Pan-Arctic riverine carbon and nitrogen exports dominated by hydrologic factors

Rivers are of critical importance in the global carbon and nitrogen cycles. Using a coherent database of in situ observations from six Pan-Arctic rivers, this study assessed the spatiotemporal dynamics of carbon and nitrogen exports and their driving factors. These Pan-Arctic rivers transported ∼35.30 Tg C yr^-1 and 1.04 Tg N yr^-1 from the Pan-Arctic region to the ocean, predominantly in dissolved forms, with organic matter exhibiting erosion and leaching drived effect. Seasonal patterns of carbon and nitrogen exports were shaped by hydrological and biogeochemical processes, with peak concentrations of organic carbon and nitrogen during spring and summer driven by cryospheric ablation, while inorganic C & N concentrations peaked in winter. Stable isotopic signatures indicated that riverine carbon was primarily influenced by C₃ plant-derived soil organic matter and riverine plankton, while nitrogen reflected both anthropogenic and natural sources. Random Forest model suggested that hydrological factors, particularly discharge (%IncMSE: 63.2 ± 15.4 %), were the primary drivers of carbon and nitrogen export. These findings provide critical insights into how warming-induced hydrological changes reshape element transport in Pan-Arctic rivers.