Tritium in the deep North Atlantic Ocean

The results are given of an experiment to determine how much water flows equatorwards at the mid-latitude western boundary and how much of this water is of far-northern origin, using tritium sampling techniques. It was shown that a distinct core of tritium (from nuclear weapons testing in the atmosphere) marks the southward flowing jet of the deep western boundary current of the North Atlantic circulation at 300N latitude. The concentrations, of the order of 0.5 - 1.0 TU, indicate a roughly 10 fold dilution of source waters in the far north. This thin jet, 50 km in width, carries water into subtropical regions which, until recently, were free of anthropogenic tritium. It underlies the more extensive distributions of tritium found in more rapidly renewed waters above the permanent thermocline. (U.K.)