Chapter 2 - The Arctic environment

Abstract

The most basic and important facts are the earth’s distance to and revolution around the sun determining the energy input by solar radiation, and the spherical shape and rapid rotation of the earth and the angle of the rotational axis to the ecliptic, which control the distribution of solar energy over the surface of the earth. The earth does not accumulate heat and an equal amount of energy is radiated back to space but at longer wavelengths. Also, the earth has an atmosphere that absorbs and re-radiates the radiation back at longer wavelengths, making the earth warmer than it otherwise would be. Due to the present day increase in atmospheric CO2 concentration, the longwave re-radiation from the atmosphere to the earth increases and the earth’s temperature must rise to maintain the energy balance. Moreover, the earth’s fluid envelopes, the atmosphere and the oceans, transport heat from lower latitudes receiving more solar radiation to higher latitudes receiving less, thus redistributing the incoming energy over the globe. This creates areas of net heat loss at high latitudes and areas of net heat gain at low latitudes. The heat balance of the earth is global, not local. The meridional heat transport is, at high latitudes, mainly carried by the atmosphere, and knowledge of the atmospheric processes and circulation is necessary to understand its impacts on Arctic conditions. Together, these features constitute the dynamic and thermodynamic forces acting on the Arctic. To understand the response of the Arctic Mediterranean Sea, its boundaries, bathymetry, and geographical setting must be considered. The connections with the world’s oceans and the names and locations of the main surface currents, perhaps better known to ancient mariners than by present-day oceanographers, are also indicated as well as the extent and seasonal variations of the sea ice cover. The presence of a permanent ice cover is perhaps the most characteristic feature of the Arctic Ocean and directly raises two questions: how is the ice cover maintained and what role does its high albedo play in the local radiation balance? Sea ice is essentially freshwater, which directly leads to one process of utmost importance for the Arctic Mediterranean and for the Arctic as a whole—meridional freshwater transport. Water vapor is carried northward by the atmosphere and released as precipitation and river runoff to the Arctic Mediterranean and then returned to lower latitudes by the ocean circulation. The freshwater input creates strong stability of the Arctic Ocean that allows sea ice to form in winter and remain throughout the year. The ice surface and snow precipitated during the cold seasons reflect the incoming solar radiation, thereby retarding seasonal heating during the Arctic spring and early summer. Water in the atmosphere, as clouds and water vapor, acts differently and instead heats the surface by absorbing and re-radiating longwave radiation downwards.