"Ocean bottom topography" is also known as bathymetry ("measurement of the depth of of large bodies of water")

On-line maps of "Measured and Estimated Seafloor Topography" are available from Scripps Institute of Oceanography, the National Oceanic & Atmospheric Administration, and Lamont Doherty Earth Observatory.

• These digital bathymetric maps were created by combining ship depth soundings with high-resolution marine gravity data from Earth-orbiting satellites.
• At this website, you can get a map of any part of the world's ocean by clicking on your area of interest.
• The data maps are color-coded for easier interpretation.

At right (>>>) is a view of bathymetry from Nova Scotia to Cape Hatteras, North Carolina. The continental margin extends from the shoreline to the deep-ocean basin. The deep ocean is shown in blue and reaches about 5000 meters depth.

• The continental shelf
  • A gently sloping surface that extends from the coastline to a marked increase in offshore slope
• The continental slope
  • A relatively steeply sloping surface found seaward of the shelf
• The continental rise
  • A gently sloping surface at the base of the slope

Let's focus on one area on the continental margin, the Gulf of Maine (its "corners" are shown as white, above ^^^ ). A detailed view of Gulf of Maine bathymetry is shown in black-and-white below (VVV).

This a contour map. Its lines join points of equal depth.

• Because black-and-white contour maps can be somewhat confusing to interpret, many oceanographers prefer to use color-coded maps to look at bathymetry data.
  • Click here to see another example of color-coded bathymetry from the Gulf of Maine.
  • See a Gulf of Maine bathmetry "fly-by" animation.

1. Visit the "Measured and Estimated Seafloor Topography" website.
   • Look at the bathymetry data from the following areas:
     • Western Pacific Ocean (near the Philippines and Japan)
     • Western Indian Ocean (off the east coast of Africa and south of India)
     • North Atlantic Ocean (off the U.S. east coast)
   • Is the bathymetry of the North Atlantic more similar to that of the Western Pacific Ocean or Western Indian Ocean?
   • Would the floor of the North Atlantic's be better described as mostly an "innie" or an "outie"?
     • BONUS QUESTION: The bathymetric maps at this website were created by "combining ship depth soundings with high-resolution marine gravity data from Earth-orbiting satellites."
       • How can marine GRAVITY data help to determine the depth of the sea floor??!!
2. Review the descriptions of the three zones within a typical continental margin.
   • Again look at the color-coded image of the bathymetry between Nova Scotia and Cape Hatteras.
     • Can you identfy:
       • the continental shelf?
       • the continental slope?
       • the continental rise?
         • [You may wish to print the image and trace these features onto it.]
3. Look at the map below (VVV) that shows bathymetry off much of North America.
   • What varies more:
     • the DEPTH of the continental shelf or the WIDTH of the continental shelf?
   • Is the continental shelf off of New England's coast relatively narrow or wide?
     • Can you guess how having this type of continental shelf might affect currents and fish population?
   • Is the continental shelf closest to where you live relatively narrow or wide?
     • Can you guess how the width of "your" continental shelf might affect currents and fish population?

4. Print a black-and-white contour map of Gulf of Maine bathymetry:

• Click here to get the small version of the map.
• Click here to get the large version of the map.
  • Using colors like those shown on this depth scale, trace over the CONTOUR LINES ONLY.
  • [NOTE: The maps do show depth below sea level although the contour lines are not marked as negative numbers.]
  • [HINT: Not all colors will be used!]
• Compare the black-and-white contour map with your color-coded map.
• Which map makes it easier to distinguish relative depths in the Gulf of Maine?
• How would you describe Georges Bank: relatively shallow or relatively deep?
  • The color-coded scale for the global "Seafloor Topography" map was created to show bathymetry from sea level to greater than 7000 meters depth.
  • The depth scale provided for the Gulf of Maine (just above, ^^^) is altered from that map.
    • Can you name three or more changes between the two scales?
    • Why was it a good idea to use a different color scale for the Gulf of Maine bathymetry map?

5. Now that you've gotten familiar with global bathymetry data, which do you think is shows more variation -- or change -- from sea level:

• Mt. Everest (highest land elevation) or the Mariana Trench (deepest ocean trench)?
• Why did you choose this feature?
  • Click here to see a color-coded map with arrows that point to Mt. Everest and the Mariana Trench.
    • Does this help you to answer the question?
    • Why or why not? [If you need more help discovering which of these features has more variation from sea level, you may want to check an atlas or world almanac.]