The authors, Whittaker et al. (2008), present three companion digital grids of the downward-continued gravity, RMS (Root Mean Square) gravity roughness, and the residual roughness of the world's ocean basins as geographic and Mercator grids with two-minute resolution. Bathymetry not related to oceanic spreading ridges has been masked; namely, continental shelves, large igneous provinces, and seamounts in the roughness and residual roughness datasets.
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Downward-Continued Gravity
- Download GMT IMG file (78mb)
- Download GMT NetCDF grd file (80mb)
- Download ASCII file with NaNs (348mb)
Gravity Roughness (100km)
- Download GMT IMG file (46mb)
- Download GMT NetCDF grd file (47mb)
- Download ASCII file with NaNs (287mb)
Gravity Roughness (160km)
- Download GMT IMG file (45mb)
- Download GMT NetCDF grd file (45mb)
- Download ASCII file with NaNs (286mb)
Residual Roughness (100km masked)
- Download GMT IMG file (47mb)
- Download GMT NetCDF grd file (50mb)
- Download ASCII file with NaNs (305mb)
Predicted Roughness (100km masked)
Related Data at NCEI
Global Grids at NCEI
Related Data at EarthByte
Additional Information
Whittaker et al. (2008) use a global grid of gravity anomalies based on satellite altimetry, downward continued to sea floor and draped onto the lowpass of the topo_8.2.img grid of the sea floor using the filters to create a global grid of oceanic basement roughness. Our roughness filter is a variable-width Gaussian filter adjusted to the local scale of the Mercator-projected data. The half-power point wavelength is 50km, reflecting gravity anomalies due to uncompensated basement topography, implemented using the grdfilter tool in the Generic Mapping Tools program. This weighted-average filter is applied to individual points to compute root mean square (RMS) marine gravity roughness. Short-wavelength roughness in gravity anomalies (20-160km wavelength) reflects the roughness of oceanic basement topography.
The 100km filter width was compared with a 160km filter width, but the latter resulted in a grid where many basement tectonic features were not well resolved. This reflects the fact that the vast majority of structural features of the sea floor such as abyssal hills, fracture zone troughs and ridges have wavelengths significantly smaller than 160km.
The RMS residual roughness grid has had roughness attributable to spreading rates and sediment cover. Analysis of the relationship between gravity-derived roughness, spreading rate and sediment thickness was conducted using global grids of sediment thickness, half-spreading rates and oceanic basement roughness. The linear relationships between spreading rate and sediment thickness and gravity-derived roughness were used to create a predicted roughness grid, which was then subtracted from the RMS gravity-derived roughness grid.
Cite As
Whittaker, J.M., Müller, R.D., Roest, W.R., Wessel, P., and Smith, W.H.F., 2008, How supercontinents and superoceans affect seafloor roughness: Nature, 456, p. 938-941, (18 December 2008) Nature Articles