In 2004-2005, Russian polar explorers measured for the first time the carbon dioxide concentration in the atmosphere in different seasons at the SP-33 and SP-34 floating stations. Specialists of the Arctic and Antarctic Research Institute, Russian Academy of Sciences, analyzed results of these measurements and came to the conclusion that seasonal fluctuations in the CO2 concentration depended on sea ice growth and thawing.
There is continuous carbon dioxide exchange between the atmosphere and the World Ocean. The CO2 atmospheric concentration changes depending on the season: it is higher in winter and it is lower in summer. When calculating the CO2 balance, the specialists normally did not take into account the role of the Arctic basin, as they assumed that the ice cover almost completely impedes gaseous exchange. However, the most intense seasonal fluctuations are recorded by meteorologists particularly in high latitudes, especially in the area where sea ice is wide spread. According to the St. Petersburg researchers, sea ice significantly impacts the seasonal cycle formation.
Sea ice in the Arctic basin is formed from sea-water with salinity of about 30‰ to 32 ‰. Sweet water freezes right through, and the sea salts brine remains in the ice, it partly flows down towards the bottom of ice surface and partly comes into the upper layers of the Ocean, and partly remains in the closed ice cavities. Calcium ions in the saline solution interact with dissolved acetic acid. As a result of such a reaction, calcium carbonate, water and carbonic acid gas are produced, at that carbonic acid gas together with the brine gets into the upper water layer under the ice and into the atmosphere through microfissures in the ice. In March and April, the air above the Arctic ice is calm, and carbon dioxide is accumulated in the bottom layer of subpolar atmosphere, thus increasing the winter concentration maximum above the frozen ocean.
In summer, ice is thawing together with the snow covering it. On the glacial surface, snowy puddles with cold sweet water appear, where poorly soluble calcium carbonate is suspended. At the zero temperature, lime water reacts with CO2, thus forming dissoluble calcium bicarbonate. Carbon dioxide dissolves excellently in cold water, therefore its summer concentration in the atmosphere decreases not only due to chemical reaction. It is absorbed by desalinated water on the surface of patches of ice-free water, cracks and channel. In summer, plankton life activates in the top water layer, and photosynthesis is taking place, which also requires CO2. As a result of all these processes, summer minimum of carbonic acid gas occurs in the air above the ice and in the water layer under the ice.
Nobody has measured yet the carbon dioxide concentration above and under the ice during the entire year in the Arctic basin and the Arctic seas. Therefore, the researchers can not experimentally prove their hypothesis. Nevertheless, they have indirect evidence. The more ice and water is involved in mutual seasonal transitions, the larger is the range in seasonal fluctuations of the CO2 concentration. Besides, monthly change of carbon dioxide concentration in Barrow during 1980 through 1990 coincides with changes in ice thickness in the Arctic basin.
The Russian researchers assume with confidence that ice formation and growth in winter may be the reason for increase in the CO2 seasonal fluctuations in high latitudes, and the Arctic may basin be the source of carbon dioxide on average during a year. The more ice freezes on in winter, the higher the CO2.concentration will be.