Colour-rich Plankton Bloom off Argentina
Saturday, 21. November 2009, 09:55:13

The colour streaks across the ocean in the image above are from a large phytoplankton bloom. Phytoplankton are plant-like organisms that live in the surface waters of the ocean. The dark blue and greenish colours are from chlorophyll. Chlorophyll is a green pigment found in most plants, algae, and cyanobacteria. Its name is derived from the Greek χλωρός (chloros "green") and φύλλον (phyllon "leaf"). Chlorophyll is vital for photosynthesis, which allows plants to obtain energy from light.
The clear, lighter blue colours on the other hand are not from chlorophyl, but probably from coccoliths or coccolithophores. Coccoliths are individual plates of calcium carbonate formed by coccolithophores (single-celled algae) which are arranged around them in a coccosphere. A large variety of these tiny microorganisms exist. Fossils of coccoliths constitute the bulk of chalk.Phytoplankton grow best in cool waters, where the temperature difference between the surface and the ocean’s depths is small enough to allow nutrient-rich deep water to mix with surface waters (upwelling). A few different factors may be contributing to the bloom seen in this image (The Moderate Resolution Imaging Spectroradiometer (MODIS) on NASA’s Terra satellite captured this image.). First, a cold current, the Falkland Current, sweeps north from Antarctica along the coast of Argentina. It flows northward along the Atlantic coast of Patagonia as far north as the mouth of the Río de la Plata. This current results from the movement of water from the West Wind Drift as it rounds Cape Horn. It takes its name from the Falkland Islands. Second, winds often drive upwelling along the continental shelf. Both the current and upwelling chill the South Atlantic in this region, making it possible for nutrient-rich deep water to reach the surface.
At the same time large amounts of nutrients are supplied from rivers like the Colorado River, seen behind the delta at the top of the image, where sediment suspended in the water is clearly visible. Some dry sediment is also blown into the sea by winds.
With access to nutrients and increasing springtime sunlight, phytoplankton thrive, developing into large blooms. There are probably many different kinds of phytoplankton growing in the waters off Argentina, accounting for the wide variations in color. Phytoplankton are the base of the marine food chain. Regular blooms such as this one make coastal Argentina a rich fishing ground.
The width of the image covers about 1000 km.
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