The Carbon Cycle
How do phytoplankton control carbon?
How do the ocean and atmosphere interact?
Make a Greenhouse
The first plants on earth, the algae, developed in the sea 3,500
million years ago. Algae, like other plants, give off oxygen as they produce
food. In time, these algae have produced enough oxygen to provide an atmosphere
in which animals could survive. Today, algae produce over half of the oxygen
that we breathe.
Photosynthesis is not the only way new food is produced in the ocean. Bacteria
living near hydrothermal vents in the deep ocean and oil and gas seeps along the
continental margins in the deep can fix carbon from carbon dioxide into
nutritious molecules using the chemical energy in hydrogen sulfide or methane.
How do phytoplankton control the carbon cycle?
Besides acting as the first link in the food chain, phytoplankton are a very
important part of ocean life. The carbon dioxide in the atmosphere is in
balance with carbon dioxide in the ocean. During photosynthesis, phytoplankton
remove carbon dioxide from sea water and release oxygen as a by-product. This
allows the oceans to absorb additional carbon dioxide from the atmosphere. If
fewer phytoplankton existed, atmospheric carbon dioxide would increase.
Phytoplankton also affect carbon dioxide levels when they die. Phytoplankton,
like plants on land, are composed of substances that contain carbon. Dead
phytoplankton can sink to the ocean floor. The carbon in the phytoplankton is
soon covered by other material sinking to the ocean bottom. ln this way, the
oceans act as a sink, a place to dispose of global carbon, which otherwise would
accumulate in the atmosphere as carbon dioxide. Other global sinks include land
vegetation and soil. However the carbon in these sinks frequently is returned to
the atmosphere as carbon dioxide by burning or decomposition. Deforestation
contributes to the accumulation of carbon dioxide in the atmosphere by reducing
vegetation that takes up carbon dioxide. Carbon dioxide acts as a "greenhouse"
gas in the atmosphere, and therefore may contribute to global warming. Sources
of carbon dioxide in the Earth's atmosphere include decomposition of organic
matter (such as trees), the carbon dioxide that animals and people exhale,
volcanic activity, and human activities such as the burning of fossil fuels and
No one yet knows how much carbon the oceans and land can absorb. Nor do we
know how the Earth's environment will adjust to increasing amounts of carbon
dioxide in the atmosphere. Studying the distribution and changes in global
phytoplankton using ocean color and other tools will help scientists find
answers to these questions.