Why Marine Heat Waves and Acidification Strike Together

Eos reports that marine heat waves and extreme ocean acidification each pose serious threats, but when they happen together their impacts can intensify. The 2013‑2015 “Blob” in the northeastern Pacific illustrated this, with fisheries closed, marine mammals stranded and seabirds dying as waters grew both warmer and more acidic. Researchers Gregor and Gruber analyzed forty‑three years of monthly surface temperature and acidity data from 1982 to 2024, defining extreme events as those exceeding the ninety‑fifth percentile for both variables. They found compound heat‑acidification events occur roughly four times more often than chance in low‑to‑midlatitude regions where permanent stratification traps heat and drives acidity upward. Most of these events cover areas smaller than five hundred thousand square kilometres—about the size of Spain—and last around a month, though the Blob persisted for more than a year. The study also showed that El Niño and La Niña influence where the combined stressors arise, with warming or cooling water lenses altering upwelling patterns in neighboring zones. The findings highlight that climate‑driven ocean changes can co‑occur more frequently than expected, underscoring the need for more research on acidification alongside heat stress.

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