Subsurface Marine Heatwaves Intensity Projected to Decrease in the Caribbean Sea Under RCP8.5

Abstract Marine heatwaves (MHWs)—extreme ocean temperature anomalies—are increasing in frequency and intensity globally, yet their vertical structure and drivers remain underexplored in the Caribbean Sea (CS), a region of critical ecological and socioeconomic importance. Using high resolution climate model simulations and reanalysis fields, we show that MHW intensity in the CS peaks in the subsurface, where vertical gradients of temperature are stronger, and that MHWs are associated with the passage of Rossby waves. Projections under the RCP8.5 scenario reveal that while the ocean continues to warm to the end of the century, subsurface MHW intensity weakens. This decline is associated with a weaker thermocline, reduced ocean currents and eddy kinetic energy, and less energetic Rossby waves. Reducing uncertainties in climate projections will be essential to improve our understanding of how marine heat extremes may evolve and affect Caribbean ecosystems.