Abstract:
© 2020 Elsevier B.V. Temperature and sea level changes in the Pleistocene are uncertain. This leads to uncertainty in the associated response of the thermal state of the subsea sediments. We quantified the upper bound of the latter uncertainty in idealised simulations with a model for thermophysical processes in the sediments. At the coast and at the shallow and intermediate–depth shelves and except during relatively isolated time intervals, this bound for permafrost base depth and for the methane hydrate stability zone (MHSZ) characteristics (depth of its bottom boundary and its thickness) is ≤45% provided that the geothermal heat flux (GHF) is not larger than 80 mW m−2. These values are much smaller than the uncertainty metrics for the forcing data, which are typically ≥65%. However, for the intermediate shelf with a larger geothermal heat flux and for the deep shelf irrespective of GHF, different forcing time series may even lead to qualitatively different behaviour of the sediment thermophysical characteristics. We found that prescription of sea level changes plays a crucial role in uncertainty of the simulated subsea permafrost and MHSZ in the deep shelf sediments. In addition, we also quantified uncertainty for estimated apparent response time scales. The relative uncertainty for permafrost base depth and hydrate stability zone thickness time scales is ≤20% for most cases. We found no systematic dependence of our results on accounting for millennium–scale temperature variability provided that timescales of the order of 104 yr are resolved by forcing datasets.
