Stripping back the modern to reveal the Cenomanian–Turonian climate and temperature gradient underneath

Abstract

Abstract. During past geological times, the Earth experienced several intervals of global warmth, but their driving factors remain equivocal. A careful appraisal of the main processes controlling past warm events is essential to inform future climates and ultimately provide decision makers with a clear understanding of the processes at play in a warmer world. In this context, intervals of greenhouse climates, such as the thermal maximum of the Cenomanian–Turonian (∼94 Ma) during the Cretaceous Period, are of particular interest. Here we use the IPSL-CM5A2 (IPSL: Institut Pierre et Simon Laplace) Earth system model to unravel the forcing parameters of the Cenomanian–Turonian greenhouse climate. We perform six simulations with an incremental change in five major boundary conditions in order to isolate their respective role on climate change between the Cenomanian–Turonian and the preindustrial. Starting with a preindustrial simulation, we implement the following changes in boundary conditions: (1) the absence of polar ice sheets, (2) the increase in atmospheric pCO2 to 1120 ppm, (3) the change in vegetation and soil parameters, (4) the 1 % decrease in the Cenomanian–Turonian value of the solar constant and (5) the Cenomanian–Turonian palaeogeography. Between the preindustrial simulation and the Cretaceous simulation, the model simulates a global warming of more than 11 ∘C. Most of this warming is driven by the increase in atmospheric pCO2 to 1120 ppm. Palaeogeographic changes represent the second major contributor to global warming, whereas the reduction in the solar constant counteracts most of geographically driven warming. We further demonstrate that the implementation of Cenomanian–Turonian boundary conditions flattens meridional temperature gradients compared to the preindustrial simulation. Interestingly, we show that palaeogeography is the major driver of the flattening in the low latitudes to midlatitudes, whereas pCO2 rise and polar ice sheet retreat dominate the high-latitude response.

Investigating Mesozoic Climate Trends and Sensitivities With a Large Ensemble of Climate Model Simulations

“…One of the major challenges in the study of warm climate periods, for example, in the Cretaceous (e.g., Laugié et al., 2020; O'Brien et al., 2017; Tabor et al., 2016) or the early Eocene (e.g., Huber & Caballero, 2011; Lunt et al., 2012; Zhu et al., 2019), is the discrepancy between more strongly elevated global temperatures with low meridional gradients inferred from proxies and the conditions simulated by climate models (e.g., Huber, 2012; Upchurch et al., 2015). Challenges lie, for example, in the correct calibration and conversion of proxy data into local and global temperature estimates.…”

“…Paleogeography was also identified as a major control of temperature gradients by Laugié et al (2020), who compiled proxy and climate model estimates of zonal mean temperatures for the Cenomanian-Turonian period (∼94 Ma). The gradients simulated here for this period fall within the range spanned by other models (Laugié et al, 2020), although some are closer to the lower gradients suggested by proxies (see supporting information section 7 and Figures S16a and b). At ∼125 Ma, simulated SST gradients compare well with those from Steinig et al (2020), who argue for an improved agreement with proxies when applying updated calibrations (also see Figures S16c and S16d).…”

“…A number of modeling studies provide insights into global climatic conditions during certain Triassic (e.g., Huynh & Poulsen, 2005; Winguth et al., 2015), Jurassic (e.g., Sellwood & Valdes, 2008), and especially Cretaceous (e.g., Donnadieu et al., 2006a; Fluteau et al., 2007; Laugié et al., 2020; Tabor et al., 2016; Zhou et al., 2012, and references therein) time intervals or events. However, only few climate model‐based studies have been conducted that can represent long‐term climatic changes during the Mesozoic in a continuous and consistent framework.…”

Exploring the Impact of Cenomanian Paleogeography and Marine Gateways on Oceanic Oxygen

“…The simulations are initialized with warm idealized conditions adapted from those described in Lunt et al (2017). The constant initial salinity field is set to 34.7 PSU, and ocean temperatures are initialized with the depth-dependent distribution of Laugié et al (2020).…”

IPSL-CM5A2 – an Earth system model designed for multi-millennial climate simulations

“…This Earth system model coupled the Laboratoire de Météorologie Dynamique zoom (LMDZ5) atmospheric model (3.75 × 1.875 • in longitude-latitude, 39 vertical levels) (Hourdin et al, 2013) and Organising Carbon and Hydrology In Dynamic Ecosystems (ORCHIDEE) land surface model (Krinner et al, 2005) with the Nucleus for European Modelling of the Ocean (NEMO) , which includes ocean and sea-ice dynamics (2 • resolution and 31 vertical levels in the ocean), together with the marine biogeochemical model PISCES (Aumont et al, 2015). IPSL-CM5A has been used for several paleoclimate studies (e.g., Kageyama et al, 2013;Roberts et al, 2014;Tan et al, 2017;Zhuang and Giardino, 2012), including studies benefiting from the explicit representation of marine biogeochemistry (Bopp et al, 2017;Ladant et al, 2018;Le Mézo et al, 2017), vegetation dynamics and land biosphere (Tan et al, 2017). Still, IPSL-CM5A computation time, which averages 10 SYPD, has hindered its use for multi-millennial experiments that are typical for Quaternary or "deep-time" paleoclimate studies in which a fully equilibrated deep ocean is mandatory.…”