Alison Glacier
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What is the effect of warming ocean water on Alison Glacier?1 OVERVIEW In this activity students will work with data collected in non-­‐summer months from two fjords in eastern Greenland, Sermilik Fjord (2011-­‐2012) and Kangerdlugssuaq Fjord (2009-­‐2010), mapping warming ocean water as it flows into the fjords where it meets two well-­‐known Greenland glaciers – Helheim and Kangerdlugssuaq. Students will consider how the warm ocean water might impact the glacier ice that is flowing from the Greenland ice sheet into the fjords. Finally they will consider how this might compare to Alison glacier in northwest Greenland. SUPPLIES: Colored pencils or crayons to complete the graph – suggested colors include deep blue, aqua blue, grey, green, yellow, orange and red. CONCEPTS •
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Glaciers in both western and eastern Greenland are losing ice, melting and retreating. The Atlantic ocean water is warmer than the Arctic ocean surface water and the meltwater from Greenland glacier’s entering the fjords. This warmer water is having an effect on the glaciers. LEARNING OBJECTIVES •
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Students will be introduced to the layering of ocean water by density. Students will graph & color temperature data collected along the fjord to create a data based visualization of the mix of water temperature in a Greenland fjord. Students will examine data collected in two Greenland fjords to determine how Atlantic ocean water flow effects water temperature in the fjord. 1
This activity is based on data from: “Externally forced fluctuations in ocean temperature at Geenland glaciers in non-­‐summer months”. Jackson, A., Straneo, F., Sutherland D., Nature Geosciences 7, 503-­‐508, 2014. Alison Glacier
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What is the effect of warming ocean water on Alison Glacier? BACKGROUND: An increase in the amount of melting of tidewater glaciers around Greenland has been connected to warming ocean water being forced into the fjords and pushed up next to the glaciers. The water around Greenland is a combination of cold Arctic ocean water measuring from -­‐1°C to 1°C, glacial meltwater where these two waters meet measuring from 2-­‐ 3°C, and Atlantic Ocean water which has been measured at up to 4°C as it moves into the fjords. Atlantic Water is pushing up into the fjords and flowing right up to the glaciers where the 4°C temperature would increase glacial melt. ACTIVITY: UNDERSTANDING WATER TEMPERATURE IN GREENLAND’S FJORDS: You will create a map of water temperature for a Greenland fjord. Different densities in water cause it to layer, with denser layers on the bottom and less dense layers above. Salt is the major cause of density differences in the ocean. Saltier layers of the ocean water are denser and therefore flow underneath less salty or fresher areas. In Greenland’s fjords the salty water comes from the oceans flowing under the fresh meltwater water flowing in from the front of the glacier. In general cold water is denser than warm water so if the water in the fjords were all the same salinity we would expect to see cold glacial meltwater flowing under the warmer Atlantic ocean water. However, the saltiness of the ocean water makes it flow under the colder meltwater. MAPPING WATER TEMPERATURE IN GREENLAND’S FJORDS: The chart you are working with contains temperature measurements collected straight down from surface of the water to the fjord bottom. Measurements are collected in several places along the fjord using an instrument called a CTD that is lowered on a rope straight down in the water. CTD stands for Conductivity (salinity), Temperature and Depth. The measurements are then put together to build a picture of the water temperature for the whole area. You will be making that picture. 1) Start with the graph paper. We have placed a ‘o’ in cells to mark elevation at the bottom of the fjord. Draw a line connecting the ‘o’s and shade below the line with grey to mark off the bottom of the fjord. There will be no water readings below this mark. 2) Using the temperature chart below, enter the numbers onto the graph paper for each km reading. The readings at the ‘0’ km have been entered onto the graph for you. You will enter the temperatures for each of the other kms 10-­‐90. 3) Once the numbers are entered you will use the temperature color key to complete the temperature chart. Select the color pencils or crayons that match the temperatures (-­‐1 is deep blue etc.) and connect the numbers on the graph with the same colors filling in the full graph square. Once you have completed the squares with numbers, color in the sections between the numbers until there is a temperature change. Note: In some places the color will not continue all the way across the graph so just end the color where you no longer see the number that matches it. The graph you make will look like a color painting of temperatures. Alison Glacier
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WATER TEMPERATURE (°C) MEASURED BY KM (X axis) FROM THE MOUTH OF THE FJORD DEPTH (Y axis) 0 km 10 km 20 km 0 -­‐1 -­‐1 -­‐1 100 175 0 0 0 200 2 2 3 225 3 3 3.5 300 4 375 3.5 3.5 400 4 4 425 Color Key for Graph Water Temp. °C Color -­‐1 Deep Blue 0 Aqua Blue 1 Grey 2 Green 3 Yellow 3.5 Orange 4 Red 30 km 40 km 50 km 60 km 70 km 80 km 90 km -­‐1 0 3 3.5 4 -­‐1 0 3 3.5 4 -­‐1 0 3 3.5 4 -­‐1 0 2 3 3.5 4 -­‐1 0 1 2 3 3.5 4 -­‐1 -­‐1 0 0 1 2 2 3 3 3.5 3.5 4 DISCUSSION FOR AFTER YOUR COMPLETE THE TEMPERATURE GRAPH 1) We have marked the glacier on the right side of the chart so you can see how the water is right up against the frozen glacier. How much of the water that touches the front of the glacier is zero degrees or colder? 2) Now consider how much colder the water is at the surface than deep at the bottom of the fjord. What do you think the effect of this would be on glacial ice? 3) We have been looking at data from two glaciers in southeastern Greenland but Atlantic ocean water circulates around the bottom of Greenland and is pulled up along the western coast as well. Do you think the warmer water from the Atlantic Ocean could affect glaciers in other parts of Greenland? Alison Glacier
Depth meters Surface 100 200 300 400 500 600 700 800 Fjord
Mouth Southeast Fjord Profile -­‐1 0 2 3 3.5 4 0 o o o o o o o o o 0
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Distance from fjord mouth kilometers 90
Glacier front 0 4