| NSF Org: |
OPP Office of Polar Programs (OPP) |
| Recipient: |
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| Initial Amendment Date: | July 14, 2014 |
| Latest Amendment Date: | February 17, 2017 |
| Award Number: | 1341658 |
| Award Instrument: | Standard Grant |
| Program Manager: |
Michael E. Jackson
OPP Office of Polar Programs (OPP) GEO Directorate for Geosciences |
| Start Date: | July 15, 2014 |
| End Date: | June 30, 2019 (Estimated) |
| Total Intended Award Amount: | $582,113.00 |
| Total Awarded Amount to Date: | $617,658.00 |
| Funds Obligated to Date: |
FY 2017 = $35,545.00 |
| History of Investigator: |
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| Recipient Sponsored Research Office: |
1850 RESEARCH PARK DR STE 300 DAVIS CA US 95618-6153 (530)754-7700 |
| Sponsor Congressional District: |
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| Primary Place of Performance: |
One Shields Avenue Davis CA US 95616-5270 |
| 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 Earth Sciences |
| Primary Program Source: |
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| Program Reference Code(s): | |
| Program Element Code(s): |
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| Award Agency Code: | 4900 |
| Fund Agency Code: | 4900 |
| Assistance Listing Number(s): | 47.078 |
ABSTRACT
Modeling fluctuations in the extent of the West Antarctic Ice Sheet (WAIS) over time is a principal goal of the glaciological community. These models will provide a critical basis for predictions of future sea level change, and therefore this work great societal relevance. The mid-Pliocene time interval is of particular interest, as it is the most recent period in which global temperatures were warmer and atmospheric CO2 concentrations may have been higher than current levels. However, observational constraints on fluctuations in the WAIS older than the last glacial maximum are rare. The investigators propose to collect geochemical data from the Ohio Range and Scott Glacier to quantify past variability in the height of the WAIS.
Limited available cosmogenic nuclide data are broadly consistent with a model indicating that Pliocene WAIS elevations and volumes were smaller than at present, and that WAIS collapse was common. The PIs will use geologic observations and cosmogenic nuclide concentrations from bedrock samples at multiple locations and at multiple elevations, including sub-ice samples, to constrain WAIS ice volume changes in a "dipstick" like fashion. Data obtained from the proposed research will provide targets for data-ice sheet model comparisons to accurately characterize Plio-Pleistocene and future WAIS behavior. As part of this project, the investigators will work with the Natural History Museum and the Earth & Planetary Science department at Harvard to develop an exhibit that will become part of the Museum's recently opened Earth and Planetary Science Gallery. The project involves mentoring of a female graduate student as well as an undergraduate student.
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.
The marine-based West Antarctic Ice Sheet (WAIS) can potentially collapse during periods of warming. During the warm Pliocene (5.33 - 2.58 million years ago) and especially the Mid-Pliocene Warm Period (3.3 - 3 million years ago), temperatures were roughly 3 degrees higher than the preindustrial average, and atmospheric carbon dioxide concentrations were comparable to today's levels. Sediments taken on the ocean floor beneath the Ross Ice Shelf show open ocean conditions, during the warm Pliocene. However, it is not entirely clear whether the WAIS collapsed during this interval. Ice sheet models calibrated to the sediment record from the Ross Sea point to a thinner Pliocene WAIS, but the predictive behavior of these models have not been tested by observations from the interior of the ice sheet.
To test the predictions of the ice sheet model rigorously, we worked to obtain the exposure history of rock samples that are currently buried underneath the ice sheet (i.e., subglacial rock samples) at the Ohio Range. The Ohio Range is an interior location in the WAIS along the Transantarctic Mountains near the present-day WAIS divide. We obtained rock cores from underneath the icesheet by drilling through the ice using the Winkie drill. In the rock cores we measured the concentration of the cosmic ray produced isotopes. The isotopes are produced by the cosmic rays only when the rocks are exposed directly to the atmosphere following loss of the overlying ice. When the ice cover returns, rocks are no longer in direct contact with the atmosphere and the production of the isotopes is shut off. By measuring multiple isotopes, the history of ice cover for these subglacial samples can be deciphered. The histroy of the ice cover in turn is related to the waxing and waning of hte WAIS. Through the drilling operation we were able to recover samples from 10 to ~30 m under the present-day ice levels. At the Ohio Range, the glacial to interglacial variations in ice sheet levels are ~120 meters. So 30 meters represent a significant fraction of the variation over the course of an ice age.
We detected high concentrations of the cosmic ray produced isotopes in the rock cores, indicating extensive periods of ice-free exposure to cosmic irradiation during the last 2 million years. Modeling of the data suggest that bedrock surfaces at the Ohio Range that are currently covered by 30 meters of ice experienced more exposure than ice cover, especially in the Pleistocene. An ice sheet model prediction for the Ohio Range subglacial sample sites however, significantly underestimates exposure in the last 2 million years, and over-predicts ice cover in the Pleistocene. To adjust for the higher amounts of exposure we observe in our samples, the ice sheet model simulations require more frequent and/or longer-lasting WAIS ice drawdowns. This has important implications for future sea-level change as the model maybe under-predicting the magnitude of sea-level contributions from WAIS during the ice-age cycles. Improving the accuracy of the ice sheet models through model-data comparison should remain a prime objective in the face of a warming planet as understanding WAIS behavior is going to be key for predicting and planning for the effects of sea-level change. These important results were communicated to the scientific community at conferences and through seminars. The broader community was engaged through the University of California Davis's Picnic Day celebration, an annual open house that attracts over 70,000 people to the campus, and through classroom vist at a local elementary school. The project helped support and train a graduate student in climate research related to Antarctica and led to a Master's Thesis.
Last Modified: 06/26/2020
Modified by: Sujoy Mukhopadhyay
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