P2C2: Collaborative Research: Quantitative Reconstruction of Past Drought Patterns in Western North America Using Lakes, Stable Isotopes, and Modeling

This collaborative grant will help address current shortcomings of the data we have on Western droughts during the last 6,000 years. Currently most data on droughts has been derived from tree-ring records, but we have realized that although tree-ring data give excellent annual resolution, trees tend to record only summer weather while they are actually growing the ring, and winter weather is under-represented because ring growth is slow or stopped during this season. Given the importance of winter precipitation for much of the West, this gap in data has made accurate modeling difficult, and this grant will attempt to address that by sampling lake sediments, which 'record' the weather throughout the year in their bottom sediments, although at less than annual resolution. This work will result in a new map of droughts throughout the study period that will incorporate previous lake and tree-ring records from a region spanning from British Columbia in the Northwest to New Mexico in the Southeast.

The grant will produce six new lacustrine sediment records (two from British Columbia, two from Alberta and two from New Mexico) that would extend 6000 years through the middle Holocene and conduct sedimentological analyses on core transects from closed-basin lakes to constrain water-level changes as a physical means of confirming the magnitude of hydrologic change inferred from the stable isotope measurements. The Penn State group will use paleodrought data produced previous efforts in Washington and British Columbia, as well as data from published research to improve intermediate complexity Earth system model (EMIC) data assimilation exercises, while the Pitt and UMN-D groups will produce new lake-level and stable isotope data from sites in the Pacific northwest and the desert southwest that have already been identified and in several cases cored. The team would combine analyses of open-basin isotope records and leaf wax deuterium measurements with the closed-basin and algal biomarker records to produce reconstructions of drought variability that are not influenced by changes in the isotopic composition of precipitation. The team has quantitatively interpreted the lake sediment oxygen isotope and lake level records using hydrologic and isotope mass balance models, and will synthesize the resulting data to produce a gridded, paleodrought network. These reconstructions would be used to investigate hypotheses regarding contrasting, North-South drought patterns in the Pacific Northwest and the desert Southwest during the Medieval Climate Anomaly, the Little Ice Age and middle Holocene.

The project will support two graduate students in the field and laboratory, as well as some undergraduate research activities, and the results will be published in peer-reviewed journals, presented at professional conferences and public meetings. The collected cores will be available for further sampling by other researchers, and the results will be made publicly accessible and available in a NOAA database.