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Proxy paleoclimatology: Development of  high resolution proxy climate observations from regions sensitive to various phenomena of interest.  Can the proxy data provide quantitative estimates of local, regional and global patterns of climate variability?  What is the uncertainty  in such estimates?  Work on corals from the central equatorial Pacific while I was a student at Lamont, under supervision of Rick Fairbanks and in collaboration with Jim Rubenstone (both at LDEO), sought answers to these questions.  As part of a NOAA-UCAR Postdoctoral Fellowship in Climate and Global Change Research, in the Dept. of Earth and Planetary Sciences, Harvard University, under the supervision of Dan Schrag, I developed an approach to deriving paleo-rainfall estimates from tropical trees which may or may not have rings, using high-resolution oxygen isotope measurements on tropical woods.  Further results, funded by the UA Faculty Small Grants Program and NSF (Earth Systems History),  have been encouraging: chronological development and the proxy raingage have now been tested in Costa Rica, Indonesia, Peru, Brazil, and Thailand, in a variety of tree genera and tropical climates.  We are exploring additional study sites in Australia, Malaysia, Indonesia, Colombia and Ecuador.  Current and past students working on exciting related projects are Pascale F. Poussart (EPS-Harvard; D.P. Schrag, supervisor; now at Prinecton), Kevin J. Anchukaitis (Ph.D. Geosciences, 2007; now at Lamont-Doherty), Sarah White (B.S., Ecology & Evolutionary Biology, now a research assistant in our group), and Sarah Grubaugh (UA-Geosciences).   Ultimately these new data will be incorporated into the paleoclimatic field reconstruction rubric described below.  We have established a continuous flow mass spectrometry laboratory for the analysis of carbon and oxygen isotopic composition of organic, carbonate and water samples, as part of a virtual laboratory for high resolution paleoclimatology; information and photos are here.

Paleoclimate modeling:  Verifiable reconstruction of  regional and global climate fields from sparse observational networks of paleoproxy data.  Our approach to the reconstruction problem is to find the best fit, in the linear least squares sense, to both the proxy observations and a model of the climate field variance in space and/or time.   We perform this analysis within the context of reduced space objective analysis, a field reconstruction technique developed at Lamont by Mark A. Cane, Alexey Kaplan, and others in the Climate Group.   Our first experiments involved the reconstruction of the Pacific basin and global sea surface temperature anomaly fields, using annual resolution proxy data extracted from stable isotopes in reef corals, and tree ring width chronologies; products are deposited here and at the National Geophysical Data Center.  Current NOAA-funded and NSF-funded research in conjunction with colleagues at Arizona, Columbia, NCAR, and the Instituto de Geofisica/Barcelona includes multivariate calibration, robust process (forward) modeling of the proxy data, comparison of reconstructed fields with general circulation model output, and state space intercomparison of the results.  We have been experimenting with a relatively simple but nonlinear process model of tree-ring formation, developed by E.A. Vaganov, of the Russian Academy of Sciences, in Krasnoyarsk.  Bernhard Reichert has successfully modeled trees across the United States and Siberia using the model with default parameters (Evans et al. 2006), and Suz Tolwinski (Mathematics) is examining simulations driven by climate model output.  Kevin Anchukaitis found that this model explains a switch in the climatic controls on tree growth in the southeastern US related to a weakening or broadening Bermuda High since the mid-1970s (Anchukaitis et al. 2006).  Brianna Muhlenkamp (Geophysics) used this model to simulate growth of tropical trees(!), and Brooke Rabe (Math/CS) is using this model to forecast forest growth changes due to climate change predicted by regional climate simulations for the continental US.  As we use these and other models (e.g. Evans et al. 2007) to seek better interpretation of the various proxy data, we expect to obtain better reconstructions of past climates.

Analysis of paleoclimatic variability: It is increasingly clear that the past century may be one of change and reorganization in the climate system in response to steadily increasing anthropogenic forcing (IPCC, 2001; US Climate Change Research Program, 2002). The tropics in particular comprise an enigmatic component of the climatic response to greenhouse forcing.  How will increases in atmospheric greenhouse gas concentrations affect the frequency and amplitude of El Nino-Southern Oscillation (ENSO) warm and cold phase events (Timmerman et al., 1999)? How stable is the mean state of the tropical ocean-atmosphere system, from the base of the thermocline to the top of the troposphere (Ramanathan and Collins, 1991; Clement et al., 1996; Rind, 2003)?  How do the mean state and the variability of the tropical ocean and atmosphere interact on seasonal to centennial timescales (Gu and Philander,1995; Fedorov and Philander, 2001)?  Ultimately, what are the physical mechanisms which explain long-term variability in the tropical ocean and atmospheres (Karspeck and Cane, 2002; Kushnir et al., 2002)?  [excerpted from funded proposal to NSF-CAREER program, MNE, 12/1/04-12/31/08].  I am interested in using state space models together with proxy observations in the literature to develop syntheses of climate states at various times of interest in the paleoclimatic record.

Interested in paleoclimatological research opportunities?  Contact me for more information about possible student and postdoctoral projects in tropical isotope dendroclimatology, statistical reconstruction of paleoclimatic fields, process modeling of proxy data, and tropical paleoclimate dynamics.  I hold faculty appointments, advise students and serve on committees in Geosciences and Atmospheric Sciences.  More info on graduate studies at the LTRR is here.  You can learn more about my teaching interests from my online teaching portfolio.

Left: isotope lab research group in Gould-Simpson 801.  Back row: Mike Evans (LTRR), Megan Rheaume (undergraduate - Geosciences) , Ruth Penniston (undergraduate - pre-Business); front row: Tone Ekvedt (visiting researcher, Norway); Sarah White. Not pictured: Lisa Wade (undergraduate - Civil Engineering); Sarah White (B.S., Biology, 2007); Sarah Grubaugh (undergraduate - Geosciences).  Other group members: Suz Tolwinski (Ph.D. candidate, Mathematics - proxy/climate modeling); Ana Kursinski (postdoctoral research scientist, Atmospheric Sciences - GPS radio occultation humidity retrievals).

Left: Research group photo (March 2005) in front of the hot dog stand across from my office in the West Stadium.  Sitting left to right: Chris Jones (undergraduate-Hydrology), April Chiriboga (graduate-Geosciences; now pursuing another project), Mike Evans (LTRR).  Standing left to right: Brianna Muhlenkamp (undergraduate-Honors Geosciences and Engineering, 2005), Jonathan Buchanan (undergraduate-Physics, 2006), Praveen Kundurthy (undergraduate-Honors Astrophysics and Biology, 2004), Kevin Anchukaitis (Ph.D., Geosciences, 2007; now a postdoc at Lamont-Doherty).  Not pictured: Mau-Chuang Foo (undergraduate - Honors Electrical Engineering), Brooke Rabe (undergraduate - Honors Math/Computer Science).

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