How Radar Altimetry Discovered Marine Geodynamics
Alexander Braun(1) , Gabriele Marquart(2) , Michael G. Sideris(1) , and C.K. Shum(3)
University of Calgary,
Dept. of Geomatics Engineering,
Calgary, Alberta T2N 1N4,
(2) University of Frankfurt, Feldbergstr. 47, 60323 Frankfurt, Germany
(3) The Ohio State University, 125 Oval Mall, Columbus, OH 43210, United States
Since the early altimeter experiments on GEOS-3 and SEASAT, radar altimetry data has been used to derive gravity and its variations over the world's oceans. Soon it became clear that altimetry is an excellent tool for mapping sea floor structures, including tectonics, sea mounts and rifts. The short wavelengths of the gravity field at the ocean surface mimics the uppermost structure of the oceanic crust, including the bathymetry, while long wavelengths reflect structures and processes in the Earth's mantle. This characteristic has been used to derive the bathymetry of the oceans, which revealed a vast amount of new geological information. However, besides the bathymetry, the derived marine gravity anomalies further allow closer insights into the structure of the lithosphere and crust, and the marine geoid. While the bathymetry - water density contrast is the most important to consider, there are remaining components in the gravity field that originate from internal crustal and lithospheric structures. Altimetry data has consequently been employed to better understand and interpret the present structure and the geological evolution of continental shelfs, mid-ocean ridges and subduction zones.
These data sets have been dramatically improved in terms of spatial resolution with the Geodetic Mission phases of GEOSAT and ERS-1. In addition, the higher inclination of ERS-1 opened the door to conduct geodynamic studies also in the polar regions. The paper outlines the contributions of radar altimetry to marine geodynamics and presents examples of geodynamic studies that include the opening history of the North Atlantic, boudinage and deformation structures in continental shelfs, and lithospheric cooling signatures at the East Pacific ridge. Today, gravity anomalies derived from altimetry data is one of the fundamental data sets frequently used in the geoscience community.