In the coming century, experts at the National Oceanography Centre (NOC) and the University of Bristol expect that the quantity of carbon stored by tiny plankton will grow.
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New research estimates that the “Biological Pump”, a process wherein tiny plants, often known as phytoplankton, take up carbon and afterward die and sink into the deep ocean where carbon is deposited for hundreds of years, will account for 5% to 17% of the overall increase in carbon uptake by the oceans by 2100, based on the most recent IPCC models. Their research has been released in the journal Proceedings of the National Academy of Sciences.
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.
Dr Jamie Wilson, Study Lead Author, School of Earth Sciences, University of Bristol
During photosynthesis, plankton, microscopic organisms that live on the ocean’s surface where the light shines, utilize carbon dioxide.
When plankton dies, their remains quickly sink through the “Twilight Zone” of the ocean (200–1000 m), where ecological and environmental factors, such as temperature and oxygen concentration, and factors such as being eaten by other plankton, control how much attains the deep ocean, where the carbon from their bodies is stored from the atmosphere for hundreds to thousands of years.
Ocean warming slows the circulation, which prolongs the period during which carbon is deposited in the deep ocean.
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.
Dr Anna Katavouta, Study Contributing Author, Department of Earth, Ocean and Ecological Sciences, National Oceanography Centre, University of Liverpool
Dr. Katavouta worked together with early-career scientist Dr. Chelsey Baker, both from the National Oceanography Centre.
“We demonstrated that the organic matter flux at 1000 m 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,” Dr. Katavouta added.
The environmental and biological processes in the Twilight Zone are not, however, consistently modeled in the IPCC models. The amount of atmospheric carbon dioxide that the Biological Pump will store through the turn of the century is therefore subject to considerable uncertainty. According to theory, the Biological Pump’s capacity to store carbon beyond 2100 might halt and begin contributing carbon dioxide to the atmosphere, which would exacerbate climate change.
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.
Dr Jamie Wilson, Study Lead Author, School of Earth Sciences, University of Bristol
Dr. Wilson stated, “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 forecast future changes.
Journal Reference:
Wilson, J. D., et al. (2022) The biological carbon pump in CMIP6 models: 21st century trends and uncertainties. Proceedings of the National Academy of Sciences. doi.org/10.1073/pnas.2204369119.