Capes and cape-associated shoals represent sites of convergent sediment transport, and can provide points of relative coastal stability, navigation hazards, and offshore sand resources. Shoal evolution is commonly impacted by the regional wave climate. In the Arctic, changing sea-ice conditions are leading to (1) longer open-water seasons when waves can contribute to sediment transport, and (2) an intensified wave climate (related to duration of open water and expanding fetch). At Blossom Shoals offshore of Icy Cape in the Chukchi Sea, these changes have led to a five-fold increase in the amount of time that sand is mobile at a 31-m water depth site between the period 1953-1989 and the period 1990-2022. Wave conditions conducive to sand transport are still limited to less than 2% of the year, however - and thus it is not surprising that the overall morphology of the shoals has changed little in 70 years, despite evidence of active sand transport in the form of 1-m-scale sand waves on the flanks of the shoals which heal ice keel scours formed during the winter. Suspended-sediment transport is relatively weak due to limited sources of mud nearby, but can be observed in a net northeastward direction during the winter (driven by the Alaska Coastal Current under the ice) and in a southwestward direction during open-water wind events. Longer open-water seasons mean that annual net northeastward transport of fine sediment may weaken, with implications for the residence time of fine-grained sediments and particle-associated nutrients in the Chukchi Sea.

Sediment dynamics on continental shelves can impact coastal geomorphology, habitat suitability, and biogeochemical cycling. In the coastal Arctic, for example, the rate at which sediment is transported to locations where it can be sequestered impacts the fate of carbon from thawing permafrost. To complement observational studies, this paper uses a numerical model to better understand variability in shelf sediment transport over timescales of hours to months. Specifically, a coupled hydrodynamic – sediment transport model, the Regional Ocean Modeling System (ROMS) - Community Sediment Transport Modeling System (CSTMS), is implemented within the Coupled Ocean-Atmosphere-Wave-Sediment Transport (COAWST) Modeling System, for the 2019 open water (nearly ice-free) season on the Alaskan Beaufort Sea shelf. Results showed that wave- and current-induced bed shear stresses frequently exceeded the critical stress for erosion and caused resuspension. Waves dominated bed shear stresses in depths shallower than 10 m and currents dominated in depths deeper than 20 m. Suspended sediment concentrations were highest during energetic wave events, although time periods with fast currents also caused resuspension, especially on the mid-to-outer shelf. When averaged over the open water season, modeled suspended sediment fluxes were westward, despite prevailing eastward currents, because of events characterized by fast westward currents. We expect these events may become more important for future sediment fluxes as storm frequency is projected to increase. Overall, the results improve our understanding of how sediment dynamics vary on the Beaufort Sea shelf during the open water season and provide insight into shelves characterized by strong currents and wave-induced resuspension.