Abstract:
This dataset is an estimate of sub ice shelf bathymetry beneath the Thwaites, Crosson and Dotson ice shelves. The output bathymetry is derived from a new compilation of gravity data collected up to the end of the 2018/19 field season. The input gravity dataset includes airborne data from Operation Ice Bridge (OIB) and the NERC/NSF International Thwaites Glacier Collaboration (ITGC), and marine gravity from the R/V Nathaniel B. Palmer cruise NBP19-02. The recovered bathymetry was constrained by swath bathymetry and onshore airborne radio-echo depth sounding data in the surrounding area. Ice shelves mask the critical link between the ocean and cryosphere systems, and hence accurate sub ice shelf bathymetry is critical for generating reliable models of future ice sheet change. Included in the data release is the input free air gravity data, constraining bathymetry/sub-ice topography, and output gravity derived bathymetry.
This work was funded by the British Antarctic Survey core program (Geology and Geophysics team), in support of the joint Natural Environment Research Council (NERC)/ National Science Foundation (NSF) International Thwaites Glacier Collaboration (ITGC).
Additional specific support came from NERC Grants: NE/S006664/1 and NE/S006419/1, and NSF Grants: NSF1842064, NSFPLR-NERC-1738942, NSFPLR-NERC-1738992 and NSFPLR-NERC-1739003.
Keywords:
Bathymetry, Gravity, ITGC, Ice shelf, Thwaites Glacier, West Antarctica
Jordan, T., Porter, D., Tinto, K., Millan, R., Muto, A., Hogan, K., Larter, R., Graham, A., Paden, J., & Robinson, C. (2020). Gravity-derived bathymetry for the Thwaites, Crosson and Dotson ice shelves (2009-2019) (Version 1.0) [Data set]. UK Polar Data Centre, Natural Environment Research Council, UK Research & Innovation. https://doi.org/10.5285/7803de8b-8a74-466b-888e-e8c737bf21ce
| Use Constraints: | This data is covered by a UK Open Government Licence (http://www.nationalarchives.gov.uk/doc/open-government-licence/version/3/) Further by downloading this data the user acknowledges that they agree with the NERC data policy (http://www.nerc.ac.uk/research/sites/data/policy.asp), and the following conditions: 1. To cite the data in any publication as follows: Jordan, T., Porter, D., Tinto, K., Millan, R., Muto, A., Hogan, K., Larter, R., Graham, A., Paden, J., & Robinson, C. (2020). Gravity-derived bathymetry for the Thwaites, Crosson and Dotson ice shelves (2009-2019) (Version 1.0) [Data set]. UK Polar Data Centre, Natural Environment Research Council, UK Research & Innovation. https://doi.org/10.5285/7803DE8B-8A74-466B-888E-E8C737BF21CE 2. The user recognizes the limitations of data. Use of the data is at the users' own risk, and there is no warranty as to the quality or accuracy of any data, or the fitness of the data for your intended use. The data are not necessarily fully quality assured and cannot be expected to be free from measurement uncertainty, systematic biases, or errors of interpretation or analysis, and may include inaccuracies in error margins quoted with the data. |
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| Creation Date: | 2020-05-21 |
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| Dataset Progress: | Complete |
| Dataset Language: | English |
| ISO Topic Categories: |
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| Parameters: |
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| Personnel: | |
| Name | PDC BAS |
| Role(s) | Metadata Author |
| Organisation | British Antarctic Survey |
| Name | Dr Tom A Jordan |
| Role(s) | Investigator |
| Organisation | British Antarctic Survey |
| Name | Dr David Porter |
| Role(s) | Investigator |
| Organisation | Lamont Doherty Earth Observatory |
| Name | Dr Kirsty Tinto |
| Role(s) | Investigator |
| Organisation | Lamont Doherty Earth Observatory |
| Name | Dr Romain Millan |
| Role(s) | Investigator |
| Organisation | Universite Grenoble Alpes, CNRS |
| Name | Dr Atsuhiro Muto |
| Role(s) | Investigator |
| Organisation | Dept. of Earth and Environmental Science, Temple University |
| Name | Dr Kelly Hogan |
| Role(s) | Investigator |
| Organisation | British Antarctic Survey |
| Name | Dr Robert D Larter |
| Role(s) | Investigator |
| Organisation | British Antarctic Survey |
| Name | Dr Alastair G C Graham |
| Role(s) | Investigator |
| Organisation | College of Marine Science, University of South Florida |
| Name | Dr John D Paden |
| Role(s) | Investigator |
| Organisation | Center for Remote Sensing of Ice Sheets (CReSIS), The University of Kansas |
| Name | Mr Carl Robinson |
| Role(s) | Investigator |
| Organisation | British Antarctic Survey |
| Parent Dataset: | N/A |
| Reference: | Main reference: Jordan, T. A., D. Porter, K. Tinto, R. Millan, A. Muto, K. Hogan, R. D. Larter, A. G. C. Graham and J. D. Paden (2020). "New gravity-derived bathymetry for the Thwaites, Crosson and Dotson ice shelves revealing two ice shelf populations." The Cryosphere Discuss. 2020: 1-20. https://doi.org/10.5194/tc-2019-294 Additional references: Becker, D., Nielsen, J. E., Ayres-Sampaio, D., Forsberg, R., Becker, M., and Bastos, L.: Drift reduction in strapdown airborne gravimetry using a simple thermal correction, Journal of Geodesy, 89, 1133-1144, 2015. Cochran, J. R. and Bell, R. E.: IceBridge Sander AIRGrav L1B Geolocated Free Air Gravity Anomalies., Boulder, Colorado USA: NASA DAAC at the National Snow and Ice Data Center., 2010, updated 2018. Forste, C., Schmidt, R., Stubenvoll, R., Flechtner, F., Meyer, U., Konig, R., Neumayer, H., Biancale, R., Lemoine, J. M., Bruinsma, S., Loyer, S., Barthelmes, F., and Esselborn, S.: The Geo-ForschungsZentrum Potsdam/Groupe de Recherche de Geodesie Spatiale satellite-only and combined gravity field models:EIGEN-GL04S1 and EIGEN-GL04C, J. Geodesy, 82, 331-346,doi:310.1007/s00190-00007-00183-00198, 02008, 2008. 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, 13, 545-556, 2019. Hogan, K. A., Larter, R. D., Graham, A. G. C., Arthern, R., Kirkham, J. D., Totten Minzoni, R., Jordan, T. A., Clark, R., Fitzgerald, V., Anderson, J. B., Hillenbrand, C. D., Nitsche, F. O., Simkins, L., Smith, J. A., Gohl, K., Arndt, J. E., Hong, J., and Wellner, J.: Revealing the former bed of Thwaites Glacier using sea-floor bathymetry, The Cryosphere Discuss., 2020, 1-36, 2020. Howat, I. M., Porter, C., Smith, B. E., Noh, M. J., and Morin, P.: The Reference Elevation Model of Antarctica, The Cryosphere, 13, 665-674, 2019. Jordan, T. A., Porter, D., Tinto, K., Millan, R., Muto, A., Hogan, K., Larter, R. D., Graham, A. G. C., and Paden, J. D.: New gravity-derived bathymetry for the Thwaites, Crosson and Dotson ice shelves revealing two ice shelf populations, The Cryosphere Discuss., 2020, 1-20, 2020a. Jordan, T. A., Robinson, C., and Porter, D.: Processed line aeromagnetic data over the Thwaites glacier region (2018/19 season). Polar Data Centre,Natural Environment Research Council,UK Research & Innovation, 2020b. Jordan, T. A., Robinson, C., Porter, D., Locke, C., and Tinto, K.: Processed line aerogravity data over the Thwaites Glacier region (2018/19 season). UK Polar Data Centre, Natural Environment Research Council, UK Research & Innovation., 2020c. Milillo, P., Rignot, E., Rizzoli, P., Scheuchl, B., Mouginot, J., Bueso-Bello, J., and Prats-Iraola, P.: Heterogeneous retreat and ice melt of Thwaites Glacier, West Antarctica, Science Advances, 5, eaau3433, 2019. Paden, J., Li, J., Leuschen, C., Rodriguez-Morales, F., and Hale, R.: IceBridge MCoRDS L2 Ice Thickness, Version 1., NASA (Ed.), NASA National Snow and Ice Data Center Distributed Active Archive Center., Boulder, Colorado USA, 2010, updated 2018. Rignot, E., Mouginot, J., Morlighem, M., Seroussi, H., and Scheuchl, B.: Widespread, rapid grounding line retreat of Pine Island, Thwaites, Smith, and Kohler glaciers,West Antarctica, from 1992 to 2011, Geophysical Research Letters, 41, 3502-3409, DOI: 3510.1002/2014GL060140, 2014. Tinto, K. J. and Bell, R. E.: Progressive unpinning of Thwaites Glacier from newly identified offshore ridge: Constraints from aerogravity, Geophysical Research Letters, 38, DOI: 10.1029/2011GL049026, 2011. von Frese, R. R. B., Hinze, W. J., Braile, L. W., and Luca, A. J.: Spherical earth gravity and magnetic anomaly modeling by Gauss- Legendre quadrature integration, Journal of Geophysics, 49, 234-242, 1981. Wei, M. and Schwarz, K. P.: Flight test results from a strapdown airborne gravity system, Journal of Geodesy, 72, 323-332, 1998. |
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| Quality: | Comparison with an independent swath bathymetric dataset indicates errors in the gravity derived bathymetry have a standard deviation of ~100 m, which we take to be representative of the error for this dataset. However, two important notes are: Firstly, away from constraining swath or radar data un-resolved geological features could lead to larger errors. Secondly, the gravity data only resolves features with a wavelength of 5 km or more. Smaller features may be present, but will not be reliably imaged. | |
| Lineage: | Input gravity data is from Operation Ice Bridge (OIB) and the ITGC 2018/19 airborne campaign, together with marine gravity data from cruise NBP19-02. The OIB free-air gravity data has an error of ~1.67 mGal in this region and resolves anomalies with a ~10 km full wavelength (Cochran and Bell, 2010, updated 2018; Tinto and Bell, 2011). The ITGC campaign data (Jordan et al., 2020c) utilised a 'strapdown' gravity approach based around an iMar Inertial Navigation System (INS) (Becker et al., 2015; Wei and Schwarz, 1998), resulting in data with an internal error from crossover analysis of 1.56 mGal and resolving wavelengths down to ~5 km. Airborne data were restricted to lines flown at <1500 m above the surface with over 95% of the data collected at 450 m +/-200 m above the surface. Upward and downward continuation of the gravity data to a common altitude was therefore neglected as continuation by ~200 m will have little impact on the amplitude of the gravity anomalies (~1 mGal) given the ~1000 m range to the key bathymetric sources. Marine gravity data from cruise NBP19-02 matched the pattern of the airborne anomalies, but was offset by 7.14 mGal above the airborne data. This shift of 7.14 mGal was removed from the marine line data as a single uniform (DC) value. All line data were then merged into a single database, interpolated onto a 1 km mesh raster and filtered with a 5 km low pass filter removing residual line to line noise. The constraining topographic observations onshore were taken from OIB line radar data (Paden et al., 2010, updated 2018), augmented with new depth sounding radar collected along with the gravity data during the ITGC campaign. This new bed elevation data was collected using a 600-900 MHz accumulation radar provided by the Center for Remote Sensing of Ice Sheets (CReSIS). Bed elevations were picked from SAR processed radargrams in a semi-automated fashion. Visual inspection revealed a few incorrect onshore bed picks in the OIB dataset on Bear Island, which gave bed elevations above the highly accurate REMA surface digital elevation model (DEM) (Howat et al., 2019). These points were deleted from the integrated line bed elevation dataset. The line bed elevation data were corrected to the GL04c Geoid (Forste et al., 2008), and the data interpolated onto a 1 km mesh raster. This gridded dataset was carefully masked to remove regions which are now covered by the floating ice shelf based on the most up to date grounding lines (Milillo et al., 2019; Rignot et al., 2014). Bed elevation values over local sub-shelf pinning points were also excluded. Beyond the ice shelves we took the values constrained by a new compilation of shipborne multibeam swath bathymetric data (Hogan et al., 2020), which was down sampled to 1 km mesh raster for this study. To calculate the sub-ice-shelf bathymetry we applied an updated version of the two-step topographic shift method (Hodgson et al., 2019). In the first step the "initial bathymetric estimate" is calculated by converting the free-air gravity anomalies to equivalent variation in topography using an iterative forward modelling approach based on a Gauss-Legendre Quadrature gravity model of the theoretical bathymetric surface. An observation altitude of 500 m was assumed, and a density contrast of -1642 kgm-3 was imposed, equivalent to the contrast between water (1028 kgm-3) and rock (2670 kgm-3). To initiate the gravity inversion, we converted the free-air anomaly to equivalent topography using the Bouguer slab formula. The bathymetric surface was then iteratively adjusted to reduce the model/observed residual. After two stages of iteration the modelled and observed gravity field had converged to better than +/- 1 mGal across most of the survey area. Topography predicted to be above the observation surface was truncated, and the model did not converge in these regions. In the second step, the algorithm corrects for differences between the initial bathymetric estimate and topographic observations. The calculated difference between the observed and initial bathymetric estimate reflects an integration of all geological factors, including long wavelength regional variations such as crustal thickness and more local factors such as sedimentary basins or intrusions. We assume that the calculated geologically-derived errors vary smoothly away from the constraining points and interpolate the difference field across the study area. In regions with control data the difference grid was taken directly from the difference values. Away from the control data the difference grid was interpolated using a tensioned spline (T=0.25) after a 5 km pre-filter was applied to the difference values. The transition between these two regions was blended using a weighted mean varying from zero to one over a 5km Gaussian smoothed transition zone around the observed data. The blended difference grid was subtracted from the initial bathymetric estimate to produce the final topographic estimate. |
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| Temporal Coverage: | |
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| Start Date | 2009-01-01 |
| End Date | 2019-12-31 |
| Spatial Coverage: | |
| Latitude | |
| Southernmost | -76.37 |
| Northernmost | -73.452 |
| Longitude | |
| Westernmost | -113.097 |
| Easternmost | -105.215 |
| Altitude | |
| Min Altitude | N/A |
| Max Altitude | N/A |
| Depth | |
| Min Depth | N/A |
| Max Depth | N/A |
| Data Resolution: | |
| Latitude Resolution | N/A |
| Longitude Resolution | N/A |
| Horizontal Resolution Range | 1 km - < 10 km or approximately .01 degree - < .09 degree |
| Vertical Resolution | N/A |
| Vertical Resolution Range | N/A |
| Temporal Resolution | N/A |
| Temporal Resolution Range | N/A |
| Location: | |
| Location | Antarctica |
| Detailed Location | Thwaites Glacier |
| Location | Antarctica |
| Detailed Location | Amundsen Sea |
| Location | Antarctica |
| Detailed Location | Crosson Ice Shelf |
| Location | Antarctica |
| Detailed Location | Dotson Ice Shelf |
| Data Collection: | Input data compilations were generated and quality checked in Geosoft Oasis Montage software package. Subsequent data processing and recovery of bathymetry used a Gauss-Legendre Quadrature gravity modelling programme (von Frese et al., 1981) coupled with basic Generic Mapping Tools (GMT V5) scripts implemented in a Linux environment. |
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| Distribution: | |
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| Distribution Media | Online Internet (HTTP) |
| Distribution Size | 1.8 MB |
| Distribution Format | netCDF |
| Fees | N/A |
| Data Storage: | 3 files in surfer V6 raster or NetCDF format, ~300 kb each, with a raster resolution of 1000 m. All files are in projected polar stereographic meters with a standard parallel of -71. Topography is referenced to the GL04c Geoid. Gravity is referenced to the WGS1984 ellipsoid. Jordan_et_al_2020_Thw_topo_from_grav - Final gravity derived bathymetric grid (m) Jordan_et_al_2020_Thw_FAA_compilation - Input free air gravity compilation (mGal) Jordan_et_al_2020_Thw_topo_control - Input radar/swath topographic control (m) |