The vertical distribution of nitrite concentration and the result of 15N incubation experiment in the Southern Ocean. The data were obtained at sampling stations L1, L9, III-5 during the cruise of TR/V Umitaka-Maru in austral summer of 2008/2009. The seawater samples for nitrite were collected at 5-10 m depth intervals in the upper 350 m of the water column, and analyzed with an autoanalyzer. As ... for the 15N incubation experiment, seawater samples were collected at three depths around temperature minimum layer, where nitrite maximum appeared. The samples were enriched with 15N-NO3-, 15N-NH4+, 15N-NO2-, and incubated on board during 24 hours. After the incubation, the samples were filtered immediately. The total nitrogen and 15N content of filters and filtrates were analyzed by a mass spectrometer.