Relation of Changes in CO2 Concentration over Large Water Areas of the Boreal and Subarctic Zones of the Northern Hemisphere with Their Phenological Phases Determined from SMOS Satellite Data

The paper presents the results of comparing the atmospheric carbon dioxide reanalysis data and phenological phases of large freshwater areas located in the boreal and subarctic zone for 2012–2020. The data from the CAMS global greenhouse gas reanalysis, which are three-dimensional fields of aerosols and chemical constituents in the atmosphere, with full coverage of the globe, were used in this work. The data used in this study were the average CO2 content in the air column over the water areas. The phenological phases of freshwater bodies (water surface, ice cover, ice destruction) were determined using data from the MIRAS microwave radiometer of the SMOS satellite. The comparison and analysis showed that the CO2 concentration in the atmosphere over the studied water areas has a seasonal cyclic character. The minimum concentration corresponds to the summer period due to strong photosynthesis in water areas, as a result of which carbon dioxide is absorbed in the water column. The maximum concentration of CO2 over water areas corresponds to the period of destruction of the ice cover, leading to the release of carbon dioxide accumulated during the winter period, which is “sealed” in the ice and in the water column under the ice. In freezing lakes located in the boreal zone, in addition to the stable spring CO2 maximum, a strong short-term release of carbon dioxide is sometimes observed, also corresponding to the stage of ice cover destruction. This emission is explained by the higher bioproductivity of water bodies in the boreal zone compared to water areas in the subarctic zone.