Radium in the Indian-Antarctic Ocean south of Australia

Abstract

The Antarctic Convergence forms a distinct boundary for surface radium distribution. To the south of the convergence radium concentrations near the surface are close to 8 X 10 -' g/l, and those of the deep waters, 10 X 10 -' g/1. To the north surface concentrations drop to 4 X 10 -' g/l, whereas bottom values remain near 10 X 10 - g/l, the transition being at a depth below 500 meters. Radium distribution in this part of the ocean strongly reflects the influence of advection and water-mass movement. Also, downward transport of radium through particle settling is clearly demonstrated. The nature of the radium-bearing particles in the ocean may be closely related to siliceous organisms. The use of radium for deducing oceanic mixing rate was based on the assumption that the distribution of this .element in the ocean was governed only by eddy diffusion and radioactive decay processes [Koczy, 1958]. Recent studies have revealed that such an assumption may be over-simplified. The complications mainly involve (a) biological uptake of radium in surface water [Szabo, 1967], (b) downward settling and subsequent resolution of radiumbearing particles in deep waters [Broecker et al., 1967], and (c) advective mixing [Koczy and Szabo, 1962]. The oceanographic conditions in the southern oceans, i.e., relatively high biological activity and deep-water upwe!ling, should aid in further evaluating the complicating factors mentioned above. In addition, as the antarctic waters act as a link between the world's oceans, problems regarding oceanic water interchange and elemental budgets are expected to be closely related to processes in the southern polar seas. This paper presents the first radium measurements from the antarctic waters. Six profiles with an approximately longitudinal trend (be