A spatiotemporal analysis of marine heatwave frequency around Malta

Abstract

As global climate change intensifies due to anthropogenic influences, marine heatwaves (MHWs) have increased in both frequency and duration, posing significant risks to marine ecosystems. These extreme warming events occur not only at the ocean surface but also at subsurface depths, where their dynamics and ecological impacts remain less understood. This study analyzes in-situ buoy data, sea surface temperature (SST) satellite data, and reanalyzed subsurface temperature model data from the Marine Copernicus Service in the central Mediterranean Sea to investigate MHW occurrence across vertical profiles over more than a decade. Using the 95th percentile temperature threshold for each grid cell and a minimum event duration of five to ten days, MHW counts were calculated spatially and complied annually to assess temporal patterns. Surface MHWs showed some correlation with atmospheric heatwaves during the same years, indicating the influence of atmospheric conditions on ocean surface warming. However, the comparison between surface and subsurface temperature anomalies revealed the presence of subsurface MHWs that often persisted independently from surface events. These subsurface heatwaves retained temperatures for extended periods, even at depths approaching 500 meters. These findings show the growing significance of subsurface MHWs and emphasize the need of increased monitoring and research of the vertical extent and duration of these events. Understanding these deeper warming events is important to prevent damage to the marine ecosystems, both pelagic and benthic. This study highlights the importance of integrating subsurface data in MHW research to improve predictions, ecological impact assessments, and inform sustainable marine management practices in a world affected by warming temperatures.