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Shifting the acidity peak from winter to summer in the Arctic Ocean and the threat to its ecosystem

​A Franco-German study coordinated by the LSCE (CEA-CNRS-UVSQ) estimates that climate change could shift the peak in Arctic Ocean acidity from winter to summer, which would be disruptive to the ecosystem.

Published on 5 October 2022

Acidity in Arctic waters is naturally highest in winter and lowest in summer, when there is less ice pack and light makes photosynthesis possible.

Scientists have studied the changing seasonality of this phenomenon under global warming, since the acidity of water increases with temperature (although the solubility of CO2 in cold water is higher than in warm water). This is because in warmer waters, the reaction of CO2 with water produces more protons.

Their simulations show that the acidifying effect of increasingly hot summers would eventually outweigh the opposite effect of photosynthesis. By the year 2100, the peak in acidity could shift by six months, from winter to summer. This would be a seasonal change of unprecedented magnitude, coinciding with the period of greatest biological activity. Clearly, this factor exacerbates the impact of acidity on ecosystems.

Calcifying marine organisms may be the most sensitive to this, especially pteropods – mollusks also known as sea butterflies that are important in the food chain – which are already showing signs of shell degradation. Nevertheless, some non-calcifying organisms are also vulnerable at certain life stages. This is particularly the case for two key species, the small crustacean Calanus glacialis and the polar cod. The latter is the main link between zooplankton and higher trophic levels, including other fish, seabirds and marine mammals.

This change – unprecedented in the biological domain, where seasonality can be shifted by a month or so – is caused by increasing atmospheric greenhouse gases, primarily CO2, which warms Arctic air temperatures, melts more sea ice, and leads to dramatic summer warming of the Arctic Ocean's surface waters.

This is the first study to examine the future potential for temporal shifts in ocean acidity seasonality. Compared to previous studies of other climate variables, this study reveals much larger changes.

This work was conducted in collaboration with LOCEAN (Laboratoire d'océanographie et du climat: expérimentations et approches numériques), the Institut Pierre-Simon Laplace, and the AWI (Alfred Wegener Institute for Polar Research) in Germany.

Read the News and Views article on the Nature website. 

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