EVIDENCES OF CLIMATE CHANGE, VOLCANIC AND HUMAN IMPACT DURING THE LATE PLEISTOCENE AND HOLOCENE: THE RECORD OF LAKE ZIRAHUEN, WESTERN CENTRAL MEXICO

Paleoclimatic studies carried out in central Mexico have documented variations in temperature and humidity during the late Pleistocene, a 6 to 8ºC decrease in temperature is estimated during the late glacial maximum. During the last deglaciation asynchronous warming occurred across the tropical band; moisture and temperature changes and the effects of meltwater input into the Gulf of Mexico affected the past climates in central Mexico. Furthermore, during the Holocene abrupt changes has been documented from paleo-records of the central Mexico highlands. An important factor promoting environmental changes in the region has been human activities that transformed the landscape.

We present paleoecological data (pollen, charcoal, magnetic susceptibility, TIC, TOC) of two well dated sedimentary sequences from the northern shore and central part of Lake Zirahuen (102°44’ W; 19°26’N) in western central Mexico. The records provides evidence of vegetation change surrounding the lake offering indications of climate change, deforestation, erosion and fire events that affected the terrestrial and aquatic ecology and hydrology in the basin during the last 17,000 cal kyr BP.

The paleoecological data from the sedimentary sequences of Lake Zirahuen reveled dynamic terrestrial and lacustrian environments during the last 17 kyr. Results indicated dry and cold conditions in the basin with a low of lake level from 17 to 15 kyr followed by increase in moisture availability from 13.5 to 12.1 kyr. The deglaciation record shows high and rapid vegetation turnover with elevated ecological changes. From 12.1 to 7.2 kyr a hiatus is present in the northern sequence probably related to sediment erosion by regression of the lake and the emplacement of La Maguyera lava flows. Warmer and humid conditions prevailed during the early Holocene and three periods of high ecological change were recorded at 9, 8.2 and 7.5 kyr. During the mid-Holocene a short phase of drier conditions between 4.5 and 4.2 was recorded and rapid changes in the terrestrial ecosystem characterize the late Holocene. Synchronic ecological change in both sequences indicates that human impact was probably the driving factor during this time.