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In Chapter 4 we will see how the concept of the euphotic zone dominates the biological productivity of the oceans. Radiation 39 Fig. 3. Energy spectrum of solar radiation at the ocean surface, but only of that scattered within the ocean back into the atmosphere, not the direct solar beam. The broken line shows a western sub-tropical North Atlantic spectrum, the solid line is from the Baltic Sea. Note the much reduced scattering in the sediment-laden waters of the Baltic. 2 Long-wave radiation The sea receives solar radiation from the Sun.

In the Greenland and Norwegian Seas during winter the surface waters are strongly cooled making them denser. This dense water then overturns, probably in very localized regions up to a few tens of kilometres in diameter. In the Southern Hemisphere, particularly in the Weddell Sea, ice formation leaves a greater concentration of salt in the water beneath, as salt tends to be expelled from the ice lattice as it forms. This dense water also sinks. These two distinct types of water, or water masses, then travel equatorwards from the polar regions, to form the deep waters of the world’s oceans.

We will see repeatedly how these substantially modify the radiative and circulatory climate of the atmosphere and ocean. One major impact that the geosphere has on climate is through geological change in these basic boundaries (continental drift). 8, and in more detail in Chapter 6 but the basic mechanism is contained in the theory of plate tectonics. This proposes that the upper region of the Earth, the lithosphere (the crust and the upper mantle), is composed of a number of basically stable platforms that move slowly, at the rate of up to a few centimetres per year, over the surface of the planet.