The Labrador Current

Transcription

1 The Labrador Current Lesson Overview: The main points covered in this lesson are the characteristics of the Labrador Current and: The importance to fish and other marine species Its climate influences on coastal areas Influences of climate variation and change in the Arctic Significance to Newfoundland and Labrador Grade Level: Grades 9-12 Time Required: Two classes maximum Curriculum Connection (Province and course): Atlantic Provinces Education Foundation curriculum for Social Studies People, Place and Environment General Curriculum Outcome: Students will be expected to demonstrate an understanding of the interactions among people, places and the environment Grades 10-12, Newfoundland and Labrador, Canadian Geography 1202 GCO 2.1.1: Basic patterns of land and water forms, which comprise the landscape of Canada. GCO 2.1.2: Elements of weather and climate and how they account for diverse climate patterns in Canada. GCO 2.1.3: Natural interrelationships in selected Canadian ecosystems and how they are typical of a northern environment. GCO 2.1.5: Activities and issues related to how Canadians use resources in the ocean environment. GCO: 2.2.1: Retrieving information from a variety of information-access tools, such as maps, globes, databases, newspapers, periodicals, videotapes and graphics. GCO 2.2.3: Convergent and divergent thinking to develop spatial and temporal patterns in geographic phenomena. GCO 2.2.6: Organizing information according to an acceptable format. Links to Canadian National Geography Standards: Essential Element #1: The World in Spatial Terms Study of the Labrador Current involves linkage to its spatial position, involving usage of maps/globe/ atlas. Conic projections are appropriate here. Location of coastal communities with respect to the current, and allocation of marine resources can also be discussed. Canadian Council for Geographic Education ( 1

2 Essential Element #2: Places and Regions The Labrador Current is the dominant physical factor shaping coastal Labrador and northeastern Newfoundland. Its interaction with the Gulf Stream over the Grand Banks has provided the basis for the fishery that sustained much of Newfoundland and impacted all societies around the North Atlantic Ocean, in a mutually interdependent manner, for more than 500 years. The Labrador Current shapes the social and cultural identity of all the communities from Iqaliut to Fortune. Changes in the fisheries associated with the Current, due both to human activity and climate variations, have had, and continue to have, significant socioeconomic impacts. Study of the Labrador Current can involve analyses at local (community), regional (coastal Newfoundland & Labrador), national and Northern Hemispheric scales. Essential Element #3: Physical Systems The Labrador Current is a key component of the physical environment of eastern Canada. It is linked to the global ocean current system, which in turn is linked to atmospheric systems and climate. The Labrador Sea and Grand Banks are important and distinct biogeographical regions. The North Atlantic and Arctic Oscillations, analogous to El Niño in the Northern Hemisphere, influence it. Essential Element #4: Human Systems The Labrador Current influences the fishery-dependent communities of Newfoundland and Labrador. Its importance in the fishery trade throughout the northern North Atlantic is indicative of the concept of Global Economic Interdependence. Essential Element #5: Environment and Society The effect of climate change on the Labrador Current creates changes in the climate of the coastal communities and in marine habitats. Thus, it serves as an example of an effect on the human environment resulting from a change in the physical environment. Relationships can be drawn to sustainability concepts and resource management. Essential Element #6: Uses of Geography Study of the Labrador Current represents an example of the value of a regional analysis in the context of the North Atlantic region as a whole. Geographic Skills: Asking Geographic Questions Study of the Labrador Current involves asking geographic questions on a number of levels, from the purely descriptive and locational, through to questions of marine processes, effects of human activity (e.g. fisheries), the influence of natural and human-induced climate change and the response of the system, to questions concerning human and community response to and interaction with the natural environment. Answering the questions will require acquisition, Canadian Council for Geographic Education ( 2

3 organization and assessment of geographical information, including that presented in this lesson as well as information obtained from other sources. Additional Resources, Materials and Equipment Required: Pictures of icebergs Atlases/maps normally used in class. Additional resources could include: Detailed map of Labrador; Topographic map of NL; Bathymetric chart Main Objective: Understand the physical characteristics of the Labrador Current Understand the interactions between the current and other elements of the physical environment Understand the socio-economic and cultural significance of the Labrador Current Learning Outcomes: In addition to fulfilling the objectives above, students can apply the same analytical techniques to the understanding of the characteristics, impact, influences and significance of any other current worldwide; Understanding the interplay between biophysical and socio-economic geographical concepts; Understanding that the concepts presented in Oceans for Life can be applied to any marine environment. Canadian Council for Geographic Education ( 3

4 The Lesson: Teacher Activity In common with all ocean basins, the water of the northwestern North Atlantic circulates vigorously. The major influences driving surface currents include wind stresses and pressure gradients on the sea surface. Student Activity Locate on map: North Atlantic Ocean In the North Atlantic, the Gulf Stream is the best-defined and strongest current. Introduction As the Gulf Stream proceeds across the North Atlantic, it branches into several currents. A main branch, the Norwegian Current, flows northwards along the western coasts of Ireland, Scotland and Norway. As the Norwegian Current flows northward, it is gradually diverted to the west through the Barents Sea, and along the Kalaallit Nunaat (Greenland) coast. This water circulates along the eastern shore of Davis Strait and Baffin Bay, extending to approximately 75 N (an area referred to as North Water ). Augmented by cold, fresh water from glaciers in Kalaallit Nunaat, the flow returns southward along the Labrador and eastern Newfoundland coast as the Labrador Current. It continues southward along the Avalon Peninsula to the Grand Banks, where it interacts with the Gulf Stream. Locate on map: Route of Gulf Stream; offshore of Florida, North Carolina; south of Sable island; south of Grand Banks Calculate how long would a water molecule take to travel from Miami to the Grand Banks in the Gulf Stream? Locate on map: Ireland, Scotland, Norway, Barents Sea, Kalaallit Nunaat, Davis Strait, Baffin Bay Locate on map: Route of Labrador Current from Cape Chidley south to Grand Banks Canadian Council for Geographic Education ( 4

5 The Labrador Current is not the strongest, largest or fastest current in the world. It transports approximately 6 million cubic metres of water each second southward, approximately 10% of the volume of the Labrador Current. The fastest-flowing belt normally is between 10 and 20 km wide. Part of the reason for the low velocity is the atmospheric low-pressure system situated over Baffin Bay and to the south of Kalaallit Nunaat ( Icelandic Low ). As the Labrador Current is flowing south, away from the lowpressure system, it is working against the atmospheric pressure gradient. Calculate how long it takes a water molecule to travel from Nain to Cape St. Francis along the Labrador Current. Speculate how variations from year to year could affect the Labrador Current. The Low Pressure system is intensified in some years and weakened in others. This cyclic process is referred to as the North Atlantic Oscillation (analogous to El Niño/La Niña cycle). A positive NAO phase (strong pressure gradient) results in stronger northeasterly winds blowing onto the shore, and a weakening of the Labrador Current. We have been in a positive phase of the NAO cycle since the late 1980s. Lesson Development Surface temperatures increase from north to south along the current. In August, the surface temperatures off Nain are typically 5-6ºC, increasing to C off Cape Race. ( Cold water from a faucet typically is 15-20ºC). The amount of salt in ocean water is controlled by temperature. Cold water can hold less salt than warm water (as cold coffee holds less sugar than warm coffee). Typically, the Labrador Current has a salt content ( salinity ) of 32 parts per thousand (i.e. 32 g of salt per kg of water). Biological productivity is enhanced in zones where cold currents (e.g. Labrador) meet warm currents (e.g. Gulf Stream, with a typical August temperature of 17 C on the Grand Banks). This meeting of the waters triggers large amounts of sinking and upwelling. This results in the distribution of nutrients throughout the water column over the shallow Banks and Flemish Cap, and is the primary factor that made these areas among the richest fishing grounds in the world. Sea ice reaches maximum extent and thickness in early February, more than 1000 km seaward of Nain and Hebron. During the spring, the ice in the north retreats towards the land, but the ice extends further southward at the same time. In late March, sea ice extends more than 800 km offshore of Hopedale and Makkovik. Approximately 2000 icebergs pass Cape Chidley each year. The number has been increasing slowly due to the gradual melting of glaciers on Baffin Island and Kalaallit Nunaat. Canadian Ongoing Council climate for Geographic change is melting Education the glaciers ( of Kalaallit Canadian Nunaat. Meteorological This feeds more and Oceanographic icebergs and cold Society water into the Labrador Current, causing it to get colder. Thus, one of the effects of global warming is to make the Labrador Current colder and less saline, and to produce more Add salt to 1 litre of water. Continue to add salt until no more salt dissolves. Compare the mass of salt that can be added to cold water with the amount that will dissolve in warm water. Locate on map: Cape Chidley, Hebron, Nain, Hopedale Makkovik If the sea ice were to leave northern Labrador earlier in the summer, what would be the effect on the coastline? What changes would people in the area notice? How would this change their lives? 5

6 Nunaat. Look at photographs of icebergs. Lesson Development Ongoing climate change is melting the glaciers of Kalaallit Nunaat. This feeds more icebergs and cold water into the Labrador Current, causing it to get colder. Thus, one of the effects of global warming is to make the Labrador Current colder and less saline, and to produce more icebergs and temporary sea ice along the coastlines of Labrador and northeastern Newfoundland. Prevailing winds along the Labrador and Newfoundland coastline are westerly (from the southwest). As the winds in Labrador are blowing from land to water, the result is to bring dry air from the interior of North America to the Labrador coastline. Thus, the influence of the Labrador Current on coastal climate in Labrador is limited to the fringe of the shoreline. The effect of the cool Labrador Current adjacent to the coastline results in cooling of exposed coastal areas. There are local differences in continentality between exposed coastal sites (e.g. Battle Harbour) and more sheltered sites (e.g. Port Hope Simpson). The effect of the North Atlantic Oscillation (NAO) is to intensify the seasonal differences during positive phases. This means that northeasterly winds (blowing from water to land) are stronger, leading to increases in wave height and coastal storms. Climate Change, changing water temperatures, will influence these fish and mammal populations primarily by changing the distribution of the species that they need for food. Seals will be less affected than will whales and the walrus. For what can icebergs be used? Should icebergs be used for economic purposes, or should they be left for tourists to look at? How long does it take to melt an ice cube in tap water? Study a map of NL. Explain how the prevailing winds, Torngat Mountains and Labrador Current combine to influence coastal Labrador s climate? On the island of Newfoundland, there are no large mountains to block the prevailing southwesterly winds; but northeasterly winds are more common. Does this allow the Labrador Current to influence coastal Newfoundland more than it influences coastal Labrador? What impacts will changes in fish species have on the people? What options are available for fishing communities, fish harvesters, fishing companies, and government managers of these fisheries? Which species will benefit from climate change? Which will be adversely affected? Look at water depths on a bathymetric chart What could be the effects on particular whale species or on walrus? Conclusion Summarize key points. Initiate discussion of the importance of marine resources to the communities, and to the region (and wider areas) Initiate discussion as to the relative importance of climate and human activities on the fisheries of the Labrador Current Discussion of any of the above points; or of the points listed in the Conclusions Canadian Council for Geographic Education ( 6

7 Lesson Extension: Any of the concepts presented here can be discussed in further detail, emphasizing local circumstances or going into greater depth. Research the history of Battle Harbour; Black Tickle; Mary s Harbour; St. Lewis; or other Labrador coastal community where transhumance occurred Can you think of any other types of communities where transhumance was a feature of life in the historical past? The hemispheric ramifications can be explored further (e.g. What is the impact of reductions in salt fish availability from the Labrador Current in Jamaica or the Dominican Republic? What role did fluctuations in the strength of the Current play in the significance of Newfoundland and Atlantic Canada in the North Atlantic region?) Another current elsewhere in the world could be analyzed in a similar or compare-and-contrast fashion. This could include student posters, displays or essays. Connections can be made to historical studies. Assessment of Student Learning: Presentation of posters, displays or essays; information maps in response to discussion points introduced above. Canadian Council for Geographic Education ( 7

8 Labrador Current Teacher Information The Labrador Current carries million cubic metres of water each second across the Atlantic Ocean from west to east. (A typical bathtub holds about ¼ of a cubic metre of water). The Gulf Stream typically has widths of km, and a peak velocity of 15 km/h. The Labrador Current typically moves at 0.4 km/h at Nain, 1 km/h at the Strait of Belle Isle, and 2-3 km/h at Cape Race. It is among the slowest currents in the ocean. (Lobsters can swim faster than the Labrador Current. 1 km/h = 1000 m/h = 16.7 m/minute; about 30 seconds to walk the width of a typical classroom). By July, the ice has dissipated off Cape Chidley sufficiently to allow grain shipments from Churchill (Manitoba). The ice in the Labrador Sea and Hudson Strait is a greater limiting factor in port operations at Churchill than is ice in Hudson Bay. Ice closes navigation around Cape Chidley by mid- September in most years. An iceberg 40 m high above the water line and 100 m long (volume 2 million m 3, mass 10 million tonnes, equal to approx. 9 million automobiles) will melt completely in 15 days in 4 C water. These large icebergs represent about 20% of the iceberg population off Cape Chidley, about 10% off Makkovik, about 5% off the Strait of Belle Isle and less than one in 2000 of the total number passing Twillingate. The average growler will last less than five days in 4 C water. Less than 10% of the icebergs passing Cape Chidley survive to reach the Strait of Belle Isle, and less than one in 1000 reach Bonavista. Until the 1960s, many people spent the summers on open shoreline sites, to take advantage of the fish resources, and then moved inland during the winter, to gain shelter and access to better supplies of wood and fresh water. This is referred to as transhumance Any species must be able to survive in cold, relatively low salinity water. Atlantic herring, for example, can survive as far north as Cape Chidley, but tend to retreat southward during cold years (e.g ). As the Labrador Current is expected to get colder over time with ongoing glacier melting in Kalaallit Nunaat, the herring populations will be restricted. Capelin requires water temperatures of 5-8ºC for spawning. Labrador Sea- Grand Banks capelin forms a single biological population, but do not mingle with stocks along the western coast of Kalaallit Nunaat. Colder water temperatures in the future could also restrict capelin populations. The inshore and near shore cod fisheries exploiting the Labrador Current ( northern cod ) populations harvested mature fish that moved south, following the current, as they matured. Cod born in coastal waters migrated to the northern parts of the Labrador Sea and did not return until they were mature (8-12 years). Fishing of only mature individuals allowed Canadian Council for Geographic Education ( 8

9 the stock to be maintained. However, the shift to offshore trawling and dragging allowed fish of all ages to be caught throughout the year, resulting in the collapse of the stock. Haddock, pollock, witch flounder, yellowtail flounder and tuna are found only in the more southerly parts of the Labrador Current. With a change to colder water temperatures, these species will retreat southward. Plaice and halibut are found in waters of fathoms ( m) depth south of Nain and Cartwright, respectively. Turbot is found throughout the area. These species inhabit waters that will remain at approximately the same temperature, and thus are not as susceptible to the effects of climate change. The harp seal population off Newfoundland and Labrador is estimated at 2 million. Other species of seals account for about 600,000 individuals. Walrus live as far south as Nain. A mature male may be as much as 3 m long, weigh 900 kg and may live up to 25 years. A mature male will eat up to 3000 clams per day. Whale species present include the Northern Bottlenose, Sperm, Beluga, Orca, Narwhal, Pilot, Minke, Sei, Blue and Humpback. Canadian Council for Geographic Education ( 9