THERMOCLINE, HALOCLINE, PYCNOCLINE LAB
This experiment is designed to help understand:
the relationship between a thermocline, a halocline and a pycnocline;
how turbulence affects a thermocline (pycnocline), and
how they ( the “clines”) affect the marine environment.
PURPOSE:
1. At what depth is the thermocline and pycnocline?
2. Does the thermocline or halocline have a great effect on the location of the pycnocline?
3. How does turbulence affect the thermocline?
1. Observe the container and water. 1Q Do you notice anything unusual about the water in the container?
2. While holding a ruler up against the container, measure and record the temperature of the water every
two centimeters from the surface down to the bottom. Measure the distance using the bottom of the
thermometer as your reference mark.
Example: Data Table
Table 1: Temperature Depth Profiles
Depth
0
2
4
6
(cm)
Temp ('C)
Before
Density
(g/ml)
Salinity
(o/oo)
Temp ('C)
After
8
10
12
14
16
18
…
3. Make a graph of the depth as a function of the temperature (Depth - vertical, Temp - Horizontal).
[Note: In a graph of oceanographic data the zero-zero values are in the upper left hand corner of the
graph. The depth proceeds down the vertical axis and the temperature goes to the right in a positive
direction. See example, Graph 1, below.]
2Q Analyze the data on the graph and estimate the depth of the thermocline? (At what depth or depth
range is the graph of the temperature most horizontal?)
[Note: The thermocline is the area of the graph where the temperature changes most rapidly within a
small change in depth. That is where the curve of the line is most horizontal.]
4. Using a refractometer measure and record the salinity and density from the surface to the bottom at
2 cm intervals as you did to measure the temperature.
3QWhat methods would you use to secure a water sample and measure the salinity and density every two
centimeters?
5. Put three to five drops of food coloring in the water. Do NOT attempt to mix the water. Allow the food
coloring to mix by diffusion for a few minutes.
4QWhat do you observe happening to the food colored water?
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THERMOCLINE, HALOCLINE, PYCNOCLINE LAB
6. Blow across the surface of the water for three to five minutes to make surface turbulence.
7. Re-measure the temperature every two centimeters from the surface to the bottom, and record the
depth of the visible pycnocline made by the food coloring.
8. Graph the results of the "After" temperature on Graph 1 with the temperature data you graphed earlier
in step 2, use a different color ink or line type.
[Note: When analyzing the data for change it is often beneficial to draw a horizontal arrow from the first
temperature measurement at each depth to the second temperature measurement to see if the
temperature increased of decreased at each depth.]
5Q? - What changes of any type are observed after blowing across the water's surface?
6Q? - How deep was (were) the effect(s) noticed?
7Q? - What happens to the thermocline? (How did the line on the graph change from the first graph?
8Q? - What data, if any, suggests CONDUCTION played a part in the temperature changes? At what
level of the water was this observed?
9Q? - Where was the least change in temperature noted? Why?
10Q? - How does question 9 relate to the ocean environment? (Where in the ocean is the temperature
most stable? least stable?)
Graph the following data and analyze the relationships between the thermocline, halocline, and
pycnocline:
a) Depth v. temperature, before and after turbulence
b) Depth v. Density
c) Depth v. Salinity
[Note: When entering data for Depth on the spreadsheet the numbers must be negative for depth.
2cm underwater = -2]
Sample Graph for data:
Graph 1: Thermocline
Tem perature ('C)
Depth (cm)
0
5
10
15
20
0
-2
-4
-6
-8
-10
-12
-14
-16
-18
2
25
30
35
40
THERMOCLINE, HALOCLINE, PYCNOCLINE LAB
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