Circulation in the Bras dʹOr Lakes

The Bras dʹOr Lakes are a system of interconnecting basins open through two narrow channels to the Sydney Bight at the mouth of the Gulf of St Lawrence. Hydrographic surveys between 1972 and 1974 showed that surface waters can warm by more than 10 °C from May to July and that horizontal salinity differences of up to 10 psu can exist between Sydney Bight (30 psu) and the innermost regions of the Lakes. Using the data from May and June 1974 to derive horizontal and vertical exchanges, a simple budget model has been set up consisting of two or three layers in each of nine separate regions. The model has a bottom inflow from Sydney Bight, deep inflow through the narrow channels to other basins and a surface outflow. The exchanges agree reasonably well with estimates derived from available current meter data. The modelʹs predicted temperatures and salinities for July 1974 had rms errors of about 1•5 °C and 0•82 psu, respectively. The dissolved oxygen concentrations in four of the more isolated basins are similar to those calculated from the model, giving support to the derived circulation