The oceans are wet, and play a major role in the hydrological cycle. They also have a high heat capacity. Section 6.2 provided the basic character of sea water and ocean structure. Figures 5.2 and 5.3 presented maps and the annual cycle of the mean surface air temperatures, and Fig. 5.4 gave the sea surface temperatures (SSTs). The latter are closely related to water vapor and precipitation in the atmosphere over the oceans. The SSTs are supported by the upper ocean temperatures and especially the mixed layer, which is the part of the ocean in direct contact with the surface through wind effects and heating from both radiation and temperatures in the atmosphere (see Fig. 8.8).