Ocean Currents Lab. Name: Section: Due Date: Lab 09A-1

Lab 09A-1 Name: Section: Due Date: Ocean Currents Lab Before Coming to Lab: Read Chapter 7, Ocean Circulation (pages 197-234), in Thurman & Trujillo...
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Lab 09A-1

Name: Section: Due Date:

Ocean Currents Lab Before Coming to Lab: Read Chapter 7, Ocean Circulation (pages 197-234), in Thurman & Trujillo, 11th ed.

The purpose of this lab is for you to review the basic ocean circulation patterns, and consider their impact on life in the ocean and climate, including the phenomenon commonly referred to as El Niño. Perhaps the most challenging aspect of this lab is that you will encounter real oceanographic data. As you will see, the pictures in your textbook often oversimplify what is actually going on in the ocean. The real world is almost always a good deal messier than you might think from reading introductory science textbooks.

Names of Group Members: 1. 2. 3.

DRIFTER #1 Month Feb May Aug Nov

(15022) Latitude 11oN 12oN 30oN 39oN

120oE

K Longitude 162oE 138oE 134oE 154oE

150oE

DRIFTER #2 Month Mar June Sept Dec

180o

Ma r Ju ne Sep t (15082) Latitude 42oN 42oN 42oN 41oN

Al – KE Longitude 172oW 168oW 160oW 151oW

120oW

(12463) Latitude 9oN 8oN

DRIFTER #4 Month Feb May

0o

15oN

30oN

45oN

NEP - EC Longitude 122oW 140oW

CA C Longitude 125oW 123oW

60oW

(12408) Latitude 35oN 24oN

90oW

DRIFTER #3 Month Mar June

Drifter #3

Feb

June

Mar

Drifter #4

May

150oW

Drifter #2

c De

60oN

Lab 09A-2

Lab 09A-3

Stamps Activity #1: Drifters

Write your name in this box.

One method for measuring ocean currents is to place an object (a “drifter”) in the water, and then to watch where it moves. Nowadays oceanographers use drifters that are carefully designed to move with the water (not the wind), and track them using satellites. 1. Using a colored pencil (you get to choose the color!), plot the data for drifter #1 in the map on the previous page:

Drifters #2, 3, & 4 have been done for you. Use them as examples.

• Put a dot at the latitude and longitude of the drifter for each month. Label each dot with its month. (In other words, write the month next to each dot.) • Connect the dots with arrows (of the same color as the dots) to show the path that the drifter took. (We call the path of a drifter the “drifter track.”) 2. Describe the overall motion of water in the North Pacific Ocean. In other words, describe the pattern revealed by the combined motion of all 4 drifters.

3. Where is the water moving fastest?

_______________________________

How can you tell from the motion of the drifters on the map? Explain your reasoning.

Lab 09A-4 4. Which drifter is in a western boundary current? (In other words, which one is on the west side of the ocean?)

__________________

Is the western boundary current carrying warm or cold water? __________________ How can you tell from the drifter track? Explain your reasoning.

How does the current affect the climate along the coast? In other words: Does the current make the climate warmer or cooler than it would otherwise be?

__________________

Does the current make the climate more humid or less humid than it would otherwise be?

__________________

5. Which drifter is in an eastern boundary current? (In other words, which one is on the east side of the ocean?)

__________________

Is the eastern boundary current carrying warm or cold water? __________________ How can you tell from the drifter track? Explain your reasoning.

How does the current affect the climate along the coast? In other words: Does the current make the climate warmer or cooler than it would otherwise be?

__________________

Does the current make the climate more humid or less humid than it would otherwise be?

__________________

6. Suppose that you wanted to sail across the Pacific Ocean, from San Francisco at 38oN, 122oW to Tokyo, Japan, at 35oN, 140oE . What course (“route,” “path”) would you take to cross the ocean? Draw your path into the figure on the previous page. Why is your course the best path? How do you benefit?

Lab 09A-5

Activity #2: Gyres 7. Sketch the winds (i.e., trade winds and westerlies) in the North Pacific into the map below in green. Then, sketch the ocean currents into the map in blue.

60oN

30oN

0o CHECK YOUR ANSWER WITH YOUR INSTRUCTOR BEFORE PROCEEDING. 8. Use the fans (which create wind) to create a gyre in the tank of water. Sketch a bird’s-eyeview of your fans, winds (in green), and the resulting ocean currents (in blue) into the picture below. Label the appropriate winds “trade winds” and “westerlies” in your picture. DON’T LET THE FANS TOUCH THE WATER! Don’t hold them over the water. Let them blow from the SIDE.

Alaska North Pacific Ocean Bits of Paper

California (North America)

Japan (Asia)

Equator Where should you put the fans?

Fan

Lab 09A-6

9. The map below shows the gyre in the North Pacific Ocean that you just modeled. Sketch the winds in green into the map below. Label the appropriate winds “trade winds” and “westerlies.”

C D

30oN

B A 0o Why does the water in the oceans move in a gyre pattern?

To answer this question, explain why the water moves in each direction at the 4 locations identified in the map above. A.

B.

C.

D.

Lab 09A-7

Activity #3: Ocean Circulation & Satellite Images of Ocean Temperature 10. Sketch the world’s subtropical gyres, the subpolar Arctic gyre, and the currents by Antarctica into the map below.

Examine the satellite image of temperature for July 1987 in the ocean circulation folder.

11. Which coast of the United States has warmer water off the coast, the east coast or the west coast? __________________ Which coast of South America has warmer water off the coast, the east coast or the west coast?

__________________

Which coast of Southern Africa has warmer water off the coast, the east coast or the west coast?

__________________

Why is the water by one coast always warmer than the water off the other coast in the subtropics? (Hint: Describe the ocean currents. Where are they coming from?)

Lab 09A-8

12. Sketch the world’s major eastern and western boundary currents of the subtropical gyres into the map below. Sketch the warm boundary currents into the map below in red and the world’s cold boundary currents in blue. (Note: DO NOT sketch the gyres.) Your map should have 10 arrows, each representing a boundary current.

13. How do warm currents affect the climate along the coast? In other words: Do the currents make the climate warmer or cooler than it would otherwise be?

__________________

Do the currents make the climate more humid or less humid than it would otherwise be? __________________ Why does the air become more humid or less humid? Explain your reasoning.

14. How do cold currents affect the climate along the coast? In other words: Do the currents make the climate warmer or cooler than it would otherwise be?

__________________

Do the currents make the climate more humid or less humid than it would otherwise be? __________________

Lab 09A-9 15. Do ocean currents warm or cool the low latitudes (near the Equator)? _________________ Do ocean currents warm or cool the high latitudes (“the Poles”)?

_________________

If the gyres stopped: ─ would the climate at the Equator get warmer or cooler?

_________________

─ would the climate at the Poles get warmer or cooler?

_________________

Look at the sea surface temperature in January 1988 in the ocean circulation folder. 16. Look at each side of the Pacific ocean at the Equator. Which side of the ocean is warmer, the eastern equatorial Pacific or the western equatorial Pacific?

______________________________

Why is one side of the ocean warmer than the other side? The answer does NOT involve the western boundary currents. They are warm because they take warm water away from the west side the Equator.

17. Compare the temperature of the Atlantic Ocean at the Canadian coast at 60oN and the Northern European coast at the same latitude. Which coast is warmer, the coast of Canada or the coast of Northern Europe?

______________________________

Why is the water off one coast warmer than the water off the other coast at this latitude?

Lab 09A-10

Activity #4: Upwelling & Downwelling 18. In this experiment, you will see an example of upwelling and/or downwelling for yourself: ● Fill the small tank with water (almost all the way to the top) ● Position the fan at one end of the tank (almost touching it) as shown, and turn it on. Wait for a minute for the water to begin a stable circulation. ● Place a drop of dye at the other end of the tank to visualize the motion of the water. ● Sketch the “wind” (with green arrows) and the resulting motion of the water (with blue arrows) into the side-view picture below, and then label any regions of upwelling and/or downwelling. In other words, write “upwelling” and “downwelling” in the places where they occurred.

Add dye here.

Fan

DUMP THE WATER & RINSE OUT THE TANK FOR THE NEXT GROUP.

19. Why was the water downwelling in the experiment? In other words, why did it go down at the location shown above?

20. Why was the water upwelling in the experiment? In other words, why did it go up at the location shown above?

Lab 09A-11 21. Examine Image E showing ocean water temperature in the ocean circulation booklet. (Note: black shows where the satellites cannot see, not cold water.) Where is the coldest water in the image?

______________________________

Circle the region where the coldest water is in blue in the figure below.

22. The large black arrow in the figure shows the coastal winds along the coast of California. Draw arrows into the picture showing the direction that the water is pushed by the coastal winds in red.

23. Why is the water coldest at the location that you circled in blue? (Hint: The answer is not “the California Current.”) ________________________________

The figure on the right shows a side-view (crosssection) of salinity near the coast of southern California. (The coast is the right hand side of the picture.)

24. Highlight the 33.4‰ contour line (isohaline) in green.

Ocean

Then, color all the water with a salinity higher than 33.4‰ green. Land 25. Add a red arrow to the side-view of salinity to show motion of the water at the surface of the ocean, and a blue arrow to show the motion of the deeper water.

Lab 09A-12 26. Where is the surface water saltiest, near the coast or in the middle of the ocean?

______________________________

Many students expect the water to be fresher (less salty) at this location. Why? What typically makes this part of the ocean fresher? ______________________________ Why is the water at this location along the coast of California (sometimes) unusually salty?

____________________________

The figure on the right shows a side-view (cross-section) of nutrient concentration. 27. Highlight the 1 ml/L contour line in green. Ocean

Then, color all the water with a nutrient concentration higher than 1 ml/L green.

28. Add a red arrow to show the motion of the water at the surface of the ocean, and a blue arrow to show the motion of the deeper water.

Land

29. Where are there more nutrients at the surface of the ocean, near the coast or in the middle of the ocean? ______________________________ Why are there more nutrients at this location? Give at least 2 reasons. (a) ___________________________

(b) ___________________________

30. What is the relationship between these nutrients and California’s fisheries? In other words, are fish more abundant or less abundant because of these nutrients? How? Why? Explain.

Lab 09A-13

Ocean Currents Lab (9A) Review: Hints & Advice Activity #1 Do not forget to answer question 2. Answers like “because it is a western boundary current” will not be accepted: •

To answer question 3, you need to discuss the locations of the drifters and the time it took the drifters to travel from one location to the next.



To explain why ocean currents are warm or cold, just discuss where they come from.

Sometimes students tell me that warm ocean currents move faster than cold ocean currents, because hot molecules move faster than slow ones. What is wrong with this reasoning? (Hint: Think about the difference between random motion and an ocean current.) Last Question: Make sure that you explain WHY you should go with a current, or why you should not go against a current.

Activity #2 Make sure that you locate the Equator and 30oN so that you can draw the winds and currents in the correct places. Do not forget to sketch the fans into the picture and show their orientation. Do not forget to write the names of the winds (“trade winds” or “westerlies”) next to the winds. To explain why the ocean currents move in each direction, you must explain what is “pushing” or “pulling” them in each directions. For example, you might say: “The current moves north (or east, south, west, up, or down) because: ● it is pushed in this direction by…” ● it is pushed out of the way by…” ● it is replacing the water taken away by…” ● its has a high (or low) density due to its temperature (warm or cold).” What could be pushing each current? There are number of possibilities: the trades winds, the westerlies, current A, current B, current C, and current D.

Lab 09A-14

Activity #3 Do not forget to draw the subpolar gyre and the currents by Antarctica. To explain why ocean currents are warm or cold, just discuss where they come from. Some students tell me “People who live near the Equator like ocean currents, because they cool down the Equator.” This answer needs more explanation. Make sure that you explain WHY you think people who live near the Equator or Poles will appreciate this. Sometimes students tell me “The western side of the ocean at the Equator is warmer, because of the western boundary current.” This reasoning is backwards: the western boundary current is warmer because it gets its water from the western side of the ocean at the Equator. To explain the temperature difference along the Equator, students need to discuss the currents that flow towards or along the Equator. As we have seen before in this lab, to explain the temperature of a location, you need to discuss where the currents are “coming from” (not “going to”).

Activity #4 Do not forget to sketch the wind in green. Do not forget to write “upwelling” and “downwelling” in appropriate places. Answers like “Downwelling is happening because the water hits the side of tank, and is forced down.” need more explanation. For example, why can’t the water just stop when it hits the edge of the tank? What is forcing the water down? Sometimes students tell me that “upwelling is happening because the currents are spreading apart.” This does NOT explain why upwelling is happening in the tank, since there are not 2 currents which are moving apart. “The California Current” or “Water from the Poles” are the same answer – neither explains the cold water by the coast in map. Remember: This activity is about UPWELLING (just look at its title!). Most of your answers to the questions on the second and third pages of the activity should be related to upwelling in some way, including the arrows that you draw in the side-view contour maps of salinity and nutrients. To figure out which way the coastal winds push the surface water, rotate your paper until the arrow representing the winds is going away from you. Now, the WIND’s right is also YOUR right, and you should be able to sketch the direction that the coastal winds are TRYING to push the water in. An answer to the last question like “more fish because of lots of nutrients” needs more explanation and implies things that are untrue (this statement implies that fish intake the nutrients directly and perhaps that the author thinks nutrients are the fishes’ “food”). An answer to the last question like “because the fish will come to the coast to eat phytoplankton” needs more explanation; for example, why are phytoplankton so abundant? Also, the answer contains a mistake.