Theresearchers combined data from the Moderate Resolution ImagingSpectroradiometer (MODIS) aboard NASA's Terra and Aqua satellites withinformation collected from ships to study the water discharge,appearing as a dark plume that stretched from the Mississippi Delta,around Florida and up to the Georgia coast. MODIS detects the color ofthe ocean due to changes in the amount of tiny ocean plants floating onthe ocean's surface known as phytoplankton, or algae and other decayingmaterials.
"This is the first time we have been able to estimatethe amount or volume of freshwater discharged and carried over suchremote distances. By combining the very detailed data from MODIS withobservations from ships, we got a three-dimensional view of theMississippi plume," said Chuanmin Hu, of the College of Marine Science,University of South Florida, St. Petersburg, Fla., and lead author ofthe study. By using MODIS data with information on sea surface currentsand sea salt levels (salinity), the scientists estimated that about 20billion tons of Mississippi River water reached the Florida Straits andGulf Stream off the Georgia coast. This is about four times the volumeof Lake Okeechobee, the largest lake in Florida.
The researchalso shows that such plumes created by the Mississippi River can travelover large distances, more than 1240 miles (2000 kilometers).
Beyondstudying the causes of such events, researchers are using satelliteinformation with observations from ships and "ocean surface drifters" -instruments resembling balloons that travel the ocean surface, to get abetter idea of how these plumes affect marine life.
"MississippiRiver water may have some impact on marine life in remote delicateecosystems like the Florida Keys. But we are still not clear about thepotential impacts of pollutants and pesticides," said Hu. "Not alleffects will be bad; in fact, some light dark water events mightactually protect bottom ocean dwellers, like coral, by providing themwith shade."
The study is published in the July 2005 issue ofGeophysical Research Letters under support of NASA, NOAA, and ONR as acontribution to the SouthEast Atlantic Coastal Ocean Observing System(SEACOOS). Coauthors include oceanographers James Nelson from theSkidaway Institute of Oceanography, Elizabeth Johns from NOAA’sAtlantic Oceanographic and Meteorological Laboratory, and ZhiqiangChen, Robert Weisberg, and Frank Muller-Karger from the University ofSouth Florida.
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