Geophysical Habitat of Subglacial Thwaites (GHOST)
GHOST is an ice- and modeling-based project that will examine the bed and interior of Thwaites Glacier. The rheology and topography of the bed affect how quickly Thwaites retreats and contributes to sea-level rise: it could rapidly collapse, or retreat might slow or pause on a subglacial ridge (GHOST Ridge) 70 kilometers inland of the current grounding line. This study will also investigate whether the region of fast-flowing ice could expand into currently slow-flowing regions. Expansion could lead to rapid deglaciation of neighboring basins, potentially raising global sea level by more than 3 meters.
The team comprises geophysicists and modelers working closely to determine the highest priority survey targets and data needs from the field. The team will use active and passive seismic, radar, and other geophysical methods (e.g., magnetotellurics, gravity, GPS, ApRES) to survey and map Thwaites Glacier’s internal stratigraphy and bed. These field data will be integrated into models to determine controlling interactions between glacier and bed, thereby improving projections of Thwaites’ evolution and its potential contribution to global sea level rise.
In the broader context of ITGC, GHOST’s focus is investigating the ice-bed boundary in the interior of the glacier. Composed of both data acquisition and modeling experts, the team places high priority on collecting synchronous data in locations and on processes known to be crucial components for model improvement.
GHOST will investigate the sediment, hydrology, and bedrock beneath Thwaites Glacier, and assess the impact of these boundary conditions on the dynamics of Thwaites. Guided by focused modeling studies, the team will conduct seismic, radar, magnetotelluric, ApRES, GPS, and gravity surveys in transects along and across the interior of the glacier, and over GHOST Ridge, which models suggest is a likely stabilizing point for Thwaites following retreat from its current position. Geophysical data collected in the field will then constrain outlet-glacier simulations that will be closely allied with data-interpretation efforts, leading to improved process understanding under a range of bed scenarios.
Projecting the retreat rate of Thwaites Glacier and evaluating whether it is likely to stabilize or retreat rapidly and collapse is essential for modeling future ice sheet behavior. In a warming world, understanding the potential contributions of glaciers such as Thwaites is critical for projecting the magnitude and timing of sea-level rise.
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GHOST has two expeditions scheduled for the 2020-2021 and 2021-2022 seasons. Both field seasons will entail spending two months on the ice. Field personnel will be split between two teams: Radar and Seismic. Teams will travel as a unit, but daily operations within the two teams will entail conducting their respective data-collection methods. Both teams will assist each other when necessary, and certain members will be designated responsible for gathering natural-source seismic, gravity, magnetotelluric, and other data that do not require continuous daily maintenance. The current goals for the two field seasons are as follows:
- Season 1 (2020-2021)
- Begin data acquisition over GHOST Ridge
- Move inland along a central flow-line 150 km long
- Season 2 (2021-2022)
- Finish collecting central line if left incomplete after season 1
- Collect data along 120 km transverse to flow from central line, over a subsurface lake, ending at eastern shear margin
- Heavy emphasis on interaction between the ice and the changing bed conditions over the lake
The goals for both season will be updated as modeling continues to inform the data-collection priorities and as the team analyzes results from the first field season.
