A NASA-sponsored study shows that by using a new technique, scientists can determine what limits the growth of ocean algae, or phytoplankton, and how this affects Earth's climate.
Phytoplankton is a microscopic ocean plant and an important part of the ocean food chain. By knowing what limits its growth scientists can better understand how ecosystems respond to climate change.
The study focused on phytoplankton in the tropical Pacific Ocean. It is an area of the ocean that plays a particularly important role in regulating atmospheric carbon dioxide and the world's climate. This area of the ocean is the largest natural source of carbon dioxide to the atmosphere.
"We concluded that nitrogen is the primary element missing for algae growth and photosynthesis in the northern portion of the tropical Pacific, while it was iron that was most lacking everywhere else," said Michael J. Behrenfeld, an ocean plant ecologist from Oregon State University, Corvallis, Ore.
Scientists determined when phytoplankton is stressed from lack of iron; it appears greener, or healthier than they really are. Normally, greener plants are growing faster than less green plants. When iron is lacking, enhanced greenness does not mean phytoplankton are growing better. They are actually under stress and unhealthy. These conclusions solved the mystery why healthy looking phytoplankton are actually not so healthy.
"Because we didn't know about this effect of iron stress on the greenness of algae or phytoplankton before, we have always assumed that equally green waters were equally productive," Behrenfeld said. "We now know this is not the case, and that we have to treat areas lacking iron differently."
For the tropical Pacific, correction for this "iron-effect" decreases scientists' estimates of how much carbon ocean plants photosynthesize for the region by roughly two billion tons. This figure represents a tremendous amount of carbon that r
Contact: Rob Gutro
NASA/Goddard Space Flight Center