Abstract
Using the moored MnO2-fiber method, we have obtained 38 determinations of Th and Pa isotope concentrations from 18 sites along the margin of the western North Pacific near Japan, from water depths of 1,330 to 5,873 m. From our data, we are able to show that (1)228Ra and227Ac are being supplied to the seawater from the slope sediments of Honshu, Japan, (2) our230Th and231Pa concentrations match those obtained byin situ pumping with a MnO2-fiber adsorber in the Japan and Izu-Ogasawara trenches but are significantly higher than those from the Panama and Guatemala basins, and (3) our232Th concentrations show a similar systematic decrease with depth as do those of trace metals like Mn, Al, Te and Bi whose concentrations are strongly controlled by particulate matter scavenging.
In contrast, our data fail to show (1) that enhanced removal of230Th and231Pa by scavenging from the water column is taking place near the western margins and (2) that231Pa is being removed in preference to230Th from the water column to the marginal sediments. This is probably due to rapid mixing of the deep waters as compared to the scavenging rates of230Th and231Pa in the water column and at the sediment/seawater interface.
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Nozaki, Y., Yangt, HS. Th and Pa isotopes in the waters of the western margin of the pacific near Japan: Evidence for release of228Ra and227Ac from slope sediments. Journal of the Oceanographical Society of Japan 43, 217–227 (1987). https://doi.org/10.1007/BF02109817
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DOI: https://doi.org/10.1007/BF02109817