Corals’ Response to Rising Sea Surface Temperatures for the Past 200 years across the Central and Western Pacific

Skeletons of the scleractinian coral Porites have been extensively utilised as archives of geochemical proxies for sea surface temperature (SST) in paleoclimate studies. However, the sensitivity of coral calcification rates to thermally induced stress from global warming across reefs in the tropical Pacific remains poorly constrained for the past 200 years. Here, we present high-resolution (annual) coral calcification rates with new regional SST data from Kiritimati Island, Kiribati (central Pacific) and Arno Atoll, Marshall Islands (western Pacific).

First, three modern Alizarin-red stained Porites corals from Kiritimati Island spanning 16-20 years growth were used to examine intra-reef variations in coral calcification and to establish in situ SST instrument calibrations. Three Porites microatolls from Kiritimati Island and three Porites microatolls from Arno Atoll were used to reconstruct calcification records over the past 200 years using Coral XDS software. SST time series were determined using δ¹⁸O and Sr/Ca-Li/Mg thermometers and were chronologically calibrated using 13 U-Th ages.

Preliminary results from our novel record of coral calcification and SST from Kiritimati Island confirm the raising SST trend of the last century with El Niño (ENSO) and Pacific Decadal Oscillation cyclicity. Coral calcification mirrors the SST trend following the past two centuries of warming trend. However, extreme and rapid SST anomalies (e.g., extremely high SST during ENSO events) may temporarily restrict coral calcification.