By Courtney Mattison
Sylvia Earle often says, “We know more about space than we do about our ocean.” That surprising fact may soon change thanks to a new map produced using satellite data of variations in Earth’s gravitational field to reveal features of the seafloor that were previously undiscovered. By tapping into data streams from the Jason-1 and CryoSat-2 satellites, researchers at Scripps Institution of Oceanography at UC San Diego and their colleagues have made a breakthrough in seafloor mapping that “is like the difference between ordinary and high-definition television.”[i]
Approximately 90% of the deep seafloor is unmapped, and this new satellite-based radar altimetry technique can help fill in sizeable blind spots by using a new marine gravity model that is at least two times as accurate as existing models.[i] While this technology is not sensitive enough to help find smaller features in the seafloor like Malaysia Airlines Flight 370, it is a major improvement in resolution from previous mapping techniques. Most of the maps that already exist of the seafloor were created from ship-based multibeam sonar systems that bounce sound waves off the seafloor and leave “big holes hundreds of kilometers across with no data” according to David Sandwell, a geophysicist at the Scripps Institution of Oceanography in San Diego, CA who led this project. In contrast these satellites collect data by repeatedly bouncing signals off the surface of the ocean multiple times a day, filling out an image of the “bumps and valleys” across the surface of the ocean that reflect features below when corrected for heights and tides.[i] “A seamount, for example, exerts a gravitational pull, and warps the sea surface outward,” Sandwell says. “So we can map the bottom of the ocean indirectly, using sea-surface topography.”
In creating this new global seafloor map, Scripps researchers discovered thousands of extinct volcanoes and seamounts over 1000 meters tall, as well as the exact location of the seafloor spreading ridge that formed the deep basin within the Gulf of Mexico. “That was a surprise to me – you’d think everyone would know everything about the Gulf because it’s so well-studied,” Sandwell told Science Magazine, which published this project. “Of course, people knew it opened from seafloor spreading, but they didn’t know exactly where the ridge and transform faults were.”
One ominous result of this new gravity mapping technique is increased interest by oil companies in using gravity maps to explore for hydrocarbons around flat seafloor areas with thick layers of sediment that occur along continental margins.[i] The Chinese Government is also interested in this technology to explore the South China Sea. Hopefully this tool will be used for environmental conservation rather than destruction. The exciting prospects of discovering more seafloor features and other secrets of the deep sea from data already collected for this project will keep scientists engaged for years.
In addition to Sandwell and Francis, coauthors of the paper include R. Dietmar Muller of the University of Sydney, Walter Smith of the NOAA Laboratory for Satellite Altimetry, and Emmanuel Garcia of Scripps. The study was supported by NSF, ONR, the National Geospatial-Intelligence Agency, and ConocoPhillips.
Featured image (top): Close-up of new seafloor map using Google Earth © 2014 Scripps Institution of Oceanography, UC San Diego