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Chapter 19 – The Ocean Basins
Today nearly ¾ of Earth’s surface is covered by oceans. The global ocean can be divided into
three or four major oceans: the Atlantic, Pacific, Indian, and Arctic (sometimes considered part
of the Atlantic). The deepest and therefore coldest is the Pacific. It is also the least salty. The
Atlantic is the most shallow, warmest, and saltiest. The Indian’s characteristics fall in between
the Pacific’s and Atlantic’s. The Arctic has the same conditions as the Atlantic (except it has a
mostly frozen surface) because it is a continuation of the Atlantic basin.
Mathew Fontaine Maury (the Maury River is just south of here) is considered the Father of
Oceanography as he recorded depths, currents, and winds in what became the earliest
oceanography textbooks. Later in the 1800’s a British navy ship named the HMS Challenger
collected data to provide the foundation for the modern science of oceanography. Today many
ships, ocean buoys, and satellites collect data on our oceans, but the depths of our oceans still
remain the least studied parts of our planet.
The ocean floor’s topography is mapped using sonar. Sound waves are sent from a ship to the
ocean floor and back to the ship. Since sound waves travel a uniform rate in seawater, 1,500
meters per second, by timing how long it takes to travel, depth can be calculated. Underwater
research vessels called submersibles (resembling small submarines) take the dangerous trip to
the depths of our oceans discovering many new and remarkable species and environments.
The ocean floor is far from being a flat, barren place. The deepest places on our planet are the
ocean trenches. There are underwater volcanoes called seamounts, and flat-topped mountains
called guyots (waves cut their tops off when sea level was lower). The continental margin
consists of a gentle continental shelf, a steep continental slope, and at the base of the slope the
continental rise.
The youngest part of the ocean basins are at divergent boundaries called spreading centers.
Here the oceanic plates are moving apart and magma rises from the mantle to form brand new
earth at these mid-ocean ridges. Ocean research ships collect core samples of the ocean floor
to reveal its past. By studying microscopic organisms such as foraminiferans in the ocean floor
sediments, scientists gain many insights into the past climates of our planet.
When substances dissolved in ocean water crystallize, these materials fall to the bottom to
form lumps of economically important minerals called nodules.