Dynamic simulations of potential methane release from East Siberian continental slope sediments

Abstract

Sediments deposited along continental margins of the Arctic Ocean presumably host large amounts of methane (CH 4 ) in gas hydrates. Here we apply numerical simulations to assess the potential of gas hydrate dissociation and methane release from the East Siberian slope over the next 100 years. Simulations are based on a hypothesized bottom water warming of 38C, and an assumed starting distribution of gas hydrate. The simulation results show that gas hydrate dissociation in these sediments is relatively slow, and that CH 4 fluxes toward the seafloor are limited by low sediment permeability. The latter is true even when sediment fractures are permitted to form in response to overpressure in pore space. With an initial gas hydrate distribution dictated by present-day pressure and temperature conditions, nominally 0.35 Gt of CH 4 are released from the East Siberian slope during the first 100 years of the simulation. However, this CH 4 discharge becomes significantly smaller ($0.05 Gt) if glacial sea level changes in the Arctic Ocean are considered. This is because a lower sea level during the last glacial maximum (LGM) must result in depleted gas hydrate abundance within the most sensitive region of the modern gas hydrate stability zone. Even if all released CH 4 reached the atmosphere, the amount coming from East Siberian slopes would be trivial compared to present-day atmospheric CH 4 inputs from other sources.

Overestimating climate warming‐induced methane gas escape from the seafloor by neglecting multiphase flow dynamics

“…To overcome the limitations of the HS approach, detailed site‐specific and regional assessments of hydrate dissociation have been conducted using more complex multiphase models [e.g., Moridis et al ., ; Reagan and Moridis , , ; Reagan et al ., ; Marín‐Moreno et al ., ; Thatcher et al ., ; Darnell and Flemings , ; Stranne et al ., ]. However, these studies have not quantitatively investigated limitations of the HS approach and how these may influence current global and basin‐scale estimates of CH 4 gas release from the seabed.…”

Mechanistic insights into a hydrate contribution to the Paleocene‐Eocene carbon cycle perturbation from coupled thermohydraulic simulations

“…[] and Stranne et al . [] using an a posteriori off‐line approach, following Daigle and Dugan 's [] normalized overpressure ratio criterion. Here we model porous flow in pristine hemipelagic sediments using an intrinsic permeability of 10 −16 m 2 and approximate fracture flow by modeling porous flow with an enhanced intrinsic permeability of 10 −13 m 2 (supporting information).…”

Bathymetry and oceanic flow structure at two deep passages crossing the Lomonosov Ridge

“…More specifically, the inflowing warm Atlantic water controls the temperature near the seabed along the continental shelf slope, which affects the location of the gas hydrate stability zone and thus impacts the storage and release of methane (Biastoch et al, 2011;Stranne et al, 2016;Westbrook et al, 2009). Further-more, the heat carried with the inflow has a large potential to melt the perennial sea ice cover (Polyakov et al, 2010), although mostly in areas with weak salinity stratification such as north of Svalbard.…”