3 What does the bottom of the ocean look like?

OR

What is the topography or bathymetry of the

ocean floor?

3

Fnft: The major plates of the earth's crusts

Courtesy of Reto Stockli, NASA Earth Observatory

3Topography 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

Figure 3.3- Side-scan SONAR (Sound Navigation and Ranging)

3

Figure 3.2- Multibeam SONAR (Sound Navigation And Ranging)

3

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

Ridges/trenches in South Atlantic Sea Floor

3

Figure 3.C

3

Fig nftBathymetry can tell you wherethings are: Oceanic ridge system

3

Figure 3.6

3

BATHYMETRY – OCEAN FLOOR CONTOURS

Fig 4-5, g

3

AtlanticOcean

3

fnft

3

Fnft: Some large-scale features of the North Atlantic seafloor

Courtesy National Geophysical Data Center/NOAA

3Mid-Atlantic Ridge between Florida and western Africa

Canyon in middleof ridge

3Topography of the

Ocean Floor

REMEMBER: • deepest part of the ocean lie near its edges

3

fnft

3Topography 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 4-9, g

3

Figure 3.8

3

Florida coast

3but

•What goes UP must go DOWN! &

•There are 2 sides to every…OCEAN!

3

3

Figure 3.7

3

Fig 4-7, g

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

3

3Continental Margins

•Active margins- – continental margins on the edge of

convergent or transform plate boundaries

– Pacific-type margins

3

Fig 4-8, g

3 Continental Margin:

Continental SHELFContinental BREAKContinental SLOPEContinental RISE

3

Fig 4-9, g

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, g

3Continental Margins

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

sediment– gradual slope

3Folded ridges of sediment cover the ocean floor west of Oregon

3Continental Margins

• Submarine Canyons– cut into the continental shelf and

slope – formed by turbidity currents

(avalanche-like sediment movements)

3

3SubmarineCanyonOff ofThe coastOf NewJersey

3

3What comes next?

• Where the Continental Slope/Rise (granite rock) meets the “deep” ocean floor you get a sediment covered area (Continental Rise) that meets the “true” ocean floor (basalt rock)…what do you find there? What does it look like?

3

Fig 4-9, g

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

3

Figure 3.15

3Ocean Basin

•Oceanic ridges– Underwater mountain chain – an active spreading center– offset at regular intervals by transform

faults– You know this as “Sea Floor Spreading”

(divergent plate boundary)

3

Fig nftWHERE THE RIDGES ARE!

3

Fig. 4-16a, p. 89

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.

3Other examples of what

“exists” on the Ocean Floor

• SeaMounts• Guyots• Abyssal Hills• Abysall Plains• Trenches• Island Arcs (seen above “land”)• Hydrothermal Vents

3Ocean Basin

• Seamounts– Inactive volcanoes that do not rise above

the surface of the ocean– They are tall with steep slopes– (Made of) Basalt!

3Ocean Basin

• Guyots– Flat-topped seamounts that were eroded

by wave action

• Abyssal Hills– abundant, small sediment-covered extinct

volcanoes

Both still BASALT!

3

guyots (G) and seamounts

3

Figure 2.26

3Ocean Basin

• Island Arcs– Curving chains of volcanic

islands and seamounts found paralleling the edge of trenches

– Part of an “Ocean-Ocean” Convergent Plate Boundary geographic result

3

3

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

3

Figure 3.12

3Ocean Basin

• Trenches– Arc-shaped depression in the deep

seafloor– a converging oceanic plate is subducted

(either Oceanic-Oceanic or Oceanic-Continental Crust)

3

Figure 3.13

3

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

Approximate locations of confirmed hydrothermal vents and cold seeps

3

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

3

3

A black smoker on the Galápagos Rift Zone.

Courtesy of UCSB, University S. Carolina, WHOI/NOAA

3

3

3

Red-plumed tube worms

Courtesy of Monika Bright, University of Vienna, hydrothermalvent.com

3Importance of

Vent Ecosystem Discovery1. Life in extreme

environments2. Life independent of sun

3Chemosynthesis = a type of

primary productionPhotosynthesis uses sunlight + carbon dioxide coverts to foodChemosynthesis uses sulfur + carbon dioxide converts to food

Photosynthesis reaction:CO2 + H2O + sunlight CH2O + O2

 Chemosynthesis reaction:O2 + CO2 + H2O + H2S   CH2O + H2SO4

  where H2S is hydrogen sulfide, H2SO4 is sulfuric acid, and CH2O is “food” or organic material

3PHOTOSYNTHESIS

+

CO2 + H2O O2 + [CH2O]

CHEMOSYNTHESISCO2 + H2O + H2S + O2 [CH2O] + H2SO4 CO2 + H2O + H2S + O2 [CH2O] + H2SO4

3Importance of Vent

Bacteria

• Base of vent ecosystem -- chemosynthesis• Possible origin of life on Earth• Illustrate link between biology and habitat

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!

3Coral Reef Development

• Fringing reefs – develop along margin of landmass

• Barrier reefs – separated from landmass by lagoon

• Atolls – reefs continue to grow after volcanoes are submerged

3Coral Reef Development

3

Fnft

3

Fnft

3

Fnft

3

3

Fnft

3

Figure 4-6c Present-Day Margin Southeast of Cape Cod

Fnft – Reefs can exist FAR offshore (relics from years ago)