Paleo-gas hydrate distribution associated with hill-hole pair formation in the SW Barents Sea

Abstract

<p>Today, gas hydrates are predicted to be stable only in the deepest parts of the Barents Sea, however under past glaciations, low pressure, high temperature subglacial conditions would have been an ideal setting for their formation. Multiple studies have documented the storage of methane beneath the Late Weichselian Barents Sea Ice Sheet, and its subsequent release following deglaciation. Furthermore, it has been hypothesised that localised subglacial gas hydrate formation increases frictional resistance at base of the ice and thus may regulate the flow of overlying ice (Winsborrow et al. 2016). This hypothesis has however, never been tested against sedimentological records of paleo-fluid flow and sediment properties.  </p><p>Here we present preliminary results on sediment and pore fluid geochemistry from nine gravity cores collected from Ingøydjupet in the SW Barents Sea. These were collected around a hill-hole pair, a glacial landform indicative of variations in subglacial frictional resistance. One of several suggested formation processes is gas hydrate stiffening of subglacial sediments.  </p><p>At present, there is a clear difference in methane fluxes between the areas inside the seafloor hole (high fluxes) and the adjacent hill (low fluxes), matching the distribution of a localized subsurface shallow gas accumulation visible in seismic data. Sediment geochemistry revealed a past episode of enhanced upward methane fluxes only recorded in sediments from the hole, resulted in the shoaling of the sulfate-methane transition and precipitation of methane-derived authigenic carbonates (MDAC) with δ<sup>13</sup>C= -35 ‰. Although the oxygen isotopic composition (δ<sup>18</sup>O) of MDACs collected from a sediment core in the hole did not show direct evidence for past gas hydrate destabilization, the reconstructed history of methane fluxes as well as the present-day fluxes and subsurface gas distribution support the hypothesis of a differential distribution of subglacial paleo-gas hydrates across the hill-hole pair, possibly controlled by stratigraphic and structural preconditioning.</p><p>This research is part of the Centre for Arctic Gas Hydrate, Environment and Climate (CAGE) supported by the Research Council of Norway through its Centres of Excellence funding scheme grant No. 223259.</p><p>Winsborrow, M., Andreassen, K., Hubbard, A., Plaza-Faverola, A., Gudlaugsson, E. and Patton, H., 2016. Regulation of ice stream flow through subglacial formation of gas hydrates. Nat. Geosci., 9(5), 370-374.</p>