Geochemical phosphorus sequestration in tundra soils limits primary production in Arctic headwater streams and rivers. Upper Kuparuk River, North Slope, Alaska, 2020-2023.

Climate warming in the Arctic region is thawing previously frozen soil (permafrost). Permafrost thaw alters landscape hydrology, increases weathering rates, and thus increases the delivery of solutes to adjacent waters. Long-term monitoring of the Kuparuk River (North Slope, Alaska) confirms significant increases in many solutes that are indicative of thawing permafrost. However, there is no evidence of an increase in phosphorus (P), the nutrient that most often limits primary production in tundra streams. Here, we show that soils in the upper Kuparuk River watershed have a high biogeochemical sorption capacity that can limit P mobility and use published data to show that this may be a pan-Arctic characteristic. While P bioavailability is restricted by vegetative cycling, we found that concentrations of Mehlich-3 extractable iron (Fe) and aluminum (Al) also impart a very high P geochemical sorption capacity across our study sites. Analysis of a pan-Arctic soils database suggests that this high P sorption capacity could be a ubiquitous feature of Arctic soils. Therefore, we conclude that while warming-induced permafrost thaw may increase P mobility, simultaneous increases in pedogenic secondary Fe/Al minerals will continue to retain P in tundra soils and limit biological productivity in adjacent aquatic systems.