Atmospheric constraints on the methane emissions from the East Siberian Shelf

Antoine Berchet,Jean-Daniel Paris,Yrjo Viisanen,Juha Hatakka,Robin Locatelli,Euan Nisbet,Rebecca Fisher,Frédéric Chevallier,Ed J Dlugokencky,Tuomas Laurila,James France,Ove Hermansen,Viktor Ivakhov,Doug E J Worthy,Isabelle Pison,Philippe Bousquet,David Lowry

doi:10.5194/acp-16-4147-2016

Abstract

Abstract. Subsea permafrost and hydrates in the East Siberian Arctic Shelf (ESAS) constitute a substantial carbon 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 yr−1. Here, we propose insights based on atmospheric observations to evaluate these estimates. The comparison of high-resolution simulations of atmospheric methane mole fractions to continuous methane observations during the whole year 2012 confirms the high variability and heterogeneity of the methane releases from ESAS. A reference scenario with ESAS emissions of 8 TgCH4 yr−1, in the lower part of previously estimated emissions, is found to largely overestimate atmospheric observations in winter, likely related to overestimated methane leakage through sea ice. In contrast, in summer, simulations are more consistent with observations. Based on a comprehensive statistical analysis of the observations and of the simulations, annual methane emissions from ESAS are estimated to range from 0.0 to 4.5 TgCH4 yr−1. Isotopic observations suggest a biogenic origin (either terrestrial or marine) of the methane in air masses originating from ESAS during late summer 2008 and 2009.

Highlights

Most long-range global climate projections forecast a warming in the Arctic of 2–8 ◦C over the decades (Collins et al, 2013)
At PAL, a site scarcely influenced by the East Siberian Arctic Shelf (ESAS) emissions, most of the atmospheric signal is explained by the lateral www.atmos-chem-phys.net/16/4147/2016/
We suggest some insights on methane emissions from the East Siberian Arctic Shelf using atmospheric methane observations, to complement the intensive in situ oceanographic measurement campaigns carried out mostly in summer in the region

Summary

Introduction

Most long-range global climate projections forecast a warming in the Arctic of 2–8 ◦C over the decades (Collins et al, 2013). Warmer Arctic temperatures could induce the thawing of continental and submarine permafrost and the destabilization of marine hydrates, causing massive methane emissions into the atmosphere, and generating positive feedbacks to the regional and global warming. Monitoring methane emissions at high latitudes in the Northern Hemisphere is of critical importance to anticipate and to interpret future climate changes. On one side, emissions of methane by the Arctic tundra estimated by flux observations and process-based models (i.e. bottom-up approaches) for the 2000s have been synthesized, respectively, at 20 [11 to 51] TgCH4 yr−1 and 28 [18 to 37] TgCH4 yr−1 (McGuire et al, 2009). Top-down atmospheric inversions, based on observations of atmospheric methane mixing

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