Thermokarst Lake to Lagoon Transitions in Eastern Siberia: Do Submerged Taliks Refreeze?

Michael Angelopoulos,Mikhail N Grigoriev,Boris K Biskaborn,Jens Strauss,Pier Paul Overduin,Lutz Schirrmeister,Guido Grosse,Georgii Maksimov,Sebastian Westermann,Susanne Liebner,Jens Tronicke

doi:10.1029/2019jf005424

Abstract

As the Arctic coast erodes, it drains thermokarst lakes, transforming them into lagoons, and, eventually, integrates them into subsea permafrost. Lagoons represent the first stage of a thermokarst lake transition to a marine 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 at Polar Fox Lagoon on the Bykovsky Peninsula, Siberia. Polar Fox Lagoon is a seasonally isolated water body connected to Tiksi Bay through a channel, leading to hypersaline waters under the ice cover. The boreholes in the center of the lagoon revealed floating ice and a saline cryotic bed underlain by a saline cryotic talik, a thin ice‐bearing permafrost layer, and unfrozen ground. The bathymetry showed that most of the lagoon had bedfast ice in spring. In bedfast ice areas, the electrical resistivity profiles suggested that an unfrozen saline layer was underlain by a thick layer of refrozen talik. The modeling showed that thermokarst lake taliks can refreeze when submerged in saltwater with mean annual bottom water temperatures below or slightly above 0°C. This occurs, because the top‐down chemical degradation of newly formed ice‐bearing permafrost is slower than the refreezing of the talik. Hence, lagoons may precondition taliks with a layer of ice‐bearing permafrost before encroachment by the sea, and this frozen layer may act as a cap on gas migration out of the underlying talik.

Highlights

Borehole observations over 10 years (2007–2016) showed that subaerial permafrost is warming rapidly at a global scale even at depths greater than 10 m (Biskaborn et al, 2019)
Lagoons may precondition taliks with a layer of ice‐bearing permafrost before encroachment by the sea, and this frozen layer may act as a cap on gas migration out of the underlying talik
We investigated the transition from a freshwater to a saltwater system at Polar Fox Lagoon on the southern Bykovsky Peninsula, northeastern Siberia

Summary

Introduction

Borehole observations over 10 years (2007–2016) showed that subaerial permafrost is warming rapidly at a global scale even at depths greater than 10 m (Biskaborn et al, 2019). Thawing subsea permafrost from warming and salt transport may degrade gas hydrates (Chuvilin et al, 2019) and increase the gas permeability of ice‐bearing sediment (Chuvilin et al, 2016) to trigger gas migration toward the seabed. Gas migration would be facilitated by the presence of open taliks These pathways could exist where deep taliks below thermokarst lakes or paleo‐river valleys are inundated with seawater (Frederick & Buffett, 2014; Nicolsky & Shakhova, 2010; Shakhova et al, 2017). The fate of submerged taliks after a freshwater to saltwater transition is uncertain It has been suggested seawater with negative mean annual bottom water temperatures refreezes

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