Comparison of δ¹⁸O, Sr/Ca and U/Ca results of recent corals BDA18-1B and BDA135-223 from Bermuda

High-resolution records of Sr/Ca, U/Ca ratios and d18O have been obtained in two recent colonies of massive corals (Diploria labyrinthiformis) from Bermuda. The three geochemical proxies display regular seasonal variations and are well correlated with each other. However, some important discrepancies are observed between the two colonies: the average seasonal variations of the three geochemical proxies are lower by almost 50% in one of the profiles, where the seasonal oscillation also displays a strong asymmetry, with narrower summer maxima. Different calculations are discussed for calibrating Sr/Ca and d18O with sea surface temperatures (SST). We show that the method using only temperature minima and maxima is slightly more accurate and is also more reliable. Our results from Bermuda corals confirm that the temperature dependency of Sr/Ca, U/Ca and d18O is species-dependent, as previously shown by others and that "vital effects" are clearly involved in the geochemical incorporation of trace elements in the coral skeleton. Finally, a simple model involving seasonal variation of the growth rate and a kinetic fractionation related to growth rate is presented to explain the differences between the two Bermuda colonies. It is shown that these factors may prevent corals from recording the complete temperature seasonality and could be the cause for the discrepancies observed between profiles, resulting in significant biases of the SST reconstructions.