A PRELIMINARY PALEOCLIMATIC AND PALEOECOLOGICAL RECONSTRUCTION FOR HIGHLAND OAXACA, MEXICO

We present preliminary data from a 5.6m lacustrine core and a ~75-year tree ring chronology collected in Oaxaca, Mexico in 2008. Oaxaca is located in southwestern Mexico. The region is characterized by significantly varying topography and climate with a savannah climate (Koppen Aw) in the lowlands and semi-arid to arid (Koppen BSh and BWh) conditions at higher elevation. Oaxacan climate is regulated by two of the planet’s most significant climate drivers: the Intertropical Convergence Zone (ITCZ) and El Nino/Southern Oscillation (ENSO), making it a promising location for globally relevant paleoclimate studies. The study site is a small lake (~0.1 ha) bounded by agricultural fields and pine forest and lies at an elevation of 2500m. The core displays visible lamination couplets as fine, white clay layers and darker coarser layers. The layers consistently fine upward from dark to light, evidence for the recurrent wet and dry season sedimentation regimes. Quantification of the lamination couplets indicate a basal age of ~4000 years. If these laminations are varves, they will offer the potential for a temporally long, annual resolution climatic record. Preliminary analyses include several non-destructive techniques including X-radiography, gamma density, magnetic susceptibility and high-resolution digital imagery. Magnetic susceptibility data suggest major fluctuations in local runoff over millennial time scales, and appear to correspond with the regional archeological history. The trees cross-date within the study site; though, correlation to annual precipitation is hindered by sparse local meteorological records.