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Satellite Sees Chlorophyll Stirred up by Hurricane Katrina
Wind and wave action from Hurricane Katrina in August 2005 stirred up sediments and chlorophyll, the pigment (ocean) plants use for photosynthesis, off the Florida coast. This event was captured by NASA's Sea-viewing Wide Field-of-view Sensor (SeaWiFS) onboard GeoEYE’s SeaStar spacecraft, and analyzed using a new Web-based software technology.

SeaWiFS global 8-day data products have recently been added to the NASA Goddard Earth Sciences Data and Information Services Center (GES-DISC) Interactive Online Visualization and Analysis Infrastructure (Giovanni). This data enabled development of a simple method for investigating chlorophyll changes in the ocean's surface after a hurricane passes. The energy from hurricanes can affect many aspects of the oceanic ecosystem.

Strong cyclonic surface winds of hurricanes are known to mix ocean surface waters, a process which brings nutrients and dissolved organic matter (carbon-based material created by biological activity in the oceans) to the sea surface from the lower depths of the ocean. With enough sunlight and the right temperatures and nutrients, phytoplankton, or free-floating unicellular aquatic algae, can grow quickly after a hurricane passes. That growth is observable as an increase in the concentration of chlorophyll on the sea surface. Hurricane-stirred sediments in coastal waters may also increase the apparent chlorophyll concentration measured by the satellite by increasing light reflection. This occurs because the sediments may mistakenly be interpreted as phytoplankton chlorophyll in the satellite data.

Suhung Shen, James Acker, Greg Leptoukh, Hualan Rui, Steve Berrick and Steve Kempler of NASA's Goddard Space Flight Center, Greenbelt, Md. will be presenting a poster on their findings at the 2006 Joint Assembly meeting at the Baltimore Convention Center in Baltimore, Md. Their poster, titled "Observing Increased Chlorophyll-a in Storm Wakes for the 2005 Atlantic Hurricane Season using 8-Day Data Products in Giovanni" will be presented Wed. May 24 at 8:30 a.m., in BCC Hall, during the Poster Session OS31A-13. Detailed results and a description of the Giovanni online tool will be presented during this poster session.

Chlorophyll concentration before Katrina. Image left: This image, created using data from the SeaWiFS instrument onboard the Orbview-2 satellite, shows the normal occurrence of higher chlorophyll concentrations (green, yellow, red) near coastal regions. This coastal chlorophyll “signal” is a mixture of chlorophyll, turbidity (murky water), and even bottom reflection. The black circles indicate the track of Katrina through the Gulf. Credit: NASA/GESDISC/OBPG.

Chlorophyll concentration after Katrina. Image right: This image, created using data from the SeaWiFS instrument onboard the GeoEYE’s Orbview-2 satellite, shows how phytoplankton chlorophyll concentrations apparently increased over an 8-day period after hurricane Katrina moved into the Gulf of Mexico. The winds and wave action of Hurricane Katrina off of Florida stirred up sediments and chlorophyll. The green, orange, and yellow colors highlighted within the white circle indicate an area where turbidity (murkier water) increased. This was interpreted by the satellite as increased chlorophyll concentration, during the period Aug. 29 – Sept. 5, 2005, off the southwestern coast of Florida. Higher turbidity is likely due to a combination of sediments and chlorophyll transported from shallow coastal waters by hurricane winds. The black circles indicate the track of Katrina through the Gulf. Credit: NASA/GES DISC/OBPG DISC/OBPG

Image of Hurricane Katrina seen by the Aqua satellite. Image right: By the morning of August 28, 2005, Hurricane Katrina strengthened into a powerful Category Five hurricane with sustained winds of 160 mph in the warm waters of the Gulf of Mexico. Before entering the Gulf, however, Katrina left much destruction in her wake in South Florida as a category 1 storm, killing as many as nine persons and causing upwards of $600 million dollars in estimated damage. This image was taken from the Moderate Imaging Spectroradiometer (MODIS) aboard NASA's Terra satellite. Credit: NASA/Jeff Schmaltz, MODIS Land Rapid Response Team

Related Links:

+ SeaWiFS instrument
+ NASA's Hurricane page

Gretchen Cook-Anderson
Goddard Space Flight Center