1. Under the Sea
Chapter 4

2. Bathymetry Discovery & study of the ocean floor History: Improvements:
throw heavy rope tied to a rock over the side of the boat
measured fathoms as arm lengths
Improvements:
Echo Sounding, Multi-beam Systems & Satellite Systems

3. Echo Soundings After Titanic (1912) & WWI increase in bathymetry. Why?
Looked for better way to study ocean
Developed a sound pulse and listen for echo
Similar to dolphins, porpoises, & ocras which use echolocation

4. Echo Sounding Problems
ship position not certain
speed of sound varies with temp, pressure, salinity and affects readings
images were fuzzy

5. Multi-beam Systems 121 beams from ship to take echo sounding
more accurate reading
Like “mowing the lawn” gave a section to interpret rather than a single point

6. Satellite Altimetry
Satellites measure small variations in the elevation of surface water
Many radar pulses each second
Used sophisticated calculations to determine the sea floor

7. Topography of Ocean Floors
Seabed topography is due to isostatic equilibrium
Balancing of less dense continental plate and more dense oceanic plate over mantle
Submerged outer edge of continent = continental margin
Deep sea floor = ocean basin

8. Continental Margins Active Margins: Passive Margins:
continental margins of converging plates
Lots of volcanic & earthquake activity
Ex: Pacific Plate
Passive Margins:
continental margins of diverging plates
Little volcanic & earthquake activity
Ex: Mid-Atlantic Ridge

9. 3 types of Continental Margins
Continental Shelf
Continental Slope
Continental Rise

10. Continental Shelf Shallow submerged extension of continent
Features: hills, depressions, sedimentary rocks, & mineral/oil deposits
Gentle incline
Consists of material from erosion (ex: river mouths) which can determine the width of shelf
Affected by sea level: ice age can change isostatic equilibrium
Used for resources: minerals & oil

11. Continental Slope
Transition between the continental shelf & the ocean floor
Sediments from shelf are transported over the side creating a slope
Often scraped off by subduction
Shelf break = abrupt transition from continental shelf to the continental slope

12. Submarine Canyons Canyons cut into shelf & slope Fan-shaped
Usually right angle to shoreline
Formed from erosion and/or earthquakes
Earthquakes create turbidity currents (avalanche of sediment)

13. Continental Rise Sediment at base of slope transported from shelf
Deep-ocean currents &/ turbidity currents

14. Deep-Ocean Basins
Oceanic ridge systems and adjacent sediment-covered plains
Includes:
Oceanic Ridges
Hydrothermal Vents
Abyssal Plains & Abyssal Hills
Seamounts & Guyots
Trenches & Island Arcs

15. Oceanic Ridges
Mountainous chain of basaltic rock at center of spreading center
Formed from divergent boundaries
Old rocks far away from center
Young rocks at center
Not in straight line, broken up by transform faults and fracture zones (remnants of transform faults)

16. Hydrothermal Vents Hot springs from ridge floor
Forms from water into cracks of ridge floor and venting out
Water is hot, acidic, filled with minerals, and gases
Unusual organisms live here

17. Abyssal Plains & Abyssal Plains
flat sediment covered floor found on periphery of all oceans
Sediment from turbidity currents or winds
Hills:
small volcanoes, from diverent boundaries, parallel / borders ridges

18. Seamounts & Guyots Formed from old hotspots Seamounts: Guyot:
old volcanoes never breeched surface
Guyot:
former islands eroded down
Ex: 100+ small islands of Hawaii

19. Trenches & Island Arcs Trenches: Island Arcs:
Deep depression in ocean floor
Deepest part of ocean
Forms from subduction zones
Island Arcs:
chain of volcanic islands from subduction zones
Ex: Aleutian Islands