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). Umitaka-maru takes almost same course every year; after leaving Fremantle, goes down to sea ice edge (ca. 65°S) along 110°E meridian and then goes back to Hobart. The course thus covers sub-tropical to polar waters in the Southern Ocean. During the cruise, water samples for chlorophyll a and macro-nutrient concentrations were obtained from underway pump 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 stations along 110°E meridian, while 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 2018/19 season.
A Tue, study studied this question.