Paleoclimate Changes in the Pacific Northwest Over the Past 36,000 Years From Clumped Isotope Measurements and 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 precipitation. We use clumped isotope (∆47) thermometry and carbonate δ18O measurements of glacial and deglacial pedogenic carbonates from the Palouse Loess to provide constraints on hydroclimate changes in the Pacific Northwest. We also employ analysis of climate model simulations to help us further provide constraints on the hydroclimate changes in the Pacific Northwest. The coldest clumped isotope soil temperatures T(△47) (13.5 ± 1.9°C to 17.1 ± 1.7°C) occurred ∼34,000–23,000 years ago. Using a soil-to-air temperature transfer function, we estimate Last Glacial Maximum (LGM) mean annual air temperatures of ∼−5.5°C and warmest average monthly temperatures (i.e., mean summer air temperatures) of ∼4.4°C. These data indicate a regional warming of 16.4 ± 2.6°C from the LGM to the modern temperatures of 10.9°C, which was about 2.5–3 times the global average. Proxy data provide locality constraints on the boundary of the cooler anticyclone induced by LGM ice sheets, and the warmer cyclone in the Eastern Pacific Ocean. Climate model analysis suggests regional amplification of temperature anomalies 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 atmospheric circulation changes and enhanced rainout upstream that brings more depleted vapor to the region during the LGM

Carbonate stable and clumped isotopic evidence for late Eocene moderate to high elevation of the east-central Tibetan Plateau and its geodynamic implications

International audienceThe topographic history of mountain belts reflects changes in lithospheric structure and rheology and exerts an influence on climate. Although substantial progress has been made to constrain the growth history of the southern Tibetan Plateau, the timing and geodynamic drivers for surface uplift of the central plateau remain poorly constrained. Here, we used both carbonate clumped isotope geothermometry and modified stable isotope-based paleoaltimetry that considers proportional mixing of two major moisture sources to infer late Eocene paleoelevations of the Nangqian Basin in the east-central Tibetan Plateau. The mean clumped isotope temperature, T(Delta(47)), of minimally altered late Eocene lacustrine carbonates is 30.0 degrees C, and the reconstructed least-evaporated paleowater delta O-18(mw) value is -9.8 parts per thousand. These two independent approaches indicate that during late Eocene time, the Nangqian Basin floor was 2.7 (+0.6/-0.4) km above sea level, and the hypsometric mean elevation of surrounding mountains was 3.0 +/- 1.1 km above sea level. These estimates are 1.1-1.2 km lower than their modern counterparts. The moderate to high late Eocene paleoelevation of the Nangqian Basin suggests that Eocene upper-crustal shortening and thickening can explain most, but not all, of the surface uplift of the east-central Tibetan Plateau. The additional 1.1-1.2 km (at most) of post-late Eocene elevation increase to the present height may have been a result of either lower-crustal flow or slab detachment

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

International audienceSince the last glacial period, North America has experienced dramatic changes in regional climate, including the collapse of ice sheets and changes in precipitation. We use clumped isotope (∆47) thermometry and carbonate δ18O measurements of glacial and deglacial pedogenic carbonates from the Palouse Loess to provide constraints on hydroclimate changes in the Pacific Northwest. We also employ analysis of climate model simulations to help us further provide constraints on the hydroclimate changes in the Pacific Northwest. The coldest clumped isotope soil temperatures T((Formula presented.) 47) (13.5 ± 1.9°C to 17.1 ± 1.7°C) occurred ∼34,000–23,000 years ago. Using a soil-to-air temperature transfer function, we estimate Last Glacial Maximum (LGM) mean annual air temperatures of ∼−5.5°C and warmest average monthly temperatures (i.e., mean summer air temperatures) of ∼4.4°C. These data indicate a regional warming of 16.4 ± 2.6°C from the LGM to the modern temperatures of 10.9°C, which was about 2.5–3 times the global average. Proxy data provide locality constraints on the boundary of the cooler anticyclone induced by LGM ice sheets, and the warmer cyclone in the Eastern Pacific Ocean. Climate model analysis suggests regional amplification of temperature anomalies 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 atmospheric circulation changes and enhanced rainout upstream that brings more depleted vapor to the region during the LGM