An official website of the United States government
Hercules Dome, Antarctica, has long been identified as a prospective deep ice core site due to the undisturbed internal layering, climatic setting and potential to obtain proxy records from the Last Interglacial (LIG) period when the West Antarctic ice sheet may have collapsed. We performed a geophysical survey using multiple ice-penetrating radar systems to identify potential locations for a deep ice core at Hercules Dome. The surface topography, as revealed with recent satellite observations, is more complex than previously recognized. The most prominent dome, which we term ‘West Dome’, is the most promising region for a deep ice core for the following reasons: (1) bed-conformal radar reflections indicate minimal layer disturbance and extend to within tens of meters of the ice bottom; (2) the bed is likely frozen, as evidenced by both the shape of the measured vertical ice velocity profiles beneath the divide and modeled ice temperature using three remotely sensed estimates of geothermal flux and (3) models of layer thinning have 132 ka old ice at 45–90 m above the bed with an annual layer thickness of ~1 mm, satisfying the resolution and preservation needed for detailed analysis of the LIG period.
more »
« less
This content will become publicly available on February 25, 2026
Radar‐Derived Crystal Orientation Fabric Suggests Dynamic Stability at the Summit of Hercules Dome
Abstract Hercules Dome is a prospective ice‐core site due to its setting in the bottleneck between East and West Antarctica. If ice from the last interglacial period has been preserved there, it could provide critical insight into the history of the West Antarctic Ice Sheet. The likelihood of a continuous, well‐resolved, easily interpretable climate record preserved in ice extracted from Hercules Dome depends in part on the persistence of ice‐flow dynamics at the divide. Significant changes in ice drawdown on either side of the divide, toward the Ross or Ronne ice shelves, could change the relative thickness of layers and the deposition environment represented in the core. Here, we use radar sounding to survey the ice flow at Hercules Dome. Repeated radar acquisitions show that vertical velocities are consistent with expectations for an ice divide with a frozen bed. Polarimetric radar acquisitions capture the ice‐crystal orientation fabric (COF) which develops as ice strains, so it depends on both the pattern of ice flow and the time over which flow has been consistent. We model the timescales for COF evolution, finding that the summit of Hercules Dome has been dynamically stable in its current configuration, at least over the last five thousand years, a time period during which the Antarctic ice sheet was undergoing significant retreat at its margins. The evident stability may result from a prominent bedrock ridge under the divide, which had not been previously surveyed and has therefore not been represented in the bed geometry of coarsely resolved ice‐sheet models.
more »
« less
- PAR ID:
- 10576465
- Publisher / Repository:
- DOI PREFIX: 10.1029
- Date Published:
- Journal Name:
- Journal of Geophysical Research: Earth Surface
- Volume:
- 130
- Issue:
- 3
- ISSN:
- 2169-9003
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
-
Abstract The West Antarctic Ice Sheet (WAIS) may have collapsed during the last interglacial period, between 132 000 and 116 000 years ago. The changes in topography resulting from WAIS collapse would be accompanied by significant changes in Antarctic surface climate, atmospheric circulation, and ocean conditions. Evidence of these changes may be recorded in water-isotope ratios in precipitation archived in the ice. We conduct high-resolution simulations with an isotope-enabled version of the Weather Research and Forecasting Model over Antarctica, with boundary conditions provided by climate model simulations with both present-day and lowered WAIS topography. The results show that while there is significant spatial variability, WAIS collapse would cause detectable isotopic changes at several locations where ice-core records have been obtained or could be obtained in the future. The most robust signals include elevatedδ18O at SkyTrain Ice Rise in West Antarctica and elevated deuterium excess andδ18O at Hercules Dome in East Antarctica. A combination of records from multiple sites would provide constraints on the timing, rate, and magnitude of past WAIS collapse.more » « less
-
null (Ed.)Abstract. In 2013 an ice core was recovered from Roosevelt Island, an ice dome between two submarine troughs carved by paleo-ice-streams in the Ross Sea, Antarctica. The ice core is part of the Roosevelt Island Climate Evolution (RICE) project and provides new information about the past configuration of the West Antarctic Ice Sheet (WAIS) and its retreat during the last deglaciation. In this work we present the RICE17 chronology, which establishes the depth–age relationship for the top 754 m of the 763 m core. RICE17 is a composite chronology combining annual layer interpretations for 0–343 m (Winstrup et al., 2019) with new estimates for gas and ice ages based on synchronization of CH4 and δ18Oatm records to corresponding records from the WAIS Divide ice core and by modeling of the gas age–ice age difference. Novel aspects of this work include the following: (1) an automated algorithm for multiproxy stratigraphic synchronization of high-resolution gas records; (2) synchronization using centennial-scale variations in methane for pre-anthropogenic time periods (60–720 m, 1971 CE to 30 ka), a strategy applicable for future ice cores; and (3) the observation of a continuous climate record back to ∼65 ka providing evidence that the Roosevelt Island Ice Dome was a constant feature throughout the last glacial period.more » « less
-
Abstract. The crystal orientation fabric (COF) of ice sheets records the past history ofice sheet deformation and influences present-day ice flow dynamics. Though notwidely implemented, coherent ice-penetrating radar is able to detect bulkanisotropic fabric patterns by exploiting the birefringence of ice crystals atradar frequencies, with the assumption that one of the crystallographic axesis aligned in the vertical direction. In this study, we conduct a suite ofquad-polarimetric measurements consisting of four orthogonal antennaorientation combinations near the Western Antarctic Ice Sheet (WAIS) Divideice core site. From these measurements, we are able to quantify the azimuthalfabric asymmetry at this site to a depth of 1400 m at abulk-averaged resolution of up to 15 m. Our estimates of fabricasymmetry closely match corresponding fabric estimates directly measured fromthe WAIS Divide ice core. While ice core studies are often unable to determinethe absolute fabric orientation due to core rotation during extraction, we areable to identify and conclude that the fabric orientation is depth-invariantto at least 1400 m, equivalent to 6700 years BP (years before1950) and aligns closely with the modern surface strain direction at WAISDivide. Our results support the claim that the deformation regime at WAISDivide has not changed substantially through the majority of theHolocene. Rapid polarimetric determination of bulk fabric asymmetry andorientation compares well with much more laborious sample-based COFmeasurements from thin ice sections. Because it is the bulk-averaged fabricthat ultimately influences ice flow, polarimetric radar methods provide anopportunity for its accurate and widespread mapping and its incorporation intoice flow models.more » « less
-
Abstract The Amundsen Sea Embayment of the West Antarctic Ice Sheet contains Thwaites and Pine Island Glaciers, two of the most rapidly changing glaciers in Antarctica. To date, Pine Island and Thwaites Glaciers have only been observed by independent airborne radar sounding surveys, but a combined cross‐basin analysis that investigates the basal conditions across the Pine Island‐Thwaites Glaciers boundary has not been performed. Here, we combine two radar surveys and correct for their differences in system parameters to produce unified englacial attenuation and basal relative reflectivity maps spanning both Pine Island and Thwaites Glaciers. Relative reflectivities range from −24.8 to +37.4 dB with the highest values beneath fast‐flowing ice at the ice sheet margin. By comparing our reflectivity results with previously derived radar specularity and trailing bed echoes at Thwaites Glacier, we find a highly diverse subglacial landscape and hydrologic conditions that evolve along‐flow. Together, these findings highlight the potential for joint airborne radar analysis with ground‐based seismic and geomorphological observations to understand variations in the bed properties and cross‐catchment interactions of ice streams and outlet glaciers.more » « less
