OCEANIC RADIOCARBON - SEPARATION OF THE NATURAL AND BOMB COMPONENTS

An improved method has been developed for the separation of the natura l and bomb components of the radiocarbon in the ocean. The improvement involves the use of a very strong correlation between natural radioca rbon and dissolved silica This method is applied to radiocarbon measur ements made on samples collected during the Geochemical Ocean Sections Study (GEOSECS), Transient Tracers in the Ocean (TTO) and South Atlan tic Ventilation Experiment (SAVE) expeditions. On the basis of this ne w separation we provide not only an estimate of the global inventory o f bomb C-14 at the time of the GEOSECS survey but also the distributio n of bomb radiocarbon along four thermocline isopycnals in each ocean. We also document the evolution of the bomb C-14 inventory and penetra tion along thermocline isopycnals in the North Atlantic Ocean between the times of the GEOSECS (1972-2973) and TTO (1980-1982) surveys and i n the South Atlantic Ocean between the times of the GEOSECS (1973) and SAVE (1987-1989) surveys. In addition, we show that the bomb tritium to bomb C-14 ratio (expressed in the tritium unit (TU) 81 units/100 pa rts per thousand) for waters entering the thermocline of the northern hemisphere is about 9 times higher than for those entering the souther n hemisphere thermocline. This contrast offers long-term potential as an indicator of inter-hemispheric transport of upper ocean waters.