Title: On the circulation and freshwater dynamics of the Hudson Bay Complex.
Abstract:
The Hudson Bay Complex (HBC), which includes Hudson, James, and Ungava Bays, Foxe Basin, and Hudson Strait, is currently undergoing change from two anthropogenic sources; industry and global warming. The communities surrounding this region use the sea for travel, hunting, and social connections, year round. Changes in the food chain and ice conditions thus impact the daily lives of the locals. The HBC also has a large drainage basin, receiving about 900 km3 of freshwater annually, making it an ideal location for the production of hydroelectricity. This riverine water traverses Hudson Bay and is advected to the North Atlantic via Hudson Strait, the main pathway for exchange between the HBC and the global ocean. Hudson Strait is also the third largest source of advected freshwater to the Labrador Sea after Fram and Davis Straits. However, our understanding of the role of riverine water in the bay is limited, and downstream effects of changes in river discharge is presently unknown. Additionally, knowledge of circulation in areas, such as Hudson Strait, is limited to a few observational datasets. These datasets focus mostly on the southern side of the strait which contains fresh eastward flow, and while valuable, there are no recent published data for the north side of the strait containing westward flowing waters entering the bay. I begin by presenting the first multi-year freshwater budget for the HBC. Using four model simulations and three river discharge datasets, I show that river discharge impacts freshwater fluxes out of the region on timescales longer than a year. Decreased river discharge and seasonality led to reduced freshwater and volume exchange within the HBC and to the North Atlantic. Model resolution had minimal impact on freshwater and volume fluxes in areas with simple flow dynamics. I also provide estimates of the Ekman, mean, and turbulent ii components of freshwater exchange between the interior and boundary regions of the bay. The mean and Ekman components import freshwater to the interior in spring and summer, and export it in the fall. Residence times of discharge in the HBC are calculated using an offline Lagrangian passive tracer tool, with an upper limit of 32 years. Using the highest resolution model simulation available at the time, I revisited the summer circulation pattern in Hudson Bay, which historically was thought to be cyclonic. Using satellite altimetry data along with model output, I showed that in summer, steric height gradients due to increased river discharge in summer, generate small scale features, including anticyclonic geostrophic flow in eastern Hudson Bay. Given this result, I present a revised summer surface flow pattern for Hudson Bay. Finally, to increase our understanding of flow and water exchange in Hudson Strait, I present the first year long observed measurements of flow on the northern side of Hudson Strait. Mooring data show a saline, weakly stratified inflow with reduced seasonality on the northern side compared to the southern side of the strait, which contains the fresh, discharge laden outflow. Source waters are from the Baffin Island Current, comprised mainly of Arctic water, with small contributions from Transitional Water and West Greenland Irminger Water.