Two alternative hypotheses which attempt to explain the position of the shelf sea fronts are (1) control by the energetics of tidal and wind mixing and (2) limitation of the penetration of tidal stresses by the effects of rotation. A turbulence-closure (T/C) point model has been used to investigate the interaction of these two constraints and predict the seasonal cycle of stratification and frontal position for varying current polarization and water depths of h=70 m and h=100 m. For clockwise-rotating tidal currents the frontal positions are in close accord with the previous prescriptive model, which is based only on the energy constraint, and with the observed positions of fronts at critical values of &khgr;=log (h/⟨u3⟩)=2.7¿0.4 (where h=depth and u=depth mean tidal current amplitude for M2, and angle brackets denote a time mean). For rectilinear tidal currents (equal clockwise and anticlockwise components), there is a small displacement (~0.25) toward lower values of &khgr;.

When the currents are predominantly anticlockwise, the frontal positions predicted by the T/C model deviate significantly from the constant &khgr; condition with a maximum discrepancy, when polarization P=+1, of Δ&khgr;=0.86 and 1.56 at h=70 and 100 m, respectively. This displacement is in the same sense as, but considerably less than, that predicted by the combined boundary layer theory. It may be detectable in the few areas of the shelf where P may reach values of up to 0.7 in depths of ~100 m. For most regions of the European shelf, where -0.3<P<0.3, the model suggests that the influence of rotation will be small and control of frontal boundaries will rest primarily with the energy constraint. ¿ American Geophysical Union 1994