Seasonal variation of trace element and isotopic composition in the shell of a coastal mollusk, Mactra isabelleana

Shells of the bivalve Mactra isabelleana taken from marine and estuarine environments along the coast of Argentina, show a cyclicity in carbon and oxygen isotope ratios from analysis of incrementally grown shell carbonate that reflect seasonal changes in temperature and salinity in the coastal waters. Trends in trace element data, from the same sample intervals, can be compared to variations in the isotope data. In the estuarine shell, there are cyclic variations in strontium, magnesium, and barium (Sr, Mg, and Ba) that match closely the variation in δ ¹⁸O and δ ¹³C. The highest concentration of these elements are coincident with δ ¹⁸O peaks and approach mean values for both isotopes and trace elements from the marine shell. However, there is a lack of statistically significant correlations between the trace element and isotope data, which suggests that the patterns of trace element variations cannot be only related to environmental parameters, although predominantly controlled by them. There is no correlation between isotopes and trace elements in the marine shell, which suggests physiological effects, rather than environmental, control the incorporation of the trace elements into the shell carbonate.