Tritium budget of the South Atlantic

Abstract

Oceanic tritium inventories of the South Atlantic are deduced from tritium observations and are compared with estimated tritium deliveries. In 1993 the total water column tritium inventory between 0°S and 50°S based on World Ocean Circulation Experiment data amounted to 2.88 × 1016 TU 81 m3 (i.e., tritium units decay corrected to 1981; 3.44 × 1018 Bq, uncertainty ±10%) with 80% residing in the upper 800 m. This is about 10% higher than observed during the South Atlantic Ventilation Experiment program in 1987–1989 but twice the amount reported for the Geochemical Ocean Sections Study survey 1972–1973. Maximum tritium water column contents are found in the subtropics, where in 1993 the bomb signal penetrated to approximately 1000 m depth and where the decay‐corrected surface water tritium concentrations were highest and still slowly increasing. The total tritium inventories agree with integrated tritium deliveries that were estimated building upon previously published global input functions, adjusted to the conditions of the South Atlantic. The agreement supports the delivery estimates, which by themselves have considerable uncertainty margins. Tritium surface water time histories of the South Atlantic are inferred for the period 1952–1995 by combining the available observations and atmospheric tritium depositions within a simple scheme. The estimated deliveries (effective uncertainty ±30%) and surface water tritium concentrations (±15%) can serve as boundary conditions in water mass dating and for employing tritium in ocean general circulation models.