Tritium measurments in the Tasman Sea and the Southern Ocean

Abstract

Tritium concentrations have been determined for seawater samples collected from the Tasman Sea and from the Southern Ocean south of Tasmania. The volume of the samples was reduced from 2000 to 16 ml by electrolysis to concentrate the tritium before counting in a liquid scintillation spectrometer.

Profiles of tritium concentrations are presented for four stations in the Southern Ocean and nine in the Tasman Sea. The tritium concentrations correlated well with the water density, regardless of their origin in the eddy field. The water must be well mixed on the isopycnal surfaces within a time scale which is much shorter than the tritium half-life of 12.3 years.

The tritium concentration in water of density σ_t = 26.8 collected in the Tasman Sea was only about 60% of the concentration found in the Southern Ocean for water of the same density. This lower tritium concentration is explained by a combination of two processes: radioactive decay during the time taken for water to flow from the Southern Ocean to the Tasman Sea, and dilution by mixing with water of low tritium concentration.