Calcium isotope fractionation in modern scleractinian corals

摘要

The Ca-44/Ca-40 ratios of cultured (Acropora sp.) and open ocean (Pavona clavus, Porites sp.) tropical reef corals are positively correlated with growth temperature. The slope of the temperature-fractionation relation is similar to inorganic aragonite precipitates. However, delta(44)/Ca-40 of the coral aragonite is offset from inorganic and sclerosponge aragonite by about +0.5 parts per thousand. This offset can neither be explained by the very fast, biologically controlled calcification of scleractinian corals, nor as a consequence of calcification from a partly closed volume of fluid. As corals actively transport calcium through several cell layers to the site of calcification, the most likely explanation for the offset is a biologically induced fractionation. Our results indicate a limited use of Ca isotopes in scleractinian corals as temperature proxy. (c) 2006 Elsevier Inc. All rights reserved.