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

• Published in: Climate of the Past
• Main Authors: T. Letulle, G. Suan, M. Daëron, M. Rogov, C. Lécuyer, A. Vinçon-Laugier, B. Reynard, G. Montagnac, O. Lutikov, J. Schlögl
• Format: Article in Journal/Newspaper
• Language: English
• Published: Copernicus Publications 2022
• Subjects: Environmental pollution; TD172-193.5; Environmental protection; TD169-171.8; Environmental sciences; GE1-350; Arctic
• Online Access: https://doi.org/10.5194/cp-18-435-2022; https://doaj.org/article/830c7d2ad3964a438f20656d4e3a2529

Periods of high atmospheric CO 2 levels during the Cretaceous–early Paleogene ( ∼ 140 to 34 Myr 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 CO 2 or systematic biases or misinterpretations in proxy data. Here, we present a reconstruction of marine temperatures at polar ( > 80 ∘ ) and middle ( ∼ 40 ∘ ) paleolatitudes during the Early Jurassic ( ∼ 180 Myr ago) based on the clumped isotope ( Δ 47 ) and oxygen isotope ( δ 18 O c ) analyses of shallow 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 ( δ 18 O w ) of − 1.5 ‰ to 0.5 ‰ VSMOW and of − 5 ‰ to − 2.5 ‰ VSMOW at middle and polar paleolatitudes, respectively, point to a significant freshwater contribution in Arctic regions. These data highlight the risk of assuming the same δ 18 O sw value for δ 18 O-derived temperature from different oceanic regions. These findings provide critical new constraints for model simulations of Jurassic temperatures and δ 18 O sw values and suggest that high climate sensitivity has been a hallmark of greenhouse climates for at least 180 Myr .