SALINITY AND DENSITY and DEEP OCEAN CURRENTS LAB
Science Inquiry
Ms. Clark
October 31, 2012
GOALS / OBJECTIVES
Ocean currents arise in many different ways. For example, wind pushes the water along the
surface to form wind-driven currents. Deep ocean currents are caused by differences in
water temperature and salinity. In this experiment, the students will hypothesize the cause of
ocean currents and then develop a model to explain the role of salinity and density in deep
ocean currents.
STANDARD
SCI.6.1 2010 - Physical Science
Explain that all objects and substances in the natural world are composed of matter in different states
with different properties. (6.1.1, 6.1.2, 6.1.3) Understand that there are different forms of energy with
unique characteristics. (6.1.4, 6.1.5, 6.1.6, 6.1.7)
MATERIALS / SUPPLIES
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Glass beakers (2 large and 2 small per group)
Salt
Food coloring
Measuring spoons
Water (hot and cold)
Stir sticks
ESTIMATED TIME NEEDED:
One class period
SAFETY STATEMENT:
This is a safe experiment with very little risk of injury.
SALINITY AND DENSITY and DEEP OCEAN CURRENTS LAB
Science Inquiry
Ms. Clark
October 31, 2012
ACTIVITY/PROCESS
Introduction
Display the maps of (1) wind-driven ocean currents, (2) sea surface temperature, and (3)
surface salinities of the oceans. Have the students look for relationships between sea surface
temperature, salinity, and the locations of warm and cold currents. Ask the students to write a
hypothesis that explains these relationships, if possible. Conduct the following experiment to
learn more about the relationship between salinity and deep ocean currents.
Experimental Procedure
1. Fill large beaker with water to within 2 inches from the top
2. Dissolve a Tbs. of salt in ¼ cup water in the small beaker and add a drop of
blue food coloring.
3. Slowly pour the “salt” water into the side of the larger beaker.
4. Use the second set of beakers to repeat the experiment. This time, the large
beaker will have cold water, and the small, “blue” will have hot water.
5. Record observations in Science notebook.
6. You may extend the activity mixing different salinity levels and different
water temperatures, or add layers using different food colors.
REFLECTION / FOLLOW ACTIVITY
What Happened:
CONCEPTS
 Salt water is more dense than fresh water, and is therefore heavier.
 When ocean water evaporates, the water becomes more dense because most of the salt
remains in the water. In some regions of the ocean, circulation is based upon the mixing
between more dense surface water and less dense layers of deeper water.
Explanation
Thermohaline circulation is the name for currents that occur when colder, saltier water sinks and
displaces water that is warmer and less dense. In this activity, you examined the relationship
between salinity and deep ocean currents. In Earth's equatorial regions, surface ocean water
becomes saltier as the water, but not the salt, evaporates. However, the water is still warm
enough to keep it from sinking. Water that flows towards the poles begins to cool. In a few
regions, especially in the North Atlantic, cold salty water can sink to the sea floor. It travels in
the deep ocean back towards the equatorial regions and rises to replace water which is moving
away at the surface. This whole cycle is very important in regulating climate as it transports heat
from the equatorial regions to polar regions of Earth. The full cycle can take a thousand years to
SALINITY AND DENSITY and DEEP OCEAN CURRENTS LAB
Science Inquiry
Ms. Clark
October 31, 2012
complete.
Follow up activity:
Vocabulary for Science Notebook
 density: mass per unit volume of a substance. Usually expressed as grams per cubic
centimeter.
 hypothesis: an assumption made to account for or relate known facts.
 model: system of data, inferences, and relationships, presented as a description of a
process or entity.
 salinity: a measure of the quantity of dissolved solids in ocean water. Formally, it is
the total amount of dissolved solids in ocean water in parts per thousand by weight
after all carbonate has been converted to oxide, the bromide and iodide to chloride,
and all the organic matter oxidized.
 temperature: a direct measure of the average kinetic energy of the molecules of a
substance. The degree of hotness or coldness of anything.
 current: a smooth and steady onward movement of a fluid (i.e., liquid or gas). The
part of any body of fluid that has a continuous onward movement.
 thermohaline circulation: the vertical movement of ocean water driven by density
differences resulting from the combined effects of variations in temperature and
salinity.
Research Questions for Science Notebook
 Is salt water heavier or lighter (higher or lower in density) than fresh water? Make
sure that you explain your answer in terms of the results that you obtained from your
experiment.
 If evaporation causes surface water to be salty, where would you expect ocean
water to be very dense?
 Does the density of ocean water have any relationship to the temperature of ocean
water?
Differentiation:
Have students compare the map of sea surface temperature to the map of surface salinity.
Based on what they’ve learned from the animation and this activity, what combination of
temperature and salinity favors the sinking of ocean water? Think about the parts of the ocean
where cold salty ocean water tends to sink. Can fresh water from nearby land masses affect the
salinity there? How might the influx of fresh water affect the process? What about global
warming and the associated melting of polar ice?