Factors Affecting Density of Seawater, Sea Ice formation and Ocean Stratification

it is a formal report about factors affecting the density of seawater, sea ice formation, and ocean stratification, the content of the report must be:

1- introduction

2- effect of Temprature and Density in seawater

3- effect of salinity and Density in seawater

4- sea ice formation

5- ocean stratification

6- results ( in the uploaded file)

7-conclusion

8- Refrensesse ( APA style)

I also posted the ppt presentation for more information, and in the Excel file you will find the graph for exercise 2 in the result file ( laboratory activity)

“ Sea Water Properties ”
Density,Temperature and Salinity
Dr. Muhammed Nayeem
MARS 101-LAB 5
Objectives
What are the basic properties of water
and sea water
 Density of sea water- measurement
 Effects of Temperature and salinity on
sea water density

Lab Overview
• Water has many unique thermal and
dissolving properties.
• Seawater is mostly water molecules but has
dissolved substances.
• Ocean is layered by salinity and density
differences.
.
Water’s Thermal Properties
Water is solid, liquid, and gas at Earth’s
surface.
 Water influences Earth’s heat budget.

Heat
Energy of moving molecules
 Calorie is the amount of heat needed to raise
the temperature of 1 gram of water by 1°C.
 Temperature is a measurement of average
kinetic energy.

What happens to solar energy
Absorbed and is stored in the mass of the
ocean as heat.
 Heating will leads to expansion-and hence
density will decreases(mass per unit volume).
 So what’s the effect of cooling and heating??

Change in salt
So what’s the effect of change in salt
content?
 What’s the salt content?

Effect of pressure

The reduction of volume by the pressure
Water Density

Density of water increases as temperature
decreases.

Thermal contraction
From 4°C to 0°C the density of water
decreases as temperature decreases.
 Ice is less dense than water.

Changes in molecular packing
 Water expands as it freezes.

Seawater Density

Density increases with decreasing
temperature

Greatest influence on density
Density increases with increasing salinity
 Density increases with increasing pressure


Does not affect surface waters
.
Temperature and Density
Variation With Depth
Pycnocline – abrupt change of density with
depth
 Thermocline – abrupt change of temperature
with depth

Layered Ocean
Three distinct water masses based on
density:
 Mixed surface layer – above thermocline
 Upper water – thermocline and pycnocline
 Deep water – below thermocline to ocean
floor
 High latitude oceans – thermocline and
pycnocline rarely develop
Isothermal
 Isopycnal

TSP
T and S important since very less effect in
the shallow regions for pressure
 Change in S by 1 per mil effect density
than change in temperature by 1 degree
 However change in temperature is more
important, why?

TDS Diagram
Experiments
Hydrometer
Sea ice formation

Fresh water freezes at 0 degrees Celsius (32
degrees Fahrenheit), but the freezing point
of sea water varies. For every 5 ppt increase
in salinity, the freezing point decreases by
0.28 degrees Celsius (0.5 degrees
Fahrenheit); thus, in polar regions with an
ocean salinity of 35 ppt, the water begins to
freeze at -1.8 degrees Celsius (28.8 degrees
Fahrenheit).
Sea ice and brine rejection

Why then does sea ice float? (because it is actually
less dense than the seawater, for several reasons…)
Brine rejection: as sea ice forms, it excludes salt from
the ice crystal lattice.
 The salt drips out the bottom, and the sea ice is
much fresher (usually ~3-4 psu) than the seawater
(around 30-32 psu)


Sea ice and brine rejection
The rejected brine mixes into the seawater below. If
there is enough of it mixing into a thin enough layer,
it can measurably increase the salinity of the
seawater, and hence its density
 This is the principle mechanism for forming the
densest waters of the world ocean.


)
Density
30
1.024
28
1.026
26
1.026
24
1.028
22
1.028
20
1.028
18
1.028
16
1.028
14
1.029
12
1.03
10
1.031
8
1.034
6
1.035
5
1.037
Temperature and density of 35 sali
1.038
1.036
1.034
Density
temp
1.032
1.03
1.028
1.026
1.024
1.022
0
5
10
15
Temperature
ture and density of 35 salinty
15
20
Temperature
25
30
35
Department of
Biological & Environmental Sciences
MARS 101
Introduction to Marine Science
Instructor: Dr. Muhammed Nayeem Mullungal
Laboratory Activity #5
Seawater density and factors affection
density
Objectives
•
Understand the concept of density and utilize this to understand the processes
during stratification and mixing
•
Understand the relationship among temperature, salinity and density
•
Investigate and understand the effect of salinity on density
•
Investigate and understand the effect of temperature on density
•
Investigate the formation of ice in a saline solution and its effect on density
Introduction
Sea water density (mass per unit volume) affects vertical circulation in the ocean. Small
density differences caused by surface heating or cooling can produce strong vertical
currents. Temperature, salinity and pressure (depth) play roles in determining the density
of a sea water sample.As temperature increases, density decreases. The increase in
temperature causes an increase in molecular activity, which translates into greater space
between molecules.As salinity increases, density increases. Salinity is usually measured
as the total dissolved salts in a standard sample. As more salt is dissolved per unit volume,
density increases. As pressure increases, density increases. The deepest waters in the
ocean are usually the densest due to the weight of the overlying water.Density can be
measured directly by weighing a known volume of sea water, measuring electrical
conductivity, using a hydrometer or by using a refractometer.
Fall 2022: MARS 101 Lab 5
PART A
Ocean Stratification:
After completing this lab, you will understand how density differences affect
stratification, some causes for stratification, and how mixing affects a water column with
different density properties.
Part 1: What is the density?
1) Weigh each empty 500ml beaker. Record the weight of the beaker below:
Beaker 1:
Beaker 2:
2) Measure 500ml of cold water into Beaker 1 and 500ml of warm water in
Beaker 2.
3) To the cold beaker (beaker 1), add the salt and 5 drops of yellow food
coloring. Stir until the salt has fully dissolved.
4) Add Red food coloring to the warm, fresh water (beaker 2)
5) Weigh each beaker (now with the water) and record the weight below:
Beaker 1:
Fall 2022: MARS 101 Lab 5
Beaker 2:
6) Calculate the mass, volume and density of the water in each beaker. (You will
have to be very precise with the volume).
Remember: Density = Mass / Volume
Cold, Salty Water
Mass
520 g
Volume
Warm, Fresh Water
500 g
500 ml
500 ml
Density
7) If the water you just measured were in the ocean instead of the lab beakers, do
you think the layers will be stratified? Which one will be on top?
Part 2: Try it out.
1) Gently pour the cold, salty water (beaker 1) into the 1000ml beaker and place
the beaker on the table. Let the water settle while you complete the next steps.
2) Add the warm fresh water to the 1000ml beaker by carefully following these
instructions:
a. Cut out a circle of cardboard that is roughly the size of the opening of the
beaker (doesn’t need to be exact).
b. Place the cardboard in the 1000ml beaker so it floats on top of the
water.
c. Gently pour the warm fresh water on top of the cardboard. The
cardboard will break the fall of the water preventing the two layers
from mixing while continuing to float.
d. After you are done pouring, remove the cardboard and let the 1000ml
beaker settle.
Part 3: Observations.
1) What do you observe in the 1000ml beaker?
2) Carefully tilt the beaker (do not spill any liquid!) and hold it at a tilt for 15
seconds. Then gently (but quickly) place the beaker back on the table and
observe what happens to the layers. Write a few sentences about what you
observed.
Fall 2022: MARS 101 Lab 5
Part 4: The big picture
The ocean has more than just two layers, and sometimes they are not so clearly defined. Do you think
you could create a third layer in your beaker? How?
1) What color do you expect the third layer to be?
2) Where do you think the third layer will be formed?
3) Using the information from the density you calculated earlier, what density do you expect this
third layer might be?
Try it out! (Hint: Use the glass stirrer very carefully)
Fall 2022: MARS 101 Lab 5
PART B
TDS Diagrams
The relationship between temperature, salinity and density is shown on the TDS (Temperature- DensitySalinity) diagram in Figure 1. Density is shown on the y-axis and salinity is plotted on the x-axis.
Temperature is shown as curved lines running diagonally across the center of the plot.
Figure 1. Temperature-Density-Salinity
Fall 2023: MARS 101 Lab 5
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Exercise 1: The Effect of Salinity on Sea Water Density
In this procedure, you will get five different samples as provided in the Table. Then you will measure
its density using a hydrometer. You will also determine a theoretical density using Figure 1.
Following this.
1. Transfer 200 mL of the sample solution to a 250 mL graduate.
2. Using a hydrometer and a thermometer, measure the density and the temperature of the mixture
and record them in Table 1. Be sure the hydrometer is floating freely. Add more water to the
graduate if necessary.
3. From Figure 1, determine the theoretical density at the given temperature and salinity.
4. Repeat this procedure (steps 4 – 6), using 20, 35, 50 and Unknown salinity samples
provided by the instructor.
Fall 2023: MARS 101 Lab 5
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Salinity
(ppt)
Table 1. Temperature, Measured and theoretical densities of three water samples
Measured Density
Theoretical Density
Temperature
(°C)
(g/cm3)
(g/cm3)
10
20
35
50
Unknown
In Table 1, are your measured densities different from the theoretical values? How can you explain these
differences? (Hint: What are the possible the sources of error?)
Exercise 2: The Effects of Temperature on Density
Temperatures in the open ocean range from 2°C in the polar seas up to 30°C in some of the warmer
regions of the Red Sea. In coastal waters, winter-time temperatures can fall below 0°C; and summer
temperatures may exceed 40°C in the shallow waters over tidal flat areas. Of all the properties
controlling seawater density temperature is probably the most important because the range is so large.
In this procedure you will use any water from the last step of Procedure 1.
First you will warm this water to 30°C. Then you will cool it, measuring the density along the way.
1. Using the water sample of known salinity water in the graduate from the previous exercise, add a
bit more until the graduate is as full as possible without overflowing when the hydrometer is in it.
Take the graduate and a glass thermometer to the warm water bath at the side of the room.
2. Stir the water in the graduate constantly but gently (the thermometers are glass!) to insure uniform
heating of the water in the graduate. Warm the graduate in the water bath provided until the
temperature is 30° C. Take the graduate back to your table and measure the density with a
hydrometer and record both the density and temperature in Table 2.
3. Fill a 2000 mL beaker about ¾ full of cold tap water.
Note: Place the beaker on a clean dry cloth towel to prevent it from
freezing to the table later in this exercise!
Fall 2023: MARS 101 Lab 5
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4. Place the 250 mL graduate containing known salinity into the beaker. Stir the water in the
graduate constantly with the thermometer except when you remove the thermometer and put in
the hydrometer to measure the density.
Record densities and temperatures in Table 2. Be
sure to
remove the hydrometer and thoroughly stir the water in the 250 mL graduate between density
readings.
NOTE: The amount of time between readings is not as important as making sure that you have a
density recorded for every drop in temperature of about 2 degrees.
5. When your known salinity water has reached a temp of 25º add a little ice to the water bath to cool it
down.
Continue to measure temperatures and densities every 2º or so. When your salt water reaches a
temperature of about 15º, your instructor will add dry ice to continue lowering the temperature. Your
instructor will dispense the dry ice as it is extremely cold.
Do not touch the dry ice with your bare hands or hold the beaker
containing the dry ice with your bare hands.
6. Continue recording densities until the temperature reaches 5°C. Reserve this chilled water in the
graduate for the next exercise. The graduate will probably be frozen in place in the beaker. Do not
try to break it free! Your instructor will assist you with transferring the contents of the graduate to
the Erlenmeyer flask.
7. Plot the data in Figure 3.
Figure 3. Density versus Temperature for a 35o/oo water sample
Fall 2023: MARS 101 Lab 5
Page 5 of 9
Table 2. Temperature and density of a known salinity (can be 35) water sample
Temperature (°C)
Density (g/cm3)
30
28
26
Add ice here
24
22
20
18
16
Add dry ice here
14
12
10
8
6
5
Stop, Take Erlenmeyer flask to back of room to
pack with dry ice (done for you). Go to
Exercise 3: The Effect of Ice Formation on Density
The densest water in the ocean is the Antarctic bottom water. The high density of this water is the result of
low temperature and the formation of sea ice. As ice forms, fresh water is “frozen” out of the sea water,
leaving behind very salty, very dense water. In this procedure you will use your chilled 35 o/oo water
sample from the last exercise. This will be chilled in an Erlenmeyer flask until about one third of the water
freezes.
1. Transfer the last temperature and density from the previous exercise (Table 2) to the appropriate
Fall 2023: MARS 101 Lab 5
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blanks in Table 3 and find the corresponding salinity using Figure 1 and insert that number in
Table 3.
2. Your teacher/lab assistant will pack the Erlenmeyer flask in the 2000 mL beaker with dry ice (Figure 4).
Go back to your seat. Do not touch the sides of the beaker with your bare hands (use a towel)! The dry
ice may freeze your skin to the beaker.
Figure 4. Experimental set –up for ice formation procedure
Why are the two temperatures of first ice formation (measured and theoretical) different? (hint:
consider sources of error in the experimental results!)
3. Let the water/ice mixture continue to form until approximately one third of the salt water is ice.
The remaining liquid that doesn’t freeze is called “brine”. When approximately half of the water in the
flask is frozen (monitor the thickness of the ice on the inside wall of the flask using the glass stirring
rod), pour approximately 200mL of the brine solution into a 250mL graduate. Measure the temperature
with the thermometer and density with a hydrometer. Determine the salinity from Figure 1. Record the
temperature, density and salinity in Table 3
Table 3. Temperature, density and salinity of 35o/oo water before and after ice formation
Sample
measured density
measured temperature
salinity (from Fig. One)
At 5°C , 35 ppt water
before ice formation
brine after ice
formation
How does the salinity of the brine differ from the salinity of the original water sample? From this, what
can you infer about the salinity of sea ice.
Fall 2023: MARS 101 Lab 5
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Figure 5. Freezing point and maximum density as a function of salinity and temperature
Fall 2023: MARS 101 Lab 5
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