March 30, 2018 — One of the consequences of pumping more and more carbon dioxide into the atmosphere is the changing chemistry of the world’s oceans. Until now, the ocean has acted as a big sponge, soaking up about one-third of the CO2 released by human activities.
But now, scientists are watching a vast experiment unfold. All that carbon dioxide is triggering chemical reactions that is turning the oceans more acidic, which in turn is making life tough for lots of marine organisms. Oysters and other shellfish have been hit by die-offs in the Pacific Northwest and Gulf of Maine, while tropical reefs are dissolving faster than they can rebuild, according to a recent study in the journal Science.
Some researchers are seriously considering geoengineering to reverse the slow acidification of the ocean. Dissolving minerals like olivine or limestone into seawater would increase its alkalinity. (Remember the pH strip in your 10 gallon fish tank? Blue=alkaline, red=acidic.) Not only would that make it easier on marine life, but it would also allow the ocean-sponge to soak up more carbon dioxide from the atmosphere. Two British scientists proposed this idea last year in a paper in the journal Reviews of Geophysics, predicting that with a bit more research (and money) it may be possible to capture hundreds of billions to trillions of tons of carbon without messing up the marine ecosystem.
But this kind of massive planetary experiment needs lots of small-scale work in the laboratory before it’s ready. So in the meantime, marine scientists are trying to find which species will come out on top in a more acidic ocean.
In Sweden, a group of researchers tested survival in an artificially acidic ocean. In a fjord, they built an enclosed, floating test tube they called a “mesocosm” and filled it with phytotoplankton, zooplankton, and tiny herring larvae. Then they turned up the dissolved carbon dioxide, tracking herring survival over time as the acidity increased.
A similar lab experiment with codfish, another important Northern European food fish, killed off the fish. “Our surprise is that we didn’t find that,” said Catriona Clemmesen-Bockelmen, a marine ecologist from the GEOMAR Helmoltz Center for Ocean Research in Kiel, Germany, and a co-author on the study in Nature Ecology and Evolution. “Instead, we had a higher survival rate.” The herring, it seemed, liked the extra acidity.