1. The Ocean Floor
Ch. 23

2. Studying the ocean floor
Submersibles, satellites, and other technology allow scientists to study the structure and composition of the ocean floor.

3. 1. Echo sounding
a system that uses transmitted and reflected sound waves to measure distances to the ocean floor; SONAR.
measure how long it takes for signal to be emitted and come back
multi-beam echo sounding measures area twice as wide as ship
use info to make seafloor maps
intensity of sound beams determine seafloor composition
rock & gravel reflect more strongly than mud

4. Echo sounding

5. 2. Sediment Sampling
Core sampling: hollow cylinder removes long cores of material from seafloor
layers are preserved
1-1500m of sediment are gathered
can analyze past climate, life, and ocean events

6. 3. Satellite observations
greater range & speed for mapping
doesn’t reach floor, bounces off surface
Ocean surface varies based on what’s below
higher over mountains, lower over trenches
determines differences down to cm’s
makes high-resolution seafloor image

7. HIGH RESOLU-TION SEAFLOOR IMAGE
Pacific and Western Atlantic Oceans

8. The CONTINENTAL MARGIN
In order to understand the continental margin, we must first understand the crust of the Earth.
The continental margin is part of the crust.

9. two types of crust Continental Crust Oceanic Crust
lighter, less dense rock
Makes up all continents, but not necessarily all islands
Oceanic Crust
darker, dense rock
any ocean floor or ocean basin

10. THE MOVING CRUST all of the crust is divided into ‘pieces’ or plates
(Called lithospheric plates or tectonic plates)
the plates move around on the semi-solid mantle
Plates meet= called plate boundaries
at plate boundaries, the crust can be moving side by side, apart, or together
different topographic features are created, depending on the type of boundary
topography: the shape of the land

11. World plate boundaries

12. The CONTINENTAL MARGIN
The underwater portion of the continental crust.
There are two types of continental margins.

13. 1. Active CONTINENTAL margins
continental margins that occur along plate boundaries
plates are moving side by side or together
when one plate sinks under another, a trench is formed
when plates move past each other, a fault is formed
continental rise is small or nonexistent
rocky, short beach w/ cliffs
rugged, coastal mountains on land
EX: West coasts of North America and South America

14. 2. Passive continental margins
continental margins that don’t occur along plate boundaries
broad continental shelf
long, sandy beach
no trenches, mountains, or faults
EX: East coast of North America

15. Parts of the continental margin
In order from land  Sea:
continental shelf: part of the continent that extends from the shoreline to the continental slope
flat, lengths vary depending on location
continental slope: begins at the shelf edge where depth decreases rapidly to the rise.
20km long; descends 3.6km
sediment builds up temporarily, then falls
continental rise: descends gradually from the slope to the ocean floor
considered part of ocean basin
very long & gradual

16. Submarine canyon
an undersea gully that cuts across the continental shelf and slope
rivers erode the continental shelf and deposit sediment on continental slope
gravity and powerful turbidity currents carry sediment down to the continental rise
Very powerful agents of erosion
coarse particles settle first, then fine such as clay

17. The Ocean Basin
Abyssal Plain – flattest of all Earth’s surfaces, composed of sediment from continents
Occur in all oceans
More in Atlantic Ocean where there are fewer trenches
Abyssal hills – small hills, occur in groups next to oceanic ridge systems

18. Deep-sea trenches
Deep-sea trenches – long, narrow, steep-sided troughs that run parallel to continental margins
occur when one plate slides beneath each other
Exist at subduction zones
Earthquakes & volcanoes common

19. Two scenarios for trenches to form:
1. Continental-oceanic collision (O-C collision):
Deep sea trench forms
Volcanic islands form on continent bordering trench
2. Oceanic-Oceanic collision (C-C collision):
Deep sea trench
Volcanic islands form on overriding plate

20. Deep-sea trenches

21. Vents and ridges
Deep ocean vents – geyser that erupts underwater, mixing hot and cold water and bringing up minerals from beneath the surface; hydrogen sulfide
Mid-ocean ridges- are
undersea mountain ranges,
where 2 plates are moving
apart & magma rises

22. Sea mounts & guyots
Seamounts- cone-shaped volcanic mountain peaks, rising high above the ocean floor
All oceans, but mainly Pacific Ocean
Volcanic in origin (ex. Hawaiian islands)
Guyots are flat-topped seamounts- extinct volcanoes; older, eroded by wind & waves

23. Coral &coral Atolls
Corals= tiny animals that live in warm shallow seas
Atolls:
reefs form around volcanic islands b/c of nutrients
volcanic island goes extinct- cools, contracts, sinks
coral atoll is left- reef surrounding shallow lagoon

24. Complete the Quick-Write on how coral atolls form.
PAGE 10 INB
Complete the Quick-Write on how coral atolls form.

25. Ocean Floor Sediments
Sediment reaches the ocean floor in several ways: turbidity currents, fall from above, settle from glaciers, remains of microscopic shells
Terrigenous sediments – come from continental rocks an minerals broken down from weathering an erosion
wash into rivers and out to sea
may come from glaciers
breaking and dropping
into sea

26. Ocean Floor Sediments
Biogenous sediments come from living sources; they are oozes made mostly of shells and skeletons from tiny marine animals
Calcareous ooze=calcium carbonate
Most common from shells
and skeletons
Dissolve as they sink below
4500 meters
Siliceous ooze=silicon dioxide
More common around
Equator and Antartica

27. Ocean Floor Sediments
Hydrogenous sediments form when chemical reactions cause minerals to crystallized from seawater.
Manganese nodules are most common – has manganese, iron oxide, nickel, cobalt, copper…
They form on the sea floor from sediment that falls on them and mixes with the sea water, a few mm every million years
Important to humans but hard to get

28. Ocean Floor Sediments
Cosmogenous- meteorites from space; rarest sediment type

29. Importance of sediments
studying sediments:
past climates
ancient water temperatures
prevailing winds
Climate
Once-living organisms
The sediments, unique organisms, magnetic records, industrial resources on the ocean floor represent a past look at Earth’s hydrosphere, biosphere, and geosphere.

30. What type of sediments are each of these?
PAGE 12 inb
What type of sediments are each of these?

31. Ocean floor
Know these features for your quiz!!!