PATTERNS AND DRIVERS OF HYDROCLIMATE VARIABILITY ACROSS WESTERN NORTH AMERICA DURING THE LAST INTERGLACIAL (Invited Presentation)

Geomorphic and proxy evidence indicates large changes in effective moisture levels in water-sensitive western North America over the past 200 ka or more. Yet, hydroclimate conditions prior to the Last Glacial Maximum (~20 ka) are relatively poorly known. During the Last Interglacial Period (LIG: ~129–116 ka), orbitally driven differences in seasonal and latitudinal distribution of incoming solar radiation led to northern hemisphere, high-latitude warming comparable to that projected in low emissions scenarios for the end of the 21st century. We synthesize existing LIG proxy information for North America, compare it to LIG (127 ka) climate model simulations from the Paleoclimate Modelling Intercomparison Project 4 (PMIP4), and examine spatial patterns and possible drivers of LIG hydroclimate. We also describe our ongoing efforts to refine LIG proxy records in western North America by improving the chronologies of long-lived, closed-basin lake records via U-Th dating and applying novel proxies (Δ47, Δ17O) to lake sediments and LIG speleothems.

Our network of moisture sensitive proxies from across North America includes 39 records derived from LIG lake and marine sediments, speleothems, and geomorphic evidence. Underlying chronologies vary in precision and accuracy since the LIG lies beyond radiocarbon range. Using the Gwet’s AC2 statistic, we compare this network with annual precipitation output from 17 individual PMIP4 models and model ensembles. The PMIP4 ensemble shows LIG wetness in Alaska, northern Canada, and the southwestern US, and the models that agree most closely with the LIG proxies also show wetness across the eastern US and aridity in the Pacific Northwest and central US. We identify a subset ensemble of the three models with the highest AC2 values that maximize agreement with the proxy network. By examining atmospheric dynamics in this subset, we find that LIG precipitation patterns in western North America were driven by pressure gradients across the North Pacific that were weaker during winter and steeper during the summer than at present. Improved chronologies and more informative lake and speleothem records from the LIG will facilitate parsing of the influence of precipitation seasonality, moisture transport, and humidity on LIG proxy records.