Ocean stratification and sea-ice cover in Barents and Kara seas modulate sea-air methane flux: satellite evidence

Abstract

The diverse range of mechanisms driving the Arctic amplification are not completely understood and, moreover, the role of the greenhouse gas methane in Arctic warming remains unclear. Strong sources of methane at the ocean seabed in the Barents Sea and other polar regions are well documented. Nevertheless, those data suggest that negligible amounts of methane fluxed from the seabed enter the atmosphere, with roughly 90% of the methane consumed by bacteria. The observations are taken during summer, which is favorable for collecting data but also characterized by a strongly-stratified water column. In winter the stratification weakens and after a breakdown of the pycnocline, convection, storms, and turbulent diffusion can mix the full-depth water column in high latitudes.TheMixed Layer Depth (MLD) in the ice-free Central/Southern Barents Sea is deepening and the ocean-atmosphere methane exchange increases.. An additional barrier for the air-sea flux is seasonally and interannually variable sea-ice cover in partially ice-covered seas. We present Thermal IR space-based spectrometer data between 2002 and 2019 that shows increased methane concentration anomalies over the Barents and Kara seas in winter months. The seasonal methane cycle amplitude north of the Kara Sea has more than doubled since the beginning of the century; this may be interpreted as an effect of sea-ice decline and/or an evidence for growth of seabed emissions. A progressing degradation of Arctic sea-ice cover may lead to increased methane flux and, through a positive feedback loop, to further warming.