Modern observations reveal that the narrow and shallow Atlantic and Pacific gateways connecting the Arctic Ocean to adjacent seas are undergoing substantial physical and biological changes due to sea ice loss and warming temperatures. Model projections suggest that these changes will intensify under future climate scenarios, while paleoclimate records demonstrate that the Arctic Ocean has experienced similar transformations in the past, emphasizing the need to contextualize modern climate change within a longer-term perspective. This session aims to convene the broad scientific community investigating the "Atlantification" and "Pacification" of the Arctic Ocean from diverse perspectives, including physical oceanography, marine ecology, paleoclimatology, and modeling. We welcome contributions encompassing in-situ physical and ecological observations, satellite remote sensing, proxy-based and model-based paleo-reconstructions, and future model projections. This session aims to foster interdisciplinary exchange among scientists with diverse backgrounds to collectively address the complex mechanisms and feedbacks driving changes at the Arctic Ocean gateways.