Ocean color

For broader coverage of this topic, see Ocean optics and Color of water.
For the music band, see Ocean Colour Scene.
Clockwise from top left: deep blue water, blue-green water, satellite image of the Bahamas where sunlight reflects off sand and reefs in the shallows, satellite image of phytoplankton bloom in the Southern Ocean, satellite image of the Pribilof Islands showing shades of color from different phytoplankton, and satellite image of the Baltic Sea with phytoplankton blooms.

Ocean color is the branch of ocean optics that specifically studies the color of the water and information that can be gained from looking at variations in color. The color of the ocean, while mainly blue, actually varies from blue to green or even yellow, brown or red in some cases.[1] This field of study developed alongside water remote sensing, so it is focused mainly on how color is measured by instruments (like the sensors on satellites and airplanes).

Most of the ocean is blue in color, but in some places the ocean is blue-green, green, or even yellow to brown.[2] Blue ocean color is a result of several factors. First, water preferentially absorbs red light, which means that blue light remains and is reflected back out of the water. Red light is most easily absorbed and thus does not reach great depths, usually to less than 50 meters (164 ft). Blue light, in comparison, can penetrate up to 200 meters (656 ft).[3] Second, water molecules and very tiny particles in ocean water preferentially scatter blue light more than light of other colors. Blue light scattering by water and tiny particles happens even in the very clearest ocean water,[4] and is similar to blue light scattering in the sky.

The main substances that affect the color of the ocean include dissolved organic matter, living phytoplankton with chlorophyll pigments, and non-living particles like marine snow and mineral sediments.[5] Chlorophyll can be measured by satellite observations and serves as a proxy for ocean productivity (marine primary productivity) in surface waters. In long term composite satellite images, regions with high ocean productivity show up in yellow and green colors because they contain more (green) phytoplankton, whereas areas of low productivity show up in blue.

  1. ^ Fleming, Nic (2015). "Is the sea really blue?". BBC - Earth. Retrieved 21 August 2021.
  2. ^ Fleming, Nic (27 May 2015). "Is the sea really blue?". BBC - Earth. BBC. Retrieved 25 August 2021.
  3. ^ Webb, Paul (July 2020), "6.5 Light", Introduction to Oceanography, retrieved 21 July 2021
  4. ^ Morel, Andre; Prieur, Louis (1977). "Analysis of variations in ocean color 1". Limnology and Oceanography. 22 (4): 709–722. Bibcode:1977LimOc..22..709M. doi:10.4319/lo.1977.22.4.0709.
  5. ^ Coble, Paula G. (2007). "Marine Optical Biogeochemistry: The Chemistry of Ocean Color". Chemical Reviews. 107 (2): 402–418. doi:10.1021/cr050350+. PMID 17256912.