What is sea colour?
The "colour" of the sea is determined by the interactions of light with the water.
The substances in seawater which most affect the colour are, phytoplankton, inorganic particles, dissolved organic
chemicals, and the water itself. Satellites using instruments that are more sensitive than the human eye, can
measure a wide array of colours, which reveal the presence of varying amounts of phytoplankton, sediments,
and dissolved organic chemicals.
What are phytoplankton?
Phytoplankton are the microscopic plant life that float in the lighted surface waters and form the base of the marine
food chain. This plant life is the primary food and energy source of the ocean’s ecosystem. When a great number of
the microscopic plants are concentrated in an area, the colour of the sea surface will change. This is called a "bloom."
Phytoplankton convert nutrients into plant material by using sunlight with the help of the green pigment chlorophyll.
The chlorophyll pigments in the plants absorb light, and the plants themselves scatter light. Together, these
processes change the colour of the sea. Very productive water with a lot of plankton appears blue-green. Very pure
(barren) water appears deep-blue, almost black.
The connection between sea colour and phytoplankton
When wind-driven surface currents carry water away from continents or when underwater obstacles disrupt circulation
patterns, an upwelling of deep, nutrient-rich sea water occurs. These cold waters have high concentrations of nutrients
and when they mix with warm surface waters, phytoplankton grow rapidly. Because they form the basis of the food chain,
phytoplankton blooms attract feed fish which, in turn, draw fish species such as tuna, marlin, and other species which
are the target of sport and commercial fishermen. If phytoplankton blooms are occurring in a location, the fish species
of interest to commercial and sport fishermen are not far away. Also because phytoplankton drift with the water,
patterns in sea colour can also be used to study sea currents.
By using sea colour images to locate areas rich in phytoplankton you can work out where the fish are feeding.
What is the trial product?
Through an arrangement with the Remote Sensing Unit of the Western Australian Land Information Authority (Landgate),
we will be trialling a free sea colour product on seasurface.com until further notice. In the trial product,
areas of water that are rich in phytoplankton are shown in green shades. Areas that contain little or no phytoplankton
are shown in dark blue. At the end of the trial we will be announcing the charges for the continued access to this product.
The sea colour images are processed estimates of the average chlorophyll concentration in each 500 metre by 500 metre
area of ocean. Chlorophyll is the active ingredient in the phytoplankton.
Sea colour information is only available from the Terra and Aqua satellites and only from day-time passes
(because even satellites have trouble seeing colour In the dark!). So in practice this means that at most there will be
2 sea colour datasets per day over each part of the Australian coast. Some days there may be none at all.
Future plans
The trial product is a simplified version of what we are hoping to introduce on seasurface.com if there is sufficient
interest and if it is economical to do so. To see what we have in mind for the future, click on one of the images below:
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| GIF animation:
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Explanation of the Animations
These animations are a mock-up of the display that we are intending to provide for a future sea colour/sea surface
temperature product. In the future system, the slide control at the bottom of the image window will allow you to gradually change from
a display showing just sea surface temperature to one just showing sea colour. By smoothly changing from one
display to the other, it is easy to see the spatial relationships.
Relationship between sea colour and sea surface temperature
Notice for example that the 22.5°C water shown in red at the top of the animations is barren of phytoplankton and
is therefore not likely to contain many fish. And notice that the band of ENE-trending water rich in phytoplankton
in the centre of the animations (which is shown in green in the sea colour image) is confined to the cooler water
(shown in light blue in the sea surface temperature image).
Remember: In the sea colour images:
Green areas contain the most life, while the blue areas are nearly empty of life.
It is as simple as: more food and the right temperatures = more fish.
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