Paving the Way for Improved Representation of Coupled Physical and Biogeochemical Processes in Arctic River Plumes—A Case Study of the Mackenzie Shelf

Processes affecting the transformation of riverine dissolved organic carbon (DOC) across the land‐to‐ocean aquatic continuum are still poorly constrained in Arctic models, leading to large uncertainties in simulated air–sea CO2 fluxes of the coastal periphery. Here we use the ECCO‐Darwin regional configuration of the Southeastern Beaufort Sea to analyze the sensitivity of simulated carbon cycling to (1) the model vertical discretization and (2) different parameterizations of Mackenzie River carbon discharge. We show that riverine DOC lifetime rather than its volume largely modulates Mackenzie River plume air–sea CO2 fluxes, leading to the Southeastern Beaufort Sea (SBS) being either a source (0.03 Tg C year−1) or sink (−0.20 Tg C year−1) of atmospheric carbon. We show that estuarine processes, such as flocculation, also play an important role and can dampen CO2 outgassing by up to 0.07 Tg C year−1. In terms of model physics, by increasing the vertical grid resolution, we better fit observed plume structure, without altering the simulated concentrations of DOC. However, the decrease in river forcing cell volume increases local pCO2 and promotes elevated outgassing in the vicinity of the Delta. Our work demonstrates that future Arctic land–ocean models must consider the intricate details of river plume systems to realistically simulate coastal‐ocean physics and biogeochemistry.