Chlorophyll a, macronutrient concentrations, and photosynthetically active radiation measured during the Umitaka-maru cruise of the 61st Japanese Antarctic Research Expedition, January 2020

The chlorophyll a concentration is the most commonly used indicator of phytoplankton biomass, which is regulated by macronutrients and light intensity. Long-term monitoring of chlorophyll a provides basic information on the ecosystem changes associated with climate change. As part of the monitoring program of the Japanese Antarctic Research Expedition (JARE), the chlorophyll a concentration and macronutrients (nitrate, nitrite, phosphate and silicic acid) have been measured by the icebreakers Fuji and Shirase since JARE-14 (1972/73) and JARE-7 (1965/66), respectively, and during the cruise of the training vessel (T/V) Umitaka-maru, of Tokyo University of Marine Science and Technology, since JARE-55 (2013/14). The Umitaka-maru follows almost the same course every year; after leaving Fremantle, it travels to the sea ice edge (ca. 65S) along the 110E meridian and then returns to Hobart. Its course covers waters in the Southern Ocean that range from sub-tropical to polar. During the cruise, water samples for determining chlorophyll a and macronutrient concentrations are obtained from an underway pump twice a day, and photosynthetically active radiation is measured continuously by a sensor mounted on the bridge of the ship. Vertical water sampling to determine the chlorophyll a concentration is conducted at six stations along the 110E meridian, and the macronutrient concentrations at the same stations are determined by another monitoring program. This report includes the latest data collected during the T/V Umitaka-maru cruise in the 2019/20 season. In 2019/20, three vertical sampling stations (KC7-9) were added to enhance the bottom water monitoring performed under the "Physical and Chemical Oceanography" routine observation program of the JARE.叶绿素a（chlorophyll a）浓度是最常用的浮游植物生物量指示指标，其水平受大量营养素（macronutrients）与光照强度的共同调控。对叶绿素a浓度的长期监测可为气候变化关联的生态系统演变研究提供基础数据。作为日本南极考察队（Japanese Antarctic Research Expedition, JARE）监测计划的组成部分，破冰船富士号（Fuji）与白濑号（Shirase）分别自第14次考察（JARE-14，1972/73年）、第7次考察（JARE-7，1965/66年）起，开展了叶绿素a浓度与大量营养素（硝酸盐、亚硝酸盐、磷酸盐及硅酸）的测定工作；自第55次考察（JARE-55，2013/14年）起，东京海洋大学的训练船海鹰丸（T/V Umitaka-maru）也加入了该监测体系。海鹰丸每年的航行航线基本固定：从弗里曼特尔（Fremantle）出发，沿东经110°子午线航行至海冰边缘（约南纬65°），随后返航霍巴特（Hobart）。其航线覆盖了南大洋从亚热带到极地的全梯度海域。航行期间，科研人员每日两次通过走航泵采集水样以测定叶绿素a与大量营养素浓度，并通过安装在船桥的传感器持续监测光合有效辐射（photosynthetically active radiation）。沿东经110°子午线共设置6个站位开展垂直取水样作业，以测定叶绿素a浓度；同期另有专项监测计划对这些站位的大量营养素浓度进行测定。本报告收录了2019/20航次海鹰丸采集的最新观测数据。在2019/20航次中，为强化日本南极考察队"物理和化学海洋学"常规观测计划下的底层水监测工作，新增了3个垂直取样站位（KC7-9）。