Bouncing internal bores of Ardmucknish Bay, Scotland

Abstract

Propagating fronts and internal waves have been observed in the sea using bottom-mounted side-scan sonar¹ in Ardmucknish Bay, north of Oban on the west coast of Scotland. The fronts, between brackish water and seawater, are generated when less saline, and so less dense, water discharges tidally into the sea from the mouth of a sea loch. The fronts appear to propagate from the direction of the loch, as might be expected, but the internal waves were found to propagate almost at right angles to this direction. A time-lapse cine camera was mounted on a nearby hill and was used to investigate the phenomena, which are visible on the surface because of their effect on surface waves and hence on the brightness of the sea surface. The internal waves are found to be generated when the fronts reflect from the coastline on one side of the bay, and this explains then- direction of propagation. The movement of fronts influence the horizontal transfer (of say nutrients) from the sea loch into the surrounding coastal water.