Like a sponge, the Earth's oceans store the greenhouse gas, carbon dioxide--but certain coastal waters can't perform this trick because they lack iron, a University of Delaware researcher reports in the June 11 issue of the journal Nature.
Just as iron-rich foods help children grow stronger, iron in the ocean gives a boost to microscopic plants called phytoplankton. Without enough iron, phytoplankton can't use the sun's energy to draw carbon dioxide from the air, says David A. Hutchins, an assistant professor in UD's College of Marine Studies and lead author of the Nature paper.
For a decade, scientists have known that three remote, open-ocean areas--the equatorial Pacific, the subarctic Pacific offshore from Alaska and the Southern Ocean around Antarctica--don't contain enough iron to support phytoplankton growth. Inadequate iron in these areas stunts the marine food chain, from bacteria to whales, and so, these waters can't store their full share of atmospheric carbon dioxide. Researchers have long believed, however, that coastal waters contain abundant iron, provided by nearby continental dust and sediments. Consequently, researchers have assumed that coastal areas support healthy food chains and act as effective carbon 'sponges.'
In fact, Hutchins and his coauthor, Kenneth W. Bruland of the University of California at Santa Cruz, discovered that a lack of iron limits phytoplankton growth in waters along one of the nation's best-known shorelines: just off the scenic cliffs of Big Sur in the Monterey Bay National Marine Sanctuary. These central California waters are rich in plant 'fertilizers' such as nitrate, silicate and phosphate, but they don't contain enough iron to help phytoplankton use nutrients through photosynthesis, Hutchins says.
"The role of the oceans in global climate change is still controversial and not
yet fully understood, but biological uptake of carbon dioxide by the coastal
ocean is one important piece of the fo
Contact: Ginger Pinholster
University of Delaware