Subtidal circulation, hydrography, sea ice and associated variability over the eastern Canadian shelf using a coupled ocean-ice model

Abstract

The subtidal circulation, hydrography, sea ice and associated variability over the eastern Canadian shelf (ECS) are examined using 17-years of model results produced by a coupled ocean-ice model. The coupled model has a fine-resolution child model (∼1/12°) embedded inside a coarse-resolution parent model (∼1/4°) of the northwest Atlantic. A combination of the semi-prognostic method and the spectral nudging method is used to reduce the model seasonal bias and drift. The model reproduces general features of the observed subtidal circulation and hydrography over the ECS. Analysis of model results demonstrates that the temporal variability in atmospheric forcing significantly affects the strength of the time-mean cyclonic circulation over the Gulf of Maine (GOM) and the outflow from the Gulf of St. Lawrence (GSL) through western Cabot Strait. The seasonal variability of salinity in the top 30 m of the Gulf of St. Lawrence, the Scotian Shelf and the Gulf of Maine (GSL-SS-GOM) is mainly affected by equatorward advection of low salinity waters from the lower St. Lawrence Estuary onto the GOM through the SS. Model results also reveal that there are significant regional differences in the interannual variability of circulation and hydrography over the ECS. Interannual variability on the Labrador Shelf is mainly affected by the advection of variability from high latitudes by the Labrador Current. Over the Newfoundland Shelf and the Grand Banks, the interannual variability is significantly affected by the non-linear interaction between the Labrador Current and the Gulf Stream. Over the Scotian Shelf and the Gulf of St. Lawrence, the interannual variability is significantly affected by advection of anomalies produced over the Tail of the Grand Banks. Net production of sea ice in the GSL during winter mainly occurs over shallow areas in the northern and southwestern Gulf. By contrast, net melting of sea ice during winter occurs over the central GSL, the eastern side of Esquiman Channel, and waters near Cabot Strait. Advection plays an important role in redistributing sea ice over different regions in the GSL. The sea ice also plays an important role in modulating the strength of winter currents in the GSL.