Topic: Properties of the Ocean
Theme: Change

Key Concepts:


  • Differences in salinity of ocean surface waters are caused by:
    • variations in the rate of ocean surface water evaporation,
    • variations in the rate of freshwater input from rainfall and land runoff, and
    • in limited areas by upwelling and downwelling.
  • Salinity distribution is related to evaporation-precipitation cycle variations at different latitudes. When seawater freezes, salinity increases in the remaining water. Regional variations in salinity exist also.
  • Salinity is generally higher in the sub-tropical latitudes that are remote from land.
  • Salinity is generally lower at the equator, in polar and sub-polar regions, and near continents.

Sea-level Height

  • Eustatic sea level changes are caused by changes of volume of ocean water as a result of extensive formation or melting of icecaps and glaciers.
  • Eustatic changes of sea level take place simultaneously and uniformly throughout the world. Eustatic equilibrium (balance) is easily and quickly attainable.
  • Human civilization has emerged during a long period of relatively stable sea level.
  • The predicted greenhouse warming of the planet could cause higher-than-average global temperatures, which, in turn, would cause the current polar ice sheets and glaciers to melt and sea level to rise.

Seafloor Topography

  • Tectonic processes (such as subduction and seafloor spreading) and sedimentation are the principal agents that shape and change the seafloor topography over time. Changes in climate can also affect it.