Rising Temperatures Increase Carbon Stored in Microscopic Plankton

According to researchers at the National Oceanography Centre and the University of Bristol, the amount of carbon stored by microscopic plankton will rise in the next century.

Biological Pump

Using the most recent IPCC models, the team predicts that the "Biological Pump" will be responsible for five to 17 percent of the total increase in carbon uptake by the oceans by 2100. This process involves microscopic plants, commonly known as phytoplankton, absorbing carbon before dying and sinking into the deep ocean where carbon is stored for hundreds of years.

Dr. Jamie Wilson, the lead author of the study from the University of Bristol's School of Earth Sciences, explained that The amount of carbon dioxide that is currently in the atmosphere is roughly doubled by the biological pump and is kept in the deep ocean. The research team set out to understand how this would change in the future as a result of climate change by looking at the most recent future projections by IPCC models because plankton are sensitive to climate change and this carbon pool is likely to change in size.

Plankton, CO2, Ocean's Twilight Zone

Plankton, tiny organisms that live on the ocean's surface where the sun shines, use carbon dioxide during photosynthesis. When phytoplankton dies, they descend between 200 and 1000 meters (m) into the ocean through the "Twilight Zone" of the ocean. The amount of carbon that enters the deep ocean depends on ecological and environmental factors in this zone, including temperature, oxygen concentration, and being consumed by other plankton. For hundreds to thousands of years, the carbon from their bodies is kept out of the atmosphere. 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 Dr. Chelsey Baker, added that in the most recent IPCC model projections, their research discovered a consistent rise in the amount of carbon stored in the ocean by the biological carbon pump for the 21st century. Both Katavouta and Baker are from the National Oceanography Centre.

In contrast, the group 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 as previously thought.

They showed that a better indicator of long-term carbon sequestration linked to the biological carbon pump is the flux of organic matter at 1000 meters.

Read also: Newly Discovered Plankton Species May be an Overlooked Food Source in the Sea 

As a result, they will be better able to comprehend the mechanisms that govern the biological carbon pump and make more accurate projections about how much of the carbon released as a result of human activity will be sequestered in the ocean in the coming years.

The environmental and ecological processes in the Twilight Zone are not, however, consistently modeled in the IPCC models. Due to this, it is highly uncertain how much atmospheric carbon dioxide the Biological Pump will store after the turn of the century. The Biological Pump's capacity to store carbon dioxide after 2100 could theoretically plateau and begin acting as a source of carbon dioxide for the atmosphere, which would exacerbate climate change.

Wilson added that this study demonstrates the critical role of the ocean's Twilight Zone region in biologically-driven ocean carbon storage. This area of the ocean is still poorly understood because it is so difficult to observe, but it is also only recently beginning to feel the effects of fishing, deep-sea mining, and environmental change. 

Wilson added that by comprehending how the Twilight Zone regulates the amount of carbon that biology stores in the ocean, people can figure out how to mitigate the worst effects of activities like mining and fishing.

The team will now focus on identifying which Twilight Zone processes are most crucial for biologically-driven carbon storage and updating ocean models to accurately predict future changes, Science Daily reports.

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