Mapping pan-Arctic riverine particulate organic carbon from space (1985 to 2022)

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 (<i>C</i>_POC) and fluxes (<i>F</i>_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 <i>C</i>_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 <i>F</i>_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 <i>C</i>_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.