Compound marine heatwaves and ocean acidity extremes

Compound extreme events in two or more oceanic ecosystem stressors are increasingly considered as a threat for marine life. A team of researchers from the University of Bern has now published a first global analysis on compound marine heatwave and ocean acidity extreme events (MHW-OAX events), during which high temperatures in the surface ocean coincide with high proton concentration ([H+]) and low pondus Hydrogenii (pH). Analyzing observation-based data, they show that MHW-OAX events are frequent in the subtropical ocean and relatively rare in the high latitudes and the tropical Pacific. The frequency of compound MHW-OAX events is expected to increase in all oceans, due to ongoing ocean warming and acidification. A large-ensemble Earth system model simulation suggests a 22-fold increase in MHW-OAX event frequency at 2 °C warming relative to a pre-industrial baseline.

Reference: Burger, F.A., Terhaar, J. & Frölicher, T.L. (2022). Compound marine heatwaves and ocean acidity extremes. Nat. Commun., 13, 4722. https://doi.org/10.1038/s41467-022-32120-7