Oceanography 100
P Anderson
Chapter 3
Marine Provinces
Bathymetry
• Bathymetry is the measurement of ocean depths and the charting of the shape or
topography of the ocean floor
• The ocean floor is a highly varied terrain that contains many interesting features
• Early methods of determining ocean depths involved using a long weighted line
(called a sounding line)
Bathymetric techniques
• Echosounders send sound through water to determine water depth and sea floor
features
• Side-scan sonar uses a “fish” towed behind a ship to give a more detailed picture of
the sea floor
• Low frequency sound is used to determine structure beneath the sea floor
• Satellites measure sea surface elevation, which mimics sea floor bathymetry
The hypsographic curve
• The hypsographic curve shows the relationship between the height of the land and the
depth of the oceans
Major regions of the North Atlantic Ocean floor
• Continental margin
• Ocean basin floor
• Mid-ocean ridge
Passive versus active continental margins
• Passive margin
– No plate boundary
• Shelf
• Slope
• Rise
• Active margin
– Plate boundary
• Convergent
 Shelf
 Slope (steep)
 Trench
• Transform
 Continental borderland
Submarine canyons and deep-sea fans
• Turbidity currents carve submarine canyons into the slope and shelf
• Debris from turbidity currents creates graded bedding deposits and deep-sea fans
• Deep flat areas formed by suspension settling
• Volcanic peaks poke through the sediment
– Abyssal hills (seaknolls)
– Seamounts
– Tablemounts (guyots)
Ocean trenches
• Deepest parts of the ocean
• Formed by plate convergence
• Most trenches are in the Pacific Ocean
• Associated with volcanic arcs
– Island arc
– Continental arc
The mid-ocean ridge
• Circles the globe like the seam of a baseball
• Mostly traverses the middle of ocean basins
• A topographically high mountain range
• Entirely volcanic in origin
• Associated with plate divergence
• In the Pacific Ocean, called the East Pacific Rise
• In the Atlantic Ocean, called the Mid-Atlantic Ridge
The Mid-Atlantic Ridge
• Traverses the center of the Atlantic Ocean
• Contains a central down-dropped rift valley
• Comes above sea level in Iceland
Features of the mid-ocean ridge
• Rift valleys
– Form when plates split apart
– Down-dropped areas associated with faults and earthquakes
• Pillow lava
– Forms when hot lava comes into contact with cold seawater and quickly cools
– Basalt composition
Features of the mid-ocean ridge
• Hydrothermal vents
– Form when seawater is heated by magma
– Black smokers emit hot water through chimneys
–
Associated with metal sulfide deposits and unusual lifeforms
Transform faults and fracture zones
• Transform Faults
– Occur between segments of the mid-ocean ridge
– Transform plate boundaries
– Movement in opposite directions
• Fracture Zones
– Occur beyond segments of the mid-ocean ridge
– Not plate boundaries
– Movement in the same direction