3What 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 wherethings 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

AtlanticOcean

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.73Florida coast

3but

•There are 2 sides to every…OCEAN!

3

Fig 4-8, p.71

32 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.

3Continental Margins

•Passive margins –

– continental margins not located on plate boundaries

– Atlantic-type margins

3Continental 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

3Continental 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)

3Continental Margins

(Shelves)

•Continental Shelves

– Shallow, submerged extension of a continent

– broad, gently sloping – 7.4% of earths Ocean area

3

Fig nft

3Continental (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).

3Continental Margins

• Continental Slopes

– Steeper than the shelf – end at the deep ocean

3

Fig 4-9, p.72

3

Fig 4-9, p.72

3Continental Margins

• Continental rises

– at the base of continental slope – covered by a blanket of accumulated

sediment– gradual slope

3Continental 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

SubmarineCanyonOff ofThe coastOf NewJersey

3

3

Fig. 4-17b, p. 78

Mid-Atlantic Ridge between Florida and western Africa

Canyon in middleof ridge

3Ocean 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

3Ocean 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.

3Examples of what “exists”

on the Ocean Floor

• Hydrothermal Vents

• SeaMounts

• Guyots

• Abyssal Hills

• Abysall Plains

• Trenches

• Island Arcs (seen above “land”)

3Ocean Basin

• Seamounts

– Inactive volcanoes that do not rise above the surface of the ocean

– They are tall with steep slopes

3Ocean 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

3Ocean Basin

• Island Arcs

– Curving chains of volcanic islands and seamounts found paralleling the edge of trenches

3

Fig 4-23, p.76

3Coral 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

3

Fnft

3

Fnft

3

Fnft

3Ocean 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

3Ocean Basin

•Hydrothermal vents

– average temp is about 8-16oC (46-61oF) much warmer than the typical 3-4oC (37-39oF)

– 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