Map Skills. Before Coming to Lab: Read Appendix III (pages ) in Trujillo & Thurman, 11 th ed.

Transcription

1 Name: Section: Due Date: Map Skills Lab 03A-1 Before Coming to Lab: Read Appendix III (pages ) in Trujillo & Thurman, 11 th ed. Names of Group Members: The primary purpose of this lab is to practice some basic map and math skills that we will be using throughout the course. These skills will be useful to you in your travels throughout your life. In addition, you will familiarize yourself with our local ocean and coastline. We will be visiting and/or studying many of the features that are discussed. This laboratory exercise will also introduce you to techniques for reading contour maps. Oceanographers use these maps to visualize and summarize large amounts of numerical measurements of depth, temperature, nutrients, and so on. Latitude and Longitude Every location on a two-dimensional surface can be specified by 2 pieces of information. In math class, you use x and y coordinates, and on a road map (or in the game battleship ) you use a letter and a number. To describe locations on the surface of the Earth, we use a grid formed by lines of latitude and longitude. Lines of latitude 1 are circles in the east-west direction that go around the Poles. The largest circle in the middle of the globe is the Equator, somewhat like a 1 Lines of latitude are sometimes called parallels, because they are parallel to the Equator.

2 Lab 03A-2 belt on the globe. It separates the northern hemisphere from the southern hemisphere. The Equator has a latitude of 0 o, the North Pole has 90 o N, and the South Pole has a latitude of 90 o S 2. (The symbol o is called a degree. ) In the example above, the dot labeled A is on the 30 o N line, so its latitude is 30 o N. Some of the locations that you will be asked to find are not on a line with a number, so you will need to estimate the latitude. The dot B is about mid-way between 30 o N and 60 o N, so its latitude is about 45 o N. Notice that lines of latitude run east-west, but they determine position north or south of the Equator. Every location along a line of latitude is the same distance from the Equator, so they all have the same latitude. Since the Equator is 0 o, the area near the Equator (the tropics) is sometimes called the low latitudes, and since the Poles are at 90 o N and S, the areas near the Poles are often called high latitudes. In between the Equator and the Poles are the midlatitudes. Regions next to the tropics are often called subtropical, and regions next to the Poles are often called subpolar. Lines of longitude are half-circles that run from the North Pole to the South Pole. The 0 o line of longitude (called the Prime Meridian 3 ) runs through Greenwich, England 4, and divides the eastern hemisphere from the western hemisphere. Dot C in the picture on the right has a longitude of 30 o E, while dot D has a longitude of about 15 o W. Halfway around the world, the 180 o line of longitude divides the eastern and western hemispheres, but ironically, the eastern hemisphere is on the western side of the line and vice versa! Notice that lines of longitude run north-south, but they determine position east or west of the Prime Meridian. Every location along a line of longitude is the same distance in time 5 from Greenwich, England o N and S for the Poles are not arbitrary. If you go from the Equator to the North Pole, then you have traveled ¼ of the way around the world. There are 360 o in a circle, so ¼ of the way around world is 90 o. 3 Lines of longitude are also known as meridians. 4 The choice for the location of the 0 o line of longitude is completely arbitrary. It was decided upon at an international conference in The main advantage of Greenwich, the site of the Royal Observatory, was that it was already used by a large number of people for determining their position on nautical charts and their time zone. 5 Notice how all the lines of longitude come together at the Poles, so the distance between them changes with latitude. Thus, they cannot measure a location s distance from the Prime Meridian.

3 Lab 03A-3 Stamps Lab 03A-3 Activity #1: Longitude & Latitude 1. Using the map below, determine the latitude and longitude of the following places. Note: Answer to the nearest degree. In other words, round up and don t use minutes or seconds: answer 34 o N instead of 33.5 o N or 33 o 30 N. Don t forget to include N, E, S, or W. Place Latitude Longitude New Orleans, Louisiana Galapagos Islands, Ecuador Sao Paolo, Brazil Alexandria, Egypt Shanghai, China Sydney, Australia Greenwich, England Write your name in this box. 2. Put dots ( ) at the locations of the following latitudes and longitudes on the map above. Label the dots. Great Barrier Reef 18 o S, 147 o E Mt. Everest 28 o N, 87 o E Los Angeles, California 34 o N, 118 o W Tahiti 18 o S, 150 o W 3. Write high latitudes, low latitudes, and mid-latitudes in appropriate places on the map above.

4 Lab 03A-4 4. New York is located along the east coast of the United States at 40 o N, 74 o W. Why is New York s longitude West instead of East? In other words, what determines whether a longitude is West or East? Activity #2: Longitude & Latitude, Minutes & Seconds For everyday navigation purposes, degrees of latitude and longitude are far too large to be useful, since a single degree of latitude is equivalent to 60 nautical miles 6 (1 o = 60 nm). To make them more precise, a degree of latitude or longitude is divided into 60 smaller parts called minutes. The symbol for minutes is (like an apostrophe), so 1 o = 60. Thus, instead of saying the latitude of dot E is 22.5 o N, we say that it is 22 o 30 N (twenty two degrees, 30 minutes north of the Equator). In other words, half a degree is 30 minutes, just as half an hour is 30 minutes. The dot E is about a quarter of the way between the 77 o W and 78 o W lines of longitude, so it has a longitude of 77 o 15 W. A quarter of a degree is 15 minutes, just as a quarter of an hour is 15 minutes. As you have probably already guessed, since 1 minute of latitude is 1 nautical mile, even minutes are not precise enough for everyday navigation. Therefore, minutes of latitude and longitude are divided into 60 smaller parts called seconds. The symbol for seconds is (like quote marks), so 1 = 60. Use the base map on the next page to answer the following questions. 5. What underwater feature is located at 33 o 40 N, 118 o 35 W? 6. What are the latitude and longitude of the city of Malibu? Latitude: Longitude: 6 A nautical mile is a little bit longer (about 15%) than an ordinary or statute mile.

5 Lab 03A-5 7. What body of water is located near 33 o 58 N, 118 o 27 W? (Note: The answer is not the Pacific Ocean. ) Sewer Line A seamount is an underwater mountain. 8. What underwater feature is located near N, W? 9. What are the latitude and longitude of Bluff Cove? Latitude: (Bluff Cove is located along the coast of Palos Verdes.) Longitude: 10. What are the latitude and longitude of the mouth of Latitude: the San Gabriel River. In other words, where does the San Gabriel River meet the coast? Longitude:

6 Lab 03A-6 Activity #3: Measuring Distances on Maps Construct a paper ruler on a separate sheet of paper using the nautical miles bar scale in the upper right corner of the map on the previous page. Be as precise as you can. (In other words, your answers should contain decimals or fractions of a nautical mile.) 11. What is the distance from El Camino College to Cabrillo Beach? 12. What is the distance from Santa Monica Canyon to the city of Santa Monica? 13. How far is Redondo Beach from the place where oil naturally seeps from the bottom of the ocean? One nautical mile is equal to 1 minute of latitude, so nautical miles are a little different from the miles that we use on land. The miles that we use on land are called statute miles. 1 nautical mile = 1.15 statute miles. 14. Chart a course from Marina del Rey to the Port of Los Angeles on the base map. (In other words, draw lines showing the path that the ship will take.) Put dots ( ) at each location where the ship changes direction. Write the latitudes and longitudes where the ship changes direction on the map next to each dot ( ). Then, estimate how long the trip would take if your ship travels at a speed of 5 knots. Hints: Only travel in straight lines. Split the journey up into several straight line segments or legs. 1 knot is a speed of 1 nautical mile per hour (1 nm/hr). (Show your work. Be clear. Circle your answer.)

7 Lab 03A-7 Activity #4: Familiarizing Yourself with Our Ocean Examine one of large maps that your instructor brought into the classroom on a cart (Chart 18744). The numbers in ocean show the depth of the ocean in fathoms, and the letters tell you about the color and kind of sediments on the ocean floor: S for sandy, M for muddy, rky for rocky, and Sh for shells. 15. Is the sea floor of Redondo Canyon (several miles offshore of Redondo Beach) covered by mud or rocks? 16. Is the sea floor of Bluff Cove covered by sand or rocks? 17. What kinds of sediments cover most of the sea floor? sand? mud? rocks? shells? 18. Locate the underwater sewer lines (the long, faint, dashed lines cleverly labeled sewer ). Which city are they closest to? 19. How long is the longest sewer line? (Answer in nautical miles.) Hint: Make a paper ruler using the bar scale at the edge of the map. 20. Locate a place where oil, tar, &/or gas leak ( seep ) from the bottom of the nearby ocean. Which city is it closest to?

8 Lab 03A-8 Activity #5: The Meaning of Map Scales Fractional maps scales are ratios. In other words, they take the form 1:2, 3:4, 1:100, 1:3000, 1:20,000 and so on. The scale tells you about the relationship between the map and the real world that it represents. For example, everything in a map with a scale of 1:10 is 10 times smaller than in the real world (or you could say that the real world is 10 times larger than what is shown on the map). You can use the scale to measure distances on a map. If a map has a scale of 1:5000, then 1 inch on the map represents 5000 inches in the real world (or 1 centimeter on the map represents 5000 centimeters in the real world or 1 foot on the map represents 5000 feet in the real world the units that you use do not matter). 21. What is the scale of Chart (the big map)? What does the scale of this map mean? In other words, what does it tell you about this map? Hint: Look for the scale in the legend, located in the corner with the name of the map Santa Monica Bay in big letters. 22. How many feet (in the real world) does an inch on Chart (the big map) represent? (Show your work. Be clear. Circle your answer.) 23. What is the scale of the Marina del Rey map? (The Marina del Rey map is in the lower left corner of Chart ) 24. Which shows more details, the main map or the map of Marina del Rey? Note: The question is not Which map covers a greater area? The question is Which map allows you to see small features? 25. Suppose that you are looking for a map, and you are told that you can choose between maps with several different scales: 1:1,000, 1:50,000, 1:100,000, or 1:500,000 Which map would show most detail?

9 Lab 03A-9 Activity #6: Reading Contour Maps Oceanographers go out into the world and measure a variety of quantities at different locations. It can be hard to understand what they mean or show from staring at the numbers, so oceanographers draw contour lines through the data to make a picture of the numbers (their data). At first, a contour map may appear to be a bunch of squiggly lines or contours. Each contour line represents locations where a quantity has one, specific value. In other words, a contour line connects locations of equal value. In the contour map of depth (bathymetry) below, the location labeled A has a depth of 10 fathoms, because it is on the 10- fathom contour line. The location labeled B has a depth of 20 fathoms. If a location is between contour lines, then use the neighboring contour lines to estimate its value. Location C is about midway between the 10- and 15-fathom contour lines, so a reasonable estimate of the depth at C is 12 or 13 fathoms. Location D, on the other hand, is much closer to the 20-fathom contour line than the 15-fathom contour line, so a value of about 19 fathoms would be reasonable. Contour lines go by other names, often using the prefix iso-. For example, isobaths show bathymetry (depth), isotherms show temperature, isohalines show salinity, and so on. Land 20 E 0 5 A C B D Unfortunately, not every contour line is labeled, typically because they get too close together. In this case, you must figure out the value of each contour line using the contour interval. The contour interval is the difference or jump in value from one contour line to its neighboring contour lines. For example, in the contour map above, the contour interval is 5 fathoms, because the difference between each contour is never more than 5 fathoms. (e.g., The 15-fathom contour line is next to the 10-fathom line and the 20-fathom line: it is 5 fathoms deeper than the 10-fathom line, and 5 fathoms shallower than the 20-fathom line.) Therefore, the blank contour line with location E on it must have a depth of 25 fathoms (mid-way between 20 fathoms and 30 fathoms, the values of neighboring contour lines). Notice that neighboring contour lines can have the same value. For example, two 20-fathom contour lines are next to one another in the map above.

10 Lab 03A-10 Reading and Interpreting Contours It takes time and practice to read, interpret, and visualize contour maps, so be patient with yourself. If the contour lines loop around and connect with themselves, then there is a relative maxima or minima in the data (the data is unusually high or low inside the loop). If you are examining isobaths (contour lines showing the depth of the ocean or bathymetry ), this means that the location is an underwater hill ( seamount: smaller numbers = shallower place) or valley ( trench or basin: larger numbers = deeper place). If the contour lines bend into a V -shape, then there is a ridge (high place) or trough (low place) in the data. If you are examining isobaths, a V -shape indicates the presence of an underwater canyon if the bottom of the V points towards shallower water or land. If the V- shape points towards deeper water, then it is a ridge. If contour lines are close together, then the quantity represented by the contours is changing quickly over a small area. We say that it has a large gradient. If you are examining isobaths, then the slope of the ocean bottom is steep where the contours are close together, and the slope is gentle (the bottom is pretty flat) where the contours are far apart from one another. Note: Contour lines can never touch one another ( cross ) or divide ( split ). A contour line can only end when it hits the edge of the map or loops back around to meet itself; it can never end in the middle of the map. Examples of "Looped" Contours Steep Underwater Hill points towards shallower water Underwater Valley or "Basin" Canyon = "V"-shaped the closer the contours, the steeper the slope 40 Gentle

11 Lab 03A-11 Examine the contour map below. Note that the contours in the ocean show fathoms below sea level, but the contours on land show feet above sea level. I used a consistent contour interval (100 fathoms = 600 feet since 1 fathom = 6 feet), but did not want to use fathoms a unit of depth for height above sea level, so I have labeled the land contours in feet instead. You may use the abbreviation fm for fathoms if you wish. You might find the 3-dimensional models in the wooden boxes useful for answering these questions. 26. What is the contour interval of the ocean contour lines? What is the contour interval of the land contour lines? 27. What is the approximate depth at the following dots on the map? (Answer in fathoms.) (a) dot W (b) dot X (c) dot Y (d) dot Z 28. Outline the shoreline in the contour map below using a green pencil. What is the value of the shoreline contour line? (In other words, what depth or height does it represent?) 0 Z W 0 0 X

12 Lab 03A Label the following with your own pencil (i.e., a regular grey pencil): Shoreline Underwater Canyon ( Submarine Canyon ) Continental Shelf Underwater Hill ( Seamount ) Continental Slope or Scarp Underwater Valley ( Basin ) Hill on Land The continental shelf is a shallow, flat area close to the shoreline. The continental slope is the steep area offshore of the continental shelf. 30. Where is the continental shelf wider, at A or B? 31. Where is the continental slope steeper, along the line C-D or the line E-F? How can you tell? 32. Using a blue pencil, draw where the shoreline would be if sea level dropped by 100 fathoms during an ice age. 33. Using a red pencil, draw where the shoreline would be if sea level rose to 600 feet above today s sea level. What would happen to El Camino College (and most students homes)? The hill is no longer a hill on the mainland. What would people call it instead? 34. How deep is the top of the seamount? (Answer in fathoms.) How deep is the bottom of the seamount? (Answer in fathoms.) How high is the seamount? (In other words, how high does it rise above the sea floor?) (Answer in fathoms.) Careful! People often find the last question above tricky. Thinking about it using of the side-view picture (cross-section) on the right might help. Write the depths of the top and bottom of the seamount in the picture. How high does the seamount rise above the bottom? Depth of top? Seamount Depth of bottom?

13 Lab 03A How many feet-high is the seamount? (Show your work. Be clear. Circle your answer.) Activity #7: More Reading Contour Maps Each contour plot that you see in this lab is the result of tremendous amounts of time and energy spent at sea by oceanographers. Each contour line represents many measurements. Temperature and other properties have to be measured directly, which takes a lot of effort. Oceanographers lower an instrument called a CTD ( conductivity-temperature-depth 7 ) and samples bottles mounted on a frame (called a rosette ). The conductivity of the water tells them the salinity of the water. (Many salts in water are electrically charged which allows water to conduct electricity and electrocute you if your hair dryer falls into your bath! The saltier the water, the better it conducts electricity 8.) On the way down (or back up), oceanographers open the sample bottles at specific depths to collect water. This allows them to measure other aspects of the water s chemistry (oxygen, nutrients, etc.), and double check that their CTD is working properly (since they can directly measure the temperature and salinity of the water). The entire trip of the CTD down and up again can take hours since it may need to travel several miles. One question that oceanographers confront is at what depths they should take samples, because there are a limited number of sample bottles on the rosette. Each dot in the figures on the next page shows where one sample bottle was opened to collect water. We take more samples where characteristics change rapidly so that we can resolve the changes. Thus, there are more dots near the surface where the Sun, winds, waves, evaporation, rain, etc. affect the water. Deeper water does not change as much. Oceanographers typically divide the ocean up into 3 layers: the mixed layer, the thermocline, and the deep ocean layer. The mixed layer is the surface layer of the ocean which is stirred by waves (caused by the wind) until all the water in the layer is almost all the same temperature, salinity, etc. The thermocline is the layer of the ocean beneath the ocean mixed layer in which the temperature (and typically other characteristics as well) change a lot as you go deeper. The root -cline means change. For example, an incline is a ramp where you can go up or down: your height changes. The thermocline ends where the temperature (and other characteristics) begin to change very little with depth: this is the deep ocean layer. 7 The CTD doesn t actually measure depth; it measures pressure, which is caused by the weight of the water above: the deeper and denser the water, the higher the pressure. So oceanographers use the temperature, salinity, and pressure of the water to calculate the water s density and divide by the pressure to calculate the depth of the CTD and sample bottles at each moment. (The line does not stay perfectly vertical, so they cannot simply use the length of the line to determine the depth.) 8 The temperature of ocean water also affects its conductivity, so to determine its salinity from its conductivity, oceanographers need to know its temperature (which they measure anyway).

14 Lab 03A-14 The side-view (cross-section) of temperature on the right is based on measurements along the coast of southern California. Mixed Layer Thermocline 36. Where is the coast of Southern California in the contour map of temperature, on the left or right side of the contour map? Write coast along this side of the map. Explain your reasoning. Hint: The dots show the depths where measurements were taken. Also, look at the longitudes along the bottom and ask yourself, is the ocean to our east or west? 37. What is the contour interval of the contour map? 38. What is the approximate temperature at a depth of 100 meters at 122 o W? (Place a red dot in the contour map at this location.) 39. Color all the water warmer than 13 o C red in the temperature contour map. Is the water in the mixed layer at the surface of the ocean warmer or colder than the deeper water of the thermocline? Does this make sense to you? Why or why not? In other words, why do you think the water at the surface is warmer or colder, or why did you expect the surface water to be warmer or colder than it is? 40. Is the water in the mixed layer near the coast warmer or colder than the water farther out in the ocean? 41. The water along our coast has a different temperature than the water far from the coast, because of the California Current which flows along the coast. Does the California Current flow north (come from Mexico) or flow south (come from Alaska)?

15 Lab 03A-15 Examine the side-view of oxygen along the coast of southern California shown below. 42. What is the contour interval of the contour map? Mixed Layer Thermocline 43. What is the approximate oxygen concentration at a depth of 200 meters at 121 o 45 W? (Place a green dot in the contour map at this location.) 44. Color all the water with an oxygen concentration of 6 ml/l or more green in the oxygen contour map above. Color all the water between 5 and 6 ml/l blue. Which layer of the ocean has more oxygen, the water in the mixed layer at the surface of the ocean or the deeper water of the thermocline? Why does the water at the surface have more or less oxygen than the deeper water? 45. Where does the water of the mixed layer have the most oxygen, near the coast or far away from the coast? 46. Which ocean organism absorbs nutrients from ocean water, phytoplankton or zooplankton? What do they need the nutrients for? 47. Where would you expect to find more nutrients in the water, near the coast or far away from the coast? Why are there more nutrients in this location?

16 Lab 03A-16 Map Skills Mini-Lecture To make a flat, rectangular map of a round world, some parts of the spherical map need to be stretched and others compressed, making some regions look too large on the flat map and other areas too small: Which parts of the world are too small on flat, rectangular map of the world? Which parts of the world are too large on a flat, rectangular map of the world? To address these questions, review the Flat Maps Distortions file for the Map Skills Lab (3A) located on the course website on the Labs page: Flat, rectangular map of the world:

17 Lab 03A-17 Map Skills Lab (3A) Review: Hints & Advice Activity #1 Do not forget to include the UNITS: o N, o E, o S, or o W should be part of every latitude or longitude answer. Be as precise as you can (to the nearest degree) when identifying latitudes and longitudes and placing dots on the map. If your answers are implausible (e.g., the dot should be next to the line instead of on the line, the dot should be mid-way between lines but is much closer to one line than the other), they will be marked wrong. The mid-latitudes are NOT located near the Equator; make sure that you read the beginning of the lab carefully. Activity #2 Do not forget to include the UNITS: all your answers for latitude and longitude should have the form XX o XX N where o is the symbol for degrees and is the symbol for minutes. Every latitude or longitude should end with N, E, S, or W. Be as precise as you can (to the nearest degree) when identifying latitudes and longitudes and placing dots on the map. If your answers are implausible (e.g., the dot should be next to the line instead of on the line, the dot should be mid-way between lines but is much closer to one line than the other), they will be marked wrong. Activity #3 You can use the abbreviation nm for nautical miles. Make sure that your ship travels through the ocean. If you travel over the land (e.g., go by El Camino College), you will be marked wrong. Make sure that your ship travels along straight lines or you will not be able to answer all of the questions (e.g., you will not be able to measure the distances). Your ship can pass over the submarine pipeline and other underwater features (e.g., canyons, seamounts) without hitting them; they are located on the bottom of the ocean far below the surface. Do not forget to write the latitudes and longitudes next to the dots on the map where your ship changes direction. Make sure that your answers have the correct UNITS, including the latitudes and longitudes that you write on the map. (Continued on the Next Page)

18 Lab 03A-18 Activity #4 For question 17, you may list the two most abundant kinds of sediments on the ocean floor if you cannot decide on one. If you doing the lab in class and using the large map to measure the length of the sewer line, make sure that you use the scale on the large map to make your ruler; do NOT use the scale on the small map in Activity 2 to measure a distance on the large map. Activity #5 Answers to question 21 like how big it is or how much is shown are too vague and not accurate. You need to have a specific answer that explains what the numbers in the scale mean. Do not forget to write the UNITS after you answer to question 22. NOTE: The correct units for a scale are NO units. In other words, you should not write feet, inches, fathoms, centimeters, or any other unit after the numbers of a scale. A scale is a ratio (one thing divided by another one); since the same units will be present in both the top and the bottom the ratio, the units cancel and the ratio itself the scale has no units. Activity #6 If a dot is located between two contour lines, you must estimate the depth at the dot using both contour lines. The closer the dot is to a contour line, the closer the value at the dot is to the value at the contour line. Use the examples on page 10 to determine what each underwater feature looks like on a contour map. You will need to be able to answer the following questions to label the contour map: How does a seamount (an underwater hill) look different from a basin (an underwater valley)? How does an underwater valley look different from an underwater canyon? The answer to question 33 is not seamount; a seamount is an underwater mountain. Activity #7 Remember: The contour maps in activity 7 are SIDE-VIEW plots. The top of the contour maps is the surface of the ocean. The bottom of the contour maps is deep in the ocean. California (the land) is on the right or left side of plots, so the upper right or left corner of the plots is the shoreline. You MUST answer question 36 where the coast is correctly before beginning to answer the other questions, otherwise many of your answers will be backwards. Check with your instructor if you are not sure. Do not forget to include the UNITS after every number. The units for each contour map are written at the top of the contour maps. When placing the green dot for question 43, many students think that the 1 o distance between 121 o W and 122 o W does contains 100 minutes; this is incorrect. How many minutes are in 1 o? How many minutes is the location halfway between 121 o W and 122 o W?