Evidence for tropical South Pacific climate change during the Younger Dryas and the Bolling-Allerod from geochemical records of fossil Tahiti corals

We present monthly resolved records of strontium/calcium (Sr/Ca) and oxygen isotope (delta O-18) ratios from well-preserved fossil corals drilled during the Integrated Ocean Drilling Program (IODP) Expedition 310 "Tahiti Sea Level" and reconstruct sea surface conditions in the central tropical South Pacific Ocean during two time windows of the last deglaciation. The two Tahiti corals examined here are uranium/thorium (U/Th)-dated at 12.4 and 14.2 ka, which correspond to the Younger Dryas (YD) cold reversal and the Bolling-Allerod (B-A) warming of the Northern Hemisphere, respectively. The coral Sr/Ca records indicate that annual average sea surface temperature (SST) was 2.6-3.1 degrees C lower at 12.4 ka and 1.0-1.6 degrees C lower at 14.2 ka relative to the present, with no significant changes in the amplitude of the seasonal SST cycle. These cooler conditions were accompanied by seawater delta O-18(delta O-18(sw)) values higher by similar to 0.8 parts per thousand and similar to 0.6 parts per thousand relative to the present at 12.4 and 14.2 ka, respectively, implying more saline conditions in the surface waters. Along with previously published coral Sr/Ca records from the island [Cohen and Hart (2004), Deglacial sea surface temperatures of the western tropical Pacific: A new look at old coral. Paleoceanography 19, PA4031, doi:10.1029/2004PA001 084], our new Tahiti coral records suggest that a shift toward lower SST by similar to 1.5 degrees C occurred from 13.1 to 12.4 ka, which was probably associated with a shift toward higher delta O-18, by similar to 0.2 parts per thousand. Along with a previously published coral Sr/Ca record from Vanuatu [Correge et al. (2004), Interdecadal variation in the extent of South Pacific tropical waters during the Younger Dyras event. Nature 428, 927-929], the Tahiti coral records provide new evidence for a pronounced cooling of the western to central tropical South Pacific during the Northern Hemisphere YD event.