Colors of the Ocean
“No water, no life. No blue, no green.” – Sylvia Earle, author of “The World is Blue – How Our Fate and the Ocean’s Are One.” [1]
Blue Planet
by Sumita Chatterjee
The earth is often called the blue planet, deriving its name from the blue waters that make up our oceans. We imagine oceans to be blue, and rivers to be green or muddy brown! But wait…did you know that our oceans showcase a range of colors? Light to darkest hues of blue, sea green, muddy to chocolate brown and even “milky way” white in some places. Ever wondered why the oceans’ colors change as we navigate from coastal regions to the deepest parts far from land? The colors mesmerize us, draw us in, we take selfies against oceanic backdrops, but do we stop to wonder at the significance of these changing colors? Why is the ocean blue, or blue green, turquoise, or green, or brown? What do these colors tell us of the health of our oceans and our planet? Let us dive in…
The Raman Scattering and the Raman Effect
A young scientist named C. V. Raman had a similar fascination for the changing colors of the ocean. In 1921, while traveling back to India from England he was struck by the deep blue of the Mediterranean Sea. At this time, the explanation for the blue of the ocean came from Lord Rayleigh, an English physicist who in 1899 theorized that the ocean color reflected the blue of the sky, using the physics of studying the scattering of sunlight. Raman, not fully convinced, did a small experiment while on ship. He used a Nicol prism which eliminated the reflected skylight and found the waters of the Mediterranean – that deep blue, to have qualities to it that could not be explained by sky’s reflection alone. He penned his findings on the ship itself and sent it off to Nature for publication in 1921. (see p. 367)
C.V. Raman noted in Nature, “Observations made in this way in the deeper waters of the Mediterranean and Red Seas showed that the colour, so far from being impoverished by suppression of sky-reflection, was wonderfully improved thereby. A similar effect was noticed, though somewhat less conspicuously, in the Arabian Sea. It was abundantly clear from" the observations that the blue colour of the deep sea is a distinct phenomenon in itself, and not merely an effect due to reflected skylight. When the surface-reflections are suppressed the hue of the water is of such fullness and saturation that the bluest sky in comparison with it seems a dull grey.”
Ocean as a Sunlight filter
According to NOAA (National Oceanic and Atmospheric Administration), the ocean acts as a sunlight filter. To nineteenth century scientists like Lord Rayleigh, the ocean appears blue because it reflects the sky. While this is partially true, there is more to oceans’ colors than meets the eye. Sunlight illuminates our oceans, and there are two processes by which the particles of the sun interact with the ocean: a) absorption, and b) scattering. Some of the sunlight is bounced back out of the ocean which is called backscattering, an important aspect of understanding the colors of the ocean, as it sends light back to our eye. Scroll through PACE’s e-brochure Sea the Light (PACE, NASA) to understand absorption and scattering visually.
Raman Effect tells us that even below the surface the water is blue, and this is because of water molecules themselves. The color blue appears when the water of the ocean absorbs the red segment of the sunlight spectrum, allowing us to see only the blue of the sunlight filter. Sunlight has a rainbow of colors with blue having the shortest wavelength and red the longest. The longest wavelengths are absorbed when it hits water the fastest, and blue being the shortest can go deeper. For instance clear water backscatters blue light with high efficiency, and not red or orange. We therefore see the ocean as blue, and not red!
Tiny Giants of Our World – the Phytoplankton
The microscopic organisms, phytoplankton are the invisible foundation of the marine food web, and because they create chlorophyll through photosynthesis, they play a vital role in producing the oxygen we breathe, and making the ocean appear green in color. During the spring and summer seasons the phytoplankton cells may flourish and grow due to available sunlight and become a bloom (large numbers of them), and as they drift in the ocean, the color of the ocean also changes to green. Some phytoplankton have a red pigment, and when the algae bloom, the ocean develops what is popularly called a red tide, but what scientists prefer to call harmful algal blooms (HAB). These can be highly toxic.
“I’ll rule the world” - Sheldon J. Plankton in Spongebob Square Pants
Planktons, so vital to the wellbeing of marine life as well as our own, are of two kinds - phytoplankton (the “plant” plankton) and zooplankton (the “animal” plankton). A Zooplankton is an iconic character named Sheldon J. Plankton in the children’s beloved television series Spongebob Square Pants!
Ocean As a Cup of Tea
According to scientists Rafael Goncalves-Araujo, Colin Stedman, and Astrid Bracher, one way to understand the changing colors of the ocean is to study not only light, sun and water molecules, wavelengths, plant life activities, but also to imagine what may be in the water to impact color. They use the metaphor of making a cup of tea and seeing the changing colors of the water as tea leaves absorb blue light and the water appears as yellow or brown. Something similar happens to oceans, particularly near estuaries and river basins, which bring soil and sediment into the water, making the ocean brown or yellowish.
Ocean’s Milky Way
Sediments such as rocks, soil, and silt carried by rivers, or churned up during storms from ocean floors can make waters take on hues of brown, from muddy, chocolate, sandstone, or even yellowish. They have pigments and scatter light in all directions, changing the color of the ocean. Scientists Araujo-Gonsalves and others liken this to what fat particles in milk do, which can make the water milky. Sediments deposited into oceans create something similar. Interestingly, coccolithopores a kind of phytoplankton, have chalk composed white plates which when in bloom, make the ocean water light blue and sometimes white!
According to the Pace program at NASA this was captured via satellite imaging in the ocean off the coast of Greenland. They observed that “a palette of swirling teal blues off the southernmost tip of Greenland may indicate that coccolithophores are present. These tiny protists make and shed tiny calcite plates that reflect sunlight back to space. This image was taken by the Ocean Color Instrument (OCI) sensor aboard the PACE satellite on June 2, 2024.
Bioluminescence
One of the most beautiful ocean phenomenon is bioluminescence, which makes the ocean glow and glitter like fine jewels. These beautiful waters are caused by bioluminescent sea creatures, who have the the ability to produce or eject light due to chemical reactions. About 90% of ocean life contains some type of bioluminescence. When coastal waters take on a glowing blue color, it is caused by millions of one celled organisms called Dinoflagellates that are emitting these bursts of light. While scientists don’t know for sure why these creatures glow, they think it may be to scare off predators or remove toxicity from their bodies. Apart from dinoflagellates and other algae, there is a diverse range of ocean life, at the shorelines and the deep sea, that shine and glow in colors ranging from blue to green, orange, and pink.
A Complex Weave of Colors: Ongoing Scientific Research
NASA’s PACE (Plankton, Aerosol, Cloud, ocean Ecosystem mission) program launched in 2024 has “two fundamental science goals: To extend key systematic ocean color, aerosol, and cloud data records for Earth system and climate studies.. To address new and emerging science questions using its advanced instruments, surpassing the capabilities of previous and current missions.” Using Ocean Color Instruments (OCI) and multi-angle polarimeters, Pace scientists will monitor the changing colors of the ocean to interpret and analyze the interactions between the atmosphere and the oceans and their impact on Earth’s ecosystem.
Ocean’s Palette - Confluence of colors and the myth of “borders” between oceans
A common myth about distinct oceans with different borders and names whose water do not mix are often explained by visual cues of distinctly different colors of the two bodies of waters, as in say between the Pacific and the Atlantic, or the Indian Ocean, the Arabian Sea, and the Bay of Bengal, or the Gulf of Alaska and the Beadle Channel. One of the explanations is the different sentiment deposits in different bodies of water. See the photograph of the Gulf Of Alaska below taken by NASA in 2007, to show the black of the gulf in contrast to the white and turquoise of the shoreline waters.
Why does this happen? Do these waters never mix? Are the borders unchanging and static? Do they mix and merge? Perhaps you can investigate this further!
Songs of the Blue Waters
Bhaswar Faisal Khan’s playlist and stories focus on colors of the ocean across time and geographies.
Global Mythology
by Sohini Sengupta
Bibliography
[1]Dr. Sylvia A. Earle is the founder and President of Mission Blue, the National Geographic Society Explorer in Residence, called Her Deepness by the New Yorker and the New York Times, Living Legend by the Library of Congress, and first Hero for the Planet by Time Magazine, is an oceanographer, explorer, author and lecturer.