World’s oceans turning acidic faster than expected
Acidification caused by carbon emissions could bring some oceans to a tipping point.
Parts of the world’s oceans appear to be acidifying far faster than scientists have expected.Skip to next paragraph
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The culprit: rising levels of carbon dioxide in the atmosphere pumped into the air from cars, power plants, and industries.
The Southern Ocean represents one of the most high-profile examples. There, scientists estimate that the ocean could reach a biologically important tipping point in wintertime by 2030, at least 20 years earlier than scientists projected only three years ago. Among the vulnerable: a tiny form of sea snail that serves as food for a wide range of fish.
Similar trends are appearing in more temperate waters, say researchers.
The studies suggest the CO2-emission targets being considered for a new global warming treaty are likely to be inadequate to prevent significant, long-lasting changes in some ocean basins.
Scientists over the past decade have detected a clear shift toward acidity since preindustrial times. But that “is not really telling you the story” as it unfolds on smaller but ecologically important scales, says David Archer, a researcher at the University of Chicago who studies the global carbon cycle.
The new research draws on long-term data on changes in ocean chemistry and the effect of those changes on marine life. The data are giving scientists their first clear look at the importance of natural swings in sea-water acidification in estimating overall acidification trends and tipping points.
But even these new studies may be conservative. Recent global CO2 emissions have been outstripping so-called business-as-usual emissions scenarios, which assume that no country adopts climate-specific limits on emissions.
From a human perspective, ocean acidification is relative; no one is talking about dissolving surf boards. On the pH scale – which runs from strong acids such as battery acid to strong bases such as laundry bleach – the oceans fall on the base side of the spectrum. The oceans have a pH of 8. Distilled water is considered neutral, with a pH of 7. Battery acid has a pH of 1.
Typically, seawater is heavily saturated with dissolved calcium carbonate from eroded limestone. This neutralizes any acid that forms from CO2 and leaves plenty of carbonate for marine creatures to use for shell- and reef-building. But as oceans absorb increasing amounts of CO2 from fossil fuels, their stores of calcium carbonate dip. Over time, this reduces carbonate available for marine creatures. Shell and coral formation slows.
Once seawater is too deficient in carbonate, these creatures find it hard to form shells or corals at all. In fact, existing shells start to dissolve, notes Ben McNeil, a researcher at the University of New South Wales in Australia.
In a recent study, he and a colleague looked at trends in the Southern Ocean. Oceans at the top and bottom of the world might be expected to lead in acidification because cold water soaks up more CO2 than warm water. But the duo also found large seasonal swings in carbonate levels. They traced increases in the water’s relative acidity to strong wintertime winds off Antarctica that bring to the surface cold water from the deep, which has low levels of carbonate.