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^{− 2}Myr⁻¹ obtained using the integrated global production rate of ¹⁰Be and the deposition rate of ¹⁰Be onto the manganese crust.