Soil micromorphology as tool for the past permafrost and paleoclimate reconstruction

Abstract

Podzols developed on glacial and periglacial features provide the opportunity to reconstruct permafrost past limits and related paleoclimatic variations using micromorphological analysis.Analyzing 10 thin sections on 8 soils classified as Podzol in two study areas in the Central Italian Alps (Stelvio Pass area and Val Cantone area), we have been able to find different microstructures or pedofeatures (i.e., granular, platy, subangular blocky microstructures, silt cappings on coarse mineral grains) induced by processes related to permafrost conditions like gelifluction and ice lenses segregation. The type and the frequency of these micropedological traits allowed us to determine the lowest limit of past permafrost at 2228 m a.s.l. in Stelvio Pass area and 2347 m a.s.l. in Val Cantone area, respectively ca. 400 m and 330 m lower than today.Moreover, the analysis of paleoprecipitation and paleotemperature derived from various proxy data and the age of soil pedogenesis allowed us to identify four different phases of podzolization dated to: 13.5–11.5 ka (I phase), 11–9.7 ka (II phase), 9.3–8 ka (III phase), and 7.7–7.3 ka (IV phase).Reconstructed paleoprecipitation and paleotemperature of the four phases of podzolization also allowed us to determine that in Val Cantone there were two different permafrost aggradation periods that were synchronous to podzolization while in Stelvio Pass area one additional permafrost aggradation period that occurred at 7.7–7.3 ka.