for National Geographic News
Virtually all life in the world's oceans is directly or indirectly dependent on one-celled plants called phytoplankton. These plants, which live at the ocean surface, feed on ocean nutrients to survive.
But about 20 to 30 percent of these crucial nutrients sink out of reach of the phytoplankton each year, according to Jorge Sarmiento, a professor of atmospheric and ocean sciences at Princeton University in New Jersey.
Through his research, Sarmiento is trying to tease out the details of how the ocean supplies the nutrients that phytoplankton need to survive and, in turn, support everything else that makes a living in or off the ocean.
Sarmiento equates the sinking nutrients in the ocean to leaves falling off trees. Bacteria break down the organic matter of fallen leaves, releasing their nutrients for reuse by plants in the future.
"The big difference in the ocean is that much of the organic matter sinks out of reach of the surface ocean, where there is enough light for photosynthesis," Sarmiento said. "Thus when bacteria break this organic matter down back into dissolved nutrients, the phytoplankton cannot get at the nutrients."
Ken Buesseler is a marine chemist at the Woods Hole Oceanographic Institution in Massachusetts who studies the flow of sinking particles. Buesseler notes that once particles like nutrients sink to the deep ocean, they remain isolated for hundreds to thousands of years.
"Ocean currents determine the mixing rates and how long certain deep waters remain isolated," Buesseler said.
According to Sarmiento's research, ocean currents eventually transport a large fraction of these deep-water nutrients to ocean around Antarctica. There, the nutrients return to the surface and are redistributed throughout the world's oceans.
Buesseler recently applied his study of the nutrient flow to the so-called iron hypothesis. Some scientists argue that by adding iron to areas of the ocean that are iron deficient, populations of iron-starved phytoplankton would blossom.
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