Exploring Earth's Oceans: The Ocean Floor and Its Remarkable Features

1. Earth’s Oceans Part 3: The Ocean Floor

2. Introduction Topography: The study or detailed description of the surface features of a region Compared to the continents, the ocean has: • Higher mountains, deeper canyons, and larger, flatter plains • More volcanoes and earthquakes • Different kinds of rock • A thinner underlying crust

3. Edges of the Continents Shoreline: • Boundary where land and water meet • Marks the average sea level • Not the edge of the continent Photo credit: 111 Emergency from New Zealand

4. Edges of the Continents Continental margin: • Where the continent and the ocean floor meet • Consists of a continental shelf, a continental slope, and a continental rise

5. Edges of the Continents Continental shelf: • Relatively flat • Covered by shallow water • Slopes gently downward • Width varies from almost none to over 1,200 km • Best area for fishing • Mineral, oil, and natural gas deposits may be found here 1 fathom = 6 feet

6. Edges of the Continents Continental slope: • Plunges steeply 4-5 km • Boundary between the continental crust and the ocean crust Continental rise: • Separates the continental slope from the ocean floor • Made of large amounts of sediment

7. Edges of the Continents Turbidity Current: • A flow of water that carries large amount of sediments • Similar to an avalanche but underwater

8. Submarine Canyons • Deep V-shaped valleys cut into the rock of the continental slope and rise • Possibly caused by turbidity currents and/or earthquakes (not sure) Continental slope and upper continental rise northeast of Hudson Canyon, showing the four newly named submarine canyons along the continental slope

9. Features of the Ocean Floor • Abyssal Plains • Seamounts and guyots (gee-OHZ) • Trenches • Mid ocean ridges • Rift valleys • Reefs

10. Abyssal Plains • Large flat areas on the ocean floor • Largest area occurs in Atlantic, less in the Indian, and rare in Pacific • At depth of 3,000-6,000m • Flattest places on Earth Sea Spider Credit: CSSF/NEPTUNE Canada Anemone Clouds of sediment stirred up from the ocean floor

11. Seamounts and Guyots Seamounts: • Volcanic mountains that rise more than 1,000 m above the surrounding ocean floor • Have steep sides and narrow summits • More than 1,000 known, most in Pacific • Seamounts that rise above the ocean’s surface form volcanic islands, including Azores and Ascension Islands in the Atlantic and Hawaiian Islands in the Pacific

12. Seamounts and Guyots Guyots (gee-OHZ): • Flat-topped seamounts • Result from wave erosion 3-D depiction of Bear Seamount, with Physalia Seamount in the background.

13. Trenches • Long, narrow crevices along the edges of the ocean floor • Can be more than 11,000 meters deep • Mariana Trench contains Challenger Deep, the deepest spot known on Earth Attribution: I, Kmusser

14. Mid Ocean Ridges • Some of the largest mountain ranges on Earth • An almost continuous mountain belt from the Artic Ocean through the middle of the Atlantic Ocean, around Africa into the Indian Ocean, then across the Pacific Ocean to North America Video: http://www.youtube.com/watch?v=GyMLlLxbfa4

15. Mid Ocean Ridges • Formed when molten rock flowed up to the crust’s surface and cooled

16. Rift Valleys • Form where the Earth’s crust, or outermost layer, is spreading or splitting apart. • Often narrow, with steep sides and a flat floor • Run along the middle of the mid ocean ridges • Regions of great earthquake and volcanic activity Great Rift Valley in Israel Attribution: איטה צנר

17. Coral Reefs • Large masses and ridges of limestone rocks • Contain shells of animals • Found in tropical water that are not too deep A Blue Starfish (Linckia laevigata) resting on hard Acropora coral. Attribution: Richard Ling

18. Coral Reefs Three types: • Fringing Reef – touches the shoreline of a volcanic island • Barrier Reef – separated from the shore by shallow water called a lagoon • Atoll – a ring of coral reefs where the island has worn away and sunk below sea level A fringing reef can take ten thousand years to form, and an atoll can take up to 30 million years. Animation from NOAA

19. Videos: http://www.youtube.com/watch?v=1aX61LzmeYA http://www.youtube.com/watch?v=wbNeIn3vVKM http://commons.wikimedia.org/wiki/File:Great_Barrier_Reef_4.JPG Atoll in the Maldives Location of coral reefs around the world

20. Oceanography Bathyscaphe • The branch of science dealing with the physical, chemical, geological, and biological features of the oceans and ocean basins Tools of an oceanographer include: • Underwater cameras • Corers to sample the ocean bottom • Bathyspheres, bathyscaphes, and other submersibles for deep water exploration Bathysphere NOAA’s Mir submersible 

21. Mapping the Ocean Floor • 1872 –HMS Challenger sailed on the first expedition to map the ocean’s floor (3 ½ years) • Used a wire to measure ocean depth, netted animals and plants from the ocean bottom, and measured ocean temperatures

22. Mapping the Ocean Floor • Video: http://www.youtube.com/watch?v=-fAAxEIFeLU • Use indirect methods including echo sounding, radar, sonar, and seismographic surveys, but given the size of the oceans only a small portion can be surveyed this way. • Satellite altimeter data from Seasat (1978), Geosat (1985), ERS-1 (1995) has provided a more complete picture. • The ocean surface has bumps and dips that mimic the ocean floor beneath, so measuring the change in the surface gives a picture of the floor.