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

2. 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

3. 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

5. 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. 1.13 A cross section of the ocean from the shoreline to the deep sea, showing the location of major marine habitats.

6. 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

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

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

9. 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?

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

11. Theory of Plate tectonics Earth’s surface is divided into large sections called plates. 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)

12. 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 http://earthguide.ucsd.edu/eoc/teachers/t_tectonics/p_map_plate_layers_bath.html http://earthguide.ucsd.edu/eoc/teachers/t_tectonics/p_map_plate_layers_bath.html

13. Why are the plates moving?

14. Plate boundaries Convergent –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

15. 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 asthenosphereOuter crust of Earth –Lithosphere contains dense ocean crust and lighter continental crust –Continents move as ocean floor moves

16. Why do we have different plate movement?

17. Evidence to support continental drift theory 1.Coastlines of present day continents “fit” together 2.Distribution of fossil species 3.Magnetic stripes in sea floor

18. 1.Coastlines of present day continents “fit” together

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

20. 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.

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

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

23. 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

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

25. 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)

26. 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

27. 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

28. Hydrothermal vents The depth creates high pressure, which can heat water up to 340 o C 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 (sometimes adding to the vents structure) –Environment provides energy source for chemosynthetic organisms

30. 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?

31. 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

32. Review of underwater features

33. 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.video –What affect do moving plates have on the continental shelf? –What happens to moving continental shelves?

34. 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

35. Isostasy produces shallow seas in continental shelves Isostasy = ‘weighing the same’Isostasy 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?

36. 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?

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