Geochemistry of west Siberian streams and their potential response to permafrost degradation

[1] Measurements of solute concentrations from previously unstudied watersheds throughout west Siberia suggest that warming and permafrost degradation will likely amplify the transport of dissolved solids to the Kara Sea and adjacent Arctic Ocean. We present concentrations of Ca²⁺, K⁺, Mg²⁺, Na⁺, Si, Cl^-, SO ₄^2-, HCO₃^-, inferred alkalinity, and total inorganic solutes (TIS) from 94 streams and rivers within the Ob'-Irtysh, Nadym, and Pur river drainage basins. The sampled sites span ∼10 ⁶ km², a large climatic gradient (∼55°-68°N), and 39 permafrost-influenced and 55 permafrost-free watersheds. The solute composition of our samples is strongly influenced by carbonate mineral dissolution. Furthermore, our results show that TIS concentrations of waters in permafrost-free watersheds average ∼289 mg L^-1, in contrast to only ∼48 mg L^-1 in permafrost-influenced watersheds. This sixfold difference likely occurs because permafrost forms a confining barrier that inhibits the infiltration of surface water through deep mineral horizons and restricts mineral-rich subpermafrost groundwater from reaching surface water pathways. A principal components analysis-based end-member mixing analysis supports the premise that mineral-rich groundwater is the primary source of solutes to streams in permafrost-free watersheds, whereas mineral-poor peat surface water is the primary source in permafrost-influenced watersheds. With climate warming and subsequent permafrost thaw this region may transition from a surface water-dominated system to a groundwater-dominated system. Additionally, should permafrost in the region completely disappear, we estimate that TIS export from the west Siberian region to the Kara Sea would increase by ∼59% (from its current value of ∼46 Tg yr^-1 to ∼73 Tg yr ^-1). Such an increase in dissolved solid delivery to the Kara Sea could have important implications for future biological productivity in arctic Eurasian shelf waters and the Arctic Ocean basin interior.