A large under-ice plume forms because of the regulated winter discharge from the La Grande River hydroelectric complex (NE James Bay, Canada), which is among the largest winter discharges in the circumpolar north. In 2016–2017, field campaigns were completed to characterize the under-ice plume's structure, extent, and short-term dynamics related to tides, weather, and discharge. Amid concerns of the freshwater's impact on eelgrass, the lateral spreading of the under-ice plume into inshore areas was also assessed. When discharges averaged 4,800 m3 s−1 throughout the January–March periods, the freshwater influence of La Grande River extended more than 100 km north along the James Bay coast, with the brackish (salinity <25) under-ice plume more than three times larger than for a natural winter discharge of ∼460 m3 s−1. The core area of the under-ice plume, defined as the area with a highly stratified water column and surface layer of salinity 20 km south. It was stable throughout the January–March 2016–2017 periods and, despite 30% higher winter discharge, was not significantly larger compared to survey periods in 1984–1987. This stability appears to be due to coastal geometry and width of the landfast ice cover, under which the plume can spread with limited mixing. Inshore salinity was about 5–10 units lower in winter versus the open-water period. The seasonal duration of reduced salinity at eelgrass habitats will depend on landfast ice duration as well as river discharge magnitude.

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Title Under-Ice Hydrography of the La Grande River Plume in Relation to a Ten-Fold Increase in Wintertime Discharge
Publication general type Journal
Project Name Eeyou Coastal Habitat Project
Keyword Vocabulary Polar Data Catalogue
Keyword Vocabulary URL http://vocab.nerc.ac.uk/
Theme Marine
Version 1.0
Publisher JGR Oceans
Date Published 2022
DOI 10.1029/2021JC018341
Language English
Field Value
Authors 1
Author Name
Chris Peck
Type of Name
Centre for Earth Observation Science - University of Manitoba
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License Name
Licence Type
Licence Schema Name SPDX
Licence URL https://spdx.org/licenses
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