Disparate acidification and calcium carbonate desaturation of deep and shallow waters of the Arctic Ocean

The Arctic Ocean is acidifying from absorption of man-made CO 2 . Current predictive models of that acidification focus on surface waters, and their results argue that deep waters will acidify by downward penetration from the surface. Here we show, with an alternative model, the rapid, near simultaneous, acidification of both surface and deep waters, a prediction supported by current, but limited, saturation data. Whereas Arctic surface water responds directly by atmospheric CO 2 uptake, deeper waters will be influenced strongly by intrusion of mid-depth, pre-acidified, Atlantic Ocean water. With unabated CO 2 emissions, surface waters will become undersaturated with respect to aragonite by 2105 AD and could remain so for ∼600 years. In deep waters, the aragonite saturation horizon will rise, reaching the base of the surface mixed layer by 2140 AD and likely remaining there for over a millennium. The survival of aragonite-secreting organisms is consequently threatened on long timescales. Anthropogenic CO 2 is acidifying the Arctic Ocean surface, with current models predicting downward penetration to deep waters. Here, based on an alternative model supported by available saturation data, the authors show simultaneous acidification of both surface and deep waters.