Preprints
https://doi.org/10.5194/cp-2021-79
https://doi.org/10.5194/cp-2021-79

  29 Jul 2021

29 Jul 2021

Review status: this preprint is currently under review for the journal CP.

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

Thomas Letulle1, Guillaume Suan1, Mathieu Daëron2, Mikhail Rogov3, Christophe Lécuyer1, Arnauld Vinçon-Laugier1, Bruno Reynard1, Gilles Montagnac1, Oleg Lutikov3, and Jan Schlögl4 Thomas Letulle et al.
  • 1Univ Lyon, UCBL, ENSL, UJM, CNRS, LGL-TPE, F-69622, Villeurbanne, France
  • 2Laboratoire des Sciences du Climat et de l’Environnement, LSCE/IPSL, CEA-CNRS-UVSQ, Université Paris-Saclay, Orme des Merisiers, F-91191 Gif-sur-Yvette Cedex, France
  • 3Geological Institute of Russian Academy of Sciences, Laboratory of Phanerozoic Stratigraphy
  • 4Comenius University, Faculty of Natural Sciences, Department of Geology and Palaeontology, Mlynská dolina G, 842 15 Bratislava, Slovak Republik

Abstract. 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.

Thomas Letulle et al.

Status: open (until 07 Oct 2021)

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Thomas Letulle et al.

Thomas Letulle et al.

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Short summary
In this study, we applied geochemical tools to well-preserved marine mollusc shells ~180 million years old, from polar and mid-latitude seas. From these results, we estimate that polar shells grew at a temperature between 8 and 18 °C, while mid-latitude shells record temperatures between 24 and 28 °C. We discuss why climate simulations used to predict future climate warming, when applied to the past, struggle to reproduce the temperature distribution observed here and in previous studies.