H2O2 TREATMENT OF RECENT CORAL ARAGONITE - OXYGEN AND CARBON ISOTOPICIMPLICATIONS

Coral skeletons contain relatively little organic material and inorgan ically precipitated carbonate cement, although these quantities are en ough to bias geochemical measurements. Preliminary treatment is theref ore often necessary to remove these materials. Hydrogen peroxide seems to be the most efficient reagent. This strong oxidant destroys organi c matter and its acid pH promotes dissolution of carbonate cements tha t precipitate after the coral skeleton has formed. We tested the isoto pic effects (both on O-18/O-16 and C-13/C-12 ratios) of such a chemica l treatment on coral aragonite. We demonstrate that only one treatment is necessary to eliminate different contents without alteration of co ral aragonite and we verified that there is no isotopic exchange betwe en the oxygen atoms from CaCO3 and H2O2. We measured carbon and oxygen isotopic compositions from samples that cover 2.5 years of coral grow th and that were split in two ways: untreated and H2O2-treated. The H2 O2-treated subsamples reveal a clear seasonal oscillation that is not evident in the untreated isotopic record. Therefore, hydrogen peroxide treatment should be systematically carried out before isotopic analys es in order to perform palaeoclimatic reconstructions. (C) 1997 Elsevi er Science B.V.