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Today, ships use a devise called a precision depth recorder to determine the distance to the sea floor. Deep-sea trenches, continental slopes, and continental shelves are features commonly found at active continental margins. The shelf edge is the boundary between the continental shelf and the continental slope. Satellites can obtain information about the sea floor because the sea surface level varies slightly with sea-floor depth.

Robert S. Dietz looks on as Robert F Robert S. Dietz looks on as Robert F. Dill monitors precision depth recorder on the Oceanographer in 1967 during its around the world cruise. (NOAA Photo Library). http://oceanexplorer.noaa.gov/history/electronic/1946_1970/media/dietz.html

http://earthnet-geonet.ca/images/glossary/continental_slope.jpg

One method of obtaining a sample of sea-floor sediment with its layers preserved involves using a gravity corer. Passive continental margins are characterized by the presence of coastal plains. Suppose sound travels at an average rate of 1500 meters per second through seawater above a particular location. How deep is the ocean if a sound pulse takes 10 seconds to reach the bottom and return to a surface ship? 7500 meters

The portions of large submarine canyons that cut through the lower continental slope are thought to have been carved out by turbidity currents. The ultimate source of most of the material found on the surface of abyssal plains is sediments carried to the ocean by continental rivers. Abyssal hills are commonly found on the sea floor next to oceanic ridge systems.

Deep-sea trenches occur at convergent plate boundaries where one tectonic plate is sinking beneath another. Where an oceanic plate descends beneath a continental plate, what features are common along the edge of the continent? Earthquakes and volcanoes. Mid-ocean ridges are undersea mountain ranges where lithospheric plates are moving apart and new oceanic crust is being formed.

Segments of mid-ocean ridges are offset relative to each other by fracture zones. Sinking volcanic islands and developing coral reefs are related to the formation of atolls. Sediments covering the ocean floor are made up of a wide range of sizes that settle to the sea floor at different rates. Sediments made from microscopic shells that settle to the bottom when the organisms that produced them die are called biogenous sediments.

As rivers carry continental sediments to the ocean, the particles most likely to be deposited on the deep-sea floor are muds and clays that can be carried great distances by currents. As icebergs melt, they release sediments and pieces of rock that sink to the ocean floor. Sediments containing 75 percent of the ocean’s siliceous sediment are found near Antarctica.

Types of Ocean Sediments Ocean bottom sediment map Types of Ocean Sediments Ocean bottom sediment map. Lithogenous areas are mauve, biogenous areas are purple and brown (purple = siliceous ooze, brown = calcareous ooze), and hydrogenous areas are blue

Terrogenous sediments

Biogenic Shell Fragments

This diagram shows a passive continental margin and a part of an ocean basin. Which region is most likely to be covered with a thick layer of relatively coarse sediments deposited by turbidity currents? Which region is most likely to be completely underlain by continental crust? What is the name of region B? Of region D? (4 points)

The diagram shows a passive continental margin and a part of an ocean basin. Which region is most likely to be covered with a thick layer of relatively coarse sediments deposited by turbidity currents? Which region is most likely to be completely underlain by continental crust? What is the name of region B? Of region D? (4 points)

Continental shelf Continental rise

Essay 1: Compare the type of information obtained with a precision depth recorder with that obtained by a gravity corer. A precision depth recorder produces a continuous record of seafloor depth under the ship as it moves over an area. A gravity corer provides information about the seafloor at one point only. A gravity corer provides a vertical sample of the layers of the seafloor.

Essay 2: Identify three ways in which the origins of oozes and manganese nodules are different. Oozes are the remains of organisms and are biological in origin; manganese nodules form as minerals crystallize from seawater and are inorganic in origin. The particles that form oozes form primarily in surface waters, while nodules form on the sea floor. Oozes form more quickly than nodules. Oozes form from calcareous or siliceous material, while nodules form from metallic minerals.