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

Abstract—This article presents the results of a comparison of atmospheric carbon dioxide reanalysis data and phenological phases of large freshwater areas located in the boreal and subarctic zones for 2012–2020. The paper uses the CAMS global greenhouse gas reanalysis data, which are three-dimensional fields of aerosol and chemical component content in the atmosphere, with full coverage of the globe. This study used data on the average CO₂ content in the air column above the water areas. Phenological phases of freshwater bodies (water surface, ice cover, and ice destruction) were determined based on data from the MIRAS microwave radiometer on the SMOS satellite. Comparison and analysis showed that the CO₂ concentration in the atmosphere above the studied water areas has a seasonal cyclical nature. The minimum concentration corresponds to the summer period due to strong photosynthesis in the 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 ice cover destruction, 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 addition to the stable spring maximum of CO₂, freezing lakes located in the boreal zone sometimes experience a strong short-term emission of carbon dioxide, 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 of subarctic zone.