| Summary: | Silicon isotope fractionation upon amorphous silica precipitation is susceptible to freeze-thaw cycles. Here we make use of this characteristic to distinguish between a closed system in freezing soils: where silicic acid concentration is increasing, leading to amorphous silica precipitation that induces Si isotope fractionation where 28Si is preferentially incorporated into the colloidal amorphous silica; and an open system in freezing soils: where silicic acid is mixing with surrounding soil pore waters and amorphous silica precipitation is not induced. We analyzed a temporal series of soil pore water collected from September to November 2021 on a natural gradient of permafrost degradation from a palsa (closed system) to a fen (open system) in Stordalen, Sweden. We compare the evolution of the δ30Si values in soil pore waters where freeze-up has occurred (closed system) or where freeze-up is delayed or absent (open system). We couple our δ30Si data with variations in redox-sensitive element (e.g., Fe) concentrations, sensitive to limited biogeochemical connectivity in a closed system. The dual-approach of silicon isotope geochemistry with redox sensitive element analysis has important implications for capturing the lateral transfer of water and nutrients from permafrost soils during winter months.
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