Southern Ocean acidification causing shells to lose weight

The shells of tiny amoeba-like creatures called foraminifera that live in the ocean's surface have become thinner relative to shells from the pre-industrial age, according to a report online in Nature Geoscience. The finding proves that increasing carbon uptake in the ocean has a direct effect on the ability of microorganisms to make shells. Globally, foraminifera comprise up to 50% of the carbonate flux to the deep sea ? sinking shells help to transport organic carbon from the surface ocean.

Using sediment traps located in the Southern Ocean, William Howard, Andrew Moy and colleagues collected the shells of one species of foraminifer, Globigerina bulloides, as they fell towards the sea floor. They compared the mass of the shells, which are about the size of a grain of sand, to the mass of older shells collected from the sea floor. The researchers found that modern shell weights were 30 to 35% lower than those that formed prior to the industrial period, which they attribute to the acidification of the Southern Ocean ? a process driven by the uptake of anthropogenic carbon dioxide.

The effect of this weight loss on the survival of the species is not immediately clear, but the study confirms the findings of previous laboratory experiments that suggest increasing carbon dioxide in the oceans could reduce the ability of marine organisms to build their shells.

doi: 10.1038/ngeo460

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