Cold sea-surface temperatures (SST), as well as high productivity (from
elevated nutrient concentrations) are possible indications of strong upwelling
currents. The images below show SSTs for northwest Africa for July (left-side
image) and January (right-side image) of 1982. The color bar at the base
of the images shows the temperature scale in degrees Celsius.
[NOTE: degrees Fahrenheit = 1.8 (degrees Celsius) + 32]
The strength of upwelling currents often changes during the year, as
wind direction and intensity varies from one season to the next. For example,
along the California coast, upwelling is strongest in the summer, when winds
are typically strong and consistently from the north (the direction that
best drives surface water away from the coast, thus inducing the upwelling
currents).
(a.) Based on the satellite images below, would you say that upwelling
currents are strongest in January or in July along the coast of northwest
Africa? Speculate about possible causes for this seasonal variation. Look
at a world map to see the latitudinal position of Africa. The currents exercise
contains a map
of latitudinal variation in atmospheric winds (generalized).
(b.) Compare these images to the global
productivity diagrams in the previous section. What do these images
suggest about the seasonal variation in equatorial upwelling in the world
oceans? Both of these images are from the eastern sides of oceans and
both show the "normal" condition that occurs there. In part II
of this exercise we will examine a variation of equatorial conditions in
the eastern Pacific called "El
Niño".