A two-dimensional finite element model was used to investigate the thermal response of subsea permafrost and gas hydrates to changes in sea level and climate over a 121 Kyr time period along a line offshore from Lonely, Alaska.

For subsea permafrost containing brines, the spatial distribution of the ice-bearing permafrost (IBP) is predicted to be wedge shaped and to extend only 19 km offshore. There is significant lateral heat flow throughout the IBP section offshore and the depth to the IBP table increases almost linearly with distance offshore. For subsea permafrost with constant thermal parameters, IBP is predicted to extend 52 km offshore (water depth ~ 50 m) and is nearly isothermal beyond 4 km offshore. Depth to the IBP table increases almost linearly with distance offshore and then becomes relatively shallow and nearly constant in depth.

Seabed temperatures and the assumed sea level history curve are especially important in determining the current distribution of subsea permafrost. The full thickness of IBP onshore can be modeled better using constant thermal parameters. Depth to the IBP table offshore may be modeled better when it is assumed that the permafrost contains brines. The predicted depth zone for stability of methane gas hydrates is between 220 m and 650 m near shore. For subsea permafrost containing brines, this zone extends 32 km offshore compared to 54 km (to the 55 m water depth) for constant thermal parameters. The time scale for producing methane gas from destablized gas hydrates in the continental shelf near Lonely is on the order of 104 years, much longer than previously predicted.

NSF Grant: Scientific personnel; T. E. Osterkamp.