New Mexico Geological Society Annual Spring Meeting — Abstracts

Two lacustrine sediment cores (70 m deep and 30 m deep respectively) were recovered from Stoneman Lake, northern Arizona in October of 2014. With these cores we plan to use multiple methods to determine regional hydroclimate variability between the Pleistocene-Holocene glacial transition ca. 14 ka. The geochemical analyses of these two cores have not yet been explored, but will provide us with invaluable information regarding age control, sources of precipitation to the basin (Gulf of Mexico vs North Pacific), and paleoprecipitation variability. I plan to use diatom oxygen isotope values to constrain precipitation source region changes to the southwest on glacial to interglacial timescales and to determine if the onset of paleomonsoonal precipitation occurs at the glacial termination (Leng and Barker, 2006, Dodd et al., in review). Other lacustrine cores from the southwest, such as the Valles Caldera, New Mexico record (Dodd et al., in review; Fawcett et al., 2011), will allow us to determine if the timing of the monsoon onset is similar in both locations, relative to the glacial termination, or if there is a lead or lag going from northern NM to north central AZ. The longitudinal extent (through NM and AZ) of the monsoon and the amount of monsoonal contribution to the glacial precipitation in Arizona (if any) can also be constrained. Other supporting data to be collected will include pollen and charcoal, total organic carbon, the δ¹³C of bulk organic matter and δ¹⁵N of total organic matter, C/N ratios, AMS radiocarbon dating, argon-argon dating, and XRF elemental information. By collecting data from this lacustrine sediment, we will be able to better reconstruct atmospheric paleocirculation patterns of the southwestern United States.

References:

1. Dodd, J. P., Fawcett, P.J., Sharp, Z.D., in review, Collapse of the summer monsoon during MIS 12 in the Southwest United States: Geology.
2. Fawcett, P.J., et al., 2011, Extended megadroughts in the southwestern United States during Pleistocene interglacials: Nature, v. 470, p. 518 – 521, doi: 10.1038/nature09839.
3. Leng, M.J., Barker, P.A., 2006, A review of the oxygen isotope composition of lacustrine diatom silica for palaeoclimate reconstruction: Earth Science Reviews, 75, 99. 5-27.