First experimental estimation of the methane ebullition fraction in water column from the bottom to the surface: application for the East Siberian Arctic Shelf

<p>The key area of the Arctic ocean for atmospheric venting of CH<sub>4</sub> is the East Siberian Arctic Shelf (ESAS). The ESAS covers >2 million square kilometers (equal to the areas of Germany, France, Great Britain, Italy, and Japan combined). This vast yet shallow region has recently been shown to be a significant modern source of atmospheric CH<sub>4</sub>, contributing annually no less than terrestrial Arctic ecosystems; but unlike terrestrial ecosystems, the ESAS emits CH<sub>4 </sub>year-round due to its partial openness during the winter when terrestrial ecosystems are dormant. Emissions are determined by and dependent on the current thermal state of the subsea permafrost and environmental factors controlling permafrost dynamics. Releases could potentially increase by 3-5 orders of magnitude, considering the sheer amount of CH<sub>4</sub> preserved within the shallow ESAS seabed deposits and the documented thawing rates of subsea permafrost reported recently.</p><p>The purpose of this work is to determine the methane ebullition fraction in water column: from the bottom to the surface, which is a key to evaluate quantitively methane release from the ESAS bottom through the water column into the atmosphere. A series of 351 experiments was carried out at to determine the quantity of methane (and other greenhouse gases) delivered by bubbles of various sizes through a water column into the atmosphere. It has been shown for depth up to 22 m (about 30% of the ESAS) that pure methane bubbles, depending on their diameter and water salinity, transported to the surface from 60.9% to 85.3% of gaseous methane.</p><p>This work was supported in part by grants from Russian Scientific Foundation (№ 18-77-10004 to DCh, DK, AK, № 19-77-00067 to EG), the Ministry of Science and Higher Education of the Russian Federation (grant ID: 075-15-2020-978 to IS). The work was carried out as a part of Federal[ПW1]  assignment № АААА-А17-117030110031-6 to AS.</p>