Modelling persistent methane seepage offshore western Svalbard since early Pleistocene

Abstract

Recent observations of extensive methane release into the oceans and atmosphere have raised concern as to whether rising temperatures across the Arctic could drive rapid destabilization of gas hydrate reservoirs. Here, we report modelling results from hydrate-modulated methane seepage from Vestnesa Ridge, offshore western Svalbard, suggesting that continuous leakage has occurred from the seafloor since the early Pleistocene up until today. Sustained by modelled deep subsurface thermogenic sources of Miocene age, large scale hydrocarbon fluid migration started ~6 million years ago and reached the seafloor some 4 million years later. The modelling results indicate that widespread methane seepage offshore western Svalbard commenced in earnest during early Pleistocene, significantly older than late Holocene as previously reported. We propose that the onset of vertical hydrocarbon migration is the response of rapid burial of potential hydrocarbon sources induced by increased sediment deposition following the onset of Northern Hemisphere glaciations, ~2.7 million years ago. From the modelling results we propose that source rock intervals capable of generating hydrocarbons and hydrocarbon reservoirs buried kilometers deep have continuously fueled the gas hydrate system off western Svalbard for the past 2 million years. It is this hydrocarbon system that primarily controls the thermogenic methane fluxes and seepage variability at the seabed over geological times.