Hot summers in the Western United States during the Late Cretaceous and Early Cenozoic

Abstract

Understanding how seasonal temperatures on land respond to global greenhouse climate conditions is important for predicting effects of climate change on ecosystem structure, agriculture and distributions of natural resources. Fossil floral and faunal assemblages suggest winter temperatures in middle and high latitude continental interiors during the Cretaceous and early Cenozoic were at or above freezing, whereas terrestrial summer temperature estimates are uncertain. Carbonate clumped isotope (Δ_(47)) temperature estimates from lacustrine and paleosol carbonates appear to be generally biased toward summer temperatures in middle and high latitudes. Though problematic for reconstructing mean annual temperature (MAT), this bias presents an opportunity to reconstruct terrestrial summer temperatures and, through comparison with paleobotanical data, estimate past terrestrial seasonality.

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