A 400,000-YEAR ENVIRONMENTAL HISTORY INTERPRETED FROM LACUSTRINE SEDIMENTS FROM THE BASIN OF MEXICO

MexiDrill, the Basin of Mexico Drilling Program recovered a ~400 kyr lacustrine record of subtropical North American environmental change at a site adjacent to Mexico City. This record has societal relevance as it provides context for consideration of changing environmental conditions in a densely populated, water-stressed region. Paleoclimatic reconstructions will enhance our knowledge of long-term natural climate variability in the North American subtropics, and its relationship to changes at higher latitudes. The site lies at the northern margin of the Intertropical Convergence Zone (ITCZ) where modern precipitation amounts are influenced by sea surface temperatures in the Pacific and Atlantic Basins. In addition, its sediments have recorded pre-Holocene volcanic history; knowledge of the magnitude and frequency relationships of the area’s explosive volcanic eruptions will improve risk assessments of future activity. Explosive eruption deposits provide the backbone of ongoing chronological work necessary for full exploitation of the paleoclimate record. Here will provide an overview of the project, and some initial results. XRF core scanning of a 350 m composite section of core provides data on the major element inorganic composition of the sediments. XRF scanning allows us to delineate aridity (Ca from preservation of calcium carbonate); estimate diatom productivity (Si/Ti); characterize tephras; evaluate changing sediment provenance (K/Ti); and estimate accumulation rates of terrigenous materials (Al and Ti). A preliminary interpretation indicates that glacial intervals (MIS 2, 6, and 8) are periods of wetter conditions, but that humid conditions were less marked during MIS 2 than earlier glacial periods. Two models from the Paleoclimate Modeling Intercomparison Project Phase 4 (PMIP4) were used to analyze hydroclimate anomalies and underlying ocean-atmosphere circulation patterns in the Neotropics during the Last Interglacial (LIG; ~127,000 years ago) and Last Glacial Maximum (LGM; ~21,000 years ago) to provide a basis of comparison for the paleoproxy data.