Modelling the ocean circulation of the mid-Cretaceous using the Community Earth System Model (iCESM1.2) and the internal wave mixing parameterization IDEMIX

The mid-Cretaceous (~90 Ma) was a natural case of the greenhouse climate state of the earth. Enhanced volcanic activity contributed to the higher atmospheric concentration of CO₂. The continental configuration was different and the global mean sea level was around 160m higher compared to the present day.  Black shales from this period's marine sediments indicate a near-anoxic deep-ocean environment. This project hypothesizes that redistribution of tidal energy dissipation from the open ocean to the large continental shelf areas reduced the energy available for mixing in the deep ocean. The objective is to investigate the effect of climate parameters and geographical configuration on ocean circulation by using the energetically consistent internal wave mixing parameterization IDEMIX in the fully coupled Earth System Model iCESM1.2. As part of the second phase of the CRC - Transregio 181, this project aims to make the Earth system model energetically consistent for improved climate projections.

The paleo-topography/bathymetry of the mid-Cretaceous is adopted from Scotese and Wright’s PALEOMAP (2018) project. The paleo-vegetation distribution is taken from Sewall’s (2007) mid-Cretaceous boundary conditions. The necessary boundary conditions and the climate-forcing files for the individual component models are prepared by using the Paleoclimate ToolKit of the CESM documentation. This mid-Cretaceous setup is spun-up with present-day trace gas concentrations for over 1000 model years. Constant tidal mixing coefficients are used in this spin-up. The first results from this spin-up indicate deep-water formation in the mid-latitudes in the Northern Hemisphere. From the equilibrium state of the spin-up, trace gas concentrations of the mid-Cretaceous will be input in the model. The ocean circulation will then be simulated with the internal wave mixing schemes KPP and IDEMIX for a comparative study. We expect improved results for deep-water formation sites and deep-ocean oxygenation with the IDEMIX parameterization.