Effects of Phytoplankton Community Composition and Productivity on Sea Surface pCO2 Variations in the Southern Ocean

Shintaro Takao1, Shin-ichiro Nakaoka1, Fuminori Hashihama2, Shimada Keishi2, Hisayuki Yoshikawa Inoue3, Toru Hirawake4, Jota Kanda2, Gen Hashida5 and Koji Suzuki3, (1)National Institute for Environmental Studies, Tsukuba, Japan, (2)Tokyo University of Marine Science and Technology, Minato-ku, Japan, (3)Hokkaido University, Faculty of Environmental Earth Science, Sapporo, Japan, (4)Hokkaido University, Faculty of Fisheries Sciences, Hakodate, Japan, (5)National Institute of Polar Research, Tachikawa, Japan
The Southern Ocean is a vast net sink for atmospheric carbon dioxide (CO2), with marine phytoplankton playing a crucial role in CO2 fixation. We assessed how changes in the dominant phytoplankton community and net primary productivity (NPP) affected variations in the partial pressure of CO2 (pCO2) in surface water in the Indian sector of the Southern Ocean during austral summer. Sea surface pCO2 was negatively correlated with total phytoplankton and diatom abundances, as estimated from pigment signatures, in the zone south of the Antarctic Circumpolar Current; however, Sea surface pCO2 was not correlated with haptophyte abundance. Additionally, a stronger correlation was found between Sea surface pCO2 and total phytoplankton NPP than between chlorophyll a concentration and Sea surface pCO2. These results suggest that phytoplankton abundance and productivity during the austral summer strongly affect Sea surface pCO2 variations, and that changes in the dominant phytoplankton community may control CO2 dynamics in the marginal ice zone of the Indian sector of the Southern Ocean.