Continental to Meter Scale Climatic, Topographic, and Geomorphological Gradients Control Soil Organic Carbon Distribution in Complex Arctic Terrain

Abstract

Arctic soils store large amounts of soil organic carbon (SOC), yet landscape-scale variability remains poorly constrained, especially in complex mountainous regions that can be found across the Arctic. Understanding climate change impacts on Arctic carbon dynamics requires in-depth knowledge of SOC controls, given multiple drivers and potential responses. We map and quantify SOC stocks at the-scale in a large catchment in the Swedish Arctic and evaluate environmental controls of SOC distribution. A total of 310 georeferenced soil profiles were compiled, and SOC stocks were modeled using a machine learning approach trained on 14 environmental predictors. Predicted SOC stocks showed substantial spatial variation, ranging from 0 to 145.1 kg C m⁻², with a catchment-wide mean (±SD) of 4.8 ± 7.0 kg C m⁻². Organic layers, including deep peat deposits, accounted for 48% of the total SOC. Two dominant gradients structured SOC distribution: (a) as the climate in the catchment transitions from maritime to continental (west to east), SOC storage increases substantially due to peatland formation; and (b) a topographic gradient promotes substantially more SOC storage in valley bottoms and depositional slopes compared to uplands and mountaintops. Further, we reveal considerable variation at meter scale due to the geomorphological complexity of the landscape. We show that SOC variability in Arctic-mountainous regions is strongly controlled by the hierarchical interaction between climate, topography, and fine-scale geomorphology. Resolving these drivers at very high spatial resolution underscores the importance of landscape-scale analyses across environmental gradients for assessing the sensitivity of Arctic SOC stocks to ongoing climate change.