Investigations of gram quantities of Atlantic and Pacific surface particulates

Krishnaswami, S. ; Lal, D. ; Somayajulu, B. L. K. (1976) Investigations of gram quantities of Atlantic and Pacific surface particulates Earth and Planetary Science Letters, 32 (2). pp. 403-419. ISSN 0012-821X

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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.

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ID Code:16762
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