Ocean color
Ocean color is the study of why seawater looks the way it does and what we can learn from the color patterns. The sea is mostly blue, but it can also look green, yellow, brown, or even red in places. These colors come from how sunlight interacts with water and what’s in it.
Why blue: Water absorbs red light more than blue light, so blue light can bounce back to the surface. Water also scatters blue light more than other colors. Because the water has few materials or only tiny particles, the open ocean often appears a deep blue.
What changes the color:
- Phytoplankton (tiny plants) contain chlorophyll that absorbs blue and red light. More phytoplankton makes the water greener.
- Dissolved organic matter and colored substances (CDOM) soak up blue light, which can make water look yellow or brown.
- Sediments from rivers or the sea floor scatter light in many colors, often turning coastal waters yellow or brown.
- Sometimes algal blooms turn the water red; these are called red tides, but not all are harmful.
How we measure ocean color: Scientists use radiometers (special light sensors) on satellites, airplanes, and ships to measure the colors of light coming from the water. By looking at the spectrum from ultraviolet to near-infrared, they estimate things like chlorophyll concentration and other substances in the water.
Why it matters: Ocean color helps scientists track phytoplankton and ocean productivity, monitor harmful algal blooms, study water quality, and understand how oceans respond to climate change. It’s a key way to observe large parts of the world’s oceans over time.
A few notes: Turning the water’s color into useful data requires removing the color signal from the air and clouds first. The water’s signal is a small part of the total light leaving the sea, so careful correction is essential.
This page was last edited on 2 February 2026, at 19:45 (CET).