Deconvolving the 18 O seawater component from subseasonal coral 18 O and Sr / Ca at Rarotonga in the southwestern subtropical Pacific for the period 1726 to 1997

To reconstruct oceanographic variations in the subtropical South Pacific, 271-year long subseasonal time series of Sr/Ca and O were generated from a coral growing at Rarotonga (21.5°S, 159.5°W). In this case, coral Sr/Ca appears to be an excellent proxy for sea surface temperature (SST) and coral O is a function of both SST and seawater O composition ( Osw). Here, we focus on extracting the Osw signal from these proxy records. A method is presented assuming that coral Sr/Ca is solely a function of SST and that coral O is a function of both SST and Osw. This method separates the effects of Osw from SST by breaking the instantaneous changes of coral O into separate contributions by instantaneous SST and Osw changes, respectively. The results show that on average Osw at Rarotonga explains 39% of the variance in O and that variations in SST explains the remaining 61% of O variance. Reconstructed Osw shows systematic increases in summer months (December–February) consistent with the regional pattern of variations in precipitation and evaporation. The Osw also shows a positive linear correlation with satellite-derived estimated salinity for the period 1980 to 1997 (r 0.72). This linear correlation between reconstructed Osw and salinity makes it possible to use the reconstructed Osw to estimate the past interannual and decadal salinity changes in this region. Comparisons of coral O and Osw at Rarotonga with the Pacific decadal oscillation index suggest that the decadal and interdecadal salinity and SST variability at Rarotonga appears to be related to basin-scale decadal variability in the Pacific. Copyright © 2002 Elsevier Science Ltd