Initial sedimentology, geocronology and oxygen isotope stratigraphy of a new core from Pretty Lake, Indiana: Exploring Midwestern hydroclimate during the last 2000 years
Thursday, 18 December 2014
Isotope-based hydroclimate records from the mid-continental United States that span the late Holocene with sub-decadal resolution are rare. As a result, the relationship between temperature and hydroclimate for this region is not well constrained. Pollen-based temperature reconstructions from North America suggest that the Medieval Climate Anomaly (MCA; 650 to 1050 CE) was warmer than the Little Ice Age (LIA; 1550 to 1850 CE), but that both were cooler than the current warm period (CWP; last 100 years). It has further been suggested that much of the mid-continental US experienced drought during the MCA and pluvial conditions during the LIA. This is supported by modern correlations between seasonal temperatures and precipitation, which are anti-correlated for much of the Midwest; however, for portions of the continental core, which includes the study region, the opposite relationship exists between temperature and precipitation (i.e., warmer is wetter and colder is drier). Within the context of this and previous paleoclimate work in the Midwest, including at Pretty Lake, we present initial geochronology, sedimentology and oxygen isotopic results from a new 12 m composite core from Pretty Lake, a 25 m deep kettle lake in LaGrange County, northeastern Indiana. Here we focus on the last 2000 years of the 16,000-year record in order to explore hydroclimate variability in response to temperature anomalies during the MCA and LIA. Pretty Lake is well suited for this type of investigation because the closed surface hydrology of the lake basin renders it sensitive to evaporation. This is reflected in oxygen isotope (δ18O) measurements of surface waters from the lake, which show that it is approximately 4‰ higher than meteoric precipitation and the surface waters of nearby, hydrologically-open Martin Lake. High-resolution down core δ18O measurements, therefore hold tremendous potential for reconstructing regional hydroclimate during the last 2000 years, particularly when combined with isotopic records of local precipitation and modeling approaches.