Deep Ocean

• Difficult to observe and sample
• Variety of techniques used

– Deep submersibles
– Remotely Operated Vehicles
– Sample collection – cores, magnetometers
– Cameras
– Remote sensing (depth sounders)

Ocean Profiles

• Atlantic profile (New England to Gibraltar)

– Wide continental shelf
– Continental slope
– Submarine canyons cut into slope
– Continental Rise
– Abyssal plains
– Seamounts
– Mid-ocean ridge – narrow with central rift
– Mirror image as continue east

• Pacific Profile (Peru-Australia)

– Narrow continental shelf
– Deep sea trench
– East Pacific rise – broad without central rift
– A second trench
– Continental rise, slope, shelf of Australia

Continental Margin

• Two types: passive and active

– Passive: not near a plate margin
– Active: at a plate margin
• subduction or transform
• Active: earthquakes and volcanoes
 

• Passive margins

– Flat lying sediment
– Terrigenous and carbonate
– Kilometers thick

• Active margins

– Narrower
– Sediment structurally deformed

• Continental shelf

– Economically important: fisheries, oil production
– Range from shoreline to about 130 m depth
– Most of shelf exposed during recent glaciation

• Continental Slope and Rise

– Water depths greater than wave base
– Much sediment transport: Turbidity currents
– Sediment and water moves downhill
– Moves fast (km/hr)
– Can erode and deposit

 
 

• Turbidites: sedimentary deposits

– Graded bed: course at bottom, fine at top
– At base of rise: called submarine fans

• Similar to aluvial fans

– Form most of the sediment in the abyssal plains
– Grand Banks earthquake

• Broken telegraph cables
• turbidites
 
 

• Submarine canyons

– Major canyons that cut across shelf, slope and submarine fans
– Origin???
– Rivers, turbidity currents

Ocean Floor

• Originate at mid-ocean ridge
• Move away
• Sediment cover as move away

• Mid-ocean ridge

– Most intense volcanism
– Highly fractured and faulted
– Covered with basalt talus

• Hydrothermal system

– Water heated at magma chambers
– Flows upward from chambers
– Vents

• Black smokers: Hydrogen sulfide and metals
• White smokers: Barite precipitates
– Chemosynthetic bacteria – no photosynthesis

• Hills and Plateaus

– Cover much of seafloor away from ridges
– Guyots: flat topped from erosion

• now deep below surface of ocean
• As ocean floor cooled and sank

– Many form as long chains

• Hot spots
 
 

• Coral Reefs and Atolls

– Reefs common at continental margins

• Low latitudes
• Clear water

– Atolls

• Rings of coral reefs in open ocean
• May have lagoon in center or island
• Darwin determined origin

Ocean Sediments

• Two major kinds:

– Terrigenous sands and clays from continents

• Common along continental margins

– Biochemically precipitated shells of marine organisms

• Deep ocean sediments

– Pelagic sediments
– Only very fine terrigenous material
– Very slow sedimentation rates
– Foraminifera: Most common biochemical sediments
 

• Forams:

– Single-celled animals
– Most commonly form carbonate shells
– Planktonic or benthic
– Can compose nearly 100% of sediment

• Carbonate compensation depth

– Carbonate material, including forams, missing below 4 km water depth
– Deep water corrosive to carbonate

• Cold
• High CO2 content
• High pressure
 

• Silica oozes: a second common type of sediment

– Formed of diatom and radiolaria shells
– Diatom: single cell algea
– Rads: single cell animals
– Form chert when recrystallize