Modelling the Ocean Circulation during the mid-Cretaceous using an Energetically Consistent Internal Wave Model in the Community Earth System Model

Deep-time climate simulations typically disregard tidal dynamics while trying to reconstruct the paleoclimate. Tidally induced mixing is a dominant part of vertical mixing in the deep ocean, which is key for maintaining ocean stratification and influences the strength of the Meridional Ocean Circulation (MOC). We add this missing tidal mixing component to the Community Earth System Model (CESM) and try to reconstruct the mid-Cretaceous (~90Ma) climate, which is known for its warm, equable climate and low meridional temperature gradient. In the next step, as an improvement over the default tidal mixing scheme, an energetically consistent internal wave model IDEMIX is used in CESM to get the vertical diffusivity coefficients in simulating the mid-Cretaceous climate. 

Initially, 90Ma simulations were performed in the conventional method with enhanced constant background diffusivity coefficients for the default vertical mixing scheme and then with the tidal mixing component enabled. Preliminary results from the simulations with tidal mixing show that there is a considerable reduction in the global ocean mean temperature and a change in the strength of MOC in the deep ocean when compared to the simulations without the tidal mixing component. We will be also presenting results from additional experiments that are being performed with the internal wave model IDEMIX as the tidal mixing parameterization in the model. IDEMIX is forced by the dissipated barotropic tidal energy, which is modelled from the mid-Cretaceous bathymetry. With the IDEMIX parameterization, we expect more realistic results for ocean circulation hoping to reduce the disagreements between proxy data and model simulations.