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Island waters
East Caicos Island, from space. The contrast between the light blue shallow water and dark blue deep water marks a sharp difference (hundreds of meters) in water depth. The shallow marine regions include sand bars and tidal channels (just right of center).
Vast slick of cyanophyte algae visible from space. The algal cells coalesce in strings and clumps. As the cells age, they become buoyant . In calm weather, the cells aggregate into huge slicks. (Australia)
The East Caicos Island highlights the shallow tropical waters typical of the Bahamas region. The coastline of the island is low and swampy, and is also greatly influenced by the tides. Further offshore, the darker regions in the slightly deeper water mark sea grass and algae beds. In the photo at right, chains of clouds forming off islands and headlands, mark the downwind direction.
Is the Red Sea red?
No. Author E.M. Forster stated that the "exquisite corridor of tinted mountains and radiant water" was named Mare Rostrum (Latin for Red Sea) by early travelers because of the region's reddish mineral-rich mountains. It is surrounded by a dessicated and largely barren landscape, and its hot, salty waters contain beautiful coral reefs. For centuries its coasts were populated by poor artisanal fishermen, subsistence farmers and small traders. A 1646 chapter from English author and physician Sir Thomas Browne reports that Sir Walter Raleigh believed the unusual color of the water to be "no more then a seeming rednesse." Raleigh never saw the Red Sea himself, but noted from others' observation that the water varied, "in some places it is very green, in others white and yellow, according to the colour of the earth or sand at the bottome."
Scientist sampling a Trichodesmium bloom. The colors of the slick are sometimes vivid due to the photosynthetic pigments in the algae, including green chlorophyll and pruple phycoerythrin.
A more common source of the name is that the Red Sea is named not for the glowing color of its coastal mountains, but rather for an occasional bloom of the cyanobacteria, Trichodesmium erythraeum algae, which clouds and muddies the usually translucent blue-green waters. It often appears like groups of red and pinkish blankets on the surface of these waters.After the bloom, the Trichodesmium erythraeum dies die, and they turn the sea reddish-brown.
Cyanobacteria
During a "bloom" of cyanobacteria the appearance of a body of water can be drastically changed. Color is also not always due to pigments alone. Lakes in the Swiss Alps have been know to be turned blood-red by blooms of Oscillatoria rubescens because they have refractive pseudovacuoles (not bounded by a tonoplast membrane) rather than by excessive phycoerythrin. While the Red Sea may have gotten its name from periodic blooms of Trichodesmium erythraceum, the aquatic disaster, red tide, is not caused by cyanobacteria, but instead by dinoflagellates (Pyrrophyta).
Why are cyanobacteria colored? The relative abundance of phycobilin pigments explain the color of cyanobacteria en masse. Microscopically, the phycocyanin (blue) pigment in combination with the chlorophyll a and the accessory pigments lead to a bluish-green color...hence the common name: blue-green algae.Species of cyanobacteria differ in their ratios of phyocyanin and phycoerythrin.
Cyanobacteria such as Hammatoidea, Heterohormogonium, Albrightia, Scytonematopsis, Thalopophila, Myxocarcina and Colteronema give thermal springs and geyser pools some beautiful color patterns from red to purple and the complete visible spectrum of colors between.
Frequently terrestrial "blooms" produce a gooey slime that is black in color; black because virtually all wavelengths of light are absorbed by the combination of chlorophyll and the accessory pigments. A disease of coral heads is caused by a cyanobacterium (Phormidium corallactinium) and is know as "black line disease." Moreover, the rocks in the supralittoral fringe (splash zone) of many tropical shores are covered with epilithic (Scytonema, Gleocapsa and Pleurocapsa) or impregnated with endolithic (Mastigocoleus) cyanobacteria . This zone is often called the "black" zone because of the color of these cyanobacteria.
The first cyanobacteria (Cyanophyta) appear in fossils about 2.8 billion years old. They have different biochemistry than Archaebacteria andwere the first dominant organisms to use oxygenic photosynthesis. Their photosystem splits water and uses its electrons and protons to drive photosynthesis. As a byproduct of this new reaction system, oxygen gas (O2) was produced for the first time in abundance. This was a fundamental change for Earth's atmosphere and its impact was observed in all surface layers. As cyanobacteria increased the oxygen in the atmosphere, the iron in surface sediments was oxidized into red ferric oxide.
In ancient sedimentary rock, the transition to an aerobic atmosphere is marked by a shift in the color of the layers from gray to red. These cyanobacteria obviously marked the planet in a very permanent way and paved the way for the subsequent evolution of oxidative respiratory biochemistry. The change in rocks occurs at about 2.5 billion years ago. This change marks the end of the Archaean Era of the Precambrian Time.
Additional information
Most vibrations between atoms absorb only at very low energies in the infrared. Just as the pitch of a vibrating string is raised if the mass of the string is reduced and the tension applied to the string is increased, so the highest-frequency vibrations occur with the lightest atoms, as with hydrogen, when most strongly bonded, as with hydrogen bonded to oxygen in water.
Vibrational states as well as the related rotational states also can modify the energy of the electronic excitations of the previous sections (Mechanisms #1 & 2), and are involved in the violet color of the iodine vapor, the reddish-brown of bromine, and the green of chlorine. Emeralds are green because trapped water molecules cause vibrational absorptions. Read more in the page about Emeralds.
Purple iodine vapor is produced by heating iodine crystals (combined electronic-vibration-rotation color).
The bluegreen light of natural gas burning on a kitchen burner emitted by an oxygen-rich gas flame as seen on a kitchen range also involves such combination vibrational, rotational, and electronic excitations in the unstable molecules CH and C2.
