When Water Gets Icy
Written by: Kyle Kinzler
Illustrated by: Brendan Koehler and Sabine Deviche

If you've accidentally taken a sip of sea water or had to gargle with salt water, you've probably realized that freshwater and saltwater have some pretty important differences. These differences exist not only when these waters are liquid, but also when they freeze. In this experiment, we will look at one major difference between frozen freshwater and frozen saltwater.

What You Need

  • Table salt
  • Water (tap water is fine)
  • Transparent container, for example a clear water bottle with the top cut off or a drinking cup (x2)
  • Food Dye (any color will work)
  • Measuring cup
  • Measuring spoon (teaspoon)
  • Tape and marker for labeling

Before You Begin

Multiple ice cores

When there is color at the bottom of the ice core, it indicates the presence of algae living within the brine channels.

As you read in the Frozen Life companion story, when sea ice forms, freshwater freezes and leaves behind a concentrated salt solution called brine. This brine is found in pockets throughout the ice. Brine pockets allow organisms that get trapped in the ice to avoid freezing and survive until the next spring. The pockets are small and isolated in winter, but in spring, as the ice begins to warm, the brine pockets get bigger and combine with other pockets to form channels which allow the organisms to move throughout the ice. You can explore the differences in channels between seasons in our channel maze.

In this experiment we are going to compare the difference between regular freshwater ice (the kind you would put in your drink) and sea ice. To do this we will create fresh and saltwater ice, then put a couple drops of dye on each type of ice and compare what happens. What do you think is going to happen? Do you think the dye will act the same in both ice types?

This should ideally be done over two days. The first four steps in the Procedure should be done on Day 1, and the remaining steps should be completed on Day 2.

Procedure (1-4 should be done ahead of time)

  1. Water placed in the freezer

    Step number 4, leave the containers of water in the freezer for a few hours until completely frozen.

    Measure out two cups of water into each of your two containers (you can use less if your container is too small). Make sure to leave a little room as the water will expand when it freezes.
  2. Using your tape and marker, label one container "water" and the other "salt water."
  3. In your "salt water" container, dissolve 1.5 teaspoons of salt for every cup of water (so, if you have two cups, use 3 teaspoons).
  4. Put the containers in a freezer (this will take at few hours to freeze, best done overnight) and keep frozen until ready to perform experiment
  5. Take the ice out of the containers and set them next to each other. These are going to melt and make a mess so put the containers on a tray or a sink.
  6. Add 5 drops of dye to the top of the freshwater ice and note what happens. (If nothing seems to happen, you can add a few more drops of dye.)
  7. Add 5 drops of dye to the top of the saltwater ice and note what happens.

Using your observations, decide whether your predictions were correct (what happened and did the dye act the same in both ice types?). Make a conclusion about what you think is happening based off of what you saw. Then, when you're done, you can move on to the next step.

After You Do the Experiment, Compare Your Results

The way the food coloring disperses in the ice lets you see the difference between sea and freshwater ice.

Take a look at these two ice core sections. The one on the left is ice made from fresh water, and the one on the right is ice made of salt water. What are some of the differences you notice in this image?

salt and freshwater ice

Sea ice (on the right) forms brine channels which food coloring is able to penetrate. This turns the inside of the ice the same color as the dye.

The freshwater ice (on the left) is solid all the way through and has no channels. This results in food coloring pooling on top or run down the side of the ice.

Kyle Kinzler is a graduate student at Arizona State University and is working on his Masters thesis focusing on Arctic sea ice algae with Dr. Susanne Neuer. To learn more about Dr. Neuer's research, visit What Lies Beneath.

View Citation

You may need to edit author's name to meet the style formats, which are in most cases "Last name, First name."

Bibliographic details:

  • Article: When Water Gets Icy
  • Author(s): Kyle Kinzler
  • Publisher: Arizona State University School of Life Sciences Ask A Biologist
  • Site name: ASU - Ask A Biologist
  • Date published: July 15, 2014
  • Date accessed: June 12, 2024
  • Link: https://askabiologist.asu.edu/experiments/when-water-gets-icy

APA Style

Kyle Kinzler. (2014, July 15). When Water Gets Icy. ASU - Ask A Biologist. Retrieved June 12, 2024 from https://askabiologist.asu.edu/experiments/when-water-gets-icy

American Psychological Association. For more info, see http://owl.english.purdue.edu/owl/resource/560/10/

Chicago Manual of Style

Kyle Kinzler. "When Water Gets Icy". ASU - Ask A Biologist. 15 July, 2014. https://askabiologist.asu.edu/experiments/when-water-gets-icy

MLA 2017 Style

Kyle Kinzler. "When Water Gets Icy". ASU - Ask A Biologist. 15 Jul 2014. ASU - Ask A Biologist, Web. 12 Jun 2024. https://askabiologist.asu.edu/experiments/when-water-gets-icy

Modern Language Association, 7th Ed. For more info, see http://owl.english.purdue.edu/owl/resource/747/08/
Ice core sample
A piece of ice core collected by researchers in the Arctic. Learn more about the frozen life found within the ice.

Download the When Water Gets Icy experiment packet.

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