Earth's biological pump may ultimately turn into a source of carbon

Throughout the end of the century, microscopic plankton will be able to store an increasing amount of carbon. This will be achieved by a process called the “biological pump” in which microscopic plants take up carbon. When the plants die, they sink into the deep ocean- where the absorbed carbon is stored for hundreds of years. 

Researchers at the University of Bristol and the National Oceanography Centre (NOC) expect this process to account for 5 to 17 percent of the total increase in carbon uptake by the oceans by 2100. 

“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,” explained study lead author Dr. Jamie Wilson.

Microscopic organisms called plankton, live in the sun-lit surface of the ocean and use carbon dioxide during photosynthesis. When these plankton die, their remains rapidly sink down through the “Twilight Zone” of the ocean (200 – 1000m). The carbon from their bodies is then stored away from the atmosphere for hundreds to thousands of years. 

However, warming of the oceans slows down the circulation, increasing the time that carbon is stored in the deep ocean. This has led the research team to find a consistent increase in the carbon stored in the ocean by the biological carbon pump over the 21st century. 

The research team relied on the latest IPCC models (Intergovernmental Panel on Climate Change) to conduct the analysis. These models however do not have a consistent representation of the environmental and ecological processes in the Twilight Zone, creating uncertainty in how much carbon the biological pump will store. 

In theory, after 2100 carbon storage by the biological pump may start acting as a source of carbon dioxide to the atmosphere, which could exacerbate climate change further.

“This research demonstrates the crucial importance of the Twilight Zone region of the ocean for biologically-driven carbon storage in the ocean,” said Dr. 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.” 

By understanding how the Twilight Zone controls carbon storage, researchers could begin to figure out how to best avoid human impacts on the ocean. To achieve this, the research team will study processes in the Twilight Zone to understand those that are most important for biologically-driven carbon storage and updating ocean models so they can reliably predict future changes.

This research was published in the journal Proceedings of the National Academy of Sciences.

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By Katherine Bucko, Earth.com Staff Writer