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The Water Planet Background Earth appears mostly blue from space because oceans cover more than 70 percent of its surface. For this reason, Earth is sometimes called the water planet. The average depth of the oceans is more than four times the average elevation of the continents. Importance of Oceanographers • Map the ocean floor • Track global ocean temperatures • Study how humans affect oceans: pollution, oil spills, deep-sea mining/drilling • Understand the consequences of global air temperature on water Major Oceans Properties of Ocean Water: Salinity • Salinity – a measure of the dissolved salts in water. • On average, 1000 grams of seawater contains 35 grams of salt, or 3.5. Variations in Salinity • In deeper ocean waters, the salinity is close to the average of 3.5 • Near the surface, it can vary between 3.3 % and 3.7 %. • Salinity is below average in places where large amounts of fresh water enter the ocean. • Salinity is also lower in areas of heavy rainfall, such as those near the equator. • Salinity tends to be above average in areas that are extremely hot. • In hot, dry climates, the oceans lose water rapidly through evaporation, leaving salts behind. – The Mediterranean Sea and the Red Sea can be as high as 4 %. – The Dead Sea has the highest salt concentration of any sea in the world. • Scientists believe the salt composition of the oceans has not changed in the past 200 million years. Properties of Ocean Water: Temperature • Almost all the energy that heats the oceans comes from the Sun. • But solar energy does not penetrate very deeply into the oceans. • Ocean temperature decreases rapidly with depth. Sea Level • Sea level has risen and fallen by hundreds of meters in response to melting ice during warm periods and expanding glaciers during ice ages. • Tectonic forces (earthquake and volcanic boundaries) also cause Earth’s crust to rise and fall. • Data shows that sea level rose at a rate of about 3 mm per year between 1993 and 2004. Properties of Ocean Water: Light Absorption Properties of Ocean Water: Layering • Ocean surface temperatures range from -2 C (30 F) in polar waters to 30 C (86 F) in equatorial regions, with the average surface temp being 15 C (60 F). • Deep ocean water is always cold, even in tropical waters.