Why marine heat waves and acidification strike together
Marine heat waves and extreme ocean acidification events are each damaging on their own. But when both stressors hit simultaneously, their individual effects can be exacerbated.
Marine heat waves and ocean acidification each pose significant threats to marine ecosystems. However, when these two climate stressors coincide, the combined impact can be even more devastating. The 2013-2015 marine heat wave known as "The Blob" in the northeastern Pacific serves as a prime example, causing widespread damage to fisheries, marine mammals, seabirds, and altering the distribution of sea creatures.
Despite the clear need for more research on compound heat-acidity events, prior studies have focused more on the marine heat wave component. By analyzing 43 years of monthly data from 1982-2024, researchers Gregor and Gruber have discovered that these compound events are more frequent than would be expected by chance. In the low to midlatitudes, such events occur about four times more often than expected, primarily in regions with permanent stratification.
The combination of heat waves and acidification in these areas exacerbates the problem, while in upwelling regions near the equator, warm surface waters prevent the surfacing of deep acidic waters, resulting in lower acidity than usual. Most compound marine heat-wave and acidification extremes are small, lasting around a month, but larger, longer-lasting events do occur, with consequences that can persist for years.
El Niño and La Niña events play a role in shaping the distribution of compound events, but their effects are often felt beyond the equatorial Pacific region.
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