The late shoulder season modifies the mobility of iron and dissolved organic carbon in rivers from distinct permafrost regions
(2026) Chemical Geology — Vol. 724, p. 123707 (2026)
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- Authors
Hirst, Catherine 
- Abstract
- Rivers are important suppliers of iron (Fe) and dissolved organic carbon (DOC) from land to sea. While elemental transport in Arctic rivers has been studied mainly during summer, their mobility during the late shoulder season (i.e., the transition between the end of summer and the beginning of winter) remains poorly constrained. Here, we investigate how Fe and DOC mobility evolve during the late shoulder season in two rivers from distinct permafrost regions and hydrological conditions (in Alaska, USA and Abisko, Sweden). Iron and DOC were characterized using their concentrations, percentage of colloidal Fe, and indirect Fe-oxides tracers (Ce anomaly and δ30Si). We show two contrasting processes: (i) in Alaska, progressive river ice formation coincides with a shift toward groundwater-dominated river input, suggesting aggregation of Fe as particles (>0.22 μm), evidenced by a decrease in Fe concentrations in the filtered water (<0.22 μm) over the late shoulder season; the concurrent higher negative Ce anomaly, and the decrease in DOC concentrations, further suggest the aggregation of particulate Fe-oxides associated with DOC; (ii) in Abisko, warmer and near-stagnant river conditions sustain soil pore water-river connectivity over the late shoulder season, enabling lateral transfer of Fe, evidenced by increase Fe concentrations; the increase in the percentage of colloidal Fe, the lower negative Ce anomaly, the slight decrease in δ30Si, and the increase in DOC concentrations, further suggest an increase in colloidal Fe-oxides associated with DOC (1 nm- 0.22 μm) in the river. These contrasting Fe size ranges have direct implications for Arctic DOC export.
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Villani, M., Hirst, C., du Bois d’Aische, E., Osy de Zegwaart-Favart, C., Thomas, M., Roux, P., Lundin, E., Ledman, J., Schuur, E. A. G., & Opfergelt, S. (2026). The late shoulder season modifies the mobility of iron and dissolved organic carbon in rivers from distinct permafrost regions. Chemical Geology, 724, 123707. https://doi.org/10.1016/j.chemgeo.2026.123707 (Original work published 2026)