Nature Geosci. 5, 881–885 (2012)

Ocean models predict that the confluence of natural (deepwater ventilation) and anthropogenic (ocean acidification) factors may cause the upper layers of the Southern Ocean to become undersaturated in aragonite — a form of calcium carbonate — by 2050. Such undersaturation is likely to affect aragonite-shelled organisms, which can dominate surface water communities in polar regions and constitute an important component of the oceanic carbon system.

Nina Bednaršek, from the British Antarctic Survey, Cambridge, UK, and co-workers sampled from surface waters with low aragonite-saturation levels (ΩA 1) in the Southern Ocean, and compared the shell structure of a pteropod (Limacina helicina antarctica) — a species of planktonic mollusc — with specimens from aragonite-supersaturated regions using scanning electron microscopy. They found severe levels of shell dissolution in the undersaturated samples.

These findings in live pteropods in their natural environment validate laboratory based studies that showed the potential vulnerability of L. helicina antarctica to ocean acidification. Furthermore, this study demonstrates that ocean acidification is already having an impact — ahead of many aragonite-saturation projections — indicating that regional declines in pteropod populations may occur sooner than previously predicted.