A fossil coral perspective on western tropical Pacific climate ∼350 ka

Abstract

The nature of tropical climate variability ∼350 ka is addressed using δ18O and Sr/Ca records from a modern and a fossil coral from Vanuatu (southwestern tropical Pacific Ocean). Modern El Niño events at Vanuatu produce positive coral δ18O and Sr/Ca anomalies; similar anomalies observed in the fossil coral records suggest that El Niño was operative 350 kyr ago. Seasonal variations in coral Sr/Ca, a sea surface temperature (SST) proxy, have the same amplitude in both corals, whereas seasonal δ18O variations are smaller in the fossil coral than in the modern coral. This is consistent with displacement of the South Pacific Convergence Zone toward the southwest during the boreal summer ∼350 ka. Mathematical modeling results preclude warmer SST and higher SSS at Vanuatu during this time, but permit the surface ocean to be ∼2°C cooler and 0-2 psu fresher than today. Assessing the potential of variations in late Quaternary seawater Sr/Ca remains the largest obstacle to accurately reconstructing tropical SST using pristine fossil corals. Copyright 2004 by the American Geophysical Union.