Modeling Terrestrial Dissolved Organic Carbon Loading to Western Arctic Rivers

The mobilization and land‐to‐ocean transfer of dissolved organic carbon (DOC) in Arctic watersheds is intricately linked with the region's climate and water cycle, and furthermore at risk of changes from climate warming and associated impacts. This study quantifies model‐simulated estimates of runoff, surface and active layer leachate DOC concentrations and loadings to western Arctic rivers, specifically for basins that drain into coastal waters between and including the Yukon and Mackenzie Rivers. Model validation leverages data from other field measurements, synthesis studies, and modeling efforts. The simulations effectively quantify DOC leaching in surface and subsurface runoff and broadly capture the seasonal cycle in DOC concentration and mass loadings reported from other studies that use river‐based measurements. A marked east‐west gradient in simulated spring and summer DOC concentrations of 24 drainage basins on the North Slope of Alaska is captured by the modeling, consistent with independent data derived from river sampling. Simulated loadings for the Mackenzie and Yukon show reasonable agreement with estimates of DOC export for annual totals and four of the six seasonal comparisons. Nearly equivalent loading occurs to rivers which drain north to the Beaufort Sea and west to the Bering and Chukchi Seas. The modeling framework provides a basis for understanding carbon export to coastal waters and for assessing impacts of hydrological cycle intensification and permafrost thaw with ongoing warming in the Arctic. Plain Language Summary Arctic rivers transfer a relatively large amount of freshwater to the Arctic Ocean compared to other oceans. The rivers contain organic carbon dissolved in the water, with the bulk arriving during the high flow in spring that follows snowmelt. There is evidence that climate warming is thawing permafrost and resulting in more carbon traveling through rivers to the Arctic Ocean, so it is important to understand how much enters river networks from soils. We used a computer model designed to capture the seasonal thawing and freezing of Arctic soils and seasonal snowpack accumulation to estimate how much dissolved organic carbon is loaded to rivers in the western Arctic over the period 1981 to 2010. For northern Alaska rivers the simulation shows a gradient in dissolved organic carbon concentration from the east side to the west, similar to the pattern in independent data derived from river measurements. Our new estimates