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Chapter 5: pp. 152-174

Main points of today's lecture:

• Temperature, salinity and density of the oceans.
• Dissolved gases in seawater.
• Light and sound transmission.
• The global water cycle.

Insights:

• The amount of solar energy received by the earth's surface, insolation, varies significantly with latitude, resulting in surface-water temperatures being highest in the tropics and decreasing with distance from the equator. Some factors affecting the global distribution of surface-water temperature include seasons and ocean currents. Temperature in the ocean varies with depth as well, usually being coldest near the bottom and warmest towards the surface.

• Density depends on the temperature, salinity and pressure of seawater, the latter affecting significantly only in the deepest parts of the ocean. It controls the vertical structure of the water column, with the more dense water underlying the less dense water thus, cold saline water is more dense than warm freshwater.

• Enormous quantities of gases are exchanged between the ocean and the atmosphere near the sea surface. Gas solubility increases with a decrease in either water temperature or salinity and as pressure increases, therefore cold slightly saline water can dissolve more gases than warm saline water at the same pressure.

• The intensity of light and the speed of sound vary greatly in the ocean. Light intensity diminishes with depth dividing the water column into a sunlit upper layer or photic zone underlaid by a dark aphotic zone, where plants cannot survive. Sound is transmitted more effectively and rapidly in water than in air, and increases as salinity, temperature and pressure increase.

• The hydrologic cycle describes the exchange of water in gaseous, liquid, and solid states among the various water reservoirs. Water is evaporated from the ocean's surface, falls as precipitation on land, and returns to the oceans as river runoff and groundwater flow, completing the cycle.

Last update: March 24, 2000
http://dusk.geo.orst.edu/oceans/lec12.html