SUBSEA PERMAFROST ASSOCIATED WITH SUBMARINE GROUNDWATER DISCHARGE DISCOVERED IN SUBARCTIC CANADA

The distribution and state of subsea permafrost is largely unknown, and present maps rely heavily on modelling that suggests its confinement to the Beaufort, Siberian and Laptev seas. Here, we show that discontinuous subsea permafrost exists along the Labrador coast (56ºN) under the influence of the Labrador Coastal Current. Newly acquired high-resolution bathymetric data reveal the presence of subsea thermokarst environments on the coastal seabed of Nain, Nunatsiavut, where an ice-rich permafrost sample was recovered on July 30, 2022 at a water depth of 27 m. Porewater analysis indicates that ground ice can persist in the sediments due to freshened submarine groundwater seepage that freezes at higher temperatures (0°C) than seawater (-1.8°C). Evidence for brackish submarine groundwater discharge in Webb’s Bay is further supported by the enrichment of bottom waters in ²²³Ra (t_1/2 = 11.4 d) in July 2023, when bottom waters were slightly below 0°C. The formation and preservation of permafrost is due to cold waters of the Labrador Coastal Current entering the coastal areas and remaining < 0°C for most of the year. Therefore, evidence of subsea permafrost in coastal Labrador and the distribution of cold bottom water in the northern hemisphere suggests that subsea permafrost is likely to be preserved elsewhere in subarctic regions, especially where freshened submarine groundwater discharge elevates the freezing temperature. This discovery highlights the potential underestimation of subsea permafrost distribution in the world’s coastal oceans.