Southern high-latitude warmth during the Jurassic–Cretaceous: New evidence from clumped isotope thermometry

Abstract

In order to understand the climate dynamics of the Mesozoic greenhouse world, it is vital to determine paleotemperatures from higher latitudes. For the Jurassic and Cretaceous climate, there are significant discrepancies between different proxies and between proxy data and climate models. We determined paleotemperatures from Late Jurassic and Early Cretaceous belemnites using the carbonate clumped isotope paleothermometer and compared these values to temperatures derived from TEX86 and other proxies. From our analyses, we infer an average temperature of ∼25 °C for the upper part of the water column of the southern Atlantic Ocean. Our data imply that for mid- to high latitudes, climate models underestimate marine temperatures by >5 °C and, therefore, the amount of warming that would accompany an increase in atmospheric CO2 of more than 4× pre-industrial levels, as is projected for the near future.

Dual clumped isotope thermometry resolves kinetic biases in carbonate formation temperatures

“…2a), suggesting that it precipitated indistinguishable from thermodynamic equilibrium at a temperature of 20.5(±1.9)°C. This temperature estimate supports southern high-latitude warmth during the Early Cretaceous 44,45 .…”

“…(66-4.65) was retrieved from DSDP Site 511 at the Falkland Plateau (51.004667 S, 46.971667 W). The investigated rostrum solidum shows excellent preservation based on cathodoluminescence, and trace element analyses 44,60 . Burial temperatures remained below 100°C for this core, which makes the solid-state alteration of the clumped isotope composition of this sample unlikely 61,62 .…”

Supplemental Material: Stress in the tropics? Impact of a latitudinal seawater δ¹⁸O gradient on Middle Jurassic temperature reconstructions at low latitudes

“…This has been interpreted in different ways, either supporting or discounting the applicability of the TEX 86 proxy. In general, TEX 86 -data might indicate warmer surface water temperatures compared to stable oxygen isotopes of bottomdwelling or deep-swimming organisms, but the exact calibration method for TEX 86 is also debated and might influence absolute temperature reconstructions (compare Jenkyns et al, 2012;Vickers et al, 2019;Price et al, 2020). Clumped isotope analyses are still very few for the Jurassic world and connected with a number of uncertainties.…”

“…Their reconstructed δ 18 O sea values span a wide spectrum, but do not necessarily correspond to openocean settings. Similarly, Vickers et al (2019) used clumped isotope analyses on samples from the Falkland Plateau, but resulting δ 18 O sea values point to a restricted situation for their study area. Finally, Price et al (2020) used clumped isotope analyses to reconstruct latitudinal gradients in the Early Cretaceous.…”

The Mesozoic Arctic: warm, green, and highly diverse

“…A series of cold events, based mostly on sedimentological evidence, is now proposed for the Early Jurassic (Ruebsam et al 2019), Late Jurassic (Rogov and Zakharov, 2010) and the Early Cretaceous (Alley et al 2019). However, most palaeotemperature proxy data, including new crenarchaeota lipid data (O'Brien et al 2017), as well as clumped isotope data (Vickers et al 2019), do not support very cold high-latitude conditions that would allow for the formation of ice caps. This debate can only be resolved by adding more high-resolution multi-proxy data from high-latitude archives.…”