| Titre : |
238U, Th isotopes, 210Pb and 239 + 240pu in settling particles on the continental margin of the East China Sea : fluxes and particle transport processes |
| Type de document : |
texte imprimé |
| Auteurs : |
Yamada, Masatoshi, Auteur |
| Importance : |
pp. 1-12 |
| Langues : |
Anglais (eng) |
| Index. décimale : |
551 Géologie, météorologie, hydrologie générale |
| Résumé : |
Settling particles were collected from four locations on the continental margin- of the East China Sea using cylindrical and conical time-series traps. Total mass fluxes and activities of 2:?XU, 232Th, 230Th, 22KTh, 210Pb and 239f24nPu were determined for the particles to elucidate their transport processes on the margin. Surface sediment samples were also analyzed for 2JKU, 2~ 2Th,: l0Th, 21(IPb and W9 + 240Pu. The total mass fluxes from the cylindrical traps were significantly higher than those from the conical traps during nearly the same time interval. There was a tendency for 2l°Pb concentrations to increase almost linearly with depth from 72 m on the continental shelf edge to 1019 m in the Okinawa Trough; the apparent rate was 17.3 dpm/gper 100 m of the water column with the correlation coefficient of 0.93. In addition, there was a marked increase of 2l°Pb fluxes with depth, with an especially large increase near-bottom. The estimated scavenging effectiveness ranged from 99% to 85% for shelf edge and middle continental slope sites, respectively, indicating that 210Pb was effectively removed from the water column at each site. Both total mass fluxes and 21l)Pb fluxes varied on a very short time scale (- 112 day). The ratios of measured versus expected ~J°Th fluxes for sediment traps were 183 and 222 in the deeper traps. The ratio of the observed 2lt)Pb fluxes to the 2H1Pb deficiency fluxes in the near-bottom traps ranged between 8.9 and 46. These results suggest that the episodic lateral transport is a key process for particle transport on this continental margin. Concentrations of 238U, 232Th, 230Th, 22yTh, 2l°Pb and -39 + 240pu in the time-series traps at a middle continental slope site had little variations throughout the sampling period. In contrast, the radionuclide concentrations at an upper continental slope site varied inversely with the total mass fluxes. The radionuclide concentrations during high total mass flux events were close to those of the surface sediment. These results suggest that the high total mass flux events observed at an upper continental slope site are mainly due to resuspension of the underlying surface sediments. |
238U, Th isotopes, 210Pb and 239 + 240pu in settling particles on the continental margin of the East China Sea : fluxes and particle transport processes [texte imprimé] / Yamada, Masatoshi, Auteur . - [s.d.] . - pp. 1-12. Langues : Anglais ( eng)
| Index. décimale : |
551 Géologie, météorologie, hydrologie générale |
| Résumé : |
Settling particles were collected from four locations on the continental margin- of the East China Sea using cylindrical and conical time-series traps. Total mass fluxes and activities of 2:?XU, 232Th, 230Th, 22KTh, 210Pb and 239f24nPu were determined for the particles to elucidate their transport processes on the margin. Surface sediment samples were also analyzed for 2JKU, 2~ 2Th,: l0Th, 21(IPb and W9 + 240Pu. The total mass fluxes from the cylindrical traps were significantly higher than those from the conical traps during nearly the same time interval. There was a tendency for 2l°Pb concentrations to increase almost linearly with depth from 72 m on the continental shelf edge to 1019 m in the Okinawa Trough; the apparent rate was 17.3 dpm/gper 100 m of the water column with the correlation coefficient of 0.93. In addition, there was a marked increase of 2l°Pb fluxes with depth, with an especially large increase near-bottom. The estimated scavenging effectiveness ranged from 99% to 85% for shelf edge and middle continental slope sites, respectively, indicating that 210Pb was effectively removed from the water column at each site. Both total mass fluxes and 21l)Pb fluxes varied on a very short time scale (- 112 day). The ratios of measured versus expected ~J°Th fluxes for sediment traps were 183 and 222 in the deeper traps. The ratio of the observed 2lt)Pb fluxes to the 2H1Pb deficiency fluxes in the near-bottom traps ranged between 8.9 and 46. These results suggest that the episodic lateral transport is a key process for particle transport on this continental margin. Concentrations of 238U, 232Th, 230Th, 22yTh, 2l°Pb and -39 + 240pu in the time-series traps at a middle continental slope site had little variations throughout the sampling period. In contrast, the radionuclide concentrations at an upper continental slope site varied inversely with the total mass fluxes. The radionuclide concentrations during high total mass flux events were close to those of the surface sediment. These results suggest that the high total mass flux events observed at an upper continental slope site are mainly due to resuspension of the underlying surface sediments. |
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