Oceans

The Oceans

I. The oceans are a dominant feature of Earth's surface.
    A. They cover 71% of Earth's surface
    B. The Northern hemisphere contains more continental land mass than the Southern hemisphere.
    C. The volume of the oceans is 18 times greater than the volume of all land above sea level.
    D. Four major oceans exist on Earth (textbook emphasizes three)

II. Origin of water? Water seems to have two likely origins.
    A. Outgassing from volanoes. Water vapor is the most abundant gas given off by volcanoes. 4.5 billion years of Earth history is plenty to allow for the accumulation of significant amounts of water on Earth
    B. Comets. Comets are fragments of ice and frozen gases. As they approach the Sun in their wide-ranging orbits, the Sun's radiation causes ice fragments to spall off. these fragments enter Earth's atmosphere and vaporize when it passes through the comet's debris trail. This is what we experience as meteor showers.

III. Ocean temperatures.
    A. Surface
          1. At the oceans surface, temperatures tend to vary with temperatures on land. At lower latitudes, temperatures are generally higher as the sun intensity is greater.
    B. Depth profile.
          1. At lower latitudes, the ocean is warmer at the surface, but cooler at greater depths.
          2. At higher latitudes (60+^o), there is little change in temperature with depth. It is cold at the surface and cold at depth.

IV. Ocean salinity
    A. Ocean salts also seems to have two likely sources.
          1. Volcanic outgassing of HCl vapor
          2. Chemical weathering of rocks on land provides Na, K, Ca, and other components to solution.
    B. Concentrations salts in ocean.
          1. The major components of ocean salinity include Na, K, Ca, Cl, SO₄.
          2. On average, sea water is 3.5% salts by weight.
          3. Salinity is usually measured in parts per thousand (‰). The average salinity of the oceans is 35‰.
    C. Surface salinity variation by latitude
          1. Surface salinity generally varies from about 34‰ to 36‰.
          2. The surface salinity around the equator is measurably lower than could be expected because the prevailing climate around the equator is one of high rainfall. High rainfall dilutes the sea water and slightly lowers the salinity.
          3. The surface salinity at about 30^o N and S latitude are measurably higher than would typically be expected because the prevailing climate at those latitudes is one of little rainfall and higher evaporation (high pressure belt).
          4. Surface salinity again falls below average at about 60^o latitude and higher because of higher rainfall (low pressure belt), and because of lower evaporation rates (lower temperatures).
    D. Salinity varies with depth