1. OCEAN BASINS
CHAPTER 4

3. Study Plan The Ocean Floor is mapped by bathymetry
Ocean-floor Topography varies with Location
Continental Margins may be Active or Passive
The Topology of Deep-Ocean Basins differs from that of the Continental Margin
The Ground Tour

4. The Ocean Floor is mapped by bathymetry
“bathymetry”: ocean floor contours
85 BCE in Greece by Posidonius
1818 – Sir James Clark Ross
Soundings of the South Atlantic – 4893 meters
1870s – HMS Challenger
Confirmed the existence of the Mid-Atlantic Ridge

5. Echo Sounders bounce Sound off the Seabed
1922 – USS Stewart – first continuous ocean basin profile of the Atlantic
: Meteor made 14 profiles in the Atlantic
Echo sounding was not perfect
Temperature, pressure, salinity

7. Multibeam Systems combine many Echo Sounders
Bounce sound off the seafloor at specific intervals to measure the depth of the ocean
Too time consuming… it would take 125 years to map the entire ocean!!!!

9. Satellites can be used to Map Seabed Contours
Geosat satellite measures ocean water elevation with a resolution of 0.03 meter (1 inch)
Gravity can reveal undersea mountains or canyons

11. Ocean-Floor Topography varies with Location
Continental margin: the submerged edge of the continent
Ocean basin: the deep-sea beyond the margin

12. Continental Margins may be Active or Passive
Passive margin: margins facing a divergent plate
Active margin: margins facing a convergent plate boundary

13. Continental Shelves are Seaward Extensions of the Continents
Continental shelf: shallow, submerged extension of a continent
Passive vs. active margins

14. Continental Slopes connect Continental Shelves to the Deep-Ocean Floor

15. Submarine Canyons form at the Junction between Shelf and Continental Slope
Submarine canyon: cut in the wedge of a submerged fan
What causes these canyons?
Turbidity currents and earthquakes

16. Continental Rises form as Sediments Accumulate at the Base of the Continental Slope
Occur along passive margins as aprons of sediments

17. The Topology of Deep-Ocean Basins
Deep-ocean basins are blanketed by 3 miles of sediments overlying basaltic rocks
Oceanic ridge: mountainous chain of YOUNG and HOT basaltic rocks
Stretches 65,000 km

18. Hydrothermal vents
1977: discovered by Ballard and Grassle of the Woods Hole Oceanographic Institution
Chimneys
East Pacific Rise
350 degrees Celsius

19. Abyssal Plains
Flat, featureless expanses of sediment-covered ocean floor

20. Volcanic Seamounts and Guyots
Seamounts: volcanoes that do not reach the surface
Guyots: flat-topped seamounts

21. Trenches Trench: arc-shaped depression in the deep ocean floor
Deepest on Earth
Mariana’s Trench 11,022 meters (36, 163 feet)

22. The Ground Tour