Contribution of metabolic carbon to mollusc and barnacle shell carbonate

TLDR: In this article, the authors show that metabolic carbon can also be incorporated into carbonate tests, as shown by experiments using 14C-labelled food during the incubation of sea urchin embryos and coral.

Abstract: Carbon in marine calcareous tests is not necessarily derived only from dissolved inorganic carbon (DIG) in ambient sea water; metabolic carbon can also be incorporated into carbonate tests, as shown by experiments using 14C-labelled food during the incubation of sea urchin embryos and coral1,2. 14C-rich organic matter (relative to seawater DIC) from terrestrial vegetation as well as marine organic matter (reflecting seawater DIC) is used as food by marine organisms in near-shore environments. This use provides the basis for a natural experiment on the systematics of metabolic carbon incorporation into carbonate tests. Here we have combined 14C/12C and 13C/12C ratio measurements on both the calcareous and the organic parts of marine organisms and on DIC, plankton and other carbon-bearing materials collected in and around New Haven Harbor (Connecticut, USA) in Long Island Sound, where the various sources of carbon can be identified, and we deduce that a large percentage of the carbon in calcareous tests is metabolic carbon. Thus, it is at best difficult to use the δ13C values of ancient biogenic carbonate from molluscs to predict the ancient δ13C values of seawater DIC