Chapter 1: Interactions of ocean currents and biology
The scene shown below is an image from the Coastal Zone Color
Scanner (CZCS) archive, centered on the island of Tasmania.
Tasmania is a large island located south of the eastern coast of the
Australian continent. The currents in this oceanic region are
particularly strong, and as they interact with the topography of the
ocean bottom and the land mass of the island, a complex pattern of swirling
motion (which oceanographers term eddies, rings, and vortices) is the
result.
CZCS image of Tasmania and surrounding waters, obtained
on November 27, 1981. The southern coast of Australia is at the top
of the image, separated from Tasmania by the Bass Strait.
The CZCS was an instrument carried on the NIMBUS-7 satellite.
It was designed to make precise measurements of the intensity of
radiation in different portions (bands) of the color spectrum. These
measurements indicated how much sunlight was being absorbed and
how much was being reflected at (and from some depth beneath)
the ocean's surface. The small living plant cells that exist near the ocean
surface--called phytoplankton--contain chlorophyll, the pigment that
allows them to convert sunlight and carbon dioxide into the organic
matter of their cellular structure. The more chlorophyll that is
present at the surface, the "greener" the reflected light will be.
At the same time, more red light will be absorbed. Thus, the measurements
made by the CZCS allow a view of the patterns of phytoplankton in
the ocean.
The image of the oceans around Tasmania is a "false color"
image. False color means a color scale is used to indicate the
approximate concentrations of phytoplankton in the water. In this
color scale, yellows and reds indicate more phytoplankton, and
greens and blues indicate less. Dark blue and purple indicate very
low concentrations of phytoplankton in very clear ocean water.
It is obvious that the current interactions around Tasmania are
very complex, and they shape the phytoplankton growing near the
island into patterns that are constantly changing. The complexity of
the patterns and the fact that they are always in motion makes it
very difficult for the traditional methods of oceanography,
conducted from a stationary ship, to make accurate estimates of the
amount of phytoplankton in a given oceanic region. It is also
difficult to determine how rapidly the phytoplankton in an entire
region are growing. The process of photosynthesis in plants
converts light and carbon dioxide to carbon in the cell. The rate at
which carbon is produced by plants is called primary productivity,
and it is one of the fundamental variables measured by biological
oceanographers.
If scientists on a ship were trying to survey the waters around
Tasmania, they could travel in a certain direction for days in clear
water, and only a few kilometers away there might be a patch of higher
primary productivity that the ship never encountered. On the other
hand, a ship could travel in high productivity waters and not
encounter any areas of low productivity. In either case the scientists'
picture of the biology around the island would be inaccurate. It
is only by taking a view from space that the biological patterns in
the whole region can be observed and measured, presumably allowing more
accurate estimates of primary productivity.
There are many different processes that influence the growth
and movement of phytoplankton in the ocean. In subsequent sections,
some of the most important processes will be discussed and
illustrated with other images from the CZCS archive.
Chapter 2: The Benguela upwelling zone
Index: Classic CZCS scenes
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Atmos Composition
