The challenge of polar ocean gateway reconstructions

At large geological timescales, the global circulation is affected by geodynamic and tectonic processes, which control the motions of the lithospheric plates as well as crustal uplift and subsidence. In particular, the geometries of oceanic gateways are key parameters for simulations of paleo-ocean current systems in paleo-climate scenarios. The reconstructions of the past geometries of ocean gateways, basins and their continental margins are essential to realistically model the effects that tectonic motions have had in the long-term transition from climatic greenhouse to icehouse conditions. The Arctic Ocean is a restricted basin receiving freshwater from rivers and exchanging seawater through three Arctic gateways. This exchange influences deepwater formation in the North Atlantic and Pacific as well as the saltwater budget of the Arctic Ocean, and it has controlled the periodic oscillations between greenhouse and icehouse conditions, including the formation of the large ice sheets in North America, Europe and Asia. In the circum-Antarctic oceans, the last barriers to development of a continuous circumpolar deep-water pathway were the South Tasman Rise, the Drake Passage and the Kerguelen Plateau. Free flow of seawater past these obstacles was a pre-requisite for the initiation of the Antarctic Circumpolar Current (ACC). Recent modeling studies yield differing results on the question of whether or not inception of the ACC was the primary cause of large-scale ice sheet development on Antarctica. However, there can be little doubt that its initiation had widespread effects on global ocean circulation and climate. In this review presentation, we will discuss summarize existing and new gateway opening models, focusing on the polar deep-water gateways Fram Strait in the Arctic as well as Drake Passage/Scotia Sea and Tasmanian Gateway in the Southern Ocean