Clumped isotope evidence for Early Jurassic extreme polar warmth and high climate sensitivity - Université Claude Bernard Lyon 1 Accéder directement au contenu
Article Dans Une Revue Climate of the Past Année : 2022

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

Résumé

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 (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 midpaleolatitudes. 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 ‰ VS-MOW 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.
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Dates et versions

hal-03607369 , version 1 (13-03-2022)

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Thomas Letulle, Guillaume Suan, Mathieu Daëron, Mikhail Rogov, Christophe Lécuyer, et al.. Clumped isotope evidence for Early Jurassic extreme polar warmth and high climate sensitivity. Climate of the Past, 2022, 18 (3), pp.435 - 448. ⟨10.5194/cp-18-435-2022⟩. ⟨hal-03607369⟩
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