Incorporation rate measurements of 10Be, 230Th, 231Pa, and 239,240Pu radionuclides in manganese crust in the Pacific Ocean: A search for extraterrestrial material
In order to estimate the deposition rate of extraterrestrial material onto a manganese crust in a search for supernova debris, we analyzed the contents of 10Be, 230Th, 231Pa, and 239,240Pu in a sample of manganese crust collected from the North Pacific Ocean. On the basis of the depth profile of 10Be, the growth rate of the manganese crust was determined to be 2.3 mm Myr−1. The uptake rates of 10Be, 230Th, and 231Pa onto the manganese crust were estimated to be 0.22–0.44%, 0.11–0.73%, and 1.4–4.5%, respectively, as compared to the deposition rates onto the deep-sea sediments near the sampling station, while that for 239,240Pu was 0.14% as compared to the total inventory of seawater and sediment column. Assuming that sinking particles represent 0.11–4.5% of the uptake rates, the deposition rate of extraterrestrial material onto the manganese crust was estimated to be 2–800 µg cm−2Myr−1 according to the uptake of 10Be onto the manganese crust. Further, our estimate is similar to the value of 9–90 µg cm− 2Myr−1 obtained using the integrated global production rate of 10Be and the deposition rate of 10Be onto the manganese crust.
KeywordsManganese crust natural and artificial radionuclides depth profile deposition rate uptake rate
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