Chlorophyll a and macro-nutrient concentrations and photosynthetically active radiation during the training vessel Umitaka-maru cruise of the 59th Japanese Antarctic Research Expedition in January 2018

Chlorophyll a concentration is the most common indicator of phytoplankton biomass, fundamentally regulated by macro-nutrients and light intensity. Therefore, long term monitoring of these parameters gives us basic information on ecosystem changes with climate changes. As part of the monitoring programs of the Japanese Antarctic Research Expedition (JARE), chlorophyll a concentration and macro-nutrients (nitrate, nitrite, phosphate and silicic acid) have been measured on board icebreakers Fuji and Shirase since JARE-14 (1972/73 season) and JARE-7 (1965/66 season), respectively. The same monitoring has also been conducted during the cruise of the training vessel (T/V) Umitaka-maru, Tokyo University of Marine Science and Technology since JARE-55 (2013/14 season). The course of the Umitaka-maru is almost same every year; leave from Fremantle, goes down to ice edge (ca. 65S) along 110E meridian and back to Hobart, covering sub-tropical to polar waters in the Southern Ocean. During the cruise, water sampling from underway pump for chlorophyll a and macro-nutrient concentrations were obtained twice a day, and photosynthetically active radiation was continuously measured by a sensor mounted on the navigation bridge deck of the ship. The vertical water sampling for chlorophyll a concentration was conducted at 6 station along 110E meridian, although concentration of macro-nutrients at the same stations were determined by another monitoring program. This report is the latest data collected during the T/V Umitaka-maru cruise in 2017/18 season.