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Abstract Marine heatwaves (MHWs) are increasing in frequency and intensity globally and are among the greatest threats to marine ecosystems. However, limited studies have characterized subsurface MHWs, particularly in shallow waters. We utilized nearly two decades of full water-column (~ 10 m) observations from a unique automated profiler in central California to characterize, for the first time, the vertical structure of MHWs in a shallow nearshore upwelling system. We found MHWs have similar average durations and intensities across all depths, but there were ~ 17% more bottom MHW days than surface MHW days. Nearly one third of bottom MHWs occurred independently of surface MHWs, indicating that satellites miss a significant fraction of events. MHWs showed distinct seasonality with more frequent and intense events during the fall/winter when weak stratification allowed for MHWs to occupy a larger portion of the water column and persist longer. During summer, strong stratification limited the vertical extent of MHWs, leading to surface- and bottom-trapped events with shorter durations and intensities. Additionally, MHW initiation and termination across depths was consistently linked to anomalously low and high coastal upwelling, respectively. This study highlights the need for expansion of subsurface monitoring of MHWs globally amid a warming planet.
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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.
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- Award ID(s):
- 2231237
- PAR ID:
- 10665470
- Publisher / Repository:
- AGU
- Date Published:
- Journal Name:
- Geophysical Research Letters
- Volume:
- 52
- Issue:
- 23
- ISSN:
- 0094-8276
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript
- Journal Article:
- https://doi.org/10.1029/2025GL117730
