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Each year trillions of scaly, one-celled marine plants called
coccolithophores slough off their microscopic plates and dump
more than 1.5 million tons of limestone dust (calcite, CaCO3)
into the sea. While these plants live in the upper layers
of the ocean, the microscopic plates they create, known as
coccoliths, could have a huge impact on the atmosphere.
William Balch at Bigelow Laboratory in Maine and Howard Gordon
at Miami University plan to use MODIS to scan the oceans for
coccolithophores. They will first locate large areas of coccolith
infested ocean, which are characterized by highly reflective
turquoise colored waters. The team will then comb through
the data to discern the amount of chlorophyll and the number
of organisms in each area.
In all vegetation chlorophyll is the chemical that absorbs
sunlight and converts it into energy. This process does not
soak up all the light from the sun, but only certain colors
(wavelengths). The rest of the radiation, which usually gives
plants their green color, is reflected.
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Alaska
and the Bering Sea from SeaWiFS on April 25, 1998.
The bright aquamarine water is caused by the huge
numbers of coccolithophores. This bloom was present
in 1997 and 1998, and appears to be re-occuring in
1999. (Image courtesy Norman Kuring, SeaWiFS Project)
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Like many plants, coccolithophores are known to absorb dark
blue light and reflect green light. The coccoliths surrounding
them reflect nearly all types of invisible light. So when the
coccolithophores move into an area of the ocean, the waters
turn white with a tinge of green. In order to determine the
coccolithophore's numbers, the scientists look at only the blue
and green radiation coming off the ocean (MODIS bands 3 and
4). They then enhance the intensity of each of their readings
to compensate for the glare from the coccoliths and form a ratio
of blue to green light. The result gives them a measurement
of the amount and location of chlorophyll in the sea. Generally
the lower this ratio is, the more coccolithophores there are
in the area taking in blue light. And for each coccolithophore
there are at least thirty coccoliths either on or beside the
plant.
Over the next few years, the scientists hope to use these data
to determine whether the coccolithophores are having a positive
or negative effect on the atmosphere. The plants seem to help
the environment in the long term. Coccolithophores make their
coccoliths out of one part carbon, one part calcium and three
parts oxygen. So each time a molecule of coccolith is made,
one less carbon atom is allowed to roam freely to contribute
to greenhouse gases and global warming.
The coccolithophores' short-term effect on the environment is
somewhat more complex. The chemical reaction that makes the
coccolith also synthesizes a carbon dioxide molecule, a potent
greenhouse gas, from the oxygen and carbon already in the ocean.
While much of the gas is sucked back in by the coccoliths (all
plants take in carbon dioxide for food), some of it may escape
into the atmosphere and immediately become part of the greenhouse
gas problem. In the short term this carbon dioxide could cause
the upper layers of the ocean to become more temperate and stagnant,
which would increase the number of coccolithophores and carbon
dioxide.
For now the scientists studying this phenomenon are uncertain
as to how much of the coccolith carbon dioxide is released into
the air. They are certain however that the coccolithophoreså
long term benefit for the environment far outweighs the potential
short-term problem.
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