IMAS researchers worried about phytoplankton and climate

PhD student Stacy Deppeler. Picture: Supplied
PhD student Stacy Deppeler. Picture: Supplied

Vital marine plants in the Southern Ocean, which play a key role in reducing atmospheric carbon, are in danger, according to new research.

Institute for Marine and Antarctic Studies PhD student Stacy Deppeler reviewed scientific research into the impact of climate change on single-celled plants at the base of the ocean food chain called phytoplankton. The research was done in collaboration with the Antarctic Climate and Ecosystems Cooperation Research Centre.

Researchers found a range of climate-induced stressors, including warming seas, increased ocean acidification, salinity reductions and sea ice, could potentially alter phytoplankton communities across the Southern Ocean.

The review revealed a clear trend of how the plants were affected, and said the changes were unlikely to become apparent until mid-century. By that time, the changes could be too far progressed to mitigate or reverse.

“While a fundamental part of the ecosystem is changing in ways that could have global implications, there’s uncertainty about exactly what the changes and their impact will be,” Ms Deppeler said.

“It’s unlikely that we’ll be able to identify clear trends until around 2050, by which time some big changes in phytoplankton communities will probably already have occurred, and it will to be too late to consider mitigating them.

Ms Deppeler said phytoplankton were important because all marine life in the Southern Ocean ultimately relied on them as a food source.

“They also draw down carbon as they photosynthesise, and capture it in the deep ocean when they sink to the seafloor.  The level of atmospheric carbon would be around 50 per cent higher without the uptake provided by Southern Ocean phytoplankton.

“Changes to phytoplankton communities therefore could have significant implications for our environment and climate.

The research showed an apparent trend towards smaller-celled phytoplankton, which could affect their nutritional value for predators and the amount of carbon captured by the carbon pump.

“Changes in the ability of phytoplankton to photosynthesise and grow, or changes in the structure of the phytoplankton community from large cells that contain a lot of carbon to smaller cells that don’t have so much, will affect the amount of carbon that sinks into the deep ocean.

“But understanding exactly what’s happening is difficult due to the complexity of the stressors affecting phytoplankton, the size and regional diversity of the Southern Ocean, and the logistical challenges of conducting research there.

“While the changes in phytoplankton might happen quite quickly they’ll take a very long time to reverse.

“Although it’s currently unknown whether the rate of environmental change will outpace the ability of Southern Ocean phytoplankton to adapt, it is inevitable that changes in the Southern Ocean will influence the food chain there, the ocean biogeochemistry and feedback on climate.”