Lab 3 Density of Seawater Answers
Questions (the colors in lab
might be different than those used in the question below):
1. What happened when we added cold blue water to warm yellow water? What does this tell you about theses two water masses?
We
would expect that the cold water to be slightly denser than the warm water and
therefore the blue water would sink to the bottom. In the lab, however, when the two were mixed, the turbulence
resulted in a mixed green solution. So
procedures were changed and the colder water was added with a syringe to a
narrow glass to minimize vertical mixing due to turbulence.
The cold, denser water formed a layer below the warm water.
Some mixing was apparent between the layers.
We
conclude from the modified experiment, that the cold water had a greater density
than the warm water mass.
(When
the syringe was lifted and the colder water was added near the top portion of
the warm layer, it sank, but mixed with the overlying layer before it reached
the cold layer below.)
A
control experiment was also conducted using water with the same temperature. The
blue (or red) water mixed with the overlying yellow water when it was added with
the syringe to the bottom.
2. What happened when we added the very salty red
water with fresh yellow water? What does this tell you about these two water
masses?
We expected that the salty water would sink below the fresh water. In the initial lab, when the red salty water was added to the yellow water, the solution turned orange. In the modified lab, a red salty layer was formed below the yellow fresh water. Some mixing was apparent at the boundary between the layers, however it was more limited than observed for water with 2 different temperatures.
We
conclude from the modified experiment, that the more saline water had a greater
density than the fresh water.
(When the syringe was lifted and the red saline water was added in the top portion of the fresh water. The water sank to the bottom layer with only limited mixing. Because the saline water sank farther and formed a more distinct boundary with the overlying layer more defined for the salinity experiment than the temperature experiment, these observations suggest that salinity has a greater effect on density than temperature.)
3. A. What happened when we added very cold more
salty blue to cold less salty yellow? B. Then when we added hot salty red water?
C. How do these three water masses interact?
D.What sea outflow to the North Atlantic is the hot salty water is
similar to?
A.
The very cold, salty blue formed a layer below the cold, less salty yellow.
B/C.
The hot salty red layer formed an intermediate layer between the other two.
Even though the red salty water was warmer than the cold, less salty
yellow layer, it had greater density due to the salinity difference.
4. Why are oceanographers concern about the
temperature and salinity “signature” of a given water mass?
As
a large mass circulates in the ocean, the temperature and salinity is relatively
constant. Therefore, the temperature and salinity signature of a given water
mass is important for oceanographers to the study the origin, transport, and
circulation of a water mass as well as interactions and mixing between water
masses.
5. Use Figure 3 to determine the density in (g/cm3)
of water with the following temperature characteristics: Use a straight edge:
accuracy counts!
|
Salinity |
Temperature °
C |
Density (g/cm3) |
|
33.0 |
6 |
1.0260 |
|
35.0 |
15 |
1.0258 |
|
34.0 |
19.5 |
1.0240 |
|
34.9 |
0 |
1.0282 |
|
33.0 |
0 |
1.0265 |
6. Use Figure 4 to fill in the tables and answers to the questions below. Plot the points on the figure (Use Letters for A. and Numbers for B. Use 2 different colors if possible.
A.The following is a list of paired temperature and salinity values obtained from a hydrocast at a single station in the Pacific Ocean, each pair represents a sample taken at a different depth, but they are not presented in any systematic order. List them in the correct order and label the surface and bottom samples. An example is provided to help you get started.
|
Sample ID |
Salinity |
Temperature ° C |
Sample ID Order |
Density (g/cm3) |
|
A |
34.8 |
13 |
Surface: D |
1.0262 |
|
B |
35.3 |
18 |
B |
1.0258 |
|
C |
34.6 |
1.5 |
E |
1.0277 |
|
D |
35.5 |
20 |
A |
1.0251 |
|
E |
35.0 |
15 |
F |
1.0259 |
|
F |
34.6 |
10 |
H |
1.0266 |
|
G |
34.6 |
4 |
G |
1.0276 |
|
H |
34.3 |
3 |
Deep: C |
1.0273 |
B. Plot the following water masses on the attached
T-S diagram (Figure 4) and record the density in this table: An example is
provided to help you get started.
|
Water Mass |
Salinity |
Temperature ° C |
Density in Sigma Units |
Density (g/cm3) |
|
1 |
35.40 |
10 |
27.25 |
1.02725 |
|
2 |
34.10 |
6 |
26.76 |
1.02676 |
|
3 |
35.00 |
0 |
28.15 |
1.02815 |
|
4 |
36.00 |
18 |
26.00 |
1.02600 |
|
5 |
34.90 |
3 |
27.76 |
1.02776 |
|
6 |
33.85 |
-1 |
27.24 |
1.02724 |
7. Refer to the results from problem 6B to answer the
following questions (Show calculations):
A. If we mix water masses 4 and 2 in equal parts, what is the density of the resulting water mass? What is the salinity? Be sure to mark this point on your T-S diagram.
(0.5
* D4) + (0.5 * D2) = DR (density of
resulting water mass)
(0.5
* 26.00) + (0.5 * 26.76) =
13
+13.38 = 26.38 sigma units
(0.5
* S4) + (0.5 * S2) = SR (salinity
of resulting water mass)
(0.5
* 36.00) + (0.5 * 34.10) =
18
+17.05 = 35.05 (note: salinity is unitless)
B. What is the density of the resulting water mass if we mix 75% water mass 5 with 25% water mass 2? What is the salinity? Be sure to mark this point on your T-S diagram.
(0.75
* D5) + (0.25 * D2) = DR (density
of resulting water mass)
(0.75
* 27.76) + (0.25 * 26.76) =
20.82
+ 6.69 = 27.51 sigma units
(0.75
* S5) + (0.25 * S2) = SR (salinity
of resulting water mass)
(0.75
* 34.90) + (0.25 * 34.10) =
26.175
+ 8.525 = 34.70 (note: salinity is unitless)