New global maps chart 40 years of ocean heat and acidification extremes

A study published in AGU Advances by ETH Zurich researchers analyzed four decades of data to map 500 'compound' events where marine heat waves and ocean acidification struck the same waters simultaneously, finding they occur more often than random chance would predict. Most events were brief and regional, lasting under three months across roughly 500,000 square kilometers, though one extreme case lasted 20 months.

The researchers used machine learning to fill gaps in acidity data, which is far sparser than temperature records, by combining shipboard CO2 measurements with satellite readings of temperature, salinity and chlorophyll. They found the compound events are tied to upwelling patterns and El Niño/La Niña cycles, with events four times more likely where ocean layers fail to mix, and outside scientists say the work could help anticipate fishery impacts from the developing 2026-2027 El Niño.

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