Coral‐Derived Western Pacific Tropical Sea Surface Temperatures During the Last Millennium

Reconstructions of ocean temperatures prior to the industrial era serve to constrain natural climate variability on decadal to centennial timescales, yet relatively few such observations are available from the west Pacific Warm Pool. Here we present multiple coral‐based sea surface temperature reconstructions from Yongle Atoll, in the South China Sea over the last ~1,250 years (762–2013 Common Era [CE]). Reconstructed coral Sr/Ca‐sea surface temperatures indicate that the “Little Ice Age (1711–1817 CE)” period was ~0.7°C cooler than the “Medieval Climate Anomaly (913‐1132 CE)” and that late 20th century warming of the western Pacific is likely unprecedented over the past millennium. Our findings suggest that the Western Pacific Warm Pool may have expanded (contracted) during the Medieval Climate Anomaly (Little Ice Age), leading to a strengthening (weakening) of the Asian summer monsoon, as recorded in Chinese stalagmites. Plain Language Summary Tropical Pacific climate variability influences global climate system on interannual and longer timescales. In contrast to the eastern and central tropical Pacific, where paleo–sea surface temperature data are relatively abundant, such data are fairly sparse in the western tropical Pacific, which limits our understanding of Pacific Warm Pool and its role in low‐frequency climate variability. Here we present a multiple coral‐based estimates of monthly resolved sea surface temperature from the Yongle Atoll, South China Sea, that span segments of the last 1,250 years. We demonstrate significant variations in mean sea surface temperature over this period—with warmer conditions during the so‐called “Medieval Climate Anomaly” and cooler conditions during the so‐called “Little Ice Age,” in keeping with compilations of Northern Hemisphere temperature over this period. Our data also reveal unprecedented warming of sea surface temperatures in the late 20th century and early 21st century that are unprecedented in the past 1,250 years. We believe that our manuscript will be of broad interest to geologists, climatologists, and coral reef scientists, given the paucity of climate records from the region. Key Points Coral Sr/Ca reconstructions indicate interannual to centennial‐scale SST variations in the tropical western Pacific over the past 1,250 years Western tropical Pacific SST was relatively cool during the “Little Ice Age” and warm during the “Medieval Climate Anomaly” The late 20th century is the warmest interval of the l