Sub-sea permafrost regime at Prudhoe Bay, Alaska, U.S.A

Abstract

A sub-sea permafrost drilling program was conducted near Prudhoe Bay, Alaska. Sub-sea permafrost was found at all offshore drill sites and was characterized as being ice bonded or unbonded. The unbonded sub-sea permafrost occurred in a thin layer at the sea bed; the near-shore thickness of this layer appears to be controlled by the bathymetry. The mean annual sea-bed temperatures were about —3.4°C at 203 m offshore, — 1.1°C at 481 m offshore and —0.7°C at 3370 m offshore. The thermal diffusivity was about 21 m² a^-1 for unbonded sandy gravel with silt. The sub-sea permafrost soils were sandy gravel with some silt overlain by a thin layer of silty sand which increased in thickness from a few meters near shore to about 14 m at 3370 m offshore. A few small ice lenses were found in a hole 195 m offshore but no massive ice was observed. Pore-water salt concentrations at the sea bed were 3-4 times that of normal sea-water where ice was frozen to the sea bed and 1–2 times that of normal sea-water otherwise. Preliminary laboratory experiments showed that the saturated hydraulic conductivity of the unbonded sub-sea permafrost was about 10^–6–10^–7 m s^–1. The permeability of the subterranean permafrost was zero.