|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]|
Possible linkages of late-Holocene drought in the North American midcontinent to Pacific Decadal Oscillation and solar activity
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.
The Last 500 Years
Droughts of the last four centuries are well documented in paleoclimatic proxies such as historical documents and tree rings. Spatial patterns of drought for every year since 1700 have been generated from a gridded network of tree-ring reconstructions and are featured in this section. Highlighted in this section are those periods with droughts that appear to have been more severe than any we have experienced in the 20th century.
The Last 2000 Years
A number of tree-ring records exist for the last two millennia which suggest that 20th century droughts may be mild when evaluated in the context of this longer time frame. The evidence from long tree-ring records is augmented with paleodrought records from other proxies, such as lake sediments that reflect changes in salinity and precipitation/evaporation balances.