Lab 4: Water column characteristics
Thermoclines & haloclines
This lab is replicated from a lab presented at a COSEE workshop by Dr. Alan Shanks.
Name: __________________________________
Objectives:
-Understand how water density causes the vertical stratification of the ocean.
-Understand thermoclines and haloclines.
-Be able to describe ocean situations that mimic those we’re setting up in the lab.
-Learn how to graph salinity and temperature data.
Experiments:
Your instructor will give you one of the conditions below. Your group will follow the directions for that particular condition and observe other groups’ conditions to answer the questions at the end of the lab.
Equipment:
-a 2-gallon tank
-a siphon tube
-a 5-gallon bucket for water storage
-dyes for coloring the water
-salt, if changing salinity between samples
-a ruler
-aluminum foil and ice
-a Vernier hand-held device with either a temperature or salinity probe
Temperature differences:
a. Add warm water to the tank, filling it 1/3 full. Color the water with dye.
b. Put cold water in a bucket and dye the water a different color. Place the siphon tube at the bottom of the tank. Slowly add the cold water into the tank until the tank reaches 3/4 full. If the colors mix, you added the cold water too quickly and will need to begin again. Carefully remove the siphon tube, leaving 2 distinct layers of water in the tank. c. Tape a ruler to the tank with the zero line at the water surface.
d. Using the temperature probe, measure the temperature from the top to the bottom in 1 cm. increments. Be sure someone records the values as you go through the readings.
e. Make a boat of aluminum and fill it with ice. Place it in the water and observe the currents that come off of the boat.
Salinity differences:
a. Add cold tap water to the tank, filling it 1/3 full. Color the water with dye.
b. Put cold water in a bucket, add salt to it, and dye the water a different color. Place the siphon tube at the bottom of the tank. Slowly add the cold water into the tank until the tank reaches 3/4 full. If the colors mix, you added the cold water too quickly and will need to begin again. Carefully remove the siphon tube, leaving 2 distinct layers of water in the tank.
c. Tape a ruler to the tank with the zero line at the water surface.
d. Using the salinity probe, measure the salinity from the top to the bottom
in 1 cm. increments. Be sure someone records the values as you go through the
readings.
e. Make a boat of aluminum and fill it with ice. Place it in the water and observe the currents that come off of the boat.
Upwelling:
The goal of this experiment is to produce 2 layers of water that are slightly different in salinity.
a. Add cold tap water to the tank, filling it 1/3 full. Color the water with dye.
b. Put cold water in a bucket, add salt to it, and dye the water a different color. Place the siphon tube at the bottom of the tank. Slowly add the cold water into the tank until the tank reaches 3/4 full. If the colors mix, you added the cold water too quickly and will need to begin again. Carefully remove the siphon tube, leaving 2 distinct layers of water in the tank.
c. Tape a ruler to the tank with the zero line at the water surface.
d. Using the salinity probe, measure the salinity from the top to the bottom
in 1 cm. increments. Be sure someone records the values as you go through the
readings.
e. Your instructor will use your tank as a demo for upwelling.
All groups will produce a graph using the data they collected. You can produce the graph using Excel and print a copy for your group or produce the graph using a ruler and graph paper. Each individual needs to answer the questions below. The group may work together, and answers may be similar, but not identical.
Lab questions:
1) What is a thermocline?
2) What is a halocline?
3) Describe a natural situation that would result in temperature differences in the ocean.
4) Describe a natural situation that would result in salinity differences in the ocean.
5) How would upwelling occur in the ocean?
6) Describe the curve you saw on your graph. Explain your results.
7) What did you observe when the aluminum boat with ice was added to the water?
8) Add a drop of food dye that contrasts the color of your water onto the surface. What did you observe? Why did it act that way?
9) What did you observe when the fan was used on the surface of the water?
10) Freddy the Fisherman was fishing at a spot near the mouth of a river. Five feet down he caught a freshwater perch. His luck was so good that he decided to let out more line. At thirty feet he caught a saltwater cod. Freddy is so perplexed by this strange occurrence that he is going to call the Sports Editor of the Post-Intelligencer. What would you tell Freddy to save him from the embarrassment?
