Profiles of strontium and barium in Mercenaria mercenaria and Spisula solidissima shells

Cross sections of two Mercenaria mercenaria shells, one modern and one Pleistocene, and one modern Spisula solidissima shell were analyzed for trace metals using laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS). These data are coupled with 18O 16O ratio profiles, which are used as a temperature proxy to determine the season of growth for a given shell parcel. The shells show Sr and Ba fluctuations in regular annual patterns. Seasonal Sr decreases associated with the winter dormant period in Mercenaria, and with the summer growth decrease in Spisula indicate that kinetic control (growth rate) plays a more important role than temperature in the incorporation of this element. Barium exhibits sharp increases that are likely linked to periods of intense phytoplankton productivity. This application of LA-ICP-MS to the analysis of mollusk shells for documenting ontogenetic trends demonstrates the power of this technique for extracting geochemical information.