Biogeochemical extremes and compound events in the ocean

While we have come to realize that the long-term trends in ocean warming, ocean acidification, and ocean deoxygenation will push the ocean into unchartered territory, we have paid so far little attention to the role of variability around these trends, especially not the role of extremes. Writing in Nature, the authors show that such extremes are intensifying strongly in response to these trends, and that these trends increase the likelihood of compound extremes, i.e., situation where the ocean is not only unusually hot, but also characterized by extreme conditions with respect to ocean acidity (extremely low pH or high [H+]) and oxygen (extremely low oxygen). Concretely the authors show that the massive heatwave that occurred off the west coast of North America between 2013 and 2015, also known as the “Blob”, was also at the same time an ocean acidification and a low oxygen extreme. 

Reference: Gruber, N., Boyd, P. W., Frölicher, T. L., et al., (2021). Biogeochemical extremes and compound events in the ocean. Nature, 600, 395–407.  https://doi.org/10.1038/s41586-021-03981-7.