Basic research for the technological advancement of the determination of the oceanic CO_2 variability

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We have designed and built a new automated spectrophotometric system for precise total alkalinity analysis in seawater. We also made and improved software to properly control it. In June-July 2005, we participated in a cruise of JMA's R/V Ryofu-maru that sailed western North Pacific along, 165^ΩE between 50^ΩN and 28^ΩN across the transition zone between western sub arctic gyre and subtropical gyre, and collected seawater samples at 18 hydrographic stations from various depths down to 1000m. After the cruise we analyzed their total alkalinity and demonstrated that the new system is capable of high-precision analysis with the precision of ±2 μmol kg^<-1> (less than 1/1000). In addition, from the change in the property-property plots between total dissolved inorganic carbon (DIC) and alkalinity, we evaluated that DIC in the upper layer of this zone has increased about 15 μmol kg^<-1> during the last 13 years due to the uptake of the increasing atmospheric CO_2.We have also designed and built a system and a sampling bottle to analyze the back-ground-level hexafluorosulfide (SF_6) dissolved in seawater. We succeeded in lower the detection limit to 0.015 femto(10^<-15>)mol/kg after investigating the optimum conditions of detector-temperature, flow rate of carrier gas, and so on. We also prepared a standard gas for low level SF_6 in a finely ground 10L aluminum-alloy cylinder, and proved that its concentration is stable at least for 9 months after preparation. In the western North Pacific along 137^ΩE during the JMA's R/V Ryofu-maru cruise in October 2006, we collected seawater samples from various depths and succeeded in obtaining vertical profiles of SF_6 that showed a maximum concentration of 1.1 femtomol/kg in the subsurface layer.