Methane Emission From Barents And Kara Seas In Winter: Satellite Evidence.

Abstract:

The diverse range of mechanisms driving Arctic amplification are not completely understood and, moreover, the role of the greenhouse gas methane in Arctic warming remains unclear. Strong sources of methane, including gas hydrates, at the ocean seabed in the Barents Sea and other polar regions are well documented. Observations are often taken during summer season, which is favorable to collect data but characterized by a strongly-stratified water column. Those data suggest that negligible amounts of methane fluxed from the seabed enter the atmosphere, with roughly 90% of the methane consumed by bacteria. In winter, the stratification weakens; after a breakdown of the pycnocline, convection, storms, and turbulent diffusion can mix the full-depth water column in high latitudes. In the year-round ice-free Central/Southern Barents Sea, this increases the ocean-atmosphere methane exchange that is reflected in the deepening of the seawater Mixed Layer Depth (MLD). An additional barrier for methane transfer into air is seasonally and interannually variable sea-ice cover. Short-Wave satellite techniques require sunlight and ineffective in the Arctic. We present Thermal IR space-based spectrometer data that shows increased methane concentration anomaly over the Barents and Kara seas in winter months between 2003 and 2019. The seasonal methane cycle amplitude over a domain 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 seabed emission growth. A progressing degradation of Arctic sea-ice cover may lead to increased methane flux and, through a positive feedback loop, to further warming.