Conductivity-temperature-depth (CTD) and mooring data from eastern James Bay, 2018-2021

This study of the oceanography of eastern James Bay relevant to the coastal habitats and eelgrass (Zostera marina) supports the aims of the Coastal Habitat Comprehensive Research Project (CHCRP; see https://www.eeyoucoastalhabitat.ca/introduction/ and the Eeyou Coastal Habitat Project on CanWIN (https://doi.org/10.34992/2enm-0h29.) The CHCRP is a Cree-led research project that seeks to assess coastal marine ecosystem change in Eeyou Istchee with a focus on eelgrass ecosystems and the migratory waterfowl, including Canada geese (Branta canadensis) and Atlantic Brant (Branta bernicla hrota), that rely on the eelgrass habitat for stopovers during fall migrations. The project represents a collaboration between Cree coastal communities (Chisasibi, Wemindji, Eastmain, and Waskaganish) and a consortium of researchers from universities across Canada. University of Manitoba researchers Jens Ehn and Zou Zou Kuzyk co-led a project focused on the coastal oceanography. As part of this research, we conducted a series of studies of the under-ice winter freshwater plume of the the La Grande River (LGR). The LGR, which discharges at the community of Chisasibi in northeast James Bay, is a large river with flow regulated for hydropower production. Following a series of dams and diversions, the annual average discharge of LGR was approximately doubled and the peak discharge was shifted into winter. Peak discharge of LGR now regularly exceeds 5000 m3/s during winter months, making it the second largest winter flow discharge among pan-Arctic rivers. The discharge creates a substantial under-ice plume beneath the 10-20 km wide landfast ice cover along the northeastern coast of James Bay, Canada. Immobile landfast sea ice that forms along high-latitude coasts during winter blocks direct wind mixing, resulting in a larger spatial extent of under-ice river plumes compared with open water conditions under similar levels of river discharge. Because eelgrass thrives in brackish to salty water and is not tolerant of very low salinity (< 5 psu), the increase in the size of the winter plume with increasing LGR winter discharge has been monitored since the early 1980s. We have conducted detailed studies to examine when, how, and to what extent the winter freshwater plume of LGR affects salinity at nearshore eelgrass beds and to improve understanding of the physical processes affecting the plume's behaviour.