THE OCEAN FLOOR: SEA FLOOR TOPOGRAPHY, SEDIMENT THICKNESS. A. Data Sets LAB#3 EXCEL GRAPHING INSTRUCTIONS AND AGE OF CRUSTAL ROCKS.

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1 GEO130 OCEANOGRAPHY FALL 2009 LAB#3 EXCEL GRAPHING INSTRUCTIONS THE OCEAN FLOOR: SEA FLOOR TOPOGRAPHY, SEDIMENT THICKNESS AND AGE OF CRUSTAL ROCKS. A. Data Sets We will analyze subsets of three oceanographic data sets. 1. Sea floor topography -depth from mean sea level to the ocean floor, either crustal rock or sediment also called bathymetric data. A combination of sounding data and depths gravimetrically estimated and verified against available sounding data. See diagram below. DATA SOURCE: 2. Sediment thickness the amount of stuff covering solid rock on the sea floor. This is actually the minimum thickness based on sounding data. Another way of looking at it is as the minimum depth from the sea floor to oceanic crust. See diagram below. DATA SOURCE: 3. Crustal age the age of the rocks on the sea floor. DATA SOURCE: linked through Data points per o Lon/per 360 o Data points per o Lat/per 180 o Global total number data pts Topography 31/ / ,272,800 Sediment 12/ /2161 9,337,682 Thickness Crustal Age 10/ /1800 6,480,000

2 DATA SUMMARY DIAGRAM Lab 3 Data Sets Indian Ocean approx. 30 o S Lat Atlantic North approx. 30 o N Lat Atlantic South approx. 47 o S Lat Pacific Far North approx. 54 o N Lat Pacific Western North approx. 13 o N Lat Pacific Eastern North approx. 13 o N Lat Pacific Western South approx. 30 o S Lat Pacific Eastern South approx. 30 o S Lat

3 B. A First Look 1. Peruse your data sets (there will be three data sets per location). Each is along approximately the same line of latitude and each begins and ends with the same longitude points. 2. Find it on the map located in the first worksheet. Note the units of longitude, if your location spans 180 longitude you will, have to use the 360 scheme to make your graphs 3. Get a feel for the data. What does the reference map say about your data set? Apply what you know about plate tectonics, sediments and the topography of the sea floor. 4. What do you know about how plate tectonics works that is relevant to your data set? 5. What do you know about the geography of plate tectonics that is relevant to your data set i.e. what major ocean floor features are in the geographic area of your data set? C. THE GRAPHS YOU WILL CREATE You will create three separate graphs: Sea floor topography, Sediment thickness and the age of the crustal rocks. All data are in meters. Latitude and longitude are in degrees and decimal degrees. I will go through an example in class and there will be class time to work on the lab. 1. Sea floor topography -You are plotting the distance below or above sea level. If Z ( z is universally used as the elevation axis in earth sciences) is negative the value is the distance from sea level down to the sea floor. The sea floor can be either sediment or crustal rock. There is no missing data in these data sets. 2. Sediment thickness is the minimum thickness from the sea floor to crustal rocks. It is never negative, some data may be missing which is indicated by a thickness of meters ( over 328,000 feet far greater than the thickest sediments in the ocean). 3. Crustal age is the age millions of years of the oceanic crustal rocks either exposed in sediment free areas, or buried under the sediment. A value of 300 indicates continental crust; a value of 999 indicates no data. D. Two Echo Sounding Examples Echo sounding uses sound pulses, just line sonar in submarines to determine how far it is to the bottom and in addition determine the structure of the sea floor. Today satellite radar and gravity are used to determine bottom topography. The first example shows the continental shelf and continental slope with a scattering layer. The scattering layer can be caused by many things, a density discontinuity from temperature or salinity differences, schools of fish. Most often this is referred to as the deep scattering layer or false bottom and is most often dense populations of marine animals. The second example shows a sea floor sounding revealing layers of sediment and buried hills and valleys. A fathom is often used to measure water depth, it is 6 feet. In modern oceanography depth measurements are made using the metric system,so you will be using meters. 1 meter = = feet.

4 D. Using MS Excel 1. The three graphs you will do will have LONGITUDE on the horizontal axis and depth/elevation, sediment thickness or crustal age on the vertical axis. 2. In MS Excel we will use XY (Scatter) graphs. 3. Select the upper left data cell by left clicking. 4. Scroll to the bottom of the data set columns and while holding <SHIFT> left click on the lower right data cell. This will select all data in the two columns. (MAC users???)

5 5. Left click on the graph icon at the top or Insert >> Chart 6. Select XY (Scatter) and click Finish. 7. Immediately delete the box that says Series 1 by left clicking and striking the delete key. 8. Double left click on any longitude value along the horizontal axis to bring up the Format Axis dialogue box. 9. Select the Scale tab and set the minimum and maximum values. These must correspond to the minimum and maximum longitude values of the data set (in whole degrees, round to the nearest integer). 10. Select the Patterns tab and change the horizontal axis to the thickest of the three line choices. For the bathymetry data you may want to make this axis blue to remind you of sea level by changing the color. 11. Select the Font tab and select the font of your choice. I use Arial Black. 12. Double left click on the data line you graphed to bring up the Format Data Series dialogue box. 13. Under the Patterns tab select none for Marker and for Line change the line weight to the middle of the three thickness choices. 14. Double left click on any elevation/depth value on the vertical axis to activate the Format Axis dialogue box. 15. Under the Patterns tab change the line weight to the thickest of the three choices and under the Font tab select the same font you selected for the horizontal axis. 16. SAVE YOUR WORK. 17. You should have a graph that looks something like this but the line will vary between data sets E. FINISHING TOUCHES (NOT OPTIONAL) 1. Right click on the anywhere on the chart to bring up the Chart Options dialogue box.

6 2. Under the Titles tab enter a chart title and the units for the axes. For topography - Depth/Altitude (meters), for sediment thickness - Thickness (meters) and for Crustal age - Age (millions of years). 3. Under the Gridlines tab be sure Major gridlines is checked for both the X- axis and the Y-axis. 4. Left click on the title and make it bigger and bolder and add geographical information. 5. Your graph should now look something like this: SEA FLOOR TOPOGRAPHY Antatctic Peninsula 66 South Latitude 120 East to 20 East Longitude Depth/Altitude (m eters) Longitude E. DO IT AGAIN FOR SEDIMENT THICKNESS AND CRUSTAL AGE There are a few differences in these data sets and you have to adjust the graph to accommodate the differences. 1. The sediment thickness data sets may have missing data and indicates missing data. 2. Set the vertical axis scale to just greater than the greatest sediment thickness in Step #14. This will eliminate the value of from the graph. 3. The crustal age data sets have two values you do not want on the graph. 300 represents continental crust and 999 represents missing data. Set the vertical axis scale on the crustal age graphs to just greater than the oldest rocks indicated so the values for continental crust and missing data do not show.

7 F. MAKING THE GRAPHS THE SAME SIZE 1. Select a graph and stretch it so it spans the width of your computer screen. 2. Select the second graph and stretch it to the same width. 3. Repeat this for the third graph. G. PRINTING THE CHARTS FOR YOUR LAB REPORT 1. Right click on a graph. 2. Select chart window. 3. Right click on the top window border and select Page Setup. Page Tab Print the graph in Landscape orientation on letter-size paper using the maximum resolution ( Print Quality ) available for your printer. Margins Tab All margins top, left, bottom and right set at 0.75 Chart Tab Select Scale to fit page. Do this for each of the three graphs.