Transport of dissolved organic carbon (DOC) from land to water is an important but poorly known component of northern carbon cycles. We examined seasonal patterns of arctic river DOC flux, focusing on the largely uncharacterized snowmelt period. High-intensity sampling of the Kolyma River showed rapid increases in DOC concentration during peak discharge, yielding unique DOC-water flux relationships compared to summer, fall and winter. Our annual DOC flux estimates were 31% higher than previous estimates for the basin based on few or no snowmelt samples. Synthesis of the sparse literature show that 55% of arctic river DOC flux occurs during snowmelt. Biogeochemical characterizations of DOC in large rivers are usually done after snowmelt runoff, and are thus unrepresentative of most DOC transported to the Arctic Ocean. Finally, the proportion of annual DOC flux at snowmelt is considerably higher than for water, suggesting that cold season production is an important but little known process regulating arctic DOC transport.