Trace and minor element records in aragonitic bivalve shells as environmental proxies

Abstract

Abstract Investigation of the geochemical composition of bivalve shells can provide information on changes in the marine environment occurring during the lifespan of an organism. Three species, locally abundant in the Adriatic Sea, were chosen in this study, namely Glycymeris pilosa, Callista chione, and Venus verrucosa. Of these, G. pilosa has the longest lifespan, exceeding 50\u202fyears, and therefore presents a potential archive of decadal climate variability. The other two species, C. chione and V. verrucosa, are commercially important. Samples were collected alive by SCUBA diving in the North Adriatic Sea, near Barbariga, Istria. Major growth increments in these shells form on an annual basis and are clearly visible in shell cross-sections enabling correct temporal positioning of geochemical data obtained from different shell parts. In this study, we applied laser ablation - inductively coupled plasma - mass spectrometry (LA-ICP-MS) in line scan mode to determine the trace and minor element composition along the major growth axis in the hinge area of the shells. Objectives of this study were to compare signals within and between species, and to relate results to available environmental parameters. High resolution time-series of Na/Cashell, Mg/Cashell and Sr/Cashell display characteristic cyclic variations. Na/Cashell minima and Mg/Cashell and Sr/Cashell maxima occur near shell annual growth lines in all three studied species. Results indicate that seawater temperature is not a main driver for incorporation of these elements. Ba/Cashell data vary between years and species and have noncyclic sharp peaks. Callista chione and V. verrucosa specimens show higher peaks and background Ba/Cashell values than G. pilosa. Most pronounced peaks in Ba/Cashell occurred at the beginning of the growing season corresponding to the end of year 2011 and beginning of year 2012 and coincided with unusual dense water formation and subsequent changes in the plankton communities in the Adriatic Sea. Implications of our study suggest that synchronous peaks in studied specimens are caused by external forcing which could occur on larger, regional scales, encouraging future studies covering wider area in the Adriatic Sea and other parts of the Mediterranean.