The Ocean Carbon Cycle Pull To Refresh
Ocean Carbon Cycle

The Ocean Carbon Cycle

By Rachel Jaeger

Carbon—a naturally occurring element found in all living organisms on earth—doesn’t like to stay in one spot. It exists in a global carbon cycle; constantly moving from one reservoir to another, staying in some places for a matter of days, and others for thousands of years or longer. After moving through the atmosphere, carbon naturally cycles into the ocean. While in the ocean, the carbon then rotates through its own little carbon cycle, which scientists often call the ocean carbon cycle.

The ocean is the largest reservoir for carbon, holding fifty times more carbon than the atmosphere. It takes so much carbon out of the atmosphere that it is often called a “carbon sink.” There are lots of carbon sinks–trees, rocks, and soil also hold carbon and store it away from the atmosphere. But the ocean is the largest carbon sink and can hold the most, making it one of our most valuable resources for carbon storage and climate regulation.

Understanding the Ocean Carbon Cycle

The surface waters of the ocean naturally exchange gases like carbon with the atmosphere. When that CO2 meets the surface of the ocean, it dissolves, and while some of it just stays as dissolved gas, phytoplankton—tiny, plant-like organisms that live in the ocean—turn the rest of it into organic matter. Other organisms in the ocean take the organic matter and incorporate it into themselves in some way, such as turning it into calcium carbonate and using it as a shell.

When the organisms die, some of the carbon is released back into the ocean, where it moves with the ocean currents and cycles back into the atmosphere at a different spot. The rest of it sinks and settles into the deep ocean, forming sediment that turns into rocks and locks the carbon away for millions of years.  

Carbon can also stay at the bottom of the ocean just by moving with the ocean currents. Cold water near the poles also sucks up carbon, and that cold water sinks to the bottom of the ocean, while the warmer water rises. The carbon in that cold water is stuck at the bottom of the ocean for as long as the cold water stays there, too. Eventually, it will rise in a different part of the ocean and cycle back into the atmosphere, but the temperature change takes hundreds of years.

Equilibrium Between The Ocean And The Atmosphere

As there is fifty times more carbon in the ocean than in the atmosphere, it may seem possible that carbon in the water would replace the sunken, locked carbon, rather than more CO2 from the air. The reason this doesn’t happen is that there is an equilibrium between the ocean and the atmosphere. The chemical forces are constantly looking for balance, so when the water doesn’t have enough carbon, the air will rebalance it. It is a 1:1 ratio—when one ton of CO2 is removed from the ocean, one ton of CO2 will also be removed from the atmosphere.

This equilibrium process can also depend on the choppiness of the water. Surface water pulls in carbon nearly instantaneously, as it is touching the air and can access it quickly. Water a little bit lower takes longer to pull it in—sometimes up to several months. Areas of the ocean where the water is choppier has a more reliable equilibrium process, as the wind stirs up waves and lets water farther down reach the surface and take in carbon immediately.

The Importance of the Ocean Carbon Cycle

In recent years, humans have swollen the amount of carbon in the atmosphere immensely. Factories and cars burn fossil fuels such as coal and oil, and those fuels emit carbon into the atmosphere. This carbon would have otherwise been stored in the geosphere–the area within the earth–so burning it into the atmosphere creates an imbalance. When there is too much carbon in the atmosphere in the form of the greenhouse gas CO2, it acts like a blanket and keeps all the warm air inside, which contributes to global warming.

The ocean holds a major key to slowing this change and reversing emissions to keep the carbon out of the atmosphere. The ocean carbon cycle acts as a natural negative emissions technology. Its biological pump keeps carbon locked in rocks, algae, other marine organisms, and silt at the bottom of the ocean. Since this storage can last between hundreds and millions of years it is one of our best carbon sequestration solutions at the current moment.

There is now so much CO2 in the atmosphere that the ocean is no longer able to store all of it. Scientists have found signs that the ocean is beginning to absorb CO2 at a slower pace than before, and the reaction of the CO2 with the surface ocean waters is creating carbonic acid that hurts ocean wildlife. Excess CO2 in the ocean is causing ocean acidification as well. The ocean may need some help to slow the rate of carbon admissions as much as possible.

Our Role in the Ocean Carbon Cycle

The ocean naturally takes in about half the carbon from the atmosphere. In order to slow down the climate change process, however, we can help the ocean to store even more carbon than it already does. One way to do this is just by learning more about it. Scientists are working towards developing technologies to help with ocean carbon storage, and one way they do this research is by collecting samples. They conduct studies based on the samples and analyze them for carbon content to learn more about how the ocean holds CO2 and how they can help it to hold more. NASA is currently using these techniques to identify specific carbon sinks within the ocean and learn how the environment is changing based on the data from those carbon sinks.

There are also ways for people to help with ocean carbon storage. One technology that Pull to Refresh is developing is seaweed sinking. Since seaweed is a living organism within the ocean’s ecosystem, it uses the carbon that the phytoplankton dissolve into the waters for its photosynthesis process. Our team at Pull to Refresh sends vessels out into the oceans to sink the carbon-filled seaweed to the bottom of the ocean, where the carbon will stay locked for more than 1000 years. We choose locations of our vessels based on the depth of the water to achieve the longest sequestration times. This is our way of helping to reverse CO2 emissions and slow climate change.

Hope for Our Future

While carbon emissions are still rising and threatening our planet, the ocean carbon cycle can give us hope for turning the tide. Since it can store so much carbon and it has such a great effect on carbon emissions, we should do our best to understand it.

One way that you can help support research and understanding of the ocean carbon cycle and reduce the carbon in the atmosphere is by buying Pull to Refresh’s seaweed sinking emission reversal! When you support this technology, you are helping develop a scalable solution to stop global warming. It benefits you by protecting our planet, and it is one step towards saving the wonderful world that we live in.

Educate yourself on how the ocean helps with carbon emission reversal and support ocean carbon removal technology so that together we can build a better world.


By Rachel Jaeger

Rachel is a third-year undergrad student at the University of Northwestern-St. Paul studying Professional Writing. She currently works as a Blog and Content Writing intern at Pull to Refresh, Inc.