In situ bottom sediment temperatures in the Siberian Arctic seas: Current state of subsea permafrost in the Kara sea vs laptev and East Siberian seas

Abstract

Features of sediment temperature on the shelf and continental slope areas of the Russian Arctic seas and its physical properties are important for understanding the current state of subsea permafrost and the gas hydrates stability zone. New data are reported for the Kara Sea region where the bottom sediment temperatures are influenced by warming effects from great Siberian rivers and the Atlantic currents. The data collected during marine expeditions in 2019–2022 are combined with results of earlier marine studies, drilling operations, and geophysical surveys in the Laptev and East Siberian seas, in order to identify major trends of in situ temperature and properties distribution of bottom sediments in the Russian Arctic region.Most (85%) of bottom sediments in the Kara Sea shelf, as well as in the Laptev and East Siberian shelves, consist of water-saturated silty clay and silt with rather uniform particle size distribution. The obtained thermal conductivity and heat capacity values for the Kara Sea sediments agree with the values of 1.0 W/(m·K) and 2900 kJ/m3, respectively, obtained previously from other Arctic seas. Thermal conductivity becomes up to 40% higher depthward from 0 to 2 m subbottom depth, possibly, because of lower moisture content and porosity in more lithified sediments.The bottom sediment temperatures in the Arctic seas are distributed unevenly, especially in the Kara Sea shelf (from +5.0 °C in the west to −1.4 °C in the east), where the high sediment temperatures in the western and central parts of the Kara Sea being due to the effect of warm water inputs. The distribution of bottom sediment temperatures correlates well with distribution of relic subsea permafrost. Ice-bearing permafrost in the Siberian Arctic shelf extends from the shoreline till sea depths of 80–100 m, within the respective offshore distances of ∼800–1000 km in some areas, but permafrost remnants may exist locally at sea depths within 120 m. Buried 100–600 m thick continuous subsea permafrost may occur in the Kara, Laptev, and East Siberian shelves under unfrozen (cryotic) saline shallow sediments. However, subsea permafrost is discontinuous and sporadic at sea depths ∼70 m and more. Thus, the bottom sediment temperature features in the Arctic seas can be used as a proxy of subsea permafrost extent contenting intrapermafrost and subpermafrost gas and gas hydrate accumulations.