Geography Reference
In-Depth Information
Going where the action is: The continental shelves
Off the coasts of continents are relatively flat expanses of ocean bottom that average about 300 feet
in depth — shallow by oceanic standards. Such a feature is called a continental shelf (see Figure 8-3).
The distances that the shelves extend from the shore vary. While the continental shelf off California
extends 2 to 3 miles, the one off Newfoundland extends seaward some 200 miles.
Altogether, the continental shelves define what is arguably the most economically important part of
the ocean. A growing human population translates into a need for more food (especially stuff that is
high in protein) and more mineral resources. Increasingly, oceans are being looked to as sources of
supply. And in that regard, the continental shelf is where the action is.
Figure 8-3: Pro-
file of the contin-
ental shelf.
Something very fishy going on
If you were a fish and lived in the ocean, then chances are you would hang out over the continental
shelf, just like almost every other fish. Schools are in session there for good reason — lots of food is
available. Here's how the food gets there:
Plant life: Because shelf water is shallow (compared to mid-ocean depths), some sunshine
hits bottom and gives rise to plant life that serves as food for small fish that serve as food for
bigger fish, and so forth.
River flow: Rivers empty onto the continental shelves. Their flow typically contains a
lot of organic matter (especially dead, decaying, or dissolved plant parts), which adds to the
abundance of fish food.
Vertical mixing: Wave action and turbulence produce a considerable amount of vertical
mixing over the continental shelves. As a result, organic matter gets distributed over the
depths, making for a very robust feeding environment.
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