Decadal changes in South Pacific sea surface temperatures and the relationship to the Pacific decadal oscillation and upper ocean heat content

Decadal changes in Pacific sea surface temperatures (SSTs) and upper ocean heat content (OHC) remain poorly understood. We present an annual average composite coral Sr/Ca‐derived SST time series extending back to 1791 from Fiji, Tonga, and Rarotonga (FTR) in the Pacific Decadal Oscillation (PDO) sensitive region of the southwest Pacific. Decadal SST maxima between 1805 and 1830 Common Era (C.E.) indicate unexplained elevated SSTs near the end of the Little Ice Age. The mean period of decadal SST variability in this region has a period near 25 years. Decades of warmer (cooler) FTR SST co‐occur with PDO negative (positive) phases since at least ~1930 C.E. and positively correlate with South Pacific OHC (0–700 m). FTR SST is also inversely correlated with decadal changes in equatorial Pacific SST as measured by coral Sr/Ca. Collectively, these results support the fluctuating trade wind‐shallow meridional overturning cell mechanism for decadal modulation of Pacific SSTs and OHC.