Improvement of an analysis system of dissolved organic radiocarbon in seawater

Jeon, H.; Otosaka, Shigeyoshi  ; Watanabe, Takahiro   ; Aze, Takahiro*; Miyairi, Yosuke*; Yokoyama, Yusuke*; Ogawa, Hiroshi*

Measurements of the dissolved organic radio carbon (DOC-14) are expected to broaden our perspective on the role of DOC in the marine carbon cycle. Although the authors had succeeded in the DOC-14 analysis in seawater, it was necessary to use a large preprocessing apparatus, and the analysis has not been applied widely. We here report on the improvements to make this system safer and easier to handle. Following the previous method, DOC-14 in seawater was extracted as carbon dioxide by irradiating ultraviolet (UV), purified in a vacuum line, and the C-14 isotopic ratio was analysed with an accelerator mass spectrometer. As a major improvement, low-pressure mercury lamp which can irradiate UV of short wavelength (172 nm and 185 nm) suitable for decomposition of organic matter was used as UV source. By this improvement, the temperature increase in sample during processing was greatly reduced, and the size of the irradiation reactor was reduced to about half.