Japan Geoscience Union Meeting 2018

Presentation information

[EJ] Poster

M (Multidisciplinary and Interdisciplinary) » M-IS Intersection

[M-IS06] Global climate change driven by the Southern Ocean and the Antarctic Ice Sheet

Mon. May 21, 2018 1:45 PM - 3:15 PM Poster Hall (International Exhibition Hall7, Makuhari Messe)

convener:Osamu Seki(Institute of Low Temperature Science, Hokkaido University), Akira Oka(Atmosphere and Ocean Research Institute, The University of Tokyo), Ryosuke Makabe(国立極地研究所, 共同), Ryu Uemura(University of the Ryukyus)

[MIS06-P06] Long-term variation of phytoplankton chlorophyll a in the Indian sector of the Southern Ocean

*Shintaro Takao1,2, Ryosuke Makabe1,2, Kohei Mizobata3, Masato Moteki1,3, Tsuneo Odate1,2 (1.National Institute of Polar Research, 2.The Graduate University for Advanced Studies (SOKENDAI), 3.Tokyo University of Marine Science and Technology (TUMSAT))

Keywords:Climate change, Southern Ocean, Phytoplankton

Long-term monitoring of phytoplankton biomass is valuable to detect climate change impact on surface ecosystems in the Southern Ocean. Chlorophyll a (chl-a) observations by Japanese Antarctic Research Expedition (JARE) started in the 1965/1966 during austral summer and continued for over 50 years in the Indian sector of the Southern Ocean. We analyzed long-term chl-a dataset along 110° E in December and January to investigate inter-annual and decadal variations of phytoplankton biomass. In the region between 40°-60°S, chl-a values exceeded 0.5 mg m−3 were detected after the 1990s more frequently than before the 1980s. The similar long-term trend was also found in vertically integrated chl-a values. There was an increasing trend in the ten-year moving average of the mean surface chl-a value in the waters between 45°-55°S over the past 50 years. Moreover, this increasing trend in chl-a was correlated with the Southern Annular Mode (SAM) index positively. The positive correlation between trends of chl-a and the SAM index could be associated with enhanced westerly winds, which can lead to the supply of cold, iron-rich waters by upwelling (e.g., Lovenduski and Gruber, 2005). Recent observation along 110° E by Umitaka-maru (TUMSAT) and satellite remote sensing dataset revealed that inter-annual variation of surface chl-a in seasonal sea ice zone in January, although relationships among chl-a, sea ice, and climate index such as the SAM are still obscure.