Ocean Regions Help (page 2)
Surrounding nearly all continents is a shallow add-on to the land called the continental shelf . This land shelf is fairly thin, 30–60m deep, compared to the thousands of meters deep in the open ocean. It stretches to the continental slope where the deep ocean drops away.
The continental shelf is formed from sedimentary erosion of the land plates and washed into the ocean by rivers and waves. This nutrient-rich sediment provides food for microscopic plants and animals at the beginning of the food chain as we saw earlier.
The amount of nutrients is so plentiful on the continental shelf that great schools of fish, such as tuna, cod, salmon, and mackerel, thrive in busy communities here. The world’s continental shelf regions also contain the highest amount of benthic life (plants and animals that live on the ocean floor).
The continental slope connects the continental shelf and the ocean’s crust. It begins at the continental shelf break where the bottom sharply drops off into a steep slope. It commonly begins at 130m depth and can be up to 20km wide. Figure 13-5 illustrates how the continental shelf slopes off to the deeper ocean bottom.
Fig. 13-5. The continental slope stretches between the continental shelf and the ocean floor.
The continental slope, counted as part of the main landmass, together with the continental shelf is called the continental margin. Undersea canyons cut through many of the continental margins. Some of these are sliced out by turbidity currents , which drive sediments across the bottom.
Past the continental slope, we find the continental rise . As currents flow along the continental shelf and down the continental slope, they pick up, carry, and then drop sediments just below the continental slope. These sediments buildup to form the wide, gentle slope of the continental rise.
The deep ocean basin, located at a depth of about 3.7–5.6km deep, covers 30% of Earth’s surface and has such features as, abyssal plains , deep-sea trenches , and seamounts .
The abyssal plain is the flat, deep ocean floor. It is almost featureless because a thick layer of sediment covers the hills and valleys of the ocean floor below it. Deep-sea trenches are the deepest parts of the ocean. The deepest one, the Mariana Trench in the South Pacific Ocean, is nearly 11.0km deep. A seamount is an extinct volcano in the ocean.
Waves, various currents, and tides all intermingle with specific land, rocks, and plates to give shorelines unique characteristics.
To most of us, a day at the beach is a day of water, sun, surf, and sand. Beaches are composed mostly of sand, pebbles, and rocks depending on the climate and nearby land mass. However, they are constantly changing. Waves and wind are the endless forces that never stop. They build beaches up and wash them away. The main factors that affect the creation and maintenance of shorelines all around the world include:
- Rising of coastal area with associated erosion
- Sinking of coastal areas with sediment deposition
- Types of rocks or sediments present
- Changes in sea level
- Common and storm wave heights, and
- Heights of tides affecting erosion and sedimentation
Some beaches go on and on for many kilometers, while others are called pocket beaches, with just a nick of sand or smooth stones in a long shoreline. Sometimes beaches are backed by rocky cliffs, while other times they are flanked by sand dunes.
Beaches are generally composed of three parts: backshore , foreshore , and offshore . The backshore extends from the dunes or land margin to the surf. The foreshore is the area with the most wave action. This includes the high-and low-tide areas of the beach. The offshore area extends from where the ocean bottom is shallow enough for waves to break, all the way out into the ocean depths.
You have probably heard of offshore oil drilling rigs. These are located in the deep waters off continental seashores. Figure 13-6 illustrates the different parts of a shoreline.
The littoral zone is a tidal depth gradient found closest to the shore. Since there are coastal currents, onshore and offshore winds, reefs, and bays in this area, the shoreline’s shape is fairly changeable. All these affecting factors make it tough to forecast water conditions accurately.
The littoral area is also where marine life, like jellyfish, is found. As many snorkellers know, there is more marine life to see near the shore than in the open ocean.
The littoral zone reaches from the shoreline to nearly 200m out into the open ocean. It is divided into three overlapping sections: the supralittoral zone, the intertidal zone, and the sublittoral zone.
The supralittoral or spray zone is only washed over during very high tides or during big storms. It begins at the leading edge of the high-tide line and goes back toward dry land. The intertidal zone is found between the high-tide and low-tide lines. The sublittoral zone extends from the low-tide line out to 200m in the water. Figure 13-7 shows the different subdivisions of the littoral zone.
Fig. 13-7. The ever-changing littoral zone is divided into different tide areas.
Practice problems of this concept can be found at: Oceans Practice Test
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