How hot was the Jurassic Greenhouse climate?

Examination of warm intervals in Earth's history help develop insight into the behavior of the climate system under elevated carbon dioxide and temperature. One such interval is the Jurassic which sees atmospheric CO2 concentrations close to current concentrations of around 400 ppm or higher. A significant feature of this warmer world was the presence of large epicontinental seaways such as the Middle-Late Jurassic Sundance Sea of North America (e.g. Danise et al. 2020). At its greatest extent the Sundance Sea stretched from Utah to the Arctic Ocean. These large epicontinental seaways are the dominant source for much of our information about ancient marine climates and biodiversity. There is, however, growing evidence that these seaways are often decoupled from open-ocean conditions because of variations in water mass, depth, salinity, and stratification and being a loci of anoxia. Hence, understanding these systems is critical to reconstruct the role epicontinental seaways play in terms of ocean circulation, carbon cycling, and climate amelioration.

This research will investigate key sites within the Sundance Sea, in the USA and Canada. Using stable isotopes and clumped isotopes biogenic carbonate samples derived from fieldwork, will be analysed to reconstruct temperature and carbon cycling at unprecedented spatial resolution. The carbonate clumped isotope thermometer is a valuable tool for reconstructing temperatures in epicontinental settings due to its independence from the isotopic composition of the water from which a carbonate precipitates (Price et al. 2019; Vickers et al. 2019; Bajnai et al. 2020; Paxton et al. 2020). Analytical techniques will be used to evaluate the geochemical character and biogenic preservation (e.g., Inductively Coupled Plasma-Atomic Emission Spectrometer (ICP-AES) and the cathodoluminescence petrography.