Transcript The Ocean Basins

The Ocean Basins
The Water Planet
Nearly 3/4ths of the
worlds surface lies
beneath a body of
water called the global
ocean.
The global ocean
contains more than
97% of all the water
on Earth
Divisions of Global Ocean
 Divided into 5 major
oceans: Atlantic,
Pacific, Indian, Arctic,
and Southern.
 Pacific is the largest
and deepest ocean on
Earth (West coast)
 Atlantic is second
largest ( East coast)
• Indian is the 3rd largest
• Southern extends from
coast of Antarctica to 60˚
• The Arctic ocean is the
smallest ocean, and
surrounds the north pole .
Ocean/ Sea
• Sea is a body of
water that is smaller
than an ocean that
may partially
surrounded by land.
They are usually
located where land
and the ocean meet.
Dead Sea
Bathymetry = study of ocean floor contours
2 km
The early, simplest
methods involved
lowering a weight
on a line.
http://www-groups.mcs.st-and.ac.uk/history/BigPictures/Posidonius.jpeg
Posidonius
• conducted the first
bathymetric studies
• 85 B.C.
Hydrography: measures the physical
features of a body of water
Tanner sounding machine
• developed around 1880
Sigbee sounding machine
• developed around 1880
http://woodshole.er.usgs.gov/operations/sfmapping/images/theb0914_small.jpg
http://www.nefsc.noaa.gov/history/ships/albatross1/sigsbee-sounding.jpg
Sometimes the weight was tipped with wax to
retrieve a sample of bottom sediment.
HMS Challenger
(1872-1876)
• made the first
systematic attempt to
chart the basins of the
world ocean
• made 492 bottom
soundings
confirmed the discovery
of the Mid-Atlantic Ridge
Scientists now use beams of sound to measure depth.
SONAR: Sound navigation and ranging
Sound travels through water at about 1500
m/s. So if you measure the time it takes to leave and bounce off
ocean floor and return you can calculate the depth.
Titanic
• sank on its maiden voyage in 1912
Reginald Fessenden
(1866-1932)
• Canadian inventor
• in 1914, developed a
type of sonar system for
locating icebergs
http://en.wikipedia.org/wiki/Reginald_Fessenden
“Iceberg Detector and Echo Depth Sounder”
Reginald Fessenden
(1866-1932)
• Canadian inventor
• in 1914, developed a
type of sonar system for
locating icebergs
http://en.wikipedia.org/wiki/Reginald_Fessenden
“Iceberg Detector and Echo Depth Sounder”
Reginald Fessenden
(1866-1932)
• Canadian inventor
• in 1914, developed a
type of sonar system for
locating icebergs
http://en.wikipedia.org/wiki/Reginald_Fessenden
“Iceberg Detector and Echo Depth Sounder”
Reginald Fessenden
(1866-1932)
• Canadian inventor
• in 1914, developed a
type of sonar system for
locating icebergs
http://en.wikipedia.org/wiki/Reginald_Fessenden
“Iceberg Detector and Echo Depth Sounder”
Echo sounders
sense the contour
of the seafloor by
beaming sound
waves to the
bottom and
measuring the
time required for
the sound waves
to bounce back to
the ship.
V = speed of sound in water
(about 1.5 km/sec)
T = time
During World War I (1914-1918)
• used to detect enemy submarines
Meteor expedition (1925-1927)
• used to study the seabed
http://www.eastlanddisaster.org/uc97.jpg
http://oceanworld.tamu.edu/resources/ocng_textbook/chapter02/Images/Fig2-2s.jpg
Heinrich Berann (1915-1999)
• Austrian artist
World Ocean Floor
Pacific Ocean
http://www.panorama-map.com/Europeans/Berann/berannpacificocean500.html
Mt. Everest
(1962)
http://www.berann.com/panorama/Everest.jpg
Two new techniques improved studies
of the seafloor:
1) multibeam echo sounders
2) satellite altimetry
Multibeam systems combine many echo sounders.
• up to 121 beams
• signal sent every 10 secs
<200 research vessels are
equipped with multibeam
systems
Seabed contours can be mapped using satellites.
Satellites cannot
measure ocean
depths directly
• but, they can
measure sea surface
height
Sea surface
Seafloor
Sea surface
Seafloor
？
Sea surface
Gravitational attraction “pulls” water
Over a 2000 m seamount, water rises about 2 m
Seafloor
Geosat satellite
Seafloor topography inferred from sea surface
height measurements
http://www.ngdc.noaa.gov/mgg/image/global_grav_large.gif
Mapped by: Geosat, TOPEX/Poseidon, and Jason-1
Ocean-floor topography varies with location
>50% of Earth’s
surface is >3,000 m
below sea level
Oceans can be divided into two major provinces:
1) continental margin: shallow parts of ocean
floor made of continental crust
2) ocean basin: deep part of ocean beyond
continental margin.
Continental margins are “active” or “passive”.
Near converging
plates
Face the edges of
diverging plates
• earthquakes
• volcanic activity
• no earthquakes
• no volcanic activity
Three parts of Continental Margins:
1. Continental shelf: part of continent that is covered
with water ( average depth is 60 m.)
2. Continental slope: depth increases by several
thousand meters
3. Continental rise: raised wedge at the base of c.slope
that is formed by sediments
Continental shelf: shallow submerged extension of a continent
• up to 350 km
• most material comes from
erosion of continent
http://media.allrefer.com/s1/l/c0601400-continental-shelf.jpg
Atlantic
http://www.cryingvoice.com/Evolution/gifs/hydroNA.jpg
The shelf width is usually determined by its
proximity to a plate boundary.
active margin –
often very narrow
passive margin –
broad
Continental shelves are greatly influenced by
changes in sea level
Sea level rise
Sea level is
now high and
rising as the
ocean warms.
Wisconsin glaciation
http://en.wikipedia.org/wiki/Image:Sea_level_temp_140ky.gif
Wisconsin glaciation
• 70,000 to 10,000 years ago
Ice sheets
• 3-4 m thick
• caused sea
level to drop
125 m
ice age
http://en.wikipedia.org/wiki/Image:Northern_icesheet_hg.png
Bering Strait
http://whyfiles.org/shorties/202mass_extinct/images/land_bridge.gif
Bering Strait
http://whyfiles.org/shorties/202mass_extinct/images/land_bridge.gif
Allowed human
migration 12,000
years ago
Bering Strait
http://whyfiles.org/shorties/202mass_extinct/images/land_bridge.gif
Continental slopes connect continental shelves to the
deep-ocean floor
shelf break
Submarine canyons form at the junction between continental
shelf and continental slope. Deep V shaped valleys often found at
the mouths of major rivers .
Monterey Bay canyon
http://www.tahoemaps.com/files/Monterey_large.jpg
Monterey Bay canyon
2000 m
http://www.marine-geo.org/gallery/images/MontereyBay3D.jpg
Suruga Bay
Submarine canyons cut
into the continental
shelf and slope, often
terminating on the
deep-sea floor in a fanshaped wedge of
sediment.
How do submarine canyons form?
turbidity current
an underwater
“avalanche” of sediment
Most geologists believe that submarine
canyons have been formed by abrasive
turbidity currents plunging down the canyons.
http://unit.aist.go.jp/igg/rg/igi-rg/beta/sl-support/R-formation/TurbidityCurrent.jpg
Continental rises form as sediments accumulate at the base of the
continental slope
continental rise
• much sediment
• most of the
sediment that forms
the continental rise
is transported to the
area by turbidity
currents
The topology of deep-ocean basins differs
from that of the continental margin
Deep-ocean basins comprise mainly:
1) Trenches- long narrow depressions . Form
when one plate subducts below another plate
2) Oceanic ridge systems- underwater
mountain ranges . Form where plates pull away
from each other
3) Sediment-covered plains- vast, flat
areas where the ocean is more than 4km deep
Oceanic ridges circle the world
• underwater mountain ranges
• stretch 65,000 km
• often covered with little sediment
Mid-Atlantic Ridge
http://www.berann.com/panorama/archive/image/PN_W_10.jpg
Mid-Atlantic Ridge
fracture zones
transform faults
http://www.berann.com/panorama/archive/image/PN_W_10.jpg
Hydrothermal vents are hot springs on
active oceanic ridges
• discovered in 1977 by Robert Ballard and J. F. Grassle
Alvin
http://www.mbari.org/molecular/images/EPR%20mussel-map.jpg
Alvin
• can carry 3 people
• can dive to 4000 m
• 1964 – 2007
• >4000 dives
manned submersible
Bathyscaph( free-moving)
• 6,500 m
unmanned submersible
Bathysphere ( remains
connected)
• 11,000 m
“black smokers”
350oC
20 m
2,800 m depth
http://www.csa.com/discoveryguides/vent/images/smoker.jpg
http://whyfiles.org/coolimages/images/csi/nur04506.jpg
solutions exiting vents are acidic (pH = ~3.5) and contain up to 300
ppm hydrogen sulfide (H2S)
• a highly reduced molecule, so much energy can be obtained when
it is oxidized
“black smokers”
seawater is heated and
reacts chemically with
the surrounding basalt
http://www.divediscover.whoi.edu/images/vent_chemistry.jpg
hydrothermal vent community
deep-sea vent mussels
• includes snails, shrimps,
crabs, tube worms, fishes
and octopuses
• depends on chemosynthetic
bacteria for food
http://www.sciencedaily.com/images/2005/02/050223124700.jpg
Tube worms
chemosynthesis
Hydrothermal vents are common on oceanic ridges
http://www.nature.com/nature/journal/v439/n7079/images/hydro_vents/index.html
AND in freshwater (Lake Baikal)
Abyssal plains and abyssal hills cover most of
Earth’s surface.
Flat
Abyssal plains
• 50% of the ocean floor
• common in the Atlantic
• rare in the Pacific
• covered by fine sediment
Abyssal hills
• small sediment-covered
extinct volcanos or rock
Volcanic seamounts and guyots project above the seabed
seamount
• >1 km in height
• important fishing
areas
• about 30,000
• about 10,000 in the Pacific
Emperor
Seamounts
http://upload.wikimedia.org/wikipedia/en/thumb/2/25/Seamount_Locations.png/350px-Seamount_Locations.png
Guyot: flat-topped seamount that once reached the surface
http://en.wikipedia.org/wiki/Image:Guyot.jpg
Trench: arc-shaped depression on the deep-ocean floor
• occur near subduction zones
• deepest places in the ocean
• most in the Pacific
•Deepest is Mariana Trench in
Pacific >11,000 m
http://geology.com/records/ocean-trench.gif
>8 km ( deepest in Atlantic
Peru-Chile
trench
Puerto Rico
trench
Peru-Chile : longest trench
3,650 miles or 5,900 km
http://en.wikipedia.org/wiki/Image:Peru-Chile_trench.jpg
Japan Trench
10,595 m
Mariana Trench
11,022 m
Trieste
• reached the bottom of the Mariana
Trench in 1960 ( manned)
Kaiko
• Japanese deep-sea submarine
• sampled bacteria from the bottom
(10,897 m) of the Mariana Trench in
1996 ( unmanned)
Sampling of the world's
deepest sea sediment by
"Kaiko" at the Mariana
Trench, Challenger Deep
Bacteria collected from the Mariana Trench
• lost at sea in
typhoon in 2003
•Cost 15 Million
DeepSea Challenger
• On March 26, 2012,
Canadian film director
James Cameron
piloted the craft to
accomplish this goal,
becoming the first
person to reach
Challenger Deep in a
one-man craft
Key Points
1. The ocean floor is mapped by bathymetry.
2. Ocean-floor topography varies with
location.
3. Continental margins are “active” or
“passive”.
4. The topology of deep-ocean basins differs
from that of the continental margin.