Weichselian Permafrost Degradation Rate Controlled by the Heat Flow and Effective Porosity—Data From the Spring‐Fed Fens' Deposits in Poland

ABSTRACT The results of the determination of bedload sediments in spring peatlands were used to determine the time of complete degradation of Weichselian permafrost at 13 spatially and geologically differentiated sites in Poland. Taking into account significant temporal differences in the termination of this process (from the end of the Late Glacial to the end of the Boreal phase of the Holocene), it was shown that, apart from climatic determinants, the value of the terrestrial heat flow and the effective porosity of the rocks, which control the maximum volume of frozen water, are decisive for the preservation versus degradation of permafrost. This second parameter was calculated for rock profiles drilled near the spring‐fed fens studied. The highest absolute value (0.81) of the Pearson correlation coefficient was obtained for the relationship between the time of permafrost degradation and the effective porosity down to a depth of 200 m, with the exception of one southernmost site. For the same set of sites and the relationship between time of permafrost degradation and heat flow density, the Pearson coefficient (0.62) indicates a moderate degree of correlation.