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Draining the Oceans Using Google Earth

David Sandwell,
Professor of Geophysics,
Scripps Institution of Oceanography

More than two-thirds of our planet is covered by deep oceans. What would the Earth look like if we could drain the oceans?

Six years ago, Google launched an initiative that opens up the possibility of exploring the ocean floor in Google Earth, enabling a new generation of virtual ocean explorers. At www.google.com/earth/explore/showcase/ocean.html, visitors can learn about a wide array of ocean subjects and follow along with deep-sea explorations.

One of the main Google Ocean components is seafloor bathymetry, which provides basic infrastructure for scientific, economic, educational, managerial and political work. Applications as diverse as tsunami hazard assessment, communications cable and pipeline route planning, resource exploration, habitat management and territorial claims under the Law of the Sea all require reliable bathymetric maps to be available on demand. Fundamental Earth science questions, such as what controls seafloor shape and how seafloor shape influences global climate, also cannot be answered without bathymetric maps having globally uniform detail. Most importantly, the public is curious about this two-thirds of our planet that is more poorly mapped than Mercury, Venus and Mars, having data gaps equivalent to the size of the state of New Jersey.

These gaps are apparent when you explore the seafloor in Google Ocean; some regions appear to have much higher resolution than other regions. These differences reflect the different technologies used for seafloor mapping. The highest-resolution seafloor maps (100 to 200 m) are provided by multibeam ship surveys. The latest upgrade to Google Ocean (February 2016) has about 11 percent of the seafloor mapped by multibeam sonar. Another 5.5 percent of the seafloor has been mapped by older, single-beam sonars that offer only about 1,000-m spatial resolution; these older data are critical for filling large coverage gaps in the most remote ocean areas.

The topography of the remaining 83 percent of the seafloor is mapped at very low resolution (approximately 6,000 m) from satellite-derived gravity measurements. The ocean surface has bumps and dips, which mimic the topography of the ocean floor. These bumps and dips can be mapped using a very accurate radar altimeter mounted on a satellite.

Over the past six years, new satellite altimeters have provided a dramatically improved view of the topography of the deep ocean floor (http://topex.ucsd.edu/grav_outreach). Most of the new information comes from the CryoSat-2 satellite launched by the European Space Agency in 2010. The CryoSat-2 data are more accurate and provide vastly improved coverage than the data from all previous satellite altimeter gravity missions.

A second major advance in the latest release of Google Ocean is a much more complete compilation of the multibeam sonar data. This has been a collaborative effort between Lamont-Doherty Earth Observatory, Scripps Institution of Oceanography, International Bathymetric Chart of the Arctic Ocean (IBCAO), General Bathymetric Chart of the Oceans (GEBCO), NOAA, the U.S. Navy and National Geospatial-Intelligence Agency (NGA), with major contributions from JAMSTEC, GEOMAR and Geoscience Australia. New areas to explore include the Philippine Sea, Ryukyu Trench, the seafloor fabric east of Hawaii, the continental margins around Australia and the Reykjanes Ridge.

Using these publicly available data, a research group in Australia discovered the first microplate in the Indian Ocean having an area larger than the state of West Virginia. They named it the “Mammerickx Microplate” after Jacqueline Mammerickx, who is the author of the original GEBCO maps in the Pacific Ocean.

The bathymetry data and products used in the latest Google Ocean are freely available to public, commercial and scientific users and include a global 500-m resolution grid called SRTM15_PLUS (ftp://topex.ucsd.edu/pub/srtm15_plus) and 100-m resolution grids derived from more than 36 years of ship-based data from nearly 1,300 global research cruises conducted aboard more than 30 ships (http://www.marine-geo.org/portals/gmrt/contributors.php). The continued pooling of publicly available data enhances research around the world and makes possible a new and expanding audience for deep-ocean discovery.

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