Name: _______________________
Variations in a Salty Ocean
Background
Anyone who ever tasted seawater knows that it is truly salty. The salty residue left on swimsuits
after they’ve been in the ocean is further evidence of the ocean’s salinity. Salinity is a measure
of how much salt is dissolved in water.
The average salinity of seawater for all Earth’s oceans is about 35 grams of dissolved salts per
kilogram of seawater. This is shown as 35 parts per thousand, or 35‰. The symbol ‰ is read
"permill." It is similar to percent, but it refers to parts per thousand instead of parts per
hundred.
The Red Sea and the Mediterranean Sea contain some of the saltiest water on Earth. In some
areas, these bodies of water show salinity measurements as high as 40‰.
Objective
In this investigation, you will examine the relationship between temperature and salinity in the
oceans and how both of these qualities affect the density of seawater. Ultimately, you’ll
estimate densities for water masses and use them to predict how water will mix in the oceans.
Procedure
Use the maps labeled “Temperature” and “Salinity” on mrsvanvliet.weebly.com to answer the
following 3 questions
1. Describe some of the general patterns you observe for temperature and salinity
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2. Describe the location of at least three places in the world’s oceans that have high
temperatures but low salinity
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3. What do you think might cause low salinity in these areas of warm ocean water?
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Name: _______________________
Background
Both salinity and temperature affect the density of seawater.
A liter of seawater has a higher mass than a liter of freshwater due to the added mass of the
dissolved salts. As density measures mass per unit volume, saltwater has a higher density than
freshwater. Increasing the amount of salt dissolved in water increases the water’s density.
Temperature affects the density of seawater by
changing the volume of the water itself. Higher
temperatures actually cause water to expand,
increasing the amount of space it takes up. The mass
of warmer water is spread over a larger volume than a
similar amount of cooler water, so the warmer water
has a lower density. Increasing the temperature of
water results in a decrease in the water’s density.
The graph allows you to estimate the density of any
mass of seawater based on its salinity and
temperature. To estimate density, find the point where
temperature and salinity values for the water intersect.
The blue line on the graph nearest the point of
intersection indicates the density of the water.
Mixing in the oceans depends on the densities of water masses. When water masses of
differing density meet, the mass with the higher density will sink to the bottom and the mass
with the lower density will float on top of it.
Procedure
Use the maps labeled “0, 50W Temperature”, “0, 50W Salinity”, “20N, 90E Temperature” and
“20N, 90E Salinity” to answer the next two questions.
4. Determine the temperature, salinity, and density of ocean water at the following
locations.
A. 0O, 50OW
Temperature: ________________
Salinity:
________________
Density (use the density graph):
_____________________
Name: _______________________
B. 20ON, 90OE
Temperature: ________________
Salinity:
________________
Density (use the density graph):
_____________________
5. What do you think is responsible for the unusually low salinity of these warm waters? (If
you need a hint, look at the land near these locations on a world map)
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Use the maps labeled “Mixing at the Panama Canal Temperature” and “Mixing at the Panama
Canal Salinity” to answer the next two questions.
6. Determine the temperature, salinity, and the density of water on the Caribbean and the
Pacific sides of the Panama Canal (The Panama Canal is at 10ON, 80OW)
A. Caribbean Side
Temperature:
________________
Salinity:
________________
Density (use the density graph):
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B. Pacific Side
Temperature:
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Salinity:
________________
Density (use the density graph):
_____________________
7. Predict what would happen to water that moves from the Caribbean Sea into the Pacific
Ocean
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Use the maps labeled “Strait of Gibraltar Temperature” and “Strait of Gibraltar Salinity” to
answer the next two questions.
8. Determine the temperature, salinity, and the density of water on the Mediterranean
and the Atlantic sides of the Strait of Gibraltar (The Strait of Gibraltar is at 35 ON, 5OW)
A. Mediterranean Side
Temperature:
________________
Salinity:
________________
Density (use the density graph):
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B. Atlantic Side
Temperature:
Salinity:
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________________
Name: _______________________
Density (use the density graph):
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9. Predict what would happen to water that moves from the Mediterranean Sea into the
Atlantic Ocean
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