Environment: Summer highs for Arctic Ocean acidity

The peak in levels of acidity of the Arctic Ocean may shift from winter to summer, a modelling paper in Nature suggests. The findings could have negative implications for marine ecosystems.

Atmospheric CO2 is able to influence levels of CO2in the ocean via processes that depend on the temperature, the amount of dissolved CO2 and pH of seawater. It has been suggested that as the level of CO2 in the atmosphere increases, seasonal variation in the levels of CO2 in the ocean and pH will also increase. In the Arctic Ocean the observed timings for peak CO2 levels are in the winter (and therefore the acidity), as biological processes in the summer manage CO2 levels.

James Orr and colleagues assessed the monthly variations and the potential future changes in ocean CO2 levels across 27 Earth systems models. While the models have similar historical timings, the authors suggest that by 2100 the summer levels of CO2 across the Arctic Ocean will gradually become higher, relative to the annual mean, under mid-to-high CO2 emissions scenarios. This inversion has not previously been observed with climate-related variables. The authors indicate that the main driver for this change is the earlier retreat of sea ice and summer sea surface warming. This change may also worsen summer ocean acidification, which could impact marine organisms by making them more vulnerable to heightened temperature.