"What Is The Evidence That Deep Water Forms In The North Atlantic Today And That This Formation Varied In The Past?"
Submitted by rustyc on 06/30/2008 05:21 PM
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"What Is The Evidence That Deep Water Forms In The North Atlantic Today And That This Formation Varied In The Past?"
The ocean-atmosphere system is a huge heat engine, for which solar radiation is the power source. Heat is redistributed over the globe by winds, surface currents and by deep flow in the thermohaline circulation.
Awareness of the global variations of factors such as sea-surface salinity, local evaporation-precipitation balances, and the various heat budget terms, is essential to quantify fluxes of water and heat across the ocean-atmosphere boundary.
There are a large number of water masses, each characterized by temperature and salinity values reflecting a particular set of surface conditions, and generally considered to originate in a particular source region. For instance the cold, dense waters of the deep originate from the conditions set at the sea surface.
The oceans may be divided vertically into 3 separate water masses; the upper surface, the intermediate and the deep water masses. The geographical distribution of the world's upper water masses is strongly influenced by the pattern of surface currents. Upper water masses are generally considered to include both the mixed surface layer and the upper part of the permanent thermocline. If the salinity is kept low by high precipitation and the temperature is high, the density of surface water will be low; the upper water column will therefore be stable, and only a very shallow water mass can form. The water masses that form in the subtropical gyres however, are upper water masses of considerable thickness. In these areas of convergence the sea surface is raised and the thermocline depressed leading to a thickening in the surface layer.
Intermediate water masses flow between the upper water masses and the deep and bottom water masses. The Western Atlantic Sub Arctic water is an example of intermediate water mass. It forms in subpolar regions where precipitation exceeds evaporation, and its salinity is therefore low. These consist largely of...
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