tidal emergence, and enrichment in delta O-18 of the water in which the clams grew. Stable oxygen-isotope samples used in conjunction with incr ement-width profiles can provide paleoenvironmental information at sub-week ly to sub-monthly resolution.