Results From Real Sea Experiment of Ocean Nutrient Enhancer TAKUMI

Abstract

Upwelling and scattering Deep Ocean Water (DOW) into the euphotic surface layer has been proposed by many oceanographers as a “fishing ground of artificial upwelling”. So far, however, there are no successful means to make it, because of the following difficulties; the very huge amount of DOW upwelling, the dilution of DOW’s nutrient salts in the sea, enduring the rough sea condition on offshore, the strength of very long riser pipe for upwelling, etc. The MARINO-FORUM 21, sponsored by Japanese government fisheries agency, organized the research and development project of an ocean nutrient enhancer named TAKUMI and real sea experiment using it, since the year of 2000. New technology concept, featuring the density current generator for avoiding dilution of nutrient salts, the spar type submersible floating structure for withstanding against the rough sea condition, and the design and analysis of riser pipe for not only in case of the 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 sub-sea, was studied and introduced for the design of TAKUMI as a proper Ocean Nutrient Enhancer. TAKUMI that upwells DOW of 100,000m3/day from 200m depth and discharges it into the euphotic layer with Diesel engine was manufactured and set-up at the center of Sagami Bay in Japan, in May 2003. More than five years continuous operation in various sea conditions, which includes very rough sea in typhoon and rapid current, caused by direction change of Kuroshio Current was carried out. Also, the behavior of the nutrient water mass and the pattern of primary production around TAKUMI was investigated using the research vessel Tansei Maru. The results from the real sea experiment lead us to believe that the TAKUMI type artificial DOW upwelling system can be feasible to increase a primary production and make a fishing ground in case of large size system of more than 1,000,000m3/day.