Seasonal and spatial variations in settling manganese fluxes in the Northern Arabian Sea |
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| Institution: | 1. Heilongjiang River Fishery Research Institute CAFS, Harbin 150070, China;2. Division of Avian Infectious Diseases, State Key Laboratory of Veterinary Biotechnology, Harbin Veterinary Research Institute, CAAS, Harbin 150001, China;3. Biopharmaceutical Laboratories, Northeast Agricultural University, Harbin 150030, China;4. Harbin Pharmaceutical Groups Bioengineering Co., Harbin 150025, China;5. College of Biological Science and Technology, HeiLongJiang BaYi Agricultural University, DaQing 163319, China |
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| Abstract: | Particulate manganese (Mn) fluxes measured with six time series sediment traps showed that the annual settling fluxes were 3–6 times higher in the west compared to those in the east and central Arabian Sea. Annual detrital Mn (Mndt) flux was nearly the same in the eastern and western Arabian Sea, but excess Mn (Mnex) fluxes were much higher (>4 times) in the western Arabian Sea. Atmospheric inputs cannot account for these high-Mn fluxes. Central and eastern Arabian Sea traps are overlain by a thick and intense denitrification layer, which may cause reductive dissolution of Mn oxides from settling particles and consequently low Mnex fluxes. As the exchange of intermediate waters between the Arabian Sea and the rest of the Indian Ocean is confined largely to the western Arabian Sea, relatively more oxic and dynamic conditions prevail in this region. Increased oxidizing conditions coupled with higher inputs of dissolved Mn through intermediate and surface advective processes might have led to in situ oxidation of Mn, thus resulting in higher vertical fluxes of Mnex. Mnex fluxes in traps at ～1000 m depth exhibited seasonal variability with a minimum during the winter monsoon (January–February) and maximum during the pre- and early- south-west monsoon (March–June). This variation is correlated with water mass movements and bacterial abundance observed during the Joint Global Ocean Flux Study (JGOFS). The possible involvement of bacteria and the microbial loop is suggested for the concentration and vertical transport of excess Mn. |
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