Central Equatorial Pacific Warming and Freshening in the Twentieth Century: Insights From a Coral Ensemble Approach

The tropical Pacific influences climate patterns across the globe, yet robust constraints on decadal to centennial-scale climate variations are difficult to extract from sparse instrumental observations in this region. Oxygen isotope (delta O-18) records from long-lived corals enable the quantitative reconstruction of tropical Pacific climate variability and trends over the twentieth century and beyond, but such corals are exceedingly rare. Here, we use multiple short coral delta O-1(8) records to create a coral 'ensemble' reconstruction of twentieth century climate in the central tropical Pacific. Ten U/Th-dated fossil coral delta O-1(8) records from Kiritimati Island (2 degrees N, 157 degrees W) span 1891 CE to 2006 CE, with the younger samples enabling quantitative comparison to a large ensemble of modern coral records and instrumental sea surface temperature. A composite record constructed of modern and fossil Kiritimati coral delta O-1(8) records shows a shift toward warmer and fresher conditions from 1970 CE onward, consistent with previously published records in this region. Plain Language Summary The tropical Pacific plays a major role in shaping global temperature and rainfall patterns, but sparse instrumental observations prior to similar to 1950 CE hamper the detection of potential anthropogenic climate signals against the rich background of natural variability in this region. This study demonstrates the utility of reconstructing twentieth century climate trends using an ensemble of multiple, short coral records in data-sparse regions of the tropics. When applied to the central equatorial Pacific, coral data from Kiritimati Atoll resolve a twentieth century shift toward warmer and wetter conditions in this region, in line with evidence from continuous, century-long coral records previously published from this region.