Clumped isotope evidence for Early Jurassic extreme polar warmth and high climate sensitivity

Abstract. Periods of high atmospheric CO2 levels during the Cretaceous–early Paleogene (∼ 140 to 34 Myr ago) were marked by very polar temperatures and reduced latitudinal gradients relative Holocene. These features represent a challenge for most climate models, implying either higher-than-predicted sensitivity or systematic biases misinterpretations in proxy data. Here, we present reconstruction marine at (> 80∘) middle 40∘) paleolatitudes Early Jurassic 180 based on clumped isotope (Δ47) oxygen (δ18Oc) analyses shallow buried pristine mollusc shells. Reconstructed calcification range from ∼ 8 18 ∘C Toarcian Arctic 24 28 Pliensbachian mid-paleolatitudes. 10–20 higher than along with gradients. seawater values (δ18Ow) −1.5 ‰ 0.5 VSMOW −5 −2.5 paleolatitudes, respectively, point significant freshwater contribution regions. data highlight risk assuming same δ18Osw value δ18O-derived temperature different oceanic findings provide critical new constraints model simulations suggest that has been hallmark greenhouse climates least Myr.