Estimates of vertical heat flux and stratification from southern Georges Bank, model descriptions and results, Winter–Summer 1995

One-dimensional energy models have long been shown to describe the location of tidal mixing fronts, separating well-mixed from stratified waters on mid-latitude continental shelf regions, such as Georges Bank, from spring-fall. The same models can also be used to describe adjustments of the fronts and changes in density stratification to time-dependent variability of surface heating, tidal stirring and wind mixing over a broad range of time scales. Findings from this study include validation of a one-dimensional model through comparison of model potential energy anomalies with independent data consisting of potential energy anomalies computed using shipboard CTD measurements from broad-scale (and other) surveys of southern Georges Bank conducted during 1995. Model results from 1995 show net buoyancy removal due to tidal stirring remaining approximately 2–5 times greater than buoyancy input due to vertical heat flux for water depths of less than 60 m (zone 1) during the spring–summer period of positive heat flux; the addition of wind mixing adding relatively little to the net result given the very strong tidal stirring within zone 1. Additional model results show development of transient stratification during late-April 1995 over regions with bottom depths of 60–80 and 80–100 m (zones 2 and 3) due to net buoyancy input caused by increased vertical heat flux, neap tidal currents and reduced wind mixing, followed by increasing tidal currents from the next spring tide and strong wind mixing associated with low pressure systems which traversed the region during early-May 1995. Lastly, model results show the development of seasonal stratification during mid-May 1995 over regions with bottom depths of 60–80 and 80–100 m (zones 2 and 3) caused by increased vertical heat flux and reduced tidal stirring and wind mixing.