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
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
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
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
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
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?