Oceans

Oceans• 71% of Earth’s surface• Pacific – largest, deepest• Atlantic• Indian – mostly in Southern Hemisphere• Arctic – smallest, shallowest, entirely in

Northern Hemisphere

Ocean FloorContinental margins, Ocean basin floor, Mid-ocean ridge

Mid-Ocean Ridges

• Near the center of ocean basins• Formed by diverging plate boundaries• Zone of new crust formation• Collectively the longest mt. range on Earth -

42,000 miles• Much quiet volcanic activity – magma rises to

fill space and cool as plates spread apart.

Mid-Ocean Ridges

Mid-Ocean Ridges

Hydrothermal Vents• Seawater seeps into crust, gets superheated &

saturated with minerals.• Ejected through gaps along mid-ocean ridge• When it hits the cold ocean water, minerals get

deposited in large masses – copper, silver, gold, iron, zinc, sulfur, & others.

• Source of energy & nutrients that supports large colonies of life far from surface & sunlight.

Hydrothermal Vents

Hydrothermal Vents

Continental Margins

• Transition zone between continents & ocean basin floor

• In Atlantic, not associated with plate boundaries, so few earthquakes or volcanoes.

• In Pacific, ocean plates forced beneath continental plates, lots of earthquake & volcanic activity – Ring of Fire

Continental Margins

Continental shelf• Gently sloping zone

from shore.• Shallow (exposed

during ice ages)• Lots of minerals, oil,

& natural gas.• Lots of sediment,

especially near mouths of rivers.

• Zone of sedimentary rock formation

• Lots of fish/feeding areas.

Continental Margins

Continental slope• Steeper than shelf• Boundary between

continental crust & ocean crust

• Submarine canyons cut into shelf from slope, form when turbidity currents (dense, sediment-rich water) flow downhill.

Continental Margins

Continental Rise• Gentler incline, farther offshore and not as

steep as cont. slope.

Ocean Basin FloorBetween continental margin & mid-ocean ridge

Ocean Basin Floor

Trenches• Long, narrow,

deepest part of oceans

• Formed at converging plate boundaries, ocean plate is denser & sinks beneath continental plate

• Lots of earthquakes & volcanoes

Ocean Basin FloorAbyssal plains• Very flat, very

deep• Formed as

sediments settle out or get deposited by turbidity currents, fill in deeper parts of ocean floor.

Ocean Basin Floor

• Seamounts – peaks of underwater, growing volcanoes, form islands if they break the surface

• Guyots – volcanic islands erode flat, sink beneath surface