About the same amount of atmospheric carbon that goes into creating plants on land goes into the bodies of tiny marine plants known as plankton. When these plants die and sink, bacteria feed on their sinking corpses and return their carbon to the seawater. When plankton sink deep enough before being eaten, the carbon can remain trapped in the deep ocean for centuries.
A new study by Moore Foundation grantee Curtis Deutsch, an investigator in the foundation's Marine Microbiology Initiative, uses a new approach to get a global picture of the fate of marine carbon. It finds that the polar seas export organic carbon to the deep sea, where it can no longer trap heat from the sun, about five times as efficiently as in other parts of the ocean.
The continual supply of organic carbon in particles from the surface to the deep sea is known as the “biological pump.” Results show that the transfer efficiency of organic carbon from the surface to the deep ocean ranges from just 5 percent in the subtropics to around 25 percent near the poles.
This pump had been thought to operate at similar strength throughout the oceans, but the new study finds a strong regional pattern. The authors find that about 25 percent of organic particles sinking from the surface in the polar oceans reach at least 1 kilometer (0.6 miles) — the depth required for long-term storage in deep waters or the seafloor.
For comparison, five percent of sinking carbon in the subtropics makes it that far, while the rest is released into shallower water where it can soon rejoin the atmosphere. The tropics have an intermediate value of about 15 percent.
“This highlights the importance of the polar ocean — the cold, high-latitude parts of the ocean — for their ability to store carbon over long time periods,” said Deutsch, an associate professor of oceanography at the University of Washington.
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