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Improved Gravity Map Reveals New Mountains Under the Sea

New marine gravity anomaly map derived from satellite altimetry

Ocean gravity maps

(A) New marine gravity anomaly map derived from satellite altimetry reveals tectonic structures of the ocean basins in unprecedented detail, especially in areas covered by thick sediments. Land areas show gravity anomalies from Earth Gravitational Model 2008. (B) Vertical Gravity Gradient (VGG) map derived from satellite altimetry highlights fracture zones crossing the South Atlantic Ocean basin (yellow line). Areas outlined in red are small-amplitude anomalies in areas where thick sediment has diminished the gravity signal of the basement topography.

17 October 2014 - An international team of remote sensing scientists that includes W.H.F. Smith of the STAR Laboratory for Satellite Altimetry developed a new global marine gravity map that is twice as accurate as previous models. Published October 3 in the journal Science, the new map reveals significant new seafloor features, including an extinct spreading ridge in the Gulf of Mexico, a major propagating rift in the South Atlantic, and as many as 25,000 previously uncharted 1.5km tall seamounts. These discoveries allow us to understand regional tectonic processes and highlight the importance of satellite-derived gravity models as a primary tool in the investigation of ocean bottom regions.

"In the previous radar dataset we could see everything taller than 2km, and there were 5,000 seamounts. With our new dataset - and we haven't fully done the work yet - I'm guessing we can see things that are 1.5km tall. That might not sound like a huge improvement but the number of seamounts goes up exponentially with decreasing size. So, we may be able to detect another 25,000 on top of the 5,000 already known."

David Sandwell
Scripps Institution of Oceanography

Knowing the locations of seamounts is important for conservation and fisheries management because ocean life tend to congregate around them. And the shape of the ocean floor influences and shapes currents and the transmission of heat through the ocean, with implications for navigation and understanding the changing climate.

The new model makes use of data from Jason-1, which was recently taken out of service, and the European Space Agency's CryoSat, whose principal mission is dedicated to exploring the shape and thickness of polar ice fields - not the shape of the seafloor. The new map's denser coverage and better radar technologies have brought a two-fold improvement in the gravity model used to describe the ocean floor. While the data thus derived has not been fully explored yet, important new findings have already been identified from it. These include an extinct ridge where the seafloor spread apart to help open up the Gulf of Mexico about 180 million years ago. And in the South Atlantic, the team sees the two halves of a different type of ridge feature that became separated roughly 85 million years ago when Africa rifted away from South America.