GEOS 595e: Journal Club
Spring 2007 Reading Focus Questions

Week 2: Tracking ENSO with tropical trees: Chronology, calibration, and case studies (Feb 2nd)
submitted by Mike E.

Introduction:  This week's session is also an IGERT seminar, so the choice of readings was somewhat dictated by the IGERT format.  McCarroll and Loader (2004) review the applications of stable isotopic measurements made in woods for paleoclimatic applications, and serves as a background reading.  Evans and Schrag (2004) describe a novel application since that paper: the development of chronological control and possibly paleoclimatic information from tropical woods lacking visual or structural chronological control, using high resolution isotopic measurements.  We'll focus our discussion on a critical evaluation of the second paper.

Reading:

• ML2004: McCarroll, D. and N.J. Loader, 2004: Stable isotopes in tree rings, Quaternary Science Reviews, 23:771-801.

• ES2004: Evans, M.N. and D.P. Schrag, 2004: A stable isotope-based approach to tropical dendroclimatology, Geochim et Cosmochim. Acta, 68(16): 3295-3305.
  

Reading questions:

• ML2004 describe the following advantages of tree rings for paleoclimate studies: (1) exact dating, (2) widespread distribution, (3) well-understood physiological controls on isotopic composition which (4) depend on conditions in the year in which the ring was formed.  Do you think these pronouncements are accurate descriptions of the situation?  How? How not?

• What are ML2004's recommended methods for sampling for isotope dendroclimatology?  Do these differ by measured isotope?  How do these differ from classical methods (e.g. Schulman, 1946 from last week; Stokes and Smiley, 1968)?  From the methods described in ES2004?

• What are the environmental and physiological controls on stable carbon and oxygen isotopic composition of tree rings?  What might we learn about environmental history or plant physiology from simultaneous collection of both carbon and oxygen isotopic data?  
  

• What assumptions are required to apply the Roden model of oxygen isotopic composition of the alpha-cellulose component of wood, as proposed in ES2004 for establishing chronology of tropical trees?  Can you think of additional means of validating the stable isotopic chronometer proposed by ES2004?

• Based on your own ideas, ML2004, and ES2004, how would you go about building (1) isotope chronologies for tropical trees and (2) paleoreconstructions of ENSO using stable isotopes from tropical trees?