Abstract: The results of studying the dynamics of parameters of the carbonate system in the middle and lower reaches of the Ob River in July 2016 were analyzed. The distributions of the carbonate characteristics of the river waters were found to follow a steady latitudinal trend determined by the landscape-geochemical conditions of the drainage basin and by the permafrost distribution. The first field data on the magnitude and direction of the CO 2 fluxes in the Ob River water–atmosphere system were presented. It was shown that the waters in the middle and lower reaches of the river are multiply supersaturated with CO 2 with respect to its atmospheric content, and the daily average evasion reaches 625.9 mmol m –2 day –1 at an average value of 102.1 mmol m –2 day –1 . It was determined that the waters of the Ob River in the studied reaches are a significant CO 2 source to the atmosphere; according to conservative estimates, the total flux in July was 2 × 10 11 g of carbon in the form of CO 2 .
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