| NSF Org: |
OPP Office of Polar Programs (OPP) |
| Recipient: |
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| Initial Amendment Date: | November 3, 2017 |
| Latest Amendment Date: | May 18, 2021 |
| Award Number: | 1643917 |
| Award Instrument: | Continuing Grant |
| Program Manager: |
Paul Cutler
pcutler@nsf.gov (703)292-4961 OPP Office of Polar Programs (OPP) GEO Directorate for Geosciences |
| Start Date: | December 1, 2017 |
| End Date: | November 30, 2022 (Estimated) |
| Total Intended Award Amount: | $448,933.00 |
| Total Awarded Amount to Date: | $591,261.00 |
| Funds Obligated to Date: |
FY 2019 = $166,326.00 FY 2020 = $133,743.00 FY 2021 = $87,811.00 |
| History of Investigator: |
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| Recipient Sponsored Research Office: |
8622 DISCOVERY WAY # 116 LA JOLLA CA US 92093-1500 (858)534-1293 |
| Sponsor Congressional District: |
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| Primary Place of Performance: |
Scripps Institution of Oceanogra La Jolla CA US 92093-0225 |
| Primary Place of
Performance Congressional District: |
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| Unique Entity Identifier (UEI): |
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| Parent UEI: |
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| NSF Program(s): | ANT Glaciology |
| Primary Program Source: |
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| Program Reference Code(s): |
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| Program Element Code(s): |
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| Award Agency Code: | 4900 |
| Fund Agency Code: | 4900 |
| Assistance Listing Number(s): | 47.078 |
ABSTRACT
The Antarctic ice sheet is underlain by a dynamic water system that lubricates the flow of ice streams and outlet glaciers, provides a habitat for a diverse microbial ecosystem, and delivers freshwater and nutrients to the Southern Ocean. However, imaging this subglacial environment is difficult: Antarctica is a vast continent with ice up to four kilometers (2.5 miles) thick. To detect water at the ice-bed interface and in deeper groundwater reservoirs, this project will adapt a technique called electromagnetic sounding that is well-established on land and in the ocean for imaging fluids beneath the surface. Groundwater is estimated to be a significant part of the subglacial water budget in Antarctica, yet previous observational approaches have been unable to characterize its volume and distribution. This project will thus yield critical information about how ice-rock-water-ocean systems interact and inform our understanding of ice-sheet processes, global nutrient cycles, and freshwater flux to the ocean. The project will provide cross-disciplinary training for a graduate student and postdoctoral scientist, and develop an educational outreach program through the Birch Aquarium.
Standard geophysical surveying techniques used in glaciology to image subglacial water (radio-echo sounding and active-source seismology) are not directly sensitive to water content. In contrast, ground-based electromagnetic (EM) methods are sensitive to water content through its impact on bulk conductivity. Although EM methods are well-established for high-precision mapping of hydrology in other geological environments, their application on ice sheets is in its infancy. The proposed work will adapt both passive- and active-source EM techniques to glaciological questions to quantify the three-dimensional structure of subglacial water beneath an ice stream and in a grounding zone. The project will perform a suite of synthetic inversion studies to determine the range of applications of EM techniques in glaciology and execute a field experiment on the Whillans Ice Plain to investigate two hypotheses about the subglacial water system based on previous observational and modeling results: (1) Subglacial Lake Whillans is underlain by a deep, saline groundwater reservoir; and (2) there is an estuary-like zone of mixing between fresh subglacial water and seawater near, and possibly landward, of the grounding line.
PUBLICATIONS PRODUCED AS A RESULT OF THIS RESEARCH
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PROJECT OUTCOMES REPORT
Disclaimer
This Project Outcomes Report for the General Public is displayed verbatim as submitted by the Principal Investigator (PI) for this award. Any opinions, findings, and conclusions or recommendations expressed in this Report are those of the PI and do not necessarily reflect the views of the National Science Foundation; NSF has not approved or endorsed its content.
Summary
We used an electromagnetic survey to search for groundwater in an Antarctic ice stream. The survey measures subsurface resistivity, which is related to water salinity, using variations in Earth’s electric and magnetic fields. Our survey revealed a deep and extensive aquifer system, which is hydrologically connected to the ice-bed environment. The aquifer is saltiest at its base, indicating a past marine incursion, and freshest at the ice-bed interface, indicating basal melt infiltration occurring after WAIS re-stabilized. Our findings suggest that groundwater can affect ice stream dynamics and subglacial hydrology, extending beyond current subglacial borehole depths. This is the first discovery of groundwater beneath an Antarctic ice stream.
Background
The Antarctic Ice Sheet is a massive layer of ice that sits on top of bedrock, averaging 2.2 km thick. The insulation, high pressure, and geothermal heat flux at the ice-bed interface leads to melting of the basal ice layers on the order of mm/year, producing high volumes of subglacial water estimated at ~65 Gt/yr, which is largely hidden from observations and difficult to access. In 2006, PI Helen Fricker discovered active subglacial water systems under the fast-flowing ice streams of West Antarctica using ICESat data. Since then, satellite measurements have shown us that ice-surface height changes on the order of several meters correspond to draining and filling of >130 “active” subglacial lakes across the whole ice sheet. However, satellite measurements have been limited by how often they collect data and their coverage.
The Subglacial Antarctic Lakes Scientific Access (SALSA) project was a 5-year interdisciplinary NSF-funded project to investigate the dynamics, history, and interactions among ice, water, sediment, rock, microbes, and carbon reservoirs of an active subglacial lake in West Antarctica (Mercer Subglacial Lake under Mercer Ice Stream) through geophysical data collection and drilling. The drilling season involved a large interdisciplinary team using clean hot-water drilling through 1090 m of ice to gain direct access to the subglacial lake.
The Scripps/Lamont team was responsible for the geophysical data collection and brought a novel technique for glaciology (electromagnetic soundings) to detect water at the ice-bed interface and in deeper groundwater reservoirs. Groundwater is estimated to be a significant part of the subglacial water budget in Antarctica, yet previous observational approaches have been unable to characterize its volume and distribution.
The Scripps/Lamont team took part in all three SALSA field seasons, with Matt Siegfried leading the Surface Geophysics team. They used an electromagnetic (EM) method called magnetotellurics to conduct measurements beneath the Whillans Ice Stream. This was the first time the method had been used to search for groundwater beneath a highly-dynamic ice stream, a glacial feature that transfers large volumes of ice from central Antarctica to the Southern Ocean. The season culminated in the successful drilling of Mercer Subglacial Lake in December 2018.
The EM data generated a map of the subsurface electrical conductivity beneath the ice sheet, identifying areas of high conductivity likely associated with groundwater. This allowed us to confirm the presence of groundwater beneath the Whillans Ice Stream and map its distribution in 3D. We found that this salty groundwater is the largest reservoir of liquid water below the Whillans ice stream, and likely others, and it may be affecting how the ice flows on Antarctica.
The project transformed our understanding of ice streams, revealing a massive amount of groundwater, including saltwater from the ocean, in a thick layer of sediments previously not accounted for in the traditional view of relatively shallow hydrologic components near the glacial surface, including subglacial channels, sediment canals, and distributed drainage networks. The updated view includes the deeper groundwater reservoir that sits in a permeable sedimentary basin, which may exchange water with the shallower hydrologic components and affect their behaviors.
This work highlights the importance of combining NSF and NASA research to better understand changes occurring over the ice sheet and how new geophysical techniques can transform our understanding of the Antarctic Ice Sheet. The study of subglacial water systems is critical for understanding ice sheet dynamics and predicting future sea level rise.
Outreach
The SALSA project team worked with Birch Aquarium at SIO for public outreach. PI Fricker gave talks about SALSA, including a Birch Aquarium Perspectives Lecture and a "Suds and Science" talk. Birch Aquarium is installing an exhibit featuring SALSA research with the video “Lake at the Bottom of the World” created by Kathy Kasic. Fricker also showed SALSA EM work during the Nye Lecture at AGU, the IGS Global Seminar and presented at the SACNAS conference. The team published a paper in Science in May 2022 and it received media coverage from BBC, CNN, NPR, and KPBS. They also wrote an article for The Conversation.
Last Modified: 04/14/2023
Modified by: Helen A Fricker
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