Transcript 2.27 ocean topography

Physical Oceanography
Ocean Topography
What is topography?
• The physical features of an area
• The shapes, patterns and physical
configuration of the surface of the ocean
basins
What do ocean basins look like?
How do we know what it looks like?
The ocean basin: Structures
1. Continental Margin:
(near continent)
Continental Shelf
Continental Slope
Continental Rise
Submarine Canyons
2. Deep Ocean Basin:
Abyssal Plains
Oceanic ridges
3.a Trenches
b Seamounts and Guyots
c Atolls
1.
Submerged, outer edge of the continents
Two types:
1. Active Margin (Pacific)
2. Passive Margin (Atlantic)
Continental Shelf:
• Much more similar to
the continent than the
deep ocean.
• They have hills,
depressions, mineral and
oil deposits.
• In Atlantic Canada, the
continental shelf hold
the best fishing areas
(Grand Banks and Scotia
Shelf)
Submarine Canyon: on the
edge of the continental
shelf
• V-shaped indentations into the
continental shelf, usually ending in
a fan shaped wedge of sediments.
How do submarine canyons form?
• Thought to be turbidity currents and
underwater landslides.
(Turbidity currents are dense, sedimentladen currents which flow on a down slope
when an unstable mass of sediment that
has been rapidly deposited on the upper
slope that fails, perhaps triggered by
earthquakes).
The Gully!
• Submarine canyon off Nova Scotia
• Marine protected area because of the rare corals found there
• The natural gas pipeline goes right by it…problems?
The Gully
• "This species forms colonies
up to two metres high and
takes between 200 and 500
years to grow such a colony.
They only grow 1.5 millimteres
a year."
L. Pertusa (Spider Hazards)
Bubble Gum coral
P. Arborea
Largest reported
from NS was 7m tall!
2.Deep Ocean Basin
•
Abyssal plains: From the Greek
meaning “without bottom”. They
are flat, cold, dark, featureless
expanses of sediment-covered
ocean floor. They are most
common in the Atlantic
• Ocean Ridges
mountainous chains of
actively spreading ocean
floor. They can rise 2km
from the ocean floor and
sometimes form islands such
as Iceland, the Azores and
Easter island.
Mid-Atlantic Ridge
3.Trenches!
• deep gap in ocean floor,
formed by movement of
plates.
• Example: Mariana Trench is
10,668 meters deep
• They are among the most
active areas on Earth.
• They are the deepest areas
of the Earth’s crust.
• 90% of trenches are found
around the Pacific rim.
4.Seamounts and Guyots
Both are undersea volcanoes that originated at a hotspot
or along a ridge
Guyots once reached the surface of the ocean and
have flat, eroded tops
Seamounts never reached the surface, so they have
pointy tops
Example:Hawaii!
5. Atolls
• A ring shaped island of coral reefs and coral debris.
These often form over sinking inactive volcanoes.