Ecological and paleoenvironmental information using stable isotope profiles from living and fossil molluscs
Stable oxygen and carbon isotopic profiles from Recent specimens of Spisula solidissima and Placopecten magellanicus collected off the Virginia coast are used to calibrate annual temperature-controlled cycles in the δ18O profile and shell growth characteristics. The amplitude of the annual δ18O cycles decreases with increasing water depth, and may be used as a relative depth indicator. The isotopic of profiles of two fossil specimens of Pleistocene Spisula are very similar in amplitude and character to modern analogues, and verify the formation of annual growth increments in these fossil specimens. Offsets between the δ18O profiles of the fossil and modern specimens are related to known temperature and ice-volume effects during the late Pleistocene and support the utility of mollusc-isotope records as a stratigraphic tool.

Carbon isotopic profiles from all specimens show light values in the spring and/or fall, associated with seasonal phytoplankton productivity. Offsets in the carbon isotopic composition between infaunal and epifaunal species may be related to sediment porewater geochemistry and oxidation of organic matter. Trends toward lighter δ13C values through ontogeny suggest the effects of metabolic changes from a fast-growing juvenile into a slower-growing, sexually-mature adult. Anomalies in both the oxygen and carbon isotopic profiles identify the formation of minor shell growth increments as corresponding to hydrographic perturbations and to winter cold temperatures.