The Arctic Ocean has maintained a geographic position around the North Pole throughout Cenozoic times. The 405 m thick Paleogene and Neogene sediment section recovered by IODP Expedition 302 (aka ACEX) from the Lomonosov Ridge at near 88°N and 1288 m present water depth thus represents deposition in a genuinely northern polar setting (Backman et al., 2006; Moran et al., 2006). Synthetic seismic modelling of physical properties of the ACEX sediment cores permitted integration to previous seismic studies from the Arctic Ocean. An analysis of physical oceanographic parameters, using fjord circulation theory, has been performed to determine the minimum width of the Fram Strait needed to generate ventilated conditions in the central Arctic Ocean. The late Paleocene to middle Eocene Arctic Ocean paleoenvironments were shaped by the basin's polar, land-locked position, its lack of deep water connection to the World Ocean, and its reduced surface water salinities. The ACEX sediments witness about a persistent shallow-marine depositional environment during late Paleocene through middle Eocene times, and that the Paleogene Arctic Ocean was characterized by limited commotion and oxygen-deficit conditions below the stably stratified, low-salinity surface waters. The late middle Eocene through early early Miocene interval is obscured by a hiatus. A 5.8 m thick transition interval of early Miocene age rests on the hiatus. This transition interval is characterized by distinct cm-thick layers alternating between poorly and well oxygenated sediments (Stein et al., in press) which possibly were influenced by wave action in a near surface setting on the rapidly subsiding ridge (O'Regan et al., 2006). A paleogeographic and paleobathymetric reconstruction suggests that the Fram Strait became sufficiently wide and deep in the late early Miocene to permit an inflow of saline and ventilated North Atlantic waters. Neogene sediments younger than the late early Miocene are consistently deposited in ventilated waters. This early Neogene widening and deepening of the Fram Strait is consistent with a new tectonic model of the strait and its neighbouring Nansen Basin (Jokat et al., 2006).