Strontium distribution in the shell of the aragonite bivalve Arctica islandica

The behavior of Sr in the aragonite shells of the bivalve Arctica islandica has been explored to determine its potential for high-resolution environmental reconstruction. The structural state of Sr in the shell was investigated using X ray absorption fine structure (XAFS) and Sr/Ca variations across the prismatic layer in the umbo and outer shell were determined by secondary ionization mass spectrometry (SIMS) and laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) respectively. XAFS data suggest that Sr randomly substitutes for Ca within the shell aragonite. Sr/Ca in both the umbo and the outer shell exhibits significant seasonal variation but does not correlate with seawater temperature. Sr/Ca varies significantly between parallel transects across the same annual bands. Sr concentrations are highest in transects along the maximum growth axis of the outer shell but lowest in these transects in the umbo. Scanning electron microscopy indicates changes in crystal morphology both within and between transects. We do not, however, observe a clear relationship between shell growth rate and Sr/Ca. Fluctuations in Sr/Ca are most likely to be controlled by a complex interaction of biological and kinetic processes.