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 then 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.
Where are atolls?
• Most of the world's atolls are in the Pacific
Ocean (with concentrations in the Caroline
Islands, Marshall Islands, Coral Sea
Islands, and the island groups of Kiribati
and Tuvalu) and Indian Ocean
• The Atlantic Ocean has no large groups of
atolls other than eight atolls east of
Nicaragua
Read “Bubblegum corals from New Zealand
seamounts and the deep sea”
1. Why are the called “bubblegum” coral?
2. What is the job of corals in an aquatic
ecosystem?
3. What is unusual about the geographical
patterns of these corals?