Vertical fluxes

Both in the atmosphere and in the ocean, exchanges of for example heat and carbon dioxide are limited by sharp density gradients. In the Arctic, the properties of the sea ice, especially the roughness at the surface and the underside, significantly affect processes that control mixing. ICE Fluxes aim to create an observational dataset that will help to improve our understanding and lead to better representation of these processes in climate models.

Free falling instrument is dropped into icy water from the side of a ship

Turbulence measurements from the ship are done with the free falling instrument. The moving ice is a rather challenging obstacle at times! Photo: Angelika Renner / Norwegian Polar Institute

EM-bird above an ice floe consisting of one big ridge

The EM-bird above an ice floe consisting of one big ridge. Features such as this ridge stick out over level ice both on the surface and on the underside and therefore alter the flow of wind and water currents, creating turbulence and mixing. Photo: Norwegian Polar Institute

In the Arctic Ocean, a sharp change in salinity and temperature causes density changes that separate cold, fresh Arctic water and the sea ice cover at the top from warm, salty Atlantic Water below. This gradient is a barrier for vertical heat flux towards the ice. The warm Atlantic Water flows around the Arctic Ocean, following the steep and inhomogeneous continental shelf slope around the Arctic Basin, making prediction of vertical mixing difficult. We are studying the role of wind-induced ice and water motions, shear currents, tides, internal waves, the effect of the ice cover and other physical processes in the upper ocean in forcing vertical mixing, as well as the effect they have on the stratification. This new knowledge will be used to improve the representation of these processes in ocean and climate models.

The lower atmosphere in the Arctic often has a very different vertical structure than that at lower latitudes. At high latitudes, the limited amount of sunlight reaching the surface leads to long periods of surface cooling, causing the air to be coldest at the surface, and warming with height. This temperature structure means the air at lower levels is much denser than the air just above, which limits vertical mixing. This means that processes controlling heat, water vapour, carbon dioxide, and other fluxes to the surface are very different from the much better understood processes controlling these fluxes in the mid-latitude atmosphere. Our measurement of these fluxes will also lead to a better representation of these processes in atmospheric and climate models.

The properties of the underside of sea ice vary significantly depending on the age of the ice, freezing or melting state, and physical features such as pressure ridges which lead to deep ice keels, refrozen leads, which produce thin sheets of smooth ice, and open melt ponds. This roughness of the ice causes horizontal variations in the speed of the water near the ice-ocean interface, which in turn creates vertical mixing. Similar effects take place at the sea ice-atmosphere boundary. We aim to create a comprehensive observational dataset that will be used to describe these processes’ effects on vertical fluxes of heat and other quantities at different horizontal scales.