Role of intraseasonal and interannual processes in ocean heat content anomalies east of Mindanao

Ocean heat content (OHC) variability in the western tropical Pacific serves as a key component of the El Niño-Southern Oscillation (ENSO) cycle. Traditionally, OHC in the western tropical Pacific is expected to be tightly correlated with ENSO. Nevertheless, CTD observations east of Mindanao Island (8°N, 126°–130°E) revealed opposite upper 200 m OHC anomalies on December 8, 2012 (CTD-12) and December 31, 2017 (CTD-17). These two events deviate markedly from the canonical ENSO–OHC relationship, indicating that dynamical processes other than ENSO may exert substantial control OHC variability in this region. To identify these processes, we conducted a comprehensive heat budget analysis using reanalysis datasets. Results demonstrate that interannual variations in the Mindanao Dome (MD) and mesoscale eddy activity act as two primary drivers of OHC anomalies east of Mindanao during 2011–2019. Further analysis reveals that ENSO-decoupled OHC anomalies arise when anomalous local wind stress curl forces MD and circulation adjustments opposite to those expected from ENSO, while coherent, intensified mesoscale eddies amplify or maintain these anomalies. On average, in ENSO-decoupled OHC anomalies the mean-flow heat transport linked to MD variability contributes 53% of the total advective heat transport, whereas mesoscale eddies contribute 39%. These findings establish that local wind forcing and mesoscale eddies jointly regulate departures from the canonical ENSO-driven thermal evolution in the western tropical Pacific, providing new insight into the dynamics governing OHC variability.