CALL FOR PROPOSALS:

ORGANIZERS

  • Harvey Thorleifson, Chair
    Minnesota Geological Survey
  • Carrie Jennings, Vice Chair
    Minnesota Geological Survey
  • David Bush, Technical Program Chair
    University of West Georgia
  • Jim Miller, Field Trip Chair
    University of Minnesota Duluth
  • Curtis M. Hudak, Sponsorship Chair
    Foth Infrastructure & Environment, LLC

 

Paper No. 38
Presentation Time: 6:15 PM

A 45,000 YEAR GEOCHEMICAL RECORD OF TEMPERATURE AND ARIDITY FROM LAKE CHALCO, MEXICO


RUBESCH, Meg, Large Lakes Observatory and Department of Geological Sciences, University of Minnesota-Duluth, 2205 E. 5th Street, Duluth, MN 55812, WERNE, Josef P., Department of Geology & Planetary Science, University of Pittsburgh, Pittsburgh, PA 15260, BROWN, Erik T., Large Lakes Observatory & Dept of Geol. Sci, University of Minnesota Duluth, RLB-109, 10 University Drive, Duluth, MN 55812, ORTEGA, Beatriz, Instituto de Geofisica, Universidad Nacional Autónoma de México, Ciudad Universitaria, México, AL 04510, Mexico, CABALLERO, Margarita, Instituto de Geofisica, Universidad Nacional Autónoma de México, México, 55280, Mexico and LOZANO, Socorro, Instituto de Geología, Universidad Nacional Autónoma de México, México, 55280, Mexico, pierc241@d.umn.edu

The water balance of the Southwestern United States and most of Mexico is dependent on regional climate systems, including the Mexican (or North American) Monsoon. The Mexican Monsoon leads to significant summer rainfall across a broad swath of the continent, which constitutes the major source of annual precipitation over much of this region. The position of the ITCZ and the strength of the accompanying monsoon are affected by variability in insolation. Stronger northern hemisphere summer insolation shifts the ITCZ northward, bringing about a more intense monsoon. Here we discuss a new geochemical climate record from Lake Chalco, Mexico, which couples inorganic (X-ray fluorescence) and organic (biomarkers and stable isotopes) geochemical proxies to reconstruct temperature and aridity over the past 45,000 years. The Basin of Mexico is a high altitude closed lacustrine basin (20ºN, 99ºW; 2240 m.a.s.l.) in the Trans Mexican Volcanic Belt. The plain of Lake Chalco, located near Mexico City in the southern sub-basin, has an area of 120 km2 and a catchment of 1100 km2. Though the present-day lake has been reduced to a small marsh due to historic diversion of its waters, over longer timescales the lake has been a sensitive recorder of hydroclimatic variations. Low Ca concentrations indicate more arid periods during the late glacial (34 – 15 kybp) compared to the last interstadial or early Holocene. This observation is supported by the ratio of terrestrial to aquatic lipid biomarkers (long vs. short chain n-alkanes), which indicate greater relative inputs of aquatic biomarkers during wetter periods. The changes in aridity as shown in these geochemical proxies are compared with temperature as reflected in glycerol dialkyl glycerol tetraether (GDGT) based paleotemperature proxies to assess the extent to which insolation may have driven aridity variations, and with terrestrial and aquatic biomarker δ13C values to assess the impact of these observed climate changes on regional vegetation.
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