ocean zones

divisions of the ocean

Oceanographers divide the ocean into zones both vertically and horizontally.

vertical divisions

To better understand regions of the ocean, scientists define the water column by depth. They divide the entire ocean into two zones vertically, based on light level. Large lakes are divided into similar regions. Sunlight only penetrates the sea surface to a depth of about 200 m, creating the photic zone ("photic" means light). Organisms that photosynthesize depend on sunlight for food and so are restricted to the photic zone. Since tiny photosynthetic organisms, known as phytoplankton, supply nearly all of the energy and nutrients to the rest of the marine food web, most other marine organisms live in or at least visit the photic zone. In the aphotic zone there is not enough light for photosynthesis. The aphotic zone makes up the majority of the ocean, but has a relatively small amount of its life, both in diversity of type and in numbers. The aphotic zone is subdivided based on depth (Figure 1.1). The average depth of the ocean is 3,790 m, a lot more shallow than the deep trenches but still an incredible depth for sea creatures to live in. What makes it so hard to live at the bottom of the ocean? The three major factors that make the deep ocean hard to inhabit are the absence of light, low temperature, and extremely high pressure.


horizontal divisions

The seabed is divided into the zones described above, but ocean itself is also divided horizontally by distance from the shore. Nearest to the shore lies the intertidal zone (also called the littoral zone), the region between the high and low tidal marks. The hallmark of the intertidal is change: water is in constant motion in the form of waves, tides, and currents. The land is sometimes under water and sometimes exposed. The neritic zone is from low tide mark and slopes gradually downward to the edge of the seaward side of the continental shelf. Some sunlight penetrates to the seabed here. The oceanic zone is the entire rest of the ocean from the bottom edge of the neritic zone, where sunlight does not reach the bottom. The sea bed and water column are subdivided further, as seen in the Figure 1.1. Click image to the left or use the URL below. URL:

instructional diagrams

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what is the submersible that descended the deepest into the challenger deep?

a) alvin

b) deepsea explorer

-->  c) trieste

d) deepspace 9

nearly all of the food is the ocean is made in the ___ zone, but nearly all of the water in the ocean is in the ____ zone.

-->  a) photic; aphotic

b) a photic; photic

c) luminescent; aluminescent

d) aluminescent; luminescent

photosynthesis takes place at the surface of the ocean, which means that

-->  a) most creatures live very near the surface of the ocean.

b) most plants live at the surface, but most animals live much deeper down.

c) most animals live at the surface, but most plants live deeper down.

d) most creatures live deeper to take advantage of the chemosynthesis taking place there.

which of these is a division in the horizontal zone?

a) intertidal

b) neritic

c) oceanic

-->  d) all of the above

the photic zone is around 200 meters in all oceans.

a) true

-->  b) false

the neritic zone is the zone where

a) photosynthesis takes place.

b) the high and low tides marks form the boundaries.

c) sunlight doesnt penetrate.

-->  d) none of these.

to live in the intertidal zone, an animal must be able to

a) photosynthesize.

-->  b) deal with change.

c) live in the dark.

d) live in a tidepool.

why is life at the bottom of the ocean sparse?

a) there is no light.

b) the pressure is extreme.

c) it is exceedingly cold.

-->  d) all of the above.

the zone at the bottom of the challenger deep is called the

a) bathy pelagic

b) epipelagic

-->  c) hadal pelagic

d) abyssal pelagic

diagram questions

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