|d18O is a proxy for precipitation and is correlated to changes over the past 3,100 years in solar activity [shown by the d14C proxy]|
Abstract: Paleorecords are key for evaluating the long-term patterns and controls of drought. We analyzed calcite in annually laminated sediments from a Minnesota lake for oxygen-isotopic composition (δ18O). The δ18O [precipitation proxy] record of the past ∼3100 years reveals that droughts of greater severity and duration than during the 20th century occurred repeatedly, especially prior to 300 AD. Drought variability was anomalously low during the 20th century; ∼90% of the variability values during the last 3100 years were greater than the 20th-century average. δ18O [the precipitation proxy] is strongly correlated with the index of the Pacific Decadal Oscillation (PDO) during the past 100 years, and periodicities of the late-Holocene δ18O record are similar to those of the PDO. Furthermore, time series of δ18O and atmospheric Δ14C [the solar activity proxy] are generally coherent after 700 AD. Both the Pacific climate and solar irradiance probably played a role in drought occurrence, but their effects were non-stationary through the late Holocene.