Abstract:
The stability of methane hydrates at the feather edge of hydrate stability on the upper continental slope (UCS) is prone to ocean warming and relative sea level (RSL) change. West of Svalbard, methane seeps on the UCS were initially proposed to result from hydrate destabilization resulting from four decades of warming of Atlantic bottom water. Alternatively, it has been proposed that hydrate dissociation was triggered by RSL fall due to isostatic rebound over the past 8,000 yr rather than recent bottom water temperature (BWT) rise. Here, we address these two contrasting hypotheses by simulating the impact of 11,000 yr of BWT and RSL change on hydrates located at the UCS off west Svalbard. Our numerical simulation considers multiphase fluid and heat flow coupled with hydrate formation and dissociation. We used two reconstructions of local ice history (UiT and ICE-6G_C) that predict contrasting results for the local sea level history. Over the past 8,000 yr, the UiT model predicts a fall in RSL on the UCS, while the ICE-6G_C model, which provides a better fit to nearby coastal RSL observations, predicts a continuous rise. Our modeling shows that whilst long-term RSL fall would progressively thin the region of hydrate stability, the abrupt rise in BWT enhances hydrate dissociation. Even in the model with an RSL rise, the increase in BWT causes hydrate destabilization and pore water freshening that matches observations. We conclude that recent ocean warming plays a critical role in hydrate dissociation west of Svalbard regardless of the longer-term sea level history.