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

• Main Authors: Letulle, Thomas, Suan, Guillaume, Daëron, Mathieu, Rogov, Mikhail, Lécuyer, Christophe, Vinçon-Laugier, Arnauld, Reynard, Bruno, Montagnac, Gilles, Lutikov, Oleg, Schlögl, Jan
• Format: Text
• Language: English
• Published: 2021
• Subjects: geo; anthro-bio; Arctic
• Online Access: https://doi.org/10.5194/cp-2021-79; https://cp.copernicus.org/preprints/cp-2021-79/

Periods of high atmospheric CO2 levels during the Cretaceous-Early Paleogene (~140 to 33 My ago) were marked by very high polar temperatures and reduced latitudinal gradients relative to the Holocene. These features represent a challenge for most climate models, implying either higher-than-predicted climate sensitivity to atmospheric CO2, or systematic biases or misinterpretations in proxy data. Here, we present a reconstruction of marine temperatures at polar (>80°) and mid (~40°) paleolatitudes during the Early Jurassic (~180 My ago) based on the clumped isotope (Δ47) and oxygen-isotope (δ18Oc) analyses of mildly buried pristine mollusc shells. Reconstructed calcification temperatures range from ~8 to ~18 °C in the Toarcian Arctic and from ~24 to ~28 °C in Pliensbachian mid-paleolatitudes. These polar temperatures were ~10–20 °C higher than present along with reduced latitudinal gradients. Reconstructed seawater oxygen isotope values (δ18Ow) of −1.5 to 0.5 ‰ VSMOW and of −5 to −2.5 ‰ VSMOW at mid and polar paleolatitudes, respectively, point to a significant freshwater contribution in Arctic regions. This highlight the risk of assuming the same δ18Osw value for δ18O-derived temperature from different oceanic regions. These findings provide critical new constraints for model simulations of Jurassic temperatures and δ18Osw values and suggest that high climate sensitivity is a hallmark of greenhouse climates since at least 180 My.