Coccolithophores: Tiny Phytoplankton Help Store Carbon in the Ocean

This is a story of tiny plated phytoplankton with a tongue-twister-like name: coccolithophores. These little plants are made out of a single cell that’s plated with limestone. They may be small, but they’re numerous, and they play a critical role in the global carbon cycle.

Increasing amounts of atmospheric carbon are cause for concern on many levels. A changing climate changes weather patterns. It changes growing conditions and creates environmental conditions that are ripe for unprecedented natural disasters, such as storms and forest fires.

We need to address this carbon overdose in the atmosphere, but how?

Carbon Sinks Regulate the Carbon in the Atmosphere

One way to regulate the amount of atmospheric carbon is to find places to put the excess carbon. These are called carbon sinks. The earth naturally has a number of carbon sinks; rocks contain carbon, so do plants. Plants are an essential part of the global carbon cycle. As they make food through photosynthesis, they take in carbon dioxide and send out oxygen.

Coccolithophores Move Carbon to the Deep Ocean

While plants play a critical role in carbon sequestration, there’s an even better place to keep that atmospheric carbon, and that’s in the deep ocean. Humans are land-dwellers, so we think about trees more often than we think about oceanic phytoplankton. However, through photosynthesis, those little organisms are also creating sugars and storing them inside, and the deep ocean is a huge natural sink for carbon.

Coccolithophores are numerous, and they also create a hard outer covering – this is critical to their role in global carbon sequestration.

The coccolithophores’ outer covering is called the coccolith. It’s made out of calcium carbonate, and the process of making it takes in a small amount of carbon. However, the most important attribute of the covering is its weight, since this helps the shell sink when the coccolithophore’s life cycle is over.

In the sunlit top layer of the ocean, there’s a lot going on. Some of the phytoplankton in this environment create long, sticky threads called transparent exopolymers. These sticky threads connect up with animal and plant life in the top layer of the ocean, forming large globs that are sometimes called marine snow.

The relatively heavy, shell-like structures of the coccolithophores help make these sticky globs heavy, and over time, the marine snow begins to drift from that top layer of the ocean down into the deep ocean. When these particles reach the deep ocean, they tend to stay there for a while, and the carbon that they contain stays there as well.

Changes in temperature and salinity drive the circulation of the deep ocean, and these changes take a long time. For thousands of years, these bits of carbon sit deep in the ocean.

Could Changes to the World’s Oceans Impact Coccolithophores?

This process of deep ocean carbon storage is one that the earth has been doing for thousands of years. In a changing climate, will this process continue to work? While it’s unlikely that climate change will alter the circulation patterns of the deep ocean, it could change something very important: the coccolithophores’ shells. Changes in these shells could change whether or not these tiny organisms float in the top layer of the water or sink into the deep ocean, where their carbon is stored. Ocean researchers are studying potential impacts of ocean acidification, nutrients, and temperature changes to see what impact these might have on the tiny organisms that play a vital role in regulating our global climate.

Resources

Ina Benner, et all. Emiliania huxleyi increases calcification but not expression of calcification-related genes in long-term exposure to elevated temperature and pCO₂. (2013). Philosophical Transactions of the Royal Society. Accessed September 3, 2013.

Fisheries and Oceans Canada. Ocean Acidification. (2013). Accessed September 3, 2013.

NASA. What is a Coccolithophore? Accessed September 3, 2013.

US Environmental Protection Agency. Future Climate Change. (2013). Accessed September 3, 2013.