Transcript Ocean Waters and the Ocean Floor

Ocean Waters and the Ocean
Floor
The Vast World Oceans
• 81% of the Southern Hemisphere is
covered by oceans
• 61% of the Northern Hemisphere is
covered by oceans
• 71% of the Earth is covered by oceans
and marginal seas
The Vast World Oceans
• Three major oceans
– Pacific (by far the
largest)
– Atlantic
– Indian
Composition of Seawater
• 3.5% dissolved
minerals in seawater
• Salinity—the
proportion of
dissolved salts to
pure water
– Open ocean—33% to
37% salinity
– Persian Gulf and Red
Sea—exceeds 42%
– Baltic Sea—below
10%
Resources from Seawater
• Salt (evaporating
ponds)
• Magnesium
• Bromine—used for
gasoline additives &
fireproofing materials
• Freshwater—
desalination
The Ocean’s Layered Structure
• Based on temperature and salinity
• Surface mixed zone—2%
– Thickness depends on latitude and season
• Thermocline (Transition zone)—18%
– Drastic drop in temperature in nonpolar
regions
• Deep zone—80%
– Around 4°C
The Ocean’s Layered Structure
• Salinity
– Below the surface zone, salinity decreases
rapidly
– Halocline—corresponds closely with the
thermocline
Earth Beneath the Sea
• Mountains, deep canyons and flat plains
• Depth mapped by H.M.S. Challenger in
the late 1800s.
• Echo sounder (sonar) invented in the
1920s.
• Three major units of topography
– Continental margins
– Ocean basin floor
– Mid-ocean ridges
Continental Margins
• Zones
– Continental shelf
– Continental slope
– Continental rise
• Deep-sea fan
– Muddy currents
deposit sediment on
the flat ocean floor
Submarine Canyons and Turbidity
Currents
• Created by a process
that operates far
below the ocean
surface such as:
• Turbidity currents—
downslope
movements of dense,
sediment-laden water,
eroding the sea floor
as they move
The Ocean Basin Floor
• Deep ocean trenches
– Challenger Deep is more than 11,000 m
(36,000 ft.) below sea level
• Abyssal plains
– Flat regions consisting primarily of sediments
transported by turbidity currents
• Seamounts
– Volcanic mountains
– Guyots
• Submerged, flat-topped seamounts
Mid-Ocean Ridges
• Sites of seafloor
spreading
• Elevated position,
faulting, and volcanic
structures
• Rift zone—where
magma moves
upward to create new
slivers of oceanic
crust
Coral Reefs and Atolls
• Coral reefs—
constructed from
skeletal remains and
secretions of corals
and algae, built up
over thousands of
years
Coral Reefs and Atolls
• Atolls—coral islands
consisting of a
continuous or broken
ring of coral reef
surrounding a central
lagoon
Seafloor Sediments
• Terrigenous sediment
– Consists primarily of mineral grains that were
weathered from continental rocks
• Biogenous sediment
– Shells and skeletons of marine animals and
plants (mainly microscopic)
• Hydrogenous sediment
– Minerals that crystallize directly from seawater
through chemical reactions