Ocean plankton is a massive brake on climate change but potentially not forever
Climate Change carbon sequestration Oceans

Ocean plankton is a massive brake on climate change but potentially not forever

Dr. Lindy Whitehouse
Dr. Lindy Whitehouse

In 10 seconds? Researchers predict that the amount of carbon stored by plankton in the ocean will increase over the coming century. However, this could stall and subsequently reverse by 2100 due to climate change, resulting in the release of carbon back into the atmosphere.

What is happening? The ocean is a carbon sink, storing some of the excess carbon dioxide (CO2) in the atmosphere and helping to mitigate climate change. Phytoplankton, the microscopic plants that are found floating in the ocean, are the main reason that the ocean is one of the biggest carbon sinks by taking up and storing carbon during photosynthesis. It is part of – what is often called – the “biological pump” or “marine carbon pump”. Using the latest climate models from the IPCC (Intergovernmental Panel on Climate Change), the researchers predict that phytoplankton will account for 5 to 17% of the increase in carbon uptake by the oceans by the end of the century.

Ok, so what exactly is this ‘biological pump?’ The biological pump or biological carbon pump is a process that enables the ocean to store excess CO2 from the atmosphere. It starts with phytoplankton taking up carbon as part of the processes involved in photosynthesis and storing it as organic matter. Phytoplankton is at the bottom of the food chain and is eaten by a range of animals found in the ocean. As a result, all living things found in our oceans consume CO2 either directly or indirectly, and when they die, they sink to the bottom of the ocean taking the carbon along with them. (Check out this digest about how much carbon whales take with them) This carbon is then stored at the bottom of the ocean for hundreds of years, reducing the CO2 found in our atmosphere.

The biological carbon pump is a complex system. Source: Wikipedia
The biological carbon pump is a complex system. Source: Wikipedia

How did the researchers discover this? The team used historical and future climate models from the Coupled Model Intercomparison Project Phase 6 (CMIP6) to provide an in-depth analysis of the biological carbon pump (BCP). The CMIP is a collaborative framework that was designed to bring experts together and help improve our knowledge of climate change. Models produced by this project help scientists understand how the climate has changed and how it may change in the future by simulating the physics, chemistry, and biology of the Earth in detail. The researchers used two future climate scenarios: mitigated carbon emissions Shared Socioeconomic Pathways (SSP) (SSP1-2.6) and continued emissions (SSP3-7.0) to quantify all processes involved in the BCP and found that while we can expect carbon storage to increase over the next century, we could see this reversing after 2100 with the oceans releasing carbon back into the atmosphere.

No way! Why would the oceans start releasing carbon? Well, when planktons die, they sink to 200 – 1,000 meters below the surface of the ocean, into an area known as the Twilight Zone. Here, several factors such as the temperature and oxygen concentration as well as whether they become food for other animals, determine how much of these dead plankton reach the ocean’s floor. As the oceans continue to warm, the process slows down, increasing the carbon-storing period. However, the Twilight Zone remains relatively understudied and there is little knowledge on how climate change could affect the processes that occur in this part of the ocean. In theory, the BCP could slow down enough to begin releasing CO2 into the air which could exacerbate climate change even further.

So, what do we need to do? The next step is to understand which processes in the Twilight Zone are the most important in ensuring that the carbon is stored and then use this information to update the climate models that assess changes in the ocean. The more information we have on the ocean process, the better we can predict future changes and look at ways to manage our oceans to help mitigate the impact of climate change.


The oceans contain 50 times more carbon than the atmosphere….

Over the last few decades, the oceans have slowed down climate change by absorbing approximately 30% of carbon emissions caused by humans …

… and are one of the sinks helping to keep the atmospheric CO2 roughly 200 parts per million (ppm) lower (approximately 400 ppm vs 600 ppm) than if natural carbon sinks did not exist.

As a result, it is essential to preserve the ocean carbon sink to help combat climate change. This will only be possible by protecting the oceans and the marine life within them.

Lindy has distilled 9 research papers, saving you 32 hours of reading time


The Science Integrity Check of this 3-min Science Digest was performed by Dr. ASM Mainul Hasan.



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