Hydrological shifts in seawater δ18O in southwest tropical Pacific since 1649 CE
Thursday, 18 December 2014
Here we present monthly resolved coral δ18O, δ13C, and Sr/Ca determinations from Porites lutea colonies offshore of Amédée Island, New Caledonia (22º28.8′S, 166º27.9′E) to investigate sea surface temperature (SST) and δ18O of seawater (δ18Osw) variability in the southwest tropical Pacific from 1649–1999 CE. Coral δ18O varies with SST and δ18Osw, which varies with oceanic and hydrologic processes whereas coral Sr/Ca varies with SST because Sr and Ca in seawater are invariant on centennial time scales. Comparison of coral δ18O-SST and Sr/Ca-SST anomalies reveals a persistent +0.3‰ divergence in coral δ18O prior to 1936 CE suggesting a shift in hydrology in which relatively 18O rich surface waters are present as the result of more evaporation than precipitation. Coral δ18O variations from 1649–1936 CE contain interannual to bidecadal variations larger than those observed from 1936–1999 CE and in the coral Sr/Ca-SST reconstruction, suggesting hydrological shifts on those time scales. Long-term coral δ13C variations provide a record of anthropogenic CO2 uptake in the ocean. Coral δ13C records reveal a shift to lower values (Δ=–0.9‰) starting ~1850 CE, a shift greater than that observed in corals from Fiji. The rate of change varies but approaches a constant rate from 1945–1980 CE and then increases from 1980–2000 CE.