The mid-Cretaceous (90-110 Ma) was a hot greenhouse period characterized by high rates of submarine volcanism including ocean crust production at mid-ocean ridges. This volcanism was accompanied by high concentrations of atmospheric CO 2 , significant sea level rise, and an accelerated hydrological cycle (Foster et al., 2017;Haq, 2014;Jenkyns, 2010;Tierney et al., 2020). CO 2 concentrations reached levels approximately 700-2,000 ppmv (2.5-7 times higher than preindustrial values; Foster et al., 2017 and references therein), and, consistent with high pCO 2 levels, sea surface temperatures have been estimated to have reached ∼30-32°C at 60°S latitude (Bice et al., 2003;Huber et al., 2018), much higher than modern-era temperatures of ∼0-1°C at these latitudes (data from Ocean Data View). Contemporary latitudinal temperature gradients were reduced to <14°C, much smaller than the present difference between tropical polar latitudes of ∼20°C (O'Brien et al., 2017 and references