The carbonate chemistry of the surface ocean is rapidly changing with ocean acidification, a result of human activities1. In the upper layers of the Southern Ocean, aragonite—a metastable form of calcium carbonate with rapid dissolution kinetics—may become undersaturated by 2050 (ref. 2). Aragonite undersaturation is likely to affect aragonite-shelled organisms, which can dominate surface water communities in polar regions3. Here we present analyses of specimens of the pteropod Limacina helicina antarctica that were extracted live from the Southern Ocean early in 2008. We sampled from the top 200 m of the water column, where aragonite saturation levels were around 1, as upwelled deep water is mixed with surface water containing anthropogenic CO2. Comparing the shell structure with samples from aragonite-supersaturated regions elsewhere under a scanning electron microscope, we found severe levels of shell dissolution in the undersaturated region alone. According to laboratory incubations of intact samples with a range of aragonite saturation levels, eight days of incubation in aragonite saturation levels of 0.94–1.12 produces equivalent levels of dissolution. As deep-water upwelling and CO2 absorption by surface waters is likely to increase as a result of human activities2,4, we conclude that upper ocean regions where aragonite-shelled organisms are affected by dissolution are likely to expand.
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This work was supported by the FAASIS (Fellowships in Antarctic Air-Sea-Ice Science), a Marie Curie Early Stage Training Network awarded to N.B. G.A.T., S.F. and P.W. carried out this work as part of the Ecosystems core-science programme at the British Antarctic Survey. G.A.T., P.W. and D.B. received further support during the analysis and synthesis stages from the pelagic consortium of the UK Ocean Acidification programme, funded by NERC, Defra and DECC (grant no. NE/H017267/1). D. McCorkle and A. Cohen of Woods Hole Oceanographic Institution helped develop a shell preparation method and commented on previous drafts of the manuscript. Image analysis was carried out at the University of East Anglia with the assistance of R. Montagna. Sampling operations were supported by the officers and crew of the RRS James Clark Ross with net-sampling equipment support from P. Enderlein of the British Antarctic Survey. P. Bucktrout assisted with graphical presentations.
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