The Ocean: Climate Control

The ocean acts as a global climate control system: it regulates the concentration of CO₂ in the atmosphere by absorbing, storing and releasing the greenhouse gas in a variety of ways and places, thereby affecting Earth's climate. In fact, the ocean is an enormous storehouse for carbon, containing 50 times more than the atmosphere. But it takes time for carbon, in the form of CO₂, to make its way into the deep ocean: so far the ocean has taken up about 30 percent of all CO₂ emissions from human activities in the past 200 years, but eventually it will absorb much more.

How the ocean acts as a global climate control system is illustrated in an exhibition graphic.
AMNH Exhibition Department

Removal by Photosynthesis

Just like trees on land, countless microscopic plants called phytoplankton absorb CO₂ as they grow near the ocean surface.

Larger organisms snack on phytoplankton, and their waste eventually falls to the deep ocean, where it decomposes, releasing CO₂ into the cold water of the deep. There it may stay for thousands of years.

Removal by Shells

Many ocean animals, from phytoplankton to more familiar snails, build shells, which takes up CO₂.

When the animals die, their shells sink to the deep ocean, where they become part of the sediment, effectively removing CO₂ from the ocean.

Alternatively, in areas of very deep ocean, the shells dissolve before reaching the bottom, releasing CO₂ to the deep water.

It may seem counterintuitive, but the formation of shells also releases CO₂.

Thus, in areas where shelled organisms form, CO₂ is actually pumped from the ocean into the atmosphere.

Removal by Water

As surface waters cool and sink far from the equator, they absorb CO₂ from the atmosphere and transport it to the deep ocean.

This CO₂-rich water may take centuries to millennia to return to the surface.