Ice-sheet melt drove methane emissions in the Arctic during the last two interglacials

P.-A Dessandier,C Labrousse,A Plaza-Faverola,J Knies,M Renoult,G Panieri

doi:10.1130/g48580.1

Abstract

AbstractCircum-Arctic glacial ice is melting in an unprecedented mode, and release of currently trapped geological methane may act as a positive feedback on ice-sheet retreat during global warming. Evidence for methane release during the penultimate (Eemian, ca. 125 ka) interglacial, a period with less glacial sea ice and higher temperatures than today, is currently absent. Here, we argue that based on foraminiferal isotope studies on drill holes from offshore Svalbard, Norway, methane leakage occurred upon the abrupt Eurasian ice-sheet wastage during terminations of the last (Weichselian) and penultimate (Saalian) glaciations. Progressive increase of methane emissions seems to be first recorded by depleted benthic foraminiferal δ13C. This is quickly followed by the precipitation of methane-derived authigenic carbonate as overgrowth inside and outside foraminiferal shells, characterized by heavy δ18O and depleted δ13C of both benthic and planktonic foraminifera. The similarities between the events observed over both terminations advocate for a common driver for the episodic release of geological methane stocks. Our favored model is recurrent leakage of shallow gas reservoirs below the gas hydrate stability zone along the margin of western Svalbard that can be reactivated upon initial instability of the grounded, marine-based ice sheets. Analogous to this model, with the current acceleration of the Greenland ice melt, instabilities of existing methane reservoirs below and nearby the ice sheet are likely.

Highlights

Arctic methane reservoirs consisting of gas hydrates and free gas on land and in marine sediments (> 300 m water depth) are potentially large enough to raise atmospheric methane concentrations if released during melting of glacial ice and permafrost (McGuire et al, 2009). a recent analysis points towards a minor contribution of geological methane to the global carbon inventory during the last deglaciation (Dyonisius et al, 2020), very little is known about pre-Last Glacial Maximum (LGM, ca. 27-19 ka) emissions (Himmler et al., 2019)
Based on foraminiferal C excursions in newly recovered boreholes, we show that Arctic methane reservoirs offshore Svalbard were leaking during SBIS wastage during the last deglacial cycle, and during the Eemian (i.e. the marine isotope stage (MIS) 5e) when significantly larger ice volumes disappeared in the circum-Arctic (Jakobsson et al, 2014)
GC2 from the Lunde pockmark shows a similar pattern for the last glacial period, the initial ice-sheet collapse is followed by a prominent “shell bed” sensu Ambrose et al (2015), characterized by chemosynthetic bivalves and extremely light 13C values in planktonic and benthic foraminifera (Fig. 2)

Summary

Introduction

Arctic methane reservoirs consisting of gas hydrates and free gas on land and in marine sediments (> 300 m water depth) are potentially large enough to raise atmospheric methane concentrations if released during melting of glacial ice and permafrost (McGuire et al, 2009). a recent analysis points towards a minor contribution of geological methane to the global carbon inventory during the last deglaciation (Dyonisius et al, 2020), very little is known about pre-Last Glacial Maximum (LGM, ca. 27-19 ka) emissions (Himmler et al., 2019). A recent analysis points towards a minor contribution of geological methane to the global carbon inventory during the last deglaciation (Dyonisius et al, 2020), very little is known about pre-Last Glacial Maximum Methane emissions are known to be episodic and have been linked to Quaternary sea-level changes and glacial cycles at various continental margins (Dickens et al., 1995). In the Barents Sea, the ice sheet evolution is the main driver of changes in gas hydrate stability and usually, depressurization due to the loss of subglacial loading greatly exceed hydrostatic compensation associated with relative sea level (Andreassen et al, 2017). The most prominent features are large gas blow-outs into the ocean and eventually the atmosphere that occurred upon the Svalbard-Barents Sea ice sheet (SBIS) retreat after the LGM (Andreassen et al, 2017).

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