1.5
Exploring waves under the ice of Arctic lakes

Did you know?
The sea and lake ice in the Arctic are disappearing.
Sea and lake ice act as a protective layer which restricts wave action near coastlines which helps lessen the impact of coastal erosion – therefore protecting shore lines (see story 5.8).
Did you know…That we don't know! Even scientists don't know how waves in lakes under ice are formed! Can you think why there might be waves under the lakes?

Get Active!
Arctic Sea and Lake Ice Erosion
You will need:
Instructions
Fill two identical glasses ¾ of the way up with water of the same temperature. Use the thermometer to check they are the same temperature.
Add one ice cube to each glass of water – these represent the sea ice on the Arctic coast. When you add the ice cubes, start the timer.
In one glass, stir the ice cube around until it melts – this represents the waves which melts the ice. In the other glass, let the ice cube sit in the water and do not touch it. When an ice cube melts, record the time in the boxes below and continue the timer until the other ice cube melts - then record that time.
Which ice cube melted the fastest?
Do you want to change the speed of the process? What happens when you use hotter water, or cold water?
How do waves cause the ice to melt faster?
Sea ice, like the ice cube in the glass of water, floats in the ocean. The ocean, even though it is cold, is not as cold as the ice so the water melts the ice surface. In fact the sea water is becoming warmer because of climate change and warm water currents from the south (see activity sheet Awesome experiments: Ocean currents and the role of the Arctic). The waves also cause friction which is when a small amount of heat is produced by two surfaces sliding across each other. Therefore, friction also has a role in the overall ice cube melt, as the heat generated by the impact of waves hitting the ice also heats the water. The consistent warm water from the circulating waves and the friction therefore cause the ice cube to melt much faster than if it were still in the water.
How would underwater waves impact sea ice in the Arctic?
Waves in the Arctic Ocean are massive, so big that they can be up to 160 kilometres long (much bigger than in lakes). These waves can be caused by storms and wind. They are also caused by ice bergs and blocks of lake and river ice breaking and flipping over. However, it is the underwater waves that may do the most damage to sea ice. Scientists believe that underwater waves can seriously impact the rate of sea ice melt in the Arctic. The reason is that the underwater waves pull warmer waters from the depths of the ocean up to the surface. The warmer waters pose a significant threat to sea ice melt which will have serious impacts for the wildlife, humans and environment that depend on it. For example, ice reflects heat from sunlight back into the atmosphere in order to regulate Earth's temperatures. If the ice melts, more sunlight will be absorbed into Earth's surface causing our atmospheric, land and water temperatures to increase. Thus causing even more sea (and lake) ice to melt – continuing the vicious cycle.
Arctic Climate Change
Ocean currents and the role of the Arctic

You will need:
Instructions
Fill the fish tank or clear container with water. This represents the ocean.
Add a little potassium permanganate or food colouring to one end.
You should see the colouring spread (diffuse) randomly.
Boil the kettle.
Add the hot water from the kettle to one end of the tank and the ice to the other end. You have just created the Gulf Stream! Watch what happens to the dye.
Use a hair dryer to heat the air above the water. This represents the wind, which
plays a big role in moving surface currents. Again, watch what happens to the dye.
What happens to the dye at different stages? Does it:
1
Move from the cold water to the hot water?
2
Move from the hot water to the cold water?
3
Stay the same and just move about randomly?
4
Move along the surface, or sink deeper into the water?
Having a balance of cold and warmer water, and strong currents to keep moving water around is important to keep our climate stable. Warm, less dense (lighter) currents rise at the tropics and move along the surface to the poles, where the water cools down, sinks (cold water is heavier than warm water) and cold, deep currents return to the tropics. The cold waters of the Arctic are vital for this.
The oceans play a big role in our climate system. Covering 71% of the Earth, our oceans absorb twice as much of the sun's heat as the air or land. Oceans act like a conveyor belt, moving very large amounts of heat around the planet. They move warm water from the equator towards the poles, and cold water from the poles back towards the tropics. Our weather – if it is hot, cold, rainy or dry — is determined largely by ocean currents.
From our experiment we know that:
When all the water is the same temperature, currents (the food colouring) are weak.
In the first part of the experiment the food colouring moved about in all directions at
the same time.
When there is a big difference in temperature, currents are strong.
In the second part of the experiment the food colouring moved quickly from the warm water to the cold water.
Why does this matter?
Currents regulate global climate. Without strong currents, temperatures in different parts of the world would be more extreme — super hot at the equator and even colder toward the poles. A lot less of Earth's land would be habitable, meaning that people could not live in those parts of the world.
Marine (sea) life is already being affected. Animals, fish and sea plants are adapted to live in different water temperatures. If these temperatures change, species may have to move or could even die. Fish in the North Sea are already moving further north to deeper, colder water. Rising water temperatures could slow the growth of plankton meaning less food for fish and other species that eat it.

References