Biogeochemical responses of the surface ocean and the lower atmosphere during the meso-scale iron enrichment experiments

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The Southern Ocean, the eastern equatorial Pacific and subarctic Pacific are recognized as HNLC (High Nutrient Low Chlorophyll) oceans, where depletion of iron is an limiting factor of primary production. Mesoscale iron-fertilization experiments have been conducted from 1993 to test the iron hypothesis and for future geoengineering as carbon sequestration. In the North Pacific, three experiments (SEEDS, SERIES and SEEDS II) have been carried out by A. Tsuda and his colleagues from 2001. This Grant-in-Aid supported the SEEDS II cruises, and detailed analysis and synthesis of other two experiments. Furthermore, preliminary bottle incubation experiments in which iron and phosphate were added, were carried out in the subtropical Pacific to test the feasibility of future mesoscale experiments. Data analysis and synthesis of these experiments have been done through a domestic workshop, domestic symposium, international workshop, international symposium, PICES-IFEP meeting and SOLAS-related m … More eetings. The main conclusion of our experiments is iron-fertilization to HNLC waters enhance the primary production but the magnitude of phytoplankton accumulation, the timing of the bloom and dominant phytoplankton species varies depending on the iron concentration, depth of surface mixed layer, zooplankton biomass and the season. More importantly, the efficiency of carbon sequestration by sinking of particulate matter was not high as what have been expected, because of respiration of microbial organisms. These results importantly affect on the formation of the international consensus that iron-fertilization is an immature technology as carbon sequestration. On the other hand, iron had almost no effect in the subtropical experiments, but these experiments contributed for the accumulation of the basic knowledge of the subtropical ecosystems and formed a groundwork of SOLAS-related project (Grant-in-Aid for Scientific Research on Priority Areas: Linkages in Biochemical Cycles between Surface Ocean and Lower Atmosphere). Less