Seasonal and Geographic Variation in Dissolved Carbon Biogeochemistry of Rivers Draining to the Canadian Arctic Ocean and Hudson Bay

The chemical composition of river water can be used to diagnose change on land, while playing a determining role in the ecology and biogeochemistry of riverine‐influenced ocean waters. Despite this, little is known about the seasonal and geographic variability of riverine chemistry throughout much of the Canadian north. Here we assess the chemical composition of a broad suite of rivers draining to the Canadian Arctic Ocean and Hudson Bay using previously unpublished government data. We focus on inorganic and organic carbon (alkalinity and dissolved organic carbon), using paired chemistry and discharge measurements to assess constituent flux. Concentrations and area‐normalized yields vary substantially across the northern Canadian landscape, with dissolved organic carbon typically highest in rivers draining the Hudson Bay Lowland, alkalinity highest in rivers draining Cordillera and Plains terrains, and the ratio of organic to inorganic species highest in rivers draining the Canadian Shield. Yields of major weathering ions show that carbonate weathering—a notable proportion of which may be driven by sulfide oxidation—dominates inorganic carbon delivery from the rivers we assess. Despite the reasonably diverse coverage of the data set, we find that clear gaps exist, including a lack of data through to the present day for many rivers, and a dearth of measurements from the Arctic Archipelago and eastern shores of Hudson Bay. We therefore use a modeling approach to extrapolate fluxes to the full Canadian Arctic drainage basin. Region‐specific differences between our results and previous models reinforce the need for targeted river water chemistry measures throughout the Canadian Arctic domain. Key Points The concentration and flux of organic and inorganic carbon vary substantially across Canadian Arctic rivers but track latitude and physiographic region Alkalinity in this region is largely derived from carbonate weathering, with sulfide oxidation potentially an important contributor to the weathering flux Geographic and temporal data gaps hamper our ability to definitively quantify riverine chemistry through large swaths of northern Canada