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Isotopic evidence for temporal variation in proportion of seasonal precipitation since the last glacial time in the inland Pacific Northwest of the USA
Authors:Akinori Takeuchi  Angela J Goodwin  Bryan G Moravec  Peter B Larson  C Kent Keller
Institution:aSchool of Earth and Environmental Sciences, Washington State University, P.O. Box 642812, Pullman WA 99164-2812, USA
Abstract:Large-scale atmospheric circulation patterns determine the quantity and seasonality of precipitation, the major source of water in most terrestrial ecosystems. Oxygen isotope (δ18O) dynamics of the present-day hydrologic system in the Palouse region of the northwestern U.S.A. indicate a seasonal correlation between the δ18O values of precipitation and temperature, but no seasonal trends of δ18O records in soil water and shallow groundwater. Their isotope values are close to those of winter precipitation because the Palouse receives not, vert, similar 75% of its precipitation during winter. Palouse Loess deposits contain late Pleistocene pedogenic carbonate having ca. 2 to 3‰ higher δ18O values and up to 5‰ higher carbon isotope (δ13C) values than Holocene and modern carbonates. The late Pleistocene δ18O values are best explained by a decrease in isotopically light winter precipitation relative to the modern winter-dominated infiltration. The δ13C values are attributed to a proportional increase of atmospheric CO2 in soil CO2 due to a decrease in soil respiration rate and 13C 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.
Keywords:Stable isotopes  Hydrologic cycle  Paleoclimate  Pedogenic carbonate  Late Quaternary  North America
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