Sea-surface temperature extremes during the last interglacial

Extreme ocean warming poses an escalating threat to coral reef ecosystems, yet the long-term frequency and magnitude of past bleaching-relevant temperature extremes remain poorly constrained. Here we apply a combined pooled geochemical and individual foraminifera analysis (IFA) approach to reconstruct sub-annual sea surface temperature (SST) variability across major interglacial maxima of the past 450 kyr at IODP Site U1467 in the Maldives and, for comparison, ODP Site 1006 on the Great Bahama Bank. IFA δ¹⁸O and Mg/Ca palaeothermometry reveal that MIS5e exhibited the warmest and most variable SSTs of all intervals examined, with strongly positively skewed temperature distributions and frequent excursions above modern coral-bleaching thresholds (49% of estimates). MIS7a also displays a high incidence of bleaching-relevant temperatures (45%), despite smaller variance. Comparison with the Bahamas indicates that although mean MIS5e SSTs were ~ 1.8°C lower there than in the Maldives, bleaching-threshold exceedances (51%) were nonetheless common. The Maldives record further reveals enhanced seasonality or climatic instability during MIS5e, likely driven by the interaction of high-eccentricity orbital forcing with regional monsoon and circulation processes. Despite thermal conditions sufficient to cause widespread bleaching, no evidence of interglacial reef collapse has been identified, implying either incomplete preservation or elevated thermal tolerance among MIS5e reef communities. Our findings highlight MIS5e as a critical interval for understanding extreme tropical warming and reef ecosystem resilience, offering rare insights into the conditions under which future coral bleaching may unfold.