The ocean is a vast body of water that covers over 70% of the planet’s surface. Despite often being depicted as a singular blue mass, the ocean actually exhibits a wide range of colors depending on location. The various colors are primarily caused by the water’s depth, the makeup of the seafloor, and the presence of organic material. Understanding what makes ocean water appear blue, green, red, or even black can provide insight into the underwater environment.
What Makes Ocean Water Blue?
The most common ocean color is blue. This is caused by the water absorbing colors from the visible light spectrum. As sunlight enters the ocean, much of the red, orange, and yellow light gets absorbed within the first few meters. Blue light has longer wavelengths and penetrates deeper, giving a blue appearance when looking at the ocean from above.
The more pure and clear the water is, the deeper the blue light penetrates before being reflected back out. This is why the open ocean far from land generally appears a deeper blue compared to coastal waters which contain more suspended particles.
Why Does Water Appear Green or Turquoise?
In some areas, the ocean takes on greenish or turquoise hues. This is primarily caused by the presence of phytoplankton, microscopic marine algae. Phytoplankton contain chlorophyll which gives them a greenish color. When present in high concentrations, they can cause green light to reflect back out of the water.
Turquoise shades are caused by a combination of the blue ocean water mixing with the green phytoplankton. Places where phytoplankton proliferate, like in colder currents upwellings, tend to appear greener compared to other regions.
What Makes Water Look Red or Brown?
Red and brown water is the result of large amounts of sediment or organic matter being suspended in the water. Particles of eroded soil, decomposing plant matter, and even some types of algae can impart a reddish-brown color.
Areas near river mouths often appear brown and murky from all the mud and particles carried in the freshwater outflow. The Red Sea gets its name from occasional blooms of red-colored algae called Trichodesmium erythraeum.
| Color | Cause |
|---|---|
| Blue | Absorption of other colors, leaving blue to predominate |
| Green/Turquoise | Presence of phytoplankton containing chlorophyll |
| Red/Brown | High concentrations of sediment, organic matter, and some algae |
Why Does the Ocean Look Black in Some Areas?
In rare instances, parts of the ocean can take on an ominous black color. This is generally caused by extensive phytoplankton blooms of certain species that appear black or dark red. One type, called Noctiluca scintillans, is bioluminescent and sometimes referred to as sea sparkle.
When massive amounts of these organisms bloom, they can make the water appear black or dark red. Low oxygen levels caused by the decaying bloom can also darken the water. These “red tide” events represent extreme phytoplankton population explosions.
How Water Clarity Affects Color
The clarity or turbidity of the water also influences its color. Clear open ocean water allows blue wavelengths to penetrate deeper, enhancing the blue appearance. Murky, sediment-laden water limits light penetration, causing muted, duller colors.
Clarity is reduced by suspended particles like sediments and organic detritus. In coastal areas, inputs from rivers and soil erosion tend to make the water more turbid and grey-colored compared to the tropical oceans.
Conclusion
The wide range of ocean colors, from deep blue to black, are ultimately determined by the unique make-up of the water in a given area. Factors like suspended particles, water depth, seafloor composition, salinity, and the presence and type of microscopic organisms combine to produce the kaleidoscope of ocean colors across the planet. Reading the ocean’s colors provides insights into the underwater processes and components that define each marine environment.
