About Amy Expertise I love understanding how things work, especially when it comes to living
things. I`ve spent most of my life studying science and love passing on
this knowledge to kids. I currently work in a children`s science museum
where I`ve designed science exhibits on all sorts of topics; including
predators, music, weather, water, technology and much, much more! I`m
happy to answer questions about anything you have problems with at
school or help you with science projects. Also, I can help teachers
with ideas for classroom activities. Please note that I don`t answer
homework questions.
Experience I have an honours degree in Biochemistry and work as a science communicator for the National Science and Technology Centre in Australia.
Question Why is the sea water turquise in some areas and dark in others.
Thanks,
Ken
PS. 1st year of College
Answer Hi Ken,
the colour of sea water is based on a number of factors including the amount of phytoplankton in the water, the weather and the amount of mud in the water and.
The sea appears to be blue for the same reason that the sky looks blue. Sunlight, composed of electro-magnetic radiation ranging in colour from red to blue, is scattered by particles suspended in the water. The shorter blue wavelengths scatter more effectively and are absorbed less quickly than the longer red and orange wavelengths. Seawater appears blue for about 100 feet under the surface although a small percentage of undetectable blue light remains in the water down to the 600 foot level. At about 400 feet, colour becomes indistinguishable and shadows disappear. After 600 feet, light absorption is so complete that the ocean appears black.
Because the sea is a mirror of the sky, clouds or a sunset can further alter the water's colour. An overcast day can change a bright blue lake to a steely grey.
Light absorption explains blue water, but why is the Red Sea red and the Yellow Sea yellow? These colours are caused by microscopic organisms, silt, and mud, suspended in the water.
Near some coastlines, microscopic floating plants exude yellow pigments which turn the normally blue water to green. Some algae release brownish-red pigments, hence the Red Sea. The Yellow Sea owes its hue to mud carried in by its contributing rivers. The colour deepens during floods.
Other factors can affect the colour we see:
1. Particles and solutes can absorb light, as in tea or coffee. Green algae in rivers and streams often lend a blue-green colour. The red sea has occasional blooms of red Trichodesmium erythraeum algae.
2. The surface of seas and lakes often reflect blue skylight, making them appear bluer. The relative contribution of reflected skylight and the light scattered back from the depths is strongly dependent on observation angle.
Water has an intrinsic colour, and this colour has a unique origin. This intrinsic colour is easy to see, as can been seen in the Caribbean and Mediterranean Seas and in Colorado mountain lakes. Pure water and ice have a pale blue colour, best seen at tropical white-sand beaches and in ice caves in glaciers (green colours are usually derived from algae). It is neither due to light scattering (like the sky), nor dissolved impurities (e.g., Cu2+). Because the absorption which gives water its colour is in the red end of the visible spectrum, one sees blue, the complementary colour of orange, when observing light that has passed through several meters of water. This colour of water can also be seen in snow and ice as an intense blue colour scattered back from deep holes in fresh snow.
Water owes its intrinsic blueness to selective absorption in the red part of its visible spectrum. The absorbed photons promote transitions to high overtone and combination states of the nuclear motions of the molecule, i.e. to highly excited vibrations. To our knowledge the intrinsic blueness of water is the only example from nature in which colour originates from vibrational transitions. Other materials owe their colours to the interaction of visible light with the electrons of the substances. Their colours may originate from resonant interactions between photons and matter such as absorption, emission, and selective reflection or from non-resonant processes such as Rayleigh scattering, interference, diffraction, or refraction, but in each case, the photons interact primarily or exclusively with electrons.
