1. The Ocean Floor and the coast
Section 1: Plate tectonics and the ocean basin

2. Drawing Assignment
Complete drawing of zones and sea floor features: abyssal zone, abyssopelagic zone, continental shelf, continental slope, epipelagic zone, hydrothermal vent, intertidal zone, mesopelagic zone, mid-ocean ridge, trench

3. The Ocean and Seas Oceans cover 71% of earth’s surface
Southern hemisphere = 80%
Northern hemisphere = 61%
84% deeper than 2000m
Greatest depth ~ 11,000 m in Marianas Trench
Seas (marginal seas)
Close to coasts with limited connection to ocean
Found mostly in Atlantic ocean
Examples: Gulf of Mexico, Mediterranean Sea

4. Ocean zones and features
Based upon depth and habitat
Intertidal zone (also known as the littoral zone): covers area of the coast from high water mark to lowest part of the shore permanently submerged (think high and low tide)
Continental shelf: area between high water mark and edge of continental shelf (approximately 10 km-300 km from shore)
Continental slope: steep slope beginning at the edge of the continental shelf

6. Pelagic zone: open ocean
Epipelagic: top 200 m
Mesopelagic: 200-1,000 m
Bathypelagic: 1,000-4,000 m
Abyssopelagic: 4,000-6,000 m
Benthic zone: seafloor
FIG A cross section of the ocean from the shoreline to the deep sea, showing the location of major marine habitats.

7. Deep-sea features:
Submarine canyons: steep sided valley located in the continental slope
Trench: deep depression in the ocean floor sometimes found near volcanic islands

8. Deep-sea features: Mid-Ocean ridge: underwater mountain ranges
Seamount: steep-sided formation
Seamount with a flat top worn down by wave action = guyot
Abyssal plains: flat bottom of ocean floor

9. Another view Continental shelf (1° slope)
Continental slope (2.9° slope)
Continental Rise
Abyssal Plain
Submarine Canyons

10. Topographical features (w/ measurements)
FIG. 2.2 Two examples of continental margins showing various topographic features and also topographic features of the deep-sea floor (vertical slope is exaggerated).
How do we know the depth of these features?

11. Brainstorm Where did all of these features come from?
Which regions of the world have more ridges, trenches and canyons?

12. Theory of Plate tectonics
Earth’s crust (lithosphere) is divided into large sections called plates.
The plates float atop the asthenosphere (viscous fluid, very hot)
Plates are bordered by ridge systems, trenches and faults.
Fault – break in Earth’s crust
Movement of plates causes underwater features and natural disasters (earthquakes, tsunamis)

13. FIG. 2.3 The ocean floor showing plate boundaries, oceanic ridges, where new oceanic crust is created by volcanism (red lines with thin arrows), fault and fracture zones (red lines without thin arrows), and trench zones (thick, dark blue bands).
Map of earth with features

14. Why are the plates moving?

15. Plate boundaries Convergent Divergent Transform
Two tectonic plates collide
Plates can buckle, shift upward or bend
Divergent
Two tectonic plates move away from each other.
Magma rises to surface
Transform
Two tectonic plates slide past each other

16. Continental Drift Theory
1912: Alfred Wegener first to suggest theory
One land mass (Pangea) slowly separated
1960’s: theory revised and accepted
Outer crust of Earth (lithosphere) floats on top of a layer called the asthenosphere
Lithosphere contains dense ocean crust and lighter continental crust (land)
Continents move as ocean floor moves
NOTE: The theory of plate tectonics supports the theory of continental drift

17. Why do we have different plate movement?

18. Evidence to support continental drift theory & plate tectonics
Coastlines of present day continents “fit” together
Distribution of fossil species
Magnetic stripes in sea floor

19. Coastlines of present day continents “fit” together

20. 2. Distribution of fossil species
Fossils from same or similar species found on continents separated by oceans today.

21. 3. Magnetic stripes in sea floor
Evidence found at divergent plate boundaries
As divergent plates move apart, new oceanic crust forms as magma rises to the surface of the lithosphere.

22. Seafloor spreading
Minerals in the magma crystallize in direction of earth’s magnetic field

23. Magnetic anomalies support theory of plate tectonics
There have been 170 reversals of earth’s magnetic field
Examination of rock minerals in ocean floor correlates with reverse of magnetic polarity
Therefore, sea floor is spreading!!!

24. Ocean floor and land features
What are the visible effects of tectonic plate movement?
Trenches, mid-ocean ridges, volcanoes, hydrothermal vents, earthquakes & tsunamis

25. Trenches Formed by subduction
Subduction: dragging of oceanic crust downward causing melting into mantle.
Occurs at convergent plates
Challenger Deep is approximately 11,020 m deep and found in Pacific ocean

26. Mid-ocean ridges Formed at divergent plates
Magma rises slowly forming a series of small “mountains” as it cools

27. Volcanoes
Formed by opening in Earth’s crust, which then allows magma and gases to escape
How do they form?
Thinning crust at divergent plates (mostly under sea)
Convergent plates (mostly land)

28. Volcanoes Effects of volcanic activity on seafloor
Formation of new seafloor
Formation of islands that rise above sea-level
Release of minerals and gases for use by deep-sea organisms
Ring of fire – area with most
volcanic activity in world

29. Hydrothermal vents
Openings that look like chimneys found near mid-ocean ridges in deep ocean (typically around 2,000m depth)
Cold sea water seeps into cracks in ocean floor near divergent zones, is heated by magma, returns to the surface and is released through vents

30. Hydrothermal vents
The depth creates high pressure, which can heat water up to 340oC
Minerals dissolve in heated water coming out of hydrothermal vents:
Contain iron, copper, zinc and sulfur
The minerals precipitate out of solution as the water cools (adding to the vents structure)
Environment provides energy source for chemosynthetic organisms

32. Earthquake
Caused by a release of large amounts of energy from the earth’s crust.
Convergent plates and transform plates may be unable to slide past each other.
Strain on plates builds up pressure and energy
Sudden movement of these plates produces burst of energy
What can underwater earthquakes cause?

33. Tsunami Large wave traveling at high speed
Caused by earthquakes from converging and transform plates on seafloor.
In open sea the wave produced is long but short in depth
As the wave approaches shallow water, the land slows the wave but causes water to pile up and form taller waves

34. Review of underwater features

35. Diagram Review In groups of 3 complete the following:
Draw and label diagrams (in color) showing the formation of the following structures:
Mid-ocean ridge
Hydrothermal vent
Trench
Volcano
Include labels on all parts (direction of movement, plates, boundaries and any features not easily identifiable).
Neatness counts!

36. Brainstorm
We have discussed plate tectonics in relationship to the deep-sea and its features. Let’s watch a review video and then answer these questions.
What affect do moving plates have on the continental shelf?
What happens to moving continental shelves?

37. Continental shelves
Many continental shelves were above sea level during ice ages
Sea level was lower (due to ice sheets)
Weathering caused changes in formation of land
Erosion, sediment deposited by rivers, waves
Melting glaciers and sea level rising covered continental shelves.
Depth of seawater over continental shelf relies upon isostasy and sea level

38. Isostasy produces shallow seas in continental shelves
Isostasy = ‘weighing the same’
Layers of the earth’s crust float on each other according to density.
Which layer is thicker: continental or oceanic crust? Which is more dense?

39. Isostasy and Collisions
Continents can collide with each other when two plates with continental crust converge.
Causes mountain ranges
Why does oceanic crust sink below the continental crust?

40. Shallow seas of Continental shelf
How does isostasy govern the depth of seawater over a continental shelf?