The improvement of the ocean model quality is intricately linked to the increase in computing power and energy efficiency due to the needs to increase model resolution, the number of simulations and the model complexity. Operational oceanography is a new and rapidly growing sector. In this context, the representation of ocean eddies is a key concern for a top quality ocean simulation, as it has been the case in the atmosphere for the representation of convection. Ocean eddies can be represented only by building upon recent advances in ocean modelling to construct more accurate, high-resolution models, which intrinsically demand more computational power, severely limiting the number of experiments that can be performed. During recent years the Performance Team of the BSC-Earth Sciences Department has made a big effort to improve the computational performance of Earth System Models such as NEMO following an interdisciplinary approach. Following this approach, and in collaboration with Mercator International, the Performance Team has assessed the suitability of the new NEMO4 code to run global simulations at extremely high-resolution and provided information on the major bottlenecks constraining its scalability. This pioneering effort will facilitate the deployment of such demanding configurations in the near future. The model was evaluated using an unprecedented global 1/36 degree equivalent resolution to build the new ORCA36 configuration by deploying it on the MareNostrum4 HPC. The model scaling capability was studied using up to 150,000 cores and comparing the results with more modest resolutions. Additionally, a single precision version of the model was run on the same platform and its performance compared to its double-precision counterpart.
