Johns Hopkins Researcher Sees Hurricanes as Catalyst for Ocean Plant Growth

Hurricanes that wreak havoc on humans are now believed to nurture the growth of tiny phytoplankton — microscopic vegetation that float on the ocean surface gobbling up harmful carbon dioxide. This finding puts researchers one step closer to a comprehensive understanding of the ocean's carbon cycle, to knowing how organisms like phytoplankton protect the Earth from global warming, and to determining what effect phytoplankton might have on climate.

The research is being led by Steven M. Babin, a meteorologist at The Johns Hopkins University Applied Physics Laboratory, in Laurel, Md. Babin had spent much of his career studying the atmosphere's influence on military radar systems. In 1998, he became curious about vegetation growth that appeared after Atlantic Coast hurricanes and started studying ocean color data from the SeaWiFS instrument on NASA's SeaStar satellite. Previous research on phytoplankton bloom was of little help because it relied largely on sporadic, incomplete data from ships.

Using the satellite data he looked at how plant life changed after each of 13 North Atlantic hurricanes passed through the North Atlantic's Sargasso Sea region from 1998 to 2001. Because phytoplankton contain most of the chlorophyll in the ocean, he analyzed levels of chlorophyll, the green pigment in plants, to determine the extent of vegetation growth. He found that, after a hurricane, there were increases in these chlorophyll levels along the hurricane tracks and that these increases persisted for two to three weeks after the storm had passed.

"Some parts of the ocean are like deserts, and there isn't enough food for many plants to grow," Babin says. "The satellite evidence indicates that hurricanes stir up the colder deep ocean water bringing necessary nutrients to the surface to feed the phytoplankton and in the process, push it toward the sunlight, causing it to bloom," he says.

The study found the physical make-up of a storm, including its size, strength and forward speed, is directly related to the amount of phytoplankton that blooms. Bigger storms appear to cause larger phytoplankton blooms. "Because 1998 was the first complete Atlantic hurricane season observed by the SeaWiFS instrument, we first noticed this effect in late 1998 after looking at hurricane Bonnie," Babin says. "This effect of hurricanes on ocean deserts has not been seen before. We believe it is the first documented satellite observation of this phenomenon."

Phytoplankton and the Carbon Cycle

Phytoplankton are a key element in the ocean carbon cycle of carbon dioxide absorption, storage and release to the atmosphere. The tiny plants absorb carbon dioxide, a heat-trapping greenhouse gas, and draw it down to the ocean floor as a carbon form when the tiny plants die, keeping it safely contained for hundreds of years.

Scientists are still trying to determine how much carbon dioxide might be removed from such a process and Babin's study is a step in that direction. "Better knowledge of the carbon cycle will improve our understanding of global ecology and how climate change might affect us," Babin says.

Detailed results of Babin's research appeared in the March issue of the Journal of Geophysical Research-Oceans. Study co-authors include: Jim Carton, University of Maryland, College Park, Md.; Tommy Dickey, Ocean Physics Laboratory, University of California, Santa Barbara, Calif.; and Jerry Wiggert, Center for Coastal Physical Oceanography, Old Dominion University, Norfolk, Va.

For images and more information on this research, visit: 
http://www.gsfc.nasa.gov/topstory/2004/0602hurricanebloom.html