Variability of an under‐ice river plume in Hudson Bay

Observations of the Great Whale River plume in the coastal waters of Hudson Bay, Canada, during late winter and early spring during four different years showed its area to vary as a power of the discharge. The under‐ice plume area was much larger than plume area in open water for comparable discharges. Differences in plume geometry were related to elapsed time since ice formation and low‐frequency variability of the coastal circulation. The strength and orientation of the coastal motion was weakly correlated with the cross‐Hudson Bay atmospheric pressure gradient. The passage of low‐pressure systems over Hudson Bay is thought to generate a progressive edge wave in the absence of direct wind forcing. The amplitude of the low‐frequency variations in coastal circulation decreased with the increasing spatial extent of the landfast ice in the study area.