ch 13 the earth's oceans

expeditions:

• hms challenger expedition - 1872-1876

  • measured deepest point in ocean

the vast world ocean:

• 71% of earth’s surface is oceans/seas

• 29% is continents and island

• northern hemisphere - land

• southern hemisphere - water

4 main ocean basins:

• pacific - largest w/ greatest depth

• atlantic - ½ size of pacific, less deep

• indian: slightly smaller than atlantic, mainly southern hemisphere

• artic: 7% size of pacific

bathymetry - measurment of ocean depth and charting shape or topography

• echo sounder (sonar)

• side-scan sonar - towed behind a ship

• multi-beam sonar

• satellite alimeter (from space)

3 topographic units of ocean floor:

• continental margins

• ocean basin floor

• mid-ocean ridge

continental margins:

• passive - found along coastal areas surrounding atlantic

  • not associated w/ plate boundaries. they experience little volcanism and earthquakes.

  • continental shelf - flooded extension of continent with <1 degree slope, contains oil and important mineral, thick accumulations of shallow-water sediments

  • continental slope - seaward edge of continental shelf, slope between 5-25 degrees, boundary b/w continental and oceanic crust

  • continental rise - gradual incline that might extend 100’s of km, found where there’s no trenches, thick accumulation of sediment, deep-sea fan

• active - continental slop desends abruptly into deep-ocean trench, usually in pacific, subduction zones don’t have sediments, accumulations of deformed sediment of ocean crust form accretionary wedges

  • deep ocean trenches - long, narrow, deepest parts of ocean, most in pacific, sites where moving lithosphereic plates plunge into mantle, associated wiht volcanic activitiy, volcanic island arcs and continental volcanic arcs

turbidiy currents: downslope movements of dense, sediment filled water. created when sand and mud on continental shelf or slope are dislodged and thrown into suspention. bc muddy water is denser than seawater, it flows down and, eroding and accumulating more sediment

ocean basin floor:

• abyssal plains

  • most level place on earth

  • all oceans

  • sites of thick accumulations of sediment. fine sediments from land, precipitated minerals, shells/skeletons of marine organisms

• seamounts and guyots

  • erupt as volcanic island then cool off/solidify

  • caused them to sink and we call them flat topped guyots

  • become flat from wave action

mid-ocean ridge:

• elevated positions, extensive faulting, and volcanic structers that have developed on newly formed crust

• longest topographic feature on earth’s surface

• 70+km / /43k miles in lengh

• 23% of earth’s surface

• winds through all major oceans

• black smoker vents represent outgassing

• along axis of some segments are deep down faulted structures, rift valleys

seafloor sediments:

• sources: turbidity currents and sediment that slowly settles to bottom from top

• thickness varies

  • pacific - 600 meters or less

  • atlantic - 500 -1000 meters

  • trenches - may approach 10 kilometers

• carbonate mud is most common sediment on deep-ocean floor

types of seafloor sediments:

• terrigenous - weathered from continental rockss, takes years to settle, oxidation produces red and brown sediments

• biogenous - shells/skeletons of marine animals/plants, most common are calcareous oozes, siliceous oozes, phosphate rich material from bones, teeth, and scales of fish

• hydrogenous sediment - minerals that crystallize directly from seawater. includes manganese nodules, calcium carbonates (limestone), metal sulfides, and evaporites/salf

seafloor resources:

• energy resources - oil, gas, gas hydrates

• other resouces - sand, gravl, evaporative salts, manganese nodules