10. Investigating the Multiplicative Effects of Climate Change on Southern Ocean Phytoplankton

Sarah M. Andrew (1)*, Michael Ellwood (2), Philip Boyd (3)

1 Australian National University, Canberra, ACT, 2602, Australia
2 Australian National University, Canberra, ACT, 2602, Australia
3 University of Tasmania, Hobart, TAS, 7005, Australia

Model projections indicate that light, temperature, iron and pH/CO2 in the Southern Ocean are likely to change simultaneously in the future due to changing climate. The individual effects of these variables on phytoplankton productivity have been extensively researched, however the combined effect on Southern Ocean phytoplankton is uncertain. The physiological response of phytoplankton to individual variables may not predict the combined effect of climate change to their fitness, so this project utilized a multiplicative approach to explore metabolic responses and adaptation strategies of Southern Ocean phytoplankton (diatoms and the haptophyte P. antarctica) to climate change. Fe and light interactions were initially explored in P. antarctica and the two diatom species, Proboscia inermis and Eucampia antarctica and photophysiological measurements revealed key differences between these two taxonomic groups. This study is the first to identify a key process that allows diatoms to photosynthesise at a comparable rate to P. antarctica in spite of their physiological limitations. This project also focussed on increasing CO2 and temperature in addition to the Fe and light experimental incubations using P. antarctica. Addition of Fe in experimental cultures with increased CO2, temperature and light resulted in increased growth rates and colony abundance plus changes in a number of photophysiological characteristics. In contrast, it was found that Fe limitation caused a significant decline in growth and photosynthetic efficiency when combined with increased CO2, temperature and light. The investigation into the antagonistic and synergistic relationships that influence phytoplankton productivity concluded that unknown changes in Fe supply will be the main control on future productivity.