Whenever a hurricane races across the Atlantic Ocean,
chances are phytoplankton will bloom behind it. According to
a new study using NASA satellite data, these phytoplankton
blooms may also affect the Earth’s climate and carbon cycle.
Dr. Steven Babin, a researcher at the Johns Hopkins
University Applied Physics Laboratory in Laurel, Md., studied
13 North Atlantic hurricanes between 1998 and 2001. Ocean
color data from the SeaWiFS instrument on the SeaStar
satellite were used to analyze levels of chlorophyll, the
green pigment in plants. The satellite images showed tiny
microscopic ocean plants, called phytoplankton, bloomed
following the storms.
“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,” Babin said.
Previous research has relied largely on sporadic, incomplete
data from ships to understand how and when near-surface
phytoplankton bloom. “This effect of hurricanes in ocean
deserts has not been seen before. We believe it is the first
documented satellite observation of this phenomenon in the
wake of hurricanes,” Babin noted. “Because 1998 was the first
complete Atlantic hurricane season observed by this
instrument, we first noticed this effect in late 1998 after
looking at hurricane Bonnie,” Babin said.
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. Larger phytoplankton
should have more chlorophyll, which satellite sensors can
see.
Hurricane-induced upwelling, the rising of cooler nutrient-
rich water to the ocean surface, is also critical in
phytoplankton growth. For two to three weeks following almost
every storm, the satellite data showed phytoplankton growth.
Babin and his colleagues believe it was stimulated by the
addition of nutrients brought up to the surface.
Whenever the quantity of plants increases or decreases, it
affects the amount of carbon dioxide in the atmosphere. As
phytoplankton grow, they absorb carbon dioxide, a heat-
trapping greenhouse gas. The gas is carried to the ocean
floor as a carbon form when the tiny plants die. This enables
atmospheric carbon to get into the deep ocean. It is one of
several natural processes that contribute to Earth’s carbon
cycle.
By stimulating these phytoplankton blooms, hurricanes can
affect the ecology of the upper ocean. Phytoplankton is at
the bottom of the food chain. The factors that influence
their growth also directly affect the animals and organisms
that feed on them. In addition, since climate-related
phenomena like El Niño may change the frequency and intensity
of hurricanes, storm-induced biological activity may have
even greater contributions to future climate change.
Scientists are still trying to determine how much carbon
dioxide might be removed from such a process. “Better
knowledge of the carbon cycle will improve our understanding
of global ecology and how climate change might affect us,”
Babin said.
The research appeared as a paper in a recent issue of the
Journal of Geophysical Research-Oceans. Study co-authors
include J.A. Carton, University of Maryland, College Park,
Md.; T.D. Dickey, Ocean Physics Laboratory, University of
California, Santa Barbara, Calif.; and J.D. Wiggert, Center
for Coastal Physical Oceanography, Old Dominion University,
Norfolk, Va.
NASA’s Earth Science Enterprise funded part of the research.
The Enterprise is dedicated to understanding the Earth as an
integrated system and applying Earth System Science to
improve climate, weather, and natural hazard prediction using
the unique vantage point of space.
For information and images about this research on the
Internet, visit:
http://www.gsfc.nasa.gov/topstory/2004/0602hurricanebloom.html
For information about NASA and agency programs on the
Internet, visit:
