INTEGRATING PROXY NETWORKS AND CLIMATE MODELS TO EVALUATE PATTERNS AND DRIVERS OF PAST HYDROCLIMATE CHANGE IN WESTERN NORTH AMERICA (Invited Presentation)

Quaternary paleoclimate archives including lakes, soils, packrat middens, and caves, document the expansion and contraction of pluvial lakes, shifting vegetation zones, and changing infiltration rates, all evidence of dramatic hydrologic changes in western North America (WNA). Here, we use this network of paleoclimate information to map patterns of hydrologic variability in WNA across space and time in order to investigate driving mechanisms of hydrologic change as well as global teleconnections. We present statistical comparisons between the network of WNA proxies and archived climate model simulations produced by the Paleoclimate Modeling Intercomparison Project at two time slices: the Last Glacial Maximum (LGM, 21 ka) and the mid-Holocene (MH, 6 ka). Further, we investigate regional and global teleconnections across the intervening deglacial period (10 to 20 ka) through statistical comparisons of well-dated, high-resolution speleothem oxygen isotope records from WNA and elsewhere.

Proxy records demonstrate that, in areas dominated by winter precipitation, WNA sees a transition from a northwest-southeast trending dry-wet dipole pattern at the LGM to a pattern of overall aridity at the MH. Climate models generally reproduce the precipitation dipole pattern of the LGM, with those that most closely match the proxy network simulating strong winter high pressure cells in the western Pacific and over the Laurentide Ice Sheet that steer the LGM storm track across WNA. Models show overall less agreement with the WNA proxy network during the MH, with many simulating a much wetter WNA than the proxies record, especially in California. However, some models that more closely match the MH proxy network display winter atmospheric patterns that resemble winter patterns seen during recent historical droughts. Speleothem time-series demonstrate a robust and consistent response across WNA to millennial-scale climate events that occurred in the transition from the LGM to the MH. We find strong statistical linkages between WNA speleothem records and others influenced by Asian monsoon variability and movement of the Intertropical Convergence Zone, demonstrating that nearly synchronous changes in atmospheric circulation measurably altered precipitation dynamics in these regions during the last deglaciation.