Spatiotemporal Characteristics and Climate Influences on Marine Heatwaves in the Maluku Sea (1996–2025)

Marine heatwaves (MHWs) threaten marine ecosystems, yet long-term MHW characteristics in the Maluku Sea, a strategic area along the Indonesian Throughflow pathway, remain poorly documented. This study analyzes the spatiotemporal characteristics of MHWs during 1996–2025 from daily NOAA OISST v2.1 data and assesses their statistical associations with the El Niño–Southern Oscillation (ENSO) and monsoon variability. MHWs were detected following Hobday et al. (90th percentile, 11-day window, minimum duration of five days). MHW frequency (+0.82 events year⁻¹ decade⁻¹) and duration (+1.8 days decade⁻¹) increased significantly (modified Mann–Kendall, p < 0.05), whereas maximum intensity decreased (−0.09 °C decade⁻¹); these trends are relative to a 1996–2025 baseline in a basin that warmed by 0.26 °C decade⁻¹. ENSO showed a stronger association with monthly MHW frequency than the monsoon index examined (lag 0: r = −0.29, p = 0.002), with more MHWs during La Niña; the monsoon association was not significant after controlling for ENSO. Together they explain less than 9% of the variance, so unexamined processes, including the Indian Ocean Dipole and ocean dynamics, remain important.