Geological Society of America

T135 Cenozoic Lakes Across Western North America – from the Varved Beds of the Green River Formation to the Ice-Covered Alpine Lakes of the Sierra Nevada

Monday, 23 September 2024
1:30 PM - 5:30 PM
213B

NORTH PACIFIC RESPONSE TO HEMISPHERIC WARMING FORCES HOLOCENE DROUGHT IN THE SOUTHWESTERN UNITED STATES

Paper number: T135-11
Program: Technical Sessions
Time: 4:00 PM – 4:15 PM

Authors

Victoria Todd Presenting Author
The University of Texas at Austin, Austin, TX
Alexander J. Thompson
Washington University, St. Louis, MO
Jiang Zhu
National Center for Atmospheric Research, Boulder, CO
Timothy Shanahan
Jackson School of Geosciences, Austin, TX
Pedro DiNezio
University of Colorado Boulder, Boulder, CO
Jeremy M. Klavans
University of Colorado Boulder, Boulder, CO
Peter Fawcett
University of New Mexico, Albuquerque, NM
R. Scott Anderson
Northern Arizona University, Flagstaff, AZ
Gonzalo Jimenez-Moreno
Universidad de Granada, Granada
Allegra LeGrande
Columbia University, New York, NY
Allegra LeGrande
Goddard Institute for Space Studies, New York, NY
Francesco S.R. Pausata
University of Quebec in Montreal, Montreal, QC

Abstract

The Southwest United States is susceptible to severe and persistent drought. Yet, the impact of human-induced climate change on both current and future precipitation patterns in this region through atmospheric circulation changes remains unclear. This study provides insights into how the climate system responds to external forcings by investigating the mechanisms driving widespread and prolonged winter aridity in response to insolation-forced changes during the mid-Holocene. We generated biomarker records of hydrologic variability from two sites in the southern Rocky Mountains and quantified mid-Holocene changes in seasonal moisture sources using a Bayesian stable isotope mixing model. To better characterize the spatial patterns of mid-Holocene climate change, we synthesized data on North Pacific sea surface temperature and North American hydroclimate from the published literature. We then used a large ensemble of climate model simulations for the mid-Holocene to assess the underlying causes of drought. The inclusion of paleoecologically realistic vegetation changes in mid-Holocene simulations drives significant warming of the Northern Hemisphere and enhances aridity in the western US, improving proxy-model agreement.Hemispheric warming drives the emergence of a negative PDO-like sea surface temperature pattern and a weakening of the Aleutian Low, resulting in winter precipitation declines. Similarly, large climate model ensembles for future scenarios show a forced PDO-like pattern in the Pacific, leading to persistent winter droughts. However, our findings indicate that models may underestimate the magnitude of winter precipitation reductions. Consequently, future drought risks may be underestimated, especially for systems reliant on winter moisture supply.

Geological Society of America Abstracts with Programs. Vol. 56, No. 5

doi: 10.1130/abs/2024AM-404046

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