OCEANOGRAPHY MEASURING THE DEPTHS OF THE OCEANS

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1 Water 2 page 1 OCEANOGRAPHY Name If all the water was drained from the ocean basins, what kind of surface would be revealed? It would not be the quiet, subdued topography as was once thought, but a surface characterized by a great diversity of features--towering mountain chains, deep canyons, and flat plains. In fact, the scenery would be just as varied as that on the continents. MEASURING THE DEPTHS OF THE OCEANS Figuring out the depths of the ocean floor and the landforms that are present used to be a very difficult task. Until the late 1920 s the only method was to use a weighted line. In deep water, the time required for a line to reach bottom could exceed 1 1/2 hours, while the task of pulling it up is even more time consuming. Hence, prior to the late 1920 s, relatively few depth recordings had been made and little was known about the topography of the ocean floor. Since the late 1920 s scientists have developed and continually perfected an instrument known as an ECHO SOUNDER. It records the time for a sound signal to travel from a ship to the ocean floor and back again. Knowing that sound waves move through seawater at an average speed of 1500 meters per second, it is easy to compute the depth below the water surface of the ocean floor using the formula: DEPTH = ECHO TIME x SPEED OF SOUND 2 For each example below, calculate the depth of the ocean: If the echo sounding time is: The depth equals (in meters): a. 5.2 seconds b. 6.0 seconds c. 2.8 seconds d seconds e. 3.6 seconds f. 8.0 seconds g seconds h seconds i. 1.5 seconds j. 9.5 seconds

2 Water 2 page 2 MAJOR DIVISIONS AND FEATURES OF THE OCEAN FLOOR Using the descriptions below, which describe the features of the ocean floor, label each of the features listed below on the OCEAN FLOOR MAP. CONTINENTAL SHELF SHELF BREAK CONTINENTAL SLOPE DEEP OCEAN FLOOR SEAMOUNTS RIFT VALLEY Oceanographers studying the topography of the ocean floor have delineated three major units: the continental margin, the deep ocean floor, and the mid-ocean ridges. THE CONTINENTAL MARGIN The features comprising the CONTINENTAL MARGIN include: a.) the continental shelf, b.) the continental slope, and c.) the continental rise. a.) The CONTINENTAL SHELF is a gently sloping submerged surface that extends from the shoreline toward the deep ocean basin. The shelf is considered to be a flooded extension of the continents. The general slope is slight and would appear to the eye as a flat surface. The outer boundary of the continental shelf is the SHELF BREAK (that point where a rapid steepening of the slope occurs). b.) The CONTINENTAL SLOPE marks the seaward edge of the continental shelf and is characterized by a relatively steep gradient. It extends from the shelf break into deep water and marks the boundary between continental crust and the oceanic crust. c.) Often a relatively steep continental slope merges into a broad zone with a more gentile slope called the CONTINENTAL RISE. This feature, which may be thought of as a transition zone between the continental slope and the deep-ocean floor, consists of a thick accumulation of sediment that moved downslope from the continental shelf. THE DEEP OCEAN FLOOR This second major subdivision, the DEEP OCEAN FLOOR, lies between the continental rise and midocean ridge and includes flat plains, mountains, and canyons. The most noticeable features in this zone that show on your profile are seamounts. SEAMOUNTS are steep sided volcanic peaks. If these volcanoes grow large enough, they may emerge as islands. THE MID-OCEAN RIDGE MID-OCEAN RIDGES are found in all of the major oceans and represent more than 20% of the earth s surface area. They are certainly the most prominent topographic features in the oceans, for they form an almost continuous mountain range, varying in width from miles, which extends for more than 40,000 miles. The crests of the mid-ocean ridges are marked by deep clefts called RIFT VALLEYS.

3 Water 2 page 3 DEPTHS CALCULATED USING AN ECHO SOUNDER REMEMBER: 1. Use the ocean floor map. 2. Take your time. 3. Complete the entire exercise. 4. Use a ruler or straight edge. Measure distances...don T GUESS. 5. Be accurate. You will be graded on accuracy. PROFILE: CAPE COD TO GIBRALTAR --THE ATLANTIC OCEAN FLOOR POINT DISTANCE (in KM) DEPTH (in M)

4 Water 2 page 4 LOCATION EXERCISE Use the world map provided. Refer to your atlas. Locate the following by placing the number that represents the body of water in its proper location. Use a red pen for clarity. 1. North Pacific Ocean 2. South Pacific Ocean 3. Indian Ocean 4. North Atlantic Ocean 5. South Atlantic Ocean 6. Arctic Ocean 7. Caribbean Sea 8. Mediterranean Sea 9. South China Sea 10. Bering Sea 11. Gulf of Mexico 12. Sea of Okhotsk 13. East China Sea 14. Yellow Sea 15. Red Sea 16. Gulf of Aden 17. Persian Gulf 18. Gulf of Oman 19. Black Sea 20. North Sea 21. Baltic Sea 22. Sea of Japan 23. Caspian Sea 24. Adriatic Sea 25. Coral Sea 26. Bay of Bengal 27. Arabian Sea 28. Aegean Sea 29. Baffin Bay 30. Labrador Sea 31. Greenland Sea 32. Hudson Bay

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