CONTACT:   Patricia Viets, NOAA               FOR IMMEDIATE RELEASE 
           Janet Howard or Cindy Clark        9/24/97
          Scripps Institution of Oceanography      

Scientists have used gravity data from satellites in addition to depth soundings from ships to produce a more defined, high-resolution map of the world's ocean floors, the Commerce Department's National Oceanic and Atmospheric Administration announced today.

The new map, which looks similar to one the scientists published in 1995, provides estimations of the ocean depths from gravity data from satellites. The 1995 map was based on gravity data, but did not provide estimations of ocean depths.

Scientists Walter H.F. Smith of NOAA's National Oceanographic Data Center and David T. Sandwell of the Scripps Institution of Oceanography, University of California, San Diego, report on their project in the September 26 issue of Science magazine.

Conventional sea floor mapping using echo sounding data from ships has been difficult because of the large gaps between surveys in remote areas. "There are places as large as the State of Oklahoma where no soundings are available," said Smith. "Traditionally, bathymetric contours are drawn by hand so that human intuition (or prejudice) fills the gaps in coverage," Smith and Sandwell write in Science. "Recent developments allow a new approach to this problem." Smith and Sandwell used gravity data from satellites to estimate depths in unsurveyed areas, thus filling the gaps in the map in an objective and high-resolution manner.

The new topography reveals all of the intermediate and large-scale structures of the ocean basins, including new mountain ranges such as the Foundation Seamounts in the South Pacific. These were not found by conventional mapping but were revealed by the satellite gravity data. Smith and Sandwell showed that uncharted seamounts are a significant source of topographic variation, and information from satellite gravity can reduce the error in estimated topographic variation by more than half.

Knowledge of sea floor topography is vital for understanding physical oceanography, marine biology, chemistry and geology. Topography influences currents, tides, and mixing and upwelling of nutrient-rich water. The new topographic features portrayed by Smith and Sandwell reveal new fish habitats and should influence computer simulations of ocean circulation, which are used to forecast global climate change.