Microscopic plankton will store more carbon dioxide in the coming century, according to scientists at the University of Bristol and the Southampton-based National Oceanography Centre (NOC). The research used the most recent Intergovernmental Panel on Climate Change (IPCC) models to predict that the “Biological Pump” – a process where phytoplankton absorb CO2 and then die and sink to the ocean to store CO2 for centuries – will take up 5 to 17% of the total CO2 ocean uptake increase by 2100.
Plankton, which are microorganisms living in the ocean’s sun-lit surface, use CO2 as part of their photosynthesis process. When plankton die, they sink to the ocean’s Twilight Zone (200-1,000 meters below the ocean surface). Then various ecological and environmental factors – like being eaten by other plankton, as well as temperature and oxygen concentration – determine how much of the plankton reaches the deep ocean where CO2 can be stored away from the atmosphere for centuries, or even millenniums. As oceans warm up, the process slows down and the CO2 storing period gets longer.
The IPCC models, however, do not offer consistent representation of Twilight Zone’s environmental and ecological processes. It is not certain how much CO2 the Biological Pump will store after 2100. Theoretically, the Biological Pump could slow down and begin releasing CO2 into ambient air, thus speeding up climate change even more.
“This research demonstrates the crucial importance of the Twilight Zone region of the ocean for biologically-driven carbon storage in the ocean,” said lead author Dr. Jamie Wilson. “This part of the ocean is still poorly understood because it is so hard to observe but it is also just now starting to come under pressures of environmental change, fishing, and deep-sea mining. Understanding how the Twilight Zone controls how much carbon is stored by biology in the ocean means we can figure out how to avoid the worst impacts from human practices like fishing and mining.”
The team behind the PNAS journal research is now trying to understand which Twilight Zone processes play the key role in biologically-driven CO2 storage and is updating ocean models to offer more reliable predictions.