Ice-sheet-driven methane storage and release in the Arctic.

Alexey Portnov,Sunil Vadakkepuliyambatta,Jürgen Mienert,Alun Hubbard

doi:10.1038/ncomms10314

Abstract

It is established that late-twentieth and twenty-first century ocean warming has forced dissociation of gas hydrates with concomitant seabed methane release. However, recent dating of methane expulsion sites suggests that gas release has been ongoing over many millennia. Here we synthesize observations of ∼1,900 fluid escape features—pockmarks and active gas flares—across a previously glaciated Arctic margin with ice-sheet thermomechanical and gas hydrate stability zone modelling. Our results indicate that even under conservative estimates of ice thickness with temperate subglacial conditions, a 500-m thick gas hydrate stability zone—which could serve as a methane sink—existed beneath the ice sheet. Moreover, we reveal that in water depths 150–520 m methane release also persisted through a 20-km-wide window between the subsea and subglacial gas hydrate stability zone. This window expanded in response to post-glacial climate warming and deglaciation thereby opening the Arctic shelf for methane release.

Highlights

It is established that late-twentieth and twenty-first century ocean warming has forced dissociation of gas hydrates with concomitant seabed methane release
Natural gas can exist in solid form of crystalline ice-like structures known as gas hydrates that are stable within the subsurface under high-pressure and low-temperature conditions bounded by the gas hydrate stability zone (GHSZ)
Post-LGM eustatic sea level rise shifted the subsea GHSZ B6.5 km laterally up the continental slope, where it attained its present location at 396 m.b.s.l. and is, today, marked by abundant gas flares that align parallel to the slope (Figs 1 and 2)

Summary

Introduction

It is established that late-twentieth and twenty-first century ocean warming has forced dissociation of gas hydrates with concomitant seabed methane release. We reveal that in water depths 150–520 m methane release persisted through a 20-km-wide window between the subsea and subglacial gas hydrate stability zone. This window expanded in response to post-glacial climate warming and deglaciation thereby opening the Arctic shelf for methane release. The kinetics of hydrate formation and dissociation critically depends on the supply and composition of gas and liquid water within available pore space of sediments, even under an appropriate envelope of GHSZ pressure and temperature conditions, gas hydrates are not, per se, guaranteed[1]. Wherever persistent subsurface methane (or heavier fractions of natural gas) and water coexist within available pore space, the GHSZ is a robust indication of the conditions under which gas hydrate is likely to form. In 1992, during exploratory drilling in Svalbard, gas blow outs from depths of 630 m beneath today’s sediment surface brought operations to a complete halt[17]

Methods

Results

Conclusion