Biogeochemical extremes and compound events in the ocean

Gruber, N., Boyd, P. W., Frölicher, T. L., & Vogt, M. (2021). Biogeochemical extremes and compound events in the ocean. Nature, 600(7889), 395–407.

The ocean is warming, losing oxygen and being acidified, primarily as a result of anthropogenic carbon emissions. With ocean warming, acidification and deoxygenation projected to increase for decades, extreme events, such as marine heatwaves, will intensify, occur more often, persist for longer periods of time and extend over larger regions. Nevertheless, our understanding of oceanic extreme events that are associated with warming, low oxygen concentrations or high acidity, as well as their impacts on marine ecosystems, remains limited. Compound events—that is, multiple extreme events that occur simultaneously or in close sequence—are of particular concern, as their individual effects may interact synergistically. In this paper authors assess patterns and trends in open ocean extremes based on the existing literature as well as global and regional model simulations. They discuss the potential impacts of individual and compound extremes on marine organisms and ecosystems and propose a pathway to improve the understanding of extreme events and the capacity of marine life to respond to them. The conditions exhibited by present extreme events may be a harbinger of what may become normal in the future. As a consequence, pursuing this research effort may also help to better understand the responses of marine organisms and ecosystems to future climate change.


Policy relevant message
Since the pre-industrial times, marine heatwaves have become 10 x more common and low oxygen extremes have become about 5 x more frequent. Ocean acidity extremes have become essentially near permanent. All three types of extreme events will increase in frequency, magnitude and intensity with continuously rising atmospheric carbon emissions and global temperature.