Abstract Marine heatwaves (MHWs) adversely impact marine ecosystems globally, yet data scarcity limits our understanding of their subsurface extent, particularly in estuaries. Using a high‐resolution regional ocean model, we characterized the horizontal extent and subsurface structure of MHWs across the Chesapeake Bay (CB). Additionally, we developed a supplementary definition for local climatology‐identified MHWs, “Vertical MHWs,” which quantifies their water column presence, and developed a new MHW vertical classification scheme. Surface MHWs were generally shorter, more frequent and intense, and impacted ∼5% of the CB surface area, while the deepest MHWs were generally longer, less frequent and intense, and regularly occupied >50% of deep‐water areas. Synchronous MHWs—a vertical MHW class which occurs simultaneously in the surface and bottom sometime during their duration—were predominant in shallow regions (isobaths 9 m) and occurred primarily during the highly stratified spring‐summer season. High synchronicity in the shallow regions indicates that a surface MHW signal likely reflects a concurrent bottom one, potentially impacting benthic communities within days, across the vast majority of the CB. Meanwhile, analyses of asynchronous events suggest surface MHWs are inconsistent predictors of subsurface events and their vertical structure, especially in the deeper regions of CB, highlighting the need for expanded monitoring to better understand, predict, and manage MHW impacts on coastal and estuarine ecosystems.
Shunk et al. (Fri,) studied this question.