Strong geologic methane emissions from discontinuous terrestrial permafrost in the Mackenzie Delta, Canada

Katrin Kohnert,Andrei Serafimovich,Torsten Sachs,Jörg Hartmann,Stefan Metzger

doi:10.1038/s41598-017-05783-2

Abstract

Arctic permafrost caps vast amounts of old, geologic methane (CH4) in subsurface reservoirs. Thawing permafrost opens pathways for this CH4 to migrate to the surface. However, the occurrence of geologic emissions and their contribution to the CH4 budget in addition to recent, biogenic CH4 is uncertain. Here we present a high-resolution (100 m × 100 m) regional (10,000 km²) CH4 flux map of the Mackenzie Delta, Canada, based on airborne CH4 flux data from July 2012 and 2013. We identify strong, likely geologic emissions solely where the permafrost is discontinuous. These peaks are 13 times larger than typical biogenic emissions. Whereas microbial CH4 production largely depends on recent air and soil temperature, geologic CH4 was produced over millions of years and can be released year-round provided open pathways exist. Therefore, even though they only occur on about 1% of the area, geologic hotspots contribute 17% to the annual CH4 emission estimate of our study area. We suggest that this share may increase if ongoing permafrost thaw opens new pathways. We conclude that, due to permafrost thaw, hydrocarbon-rich areas, prevalent in the Arctic, may see increased emission of geologic CH4 in the future, in addition to enhanced microbial CH4 production.

Highlights

The emission of biogenic methane (CH4) from arctic permafrost landscapes caused by microbial decomposition of carbon is widely discussed[1,2,3,4,5,6]
Strong natural gas seeps have been described sporadically[17, 18], some of which are fed by thermogenic CH4
The median of all 2012 and 2013 CH4 flux data was 1.1 mg m−2 h−1, which corresponds to fluxes measured by the EC technique in similar ecosystems[25,26,27,28,29]

Summary

Introduction

The emission of biogenic methane (CH4) from arctic permafrost landscapes caused by microbial decomposition of carbon is widely discussed[1,2,3,4,5,6]. In terrestrial permafrost landscapes geologic CH4 can reach the surface through open taliks (=thaw bulbs) below lakes[13], or in the unfrozen areas of discontinuous permafrost, comparable to what was shown for lower latitudes[11, 16]. The overall aim of this study is to improve our understanding of geologic CH4 emissions on a regional scale in the Mackenzie Delta region, Canada (Fig. 1). The purpose of this study is twofold: (i) to map the CH4 flux and its spatial variability at high spatial resolution and to derive the abundance of geologic CH4 emission hotspots and (ii) to assess the relative contribution of biogenic and geologic sources to the annual CH4 budget of the Mackenzie Delta region

Objectives

Methods

Results

Conclusion