Plankton will store more carbon as Earth’s climate warms

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The amount of carbon stored by microscopic plankton will increase over the next century, predict researchers from the University of Bristol and the National Oceanography Center (NOC).

Using the latest models from the IPCC (Intergovernmental Panel on Climate Change), the team expects the “Biological Pump” – a process where microscopic plants, often called phytoplankton, absorb carbon, then die and sink into the deep ocean where the carbon is stored for hundreds of years – to account for 5-17% of the total increase in carbon uptake by the oceans by 2100. Their findings have been published in the magazine PNAS (Proceedings of the National Academy of Sciences).

Lead author Dr Jamie Wilson, from the School of Earth Sciences at the University of Bristol, explained: The biological pump stores about twice the amount of carbon dioxide that is currently in our atmosphere in the ocean depths. Because plankton are sensitive to climate change, this carbon pool is likely to change in size, so we sought to understand how this would change in the future in response to climate change by looking at the latest future projections from IPCC models.

Microscopic organisms living on the sunlit surface of the ocean, called plankton, use carbon dioxide during photosynthesis. When these planktons die, their remains rapidly sink through the “twilight zone” of the ocean (200 to 1,000 m) where environmental factors, such as temperature and oxygen concentration, and ecological factors, such as being eaten by other plankton, control how much of it reaches the deep ocean where their body carbon is stored away from the atmosphere for hundreds to thousands of years. Warming oceans slow circulation, increasing the time carbon is stored in the deep ocean.

Contributing author Dr Anna Katavouta, who worked alongside early-career scientist Dr Chelsey Baker, both from the National Center for Oceanography, added: “Our research has revealed a steady increase in stored carbon in the ocean by the biological carbon pump over the 21st century in the latest IPCC model projections. In contrast, we have seen a decline in global export production (the amount of organic matter, such as dead plankton, sinking beneath the ocean surface), suggesting that export production is not perhaps not as accurate a measurement for the biological carbon pump as before. thought. We demonstrated that the flux of organic matter at 1,000 meters is instead a better predictor of the long-term carbon sequestration associated with the biological carbon pump. This result will help us better understand the processes that control the biological carbon pump and more reliably predict the amount of carbon released due to human activity that will be stored in the ocean in the future.

However, IPCC models do not have a consistent representation of environmental and ecological processes in the twilight zone. This leads to great uncertainty about how much carbon dioxide from the atmosphere the biological pump will store beyond the end of the century. In theory, after 2100 the storage of carbon by the biological pump could stop and start acting as a source of carbon dioxide in the atmosphere, which could further aggravate climate change.

Wilson added: This research demonstrates the crucial importance of the twilight zone region of the ocean for the biological storage of carbon in the ocean. This part of the ocean is still poorly understood because it is so difficult to observe, but it is just beginning to experience pressure from environmental change, deep-sea fishing and mining. Understanding how the twilight zone controls the amount of carbon stored by biology in the ocean means we can understand how to avoid the worst impacts of human practices like fishing and mining.

The team will now work to determine which processes in the twilight zone are most important for biological carbon storage and update ocean models so they can reliably predict future changes.

– This press release was originally published on the University of Bristol website

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