A model for interpreting continental-shelf hydrographic processes from the stable isotope and cadmium: calcium profiles of scallop shells

Abstract Stable oxygen and carbon isotope, and cadmium:calcium profiles from the shells of scallops collected from the outer continental shelf of the South Atlantic Bight and the Virginia Bight appear to trace the hydrographic processes of the two regions. A model is developed to distinguish two principal modes of nutrient and trace metal input to the outer shelf from the biogeochemical profiles of the shell. The oxygen isotope profiles record bottom-water temperature changes caused by seasonal temperature cycles and water-mass movements. Nutrient input and subsequent phytoplankton blooms are recorded in the carbon isotope and Cd:Ca profiles. The shell profiles from the South Atlantic Bight record the dominant effect of upwelling caused by Gulf Stream meandering. The shell profiles from the Virginia Bight show the influence of spring river runoff and summer water-column stratification. Biogeochemical profiles in mollusk shells are potentially important tools for studying the dynamics of both modern and ancient continental-shelf upwelling systems.