Home / SCUBA Knowledge / The Ocean as the Largest CO₂ Supplier – The Hidden Role of Oceans in Climate Change

The Ocean as the Largest CO₂ Supplier – The Hidden Role of Oceans in Climate Change

Introduction:

When we talk about carbon dioxide (CO₂) and climate change, most people think of emissions from industry, transportation, and energy production. However, one of the largest natural sources of CO₂ is not on land – but in the ocean. The oceans contain about 50 times more CO₂ than the atmosphere and play a crucial role in the global carbon cycle.

As divers, we experience the ocean not only as a fascinating habitat but also as a dynamic system that constantly interacts with the atmosphere. During our dives with Chang Diving Center on Koh Chang, we can see firsthand how the underwater world is changing – and why the ocean is more than just a CO₂ reservoir.

How Does the Ocean Store CO₂?

The oceans absorb CO₂ and store it through various mechanisms:

1. The Physical-Chemical Pump (Solubility Pump)

CO₂ is soluble in water and enters the ocean through physical processes:

• Temperature Dependence: Cold water can absorb much more CO₂ than warm water. This is why polar regions take up a significant amount of CO₂, while it escapes more in warmer areas.
• Wave Action: CO₂ dissolves in water through exchange at the surface. This happens constantly and in both directions – depending on the concentration difference between water and air.
• Currents and Deep Water: Once dissolved, CO₂ is transported into deeper layers by ocean currents. In the deep sea, it often remains stored for centuries.

2. The Biological Pump – Plankton as a CO₂ Sink

A large portion of CO₂ is bound biologically. Plankton and algae use CO₂ for photosynthesis, binding it in their biomass and releasing oxygen.

• Phytoplankton, algae, and seagrass use CO₂ for photosynthesis and produce oxygen. They remove carbon dioxide from the water, contributing to storage.
• When these organisms die, they sink into deeper water layers, taking the bound CO₂ with them. There, it is broken down by bacteria or stored in sediments long-term.
• Some carbon is bound in the skeletons and shells of mussels, corals, and other marine organisms as calcium carbonate (CaCO₃). These structures settle as sediments on the seabed over thousands of years.

3. The Carbonate Pump – The Chemical Reaction of CO₂ with Seawater

CO₂ reacts with water to form carbonic acid (H₂CO₃), which breaks down into bicarbonate and carbonate. These chemical reactions regulate the ocean’s pH balance.

Why Does the Ocean Release CO₂?

Despite the ocean’s immense storage capacity, it is not only a CO₂ sink but also a source. It releases significant amounts of carbon dioxide back into the atmosphere for several reasons:

• 1. Rising Water Temperature

Since warm water can hold less CO₂ than cold water, the ocean releases CO₂ as temperatures rise. This effect is intensified by global warming, meaning that a warming ocean emits even more CO₂ into the atmosphere, further driving climate change.

• 2. Upwelling Currents – The Hidden CO₂ from the Depths

In certain areas, deep water layers rise, bringing CO₂-rich water to the surface. This phenomenon is particularly pronounced in upwelling zones, such as off the coast of South America, where cold, nutrient-rich water from the deep reaches the surface and releases large amounts of CO₂.

• 3. Biological Decomposition Processes

When plankton and other marine organisms die and sink into deeper layers, their organic material is decomposed by microorganisms – releasing CO₂, which later returns to the surface through ocean currents.

• 4. Underwater Volcanoes and Hydrothermal Vents

Numerous volcanic sources on the seafloor continuously emit CO₂ into the water. In some regions (e.g., in the Pacific or Atlantic), this significantly contributes to the ocean’s CO₂ balance.

How Does CO₂ Affect Diving?

Changes in CO₂ levels in the ocean have significant impacts on the marine environment – and therefore on diving:

• Coral Bleaching and Ocean Acidification: Higher CO₂ concentrations lower the ocean’s pH, making it harder for corals, mussels, and snails to form calcium carbonate structures. Reefs die, and dive sites change drastically.
• Changes in Marine Biodiversity: Many fish species are sensitive to pH changes, leading to shifts in marine ecology. Some species could disappear from popular dive sites.
• Visibility: Changes in CO₂ levels can affect plankton growth, leading to more frequent algal blooms and reduced underwater visibility.

What Can We Do as Divers?

Although we cannot directly influence the global CO₂ cycle, there are things we can do as divers:

• Protect Reefs and Seagrass Beds: These natural carbon sinks are crucial for the climate system. Divers can help by practicing responsible diving (e.g., avoiding contact with corals) and supporting marine conservation projects.
• Raise Awareness: Many people do not know that the ocean is the largest CO₂ reservoir and also a major source. Education and awareness about this topic are essential.

Conclusion

The oceans are not only spectacular dive sites but also a crucial part of the global climate system. They store vast amounts of CO₂ but also release significant quantities – mainly due to warming, currents, and biological processes.

For us as divers, this means: Our underwater world is changing. Coral reefs are dying, fish populations are shifting, and water quality may decline. However, through informed choices and sustainable diving practices, we can help protect the oceans – so they remain not only CO₂ buffers but also thriving habitats for countless species.

Experience firsthand how fascinating and worth protecting the oceans are! Discover the underwater world of Koh Chang with Chang Diving Center – from vibrant coral reefs to mysterious shipwrecks.

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