Quasi-permanent density front at the entrance to the Gulf of Finland: response to wind forcing

A quasi-permanent density front separates the saltier water of the northern Baltic Proper spreading along the Estonian coast from the less saline waters originating from the Gulf of Finland. Daily mapping of the area with a high-horizontal-resolution towed CTD was performed over a 12-day period onboard R/VAranda in July 1993. Easterly winds (parallel to the front) cause offshore movement of denser water, as well as a stronger inclination of the front to the sea surface. With westerly winds, the less dense water moves onshore and overrides the denser water, thus forming a shallower upper mixed layer. Spatio-temporal changes in the frontal zone are tested by a simplified semi-empirical model, with consideration only to wind forcing. Deviations from the assumed relationship are explained by the along-front buoyancy advection.