Download Ocean Salt and Circulation

 Ocean Salt and Circulation Overview Have you ever wondered why oceans are salty? Do you know what affects how much salt is in the water? On average the salinity of the world’s oceans is about 35 parts per thousand (ppt). However, the salinity of the water can change due to numerous environmental and physical factors. These factors include rainfall, heat, weather patterns, and global ocean circulation processes. The salinity of the ocean also plays an important role in the Earth’s climate and weather patterns. Differences in water temperature and salinity drive what is known as the ocean conveyor, a giant circulation system that connects all the world’s oceans. This conveyor is formally known as the Thermohaline circulation. "Thermohaline Circulation 2" by Robert Simmon, NASA. Minor modifications by Robert A. Rohde also released to the public domain -­‐ NASA Earth Observatory. Licensed under Public domain via Wikimedia Commons -­‐ http://commons.wikimedia.org/wiki/File:Thermohaline_Circulation_2.png#mediaviewer/File:Thermohaline_Circulation_2.png In this lesson, students will gain an understanding of the dynamic environment of oceans that causes changing conditions, using differences in salinity and temperature as key examples. NGSS* ESS2.C: The Roles of Water in Earth's Surface Processes ESS2.D: Weather and Climate Learning Goals •
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Ocean water is salty due to dissolved minerals, evaporation, and hydrothermal vents. Several processes change salinity across the oceans. Salinity of the ocean can be calculated in different locations on Earth. Salinity of the ocean is related to climate and weather. www.oceanclassrooms.com ©2014 Ocean Classrooms Focus Questions •
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Why are ocean salinities different and how do they change over time? Why are salinities not stable across the world’s oceans? How do environmental and climatic processes affect the salinity of the ocean? Key Terms Salinity Thermohaline circulation • Concentration (ppt) • Density •
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Variation Climate Weather Hydrothermal vents •
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Observation Data collection, analysis, and interpretation Calculations (Average; Standard Deviation) Background Knowledge The ocean is salty due to dissolved minerals, mainly sodium and chloride, which make up approximately 90% of the dissolved mineral content of the oceans. Other minerals include magnesium, sulfur, and potassium. There are several reasons why the oceans became salty. First, rain falling over land erodes rock and dissolves its contents, which are then transported to the ocean via rivers and streams. The concentration of salt increased over time (millions of years). Fresh water evaporates from ocean surfaces due to heat from the sun’s rays, and solids such as salt are left behind. Second, dissolved minerals are introduced from the sea floor at hydrothermal vents where the heat from the Earth’s crust helps dissolve the sea floor. This more recent discovery of the last century adds to our understanding of ocean salinity. Salinity plays a role in the big overturning of the world’s oceans from top to bottom. This circulation is called thermohaline circulation and is driven by density differences that depend on temperature and salinity. When the surface of ocean water at the poles gets very cold, it forms sea ice and the salt that is left behind increases the salinity of the surrounding seawater. As the water gets saltier, its density increases. Water with a higher density sinks and less dense water replaces it. Eventually, the less salty water becomes saltier at the surface and sinks again. This continuous process creates a sort of conveyor belt that drives the deep mixing of ocean water. The circulation of the world’s oceans affects the climate of the Earth. A good example is the effect of the thermohaline circulation on the climate of the United Kingdom and Ireland. As warm, less-­‐dense water cruises past these islands to return to the North Atlantic, it creates a temperate climate in that region that is warmer than the latitude of the land masses would suggest. Although the global conveyor belt is a strong one, a sequence of climate change events can easily interrupt it. If there is increased rainfall in the North Atlantic, more glacial melting, and an influx of warm water at the surface of oceans due to global warming, the conveyor belt could slow or stop altogether. Scientists have predicted that changes such as these might affect the climate in Europe and elsewhere on the planet. www.oceanclassrooms.com ©2014 Ocean Classrooms 2 Materials Computer access with Internet connection Advance Preparation Visit the Blue Eyes Network data portal at www.oceanclassrooms.com to familiarize yourself with the data manipulation. Identify a site in the Pacific that is temperate (i.e. California) and a site near the Atlantic that is tropical (i.e. Caribbean) that have temperature and salinity data to support this lesson. Identify a site in the Indo-­‐Pacific where salinities have higher fluctuations due to monsoonal rains. Potential sites include the Philippines, Indonesia, or Papua New Guinea. Check to see that the temperature and salinity data for this site are robust. Potential Misconceptions •
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Ocean salinity is the same everywhere. Oceans are static and the properties of the water are stable and universal. Eliciting Prior Knowledge •
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Ask students to name the five oceans on Earth: Arctic, Atlantic, Indian, Pacific, and Southern. Using a globe or world map, ask students to locate the oceans and compare their locations in terms of general temperature differences (Which are warmer? Which are colder? Are parts of some oceans frozen?). Based on their ideas about temperature, ask students to label each ocean “temperate” or “tropical”. With students, come up with one thing that they can all agree upon that is a characteristic of all ocean water (they are salty). Process and Procedures 1. Mix one gallon of fresh water with a few drops of green food coloring. Mix a second gallon of fresh water with 1 cup of kosher salt and a few drops of blue food coloring. Let both mixtures sit overnight so that the salt is completely dissolved in the blue water. 2. Without telling students the difference between the two waters, set up a demonstration that shows the layering of the two waters due to their differences in density. This can be done by filling a smaller jar half full with the fresh water and syphoning the salt water through a long tube into the bottom of the jar. The salt (blue) water will layer on the bottom. Ask students to predict what will happen if you reverse the demonstration. Then, fill a small jar half full with the salt water and syphon the fresh water into it. The fresh water (green) will layer on the top of the salt water. www.oceanclassrooms.com ©2014 Ocean Classrooms 3 3. Ask students to determine what made the blue water layer under the green water. When they begin to talk about how one type of water seems “heavier” than the other water, introduce the concept of density. What would make the blue water contain more matter per unit volume than the green water? Probe until students recognize that, in the context of oceans, the green water contains no salt while the blue water contains salt. 4. Discuss the mechanisms by which ocean water becomes salty. Introduce the term salinity and its units (parts per thousand). Ask students to discuss in small groups whether they think all ocean water would have the same salinity given the way in which salinity occurs. What factors affect salinity? [Hint: The availability of different salts in surrounding rocks or in ocean vents affects what minerals and how much of each end up in ocean water. Evaporation rates that concentrate salts can affect salinity. The temperature of the air and water that affect evaporation also is a factor.] 5. Direct students to the website (if able to access individually) or take them to the website utilizing an in-­‐class projector or large monitor. Access the data portal for the temperate ocean site you identified in the Advance Preparation. Ask students what data might be important to collect from those that are available. [Hint: Based on the discussion from step 4, get students to focus on ocean temperature and salinity.] 6. With students, design a table in which to collect data similar to the examples below. Leave room to add other ocean locations in rows and make columns for temperature and salinity data over a period of time. [Hint: Decide what time period is useful for data collection: several years, 12 months, or 30 days?] Temperate Ocean Tropical Ocean Indo-­‐Pacific Ocean Ocean Data: Temperature and Salinity Temperature (for previous Mean (M); Salinity (for previous 12 12 months) in degrees C Standard months) in ppt Deviation (s) M: s: M: s: M: s: Mean (M); Standard Deviation (s) M: s: M: s: M: s: 7. Calculate the mean for the temperate ocean’s temperature and salinity over the past 12 months. Show students how to calculate the standard deviation and record that on the table. 8. Direct students to complete their tables by exploring the data from two other ocean regions: a tropical ocean location and an Indo-­‐Pacific ocean location. 9. Discuss differences in the mean salinities and temperatures between regions. Solicit ideas from students about why some places in the ocean are warmer/colder or have increased/decreased salinity. www.oceanclassrooms.com ©2014 Ocean Classrooms 4 10. Introduce students to Thermohaline circulation. Distribute a handout that maps the path of water that flows due to the variation of temperatures and salinity in ocean waters. Discuss the affect that the conveyor belt has on climate around the globe, using the United Kingdom and Ireland as an example. 11. Read and discuss the National Geographic article “Signs from Earth: Now What?” (http://environment.nationalgeographic.com/environment/global-­‐warming/time-­‐signs/#page=7) about how global climate change might affect the temperature and salinity of the world’s oceans and, as a result, affect the conveyor belt of ocean water circulation. Formative assessment strategies •
How does temperature affect salinity? Ask students to make predictions about the amount of salt that can be completely dissolved in cold water versus warm water. Conduct an experiment to test their predictions. Summative assessment Have students use their handout of the ocean’s conveyor belt to highlight the sites they have studied in this lesson. Once students have located the sites, evaluate their understanding by asking students to discuss the following: • Describe the processes that have contributed to differences in salinities among the three sites. • Explain why the salinity of ocean water fluctuates more on the surface than at deeper depths. • Predict how the temperatures of the ocean and the continents would change if the circulation of the ocean’s waters was disrupted. *Next Generation Science Standards addressed Performance Expectation MS-­‐ESS2-­‐4. Develop a model to describe the cycling of water through Earth’s systems driven by energy from the sun and the force of gravity. MS-­‐ESS2-­‐5. Collect data to provide evidence for how the motions and complex interactions of air masses results in changes in weather conditions. MS-­‐ESS2-­‐6. Develop and use a model to describe how unequal heating and rotation of the Earth cause patterns of atmospheric and oceanic circulation that determine regional climates. Disciplinary Core Idea(s) MS-­‐ESS2 Earth’s Systems ESS2.C: The Roles of Water in Earth’s Surface Processes •
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Water continually cycles among land, ocean, and atmosphere via transpiration, evaporation, condensation and crystallization, and precipitation, as well as downhill flows on land. (MS-­‐ESS2-­‐4) The complex patterns of the changes and the movement of water in the atmosphere, determined by winds, landforms, and ocean temperatures and currents, are major determinants of local weather patterns. (MS-­‐ ESS2-­‐5) Global movements of water and its changes in form are propelled by sunlight and gravity. (MS-­‐ESS2-­‐4) Variations in density due to variations in temperature and salinity drive a global pattern of interconnected ocean currents. (MS-­‐ESS2-­‐6) Science and Engineering Practices •
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Developing and Using Models Planning and Carrying Out Investigations Analyzing and Interpreting Data Constructing Explanations and Designing Crosscutting Concept(s) •
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Patterns Cause and Effect Systems and System Models Energy and Matter Stability and Change www.oceanclassrooms.com ©2014 Ocean Classrooms 5 Solutions ESS2.D: Weather and Climate •
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Weather and climate are influenced by interactions involving sunlight, the ocean, the atmosphere, ice, landforms, and living things. These interactions vary with latitude, altitude, and local and regional geography, all of which can affect oceanic and atmospheric flow patterns. (MS-­‐ESS2-­‐6) The ocean exerts a major influence on weather and climate by absorbing energy from the sun, releasing it over time, and globally redistributing it through ocean currents. (MS-­‐ESS2-­‐6) NGSS Lead States. 2013. Next Generation Science Standards: For States, By States. Washington, DC: The National Academies Press. Teaching Notes www.oceanclassrooms.com ©2014 Ocean Classrooms 6 Ocean Salt and Circulation: Student Handout NASA Earth Observatory [Public Domain]
Notes www.oceanclassrooms.com ©2014 Ocean Classrooms 7