Paleoclimate Changes in the Pacific Northwest Over the Past 36,000 Years from Clumped Isotope Measurements and Isotope-Enabled Model Analysis

Since the last glacial period, North America has experienced dramatic changes in regional climate, including the collapse of ice sheets and changes in effective precipitation. We use clumped isotopes and analysis of transient climate simulations to provide constraints on hydroclimate changes in the Pacific Northwest. The coldest soil temperatures (~10.5 ±1.°C to 14.9 ±1.2°C) occurred ~34,000−23,000 years ago. Glacial warm average monthly temperatures (~1°C) and mean annual air temperature (~-9°C) indicate regional warming of 20.1 ± 2.6°C was about three times the global average. Proxy data confirm the boundary of the cooler anticyclone induced by LGM ice sheets, and the warmer cyclone in the Eastern Pacific Ocean. Model analysis suggests regional amplification is due to the proximal location of the study area to the Laurentide Ice Sheet margin and the impact of the glacial anticyclone on the region, as well as local albedo. Isotope-enabled model experiments indicate variations in water δ18O largely reflect circulation changes, with westerly winds and associated storm tracks bringing more depleted vapor to the region during the LGM.