Experimental validation of environmental controls on the δ13C of Arctica islandica (ocean quahog) shell carbonate

The marine bivalve species, Arctica islandica, was reared under experimental conditions for 29 weeks in the Gulf of Maine in order to determine the relationship between the carbon isotope composition of shell carbonate (delta C-13(S)) and ambient seawater dissolved inorganic carbon (delta C-13(DIC)), as well as to approximate the metabolic contribution (C-M) to shell material. Three experimental environments were compared: two flow-through tanks (one at ambient seawater conditions, one with a supplemental food source) and an in situ cage. Each environment contained 50 juveniles and 30 adults. Both juvenile (2-3 years) and adult (19-64 years) specimens displayed average percent C-M of less than or equal to 10% when using three different proxies of respired carbon: digestive gland, adductor muscle and sediment. Hence, the primary control on delta C-13(S) values is ambient DIC. The relationship between delta C-13(DIC) and delta C-13(S) for 114 individuals used in the study was: delta C-13(DIC) = delta C-13(S) - 1.0 parts per thousand (+/- 0.3 parts per thousand) No ontogenetic effect on delta C-13(S) was observed, and growth rates did not generally impact delta C-13(S) values. Based on the results of this study, shell material derived from the long-lived ocean quahog (A. islandica) constitutes a viable proxy for paleo-DIC from the extratropical Atlantic Ocean. (C) 2012 Elsevier Ltd. All rights reserved.