OCEAN FEATURES

• Oceans cover about 70 percent of the surface of Earth.

• Important features of the ocean floor near the continents are the continental shelf, the continental slope, and the continental rise.
• These areas are covered with thick layers of sediments (sand, mud, rocks).
• The depth of the ocean varies. Ocean trenches are very deep, and the continental shelf is relatively shallow.

OCEAN WATER

• Ocean water is a complex mixture of gases (air) and dissolved solids (salts, especially sodium chloride).
  • Marine organisms are dependent on dissolved gases for survival.
  • The salinity of ocean water varies in some places depending on rates of evaporation and amount of runoff from nearby land.

OCEAN MOTION

• The basic motions of ocean water are the waves, currents, and tides.
  • Ocean currents, including the Gulf Stream, are caused by wind patterns and the differences in water densities (due to salinity and temperature differences).
  • Ocean currents affect the mixing of ocean waters. This can affect plant and animal populations. Currents also affect navigation routes.
  
  

OCEAN LIFE

• As the depth of ocean water increases, the temperature decreases, the pressure increases, and the amount of light decreases. These factors influence the type of life forms that are present at a given depth.

• Plankton are tiny free-floating organisms that live in water.
  • Plankton may be animal-like or plant-like.
  • Animal-like plankton are called zooplankton.
  • Plant-like plankton (phytoplankton) carry out most of the photosynthesis on Earth. Therefore, they provide much of Earth’s oxygen. Phytoplankton form the base of the ocean food web.
  • Plankton flourish in areas where nutrient-rich water upwells from the deep.