Hurricanes spur growth of plankton in the ocean

WASHINGTON -- Like a desert bursting into flower after a rare rainstorm, seemingly barren stretches of the ocean bloom with plankton after hurricanes pass by.

The bursts of life were measured by satellite studies following 13 hurricanes from 1998 to 2001.

"I was pleasantly surprised," said Steven Babin of Johns Hopkins University, who led the research.

Babin said sudden blooms of phytoplankton -- tiny plants that float in the ocean -- have been reported in areas of ocean upwelling where rising water brings nutrients to the surface. He said similar effects from hurricanes had not been widely studied.

"Some parts of the ocean are like deserts, because there isn't enough food for many plants to grow. A hurricane's high winds stir up the ocean waters and help bring nutrients and phytoplankton to the surface, where they get more sunlight, allowing the plants to bloom," he said.

Russell L. Cuhel of the University of Wisconsin, Milwaukee, said similar effects have been found after storms cross the Great Lakes.

A plankton bloom following one severe Lake Michigan storm lasted a "couple of weeks" and led to a big improvement in the growth of larval perch, which fed on the algae, said Cuhel, who was not part of the research team.

"It doesn't surprise me," Cuhel said of the report, noting there are two inputs to the growth of plankton, rain and rising nutrients stirred by the wind.

He said one hurricane he studied showed mixed water more than 175 yards deep after a storm.

Babin's team studied satellite data collected by NASA. The images showed changes in color of the sea surface, lasting days to weeks, as plankton grew in areas where a hurricane had passed through.

Babin said he focused on a section of the Atlantic Ocean known as the Sargasso Sea which is away from the coasts and generally has little plankton because of a lack of nutrients near the surface.

The stronger the storm, the larger and longer the bloom of plankton, he said.

These tiny plants grow in great numbers when they bloom, absorbing carbon dioxide from the atmosphere. When they die they sink to the bottom, trapping the excess carbon for thousands of years.

"The physical response of the ocean to hurricanes is complex," Jerry Wiggert, of the Center for Coastal Physical Oceanography at Old Dominion University, said.

"No one has considered the biological contribution to the altered carbon flux balance that takes place when hurricanes pass over oceans," said Wiggert, who was part of Babin's research team.

Whether the amount of carbon dioxide removed by plankton blooms after a hurricane is significant remains to be determined, Babin said.

And, he added, there is a competing effect, because when the storms toss the sea around the water can release dissolved carbon dioxide, somewhat like a shaken can of soda loses its fizz.

It's not known whether the two effects balance out or if the plankton helps reduce gasses in the air, Babin said.

Such studies help improve understanding of the global carbon cycle, Babin said, "the more we understand, the easier it will be to try to live with the changes we can't control" or figure out how to control what we can.

Scientists concerned about global warming, which has been tied to excess gasses such as carbon dioxide, have debated whether such plankton growth could be encouraged as a way of reducing the carbon dioxide.

That has even led to experiments in which seemingly empty areas of the ocean were seeded with nutrients such as iron in hopes of encouraging such growth.

In some cases the bloom of plant plankton was quickly followed by a growth of zooplankton -- tiny animals that eat the plants, Cuhel said.

"They came in and grazed down all the new food. From the food web point of view, what a great thing," said Cuhel. "There is a pretty well developed food chain that's always hungry."

Babin's research was funded by NASA's Earth Science Enterprise.