OC 201e – Introduction to Oceanography
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Lab 3 – Density, mixing and stratification
In this lab you will explore on a small scale the
... [Show More] influence of temperature, salinity and mixing on
seawater stratification. These same processes operate in the ocean over much larger scales and
have far-ranging physical, chemical and biological implications.
Spring 2020: I realize that some of you may not be able to get to the grocery store for the
supplies need for this lab. Therefore, I will provide you with pictures and videos of the activities
described below. They can be found on my science Instagram account @oceans_past
You will need to log in with either a Facebook or Instagram account.
Now, if you can get the supplies please try these activities/experiments. There is no pressure
now so it should be fun, especially if you involve the people you live with.
HINTS:
1. Density is controlled by temperature and salinity. Cold salty water is more dense than
warm, fresh water.
2. A stable water column (i.e., stable stratification) is less dense water over more dense
water.
Lab Supplies: Table salt (lots), food coloring/dye, eyedropper, spoon, 2 large clear water
glasses, and ice cubes made from both plain and dyed freshwater.
Lab Set-up: Make your own saltwater by mixing salt into water – you don’t need to be
delicate with this because the saltier it is the better it will perform in the lab.
Approximately 2 tablespoons of salt in 1 liter of water will give you “typical” seawater
(i.e., a salinity of 35). You will need at least 2 liters of saltwater, but I suggest making
extra. Also, for some of the experiments you require cold salt water (the colder the
better). I would place at least 1 liter of salt water in the freezer for about 20 minutes
before you try Activity 4.
Activity 1: Salt water with dye (6 pts)
In this activity, you will explore the role of mixing on water mass interaction.
Materials: Freshwater at room temperature, cold saltwater and food dye
Preparation: Fill a large glass with the room temperature freshwater.
In a separate container add food dye to a small amount of cold saltwater.
Part 1 – Answer part “i” below before doing the following:
Using an eyedropper, drop a single drop of dyed saltwater into the freshwater at a time.
Try from very near the surface so that the drop does not enter the water going fast.
Next, try from higher up. Observe the mixing.
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OC 201e – Introduction to Oceanography
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i) Before the experiment, write down what you think you will see.
a) Droplet very close to surface (moving slowly):
The droplet will disperse in the water slightly after it hits the surface and dye will disperse
b) Droplet far above the surface (moving fast):
Droplet will disperse farther down in water compared to the very close to surface droplet
ii) Now, write down what you actually observe and comment on the difference from your
initial guess.
a) Droplet very close to surface (moving slowly) [Show Less]