Response of Arctic Methane hydrate to the rise in bottom water temperature and relative sea-level over past 11000 years

Abstract

The fate of the methane hydrate at the feather edge of hydrate stability on the upper continental slope is governed by bottom water temperature (BWT) and relative sea-level (RSL) change. Off west Svalbard, methane seeps were discovered at the edge of hydrate stability and linked with the last 30 years of warming-induced hydrate dissociation due to the influence of Atlantic water. Hydrate dissociation off west Svalbard was first geochemically confirmed through the MeBo drilling experiment. Pore water samples collected during the MeBo drilling experiment at a water depth of 391 m from sediments showed a decline in chloride concentration at 15–22 m below the seabed, indicating freshening caused by hydrate dissociation. However, a new hypothesis proposed the role of RSL fall over the past 8000 years, triggering the hydrate dissociation instead of the recent 30 years’ BWT rise. This model considered the RSL change scenario based on the University of Tromsoe (UiT) ice load history and Earth rheology model. However, the RSL predicted from the UiT model does not match the values based on geological observations at Prins Karl Forland. We checked other glacial isostatic adjustments (GIA) scenarios and found that the ICE-6G_C model shows a better fit to the observed values. Using the ICE-6G_C scenario, we predicted the far-field RSL values on the upper continental slope by calculating the difference between eustatic sea level and seabed elevation. The UiT model predicts a decline in RSL, while the ICE-6G_C model predicts a rise over the past 8000 years. For analyzing the response of the hydrate layer, we forced the model with the ICE-6G_C derived RSL values and the reconstructed BWT over the past 11000 years. The numerical simulation considers the multiphase fluid and heat flow coupled with hydrate formation and dissociation. Modeling shows that although long-term RSL rise stabilizes the hydrates, the sharp increase in BWT causes hydrate destabilization, pore water freshening, and a negative chloride anomaly that matched observations. We propose that RSL fluctuations do not exclusively control hydrate dynamics, and ocean warming plays a critical role