Subsea permafrost and associated methane hydrates: how long will they survive in the future?

Abstract

Abstract. We performed simulations with SMILES (the Sediment Model Invented for Long-tErm Simulations) for 100 kyr in future forced by the output of an Earth System model with internally calculated ice sheets. This Earth System model was driven by idealised scenarios of CO2 emissions (applied at time instant t = 0 loosely corresponding to common era year 1950) and by changes of the parameters of the Earth orbit. The simulations are carried out with different values of the heat flux from the Earth interior. We neglected possible impact of hydrostatic pressure changes due to future sea level changes on freeze/thaw temperature and on thermodynamic stability of methane hydrates. We found that at the outer shelf permafrost disappears either before t = 0 or during few centuries in future. In contrast, for the middle and shallow parts of the shelf, in the CO2-emission forced runs the subsea permafrost survives, at least, for 5 kyr after the emission onset or even for much longer. Without an applied greenhouse forcing permafrost exists here at least until 22 kyr after the CO2 emission onset or even survives till the end of the model runs. At the same parts of the shelf, methane hydrate stability zone disappears not earlier that at t = 3 kyr after the CO2 emission onset, but, typically, it survives until 11 to 41 kyr after this onset. Time instants of local extinction of both the subsea permafrost and methane hydrates stability zone (MHSZ) are negatively correlated with the geothermal heat flux because of both permafrost thaw and MHSZ shrinking basically occurs from bottom. However, thaw from the top and the deepening of the MHSZ table is basically determined by the applied CO2 forcing scenario; this is more important for the permafrost than for MHSZ. In general, the CO2-induced warming in our simulations is able to enhance the pan-Arctic subsea permafrost loss severalfold during 1 kyr after the emissions onset, but is less instrumental for the respective MHSZ loss.