Seismic reflection soundings of ice thickness and seabed depth were acquired on the Larsen C Ice Shelf in order to test a sub-shelf bathymetry model derived from the inversion of IceBridge gravity data. A series of lines were collected, from the Churchill Peninsula in the north to the Joerg Peninsula in the south, and also towards the ice front. Sites were selected using the bathymetry model derived from the inversion of free-air gravity data to indicate key regions where sub-shelf oceanic circulation may be affected by ice draft and sub-shelf cavity thickness. The seismic velocity profile in the upper 100 m of firn and ice was derived from shallow refraction surveys at a number of locations. Seismic velocities in the water column were derived from previous in situ measurements. Uncertainties in ice and water cavity thickness are in general < 10 m. Compared with the seismic measurements, the root-mean-square error in the gravimetrically derived bathymetry at the seismic sites is 162 m. The seismic profiles prove the non-existence of several bathymetric features that are indicated in the gravity inversion model, significantly modifying the expected oceanic circulation beneath the ice shelf. Similar features have previously been shown to be highly significant in affecting basal melt rates predicted by ocean models. The discrepancies between the gravity inversion results and the seismic bathymetry are attributed to the assumption of uniform geology inherent in the gravity inversion process and also the sparsity of IceBridge flight lines. Results indicate that care must be taken when using bathymetry models derived by the inversion of free-air gravity anomalies. The bathymetry results presented here will be used to improve existing sub-ice shelf ocean circulation models.
The South Georgia Bathymetric Dataset (SGBD) is a continuous grid at 150m resolution of the sea floor around South Georgia. Available in a number of formats and projections, the dataset has been compiled from eleven different data sources.
Ship underway data collected aboard the James Clark Ross during cruise no JR158 in 2007. Includes data from navigation and vessel-mounted ADCP (Acoustic Doppler Current Profilers). On the ship the position and observed data were interpolated to five-second records to merge the navigation with the underway data. These one-minute averages are averages over 12 of the interpolated points.
This gridded dataset contains the revised bathymetry model beneath the Brunt Ice Shelf and Stancomb-Wills Glacier Tongue, Antarctica, The revised bathymetric model integrates existing direct bathymetry observations and free air gravity anomaly data to provide the best possible estimate of sub-ice shelf bathymetry. The input direct bathymetric/topographic observations, observation locations, and the input free air compilation are also available as additional separate grid files. All files are provided in NetCDF format in Antarctic Polar Stereographic (EPSG:3031) projection with a horizontal resolution of 2km. The output bathymetry model (Final_adjusted_topography.nc), input topographic observations (Topographic_value_grid.nc) and input topographic observation coverage (Topographic_observation_coverage.nc) have elevation values of metres, positive upwards. The input free air gravity anomaly grid (Brunt_FAA_compilation_grid.nc) has values of mGal. The bathymetric model was produced for the paper of Hodgson et al., (2019) investigating the past and future dynamics of the Brunt Ice Shelf. The publication reference is; Hodgson, D. A., Jordan, T. A., De Rydt, J., Fretwell, P. T., Seddon, S. A., Becker, D., Hogan, K. A., Smith, A. M., and Vaughan, D. G.: Past and future dynamics of the Brunt Ice Shelf from seabed bathymetry and ice shelf geometry, The Cryosphere Discuss., https://doi.org/10.5194/tc-2018-206, in review, 2018.