The Marine Physical Environment During the Polar Night

The physical environment of the Arctic is captured in popular perception as being an isolated, frozen and intensely cold ocean. The reality is surprisingly different; an ocean system that supports warm inflow to the Arctic and exchange with the adjacent ocean basins, influenced by stormy weather systems that can originate in mid-latitudes, and having a sea-ice cover that is experiencing ongoing reduction in its extent and thickness. We review the primary oceanographic and bathymetric features of the Arctic Ocean, highlighting the significance of the Arctic in terms of the global oceans. An important feature of the Arctic is the increasing dominance of water originating in the Atlantic that brings heat to the Arctic influencing both the ocean and the sea ice. Within the seasonal cycle of the shallow coastal waters, we demonstrate fundamental ideas of how Polar Night is characterised by relative warmth, differing from the oceanic winter where water is close to freezing. The advective nature of the atmosphere is a further source of heat, and we consider the changes in storm systems during the Polar Night and the impact on ocean and ice through direct surface fluxes but also by driving shelf-exchange processes. Finally, the ice cover during the Polar Night is shown to be vulnerable to future changes to the heat balance in the Arctic both in terms of ice formation, thickness, and snow cover.