Permafrost in tidal-marsh sediments was studied along the estuary of George River, Ungava Bay, northern Quebec. In this macrotidal environment, wide tidal flats and marshes lie in bays along the shoreline. Discontinuous permafrost bodies occur in the silty sediments underlying the marshes in the upper part of the intertidal zone, where submersions by large tides and storm surges are rare and where the icefoot freezes to the ground in winter. The permafrost is about 5 m thick, saline, and ice poor. According to logged thermal data, a freezing-point depression of 0.9 °C is estimated for the intertidal sediments. Tidal submersions during the ice-free season have a transient warming effect on the soil profile due to water percolation in the active layer and delay freeze back at the beginning of winter. Observations in shallow drill holes and along a thermistor cable indicate that the intertidal permafrost degraded at the Kangiqsualujjuaq observation site from 1984 to 1987. From 1987 to 1990, observations and logged data clearly show aggradation and cooling of the permafrost. Those changes in ground thermal regime are the result of recent climatic variations.

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