EGU2020-1331, updated on 12 Jun 2020
https://doi.org/10.5194/egusphere-egu2020-1331
EGU General Assembly 2020
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

Thwaites and Dotson Ice Shelves: Field Site Selection and Early Results of Field Measurements

Erin Pettit1, Atsu Muto2, Christian Wild1, Karen Alley3, Ted Scambos4, Bruce Wallin5, Martin Truffer6, and Dale Pomraning6
Erin Pettit et al.
  • 1Oregon State University, College of Earth, Ocean, and Atmospheric Science, Corvallis, Oregon, USA (pettiter@oregonstate.edu)
  • 2Temple University, Department of Earth and Environmental Sciences, Philadelphia, Pennsylvania, USA (amuto@temple.edu)
  • 3College of Wooster, Department of Geology, Wooster, Ohio, USA (kalley@wooster.edu)
  • 4University of Colorado Boulder, Cooperative Institute for Research in Earth Sciences, Boulder Colorado, USA (tascambos@colorado.edu)
  • 5University of Colorado Boulder, National Snow and Ice Data Center, Boulder Colorado, USA (bruce.walling@nsidc.org)
  • 6University of Alaska Fairbanks, Geophysical Institute, Fairbanks, Alaska, USA (mtruffer2@alaska.edu)

As part of the International Thwaites Glacier Collaboration (ITGC) field activity in West Antarctica for the 2019-2020 season, the Thwaites-Amundsen Regional Survey and Network (TARSAN) team drilled boreholes using hot water, deployed long-term instruments, and gathered several ground-based geophysical data sets to assess the ice-shelf stability and evolution.

The Thwaites Eastern Ice Shelf is an important buttress for a broad (25 km) section of Thwaites Glacier outflow and is restrained at present by a few pinning points at the northwestern edge of the shelf. The grounding line of this buttress has retreated within the last 5 years indicating instability. Recent imagery shows major new rifting and shearing within the ice shelf.

In the Dotson-Crosson Ice Shelf (a single ice shelf with a rapidly evolving central region that has thinned and ungrounded over the past 80 years), satellite data show significant ice flow speed and direction changes, as well as retreating grounding lines where tributary glaciers start to float and where ice flows over and around isolated bedrock pinning points. A complex geometry of deep seafloor troughs underlie the central ice-shelf area which lies at the convergence of the two major troughs that extend to the continental shelf edge at two widely separated locations (roughly 103°W and 117°W longitude along the continental shelf break).

We surveyed the central Thwaites Eastern Ice Shelf (‘Cavity Camp’, 75.05°S, 105.58°W) and central Dotson-Crosson Ice Shelf (`Upper Dotson’, 74.87°S, 112.20°W) to the extent possible considering site safety and scientific interest. Cavity Camp is located approximately 17 km down-flow of the 2011 Thwaites Glacier grounding line. Ground-penetrating radar data show the ice thickness near Cavity Camp to be 300m, which is ~200m thinner than in 2007 estimated from hydrostatic assumption using altimetry analysis by other researchers. The seafloor below Cavity Camp is 816m, based on pressure from a CTD profile (a ~540 m water column and ~40m of firn).   

Across the central Dotson-Crosson Ice Shelf, a network of basal channels creates variable thinning rates from near-zero to over 30 m/yr (estimated in several previous remote-sensing-based studies). Ice thickness near our camp over a subglacial channel is 390m and the ice has been thinning at ~25 m/yr estimated from satellite data. Seafloor elevation at the Dotson site is estimated at -570 m, but seismic surveys suggest that the seabed topography varies considerably beneath Dotson. 

On each ice shelf, we conducted ~200 km of multi-frequency ground-penetrating radar profiles. We also conducted 46 (Thwaites) and 17 (Dotson) autonomous phase-tracking radio echo-sounding (ApRES) repeat point measurements, as well as 37 (Thwaites) and more than 20 (Dotson) active-seismic spot soundings to characterize the sub-ice-shelf cavity shape, thinning rates, basal ice structures, and ocean circulation. We deployed two Automated Meteorology Ice Geophysics Ocean observation Systems (AMIGOS-III stations) on the Thwaites Ice Shelf that include a suite of surface sensors, a fiber-optic-based thermal profiler, and an ocean mooring. Additionally, we deployed four long-term ApRES on the two ice shelves to monitor temporal variability in ice melt.

How to cite: Pettit, E., Muto, A., Wild, C., Alley, K., Scambos, T., Wallin, B., Truffer, M., and Pomraning, D.: Thwaites and Dotson Ice Shelves: Field Site Selection and Early Results of Field Measurements, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-1331, https://doi.org/10.5194/egusphere-egu2020-1331, 2019

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