Abstract
The nature of sedimentation and mixing are examined in abyssal red clay sediments from the North Central Pacific using three types of indicators: 230Th/ 232Th , organic 14C, and 137Cs and 239.240Pu. 230Th/ 232Th analysed revealed that the clay sedimentation rate in three box cores collected within a 50 km radius was less than 1.0 mm/10 3 yr. However, analyses of the organic carbon in thin layers of sediment revealed that radiocarbon was present much deeper in the cores (down to 20 cm) than was expected from the 230Th/ 232Th distribution. In addition, both the stratigraphy and inventory of radiocarbon was significantly different between box cores. The distributions and inventories of 137Cs and 239.240Pu were similar to that found for radiocarbon, further illustrating the spatial variability of radionuclides in oligotrophic North Pacific red clays. These data suggest that bioturbational processes are important for transporting organic carbon down into the sediment column.
Highlights
Sedimentation rates determined using the 23°that included long-lived (Th)/232Th method were reported by Goldberg and Koide [1] for several locations in the Pacific
These data were corroborated by 239'24°pu measurements in box cores collected in the central North Pacific, which
It is of utmost importance that this variability be defined before a broad brush approach is used for predicting the fate of nuclear waste, fossil fuel CO 2 or other contaminants introduced to the oceans
Summary
Sedimentation rates determined using the 23°Th/232Th method were reported by Goldberg and Koide [1] for several locations in the Pacific. Williams et al [2] reported a study of cores from the North Pacific that included long-lived (Th) as well as short-lived (14C) radioisotopes and other chemical parameters (organic C, 239"24°pu, 813C). They observed that radiocarbon was present below the mixed layer and concluded that of the two feasible mechanisms, bioturbation was more important for pumping 14C down into the sediments than was diffusion. Hessler and Jumars [4] conducted an extensive study of the benthic macrofauna in the North Pacific One of these cores (BC-33) was studied by Williams et al [2] and the data are included in this report for comparison. Defined before a broad brush approach is used for predicting the fate of nuclear waste, fossil fuel CO 2 or other contaminants introduced to the oceans
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