Climatological Drivers of Plio-Pleistocene Lakes in Western North
America: Evaporation, Precipitation, or El Niño?
San Jose State University Geology Club, November 30th 2015
Presenter: Daniel Ibarra, Stanford University
Collaborators: Andrea J. Ritch, Jessica L. Oster, Matthew J. Winnick, Jeremy K. Caves, Anne
E. Egger, Kate Maher, C. Page Chamberlain
Abstract
Evidence for the persistence of large inland lakes in western North America during the
Pliocene and Pleistocene provides first-order constraints on the regional water balance. The
spatial distribution of terminal lakes records changes in regional moisture delivery dynamics,
such as El Niño teleconnections and steering of the westerlies. In this talk I will discuss
completed and ongoing work to investigate the climatological conditions driving lake levels in
western North America during the mid-Pliocene warm period and Pleistocene glacial maxima.
Geologic evidence suggests wet conditions persisted in this region during both periods despite
dramatically different boundary conditions and pCO2 levels. I will present results of lake isotope
mass balance modeling and compare them to climate model simulations of the Last Glacial
Maximum (LGM) and mid-Pliocene produced by the Paleoclimate Modelling Intercomparison
Project (PMIP and PlioMIP). Reduced evaporation and moderate increases in precipitation,
relative to modern, led to moderate lake levels during the LGM. In contrast, larger precipitation
increases may be the primary driver of lake levels during the Pliocene, suggesting a role for El
Niño teleconnections during the mid-Pliocene. In addition, I will present a proxy-model
synthesis for the LGM and demonstrate that similar synthesis work on the mid-Pliocene is
possible with existing geologic observations.
Pleistocene shorelines of Surprise Valley, California (Anne Egger)
Lake level reconstruction for Lake Surprise, California (Ibarra et al., 2014)
Steering of the westerly storm track during the last glacial (Oster et al., 2015; Putnam, 2015)
Published References:
Maher, K., Ibarra, D.E., Oster, J.L., Miller, D.M., Redwine, J.L., Reheis, M.C., Harden, J.H.,
2014, Uranium isotopes in soils as a proxy for past infiltration and precipitation across
the western United States, American Journal of Science, 341 (4), 821-857. doi:
10.2475/04.2014.01
Ibarra, D.E., Egger, A.E., Weaver, K.L., Harris, C.R., Maher, K., 2014, Rise and fall of late
Pleistocene pluvial lakes in response to reduced evaporation and precipitation: Evidence
from Lake Surprise, California, Geological Society of America Bulletin, 126 (11-12),
1387-1415. doi: 10.1130/B31014.1
Oster, J.L., Ibarra, D.E., Winnick, M.J., Maher, K., 2015, Steering of the westerly storm track
over western North America at the Last Glacial Maximum, Nature Geoscience, 8 (3),
201-205. doi: 10.1038/ngeo2365