| Summary: | As the Arctic coast erodes, it drains thermokarst lakes, transforming them into lagoons, and, eventually,integrates them into subsea permafrost. Lagoons represent the rst stage of a thermokarst lake transition to amarine setting and possibly more saline and colder upper boundary conditions. In this research,borehole data, electrical resistivity surveying, and modeling of heat and salt diffusion were carried out atPolar Fox Lagoon on the Bykovsky Peninsula, Siberia. Polar Fox Lagoon is a seasonally isolated waterbody connected to Tiksi Bay through a channel, leading to hypersaline waters under the ice cover.The boreholes in the center of the lagoon revealed oating ice and a saline cryotic bed underlain by asaline cryotic talik, a thin icebearing permafrost layer, and unfrozen ground. The bathymetry showedthat most of the lagoon had bedfast ice in spring. In bedfast ice areas, the electrical resistivity profilessuggested that an unfrozen saline layer was underlain by a thick layer of refrozen talik. The modelingshowed that thermokarst lake taliks can refreeze when submerged in saltwater with mean annual bottomwater temperatures below or slightly above 0°C. This occurs, because the top-down chemical degradationof newly formed icebearing permafrost is slower than the refreezing of the talik. Hence, lagoons mayprecondition taliks with a layer of ice-bearing permafrost before encroachment by the sea, and this frozenlayer may act as a cap on gas migration out of the underlying talik.
|
|---|