\n As depth increases the scattering and absorption of...

\n As depth increases the scattering and absorption of shorter wavelengths (yellows and greens) becomes evident. By about 150 m depth, even in the clearest water, human eyes can only see blue light. Beyond about 800 m the human eye can detect no visible light from the surface. At these depths the only visible light is made by living organisms.\u00a0 The eyes of some deep-sea fishes are 15 to 30 times more light-sensitive than human eyes.

Some deep-sea fishes can detect light in depths down to 1300 m. [77] \n The history of deep-sea exploration begins relatively recently, mainly because advanced technology is needed to explore the depths. However, some earlier observations may have unknown the darkness increase with depth in a sea, the earliest such observations are reported to have taken place in 16 th century, i.e., Ferdinand Magellan in 1521 attempted to measure the depth of the Pacific Ocean.

He used a 2,400-foot weighted line, but did not touch bottom. [78] \n In another report: Scientific deep-sea exploration can be said to have begun when French scientist Pierre-Simon Laplace investigated the average depth of the Atlantic Ocean by observing tidal motions registered on Brazilian and African coasts circa the late 18th or early 19th century. However, the exact date of his investigation is unknown.

He calculated the depth to be 3,962 metres (12,999 ft), a value later proven quite accurate by echo-sounding measurement techniques.

[79] [80] \n The new findings from a team effort involving MIT and several other institutions, highlights the effectiveness of internal wave in sea are produced and are compared with the surface waves: In new research, both in the ocean as well as in the largest-ever laboratory experiments to investigate internal waves, has solved a longstanding mystery about exactly how the largest known internal waves, in the South China Sea, are produced.

Seen in cross-section, these waves resemble surface waves in shape. The only difference between an underwater wave and the water around it is its density, due to temperature or salinity differences that cause ocean water to become stratified.\u00a0 Though invisible to the eye, the boundary between colder, saltier water below and warmer, less-salty water above can be detected instrumentally.