Background Info

The bright blue of the Pacific, near the Galapagos Islands, above, fades to darkness as the ocean deepens. Light intensity fades for two reasons: absorption and scattering.

Many substances absorb light in the ocean. Water itself absorbs light, mostly red light—which is why "clear" water appears blue. (The red light is absorbed, while the blue light is not. It is reflected.) Microscopic particles in the ocean, invisible to the human eye, also absorb light. Some of this microscopic material is organic, such as algae. Other microscopic materials are compounds released by chemical reactions in the ocean, such as the decay of plants.

Light scatters as it hits microscopic particles and changes direction. Many of these particles are the same ones (algae and chemicals) that absorb light. Light is also scattered by sediment and other larger particles.

Absorption and scattering darken the ocean to pitch-black at about 1,000 meters (3,280 feet) below the surface.

For Further Exploration

Vocabulary

Term Part of Speech Definition Encyclopedic Entry

absorb

Verb

to soak up.

algae

Plural Noun

(singular: alga) diverse group of aquatic organisms, the largest of which are seaweeds.

chemical reaction

Noun

process that involves a change in atoms, ions, or molecules of the substances (reagents) involved.

decay

Verb

to rot or decompose.

electromagnetic spectrum

Noun

continous band of all kinds of radiation (heat and light).

microscopic

Adjective

very small.

ocean

Noun

large body of salt water that covers most of the Earth.

Encyclopedic Entry: ocean

organic

Adjective

composed of living or once-living material.

reflect

Verb

to rebound or return light from a surface.

sediment

Noun

solid material transported and deposited by water, ice, and wind.

Encyclopedic Entry: sediment

Credits

Media Credits

The audio, illustrations, photos, and videos are credited beneath the media asset, except for promotional images, which generally link to another page that contains the media credit. The Rights Holder for media is the person or group credited.

Photographer

Julian Osinski

Producer

Caryl-Sue, National Geographic Society

User Permissions

For information on user permissions, please read our Terms of Service.

If you have questions about licensing content on this page, please contact natgeocreative@ngs.org for more information and to obtain a license.

If you have questions about how to cite anything on our website in your project or classroom presentation, please visit our FAQ page.

Media

Some media assets (videos, photos, audio recordings and PDFs) can be downloaded and used outside the National Geographic website according to the Terms of Service. If a media asset is downloadable, a download button appears in the lower right hand corner (download) of the media viewer. If no button appears, you cannot download or save the media.

Text

Text on this page is printable and can be used according to our Terms of Service.

Interactives

Any interactives on this page can only be played while you are visiting our website. You cannot download interactives.