Isotopic evidence for temporal variation in proportion of seasonal precipitation since the last glacial time in the inland Pacific Northwest of the USA

• Published in: Quaternary Research
• Main Authors: Takeuchi, Akinori, Goodwin, Angela J., Moravec, Bryan G., Larson, Peter B., Keller, C. Kent
• Format: Article in Journal/Newspaper
• Language: English
• Published: Cambridge University Press (CUP) 2009
• Subjects: Pacific; Ice Sheet
• Online Access: http://dx.doi.org/10.1016/j.yqres.2009.06.001; http://api.elsevier.com/content/article/PII:S0033589409000696?httpAccept=text/xml; http://api.elsevier.com/content/article/PII:S0033589409000696?httpAccept=text/plain; https://www.cambridge.org/core/services/aop-cambridge-core/content/view/S003358940000644X

Abstract Large-scale atmospheric circulation patterns determine the quantity and seasonality of precipitation, the major source of water in most terrestrial ecosystems. Oxygen isotope (δ 18 O) dynamics of the present-day hydrologic system in the Palouse region of the northwestern U.S.A. indicate a seasonal correlation between the δ 18 O values of precipitation and temperature, but no seasonal trends of δ 18 O records in soil water and shallow groundwater. Their isotope values are close to those of winter precipitation because the Palouse receives ∼ 75% of its precipitation during winter. Palouse Loess deposits contain late Pleistocene pedogenic carbonate having ca. 2 to 3‰ higher δ 18 O values and up to 5‰ higher carbon isotope (δ 13 C) values than Holocene and modern carbonates. The late Pleistocene δ 18 O values are best explained by a decrease in isotopically light winter precipitation relative to the modern winter-dominated infiltration. The δ 13 C values are attributed to a proportional increase of atmospheric CO 2 in soil CO 2 due to a decrease in soil respiration rate and 13 C discrimination in plants under much drier paleoclimate conditions than today. The regional climate difference was likely related to anticyclonic circulation over the Pleistocene Laurentide and Ice Sheet.