Pressure term:

Just as in the atmosphere, the pressure in the ocean varies from place to place and those differences are expressed as a gradient, represented by the symbol . These pressure gradients, which can be thought of as a parcel of water being pushed harder from one side than the other cause movement to occur. The two contributing factors to pressure gradients are sea level slopes (this is the barotropic component) and changes in density (this is the baroclinic component).