The Northwest Atlantic Marine Ecozone, as defined by the Commission for Environmental Cooperation (CEC), is a Canadian marine ecozone forming a transitional region between the cold northern waters of the Arctic Ocean and the more temperate waters in its southern extent.

Moreover, in this ecozone the cold Labrador Current meets the Gulf Stream at the Grand Banks, and together with the freshwater discharge from the Saint Lawrence River, moderate the climate of the coastal areas of the Maritimes.

[2] Surface sea ice forms throughout this region, and thousands of icebergs may be observed between the northeast coast of Newfoundland and the Grand Banks.

The Saint Lawrence River freezes over during the winter, closing the important shipping channel until the ice clears in the summer.

Summer tides may reach 9 to 12 m, though they tend to be exaggerated in Ungava Bay and more subdued in the Gulf of Saint Lawrence.