Abstract
Carbon release from high-latitude regions is intensifying, with profound consequences for the Arctic carbon cycle. Here, we provide a comprehensive analysis of changes in fluvial particulate organic carbon (POC) concentrations (C(POC)) and fluxes (F(POC)) during ice-free seasons of pan-Arctic rivers from 1985 to 2022 on the basis of satellite observations. Across 578,000 kilometers of river length, 18% of the total length experienced a significant increase in C(POC), which exceeds the 11% that exhibited declines, resulting in a net rise. Most increases occurred after 2005, contributing to a 12.6% (0.49 teragrams per year) increase in total F(POC) to the Arctic Ocean between 1985 to 2005 and 2006 to 2022. Regional contrasts highlight distinct possible drivers: increased precipitation in the North American Arctic and atmospheric warming in the Eurasian Arctic. Deepening of the permafrost active layer is also significantly correlated with C(POC) increases. These findings highlight climate-driven fluvial POC export as a key contributor to the Arctic carbon budget and provide a high-resolution, satellite-based dataset that can inform carbon cycle models and data assimilation efforts.