Loess–paleosol carbonate clumped isotope record of late Pleistocene–Holocene climate change in the Palouse region, Washington State, USA

The Channeled Scabland-Palouse region of the Pacific Northwest (PNW) of the United States preserves geomorphic and pedosedimentary records that inform understanding of late Pleistocene-Holocene paleoclimate change in a region proximal to the last glacial period Cordilleran Ice Sheet. We present a clumped (Delta(47)) and conventional (delta O-18, delta C-13) isotopic study of Palouse loess-paleosol carbonates in combination with carbonate radiocarbon (C-14) dating to provide new measures of regional late-last glacial (similar to 31-20 cal ka BP) and Holocene soil conditions. Average clumped isotope temperatures (T(Delta(47))) for last glacial Palouse loess-paleosol carbonates (9 +/- 4 degrees C) are significantly lower than those for Holocene-aged carbonates (T(Delta(47)) = 18 +/- 2 degrees C) in study sections. Calculated soil water delta O-18(VSMOW) values (-16 +/- 2 parts per thousand) for last glacial carbonates are also offset relative to those for Holocene-aged samples (-11 +/- 1 parts per thousand), whereas calculated soil CO2 delta C-13(VPDB) values are similar for the Holocene (-16.9 +/- 0.2 parts per thousand) and late-last glacial (-16.7 +/- 1.1 parts per thousand) periods. Together, these paleoclimate metrics indicate late-last glacial conditions of pedogenic carbonate formation in the C-3 grassland soils of the Palouse were measurably colder (9 +/- 5 degrees C) than during the Holocene and potentially reflect a more arid last glacial paleoclimate across the Palouse, findings in agreement with previous proxy studies and climate model simulations for the region.