Nearshore erosion by combined ice scouring and near-bottom currents in eastern Hudson Bay, Canada

A study of nearshore sedimentary processes was carried out in Manitounuk Sound, a sheltered environment protected by rocky islands along eastern Hudson Bay. High-resolution seismic profiles suggest that up to 10 m of Holocene sediments were eroded in less than 15 m water depth although these shallow depths are affected by low-energy waves and currents. According to our measurements of near-bottom currents at 3.7 and 5.6 m water depths, the threshold velocity for sediment motion (20 cm s(-1)) is only seldom exceeded, and consequently the significant erosion of the nearshore deposits can hardly be explained by hydraulic processes alone. Geophysical data (seismic and echosounding profiles) suggest that the observed erosion is mainly due to bottom scouring by dragging ice keels. These data show that the zone of maximum ice scouring, between 8 and 12 m water depths, corresponds to the zone of maximum erosion of Holocene sediments. Because ice scouring in this area occurs when the sea is largely ice-free, wind-induced near-bottom currents probably contribute to the dispersal of the sediments resuspended by ice. (C) 1999 Elsevier Science B.V. All rights reserved.