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.
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.