Make four ‘ice core samples’ and bring Arctic science into the classroom or home. Students will take each of the samples, melt it, and analyse its contents for evidence of algal growth.

Activity preparation

To prepare for this activity, you will need to create four different samples that represent ice cores taken from the Arctic sea ice with varying seasonal conditions.

These ‘ice core samples’ are ice cubes made from a brine solution (c. 30 g of salt per litre of tap water) mixed with different quantities of dried herbs to represent algal growth. The addition of salt will make the ice cores easier to crumble by hand.

Sample 1 – ¼ tsp dried herbs per ice cube

Sample 2 – ½ tsp dried herbs per ice cube

Sample 3 – no dried herbs

Sample 4 – small sprinkle to dried herbs per ice cube

Depending on the size of your ice cube tray, you may need to adjust the amount of dried herbs, but ensure that you keep the ratios described above. You will need one of each sample per student or group doing the activity.

Activity steps

1. Hand out four filter papers or pieces of paper towel to each student or group. These are to soak up the water as the ice is melted.
2. Place one of each type of ‘ice core sample’ on each of the filter papers or sheets of paper towel.
3. Students should melt that ice, either using the warmth of their fingers or, if you have time, by waiting for the ice cubes to melt. The salt in the water will make the ice cubes easier to crumble.
4. Students should then observe the amount of algae (dried herbs) in each sample.
5. Hand out a copy of the student record sheet to each student or group. Go through the sheet with the class, highlighting the difference in seasonal conditions for each row. There are some time-based calculations for students to try.
6. Students should then complete the record sheet matching each row of the observed amounts of algae (dried herbs) with the varying seasonal conditions listed.
7. An extension activity asks students to give reasons for their answers.

Activity materials

• Ice cube trays
• Water
• Salt
• Dried herbs
• Filter paper

Activity resources

• Polar photosynthesis student record sheet

Algae and the sea ice

Extracts from one of Dr Victoria Hill’s blog posts during the Catlin Arctic Survey written on 28 April 2011.

"Hi, my name is Dr Victoria Hill and I am one of the scientists at the Catlin Arctic Survey Ice Base. It's exciting to be here in the Catlin Ice Base at the seasonal change from winter to spring. Warmer temperatures make living on the sea ice much more pleasant. and the plankton world is feeling the coming of spring too.

Already this year I have seen visible changes in the amount of algae in the sea ice. A few nights ago, I was crushing a filter from an ice core sample, and saw clearly a green colouring. This was from the bottom of the ice core, in the 5 cm nearest the ocean and its nutrients.

Just yesterday, I found chlorophyll in the whole bottom 20 cm of the ice core. This indicates that the ice algae are really starting to increase production and my colleagues have found similar increases in zooplankton numbers which feed on the algae.

This speed of change in the high Arctic is astounding. Three weeks ago we had clear periods of night, of darkness. Now the days run into one another, without it ever getting properly dark. It's important to be up here during these swift changes, and as Arctic marine life blooms."