[M-IS08] Global climate change driven by the Southern Ocean and the Antarctic Ice Sheet

[MIS08-11] Phytoplankton response to the Southern annular mode and El Niño-Southern Oscillation in the Southern Ocean

*Kohei Mizobata¹, Moe Fujita¹ (1.Tokyo University of Marine Science and Technology)

Keywords:Southern Ocean, Phytoplankton, Southern Annula mode, El Niño–Southern Oscillation

The mechanisms of variation in the abundance and distribution of phytoplankton in the Southern Ocean, which is considered a sink for anthropogenic CO₂, remain largely unknown. Spatiotemporal variations in phytoplankton distribution have so far been attributed to factors such as sea ice distribution at the local scale and surface mixed layer thickness at the ocean basin scale. Recently, the response of phytoplankton to the Southern Annular mode (SAM), a major climate driver, has been discussed, but it does not fully explain the phytoplankton variability in the Southern Ocean, including the Antarctic coastal region. On the other hand, it is known that oceanic environmental changes that significantly affect phytoplankton are not only caused by SAM but also by El Niño–Southern Oscillation (ENSO) events, whereas the response of phytoplankton to ENSO events has not been discussed. In this study, statistical analyses on satellite data and climate reanalysis data were conducted to investigate the response of phytoplankton to two major climate patterns. The results show that the spatio-temporal variability of phytoplankton distribution and abundance in the Southern Ocean can be explained by the SAM and ENSO indices. The results also suggest that the dominant factors of phytoplankton variability differ among the Atlantic, Pacific, and Indian Ocean sectors, even under the same climate pattern. Furthermore, in views of future global warming scenarios, it is expected that primary production will decrease in the Pacific and Indian Ocean sectors in the future, while it will increase in the Atlantic sector.