In simple terms, it was thought that the sea ice cover restricts the exchange of gases between the water and the atmosphere, and that this also limits primary production in the area – which also influences gas exchange. Recent research has shown that this is not quite correct, since there are a number of processes associated with sea ice that increase the gas exchange. Researchers are working to quantify the effects of all the different processes in order to produce better estimates of the development of ocean acidification in the Arctic.
More CO2 can be dissolved in cold than in warmer water, so, in respect of ocean acidification, there is a special focus on the Arctic. In addition, the light conditions (24-hour daylight) mean that phytoplankton are active more continuously around the clock, which also results in less pH variation over each 24-hour period. In these areas, it is more interesting to study the annual fluctuations in the phytoplankton’s effect on pH in the upper water layer. Large spatial variation of pH in the Barents Sea has also been documented, which may be due to the oxidation of organic material transported from the land and rivers.
The Arctic is the part of the Earth where the first studies of the effects of ocean acidification are expected to take place. It is at higher latitudes that the sea is expected to first become undersaturated in calcium carbonate. In fact, seasonal undersaturation of aragonite has already been measured at the surface in northern parts of the Arctic Ocean, and models show expectations of constant undersaturation by the middle of this century.
The volume of the summer ice in the Arctic has been dramatically reduced over a few decades, which has led to accelerated absorption of CO2 in the Arctic Ocean, while the brackish water from melting is poor in calcium ions (Ca2 +). Increasing runoff from rivers, where the river water also has a low calcium content, is also contributing to the undersaturation of aragonite in the surface water. Researchers believe we are now heading at full speed towards a tipping point for aragonite in the Arctic Ocean.
Global warming may potentially destabilise large amounts of methane clathrates (frozen methane) stored in the seabed sediments, especially on the continental slopes. This will cause the release of methane into the water column and the atmosphere, which increases vulnerability to ocean acidification in the Arctic. In the East Siberian Sea, large quantities of methane have already been observed leaking from the seabed.