World Ocean Census - Extract 2 - The great unknown

14 December 2009

Second amazing extract from The World Ocean Census: A global survey of marine life: The Light zone and The Dark zone

Even now, at the beginning of the 21st century, 95 percent of the world’s ocean basins and seas has yet to be explored (some put this figure as high as 98 percent). Part of the reason is simply the global ocean’s vast size: it comprises approximately 71 percent of the planet’s surface and covers 361 million square kilometers (139 million square miles). And there is more to the world’s ocean than meets the eye – a vast story unfolds below the surface. The global volume of ocean water is 1,370 million cubic kilometers (329 million cubic miles), with an average depth of 3.8 kilometers (2.4 miles). The deepest ocean trench areas extend 10.5 kilometers (more than 6.7 miles) below the sea surface. And if the obstacles of size, volume and mass were not enough, other deterrents to exploration – darkness and pressure – greatly increase the challenge, cost and risk for those who dare to venture below the surface. Only recently have technological advances allowed scientists to successfully tackle the physical challenges of exploring dark ocean extremes at intense pressures.

Studying the world’s ocean is further compounded by the fact that all oceans are really one vast body of water. Each of the five ocean basins – the Pacific, Atlantic, Southern, Indian and Arctic oceans – are interconnected by major surface and deep-water currents in a circulation system that creates a single body of water. All ocean life is connected by this system, so we have to understand it in order to understand its biodiversity.

Text and images reprinted with permission from World Ocean Census: A Global Survey of Marine Life by Darlene Trew Crist, Gail Scowcroft and James M. Harding Jr., Firefly Books, 2009.

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