g) Use the map compass to provide the general locality of the knoll on the chart.

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Stewart Wheeler
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1 The horizontal scale (x axis) of your cross-section/profile is the linear map distance between point A and point B on the map (or between X and Y and Z). It conforms to the map scale. In other words, the distance between each point/contour on your transect line is measured using the map scale. The vertical scale (Y axis) of your cross section is usually manipulated to be a larger scale than the map scale to emphasize topographical/bathymetric highs and lows. The vertical axis depends upon the contour interval of your topographic map and the spacing you choose to emphasize topography on your Y axis (how many squares/inch or how many squares /centimeter). 1

2 g) Use the map compass to provide the general locality of the knoll on the chart. 2

3 h) On the San Pedro Channel chart which side of the knoll is steeper? Circle one Southwest Northeast i) Approximately how high is the knoll above the surrounding sea floor? Show your calculation: 3

4 Fig 2b Hint: on the above profile you are dealing with a contour interval of 100 fathoms. Label your vertical axis accordingly: each line represents 100 fathoms of depth. You are profiling depth; therefore, 0 fathoms will be the depth indicated on the topmost line. Zero fathoms is the shoreline at A. Locate Hudson Submarine Canyon on the chart indicating its axis with a dashed line. Label the continental shelf and continental slope on the profile and on the chart. The continental slope descends from 100 fathoms to about fathoms. How many feet is the slope s descent? Between the base of the slope and the flattening of the abyssal plain, there is a gentle mounding of sediment. This is called the continental. 4

5 Label the continental shelf and continental slope on the map and on your profile Label the Middle Americas Trench on the map and on your profile Label the Abyssal plain on the map and on your profile Sediments transported by rivers down from the mountains to the sea eventually wash out to the edge of the continental shelf. They will not reach the abyssal plain. Why not? 5

6 4) Nautical Miles On a marine chart, the latitude scale (denoted on the sides of the chart) can be used as a distance scale. This is because on the globe, all parallels of latitude are both parallel and equidistant. Thus 1 minute ( ) of latitude = 1 nautical mile a) Looking at the margins of the San Pedro Channel Chart (Fig. 1a), use your ruler to draw a line below that represents the map distance of 5 minutes of latitude. b) Looking at the margins of the San Pedro Channel Chart, use your ruler to draw a line below that represents the map distance of 5 minutes of longitude. c) Of the two lines, which one represents 5 nautical miles (circle one): a or b d) How would the length of lines compare if you were using a nautical chart that showed a portion of the equatorial region (refer to the globe)? e) How would the length of longitude and latitude lines compare if you were using a nautical chart that showed a portion of the Bering Sea? 6

7 Hint: After line 5, the sound energy is traveling through sediments and rocks. b) Does the velocity of sound increase or slow as it leaves liquid medium to travel through the solid medium of sediments and rocks? c) The speed of sound in seawater depends on seawater s density, which is affected by temperature: warmer water transmits sound faster than cooler water. Thus, the speed of sound in seawater varies between meters per second. San Pedro Bay California, near Los Angeles, is at 33º N Latitude; 118 º W Longitude. What is the latitude of waters in the shipping lanes offshore Miami? What is the longitude of waters in the shipping lanes offshore Miami? Based on our relative latitude, would you expect the speed of sound to travel slower or faster through seawater offshore Miami than it travels in the San Pedro Channel?. 7

8 6) Additional practice with profiling, vertical exaggeration, nautical miles Profile the cross section of the ocean bottom along transect line A - A in Fig 6. Refer to Figure 6 below to tabulate depth as a function of distance in Table 1. Line A-A is 3 km long and is marked off in 100 m intervals. Interpolate depths using whole numbers Next Using your Table 1. depths, construct a cross section profile with no vertical exaggeration (upper graph of Fig 7, Pg 10) showing the shape of the ocean bottom along line A -A in Fig 6. Then draw the cross section profile on the graph paper (Fig 7. lower graph) with vertical exaggeration X 10 (lower graph). How many nautical miles does the 3 km transect line represent? How many nautical miles is it from the end of the pier to Boomer Beach? How many statute miles is it from the end of the pier to Boomer Beach? How many kilometers is it from the end of the pier to Boomer Beach? Table 1. Depth as a function of distance in Figure 6 Distance from A (meters) Depth (meters) Distance from A (meters) 0 1, , , , , , , , , ,500 1,000 2,600 1,100 2,700 1,200 2,800 1,300 2,900 1,400 3,000 1,500 Depth (meters) Fig. 6 8

9 Fig 6. Bathymetric chart of the ocean bottom near Scripps Institute of Oceanography (LaJolla, California). For use in problem 6. Contour interval is 10 meters for depths to 20 meters; 20 meters for depths between 20 meters and 100 meters and 100 m; and, 50 meters for depths greater than 100 meters. Note: the unlabeled values on the top scale bar are nautical miles, e.g. 0.2 nautical miles is approximately 400 yards. (Adapted from F.P. Shepard and R.F. Dill, Submarine Canyons and Other Sea Valleys, Rand McNally, 1966.) Fig.7 9

10 Fig. 7 Graph paper for plotting cross section profiles along line A-A (Problem 6) 10

Test 1: Ocean 116 (Oceanography Lab.)

GLENDALE COMMUNITY COLLEGE Name Marks secured /25 Test 1: Ocean 116 (Oceanography Lab.) Dr. Poorna Pal Note: Answer all questions/solve all problems, giving detailed answers, as may be needed. Show all