Atmospheric forcing controls cross-shelf exchange and bay-scale circulation in Hudson Bay

Сyclonic circulation of water in Hudson Bay, maintained by cyclonic wind forcing, transports riverine water along the shore through Hudson Strait to the Labrador Sea. Synoptic, seasonal and interannual variability of the freshwater outflow from Hudson Bay remains unclear. Two oceanographic moorings deployed along the western coast of Hudson Bay in September 2016 recorded temperature, salinity and current velocities through depths of 35–105 m until September 2018. Data analysis revealed that the along-shore southward current in eastern Hudson Bay is amplified through the entire water column in response to storms generated by Pacific born cyclones passing over Hudson Bay eastward toward the North Atlantic. A surface Ekman on-shore transport and associated increase of the sea surface heights over the shelf produce a cross-slope pressure gradient that drives an along-slope southward flow, in the same direction as the wind. This is consistent with coastal downwelling. Conversely, southerly upwelling-favourable winds associated with the Beaufort High, extending over the Canadian Arctic Archipelago, leads to along-shore northward flow that disrupts the mean cyclonic transport. The wind-driven water dynamics are consistent with (i) sea ice dynamics revealed from satellite imagery and trajectory of ice beacons deployed in western Hudson Bay in February 2017 and (ii) sea surface height data derived from satellite altimetry and a tide gauge in Churchill. Finally, below the surface mixed layer, the wind-driven water dynamics significantly contribute to the variability of temperature and salinity due to the cross-shelf displacement of water masses as per upwelling and downwelling.