How Does Frozen Water Shape Our World? GRADE 8 Freshwater and Saltwater Systems SECTION 2 How Does Frozen Water Shape Our World? How Does Frozen Water Shape Our World? Part 1 of 3 #1 Narration Part 1: Where is the world’s ice? Why does frozen water matter? We can’t access it when it’s frozen and far away at the poles or in high mountains, so how does frozen water around the world affect us? And how do we affect frozen water? What is the difference between ice in a drink and ice in Antarctica?

You will learn to: Identify and describe snow, glaciers, and polar ice caps. Identify evidence of glacial erosion. Identify factors that affect the size of glaciers and ice caps. Describe how humans impact glaciers and ice caps. o o o o #2 Narration In this section, you will learn to: Identify and describe snow, glaciers, and polar ice caps, Identify evidence of glacial erosion, Identify factors that affect the size of glaciers and ice caps, and Describe how humans impact glaciers and ice caps. Let’s get started! Let’s get started!

How much fresh water is frozen water? 77% of the world’s fresh water is frozen. Antarctica Greenland #3 Narration Seventy-seven percent of the world’s fresh water is locked up in ice. 99% of that ice is in the ice sheets of Greenland and Antarctica. The ice sheet in Antarctica alone contains almost 95% of the world’s freshwater ice. The ice in Antarctica is several kilometres thick in some places. Fact! These and other ice facts can be found at the website of the United States’ National Snow & Ice Data Center (NSIDC): http://nsidc.org/cryosphere/ quickfacts/icesheets.html The Antarctic and Greenland ice sheets contain more than 99% of the world’s frozen fresh water. Antarctica alone contains 95%.

Is all of Earth’s ice at the poles? Glacial ice is also found in mountains all over the world, even at the equator. #4 Narration Throughout the rest of the world, small pockets of ice can be found high up in mountains, even at the equator. How did this freshwater ice get to these places? Tanzania Switzerland

What happens to water molecules at temperatures below 0ºC? ice Because of the shape of water molecules, they lock into crystal patterns when cooled. #5 Narration When water is cooled, the vibrations of the molecules slow down. Below zero degrees Celsius, water molecules lock into crystal patterns because of their shape. When warm, moist air meets cold air, at ground level we see these solid crystals form as frost on surfaces, or as solid ice on top of liquid water. Within clouds in the atmosphere, the moisture freezes into delicate snowflakes. Fact! How does ice fall from a summer storm as hail? Rising hot winds in a storm are powerful enough to keep the frozen particles from falling from cold air above. The particles bounce in the cloud, growing in size, until they are too big to stay up any longer. In very powerful storms, hail can be as big as baseballs! frost snow

How does snow become glacial ice? Newer layers of snow press down on older, slightly melted snow, forcing air out from between the crystals, creating solid ice. #6 Narration At high altitudes in the mountains and in the Arctic and Antarctic, the constant cold lets snow pile up over many years without melting away. Then, in summer, some snow melts. When winter returns, the slightly melted old snow re-freezes into loose ice. New snow buries the old snow, and as layers build up, the weight presses down. This pressure pushes air out from between the ice crystals to make solid ice. Eventually enough ice accumulates that the weight of it causes it to move slowly downhill. This slow-moving mass of ice is a glacier. A glacier is a large, slow moving mass of snow and ice.

What are mountain glaciers, ice fields, ice caps, and ice sheets? NASA They are all glaciers of different sizes. #7 Narration Glaciers may be referred to by different names depending on their size. Mountain glaciers can be found flowing down mountain peaks. Some reach into valleys, where they are called valley glaciers. An ice field is a mass of ice contained between mountains. Valley glaciers may flow out from it. satellite view of an ice field in British Columbia mountain glaciers flowing into a valley in Italy

How big is an ice cap and how is it different from an ice sheet? An ice cap is less than 50,000 km2 and is not bound by mountains. satellite view of ice cap on Baffin Island #8 Narration Ice caps are large expanses of ice that are not contained by mountains, but are on land. They can be up to 50,000 km square, or about the size of Nova Scotia. Iceland, Norway, and some islands in northern Canada have ice caps. Fact! The term “polar ice cap” is popularly used in the media to describe the collective mass of ice in a polar region. Strictly speaking, an ice cap is a single piece of freshwater ice less than 50,000 km2 and on land, unrestrained by mountains. NASA

How big is an ice sheet? Ice sheets are greater than 50 000 km2. They can cover entire continents. satellite view of the Greenland ice sheet #9 Narration Ice sheets are enormous pieces of glacial ice that can cover entire continents. Ice sheets cover Antarctica and Greenland today. Fourteen thousand years ago, ice sheets covered much of North America and Europe. If an ice sheet is glacial ice on land, what kind of ice is at the North Pole? ice cap on Iceland for comparison

How does salt water freeze? Salt in sea water prevents water molecules from sticking to one another. Sea water freezes at -1.7ºC. #10 Narration There is no land at the North Pole, there is only floating sea ice. Sea ice is frozen salt water from the ocean. While fresh water will freeze at zero degrees Celsius, saltwater must be about two degrees colder to freeze. This is because of the salt dissolved in the water between the water molecules; the water molecules must push the salt out of the way before they can lock onto one another. Saltwater is also denser than freshwater, so when it cools, it sinks before it can freeze. Sea water must be at the freezing point as deep as 150 metres below the surface for sea ice to form. Although salt gets squeezed out of the ice crystals, it remains trapped in tiny holes in the new ice. As a result, sea ice forms much more slowly than ice in freshwater. Cold, salty water is dense, so it sinks before it can freeze. A deep layer of very cold water is needed for sea ice to form.

How does sea ice grow? Sea ice that does not melt in the summer will float on top of new ice formed in the winter. Salt that is trapped between ice particles tunnels down to the bottom of the ice and drains out. Old sea ice is less salty than new sea ice. #11 Narration If sea ice doesn’t melt over the summer, new ice will grow beneath it in the winter. The older ice floats up, and the trapped pockets of very salty water become tiny tubes that drain into the water below. This very salty water is also very dense and very cold so it sinks. This sinking briny water is an important part of ocean currents that we’ll learn more about later in the section. Fact! Ice that has survived for more than two winters is called multi-year ice. Enough salt has drained out of it that it can be melted for drinking water.

What happens to the pack of sea ice in winter? New sea ice freezes from ocean water and the ice pack expands. #12 Narration In the winter, the ice packs grow. Some snow accumulates on top of the ice, but most of the ice comes from the cold ocean water freezing into new sea ice. Fact! A sheet of floating sea ice is an ice floe. An ice berg is a piece of freshwater glacial ice that has broken off and fallen into the ocean. Arctic sea ice, April 26, 2006

What happens to the pack of sea ice in summer? The white ice reflects the sun’s energy back into space. Dark water absorbs heat from the sun. The warm water melts the ice. #13 Narration In the summer, the ice packs melt. Most of the sun’s heat energy is reflected back into space by the white ice, but some is absorbed by the surrounding dark water. This warm water is what melts the ice. Satellites have monitored the northern polar ice pack since 1979. Since that time, the ice pack that survives the summer has shrunk by an average of seven percent per decade. What would happen if there were no sea ice at the North Pole? Discussion Question #13 Ask students to imagine what impacts an ice-free Arctic might have on the movements of humans and animals. What about the movements of water? These questions will be explored further in the activity that follows, and in Section 4. Arctic sea ice, September 25, 2005

Why don’t glaciers form from rain? #14 Summative Question Why don’t glaciers form from rain? Answer Key #14 Precipitation falling as rain usually means that the air temperature is above freezing, so the liquid water will flow away or evaporate when it hits the ground. Rain falling on an existing glacier might freeze if the temperature is already close to freezing, but the warmer water will melt some of the ice. Although freezing rain can happen when rain is super-cooled as it falls through very cold air so it turns to ice when it hits a surface, this requires unusual conditions.

How is ice at the North Pole different from ice at the South Pole? #15 Summative Question How is ice at the North Pole different from ice at the South Pole? Answer Key #15 There is no land at the North Pole, only ocean water. This salt water freezes each winter to become sea ice. Some ice survives through the summer. At the South Pole is the Antarctic continent. Glacial ice has formed here from snow building up over millions of years.

So far you’ve learned to: Identify and describe snow, glaciers, and polar ice caps. Identify evidence of glacial erosion. Identify factors that affect the size of glaciers and ice caps. Describe how humans impact glaciers and ice caps. þ o o o End of Objective Let’s try an activity!