OCEAN BASINS CHAPTER 4

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

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

Echo Sounders bounce Sound off the Seabed 1922 – USS Stewart – first continuous ocean basin profile of the Atlantic 1925-1927: Meteor made 14 profiles in the Atlantic Echo sounding was not perfect Temperature, pressure, salinity

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!!!!

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

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

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

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

Continental Slopes connect Continental Shelves to the Deep-Ocean Floor

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

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

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

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

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

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

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

The Ground Tour