19 November, 2008 How supercontinents and superoceans affect seafloor roughness Reference J.M. Whittaker, R.D. Muller, W.R. Roest, P. Wessel & W.H.F. Smith, 2008, How supercontinents and superoceans affect seafloor roughness: Nature, 456, p. 938-941, (18 December 2008) doi:10.1038/nature07573 ### Version 1 ### grav_down.15.2.img Downward continued gravity. A 10800 by 6336 grid of 2-byte integers = 136,857,600 bytes. Byte order is big_endian. Stored in an integer*2 format without any header or record information. The gravity units are in mGals, multiplied by 10 (to enable storage as short integers) Grid cells without data (i.e. on continental crust) are assigned values of 32767. The Mercator projected image spans longitudes from 0 E to 360 E and latitudes from 72.006 N to -72.006 S. A spherical earth is used for the Mercator projection. 2 minute resolution, pixel-registered. grav_down.15.2.nc Downward continued gravity. A short integer netCDF formatted file. The gravity units are in mGals, multiplied by 10 (to enable storage as short integers) The geographic grid spans longitudes from 0 E to 360 E and latitudes from 72.006 N to -72.006 S. 2 minute resolution, pixel-registered. grav_down.15.2.xyz A simple ASCII file (long, lat, DownGrav). The units are in mGal with no scaling. The file spans longitudes from 0 E to 360 E and latitudes from 90 N to -90 N. 2 minute resolution. roughness_100km.15.2.img Seafloor roughness using 100 km filter width, unmasked. A 10800 by 6336 grid of 2-byte integers = 136,857,600 bytes. Byte order is big_endian. Stored in an integer*2 format without any header or record information. The roughness units are in mGals, multiplied by 100 (to enable storage as short integers) Grid cells without data (i.e. on continental crust) are assigned values of 32767. The Mercator projected image spans longitudes from 0 E to 360 E and latitudes from 72.006 N to -72.006 S. A spherical earth is used for the Mercator projection. 2 minute resolution, pixel-registered. roughness_100km.15.2.nc Seafloor roughness using 100 km filter width, unmasked. A short integer netCDF formatted file. The roughness units are in mGals, multiplied by 100 (to enable storage as short integers) The geographic grid spans longitudes from 0 E to 360 E and latitudes from 72.006 N to -72.006 S. 2 minute resolution, pixel-registered. roughness_100km.15.2.xyz A simple ASCII file (long, lat, 100kmRoughness). The units are in mGal with no scaling. The file spans longitudes from 0 E to 360 E and latitudes from 90 N to -90 N. 2 minute resolution. roughness_160km.15.2.img Seafloor roughness using 160 km filter width, unmasked. A 10800 by 6336 grid of 2-byte integers = 136,857,600 bytes. Byte order is big_endian. Stored in an integer*2 format without any header or record information. The roughness units are in mGals, multiplied by 100 (to enable storage as short integers) Grid cells without data (i.e. on continental crust) are assigned values of 32767. The Mercator projected image spans longitudes from 0 E to 360 E and latitudes from 72.006 N to -72.006 S. A spherical earth is used for the Mercator projection. 2 minute resolution, pixel-registered. roughness_160km.15.2.nc Seafloor roughness using 160 km filter width, unmasked. A short integer netCDF formatted file. The roughness units are in mGals, multiplied by 100 (to enable storage as short integers) The geographic grid spans longitudes from 0 E to 360 E and latitudes from 72.006 N to -72.006 S. 2 minute resolution, pixel-registered. roughness_160km.15.2.xyz A simple ASCII file (long, lat, 160kmRoughness). The units are in mGal with no scaling. The file spans longitudes from 0 E to 360 E and latitudes from 90 N to -90 N. 2 minute resolution. roughness_100km_mask.15.2.img Seafloor roughness using 100 km filter width with COBs, LIPs and seamounts masked out. A 10800 by 6336 grid of 2-byte integers = 136,857,600 bytes. Byte order is big_endian. Stored in an integer*2 format without any header or record information. The roughness units are in mGals, multiplied by 100 (to enable storage as short integers) Grid cells without data (i.e. on continental crust) are assigned values of 32767. The Mercator projected image spans longitudes from 0 E to 360 E and latitudes from 72.006 N to -72.006 S. A spherical earth is used for the Mercator projection. 2 minute resolution, pixel-registered. roughness_100km_mask.15.2.nc Seafloor roughness using 100 km filter width with COBs, LIPs and seamounts masked out. A short integer netCDF formatted file. The roughness units are in mGals, multiplied by 100 (to enable storage as short integers) The geographic grid spans longitudes from 0 E to 360 E and latitudes from 72.006 N to -72.006 S. 2 minute resolution, pixel-registered. roughness_100km_mask.15.2.xyz A simple ASCII file (long, lat, 100kmRoughness). The units are in mGal with no scaling. The file spans longitudes from 0 E to 360 E and latitudes from 90 N to -90 N. 2 minute resolution. roughness_160km_mask.15.2.img Seafloor roughness using 160 km filter width with COBs, LIPs and seamounts masked out. A 10800 by 6336 grid of 2-byte integers = 136,857,600 bytes. Byte order is big_endian. Stored in an integer*2 format without any header or record information. The roughness units are in mGals, multiplied by 100 (to enable storage as short integers) Grid cells without data (i.e. on continental crust) are assigned values of 32767. The Mercator projected image spans longitudes from 0 E to 360 E and latitudes from 72.006 N to -72.006 S. A spherical earth is used for the Mercator projection. 2 minute resolution, pixel-registered. roughness_160km_mask.15.2.nc Seafloor roughness using 160 km filter width with COBs, LIPs and seamounts masked out. A short integer netCDF formatted file. The roughness units are in mGals, multiplied by 100 (to enable storage as short integers) The geographic grid spans longitudes from 0 E to 360 E and latitudes from 72.006 N to -72.006 S. 2 minute resolution, pixel-registered. roughness_160km_mask.15.2.xyz A simple ASCII file (long, lat, 160kmRoughness). The units are in mGal with no scaling. The file spans longitudes from 0 E to 360 E and latitudes from 90 N to -90 N. 2 minute resolution. res_roughness_rate_sed_100km_mask.15.2.img Residual seafloor roughness (100 km) from seafloor spreading rate and sediment thickness, masked. A 10800 by 6336 grid of 2-byte integers = 136,857,600 bytes. Byte order is big_endian. Stored in an integer*2 format without any header or record information. The roughness units are in mGals, multiplied by 100 (to enable storage as short integers) Grid cells without data (i.e. on continental crust) are assigned values of 32767. The Mercator projected image spans longitudes from 0 E to 360 E and latitudes from 72.006 N to -72.006 S. A spherical earth is used for the Mercator projection. 2 minute resolution, pixel-registered. res_roughness_rate_sed_100km_mask.15.2.nc Residual seafloor roughness (100 km) from seafloor spreading rate and sediment thickness, masked. A short integer netCDF formatted file. The roughness units are in mGals, multiplied by 100 (to enable storage as short integers) The geographic grid spans longitudes from 0 E to 360 E and latitudes from 72.006 N to -72.006 S. 2 minute resolution, pixel-registered. res_roughness_rate_sed_100km_mask.15.2.xyz A simple ASCII file (long, lat, ResidualRoughness). The units are in mGal with no scaling. The file spans longitudes from 0 E to 360 E and latitudes from 90 N to -90 N. 2 minute resolution. pred_roughness_rate_sed_100km_mask.15.2.img Predicted seafloor roughness (100 km) based on seafloor spreading rate and sediment thickness dependence, masked. A 10800 by 6336 grid of 2-byte integers = 136,857,600 bytes. Byte order is big_endian. Stored in an integer*2 format without any header or record information. The roughness units are in mGals, multiplied by 100 (to enable storage as short integers) Grid cells without data (i.e. on continental crust) are assigned values of 32767. The Mercator projected image spans longitudes from 0 E to 360 E and latitudes from 72.006 N to -72.006 S. A spherical earth is used for the Mercator projection. 2 minute resolution, pixel-registered. pred_roughness_rate_sed_100km_mask.15.2.nc Predicted seafloor roughness (100 km) based on seafloor spreading rate and sediment thickness dependence, masked. A short integer netCDF formatted file. The roughness units are in mGals, multiplied by 100 (to enable storage as short integers) The geographic grid spans longitudes from 0 E to 360 E and latitudes from 72.006 N to -72.006 S. 2 minute resolution, pixel-registered. pred_roughness_rate_sed_100km_mask.15.2.xyz A simple ASCII file (long, lat, Predictedroughness). The units are in mGal with no scaling. The file spans longitudes from 0 E to 360 E and latitudes from 90 N to -90 N. 2 minute resolution. All grid file names follow the convention to use two numbers to indicate the file version number of the downward continued gravity grid followed by the resolution in minutes. Therefore grav_down.15.2.img corresponds to version 15 with 2 minute resolution. About .img files: The Mercator projected .img files can be accessed with Wessel and Smith's Generic Mapping Tools (GMT) program img2mercgrd: img2mercgrd roughness_100km.15.2.img -R/// -Ggrav_down.15.2_myregion.grd -T1 -S0.01 The exact usage of img2mercgrd may depend on the GMT version you use. Note that any inverse projection of the Mercator grid is unnecessary, as we provide a geographic age grid: grav_down.15.2.nc The .img files have big_endian byte format (reflecting e.g. old Macs with Motorala CPU's and Sun SPARC computers). GMT's img2grd and img2mercgrd expects the files to be in the big-endian format (as we supply) and will automatically apply a byte swap when used on little-endian hardware (e.g. based on Intel or AMD chips). If you use a program to read these files that require little-endian data input use dd (on unix machines) to byte swap the img files: dd if=orig.img of=new.img conv=swab. The .img files are pixel-registered (i.e. nodes centered on the grid boxes). This differs from gridline-registered grids where nodes are at gridline intersections. Gridline-registered grids therefore have 1 row/column more than pixel-registrated grids. About .nc files: These are netCDF files adhering to the COORDS convention and may be used with any programs that supports such files, such as the GMT programs (eg grdreformat for converting the file to another format if desired, grdmath for division of the grids by 100 and grdimage for plotting. GMT format file code is ns (short integer netCDF format). Convert short integer .nc files to default GMT grd files as follows (for example). grdmath roughness_100km.15.2.nc=ns 0.01 MUL = roughness_100km.15.2.grd=nf -V This example only works for GMT4.1 or above. For older versions of GMT, you may have to run grdreformat and grdmath separately. If you just want to convert a .nc file to xyz, run, for example grd2xyz roughness_100km.15.2.nc=ns/0.01/0 > roughness_100km.15.2.xyz The .nc files are pixel-registered. About .xyz files: These are simple ASCII files (long, lat, z). The units are in mGal with no scaling. The file spans longitudes from 0 E to 360 E and latitudes from 90 N to -90 N. 2 minute resolution. All files are compressed with gzip. Use gunzip for unzipping of the files. Any questions, please email: Joanne Whittaker jo.whittaker@sydney.edu.au Dietmar Muller dietmar.muller@sydney.edu.au