Arctic rivers drain vast northern landscapes and flow into the Arctic Ocean, forming critical land-ocean linkages. Studies of these linkages provide data that are influential for U.S. interests in the Arctic, including economic development, food security, community resilience, and weather patterns across the U.S. and the globe. Since 2003, the Arctic Great Rivers Observatory (ArcticGRO) has provided essential time-series data of water discharge and chemical analyses for the six largest Arctic rivers – the Yukon in the USA, the Mackenzie in Canada, and the Yenisey, Ob’, Lena, and Kolyma in Russia – as well as the curation and dissemination of discharge data for nine additional rivers. This proposal supports the continued sampling of water chemistry in the Yukon and Mackenzie rivers, ensuring the continuity of these crucial time-series. The team will curate and disseminate discharge data for all ArcticGRO rivers and will expand the dataset through analysis of archived samples to explore potential causes of documented changes in Arctic river water chemistry over the past 20 years. The ArcticGRO research team will also work with communities in the Yukon River watershed to address questions about local water quality. Data generated by ArcticGRO will be disseminated broadly and used by the scientific community to understand watershed dynamics and ocean processes at local, regional, and global scales. Continued sampling of the Yukon (at Pilot Station) and Mackenzie (at Tsiigehtc