LATE HOLOCENE NORTH AMERICAN HYDROCLIMATE REVEALED FROM HIGH-RESOLUTION MID-CONTINENTAL LAKE SEDIMENT RECORDS: NEW PERSPECTIVES ON MEGA-DROUGHTS, PLUVIALS AND HUMAN RESPONSES

Severe and prolonged droughts are a common feature of late Holocene North American climate. The spatiotemporal patterns of droughts and pluvials (wet periods), however, are not well constrained for some regions of the US, especially in the Midwestern US. Improving drought reconstructions from this region is critical in order to improve a mechanistic understanding of their timing, distribution, magnitude and forcing mechanisms. Several periods of profound and persistent drought during the last 2000 years have been identified in North America in recent decades. Among the most severe were a series of multi-decadal mega-droughts during the so-called Medieval Climate Anomaly (900 to 1300 CE). These Medieval mega-droughts have been suggested to reflect mid-latitude atmospheric circulation anomalies associated the Pacific Decadal Oscillation that are consistent with modes of the Pacific North American pattern (PNA). Because the PNA influences climate across the continental US in predictable ways, an improved network of late Holocene hydroclimate records can be used to evaluate its contribution to North American droughts and pluvials. Here, sedimentological, geochemical and isotopic results are presented from finely laminated Midwestern lake sediment archives that span the last 2300 years at sub-decadal resolution. These lake records capture climatic variability at in-lake, watershed, and synoptic spatial scales and provide new insight into Midwestern and North American hydroclimate dynamics including mega-droughts and pluvials. Our results support the idea that the tropical Pacific, Northern Hemisphere temperatures and the PNA have been tightly linked during at least the late Holocene and that variability in these systems manifested as a bi-modal distribution of precipitation with the western and eastern continental United States exhibiting largely antiphased hydroclimate responses. Comparison of these new results with existing archaeological data additionally supports strong linkages between hydroclimate and pre-Columbian population and cultural dynamics that are consistent with the observed west-east hydroclimate antiphasing.