210Pb and 137Cs in sediments from Sagami Bay, Japan: sedimentation rates and inventories

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公開日
2003-04
権利情報
  • https://www.elsevier.com/tdm/userlicense/1.0/
  • https://www.elsevier.com/legal/tdmrep-license
DOI
  • 10.1016/s0079-6611(03)00052-1
公開者
Elsevier BV

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Abstract Profiles of the radioisotopes 210 Pb and 137 Cs were determined in 15 sediment cores collected from Sagami Bay, Japan. The activities of 210 Pb ex (unsupported) in core top sediments increased with water depth from 25 dpm g −1 on the upper continental slope off the mouth of Tokyo Bay to an average of 283 dpm g −1 at the deep-sea station SB. The high 210 Pb trapping efficiency of settling particles expected from the results of the sediment trap experiment near the SB site suggests that effective 210 Pb enrichment in surface sediments may occur during resuspension and lateral transportation of particles via the benthic nepheloid layer on the continental slope. In several cores, 137 Cs profiles showed an increase, a distinct peak, and then a decrease to an undetectable level downcore. These profiles can be compared with the temporal change of bomb-produced 137 Cs fallout. The mean sedimentation rates estimated by the 210 Pb ex inventory method, rather than using 210 Pb ex profiles, ranged from 0.06 g cm −2 y −1 to 0.14 g cm −2 y −1 . The average value of the rates in SB cores was calculated to be 0.11 g cm −2 y −1 , which was similar to that calculated under the assumption that the age of the 137 Cs peak corresponds to its maximum fallout year in 1963. Although 137 Cs inventories represented one tenth of the anthropogenic fallout of 137 Cs until 1997, they correlated with the increase in 210 Pb ex inventory. This suggests that the scavenging of refractory 137 Cs as well as 210 Pb by settling particles in the water column can lead to the formation of a time marker layer even in deep-sea sediment core, such as at the SB site.

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