Articles | Volume 11, issue 9
Research article
30 Sep 2015
Research article |  | 30 Sep 2015

Climatic variability and human impact during the last 2000 years in western Mesoamerica: evidence of late Classic (AD 600–900) and Little Ice Age drought events

A. Rodríguez-Ramírez, M. Caballero, P. Roy, B. Ortega, G. Vázquez-Castro, and S. Lozano-García

Abstract. We present results of analysis of biological (diatoms and ostracodes) and non-biological (Ti, Ca / Ti, total inorganic carbon, magnetic susceptibility) variables from an 8.8 m long, high-resolution (~ 20 yr sample−1) laminated sediment sequence from Lake Santa María del Oro (SMO), western Mexico. This lake lies at a sensitive location between the dry climates of northern Mexico, under the influence of the North Pacific subtropical high-pressure cell and the moister climates of central Mexico, under the influence of the seasonal migration of the intertropical convergence zone and the North American monsoon (NAM). The sequence covers the last 2000 years and provides evidence of two periods of human impact in the catchment, shown by increases in the diatom Achnanthidium minutissimum. The first from AD 100 to 400 (Early Classic) is related to the shaft and chamber tombs cultural tradition in western Mexico, and the second is related to Post-Classic occupation from AD 1100 to 1300. Both periods correspond to relatively wet conditions. Three dry intervals are identified from increased carbonate and the presence of ostracodes and aerophilous Eolimna minima. The first, from AD 500 to 1000 (most intense during the late Classic, from AD 600 to 800), correlates with the end of the shaft and chamber tradition in western Mexico after ca. AD 600. This late Classic dry period is the most important climatic signal in the Mesoamerican region during the last 2000 years, and has been recorded at several sites from Yucatan to the Pacific coast. In the Yucatan area, this dry interval has been related with the demise of the Maya culture at the end of the Classic (AD 850 to 950). The last two dry events (AD 1400 to 1550 and 1690 to 1770) correspond with the onset of, and the late, Little Ice Age, and follow largely the Spörer and Maunder minima in solar radiation. The first of these intervals (AD 1400 to 1550) shows the most intense signal over western Mexico; however this pattern is different at other sites. Dry/wet intervals in the SMO record are related with lower/higher intensity of the NAM over this region, respectively.

Short summary
We present results from western Mexico, where very few palaeoclimatic research sites exist. The record has good chronological resolution (ca. 20 years) and clear climatic trends during the last 2ka. The most important signals are: dry conditions during the late Classic (AD 500 to 1000), especially from AD 600 to 800, and low lake levels during the LIA, in two phases that follow Spörer and Maunder solar minima. Drier conditions are related with a lower intensity of the North American monsoon.