In the coming century, experts at the National Oceanography Centre (NOC) and the University of Bristol expect that the quantity of carbon stored by microscopic plankton will grow.
By 2100, the team projects that the “Biological Pump,” a process in which microscopic plants, commonly known as phytoplankton, absorb carbon before dying and sinking into the deep ocean where carbon is stored for hundreds of years, will be responsible for five to 17 percent of the total increase in carbon uptake by the oceans.
Their findings were published today in the journal PNAS (Proceedings of the National Academy of Sciences). Lead author, Dr. Jamie Wilson, of the University of Bristol’s School of Earth Sciences, explained:
“The Biological Pump stores roughly double the amount of carbon dioxide that is currently in our atmosphere in the deep ocean. Because plankton are sensitive to climate change, this carbon pool is likely to change in size so we set out to understand how this would change in the future in response to climate change by looking at the latest future projections by IPCC models.”
Plankton, tiny organisms that live on the ocean’s surface where the sun shines, consume carbon dioxide during photosynthesis. When these plankton die, their remains quickly sink through the “Twilight Zone” of the ocean (200-1000m), where ecological and environmental factors, including temperature and oxygen concentration, and factors such as being eaten by other plankton, control how much reaches the deep ocean, where the carbon from their bodies is stored away from the atmosphere for hundreds to thousands of years.
This research demonstrates the crucial importance of the Twilight Zone region of the ocean for biologically-driven carbon storage in the ocean. 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.
Dr. Jamie Wilson
Ocean warming slows the circulation, extending the amount of time that carbon is held in the deep ocean. Contributing author Dr. Anna Katavouta, who worked alongside early-career scientist Dr. Chelsey Baker, both from the National Oceanography Centre, added:
“Our research found a consistent increase in the carbon stored in the ocean by the biological carbon pump over the 21st century in the latest IPCC model projections. In contrast, we found a decline in the global export production (the amount of organic matter, such as dead plankton, sinking below the ocean surface) which suggests that export production may not be as accurate a metric for the biological carbon pump than previously thought.”
“We demonstrated that the organic matter flux at 1000 meters is instead a better predictor of long-term carbon sequestration associated with the biological carbon pump. This outcome will help us to better understand the processes that control the biological carbon pump and to predict more reliably how much of the carbon released due to human activity will be stored in the ocean in the future.”
The environmental and ecological processes in the Twilight Zone are not, however, consistently modeled in the IPCC models. Due to this, it is highly unknown how much atmospheric carbon dioxide the Biological Pump will retain beyond the turn of the century.
The Biological Pump’s capacity to store carbon dioxide after 2100 might theoretically plateau and begin serving as a source of carbon dioxide for the atmosphere, which would worsen climate change.
Dr. Wilson added: “This research demonstrates the crucial importance of the Twilight Zone region of the ocean for biologically-driven carbon storage in the ocean. 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 researchers will now focus on identifying which Twilight Zone activities are most crucial for biologically-driven carbon storage and upgrading ocean models to accurately predict future changes.
