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Recent investigations in polar environments have examined solid-Earth-ice-sheet feedbacks and have emphasized that glacial isostatic adjustment, tectonic, and geothermal forcings exert first-order control on the physical conditions at and below the ice-bed interface and must be taken into account when evaluating ice-sheet evolution. However, the solid-Earth structure beneath much of Antarctica is still poorly constrained given the sparse distribution of seismic stations across the continent and the generally low seismicity rate. One region of particular interest is the Wilkes Subglacial Basin (WSB) in East Antarctica. During the mid-Pliocene warm period, the WSB may have contributed 3-4 m to the estimated 20 m rise in sea-level, indicating that this region could also play an important role in future warming scenarios. However, the WSB may have experienced notable bedrock uplift since the Pliocene; therefore, past geologic inferences of instability may not serve as a simple analogue for the future. Using records of ambient seismic noise recorded by both temporary and long-term seismic networks, along with a full-waveform tomographic inversion technique, we are developing improved images of the lithospheric structure beneath East Antarctica, including the WSB. Empirical Green’s Functions with periods between 40 and 340 s have been extracted using a frequency-time normalization technique, and a finite-difference approach with a spherical grid has been employed to numerically model synthetic seismograms. Associated sensitivity kernels have also been constructed using a scattering integral method. Our preliminary results suggest the WSB is underlain by slow seismic velocities, with faster seismic structure beneath the adjacent Transantarctic Mountains and the Belgica Subglacial Highlands. This may indicate that the WSB is associated with a region of thinner lithosphere, possibly associated with prior continental rifting. The seismic heterogeneity highlighted in our model could have significant implications for understanding the geodynamic origin of WSB topography and its influence on ice-sheet behavior.
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Wilkes subglacial basin: Ice-sheet Dependence on GEology and Tectonics (WIDGET)
Inward-sloping marine basins in polar environments are susceptible to an effect known as the marine ice-sheet instability (MISI): run-away ice stream drainage caused by warm ocean water eroding the ice shelf from below. The magnitude and timing of the MISI response strongly depend on the physical conditions along the ice-bed interface, which are controlled by the tectonic evolution of the basin. Solid Earth parameters, such as topography, geothermal heat flux, and mantle viscosity, play critical roles in ice-sheet stability. However, in most cases, these solid-Earth parameters for regions susceptible to the MISI are largely unknown. The Wilkes Subglacial Basin (WSB) is a critical region in East Antarctica that may be susceptible to the MISI, which may have led to significant sea-level contributions in the past and which could play an important role in the future. During the mid-Pliocene warm period, the WSB may have contributed 3-4 m to the estimated 20 m increase in sea-level compared to present day. However, recent work has suggested that the WSB may have undergone significant bedrock uplift since the Pliocene; therefore, geological inferences of instability during the Pliocene may not serve as a simple analogue for future warming scenarios. Further constraints are required to assess the geodynamic origin of WSB topography and the influence of geologic parameters on past, current, and future ice-sheet behavior. To this end, we have proposed an integrated investigation of the WSB, combining geophysical analyses with both mantle flow and ice-sheet modeling. Using seismic and magnetotelluric observations from a new field deployment (WIDGET), in conjunction with existing geophysical and geological data, we will develop an improved tectonic model for the region and will estimate the thermal, density, and viscosity structure of the crust and upper mantle beneath the WSB. These solid Earth constraints will be used to simulate mantle flow and to assess paleotopography, which will allow us to model both past and future ice-sheet stability, thereby creating scientifically and societally relevant estimates of sea-level change.
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- Award ID(s):
- 1914698
- PAR ID:
- 10488349
- Publisher / Repository:
- Instabilities & Thresholds in Antarctica (INSTANT) Conference
- Date Published:
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Recent investigations in polar environments have examined solid-Earth-ice-sheet feedbacks and have emphasized that glacial isostatic adjustment, tectonic, and geothermal forcings exert first-order control on the physical conditions at and below the ice-bed interface and must be taken into account when evaluating ice-sheet evolution. However, the solid-Earth structure beneath much of Antarctica is still poorly constrained given the sparse distribution of seismic stations across the continent and the generally low seismicity rate. One region of particular interest is the Wilkes Subglacial Basin (WSB) in East Antarctica. During the mid-Pliocene warm period, the WSB may have contributed 3-4 m to the estimated 20 m rise in sea-level, indicating that this region could also play an important role in future warming scenarios. However, the WSB may have experienced notable bedrock uplift since the Pliocene; therefore, past geologic inferences of instability may not serve as a simple analogue for the future. Using records of ambient seismic noise recorded by both temporary and long-term seismic networks, along with a full-waveform tomographic inversion technique, we are developing improved images of the lithospheric structure beneath East Antarctica, including the WSB. Empirical Green’s Functions with periods between 40 and 340 s have been extracted using a frequency-time normalization technique, and a finite-difference approach with a spherical grid has been employed to numerically model synthetic seismograms. Associated sensitivity kernels have also been constructed using a scattering integral method. Our preliminary results suggest the WSB is underlain by slow seismic velocities, with faster seismic structure beneath the adjacent Transantarctic Mountains and the Belgica Subglacial Highlands. This may indicate that the WSB is associated with a region of thinner lithosphere, possibly associated with prior continental rifting. The seismic heterogeneity highlighted in our model could have significant implications for understanding the geodynamic origin of WSB topography and its influence on ice-sheet behavior.more » « less
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