Dagmar Brandová

Combination of Numerical Dating Techniques Using 10Be in Rock Boulders and 14C of Resilient Soil Organic Matter for Reconstructing the Chronology of Glacial and Periglacial Processes in a High Alpine Catchment during the Late Pleistocene and Early Holocene

Glacier fluctuations and paleoclimatic oscillations during the Late Quaternary in Val di Rabbi (Trentino, northern Italy) were reconstructed using a combination of absolute dating techniques (14C and 10Be) and soil chemical characterization. Extraction and dating of the stable fraction of soil organic matter (SOM) gave valuable information about the minimum age of soil formation and contributed to the deciphering of geomorphic surface dynamics. The comparison of 10Be surface exposure dating (SED) of rock surfaces with the 14C ages of resilient (resistant to H2O2 oxidation) soil organic matter gave a fairly good agreement, but with some questionable aspects. It is concluded that, applied with adequate carefulness, dating of SOM with 14C might be a useful tool in reconstructing landscape history in high Alpine areas with siliceous parent material. The combination of 14C dating of SOM with SED with cosmogenic 10Be (on moraines and erratic boulders) indicated that deglaciation processes in Val di Rabbi were already ongoing by around 14,000 cal BP at an altitude of 2300 m asl and that glacier oscillations might have affected the higher part of the region until about 9000 cal BP. 10Be and 14C ages correlate well with the altitude of the sampling sites and with the established Lateglacial chronology.

Soil formation and weathering in a permafrost environment of the Swiss Alps: A multi-parameter and non-steady-state approach

Spatially discontinuous permafrost conditions frequently occur in the European Alps. How soils under such conditions have evolved and how they may react to climate warming is largely unknown. This study focuses on the comparison of nearby soils that are characterised by the presence or absence of permafrost (active-layer thickness: 2 – 3 m) in the alpine (tundra) and subalpine (forest) range of the Eastern Swiss Alps using a multi-method (geochemical and mineralogical) approach. Moreover, a new non-steady-state concept was applied to determine rates of chemical weathering, soil erosion, soil formation, soil denudation, and soil production. Long-term chemical weathering rates, soil formation and erosion rates were assessed by using immobile elements, fine-earth stocks and meteoric 10Be. In addition, the weathering index (K + Ca)/Ti, the amount of Fe- and Al-oxyhydroxides and clay minerals characteristics were considered. All methods indicated that the differences between permafrost-affected and non-permafrost-affected soils were small. Furthermore, the soils did not uniformly differ in their weathering behaviour. A tendency towards less intense weathering in soils that were affected by permafrost was noted: at most sites, weathering rates, the proportion of oxyhydroxides and the weathering stage of clay minerals were lower in permafrost soils. In part, erosion rates were higher at the permafrost sites and accounted for 79 – 97% of the denudation rates. In general, soil formation rates (8.8 – 86.7 t/km2/y) were in the expected range for Alpine soils. Independent of permafrost conditions, it seems that the local microenvironment (particularly vegetation and subsequently soil organic matter) has strongly influenced denudation rates. As the climate has varied since the beginning of soil evolution, the conditions for soil formation and weathering were not stable over time. Soil evolution in high Alpine settings is complex owing to, among others, spatio-temporal variations of permafrost conditions and thus climate. This makes predictions of future behaviour very difficult. This article is protected by copyright. All rights reserved.