Investigations of gram quantities of Atlantic and Pacific surface particulates

Abstract

Particulates amounting to 0.1-2.0 g efficiently collected from large volumes of Atlantic and Pacific surface waters have been analyzed for carbonate, opal, quartz and several natural and man-made radioisotopes. The concentrations of particles range between 10 and 600 µg/kg. In the equatorial regions particle concentrations are low and similar in both the oceans. At higher latitudes (>30°N or S), the Atlantic waters, however, have higher concentrations of particles compared to those in the Pacific. The latitudinal distribution exhibits a north-south symmetry with higher concentrations in the 30°-60° belt. Based on the particulate abundance for CaCO₃ and opal and their sedimentation, we have estimated their production and in-situ integrated dissolution rates for a few regions. Radioisotopes having different source functions, namely ¹⁴C and ²³⁹Pu injected due to nuclear weapon tests, ²³⁴Th, ²³⁰Th and ²²⁸Th produced in-situ in seawater, ²³²Th which derives primarily from land, ²¹⁰Pb introduced via wet precipitations and ²²⁶Ra introduced through diffusion from deep-sea sediments have been measured in the particulates. The relative enrichment factors for these nuclides in particles vary as Th ⋍ Pu > Pb > Ra. The atmospheric bomb fallout pattern is discernible in the surface particulates; the ²³⁹Pu concentration increases with latitude in both the hemispheres; however, the values are about a factor of two lower in the southern hemisphere. The distribution pattern of radioisotopes is found to be complex, even for ²³⁴Th whose source function in the oceans is uniform. In view of the differences in the source functions it becomes possible to delineate the principal geochemical/geophysical processes which determine the concentrations of these nuclides in surface waters.