Bottom marine heatwaves along the continental shelves of North America

Recently, there has been substantial effort to understand the fundamental characteristics of warm ocean temperature extremes-known as marine heatwaves (MHWs). However, MHW research has primarily focused on the surface signature of these events. While surface MHWs (SMHW) can have dramatic impacts on marine ecosystems, extreme warming along the seafloor can also have significant biological outcomes. In this study, we use a high-resolution (similar to 8km) ocean reanalysis to broadly assess bottom marine heatwaves (BMHW) along the continental shelves of North America. We find that BMHW intensity and duration varies strongly with bottom depth, with typical intensities ranging from similar to 0.5 degrees C-3 degrees C. Further, BMHWs can be more intense and persist longer than SMHWs. While BMHWs and SMHWs often co-occur, BMHWs can also exist without a SMHW. Deeper regions in which the mixed layer does not typically reach the seafloor exhibit less synchronicity between BMHWs and SMHWs. The authors investigate marine heatwaves on the ocean bottom in the shallow waters surrounding North America. Relative to their surface counterparts, bottom marine heatwaves are often more intense, more persistent, and can occur independently.

Automated summary

Recently, there has been considerable focus on understanding marine heatwaves (MHWs), known as warm ocean temperature extremes. However, most research has concentrated on surface MHWs (SMHW), neglecting the impacts of extreme warming on the seafloor. This study examines bottom marine heatwaves (BMHW) using high-resolution ocean reanalysis, revealing that BMHWs can be more intense and long-lasting than SMHWs, and they can occur independently of SMHWs in deeper regions where the mixed layer does not reach the seafloor with synchronicity between BMHWs and SMHWs typically decreasing.