3 What does the bottom of the ocean look like? OR What is the topography or bathymetry of the ocean floor?

3 Topography of the Ocean Floor echo soundings (1920’s) ocean was not deepest in the center deepest part of the ocean lie near its edges

3 Fig 4-2a, p.67

3 Fig 4-3a, p.67

3 Fig. 4-2b, p. 67 An echo sounder trace. A sound pulse from a ship is reflected off the seabed and returns to the ship. Transit time provides a measure of depth. For example, it takes about 2 seconds for a sound pulse to strike the bottom and return to the ship when the water depth is 1,500 meters (4,900 feet). Bottom contours are revealed as the ship sails a steady course. In this trace, the horizontal axis represents the course of the ship, and the vertical axis represents the water depth. The ship has sailed over a small submarine canyon.

3 Fig. 4-4c, p. 68 Ridges/trenches in South Atlantic Sea Floor

3 Fig nft Bathymetry can tell you where things are: Oceanic ridge system

3 BATHYMETRY – OCEAN FLOOR CONTOURS Fig 4-5, p.69

3 Fnft: The major plates of the earth's crusts Courtesy of Reto Stockli, NASA Earth Observatory

3 Fig. 4-17a, p. 78 Atlantic Ocean

3 Fnft: Some large-scale features of the North Atlantic seafloor Courtesy National Geophysical Data Center/NOAA

3 Fig. 4-11, p. 74 Folded ridges of sediment cover the ocean floor west of Oregon

3 Topography of the Ocean Floor REMEMBER: deepest part of the ocean lie near its edges

3 fnft

3 Topography of the Ocean Floor Submerged outer edge of the continents are called continental margins Deep-sea floor beyond these is called the ocean basin

3 Fig 4-6, p.70

3 Fig. 4-25, p. 84

3 Fig 4-9, p.72

3 Fig 4-10, p.73 Florida coast

3 but There are 2 sides to every…OCEAN!

3 Fig 4-8, p.71

3 2 types of “margins” PASSIVE MARGIN: Continental margins that face diverging plates. These do not coincide with plate boundaries. Little or no activity. Typically associated with the Atlantic. ACTIVE MARGIN: Continental margins that face converging plates. These coincide w/plate boundaries. A lot of activity (earthquake/volcano). Typically associated with the Pacific.

3 Continental Margins Passive margins – –continental margins not located on plate boundaries –Atlantic-type margins

3 Continental Margins Active margins- –continental margins on the edge of convergent or transform plate boundaries –Pacific-type margins

3 Fig 4-8, p.71

3 Fig 4-9, p.72

3 Continental Margins (Shelves) Width of Continental Shelf is determined by : proximity to a plate boundary (active margins have narrow shelves while passive margins have broad shelves)

3 Continental Margins (Shelves) Continental Shelves –Shallow, submerged extension of a continent –broad, gently sloping –7.4% of earths Ocean area

3 Fig nft

3 Continental (Passive) Margins Shelf break – –transition between the continental shelf and the continental slope There are also changes from the continental slope (edge of shelf) to the continental rise (ends at edge of ocean floor).

3 Continental Margins Continental Slopes –Steeper than the shelf –end at the deep ocean

3 Fig 4-9, p.72

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3 Continental Margins Continental rises –at the base of continental slope –covered by a blanket of accumulated sediment –gradual slope

3 Continental Margins Submarine Canyons –cut into the continental shelf and slope –formed by turbidity currents (avalanche-like sediment movements)

3 F 4.12

3 Fig 4-13, p.75 Submarine Canyon Off of The coast Of New Jersey

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3 Fig. 4-17b, p. 78 Mid-Atlantic Ridge between Florida and western Africa  Canyon in middle of ridge

3 Ocean Basin thick layer of sediment (up to 5 km or 3mi thick) covering basaltic rocks Make up more than ½ of the earth’s surface

3 Ocean Basin Oceanic ridges –Underwater mountain chain –an active spreading center –offset at regular intervals by transform faults

3 Fig nft WHERE THE RIDGES ARE!

3 Midoceanic Ridge Province consists of a continuous submarine mountain range. It covers about one third of the ocean floor. It extends for about 60,000 km around the Earth.

3 Examples of what “exists” on the Ocean Floor Hydrothermal Vents SeaMounts Guyots Abyssal Hills Abysall Plains Trenches Island Arcs (seen above “land”)

3 Ocean Basin Seamounts –Inactive volcanoes that do not rise above the surface of the ocean –They are tall with steep slopes

3 Ocean Basin Guyots –Flat-topped seamounts that were eroded by wave action Abyssal Hills –abundant, small sediment-covered extinct volcanoes

3 Fig. 4-23a, p. 82 guyots (G) and seamounts

3 Ocean Basin Island Arcs –Curving chains of volcanic islands and seamounts found paralleling the edge of trenches

3 Fig 4-23, p.76

3 Coral Reefs? All of these different land/(under)water formations can yield MANY different types of coral reefs (a very diverse, valuable, marine community) too!

3 Fnft

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3 Ocean Basin Abyssal Plains –Flat, featureless, sediment-covered ocean floor Trenches –Arc-shaped depression in the deep seafloor –a converging oceanic plate is subducted

3 Deep Ocean Province is between the continental margins and the midoceanic ridge. It includes a variety of features from mountainous to flat plains: –Abyssal plains –Abyssal hills –Seamounts –Deep sea trenches

3 Ocean Basin Hydrothermal vents –average temp is about 8-16 o C (46-61 o F) much warmer than the typical 3-4 o C ( o F) –support a unique community of organisms that depend on bacteria

3 Cross-section of a ridge axis and the plumbing connected to a vent chimney

3 Fig 4-20, p.80

3 Sidescan sonar image overlaid onto multibeam bathymetry

3 Approximate locations of confirmed hydrothermal vents and cold seeps

3 Red-plumed tube worms Courtesy of Monika Bright, University of Vienna, hydrothermalvent.com

3 A black smoker on the Galápagos Rift Zone. Courtesy of UCSB, University S. Carolina, WHOI/NOAA

3 Fig 4-19, p.79