|
Dust
from Africa Leads to Large Toxic Algae Blooms in Gulf of Mexico, Study Finds
(Images below story)
 |
|
 |
| |
| This
image is of a large dust cloud leaving the West coast of Africa on February 26,
2000. | Saharan
dust clouds travel thousands of miles and fertilize the water off the West Florida
coast with iron, which kicks off blooms of toxic algae, according to a new study.
The research was partially funded by a NASA grant as part of ECOHAB: Florida (Ecology
and Oceanography of Harmful Algal Blooms), a multi-disciplinary research project
designed to study harmful algae. Toxic
algal blooms, sometimes called red tides, have in the past killed huge numbers
of fish, shellfish, marine mammals, birds, and can cause skin and respiratory
problems in humans. Each
year iron from Saharan dust clouds is deposited in the waters off the West Florida
coast. Once there, plant-like bacteria use the iron to set the stage for red tides.
When iron levels go up, this bacteria, called Trichodesmium, 'fixes' nitrogen
in the water, converting it to a form usable by other marine life. The addition
of biologically usable nitrogen in the water makes the Gulf of Mexico a more likely
environment for toxic algae to bloom. "This
is one of the first studies that quantitatively measured iron from the dust and
tied it to red tides through Trichodesmium," said Jason Lenes, a graduate
student at University of South Florida's College of Marine Science, and the lead
author in the study. Lenes works under John J. Walsh, one of the principal investigators
for ECOHAB, and one of the paper's coauthors. The research appears in the September
issue of the scientific journal, Limnology and Oceanography. Storm
activity in the Sahara Desert region generates clouds of dust that originate from
fine particles in the arid topsoil. Easterly trade winds carry the dust across
the Atlantic Ocean and into the Gulf of Mexico. "Because iron is one of the
most common elements in most soils, a certain percentage of the dust contains
iron," said Lenes. The
study used satellite and ground based measurements to track large dust clouds
leaving Africa on June 17, 1999. Lenes and his colleagues followed the clouds
using data from the Advanced Very-High-Resolution Radiometer (AVHRR), an imager
aboard the National Oceanic and Atmospheric Administration's (NOAA's) Polar Orbiting
Environmental Satellites (POES). The
Saharan dust reached the West Florida shelf around July 1st, increasing iron concentrations
in the surface waters by 300 percent. As a result, Trichodesmium counts shot up
10 times what they had been prior to this event. Through a complex process involving
a special enzyme called nitrogenase, the Trichodesmium used the iron to convert
nitrogen in the water to a form more usable for other marine life. In October,
after a 300 percent increase of dissolved organic nitrogen, a huge bloom of toxic
red algae (Karenia brevis) had formed within the study area, an 8,100 square mile
region between Tampa Bay and Fort Myers, Florida. Scientists
have labored for several years in an effort to develop a reliable method to predict
red tides, particularly because the results of these blooms can be both physically
and economically devastating to a region. "The
West Florida shelf is a hot spot for fishing, aquaculture and tourism, all of
which can be drastically affected by a surprise visit from a red tide," said
Lenes. Humans
who swim in the Gulf can experience respiratory problems by breathing toxins from
K. brevis that get in the air. Also, eating shellfish poisoned by red tides can
lead to paralysis and memory problems. Around the Gulf of Mexico, scientists and
others have recorded fish kills totaling in the millions and manatee deaths in
the hundreds resulting from a single red tide bloom. By
using satellites to monitor dust arrivals and Trichodesmium blooms, Lenes said
this research could lead to forecasting of red tides. "If you could predict
when a red tide is coming, you could close beaches and fisheries ahead of time,"
Lenes said. The
paper was funded through a number of grants connected with the ECOHAB program.
Other funding for this study included grants from the National Oceanic and Atmospheric
Administration, the Office of Naval Research and the Environmental Protection
Agency. The ECOHAB: Florida Mission is to better understand the factors involved
in the occurrence and dispersal of Florida's predominant red tide algae, K. brevis,
and to predict and manage harmful algal bloom events.
Satellite
Images of Saharan Dust Moving Across Atlantic, June and July, 1999
| | 
|
|
| Image
2 | | |
Credit: NOAA Satellite Active
Archive
These
two images above (click on each image to enlarge) from a National Oceanic and
Atmospheric Administration (NOAA) satellite show iron-containing dust clouds blowing
from the African continent across the Atlantic Ocean in the months of June and
July, and reaching the eastern Gulf of Mexico and west coast of Florida in July.
The iron in the dust is the key ingredient that sets off an environmental chain
reaction in the Gulf of Mexico waters that could lead to a Red Tide. Every
year, during northern Africa's dry season, storm activity in the Saharan Desert
region generates clouds of iron-rich dust from fine particles of the arid topsoil.
The dust may be carried more than 10,000 feet high into the atmosphere by easterly
trade winds. The
trade winds then carry the dust over the Atlantic Ocean to Florida. Typically,
it takes one to two weeks for the Saharan dust clouds to reach the continental
United States. The
study used satellite and ground based measurements to track large dust clouds
leaving Africa on June 17, 1999. The study's lead author, Jason Lenes, and his
colleagues, followed the clouds using data from the Advanced Very-High-Resolution
Radiometer (AVHRR), an imager aboard the National Oceanic and Atmospheric Administration's
(NOAA's) Polar Orbiting Environmental Satellites (POES). The
second image depicts the Saharan dust as it reached the West Florida shelf around
July 1st, increasing iron concentrations by 300 percent. As a result, Trichodesmium
counts shot up 10 times what they had been before this one event. Trichodesmium
is a plant-like bacteria that utilizes iron in the dust to bring nitrogen into
the ocean water, a component required for the red tide algae to bloom. By
October, a huge bloom of Karenia breve, (a red tide), developed within the research
area, an 8,100 square mile area between Tampa Bay and Fort Myers, Florida.
|
|
|
| Image
3 | | TOMS
dust and smoke (equatorial Africa) image from 17 June 1999. |
Satellite
Images of Saharan Dust Moving Across Atlantic, June 17 and July 2, 1999 While
the previous NOAA images show aerosols blowing across the ocean, these two images
from NASA's Total Ozone Mapping Spectrometer (TOMS) instrument show dust coming
off regional land sources in Africa as they follow their path across the Atlantic.
The TOMS instrument aboard the Earthprobe TOMS satellite, captured these images
of the dust event from June 17, 1999, as it leaves Africa.
|
|
|
| Image
4 | | TOMS
dust and smoke (equatorial Africa) image from 2 July 1999. |
The
second image from July 2, 1999, shows the progression of this event as it approaches
North America. Credit: "Laboratory for Atmospheres TOMS Project, NASA Goddard
Space Flight Center"
|
|
|
| Image
5 | | This
image is of a large dust cloud leaving the West coast of Africa on February 26,
2000. | Image
of Saharan dust cloud leaving the west coast of Africa
Credit: February 26, 2000 SeaWiFS
image.
Back
to Top | 
