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Geophysical Investigations of Marie Byrd Land Lithospheric Evolution (GIMBLE) The PIs propose to use airborne geophysics to provide detailed geophysical mapping over the Marie Byrd Land dome of West Antarctica. They will use a Basler equipped with advanced ice penetrating radar, a magnetometer, an airborne gravimeter and laser altimeter. They will test models of Marie Byrd Land lithospheric evolution in three ways: 1) constrain bedrock topography and crustal structure of central Marie Byrd Land for the first time; 2) map subglacial geomorphology of Marie Byrd Land to constrain landscape evolution; and 3) map the distribution of subglacial volcanic centers and identify active sources. Marie Byrd Land is one of the few parts of West Antarctica whose bedrock lies above sea level; as such, it has a key role to play in the formation and decay of the West Antarctic Ice Sheet (WAIS), and thus on eustatic sea level change during the Neogene. Several lines of evidence suggest that the topography of Marie Byrd Land has changed over the course of the Cenozoic, with significant implications for the origin and evolution of the ice sheet. Two seasons were flown. ICP5 operated from Byrd Camp using Basler C-GJKB and the HiCARS2 radar in January 2013, and ICP6 operated from WAIS Divide Camp using Basler C-FMKB and the MARFA radar in late 2014, both supported by the US Antarctic Program and Kenn Borek Air. ICP6 experienced issues with data overflow on the MARFA system, with resulted in missing radar records and timing ambiguities. GIMBLE data can be found at https://www.usap-dc.org/view/project/p0000435. Dataset organization Transects are provided a P/S/T nomenclature, organized by the Project they are flying in, the acquisition System (typically named after the aircraft) and the Transect within the Project. Transects were collected in preplanned systems with the following parameters: MBL corridor (MBL/MKB##/X|Y###) rotated from the EPSG:3031 polar stereographic projection at 61.75 degrees and separated by 7.5 km in the Y direction and 5 km in the X direction, with an origin of X -579.6 km and Y -803.3 km Untargeted transit lines used the name of the expedition (ICP5|ICP6) as the project, and used the flight and the increment within the flight to name the Transect (eg (ICP6/MKB2l/F19T01a). Processing These data represent focused VHF radargrams. The data are from the HiCARS2/MARFA radar system, a 60 MHz ice penetrating radar system that has operated in several different guises over the years. HiCARS2/MARFA operates with a 1 microsecond chirp with a design bandwidth of 15 MHz, allowing for ~8 range resolution. The record rate after onboard stacking is 200 Hz. High and low gain channels are collected from antennas on each side of the aircraft, for MARFA the antennas are recorded separately. In ground processing, the data was processed using focusing SAR over a range delay of 100 nsec following Peters et al, 2007 (doi:10.1109/TGRS.2007.897416). Where data loss in ICP6 prevented the generating of focused data, simpler unfocused 'pik1' data was substituted, with 10 coherent stakes and 5 incoherent stacks. Data format These data collection represents georeferenced, time registered instrument measurements (L1B data) converted to SI units. The data format are netCDF3 files, following the formats used for NASA/AAD/UTIG's ICECAP/OIB project at NASA's NSIDC DAAC (10.5067/0I7PFBVQOGO5). Metadata fields can be accessed using the open source ncdump tool, or c, python or matlab modules. A Keyhole Metadata Language (KML) file with geolocation for all transects is also provided. See https://www.loc.gov/preservation/digital/formats/fdd/fdd000330.shtml for resources on NetCDF-3, and https://nsidc.org/data/IR2HI1B/versions/1 for a description of the similar OIB dataset. Acknowledgements This field work was supported by NSF grant 1043761 to Young; ICP5 aircraft lease costs were supported by NASA Operation Ice Bridge grant NNX11AD33G. Data processing costs were supported by a gift from the G. Unger Vetlesen Foundation and the Open Polar Radar project (NSF grant 2127606) 

Abstract. One of the key components of this research has been the mapping of Antarctic bed topography and ice thickness parameters that are crucial for modelling ice flow and hence for predicting future ice loss andthe ensuing sea level rise. Supported by the Scientific Committee on Antarctic Research (SCAR), the Bedmap3 Action Group aims not only to produce newgridded maps of ice thickness and bed topography for the internationalscientific community, but also to standardize and make available all thegeophysical survey data points used in producing the Bedmap griddedproducts. Here, we document the survey data used in the latest iteration,Bedmap3, incorporating and adding to all of the datasets previously used forBedmap1 and Bedmap2, including ice bed, surface and thickness point data from all Antarctic geophysical campaigns since the 1950s. More specifically,we describe the processes used to standardize and make these and futuresurveys and gridded datasets accessible under the Findable, Accessible, Interoperable, and Reusable (FAIR) data principles. With the goals of making the gridding process reproducible and allowing scientists to re-use the data freely for their own analysis, we introduce the new SCAR Bedmap Data Portal(https://bedmap.scar.org, last access: 1 March 2023) created to provideunprecedented open access to these important datasets through a web-map interface. We believe that this data release will be a valuable asset to Antarctic research and will greatly extend the life cycle of the data heldwithin it. Data are available from the UK Polar Data Centre: https://data.bas.ac.uk (last access: 5 May 2023​​​​​​​). See the Data availability section for the complete list of datasets. 

Key Points Using airborne radar, we trace four isochronous internal reflecting horizons over Pine Island Glacier, West Antarctica Isochrone ages calculated using the WAIS Divide ice core and a 1‐D model are 2.31–2.92, 4.72 ± 0.28, 6.94 ± 0.31, and 16.50 ± 0.79 ka We show that these isochrones are widespread across Pine Island Glacier and extend into neighboring Weddell and Amundsen Sea regions