ABSTRACT

This research will test several hypotheses about the causes and spatial pattern of major drought at multi-decadal to millennial time scales in two drought prone regions of the North American continental interior: the northern Great Plains and northern Rocky Mountains. The first quantitative reconstruction of precipitation variation at decadal resolution that spans the entire Holocene will be generated for the northern Great Plains from inorganic and organic geochemical records preserved in regional lake sediments. In addition, the research will develop a relatively new geochemical indicator for continental settings, specifically the use of alkenones to reconstruct temperature variation in saline lakes.

Intellectual Merit
High-resolution paleoclimatic data suggest that, during the last two millennia, much of western North America experienced widespread severe drought that was more persistent than the droughts of the 20th century. It is unclear what produces these so-called megadroughts, because only a handful of high-resolution continental paleoclimatic records span more than the last 1000 to 2000 years. The proposed research will compare high resolution (decadal) records that extend through the entire Holocene from the northern Great Plains with records from the northern Rocky Mountains. The generation of records that span many millennia will enable an assessment of how the frequency of multi-decadal drought is influenced by changes in large-scale boundary conditions, such as the seasonal insolation differences that characterize the early versus late-Holocene. The long reconstructed time series of major drought in the mid continent will be compared with Pacific and North Atlantic sea-surface temperature records to evaluate 1) whether the northern Rockies and northern Great Plains are differentially sensitive to Atlantic versus Pacific variability, and 2) whether the relationship between drought and potential oceanic forcing is stationary through time. The research also will develop and apply a relatively new and powerful geochemical proxy for temperature reconstruction in continental settings, which has the potential to greatly improve our ability to interpret past climates and hydrologic responses.

Broader Impacts
Understanding the factors associated with severe persistent drought in the past is of societal benefit, because it enables an assessment of whether or not current water management plans are based on a sound understanding of the natural long-term variability of climate. To enhance the scientific understanding of the public and the people directly impacted by drought, the research will create an exhibit for a new state park in eastern Montana, located on the shores of the primary lake to be studied in this project. The exhibit will describe how lake sediments can be used to generate a history of climate and landscape evolution and the insights about drought history suggested by research carried out on this lake. In addition, three graduate students will receive training in interdisciplinary research of societal relevance.

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