Tritium and helium 3 in the northeastern Atlantic Ocean during the 1983 TOPOGULF cruise

This study is part of the TOPOGULF program, in which tracer measurements were closely associated with the hydrological data. The sampled area was located near the Azores Islands on the both sides of the Mid‐Atlantic Ridge. The tritium content of the surface waters reveals a strong front along the Azores current. The 3He distributions are used to identify some areas where ventilation processes are active. At depth, the spatial distribution of tritium is studied along isopycnals. In the thermocline it is essentially the anticyclonic gyre which is responsible for the northeast‐southwest gradient in tritium concentrations. The respective influences of the Labrador Sea Water and the Mediterranean Water are noticeable through the tritium data. The Mediterranean Water seems to be an end member responsible for a decrease of the tritium contents in the north and for an increase in the south, by mixing. A quantitative approach using a mixing model is used to check the validity of the 3He‐3H “age.” The model leads to two extreme values of the time scales for the middepth circulation in the studied area: 35 years for the ventilation time of the Labrador Sea Water and around 200 years for the residence time of the oldest waters in the southeastern area.