Abstract:
The geology underlying Thwaites Glacier plays a critical role in mediating ice flow in this region yet is extremely poorly known. Using new compilations of airborne radar, magnetic and gravity data, supported by published geological evidence, we have interpreted the subglacial geology of the Thwaites Glacier region. Here we provide the new data compilations, results of 3D inversions and vector components defining the lithological units on our new geological sketch map.
British Antarctic Survey (BAS) National Capability contribution to the International Thwaites Glacier Collaboration (ITGC) (TJ), NERC Grant NE/S006621/1 (Geophysical Habitats of Subglacial Thwaites (Ghost)) (BK), Antarctic Science Collaboration Initiative program (Australian Government) (ST), European Space Agency (ESA) 4D Antarctica project (FF).
Keywords:
Thwaites glacier, basal roughness, bed elevation, geological map, gravity, magnetic
Jordan, T., Thompson, S., Kulessa, B., & Ferraccioli, F. (2023). Thwaites Glacier geological map and associated geophysical information. (Version 1.0) [Data set]. NERC EDS UK Polar Data Centre. https://doi.org/10.5285/189823ed-6a14-4eba-87fb-38ba3e5e30fb
| Access Constraints: | None |
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| Use Constraints: | This data is supplied under Open Government Licence v3 http://www.nationalarchives.gov.uk/doc/open-government-licence/version/3/. Use the following citation: Jordan, T.A., Thompson, S., Kulessa, B., & Ferraccioli, F. (2023). Thwaites Glacier geological map and associated geophysical information. (Version 1.0) [Data set]. NERC EDS UK Polar Data Centre. https://doi.org/10.5285/189823ED-6A14-4EBA-87FB-38BA3E5E30FB |
| Creation Date: | 2023-03-17 |
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| Dataset Progress: | Complete |
| Dataset Language: | English |
| ISO Topic Categories: |
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| Parameters: |
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| Personnel: | |
| Name | UK Polar Data Centre |
| Role(s) | Metadata Author |
| Organisation | British Antarctic Survey |
| Name | Dr Tom A Jordan |
| Role(s) | Investigator |
| Organisation | British Antarctic Survey |
| Name | Sarah Thompson |
| Role(s) | Investigator |
| Name | Bernd Kulessa |
| Role(s) | Investigator |
| Organisation | Swansea University |
| Name | Dr Fausto Ferraccioli |
| Role(s) | Investigator |
| Organisation | British Antarctic Survey |
| Parent Dataset: | N/A |
| Reference: | T.A. Jordan, S. Thompson, B. Kulessa and F. Ferraccioli. Geological sketch map and implications for ice flow of Thwaites Glacier, West Antarctica, from integrated aerogeophysical observations. Sci. Adv.9,eadf2639(2023). DOI:10.1126/sciadv.adf2639 Diehl, T.M., Holt, J.W., Blankenship, D.D., Young, D.A., Jordan, T.A., Ferraccioli, F., 2008. First Airborne Gravity Results over the Thwaites Glacier Catchment, West Antarctica. Geochemistry, Geophysics, Geosystems 9, doi:10.1029/2007GC001878. Elllis, R.G., de Wet, B., Macleod, I.N., 2012. Inversion of Magnetic Data from Remanent and Induced Sources. ASEG Extended Abstracts 2012, 1-4. Fretwell, P., Pritchard, H.D., Vaughan, D.G., Bamber, J., Barrand, N., Bell, R., Bianchi, C., Bingham, R., Blankenship, D., Casassa, G., Callens, D., Conway, H., Cook, A.J., Corr, H.F.J., Damaske, D., Damm, V., Ferraccioli, F., Forsberg, R., Fujita, S., Gogineni, P., Griggs, J.A., Hindmarsh, R., Holmlund, P., Holt, J.W., Jacobel, R.W., Jenkins, A., Jokat, W., Jordan, T.A., King, E.C., Kohler, J., Krabill, W., Riger-Kusk, R., Langley, K.A., Leitchenkov, G., Leuschen, C., Luyendyk, B.P., Matsuoka, K., Nogi, Y., Nost, O.A., Popov, S., Rignot, E., Rippin, D.M., Riviera, A., Roberts, J., Ross, N., Siegert, M.J., Smith, A.M., Steinhage, D., Studinger, M., Sun, B., Tinto, B.K., Welch, B.C., Young, D.A., Xiangbin, C., Zirizzotti, A., 2013. Bedmap2: improved ice bed, surface and thickness datasets for Antarctica. The Cryosphere 7. Golynsky, A.V., Ferraccioli, F., Hong, J.K., Golynsky, D.A., Frese, R.R.B., Young, D.A., Blankenship, D.D., Holt, J.W., Ivanov, S.V., Kiselev, A.V., Masolov, V.N., Eagles, G., Gohl, K., Jokat, W., Damaske, D., Finn, C., Aitken, A., Bell, R.E., Armadillo, E., Jordan, T.A., Greenbaum, J.S., Bozzo, E., Caneva, G., Forsberg, R., Ghidella, M., Galindo-Zaldivar, J., Bohoyo, F., Martos, Y.M., Nogi, Y., Quartini, E., Kim, H.R., Roberts, J.L., 2018. New Magnetic Anomaly Map of the Antarctic. Geophysical Research Letters 45, 6437-6449. Holt, J.W., Blankenship, D.D., Morse, D.L., Young, D.A., Peters, M.E., Kempf, S.D., Richter, T.G., Vaughan, A.P.M., Corr, H., 2006. New Boundary Conditions for the West Antarctic Ice Sheet: Subglacial Topography of the Thwaites and Smith Glacier Catchments. Geophysical Research Letters 33, doi:10.1029/2005GL025561. Jordan, T., Robinson, C., Porter, D., 2020a. Processed line aeromagnetic data over the Thwaites glacier region (2018/19 season). Natural Environment Research Council, UK Research & Innovation, UK Polar Data Centre. Jordan, T.A., Ferraccioli, F., Vaughan, D.G., Holt, J.W., Corr, H., Blankenship, D.D., Diehl, T.M., 2010. Aerogravity evidence for major crustal thinning under the Pine Island Glacier region (West Antarctica). Geological Society Of America Bulletin 122, 714-726, doi: 710.1130/B26417.26411. Jordan, T.A., Porter, D., Tinto, K., Millan, R., Muto, A., Hogan, K., Larter, R.D., Graham, A.G.C., Paden, J.D., 2020b. New gravity-derived bathymetry for the Thwaites, Crosson, and Dotson ice shelves revealing two ice shelf populations. The Cryosphere 14, 2869-2882. Jordan, T.A., Robinson, C., 2021a. Processed airborne radio-echo sounding data for the Thwaites Glacier 2019 survey, West Antarctica (2019/2020) (Version 1.0) NERC EDS UK Polar Data Centre. Jordan, T.A., Robinson, C., 2021b. Processed line aerogravity data over the Thwaites Glacier region (2019/20 season) (Version 1.0). NERC EDS, UK Polar Data Centre. Jordan, T.A., Robinson, C., 2021c. Processed line aeromagnetic data over the Thwaites glacier region (2019/2020 season) (Version 1.0) NERC EDS UK Polar Data Centre. Jordan, T.A., Robinson, C., Porter, D., Locke, C., Tinto, K., 2020c. Processed line aerogravity data over the Thwaites Glacier region (2018/19 season). Natural Environment Research Council, UK Research & Innovation, UK Polar Data Centre. Paden, J., Li, J., Leuschen, C., Rodriguez-Morales, F., Hale, R., 2010, updated 2021. IceBridge MCoRDS L2 Ice Thickness, Version 1., in: NASA (Ed.). NASA National Snow and Ice Data Center Distributed Active Archive Center., Boulder, Colorado USA. Tinto, K., Bell, R., Cochran, J.R., 2010, updated 2019. IceBridge Sander AIRGrav L1B Geolocated Free Air Gravity Anomalies, Version 1. NASA National Snow and Ice Data Center Distributed Active Archive Center., Boulder, Colorado USA. Vaughan, D.G., Corr, H., Ferraccioli, F., Frearson, N., O'Hare, A., Mach, D., Holt, J.W., 2006. New boundary conditions for the West Antarctic Ice Sheet: subglacial topography beneath Pine Island Glacier. Geophysical Research Letters 33, doi:10.1029/2005GL025588. |
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| Quality: | See Lineage for data quality of data compilations. | |
| Lineage: | This dataset includes three components: Input geophysical compilations, inversion results and interpreted geological boundaries. Details of the data compilation, inversion and basic geological interpretation are presented here. This dataset is the companion to the following paper Jordan et al., (in prep) Geological sketch map and implications for ice flow of Thwaites Glacier, West Antarctica, from integrated aerogeophysical observations, Science Advances., which contains full details of the geological interpretation and should be cited when this dataset is used. Input geophysical compilations: This dataset includes compilations of aerogeophysical data collected across the Thwaites Glacier region of West Antarctica over the past several decades. Surveys used include: AGASEA and BBAS which collected radar, magnetic and gravity data (Diehl et al., 2008; Holt et al., 2006; Jordan et al., 2010; Vaughan et al., 2006). NASA Operation Ice Bridge (OIB) which collected radar and gravity data (Paden et al., 2010, updated 2021; Tinto et al., 2010, updated 2019). The International Thwaites Glacier Collaboration (ITGC) which collected radar, magnetic and gravity data (Jordan et al., 2020a; Jordan and Robinson, 2021a; Jordan and Robinson, 2021b, c; Jordan et al., 2020c). Additional magnetic data was taken from the ADMAP2 compilation (Golynsky et al., 2018). The presented bed-elevation dataset was created from the radar-derived bed elevation picks from the surveys noted above interpolated onto a 2 km mesh raster, padded with gravity derived bathymetry beneath adjacent ice shelves (Jordan et al., 2020b) and BEDMAP2 in more distal areas (Fretwell et al., 2013). All topographic data were corrected to an ellipsoidal reference frame prior to integration. The presented subglacial topographic roughness grid was created from the along track standard deviation of the picked radar bed elevation within a 1 km wide moving window, interpolated onto a 2 km mesh raster. Areas where the bed was poorly resolved, defined as having along-line data gaps more than 50 percent of the analysis window (500 m), were excluded from the gridded product. The presented aeromagnetic compilations were created from line data available through the ADMAP2 project (Golynsky et al., 2018) and incorporating new ITGC data (Jordan et al., 2020a; Jordan and Robinson, 2021c). Data were upward/downward continued to 500 m above the ice/sea surface to place all observations on a common surface prior to reapplication of statistical levelling. After levelling and continuation crossover errors were 18.79 nT. An alternative continuation to 2500 m above the underlying rock was also carried out to give a view of the data with a consistent distance to the closest possible source. The two versions of the final continued line data were interpolated onto a 1 km mesh, and subject to a 3 pass Hanning filter. The presented free air gravity anomalies are from the surveys noted above after detailed data editing and levelling. Note that strictly the presented gravity compilation reflects ''gravity disturbances'', rather than anomalies as they are referenced to the ellipsoid. The line data from ITGC, AGASEA and BBAS were statistically levelled and edited using the OIB dataset as a reference after high altitude (more than 1500 m above ice surface) OIB survey lines had been removed. The line free air data was continued to a uniform level of 2500 m. After levelling and continuation the free air gravity data had an internal crossover error of 2.94 mGal. The line data were interpolated onto a 2 km raster mesh using a minimum curvature method. The presented Bouguer gravity anomaly includes correction for a full 3D model of the gravity effect of the topography, bathymetry and ice, based on the topographic compilation noted above and ice surface elevations taken from the BEDMAP2 (Fretwell et al., 2013). An observation altitude of 2500 m was used, as it is above the surface elevation across most of the study area. Where topography is above 2500 m (for example Mt Takahea), the presented anomalies cannot be interpreted. We also note that the Bouguer correction is not robust over the floating ice shelves, as the bathymetry is derived from gravity data. The gravity effect of four layers with fixed densities were considered. Ice (915 kgm^-3), water (1028 kgm^-3), topography above sea level (2670 kgm^-3) and topography below sea level (-2670 kgm^-3). Summation of the gravity effect of these four layers provided the Bouguer correction which was sampled onto the flight lines and subtracted from the levelled and continued free air anomaly. The resulting Bouguer anomaly was interpolated onto a 2 km mesh raster. The presented Bouguer gravity anomaly grid was filtered with 3 passes of a 9x9 Hanning filter to minimise residual line to line noise. The presented Airy isostatic anomaly was calculated by subtracting a gravity model for the isostatic compensation of the surface topography and ice load from the Bouguer anomaly. The size and gravity effect of the compensating low density crustal root was calculated using a fast Fourier transform routine within the GMT software package, assuming a uniform crustal density of 2670 kgm^-3, a mantle density of 3330 kgm^-3and a reference Moho compensation depth of 29 km. Inversion results: The 3D inversion used the VOXI 3D inversion module of the Geosoft software suite (Elllis et al., 2012) to estimate the sub-surface distribution of susceptibility or density values for a sub-set of the wider survey area. For both the magnetic and gravity inversion cells within the ice column were fixed to zero susceptibility or density contrast respectively, ensuring recovered geophysical sources were below the ice-bed interface. The recovered subsurface distribution of susceptibility or density provides a model with a good fit to the observed magnetic or gravity data, within the constraints of the inversion setup. Given the lack of independent constraints, these results should be considered as a first-order estimate of sub-surface properties, not a definitive solution. The input field for the 3D susceptibility inversion was the magnetic anomaly continued to 500 m above the ice surface, with a mean and best fit linear trend removed. Susceptibility values were constrained to be more than 0 and less than 75x10^-3 SI. The recovered source properties implicitly include the impact of any magnetic remanence and are therefore apparent susceptibility values. An active magnetic model volume extending from 0 km to -10 km elevation, with a mesh resolution of 1.25/1.25/0.5 km was used, with an expansion ratio of 1.5 with depth. Five padding cells were included below the active model. An additional linear weighting scheme favouring higher susceptibility values at shallower depths was also imposed. When inverting for density the residual Airy isostatic gravity anomaly, with a mean and best fit linear trend removed, was considered as the input data. Density was constrained to lie between +/-1 gcm^-3, and recovered values reflect a density contrast, rather than absolute density values. An active model volume extending from 2.5 km to -12 km elevation, with a mesh resolution of 2.5/2.5/1.25 km was used, with an expansion ratio of 1.5 with depth. Five padding cells below the active model were included. Geological sketch map: Utilising the datasets outlined above and other regional geological information, we identify and interpret four distinct lithological units in the Thwaites Glacier region: Sedimentary basins, Mafic intrusions, Felsic granitoids and Intermediate igneous rocks. These units are generally spatially distinct, but in some cases overlap. The sedimentary basins and mafic intrusions are interpreted to most likely be Late Cretaceous in age. The age of the other units is not known. Our basic assumption is that the areas between the geophysically characterised lithologies contain the regional low grade metasedimentary basement, known as the Swanson Formation, or higher metamorphic grade equivalents, although other lithological units are possible. |
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| Spatial Coverage: | |
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| Latitude | |
| Southernmost | -75.48 |
| Northernmost | -75.48 |
| Longitude | |
| Westernmost | -107.09 |
| Easternmost | -107.09 |
| Altitude | |
| Min Altitude | N/A |
| Max Altitude | N/A |
| Depth | |
| Min Depth | N/A |
| Max Depth | N/A |
| Data Storage: | All datasets are provided as ASCII to aid interoperability between software systems. Input geophysical compilations are collected as a single compressed zip archive. Within this each of the seven datasets is presented as ASCII comma separated tables with the following information: Lon, Longitude DDD.DDDDDDDD Lat, Latitude DD.DDDDDDDD X, Projected Polar Stereographic meters (x), true scale -71, meridian 0 longitude. Y, Projected Polar Stereographic meters (y), true scale -71, meridian 0 longitude. Data_value Geophysical parameter. asterix = no valid data. The seven input datasets are: 1/ Subglacial topography and offshore bathymetry (m - ellipsoidal reference), 2/ Basal roughness (m standard deviation of bed elevation within a 1 km moving window). 3/ Free Air gravity (mGal - ellipsoidal reference), 4/ Bouguer gravity anomaly (mGal), 5/ Airy isostatic gravity residual anomaly (mGal), 6/ Magnetic anomaly at 500 m above the ice/sea surface (nT). 7/ Magnetic anomaly at 2500 m above the bed topography/bathymetry (nT). Inversion results are compiled into a single zip archive containing two datasets: recovered susceptibility and recovered density. The inversion output is on a regular horizontal mesh, with a variable vertical mesh with an expansion ratio of 1.5 with depth. The presented files are in ASCII comma separated format with the following information: X, Projected Polar Stereographic meters (x), true scale -71, meridian 0 longitude. Y, Projected Polar Stereographic meters (y), true scale -71, meridian 0 longitude. Z, Ellipsoidal elevation in meters, positive upwards. Data_value Inversion output as either density (gmc^-3) or magnetic susceptibility (SI). Geological sketch map includes a zip compressed ascii comma separated table with the coordinates for all the geological boundaries identified in this study. The table includes the following fields: Line, Numerical flag for each distinct geological body. Type, Flag for body lithology 1 = mafic, 2 = granitic, 3 = intermediate, 4 = sedimentary basin Lon, Longitude DDD.DDDDDDD Lat, Latitude DD.DDDDDDDD X, Projected Polar Stereographic meters (x), true scale -71, meridian 0 longitude. Y, Projected Polar Stereographic meters (x), true scale -71, meridian 0 longitude. |
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