Spatiotemporal Characteristics and Driving Mechanisms of Marine Extreme Temperature Events in the Northwest Pacific and Adjacent Continental Shelves

Marine extreme temperature events increasingly perturb marine ecosystems under global climate change, yet it remains unclear whether their characteristics and driving mechanisms are consistent across dynamically distinct regions of the Northwest Pacific (NWP). In particular, a unified understanding spanning the open ocean, western boundary current systems, and adjacent continental shelves is still lacking. Here we synthesize existing findings with new analyses to systematically compare marine extreme temperature events across the open NWP, the Kuroshio Extension (KE), and the Chinese continental shelf. Using GLORYS12V1 reanalysis and OISST v2.1 datasets, surface and seabed extreme events during 1993-2023 were identified, allowing cross-regional comparisons of their spatiotemporal features and governing mechanisms. NWP surface MHWs showed consistent spatial and interannual patterns in GLORYS12V1 and OISST V2.1 datasets. Notably, GLORYS12V1 captured more prolonged MHW events (duration ≥7 days) with longer total durations than OISST V2.1, attributed to its superior representation of complex ocean-atmosphere coupling processes. Seasonally, summer had the widest MHW coverage across both continental shelf and deep-water areas, while spring had the narrowest, with MHWs mostly limited to open ocean regions. During 1993–2019, MHW occurrences in the central NWP showed a statistically significant increasing trend, closely linked to the region’s long-term ocean warming. Distinct seasonal teleconnection patterns were identified: Summer MHWs in the South China Sea (SCS) and low-latitude Pacific correlated positively with the Western Pacific Subtropical High (WPSH) and negatively with the East Asian Summer Monsoon (EASM), indicating that intensified WPSH and weakened EASM collectively favor MHW formation and persistence. Winter MHWs in the western SCS correlated positively with both WPSH and the East Asian Winter Monsoon (EAWM). Strong El Niño events significantly enhanced subsequent MHW occurrences: increasing frequency in the western SCS the following winter and elevating probability across the entire SCS and low-latitude Pacific the next summer. KE extreme events were classified as extended (>70% water column penetration) and shallow (upper 70%). Shallow events featured stronger intensity, shorter duration, and "rapid onset and decay", driven by surface heat flux anomalies (shortwave radiation for MHWs, latent heat flux for MCSs). Extended events exhibited uniform vertical penetration, slow intensity decay, and longer durations, regulated by mesoscale eddies (anticyclonic for MHWs, cyclonic for MCSs). Additionally, Kuroshio Extension current variability indirectly influenced event distribution via horizontal advection of heat and momentum. Turning to the continental shelf, MCSs concentrated in late autumn to spring, while the MHW peak was slightly delayed compared to the open ocean. Vertical synchronicity between surface and seabed events was higher in winter (with a deepened mixed layer) than in summer. Seabed MCS intensity decreased significantly with increasing water depth (Spearman’s r=0.30-0.43, p