Particle flux in the twilight zone of the eastern Indian Ocean: A constraint from U-234-Th-230 and Ra-228-Th-228 disequilibria

• Published in: Deep Sea Research Part I: Oceanographic Research Papers
• Main Authors: Okubo, Ayako, Obata, Hajime, Luo, Shangde, Gamo, Toshitaka, Yamamoto, Yoshiyuki, Minami, Hideki, Yamada, Masatoshi
• Other Authors: Department of Earth Sciences
• Format: Article in Journal/Newspaper
• Language: English
• Published: Elsevier 2007
• Subjects: Southern Ocean; Indian
• Online Access: https://doi.org/10.1016/j.dsr.2007.06.009; http://ir.lib.ncku.edu.tw/handle/987654321/60266

Total Th-230 and Th-228 vertical distributions were measured in the eastern Indian Ocean. Based on disequilibria of U-234- Th-230 and Ra-228- Th-228, we estimated the particle flux from the surface to 950m. The estimated particle flux ranged from 190 +/- 60 (150m in the Southern Ocean) to 8.4 +/- 2.5mg/m(2)/day (950m in the West Australian Basin). The particle fluxes correlate well with estimates of nitrate supply by vertical mixing to the euphotic zone, suggesting local control by new production. Flux attenuation at mesopelagic depths appears to be related to biogenic carbonate and silica remineralization based on comparison to alkalinity and dissolved silicate distributions, with possible additional control by lithogenic particle inputs. The particle flux estimates obtained by combining the U-234- Th-230 and Ra-228- Th-228 disequilibria offer advantages over those from Ra-228- Th-228 disequilibrium alone, in that they can account for some aspects of vertical mixina and thus are applicable to a wider range of oceanographic settings.