Geoderma (Sep 2024)
Links between environmental conditions and pedogenic phyllosilicates in Podzols in the Tatra Mountains (Poland) – II. Hydrogen and oxygen isotope compositions
Abstract
Stable isotope compositions of pedogenic clay minerals can be used as a paleoclimatic proxy. The underlying fundamental assumption is that pedogenic clays are formed in isotope equilibrium with the environment, which is well-documented for hot and humid climates. However, observational and experimental data on oxygen and hydrogen isotope composition of pedogenic clay minerals developed in colder climates remain scarce. The present study aims to fill this gap by providing data on the stable isotope composition of the fine clay fraction (<0.2 μm) from four Podzols developed in the alpine climate of the Tatra Mountains, Poland. Investigated material was dominated by common products of granite weathering in alpine conditions (mean annual temperature: 2.6 °C, mean annual precipitation: 1100 mm): mixed-layer minerals of illite–smectite type and kaolinite. Oxygen and hydrogen isotope compositions of the fine clay fractions were measured, elemental budgets of the studied samples were calculated, and the pedogenic end-member isotope composition was estimated with two methods: (i) using linear regressions of samples’ isotope compositions on the fraction of O or H contained in the pedogenic pool and (ii) isotope modeling assuming isotope equilibrium between pedogenic component and soil water for a range of temperatures. The obtained results revealed that the isotope composition of fine clay fraction mostly plots between the composition of bulk parent granitoids and assumed weathering end-member in the δ2H-δ18O space, with isotope compositions of pedogenic phyllosilicates reconstructed from mass-balance calculations broadly reflecting alpine climate conditions. Oxygen isotope composition was correlated with the cation exchange capacity (CEC) of the investigated samples, which reflects the weathering nature of expandable phyllosilicates in the soil. Weathering in the alpine climate leads to the formation of material containing less pedogenic components that record the environmental conditions in their oxygen and hydrogen isotope composition than weathering in tropical environments.
