Zahn, M., Fournier, S., Fenty, I.G., Steele, M., Wood, M., and Gaube, P. (2026)
Presented at:
Ocean Sciences Meeting 2026Coastal sea ice formation and melt are driven by complex interactions between oceanic, atmospheric, and terrestrial processes, including riverine freshwater input. In the Arctic, salinity governs upper ocean stratification and thus modulates vertical heat exchange, yet the role of freshwater discharge from large rivers in shaping sea ice formation remains underexplored. Here, we combine satellite observations with a high-resolution coupled ocean-sea ice model to investigate how freshwater anomalies from the Mackenzie River influence early fall sea ice formation in the Beaufort Sea, one of the Arctic Ocean’s most rapidly changing regions. Both satellite and model results consistently show the early development of an “ice bridge” across the Mackenzie River plume, connecting the offshore ice edge to the coastline. The timing and extent of this feature vary interannually with the distribution of the freshwater plume. Enhanced salinity stratification from riverine input reduces mixed layer depth and thus upper ocean heat content, promoting earlier sea ice formation by up to three weeks compared to adjacent saltier waters. These findings highlight the strong influence of terrestrial freshwater discharge on coastal sea ice processes and suggest that continued increases in Arctic runoff may significantly alter sea ice phenology and fall ice extent.
