Ventilation of the Deep Western Boundary Current and Abyssal Western North Atlantic: Estimates from Tritium and3He Distributions

Abstract

The tritium and excess 3He data from the 1981 TTO/NAS program are used to study the time scales for the ventilation of the deep western basin by recently formed North Atlantic Deep Water (NADW). The large-scale distributions of tritium and 3He in the deep North Atlantic are presented, and tracer inventories are computed for individual deep water basins. The bulk of the bomb tritium (and thus new NADW) resided in 1981 in the deep Labrador Sea and western subpolar gyre, with a slightly smaller amount in the deep western subtropical gyre. The maximum excess 3He values were located south of the overflows in the Labrador Sea the result of competition between ventilation and in situ tritium decay. The subpolar gyre was also the site of the strongest increase in decay-corrected tritium (∼120%) and excess 3He (∼100%) between the 1972 GEOSECS survey and the 1981 TTO/NAS program. The observed deep water tritium inventory is in reasonable agreement with model tracer inputs computed for the combined overflow... Abstract The tritium and excess 3He data from the 1981 TTO/NAS program are used to study the time scales for the ventilation of the deep western basin by recently formed North Atlantic Deep Water (NADW). The large-scale distributions of tritium and 3He in the deep North Atlantic are presented, and tracer inventories are computed for individual deep water basins. The bulk of the bomb tritium (and thus new NADW) resided in 1981 in the deep Labrador Sea and western subpolar gyre, with a slightly smaller amount in the deep western subtropical gyre. The maximum excess 3He values were located south of the overflows in the Labrador Sea the result of competition between ventilation and in situ tritium decay. The subpolar gyre was also the site of the strongest increase in decay-corrected tritium (∼120%) and excess 3He (∼100%) between the 1972 GEOSECS survey and the 1981 TTO/NAS program. The observed deep water tritium inventory is in reasonable agreement with model tracer inputs computed for the combined overflow...