Figure 10.15 Distribution of tritium along a section through the western basins in the North Atlantic, measured in 1972 (Top) and remeasured in 1981 (Bottom). Units are tritium units, where one tritium unit is 1018 (tritium atoms)/(hydrogen atoms) corrected to the activity levels that would have been observed on 1 January 1981. Compare this figure to the density in the ocean shown in figure 13.9. From Toggweiler (1994)