The School of Oceanography's Curtis Deutsch.
The School of Oceanography’s Curtis Deutsch.

A University of Washington study published this week in the Proceedings of the National Academy of Sciences 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 planet has many carbon sinks, or routes that transfer heat-trapping carbon from the atmosphere into other parts of the Earth system. This sink is a literal one. Carbon-rich plankton detritus clumps together to form marine snow that drifts down through the water and provides food for deeper-dwelling organisms. The continual supply of organic carbon in particles from the surface to the deep sea is known as the “biological pump.”

This pump had been thought to operate at a 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. Just 5 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 co-author Curtis Deutsch, a UW associate professor of oceanography at the College of the Environment.

Read more at UW Today »