The K-D Sr/Ca in cultured massive Porites spp. corals are reduced at low seawater pCO(2)

Coral skeletal Sr/Ca has valuable potential as a proxy of sea surface temperatures (SSTs). However seawater pCO(2) can influence skeletal Sr incorporation and Sr/Ca-SST calibrations derived from present day corals may not be applicable to ancient specimens or older sections of modern corals deposited under lower seawater pCO(2) than the present day. In this study we analysed skeletal Sr/Ca in multiple genotypes of massive Porites spp. cultured over a range of seawater pCO(2) (from 180 to 750 mu atm) and temperature (25 degrees C and 28 degrees C). Multiple linear regression analysis indicates that the Sr/Ca aragonite partition coefficient, K-D Sr/Ca is inversely related to seawater temperature and positively related to seawater pCO(2) (equivalent to changes in skeletal Sr/Ca of 0.046 mmol mol(-1) degrees C-1 and 0.0002 mmol mol(-1) mu atm(-1) respectively). Applying present day Sr/Ca-SST equations to older coral skeletons growing at lower pCO(2) could underestimate seawater temperatures. However K-D Sr/Ca vary significantly between some coral genotypes cultured at the same seawater pCO(2) indicating that other unidentified processes also influence skeletal Sr/Ca and it is unknown how these processes varied when ancient corals were deposited. We do not observe a significant relationship between K-D Sr/Ca and coral calcification rate after combining all coral genotypes to allow identification of the correct K-D Sr/Ca to apply to coral records. (C) 2021 Elsevier Ltd. All rights reserved.