Changing Planet: The Case of the Leaky Gyre
|Students model circulation in ocean gyres, explore characteristics of ocean gyres found around the world, and predict the climate impacts of changes to the circulation in these gyres.||Materials:
Parts I & III:
For each student team:
Parts I, II, and III:
|Adapted by NESTA/Windows to the Universe team members Missy Holzer, Jennifer Bergman, and Roberta Johnson from resources on Windows to the Universe as well as an EarthLab Activity and an IPY activity.|
|7-9, although it may be adapted to higher grade levels using the extensions below.|
| Part I: student exploration, 30 minutes
Part II: plotting currents and interpretation, 45 minutes
Part III: predicting, modeling, and analyzing, concluding, 30 minutes
Total: 105 minutes - approximately 2 class periods
Student Learning Outcomes:
|Hands-on activity, including modeling and data plotting.|
1. View NBC Learn's Changing Planet video called Fresh Water in the Arctic. It will emphasize important connections and show why the topic of this lesson is important.
2. For background information on ocean gyres and climate impacts of ocean circulation explore the links from the Windows to the Universe website.
3. Gather materials and print out the worksheet.
4. As an entry point to the lesson, ask the students to write their descriptions of water found in the North Pole, and in each of the ocean basins, including the temperature of the water along with how it moves. Ask them to share their descriptions.
5. Share the stories of the Nike Shoe Spill or the Great Pacific Garbage Patch to encourage students to begin thinking about how ocean surface water travels from one location to another, leading them to think about global wind belts and atmospheric circulation. Be sure to touch upon the mechanisms for surface circulation which include the Coriolis effect as well as global atmospheric circulation.
6. For Part I, student teams are to explore the circulation of ocean water in gyres following the procedure outlined on the worksheet. Be sure they draw their observations on the worksheet, and answer the questions. Assist students in creating the circular motion of the gyres, where if they blow the sequins across the surface of the tray to the other side, they will begin to see a circular motion form. If the sequins sink, have the students simply move them back to the surface.
7. For Part II, students are to read the descriptions of each of the currents within the gyres, and then hypothesize the general temperature of the particular current. Assist students with their geography skills as necessary. Next, the students are to use the red and blue colored pencils to map the major ocean currents found around the world, and answer questions that tie in the results from Part I.
8. For Part III, show students this animation of circulation in the Beaufort gyre. Ask students what would happen should an ocean gyre (in this case, the Beaufort gyre) slow, and then model this using the procedure on their worksheet (use both colors of the sequins).
9. Close the lesson with a discussion of the Arctic Oscillation, how oceans and the atmosphere are connected in the global climate system.
ASSESSMENT:As an assessment, visit the website for this project as well as the NSDIC website (see links below) and ask students to reflect upon the accuracy of their classroom model in explaining what scientists are seeing in the Arctic Ocean. As a next step, ask students to brainstorm what other aspects of the oceans should be considered while discussing this phenomenon.
LAB SAFETY:Use safe laboratory practices at all times.
CLEAN-UP:Gently pour water from trays through a sieve or colander to catch the sequins. Dry the sequins for future use. Discard the straws, and store the trays for future use.
- To reinforce the above concepts, ask students to plot the global prevailing winds on top of the lines drawn for the ocean gyres.
- The above lesson focuses on surface circulation, and does not address the stratification of ocean water with depth, nor does it address deep ocean circulation. Consider tying in these concepts as an extension utilizing samples of salty, warm, and cold water.
- Another extension may focus on climate interactions that include the cryosphere. Consider showing the NASA video introducing the cryosphere. It is available for download or streaming at http://www.nasa.gov/vision/earth/environment/cryosphere.html
A gyre is another name for a swirling vortex. Ocean gyres are large swirling bodies of water that are often on the scale of a whole ocean basin or 1000's of kilometers across (hundreds to thousands of miles across). Ocean gyres dominate the central regions of open ocean and represent the long-term average pattern of ocean surface currents. Ocean gyres in the Northern hemisphere rotate clockwise and gyres in the Southern hemisphere rotate counter-clockwise due to the Coriolis Effect. The major gyres of the ocean include: North Atlantic, South Atlantic, North Pacific, South Pacific and Indian Ocean gyres. Of course, many other smaller gyres exist in the ocean too.
Gyres can actually capture and hold water or suspended material. For instance, one of the largest ocean gyres, the North Pacific gyre, is home to an area called the Great Pacific Garbage Patch. This area contains a relatively high concentration of marine litter. It is estimated to cover an area roughly twice the size of Texas and contain approximately 3 million tons of plastic litter, though much of this plastic is broken up into pieces too small to see with the naked eye. Although the precise origin of the litter is not known, scientists believe that the Garbage Patch was created gradually as the Northern Pacific Gyre captured foreign material and that material was transported to the center of the gyre by centripetal forces and wind-driven surface currents, creating an area with concentrated litter.
Another gyre, the Beaufort Gyre found in the Arctic Ocean, actually holds fresh water. The Beaufort Gyre is a huge vortex of water being driven by strong wind that force currents in a clockwise direction. It is full of relatively fresh water as Siberian and Canadian rivers drain into it. Scientists have been keeping a close eye on the Beaufort gyre. When winds slack off and the gyre weakens, fresh water leaks out of the gyre and into the North Atlantic Ocean, where many scientists think it will have a major impact on global climate. Of course, water can go both ways, and water does come into the Arctic Ocean from the North Atlantic. This water is warmer and relatively salty. Because of its increased salinity, it is denser and sinks below Arctic waters. This seems to be the 'normal' long-term course of water moving into and out the Arctic region.
All the while water is coming into the Arctic system, being held in the Beaufort Gyre, and exiting into the North Atlantic, ice is being made at the very beginning of this process. Frigid cold air coming from the Alaskan interior freezes the water entering the Arctic just after it passes through the Bering Strait. The cold air freezes the seawater forming sea ice, and then the wind continues to push this sea ice farther into the Arctic Ocean basin, making room for more sea ice to be made. This process is often referred to as the Arctic 'sea ice factory'. Now when sea ice is created, salt is released into the remaining non-frozen water. This surface water becomes very salty and very dense and so it sinks forming a layer known as the Halocline. The Arctic waters are thus stratified with the top layer being relatively fresh, cold water, a middle layer (the Halocline) being salty, cold water, and a third and deeper layer of warm, salty water that has entered from the Atlantic. This layering of Arctic waters is essential to the survival of sea ice in the region. Without the Halocline layer acting as a buffer, warm, salty water from the Atlantic would enter the Arctic and would begin to melt existing sea ice.
In the last decade, scientists have become increasingly aware of the Arctic region's impact on global climate. Melting sea ice due to increasing global temperatures is a grave concern. Some fresh water flowing out of the Beaufort Gyre and into the North Atlantic is expected as a result of natural processes. However, with the increase of fresh water coming from melting sea ice being added to this huge vortex, more and more fresh water is spilling out into the Atlantic, and many scientists think this could be a big problem and cause major climate shifts in North America and Western Europe. Normally, these regions have mild climates because a system of ocean currents called the Global Ocean Conveyor carries heat as well as matter around the globe, and as it passes North America and Western Europe it warms those regions by releasing heat that it picked up in the tropics. If, however, there is a larger-than-normal layer of fresh water on top of the North Atlantic Ocean, scientists believe that it might act as a barrier (just as it does in the Arctic Ocean), preventing the warmer water from releasing its heat (and therefore causing cooler temperatures in North America and Europe).
There has been a considerable focus on Arctic research in the last decade. Findings will be integral in our understanding of Arctic system dynamics as well as global ocean, atmosphere and climate projections. Now it should be noted that the Arctic region poses a lot of challenges to researchers—high winds, very low temperatures, and thick sea ice all make studying this part of the world difficult. So in exploring Arctic currents, scientists have had to be creative. From autonomous underwater vehicles that have newly developed navigation systems tailor-made for Arctic sea exploration to an experimental device designed to monitor the flow of fresh water from the Arctic to the North Atlantic, over the past decade scientists have had to adapt or invent new techniques or instruments to study the Arctic Ocean. Now a new tool -- Ice-Tethered Profilers (ITP's)—promise to give researchers a whole new way to measure temperature, salinity, and other water properties as they travel up and down a wire rope hanging down to 800 meters (~0.5 miles) into the Arctic Ocean. They can also measure surface currents as they drift through the Arctic. Although the floats won't replace in-person measurements by scientists, they will allow year-round research in many areas that are too remote or dangerous for people (they are indeed polar bear proof!). In fact, ITP's make their measurements and send the data to computers via satellite so scientists can access the data from anywhere in the world. ITP's are just one more step forward in research that will hopefully shed more light on the Arctic Ocean, its currents, and its contributing role in regional and global climate.
Surface ocean currents, ocean gyres, deep ocean circulation and the atmosphere are all parts of the complex Earth system. Understanding ocean-atmosphere interactions is a key part of understanding global climate change as well as how different things like water, energy, nutrients or pollutants move through (or get trapped within!) different parts of the Earth system.
RELATED SECTIONS OF THE WINDOWS TO THE UNIVERSE WEBSITE:
NSDIC (this page and others at this link)