The subsidence history of the Greenland-Scotland Ridge (GSR) from subaerial to current ocean depths has been investigated by several studies, and the initial hydrographic opening of the North Polar Seas, “NPS” (Arctic Ocean, Nordic Seas) has been linked to major reorganizations of the global oceans and climate throughout the Neogene (23‒3 Myrs ago). However, the current understanding of the GSR subsidence affecting the hydrographic evolution of the Greenland Scotland Seaway and of the critical GSR depth providing effective water mass exchange between the oceans are largely based on conceptual models. Here, we emulate the GSR subsidence by means of a fully coupled ocean-atmosphere General Circulation Model (GCM) with integrated terrestrial vegetation dynamics (community of earth system models, COSMOS). The model setup comprise a global reconstruction of the mid-Miocene 20‒15 Myrs ago (continental geography, orography, bathymetry, ice-sheet geography and topography) and a change of CO2 levels in the atmosphere. Especially, we additionally integrated a high resolution bathymetric dataset for the area of interest (northern North Atlantic, GSR, Nordic Seas and the Eurasian Basin). In different experiments we deepen GSR depth levels by increments of 100 m, ranging from a quasi-enclosed North Polar basin to an open gateway configuration. We identify thresholds in hydrographic communication across the seaway and discuss consequences in climate change and ocean characteristics. Secondly, we use the model setup close to the allocated depth threshold and test the models sensitivity by changes of greenhouse gas concentrations within the spectrum of CO2 reconstructions. We find that a shift in the modeled climate by CO2 changes directly impact the exchange of water masses across the GSR. Based on our model results, we provide a mechanism on the hydrographic opening of the NPS by controls of tectonic activity and CO2.