Part 2—Take a Virtual Cruise across the Atlantic
Step 1 – Prepare to Gather Data from the North Atlantic Ocean
- To return to the initial map view, from the main drop-down menu, select Bookmarks > Zoom to Global Scale.
- Select the Overlays drop-down menu. Click Global Map Inset to turn it off (unchecked).
- Click the magnifying glass with a plus sign on it. Drag a zoom box that covers the North Atlantic ocean between North America and Africa.
- Once you've zoomed in, choose the arrow pointer tool on the tool bar to "put away" the magnifying glass and avoid accidental zooming.
- Click the Grid button (show/hide grid dialog) to load the topography information for this region.
- Once the grid is loaded, you'll see the Layer Manager and Global Grid Options dialog boxes. These graphics show information about how colors are used to generate the visualization from the numeric data. Make sure that Global Multi-Resolution Topography (GMRT) and GMRT Image are checked.
For now, minimize these dialog boxesdon't close them, or you will need to reload the grid.
When you use the zoom tool, GeoMapApp generates a request to its server to bring in higher resolution data for that area; the blurry look will clear up when the data are loaded. The speed of your Internet connection controls how long it takes to update the view.
Step 2 – Collect Depth Data along a Latitude Line
- Move your cursor across the image again. Notice that in addition to the latitude and longitude coordinates, the ocean depth is reported at the top of the GeoMapApp window. The depth value is shown as a negative numberthe value is the vertical distance from sea level to the seafloor.
- Collect depth data along the 32°N latitude line. Start at 80°W and record the depth every 200 km as you move to the east.
- Use the horizontal and vertical scroll bars to position the map image so that the zero point of the Map Scale is near 80°W and the tick marks align along the 32°N latitude line.
- Place your cursor at 80°W, 32°N and record the ocean depth at that location.
- Move your cursor 200 km to the east and record the depth at that location.
- When you reach the end of the scale bar, scroll the image over to reposition it. Continue collecting depth data every 200 km until you reach Africa.
Imagine that your cursor is a ship, taking a virtual cruise across the Atlantic. You'll head east from North America along the 32°N latitude line. On your cruise along this line, you'll stop every 200 kilometers to collect depth data. Begin at 80°W and continue until you reach Africa.
Step 3 – Graph your Data to Visualize the Seafloor Profile
- Use graph paper or a spreadsheet application to create a graph (profile) of your results. Put sea level (0) at the top and increasing depth values down to the bottom.
- Once you've created your graph, consider what the visual representation you've made actually means about the seafloor.
- What do the high and low points along your graph mean?
- Does your profile represent the actual shape of the seafloor? Discuss how the profile is similar to and different from the seafloor it represents.
- From the single profile you created (along the 32°N latitude line), what can you infer about the three-dimensional shape of the North Atlantic ocean?