Physical oceanography and water exchange in the Northern Kvark Strait

The Northern Kvark connects the very fresh Bothnian Bay to the slightly saltier Bothnian Sea in the northern Baltic Sea. Intense field experiments were made in the strait in May 2003 and October–December 2004 to describe the physical oceanography of the strait. Three different hydrographic regimes were identified and first-order analyses were made on each regime, neglecting friction, rotation, and horizontal gradients. The strait is shown to be barotropically blocked about 45% of the time. The rest of the time there is vertical stratification, which can be described either by two homogenous layers or by linear density and velocity profiles. The flows in the two stratified regimes are shown to be hydraulically controlled.