Competition of Tidal Mixing and Freshwater Forcing in Shaping the Outflow from Hudson Strait

摘要

Freshwater discharge in narrow, surface trapped, boundary plumes is a common feature of many coastal areas and straits, especially in the high latitudes. Such plumes have typically been described with synoptic measurements or steady state theoretical models and little is know about their variability or the factors which may influence it. Here we take advantage of there years of moored data across the outflow from Hudson Strait, which transport a large volume of riverine fresh water from Hudson Bay to the Labrador Sea, to investigate the tidal to interannual variability in the export and its forcings. Our analysis shows that the outflow is seasonally and interannually modulated by the storage and release of fresh water from the upstream Hudson Bay and that this can be explained in terms of Ekman convergence and divergence acting over the larger Bay. On shorter timescales, we found that a considerable fraction of the freshwater transport is associated with coherent, fresh, anticyclonic eddies embedded in the mean flow. Model results and analysis of the historical data indicates that these eddies are associated with the periodic release of fresh water from Hudson Bay as a result of transiting storms. A comparison of the tidal energy flux from the moorings and from a global tidal model yielded inconclusive results likely due to the limited resolution of the tidal model, and the study of the mixing driven by tides in the region is ongoing.