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Geochronology
A critical aspect of paleoenvironmental research is the development of reliable chronologies for the paleoenvironmental records being investigated. For this reason our lab has several projects directed at developing new and improved methods for dating paleoclimate proxy records. One large effort is aimed at improving the way annually laminated (i.e., varved) lake and marine sediments are used for paleoenvironmental research. We have developed field sampling methods and laboratory techniques to improve varve analysis, and are working on varved sediments from around the world, including sites in the Arctic, Africa, and South America. Most recently, we have teamed up with dendroclimatologist Malcolm Hughes and computer engineer/image processing expert Robert Schowengerdt to build a new system for computer-assisted varve study (VARVES) based on a new system being developed for tree-ring research (TREES). Former graduate student Tim Shanahan and graduate student Jessica Conroy are both involved in varve-based research. A second major geochronology thrust of the laboratory involves the study of radiocarbon over the last 50,000 years, the period over which 14C is generally employed in paleoenvironmental research. For his Ph.D. work in the laboratory (then at the University of Colorado) and continuing to the present, Konrad Hughen has led in the use of varved sediments from the Cariaco Basin to extend the record of atmospheric radiocarbon beyond the limits of tree-ring based records of 11,500 years ago to the limits of radiocarbon. Much of this work has been incorporated into the widely used 14C CALIB Calibration Program. Acknowledging that many uncertainties still exist, former graduate student Tim Shanahan has lead efforts with the National Science Foundation (NSF)-University of Arizona Accelerator Mass Spectrometer (AMS) Laboratory to use varved sediments of Lake Bosumtwi in Ghana to continue our improvement of radiocarbon calendar age time scales. Lastly, members of our lab are also creating innovative approaches in order to obtain reliable (e.g., free of “old-carbon” or “reservoir” effects) dates from lake sediments. This work is significantly improved by our close collaboration with the NSF-University of Arizona AMS Laboratory and the fact that our students can work in the AMS laboratory to prepare their own samples.
Atlantic
Variability 14C
CALIB Radiocarbon Calibration Program
W. Beck, K. Hughen, M. Hughes, S. Lehman, R. Schowengerdt, T. Shanahan, J. Southon
Hughen, K., S. Lehman, J. Southon, J. Overpeck, O. Marchal, C. Herring, and J. Turnbull. 2004. 14C activity and global carbon cycle changes over the past 50,000 years. Science 303: 202-207. Hughen, K.A., J.R. Southon, S.J. Lehman, and J.T. Overpeck. 2000. Synchronous radiocarbon and climate shifts during the last deglaciation. Science 290: 1951-1954. Hughen, K.A., J.T. Overpeck, S.J. Lehman, M. Kashgarian, and J.R. Southon. 1998. A new C-14 calibration data set for the last deglaciation based on marine varves. Radiocarbon 40: 483-494. Hughen, K.A., J. Southon, L.C. Peterson, R. Alley, D.M. Sigman, J.T. Overpeck, S.J. Lehman, and M. Kashgarian. 1998. Deglacial changes in ocean circulation from an extended radiocarbon calibration. Nature 391: 65-68. Overpeck, J.T. 1996. Varved sediment records of recent seasonal to millennial-scale environmental variability. In: Climatic Variations and Forcing Mechanisms of the Last 2,000 Years, P.D. Jones, R.S. Bradley, and J. Jouzel, eds., Springer-Verlag, Berlin, pp. 479-598. |
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Studies Laboratory, Department of Geosciences, The University of Arizona Last updated
January 8, 2008
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