ABSTRACT: Effects of seasonal changes on the sedimentary regime of a subarctic estuary, Rupert Bay (Canada).

CGRG Bibliography of Canadian Geomorphology
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Abstract

Rupert Bay is a large (875 kmSUP-2 ) shallow estuarine embayment opening in James Bay south of Hudson Bay, Canada. Three large rivers with a combined annual mean discharge of 2350 mSUP-3 /s converge into the bay. Due to ice unloading and crustal readjustment, at a current rate of 1 m/100 years, these rivers have excavated their channels into marine sediments of the early post-glacial Tyrrell Sea invasion. These provide the main source of the poorly sorted silty clays forming the present deposits. Sediment transport and deposition are influenced by strong seasonal fluctuations in climate, with a continuous ice cover for nearly six months of the year, a rapid break-up and spring discharges which are as much as sixteen times the yearly minima. During the open season, high turbidity prevails with a pronounced streakiness in the flow direction and stable fronts at the boundaries of the river plumes. Both the turbulence by local wind waves and tidal action hinder deposition. Determinations of the suspended load and velocity at tidal stations indicate that conditions are met for seaward tidal flushing of the sediments brought in by the rivers. Under ice-covered conditions, there is a pronounced decrease of the suspended-matter concentrations in the reduced volume of the bay, suggesting that settling occurs below the ice cover, the winter deposits being largely returned to the water column in the following spring. Low present depositional rates are confirmed by SUP-137 Cs activity in the surface deposits. On a longer-term basis, crustal rebound maintains a slight regional uplift which forms entrenchment of the river channels as well as slow progradation of the supratidal marshes.

Bibliography of Canadian Geomorphology