WELCOME BACK: Procedure continued from Investigations Manual, Investigation 2B.
In the first part of this investigation, we examined the vertical cross-sectional profile of the ocean bottom in the continental margin. In this part, we utilize bathymetric data to take a closer look at the profile of the continental margin off the Southeast United States and observe how ocean bottom topography can influence the direction of flow of surface ocean currents.
Image 1 is a bathymetric chart showing the depth of the ocean bottom in meters below mean sea level off the Southeast U.S. coast from Florida northward to North Carolina. (This image was obtained, with minor modification, from NOAA's Ocean Explorer that may be accessed via the DS Ocean website under "Earth System." To find the original chart, click on "Gallery," then "Maps," and then "Collection 1 – Atlantic." Scroll down to "Southeast coast bathymetry," and click on the image. Latitude is plotted on the left side of the chart and longitude is plotted across the top.
Note that contour lines of ocean depth are drawn at intervals of [(10)(100)(1000)] meters for depths shallower than 1000 m and at intervals of [(10)(100)(1000)] meters for depths greater than 1000 m.
The shelfbreak (labeled in Image 1) where the continental shelf ends and the continental slope begins is indicated at a water depth of _______ meters.
From North Carolina southwestward to south Florida, the continental shelf is [(uniform)(non-uniform)] in width.
Plot a point at latitude 33 degrees N, longitude 78 degrees W, and at latitude 32 degrees N, longitude 77 degrees W. Using a straight edge and pencil, draw a line connecting the two points. Between the two points, the ocean bottom slopes downward toward the [(southeast)(northwest)] by about [(140)(1400)(14,000)] meters.
A gradient is a rate of change over distance and is always measured in the direction of greatest change per unit distance. Along the continental slope, the gradient of the slope of the ocean bottom is always measured [(parallel) (perpendicular)] to the contour lines and is steepest where the contour lines are [(farthest apart) (closest together)]. The distance between the two points you plotted on the map is 146 km. Since the line you drew essentially meets gradient criteria, the gradient along the line is about [(0.96) (9.6) (96)] m/km.
Off the coast of North Carolina and South Carolina, features that would indicate tectonic activity (e.g., deep-sea trench associated with subduction) [(are)(are not)] present.
Let's take a look at another type of representation of the bathymetry of the ocean floor off the Southeast U.S. Go to the DataStreme Ocean website and under "Geological," click on "Bathymetry." These images are color coded to portray the relief of the Earth's surface above (+) and below (-) mean sea level and are provided by NOAA's National Geophysical Data Center. Greens, yellows and browns depict land areas. Images were generated from digital databases of seafloor and land elevations on a 2-minute latitude/longitude grid. On the global map click on the 45 degree by 45 degree square that includes the Southeast U.S. Click on the image again for greater resolution. Use the image scroll bars if necessary to view the same area as in Image 1.
The color-coded bathymetric map indicates that the shelfbreak off the coasts of Georgia to North Carolina is oriented [(east - west) (northwest - southeast) (southwest - northeast)]. This orientation [(is)(is not)] consistent with the bathymetric contour pattern in Image 1.
The color-coded bathymetric map indicates that portions of the [(Blake Plateau)(Bahama Banks)] shown in Image 1 rise above sea level as islands.
The gray band in Image 1 marks the typical path of the warm Gulf Stream, a surface ocean current in the western North Atlantic basin that flows north and northeastward generally parallel to the Southeast U.S. coast. The "SST Front" is the western boundary of the Gulf Stream. (SST is the abbreviation for sea surface temperature.) The bathymetric chart of Image 1 indicates that the Gulf Stream flows [(over the continental shelf) (as far west as the continental slope)].
Variations in the width of the continental shelf means that the Gulf Stream flows closer to the coastline of [(Georgia)(south Florida)].
Go to the DataStreme Ocean website and under "Physical & Chemical," click on "Gulf Stream Current." Displayed are recent maps of current velocities of the Gulf Stream color-coded in meters per second (m/s). Current velocities are derived from near real time data acquired by radar altimeters onboard four Earth-orbiting satellites. The location of the Gulf Stream as shown in Image 1 [(is)(is not)] generally consistent with the pattern of observed Gulf Stream current velocities.
This investigation demonstrates that ocean bottom topography—represented by either contour lines or color-coding—provides information that is useful in inferring the geological processes operating along the continental margin. For example, ocean bottom topography indicates whether or not the coastline is tectonically active or passive. Furthermore, in this investigation we found that ocean bottom topography can influence the location of ocean currents such as the Gulf Stream.
Self-Assessment Revisited: Respond to the statements below. Compare your responses now with those you made at the beginning of the investigation. Has learning taken place?
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True, False |
Confidence |
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The ocean drops off rapidly from shore into a deep, flat basin. |
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The vertical profile of the continental margin to ocean basin is the same along both the West and East Coasts of North America. |
Professional Practice Transfer:
Driving Question: State an additional Driving Question appropriate to your classroom that you have conceived as the result of conducting this Investigation.
Implementation: Describe how you would use what you have learned in this investigation to implement inquiry-based learning experiences for your students.
Place the answers to questions from Investigations 2A and 2B on the Investigations Response Form linked from the DataStreme Ocean website.
Faxing Instructions: After completing this week's investigations, fax the following pages to your LIT mentor by Monday, 6 February 2006, or as coordinated with your mentor:
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