Stevens, Lora R. , Stone, Jeffery R. , Campbell, Josh , Fritz, Sherilyn C.

A 2200-yr record of hydrologic variability from Foy Lake, Montana, USA, inferred from diatom and geochemical data

Stevens, L. R., Stone, J. R., Campbell, J. and Fritz, S. C.: A 2200-yr record of hydrologic variability from Foy Lake, Montana, USA, inferred from diatom and geochemical data, Quaternary Research, 65(02), 264–274, doi:10.1016/j.yqres.2005.08.024, 2006.

Finnigan MAT 252 isotope-ratio mass spectrometer (IRMS) interfaced with an automated Kiel device

We sampled the sediments contiguously at 3-year intervals for the past 250 years and at 5-year intervals for the remainder of the past 3100 years.

The d18O 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. d18O is strongly correlated with the index of the Pacific Decadal Oscillation (PDO) during the past 100 years, and periodicities of the late- Holocene d18O record are similar to those of the PDO. Furthermore, time series of d18O and atmospheric D14C 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.;a highly significant, positive correlation (r = 0.63, n = 32, p < 0.0001) exists between d18O and the PDO. This pattern can be explained by the negative correlation of the PDO with measured winter (r = 0.44, n = 103, p < 0.001) and summer (r = 0.35, n = 103, p < 0.001) precipitation near Steel Lake. Dry winters likely decrease the proportion of 18O-depleted winter precipitation entering the lake, and dry summers enhance evaporative 18O-enrichment of lake watea highly significant, positive correlation (r = 0.63, n = 32, p < 0.0001) exists between d18O and the PDO. This pattern can be explained by the negative correlation of the PDO with measured winter (r = 0.44, n = 103, p < 0.001) and summer (r = 0.35, n = 103, p < 0.001) precipitation near Steel Lake. Dry winters likely decrease the proportion of 18O-depleted winter precipitation entering the lake, and dry summers enhance evaporative 18O-enrichment of lake wate