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

• Published in: Deep-sea research. Part I, Oceanographic research papers Vol. 54; no. 10; pp. 1758 - 1772
• Main Authors: Okubo, Ayako, Obata, Hajime, Luo, Shangde, Gamo, Toshitaka, Yamamoto, Yoshiyuki, Minami, Hideki, Yamada, Masatoshi
• Format: Journal Article
• Language: English
• Published: Oxford Elsevier Ltd 01.10.2007; Elsevier
• Subjects: Animal and plant ecology; Animal, plant and microbial ecology; Biological and medical sciences; Earth sciences; Earth, ocean, space; Exact sciences and technology; External geophysics; Fundamental and applied biological sciences. Psychology; Geochemistry; Mineralogy; Physical and chemical properties of sea water; Physics of the oceans; Sea water ecosystems; Silicates; Synecology; Water geochemistry; particulate matters; Disphotic zone; Indian Ocean; Oceanographic survey; Particulate carbon; Biogeochemical cycle; biogeochemistry; Thorium 230; Ship observation; Suspended particle; Flux density; marine environment; Thorium 228; Mesopelagic zone; organic carbon; radioactive tracers
• ISSN: 0967-0637; 1879-0119
• DOI: 10.1016/j.dsr.2007.06.009

Total 230Th and 228Th vertical distributions were measured in the eastern Indian Ocean. Based on disequilibria of 234U– 230Th and 228Ra– 228Th, we estimated the particle flux from the surface to 950 m. The estimated particle flux ranged from 190±60 (150 m in the Southern Ocean) to 8.4±2.5 mg/m 2/day (950 m 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 234U– 230Th and 228Ra– 228Th disequilibria offer advantages over those from 228Ra– 228Th disequilibrium alone, in that they can account for some aspects of vertical mixing and thus are applicable to a wider range of oceanographic settings.