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7.   Salinity Summary



The Briny Deep

1. Introduction
2.  Salt in Seawater?
3. Ions of Salt
4. Source of the Salt?
5. Salinity Variability
6.Salinity & Precipitation
7. Salinity Summary
8. Calculating Salinity
9. Ocean Temperature
10. Solar Radiation
11. Properties
12. Light Penetration
13. Temperature
14. Thermocline
15. Density
16. Layering

Here is a map showing the salinity of the surface waters of the ocean, down to a water depth of 50 meters, in parts of dissolved salt per 1000 (o/oo) parts of sea water.

Image produced by WOCE Ocean Modeling at the Naval Postgraduate School
  • Compare your observations in this map with your answers to the question in section 6 

    Where do you find the high salinity waters in the surface of the ocean?

    Where do you find low salinity sea water in the surface of the ocean?

Low salinity water (light blue region at 10-150 north) lies in the polar and subpolar regions and near the equator.  The equatorial region of low salinity ocean water lies below an atmospheric region called the "intertropical convergence zone". 

Intertropical Convergence Zone

The intertropical convergence zone moves about the equator as the intense heat in the equatorial area produces a rising mass of moisture-laden air, thereby creating a region of low atmospheric pressure. 

The equatorial low pressure system pulls air and moisture from adjacent regions towards the equator.  Consequently, air masses converge in this region from north and south of the equator, bringing moisture acquired by evaporation in the subtropical regions.  

The warm, humid air along the equator rises (because of its low density) and cools, allowing  water vapor to condense, which results in rainfall, causing precipitation to exceed evaporation in equatorial regions.

Draw a picture of the intertropical convergence zone in your handou

  • Moving poleward, another region of low sea surface salinity lies around 60o north and south of the equator, where once again precipitation is greater than evaporation, due to rising masses of air that produce heavy rainfall.

Image produced by WOCE Ocean Modeling at the Naval Postgraduate School


In contrast to these low salinty areas, where do you find regions of high salinity sea water?

Regions of high salinity sea water are centered around 30o north and 30o south of the equator (orange regions on map above)  because of excess evaporation in these regions.

As we will see in a future expedition, these areas of high evaporation and ocean salinity are located below high pressure systems in the atmosphere marked by cold, sinking air, which pushes rain clouds away from these regions by the wind.

Watch the video below to review ocean salinity and recent research

You Should Now Be Able to Develop a Hypothesis 
about Each of the Following Questions

How would the salinity be affected by the freezing of ice from seawater, so-called sea ice?

Sea Ice "Pancakes"
Photo From the
Alfred Wegener Institute


How would the ocean's salinity change as a result of rainfall, runoff, or the melting of ice?


ęCopyright 1999
March 13, 1999

Send to Don Reed

Department of Geology
San Jose State University



Let's Examine the Constancy of Composition and its Use in Calculating the Salinity of Seawater