The Transpolar Drift conveys methane from the Siberian Shelf to the central Arctic Ocean

E Damm,M Korhonen,D Bauch,T Krumpen,E Vinogradova,B Rabe,C Uhlig

doi:10.1038/s41598-018-22801-z

Abstract

Methane sources and sinks in the Arctic are poorly quantified. In particular, methane emissions from the Arctic Ocean and the potential sink capacity are still under debate. In this context sea ice impact on and the intense cycling of methane between sea ice and Polar surface water (PSW) becomes pivotal. We report on methane super- and under-saturation in PSW in the Eurasian Basin (EB), strongly linked to sea ice-ocean interactions. In the southern EB under-saturation in PSW is caused by both inflow of warm Atlantic water and short-time contact with sea ice. By comparison in the northern EB long-time sea ice-PSW contact triggered by freezing and melting events induces a methane excess. We reveal the Ttranspolar Drift Stream as crucial for methane transport and show that inter-annual shifts in sea ice drift patterns generate inter-annually patchy methane excess in PSW. Using backward trajectories combined with δ18O signatures of sea ice cores we determine the sea ice source regions to be in the Laptev Sea Polynyas and the off shelf regime in 2011 and 2015, respectively. We denote the Transpolar Drift regime as decisive for the fate of methane released on the Siberian shelves.

Highlights

Arctic methane sources are considered to contribute to Arctic amplification of global warming as significant methane emissions into the atmosphere may generate positive feedbacks to global warming[1]
Instead of efflux on shelves, methane might be trapped in sea ice or in dense shelf water formed during ice formation and subsequently transported by shelf outflow towards the interior Arctic Ocean
There is growing evidence that sea ice is crucial to Arctic methane cycling: atmospheric concentrations are higher over open leads[7], methane is over-saturated beneath multi-year sea ice[8] and observed to be taken up in fast ice by freezing[9]

Summary

Results

Methane inventory in Polar surface water (PSW). We detected different levels of methane saturation related to the atmospheric equilibrium in ice covered Polar surface water (PSW) in the Eurasian Basin (EB) (Fig. 1). The effect of sea ice-released methane to enhance the saturation level remains small in this region as the opposite direction of the ocean current along the Svalbard and Barents Sea continental margin (from south-west)[17] to the wind driven sea ice drift (from north-east)[18] results in just a short contact of sea water with the sea ice cover on top In this regard, the “non-common history” of sea ice and PSW advected along the southern EB focuses the view to the duration of sea water-sea ice contact for the level of saturation generated in PSW. The variations might be: (I) source –triggered i.e. different sea ice types with different methane amounts incorporated therein, (II) related to varying amounts of methane released from sea ice into the PSW and (III) coupled to differences in preservation of methane excess over a time period of several seasons to a year in PSW

Discussion

Methods

ICCP Climate Change 2013