A11C-0086
What atmospheric measurements tell us about methane emissions in the East Siberian Arctic Shelf
Abstract:
Atmospheric methane is the second anthropogenic greenhouse gas after carbon dioxide, contributing 20% to climate forcing since pre-industrial times. It is emitted by a variety of surface sources and mostly destroyed in the atmosphere by the OH radicals. Although methane emission types are identified, large uncertainties remain in their regional quantification. This is the case in the Arctic, where natural methane emissions are significant and estimated in the range of 11-51 TgCH4.y-1 for lands and 1-12 TgCH4.y-1 for ocean (north of 60°N).Subsea permafrost and hydrates in the East Siberian Arctic Ocean Continental Shelf (ESAS) constitute a substantial methane pool, and a potentially large source of methane to the atmosphere. Previous studies based on interpolated oceanographic campaigns estimated atmospheric emissions from this area at 8–17 TgCH4.y-1. Here, we propose insights based on atmospheric observations to evaluate these estimates. Isotopic observations suggest a biogenic origin (either terrestrial or marine) of air masses originating from ESAS during summer. We compare high-resolution simulations of atmospheric methane mole fractions to continuous methane observations to confirm the high variability and heterogeneity of the methane releases from ESAS. Simulated mole fractions including a 8 TgCH4.y-1 source from ESAS are found largely over-estimated compared to the observations in winter, whereas summer signals are more consistent with each others. Based on a statistical analysis of the observations and of the simulations, we find that methane emissions from ESAS are in a range of 0.5–4.5 TgCH4.y-1.