Award Abstract # 0819714
Improving the Accuracy of U-Th Coral Dating: A Test of Diagenetic Pathways, Models, and Effects
| NSF Org: | EAR Division Of Earth Sciences |
| Recipient: | |
| Initial Amendment Date: | March 12, 2009 |
| Latest Amendment Date: | April 5, 2011 |
| Award Number: | 0819714 |
| Award Instrument: | Continuing Grant |
| Program Manager: | Paul Filmer EAR Division Of Earth Sciences GEO Directorate For Geosciences |
| Start Date: | March 15, 2009 |
| End Date: | February 29, 2012(Estimated) |
| Total Intended Award Amount: | $420,000.00 |
| Total Awarded Amount to Date: | $420,000.00 |
| Funds Obligated to Date: | FY 2010 = $150,000.00 FY 2011 = $120,000.00 |
| History of Investigator: |
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| Recipient Sponsored Research Office: | 266 WOODS HOLE RD WOODS HOLE MA US 02543-1535 (508)289-3542 |
| Sponsor Congressional District: | |
| Primary Place of Performance: | 266 WOODS HOLE RD WOODS HOLE MA US 02543-1535 |
| Primary Place of Performance Congressional District: | |
| Unique Entity Identifier (UEI): | |
| Parent UEI: | |
| NSF Program(s): | Sedimentary Geo & Paleobiology |
| Primary Program Source: | 01001011DBNSF RESEARCH & RELATED ACTIVIT 01001112DBNSF RESEARCH & RELATED ACTIVIT |
| Program Reference Code(s): | |
| Program Element Code(s): | |
| Award Agency Code: | 4900 |
| Fund Agency Code: | 4900 |
| Assistance Listing Number(s): | 47.050 |
ABSTRACT Intellectual merit: In light of current concerns over the impacts of rising sea levels on human welfare, understanding potential magnitudes and rates of future sea level change is crucial. A well-dated and detailed history of past sea level change would provide important information in this regard. One of the premier methods for reconstructing the history of sea level is the dating of fossil corals that once grew near the sea surface. The advantages of this approach include the wide spread distribution of fossil corals, improvements in mass spectrometry allowing precise dating as far back as 600,000 years, and detailed stratigraphic correlations that can be used to determine abrupt, sub-meter scale sea-level changes. Unfortunately, these potential advantages are largely unrealized due to the widely recognized but poorly understood mobility of the uranium and thorium isotopes used for dating. Observations of systematic alteration trends in fossil corals and the idea that these trends might be explained by the systematic addition of recoil-mobilized uranium decay products have reinvigorated interest in coral diagenesis. Several models have been proposed to correct U-Th coral ages for such daughter addition, and have been shown to improve the age agreement of corals from the same fossil reef. However, the accuracy of such corrected ages remains controversial, in part because the physical mechanisms assumed by the models have not been tested directly. There is an urgent need to better understand these mechanisms, so that we might improve our understanding of past and future sea level change. This grant will undertake a series of experiments designed to test these critical assumptions.
This grant will attempt to answer three key questions regarding the apparent mobility of uranium and thorium isotopes that severely compromises the accuracy of uranium-thorium dating performed on fossil corals:
1) To what extent are the isotopes produced by uranium decay mobilized by the energy of alpha decay?
2) Are excess uranium decay products, which are frequently observed in fossil corals, adsorbed onto the crystal surfaces?
3) Can exchange of uranium between corals and water alter the isotopic composition of the coral with no change to the coral?s uranium concentration?
Broader Impact: The data that collected will provide fundamental information for scientists studying a broad variety of fields: carbonate chemistry, mineral-fluid interactions, paleoceanography, geochronology, and paleoclimate. Results and methods will be made available to the scientific community through publications in peer-reviewed journals and presentations at international conferences. Results and implications will be communicated to the public through interviews and talks. The team will use small-scale projects related to this research to introduce undergraduate students to laboratory techniques and the theory and practice of U-Th dating. Internships will take place through the WHOI Summer Student Fellowship Program. In addition, this proposal will support the careers of two junior scientists engaging in collaboration as a way of amplifying the impact of their combined scientific insights.
PUBLICATIONS PRODUCED AS A RESULT OF THIS RESEARCH
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Burke, A; Robinson, LF "The Southern Ocean's Role in Carbon Exchange During the Last Deglaciation" SCIENCE , v.335 , 2012 , p.557 View record at Web of Science 10.1126/science.120816
Thompson, WG; Curran, HA; Wilson, MA; White, B "Sea-level oscillations during the last interglacial highstand recorded by Bahamas corals" NATURE GEOSCIENCE , v.4 , 2011 , p.684 View record at Web of Science 10.1038/NGEO125
Siddall, M; Abe-Ouchi, A; Andersen, M; Antonioli, F; Bamber, J; Bard, E; Clark, J; Clark, P; Deschamps, P; Dutton, A; Elliot, M; Gallup, C; Gomez, N; Gregory, J; Huybers, P; Kawarnura, K; Kelly, M; Lambeck, K; Lowell, T; Milrovica, J; Otto-Bliesner, B; Ri "The sea-level conundrum: case studies from palaeo-archives" JOURNAL OF QUATERNARY SCIENCE , v.25 , 2010 , p.19 View record at Web of Science 10.1002/jqs.127
Jackson, CS; Marchal, O; Liu, YR; Lu, SP; Thompson, WG "A box model test of the freshwater forcing hypothesis of abrupt climate change and the physics governing ocean stability" PALEOCEANOGRAPHY , v.25 , 2010 View record at Web of Science 10.1029/2010PA00193
Chen, MT; Lin, XP; Chang, YP; Chen, YC; Lo, L; Shen, CC; Yokoyama, Y; Oppo, DW; Thompson, WG; Zhang, R "Dynamic millennial-scale climate changes in the northwestern Pacific over the past 40,000 years" GEOPHYSICAL RESEARCH LETTERS , v.37 , 2010 View record at Web of Science 10.1029/2010GL04520
Thompson, W. G., Andersen, M. B., Dutton, A. and Siddall, M. "Understanding future sea level rise: The challenges of dating past interglacials" PAGES news , v.18(1) , 2010 , p.39
Thompson, W. G. and Andersen, M. B. "Facilitating progress on the Quaternary history of sea level change" EOS, Transactions AGU , v.91(17) , 2010 , p.155
Andersen, M. B., Gallup, C. D., Scholz, D., Stirling, C. H. and Thompson, W. G. "U-series dating of fossil coral reefs: consensus and controversy." PAGES news , v.17(2) , 2009 , p.54
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.
Understanding potential magnitudes and rates of future sea level change is an urgent scientific and societal problem. An accurate history of sea level would provide crucial information on magnitudes and rates of sea level change. One of the premier methods for reconstructing the history of sea level is the dating of fossil corals that once grew near the sea surface. U-Th dating of reef corals has the potential to provide a detailed and well-dated record of sea level change for the last 600,000. Reef building corals grow near the sea surface so that fossil corals mark the position of past sea levels, and the ages of fossil corals can, in principle, be determined with very high precision. Given the prolific and relatively continuous growth of coral reefs in tropical seas, and the continuing technical advances in U-Th measurement techniques, the construction of a detailed and accurately dated sea level history should be a straightforward task. Such a record, if available, would be one of the fundamental records of global climate change, alongside the temperature and atmospheric gas records from the polar ice cores and oxygen isotope records from the deep sea. Unfortunately, despite decades of effort, this crucial goal remains elusive, primarily due to a lack of understanding of secondary alteration that changes the ages of fossil corals. With a combination of experiments and micro-sampling techniques, we have tested models of to explain the dating problems encountered with corals. The results of our experiments provide new information that will enable more accurate reconstructions of sea level history. Technical advances developed during the course of our project have improved the accuracy and precision of coral dating.
Last Modified: 05/30/2012
Modified by: WilliamThompson
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