Role of paleogeography on large-scale circulation during the early Eocene

Abstract. The configuration of continents and oceans has a major influence on Earth’s climate by shaping large-scale atmospheric circulation patterns. In this study, we investigate the effect of early Eocene paleogeography, specifically from the Ypresian stage, on extratropical eddies. We analyse the influence of the epicontinental West Siberian Sea as well as the impact of the absence of the Antarctic Circumpolar Current on mid-latitude cyclones and blocking events. Previous work from the Deep-Time Model Intercomparison Project (DeepMIP) has shown that during the early Eocene, heat transport through cyclonic systems was more intense than under modern conditions at the northern mid-latitudes, and less intense at the southern mid-latitudes. We analyse cyclone tracks and blocking systems of the early Eocene in an atmosphere-only CESM1.2 simulation, continuing the DeepMIP 1xCO₂ experiment. Sea surface temperatures from the DeepMIP experiment are used as boundary conditions. The simulation output is six-hourly, which enables direct cyclone tracking in the pressure field. In parallel, a decrease in heat transport of stationary eddies at the northern mid-latitudes in DeepMIP data, motivates the analysis of blocking climatology based on the 500 hPa geopotential height field. Our results show that, through air–sea interactions, paleogeographic features of the early Eocene enhance cyclonic activity at northern mid-latitudes while reducing it at southern mid-latitudes compared to modern conditions.