OCEAN BASINS CHAPTER 4 Study Plan The Ocean

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 • 1870 s – 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