Methane anomalies in the near-water atmospheric layer above the shelf of East Siberian Arctic shelf

Abstract

Simultaneous measurements of methane in the nearwater atmospheric layer and in the surface water layer were carried out for the first time in a shallow-water region of the East Siberian shelf. It follows from the data obtained that the regions of anomalously high values of methane concentration in the air (up to 8 ppm) spatially coincide with the patches of anomalously high concentrations of methane dissolved in water (up to 5 · 10 2 nM). The analysis of possible sources allowed us to formulate a hypothesis that the genesis of the distinguished anomalies can may be related to the deep sources of methane anomalies. Deep sources of methane include modern methane and/or ancient methane accumulated in the deposits of natural gas and methane gas hydrates. During warm interglacial epochs, the high latitudes of the Northern Hemisphere deliver methane into the atmosphere maintaining methane concentrations in the Arctic atmosphere higher by 8‐10% than that in the Antarctica atmosphere. During cold glacier epochs, this gradient decreases to practically insignificant levels [1]. Land ecosystems are considered the main sources of methane in the arctic region. A special role belongs to wetlands and thermal karst sink lakes underlining yearround by non-freezing talics regions. The total contribution of such ecosystems in the global methane cycle is estimated at 27‐28% (140‐145 Tg, where 1 Tg = 10 12 g) [2]. It is known that the Barrow atmospheric monitoring station in Barrow (Alaska, United States) annually records increased concentrations of methane in the atmosphere. Their maximums are continue from the summer season to the autumnal‐winter interseasonal period, when the production of land Arctic ecosystems decreases gradually and terminates [3]. Hence, the source maintaining high methane emission in the autumn‐winter period should possess a potential related to the influence of the other factors that are endemic for the Arctic region. Thus far, the role of marine Arctic ecosystems as methane sources has been considered insignificant. At the same time, data in [4, 5] indicate that the role of the Arctic Ocean (AO) is significantly underestimated. For example, the total flux contribution of methane into the atmosphere from the shallow-water part of the shelf only in the Russian seas of to the arctic region can reach the values comparable with the contribution of all continental seas the World Ocean [4]. In our opinion, the East Siberian Arctic shelf should be considered with special attention.