Observations of Water Trajectories in the Open Sea

Abstract

DIRECT observations of continuous movements of water masses in the open sea do not appear to have been carried out before. We have, for this purpose, for some years been using free drifting current-crosses, followed by our research steamer the Skagerak. The crosses are made from two sheets of corrugated iron, intersecting at right angles, with the line of intersection vertical, and presenting an area to the current of approximately one square metre. They are suspended from a cylindrical buoy of small dimensions drifting at the surface with its axis vertical. The buoy carries a very light rod projecting upwards with a small electric lamp at the top, of the type used by drifters for their nets. By varying the length of the thin wire rope by which the cross is suspended from the buoy, one may study the water movements in different depths, since the small resistance due to the surface buoy does not affect the movements of the cross to any large extent, so long as the current below is not too weak relatively to the surface current. The positions of the buoy are observed at intervals of an hour or less by bringing up the ship as close to the drifting system as possible, without interfering with its movements. In daytime, with moderately strong currents, the movements of the buoy are followed from the ship at anchor by means of a Zeiss tele-meter. Such drifting systems have occasionally been followed right across the Skagerak from Skagen to the lighthouse Måseskär on the Swedish coast.