The role of river runoff in the Kara Sea surface layer acidification and carbonate system changes

Abstract

This study aims to perform the results of the investigation of the Kara Sea carbonate system (CS) changes and the factors that determine it. The important feature of the Kara Sea water structure is strong stratification caused mainly by the Ob' and Yenisey rivers discharge which is estimated as 81% of the total continental runoff to sea. Occurring climate changes, as an increase in the total volume of the Arctic Ocean water (due to melting of glaciers, sea ice decline and river runoff increase), air temperature and CO 2 concentration growth should affect greatly the Kara Sea CS. However, riverine water influence seems to be the main driver of future acidification of the Kara Sea water due to permafrost thawing as it stores a great amount of buried carbon. An increase of carbon (mainly inorganic) flow to the sea will lead to carbonate equilibrium shift, oxidation of organic matter and release of CO 2 that ultimately leads to a decrease in pH and therefore acidification. The area of the riverine plume depends on the amount of freshwater flowing into the sea and the conditions of the wind forcing. According to the data from Shirshov Institute cruises within the plume area aragonite saturation is below 1 that shows its state as acidified. Prevalence of pCO 2 values in the freshened surface layer over the atmospheric shows that atmospheric carbon dioxide, apparently, cannot serve as the main driver for the acidification of the surface waters of the Kara Sea. At the shallow shelf to the north of the Ob′ Inlet mouth we observe acidification of the whole water column from surface to the bottom layer due to elevated riverine discharge and increase of flowing terrestrial carbon.

Water Exchange Between the Gulf of Ob and the Kara Sea During Ice-Free Seasons: The Roles of River Discharge and Wind Forcing

“…Finally, the process of mixing of saline seawater and river discharge in the Gulf of Ob determines the initial formation of the Ob-Yenisei plume, which spreads over a wide area in the Kara Sea and is among the largest freshwater reservoirs in the Arctic Ocean. As a result, the study on the formation of the Ob-Yenisei plume is important for understanding many local processes in the Kara Sea, including circulation (Osadchiev et al, , 2020a(Osadchiev et al, , 2021a, sediment transport , carbon cycle and acidification (Polukhin, 2019), anthropogenic pollution (Pogojeva et al, 2021;Yakushev et al, 2021), as well as the large-scale freshwater transport in the Eastern Arctic (Haine et al, 2015;Janout et al, 2015;Carmack et al, 2016;Nummelin et al, 2016;Osadchiev et al, 2020bOsadchiev et al, , 2021b.…”

Interplay between eutrophication and climate warming on bacterial communities in coastal sediments differs depending on water depth and oxygen history

“…Shallow coastal areas are in general more exposed to anthropogenic influenced changes related to climate change or eutrophication, such as input of nutrients from land 47 , increased acidification 48 , and faster warming 49 of the water column reaching the sediments. However, these sediments have due to their nature a constant oxygen input from e.g.…”

Carbon Dioxide Flux at the Water–Air Boundary at the Continental Slope in the Kara Sea

“…2 and 3b). In the freshening surface layer on the outer shelf between stations 6879 and 6883, pCO 2 was above 400 ppm, which is typical for the Kara Sea affected by river runoff [20]. At the seaward stations of the section (stations 6884-6887), in the upper biologically active layer 0-60 m, pCO 2 was 252-353 ppm.…”

“…Model calculations [23] and analysis of field data [20] have shown high variability of the parameters of the carbonate system of the Kara Sea, a decrease in pH of its water, and its saturation with aragonite, which is an indicator of the acidification process. The dynamics of the runoff of the largest Siberian rivers, Ob and Yenisei, has been ascertained to be an important factor of this variability [13,20]. However, the direction and intensity of CO 2 flux at the ocean-air boundary has been insufficiently studied for different regions of the Kara Basin.…”