Design concept and experiment of ocean nutrient enhancer "TAKUMI"

To increase a primary production in the sea, upwelling and discharging a Deep Ocean Water (DOW) which has very rich nutrient salts into the euphotic surface layer has been proposed by many oceanologists as a "fishing ground of artificial DOW upwelling". But, so far, there are no successful means to make it, because of the problems of the large amount of upwelling DOW, the dilution of nutrient salts in the sea, enduring the rough sea condition, the strength of very long riser pipe for upwelling, etc. The design concept of ocean nutrient enhancer TAKUMI, featuring the density current for avoiding the dilution of nutrient salts, the spar type submersible floating structure for withstanding the rough sea condition, and the design and analysis of riser pipe for not only in case of rough sea but also in case of the upending which is world first challenge of election of steel riser pipe with gravity fall in the subsea, is introduced. Also, about one year continuous running operation of TAKUMI and the investigation results of the water mass discharged from TAKUMI are reported.