Physical properties

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The area of the World Ocean is 361 million square kilometers (139 million sq mi),^[5] its volume is approximately 1.3 billion cubic kilometers (310 million cu mi)^[6]. This can be thought of as a cube of water with an edge length of 1,111 kilometers (690 mi). Its average depth is 3,790 meters (12,430 ft).^[5] Nearly half of the world's marine waters are over 3,000 meters (9,800 ft) deep.^[2] The vast expanses of deep ocean (anything below 200m) cover about 66% of the Earth's surface.^[7] This does not include seas not connected to the World Ocean, such as the Caspian Sea.

The total mass of the hydrosphere is about 1.4 × 10²¹ kilograms, which is about 0.023% of the Earth's total mass. Less than 3% is freshwater; the rest is saltwater, mostly in the ocean.

Colour

A common misconception is that the oceans are blue primarily because the sky is blue. In fact, water has a very slight blue color that can only be seen in large volumes. While the sky's reflection does contribute to the blue appearance of the surface, it is not the primary cause.^[8] The primary cause is the absorption by the water molecules' nuclei of red photons from the incoming light, the only known example of colour in nature resulting from vibrational, rather than electronic, dynamics.^[9]

Glow

A number of sailors and professional mariners have reported that the ocean often emits a visible glow, or luminescence, which extends for miles at night. In 2005, scientists announced that for the first time, photographic evidence had been obtained of this glow.^[10] It may be due to bioluminescence.