Benguela Upwelling

Questions to Explore

• What is the extent of the Benguela upwelling?
• How are sea surface temperature and chlorophyll concentration in this region related?   What causes this relationship?

Data Frames for this Chapter

Sea Surface Temperature (MODIS)

Chlorophyll (MODIS)

Visualizations for this Chapter

Animation (Giovanni)

Scatter Plot (Giovanni)

Line Fit (Giovanni)

Scatter Plot (NEO)

Transect (NEO)

Location and Map Coordinates

Just off the western coast of South Africa lies the Benguela upwelling system.  Upwelling occurs when cold water from beneath the surface rises to the surface, bringing nutrients from the deep ocean.  Phytoplankton benefit from the increase in nutrients and grow rapidly as a result.  Therefore, both chlorophyll and sea surface temperatures are appropriate parameters to measure the scope of the upwelling. 

Animation (Giovanni)

Although this shows the large-scale upwelling, we can zoom in to see more accurate changes in chlorophyll and sea surface temperature.

Scroll down the Giovanni output page to set more specific parameters.

Coordinate System:

To see the change on a much smaller scale, zoom into the following coordinates:

Custom Color Scale:

For the sea surface temperature plot -

Under Edit Preferences, change the Color Scale to Custom.

Choose the Custom scale:         Min: 4

                                                   Max: 19

Color Palette:

You can also try out different color palettes to see how they display the data:  for example, change to the “Ocean” color palette.  The result of these steps is shown below.

Scatter Plot (Giovanni)

1. Select the area specified above.

2. Parameters:            Sea Surface Temperature (MODIS)

                                   Chlorophyll a Concentration (MODIS)

3. Temporal:    Begin Date = 2002, Jan

                       End Date = 2007, Dec

4. Select Visualization: Scatter Plot, Time-Averaged
5. Generate Plot

Line Fit (Giovanni)

1. Create a scatter plot for a small area of the Benguela upwelling using these  latitude-longitude coordinates:
2. Under Edit Preferences, choose Yes for Line Fitting
3. Record the equations and the r-value. 

Scatter Plot (NEO)

1. Use the following coordinates:
2. Select the following data sets:

   Sea Surface Temperature (MODIS) for August 2006

                               Chlorophyll a Concentration (MODIS) for August 2006   

3. Under Area, enter the coordinates used for the Giovanni example.
4. Click on ‘Zoom and Roam.’  Use the right click to zoom in and the left click to zoom out.  By holding and moving the mouse, you can roam the image.  Use this until you are sufficiently zoomed into the image.
5. Click Outline Region.  Using an irregular shape, outline the closest region to the shore.
6. Click Scatter Plot.
7. Make various scatter plots farther from the coastline. 

As in the Giovanni example, change the area to these zoomed coordinates:

Again, outline the area and create scatter plots.

Transect Plot (NEO)

1. Under Area, enter the zoomed coordinates above.
2. Click on ‘Zoom and Roam’ and then click Probe.
3. Click ‘Plot Transect’ 
4. Chose region to draw the transect.  Make sure to record the coordinates of this line.

Although hard to see, the temperature actually drops off 3°C (from 15°C to 12°C.)  Look closely near the red arrow to see the decrease in temperature which occurs right at the coast, where the upwelling occurs.  

Questions

• Using the Outline Region function, map the boundary of the upwelling according to the sea surface temperature and the chlorophyll.  What is the area of the upwelling?  What are the approximate coordinates?
• What does the scatter plot tell us about the relationship between temperature and chlorophyll?  Why does this relationship occur?  How strong is the relationship?
• The r-value is the correlation coefficient.  In other words, it shows how well the points fit a line.  R ranges from -1 to 1.  1 signifies a perfect direct correlation.; -1 signifies a perfect inverse correlation; and 0 signifies no correlation. What is the r-value for both Giovanni scatter plots?  Which data has a better fit and why?
• The relationship or slope between chlorophyll concentration and sea surface temperature varies based on the scale of the plot in NEO.  Why does the scale change over smaller areas?