Meltwater chemistry at two rapidly retreating Arctic Sweden glaciers: Implications for downstream nutrient supply in a warming climate

The cryosphere is experiencing rapid decline due to climate change, with 25-54% mass loss of the world’s glaciers predicted over the next century. These changes have far-reaching implications including impacts on local geohazards, regional freshwater availability, global sea-level rise, and downstream nutrient supply. Though many studies have examined the physical processes associated with glacier change, we still lack a complete understanding of the associated geochemical consequences. This is especially important to constrain as glaciated catchments are important sources of lithogenic nutrients due to mechanical and chemical weathering, and meltwater transport in turn influencing downstream ecosystems.

To better constrain the effects of subglacial weathering on glacial runoff chemistry, water and ice samples were collected at Storglaciären and Isfallsglaciären, two polythermal glaciers in the Tarfala Valley, Arctic Sweden in the summers of 2024 and 2025. These glaciers have experienced dramatic thinning and retreat for the past century, with this trend recently accelerating. Water temperature, conductivity, pH and other parameters were measured in situ. Samples were analyzed for major and trace ion concentrations, total carbon, and stable water isotopes. These are the first reported geochemical measurements of this kind for the reference glacier Storglaciären.

Aqueous geochemistry results indicate that chemical weathering of the bedrock is likely driven by a combination of both carbonic (H₂CO₃) and sulfuric (H₂SO₄) acid dissolution, resulting in major cations (e.g., Ca, Mg), Si, and Fe being released from subglacial sediment. Solute concentrations are highest at the cold-based ice margins, indicating increased dissolution of Fe- and Mg-rich bedrock in these areas. Concentrations of sulfate are also highest under the cold ice, most likely due to increased FeS₂ oxidation at the cold-based margins of the glacier.

These results indicate that heterogeneous oxidation most likely drives acidic weathering in the subglacial environment, and that this process appears to be more effective in the more stable, cold-based margins of the glacier where residence times of sediment are longer. Localized silica precipitation is more prevalent in the warm-based portions dominated by subglacial meltwater, glacial sliding, and seasonal flushing of sediment and water. These results suggest that there may be detectable differences in alteration processes between cold- and warm-based glacial thermal portions of ice sheets and glaciers, that these differences are detectable in local meltwaters, and that significant amounts of solutes are generated by subglacial alteration processes and transported to lower elevation Arctic ecosystems. It is imperative that future studies include repeat meltwater monitoring at these rapidly changing systems to understand the ongoing effects of climate change on glacial water chemistry and downstream nutrient supply.