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Education: Ocean Circulation

With temperature, salinity determines seawater density and buoyancy, driving the extent of ocean stratification, mixing and water mass formation.

Aquarius will be highly complementary to existing satellite programs that monitor sea surface temperature because, together, salinity and temperature control density at the ocean surface. Sea-surface density drives formation of ocean water masses and three-dimensional ocean circulation. Thus better understanding of SSS patterns will improve understanding of the ocean's capacity to store and transport heat.

Salinity plays a major role in how ocean waters circulate around the globe. Salinity changes can create ocean circulation changes that, in turn, may impact regional and global climates. The extent to which salinity impacts our global ocean circulation is still relatively unknown, but NASA's new Aquarius mission will help advance that understanding by painting a global picture of our planet's salty waters.

The link between ocean temperature, salinity, and density also has these following consequences:

Great Salinity Anomalies - Research shows that over the past few decades, vast regions of abnormal sea surface salinity - called Great Salinity Anomalies - have propagated around the far north Atlantic, impacting local ecosystems and the sinking of water masses. An excellent article, "If Rain Falls on the Ocean - Does It Make a Sound?", is available from the Woods Hole Oceanographic Institution. Click here for .pdf version.

Water Mass Development at Various Latitudes

  • At mid-latitudes, salinity influences the depth to which water masses sink and how far they extend through the ocean. The location and depth of these water masses controls how heat and salt are transported between the tropics and high latitudes. Like atmospheric fronts that bring unstable weather, ocean fronts found at the interface between water masses are areas of high activity often correlated with important fisheries such as tuna.
  • In the tropics, sea surface salinity is primarily controlled by rainfall and river runoff; these sources of freshwater regulate how the oceans interact with the atmosphere. Affecting almost half of the world's human population each year, monsoons are driven by exchanges at the air-ocean boundary.
El Niño - El Niño has profound effects on humankind and is, to an unknown extent, governed by ocean salinity. In fact, recent studies indicate that understanding salinity's effect on upper ocean buoyancy may be the key to better El Niño forecasts. A NASA Press Release, "Ocean Surface Saltiness Influences El Niño Forecasts", is available at

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