Assignment Task: GeoMapApp Exercise
In this exercise, you will explore CaCO3 deposition in both the modern and ancient ocean. Make two base maps:
1) A region of the North Atlantic Ocean north of the equator (anywhere between 10N-40N, avoid the margins if you can);
2) A region of the South Pacific (anywhere between 10S-40S, avoiding the margins). - Using GeoMapApp, include the core locations of the Archer, 1999 coretop dataset (Datalayers>Geochemistry>Seafloor Composition>CaCO3... > Archer (1999)).
Use the color tool to color points by CaCO3%. Please print these maps and use a color pencil (or crayon) to color/fill in the general distribution.
Problem 1: What is the general relationship you observe concerning the dominant control of CaCO3 percentages?
Problem 2: Now copy all data from the data-cells area for each of your study areas (select all cells in GMA window and paste into excel or some other analysis program). Make a plot of CaCO3% (x) vs water depth (y) for each basin. [Note: this works best if you use a region large enough to produce ~100-150 coretop values.] The Lysocline and CCD are sedimentary indicators of the ocean chemical process of dissolution. The lysocline is where CaCO3 'starts to dissolve', whereas the CCD is sometimes operationally defined by <10% CaCO3.
A) What are the approximate depths of the lysocline for the Atlantic and Pacific?
B) What are the depths of the CCD in the Atlantic and Pacific?
C) Now for each basin, plot CaCO3% (x) versus "dCO32--" (y) (which is bottom water under saturation, ?CO3 2- ). Comment on the relationship you observe in each basin, what does this tell you about where CaCO3 accumulations in the world oceans?
D) Why do you observe the trends you see in (2.2c)?
Problem 3: Clear the workspace using the "close" button. Now upload Datalayers>Geochemistry>Seafloor Composition>Calcium Carbonate (CaCO3)...> Ruddiman and Farrell (1992) compilation. (downcore CaCO3% measured at core sites around the world). Use the zoom tool to zoom in on the 25N - 60N region of the North Atlantic. Pick 3 (or more) core sites between 3000-5000 m and plot %CaCO3 vs. depth (using Excel or some other program). Click on a core top and download the data and be sure to pick cores with lots of downcore data (the columns of data are first cm depth in the core and then % CaCO3). A good example is core V30-94 at 35 N, 37 W and 3685 m with over 900 cm of data. The observed downcore changes at any core site mostly reflect changes in CaCO3 preservation due to variable bottom water dissolution from glacial-interglacial deep circulation changes (the last glacial maximum was 20 ka ago and last interglacial 120 ka). Sedimentation rates are typically 2-4 cm/ka, so ~1 meter (or 100 cm) is about 25-50 ka in time.
A) Do these dissolution cycles affect the full 3000-5000 m water depth range? What are your general observations?
B) Explore core data in this region to find the depth at which the cycles start to appear. Why do you think changes in %CaCO3 exist and why do you think they exist at certain depths and not at others? Basically, why do you think all of these changes exist?
C) Any ideas on how to test your hypothesis?