Ocean Tides and Tidal Ranges
Purpose
Students will:
a. Plot tide data for three different locations.
b. Compare tides at three different locations.
Background
For most coastal locations, high tides and low tides follow each other in a regular pattern. The level of the water at each high tide and at each low tide, however, varies from day to day and from location to location. In the same way, the difference in water level between high tide and low tide, called the tidal range, is constantly changing. The greatest tidal ranges occur near the times of the new moon and the full moon and are called spring tides. The smallest tidal ranges occur near the times of the quarter moon phases and are called neap tides.
Another factor that influences tidal range is the shape of the bay in which the tide occurs. Bays that become narrower away from the ocean cause the water level to rise higher as the tide moves into the bay. Such bays tend to have a large tidal range. On the other hand, bays that widen away from their mouths allow the water to spread out. These bays tend to have small tidal ranges. This activity examines the tides at three locations: Boston, Massachusetts, on Boston Harbor; Saint John, New Brunswick, on the Bay of Fundy; and Mobile, Alabama, on Mobile Bay.
Procedure
1. Table 1 contains sample data for Boston spring and neap tides, Table 2 contains sample data for Saint John spring and neap tides, and Table 3 contains sample data for Mobile spring and neap tides. Find the tide data for Boston at spring tide. In Microsoft Excel, plot the data for the spring tide in one color and the neap tide in another color for each location. (You will be creating three charts…one for Boston, one for Saint John, one for Mobile; you’ll likely want to use a scatter plot). Connect the points with a smooth curve. Be sure to give each tide chart a title, and be sure to label your x- and y-axis.
2. Answer the Analysis and Conclusions questions.
TABLE 1: BOSTON, MASSACHUSETTSTime / Spring Tide Water Level (m) / Neap Tide Water Level (m)
0 / 2.4 / 1.6
1 / 3.1 / 2.1
2 / 3.5 / 2.5
3 / 3.4 / 2.5
4 / 3.0 / 2.3
5 / 2.3 / 2.0
6 / 1.4 / 1.5
7 / 0.5 / 1.0
8 / -0.2 / 0.6
9 / -0.3 / 0.6
10 / 0.0 / 0.8
11 / 0.6 / 1.2
12 / 1.4 / 1.7
TABLE 2: SAINT JOHN, NEW BRUNSWICK
Time / Spring Tide Water Level (m) / Neap Tide Water Level (m)
0 / 4.5 / 4.5
1 / 6.3 / 5.6
2 / 7.7 / 6.3
3 / 8.2 / 6.5
4 / 7.8 / 6.2
5 / 6.7 / 5.4
6 / 5.1 / 4.4
7 / 3.2 / 3.3
8 / 1.5 / 2.5
9 / 0.5 / 2.2
10 / 0.7 / 2.5
11 / 1.6 / 3.3
12 / 3.2 / 4.4
TABLE 3: MOBILE, ALABAMA
Time / Spring Tide Water Level (m) / Neap Tide Water Level (m)
0 / 0.43 / 0.31
1 / 0.53 / 0.36
2 / 0.54 / 0.37
3 / 0.45 / 0.32
4 / 0.30 / 0.23
5 / 0.12 / 0.14
6 / -0.02 / 0.06
7 / -0.10 / 0.03
8 / -0.12 / 0.03
9 / -0.08 / 0.06
10 / 0.03 / 0.13
11 / 0.18 / 0.22
12 / 0.34 / 0.31
Analysis and Conclusions
1. Assume you are standing in a classroom that has a height of 2.5 meters. Imagine that the lowest water level for the spring tide is represented by the floor of the classroom. Relative to yourself and to the room’s ceiling, where would the highest water level occur for each of the three locations? Would these water levels change for neap tide?
2. Order the three locations of Boston, Saint John, and Mobile from greatest to smallest tidal range.
3. How do the maximum water level values on your graphs compare for the spring and neap tides?
4. Use pages 541-542 of the textbook to sketch the alignment of Earth, the sun, and the moon for spring tides and neap tides.
5. Even though the water levels of all three locations change drastically, the percentage by which the tidal range decreases from spring tide to neap tide is about the same for all three locations. Why do you suppose this is true?
6. Based on your graphs, how long would you expect the interval between high tides to be for each of the three locations?
7. Saint John is located on a long, narrow bay that is cut off from the Atlantic Ocean, while Boston is located on a relatively wide harbor that opens into the Atlantic Ocean. How do these facts help explain the difference in tidal ranges for Boston and Saint John?
8. Mobile is located on Mobile Bay, which opens into the Gulf of Mexico. Boston Harbor is comparable in size, but opens into the Atlantic Ocean. How do these facts help explain the difference in tidal ranges for Boston and Mobile?
Maps