Ch. 13: Ocean Floor

Earth is referred to as:

"Blue planet"

Northern Hemisphere is called

"Land Hemisphere"

Southern Hemisphere is called

"water hemisphere"

Sediment Sources:

- Turbidity currents( underwater landslides) - Sediment that slowly settles to the bottom from above (this includes dead organisms). - Thickest in the trenches

Deep-ocean trenches are associated with volcanic activity like...

- Volcanic Islands Arcs (two oceanic plates converge) - Continental Volcanic Arcs (oceanic and continental convergence)

Oceans preserve a hot-spot seamounts

- Volcano forms an island over hot spot - After volcano goes extinct, it is eroded to sea level - Continued cooling and erosion submerges remnant

How much of Earth's surface is represented by oceans and marginal seas?

71%

Bathymetry is the measurement of...

Ocean depths and the charting of the shape or topography of the ocean floor.

Arctic Ocean Basin

Only about 7% the size of the Pacific

Passive Continental Margin: Submarine canyons cross cut what?

They cross cut continental shelves - Associated with large rivers - Erosion carved out canyons during sea-level low-stands - Submerged canyons funnel sediments into deeper water - Submarine fans grow where canyons empty onto the rise

Continental Shelf

A flooded extension of the continent (not the slope)

Coral Atoll

a ring of coral reef that builds up to surround a central lagoon

Guyots

a submerged flat-topped seamount

Active Continental margins occur where..

continental slope descends abruptly into a deep-ocean trench. - Located primarily around the Pacific Ocean - "Ring of Fire" where subduction occurs - Forms Accretionary wedges

Turbidity Currents are downslope movements of dense....

sediment water; mass wasting event. Underwater Landslides! - Deposits formed from this type of mass wasting are called turbidites

Continental Rise is composed of a thick accumulation of....

sediment. - Turbidity currents deposit sediment on the rise that forms deep-sea fans.

Deep Ocean Trenches are created due to

subduction where moving lithosphere plates plunge into the mantle

Echo Sounder(sonar)

- 1920's - Primary instrument for measuring water depth - Reflects sound from the ocean floor; measures time required for an acoustic wave to travel from the ship to the sea floor and back.

HMS Challenger: (Dec. 1872- May 1876)

- First scientific expedition to study the world's oceans; visited every ocean except the Arctic. - Voyage covered nearly 80,000 miles!

Examples of Guyots include:

- Hawaiian Islands and Emperor Seamount Chain - The Galapagos Islands (off coast of Ecuador in S.A.)

Echo Sounder

- High Resolution Multi beam Sonar: developed in the 1990's.

Abyssal Plains are deep, incredibly flat ocean features they...

- Likely the most level places on Earth - Sites of thick accumulations of layered sediment - Found in all oceans Example: Abyssal plain - off the coast of Argentina has less than a 10 foot rise in topography.

Characteristics of a Continental Slope

- Marks the seaward edge of the continental shelf - Relatively steep structure

Seafloor sediment: Terrigenous (land-based) sediments

- Material weathered from continents - Most common along the continental margins; coarse grains deposited near the shore - Oxidation often produces red and brown colored sediments

Seamounts characteristics:

- May grow large enough to emerge above sea-level to become an island, but most don't - More than 1 million seamounts exist on ocean floor - May erode and sink over time to form flat-topped seamounts called guyots or tablemounts

Bathymetry reflects tectonic plate boundaries...

- Mid-ocean ridges mark divergent boundaries - Oceanic transform faults trace strike slip boundaries - Deep- ocean trenches signify convergent boundaries

Seafloor Sediment: Hydrogenous sediment

- Minerals that crystallize directly from seawater - Comprises only a very small portion of the deposits in the ocean *types: Manganese nodules, metal sulfides, evaporites - Halite, Gypsum

Example of an Active Continental Margin

- Nazca plate(Oceanic plate) being subducted underneath the South American plate(continental plate)

Seafloor Sediments

- Ocean floor is covered with sediment - Only a few places where sediment doesnt accumulate like the mid-ocean ridge

Four main ocean basins

- Pacific Ocean - Atlantic Ocean - Indian Ocean - Arctic Ocean

Characteristics of Continental Shelf

- Shelf varies in width - Gently sloping - Contains rich oil and important mineral deposits - Most shelves consist of thick deposits of shallow-water sediments

Continents and Islands comprise: what percent of Earth?

29%

Mid-Ocean Ridge

An elevated ridge in the center of each ocean with extensive faulting where new sea floor is always forming. - Longest topographic feature on earth!

Radar Altimeter does what?

Bounces microwaves off sea surface from space to measure surface irregularities present due to gravity

Continental Margins: Passive

Found along most coastal areas that surround the Atlantic Ocean

Passive Margins are those that are what??

NOT associated with tectonic plate boundaries - Experience very little volcanism and - Only few earthquakes

Pacific Ocean Basin

LARGEST and Deepest; average depth of 12,927 ft. (2.5miles)

HMS Challenger: sampled what?

Sampled water depth by lowering weighted lines overboard(ropes); these were the first systematic bathymetric measurements.

Indian Ocean Basin

Slightly smaller than the Atlantic, largely a southern hemisphere ocean

Oceanography is the interdisciplinary study of what?

The oceans that draws on Geology, Biology, Chemistry and Physics.

Types of seafloor sediments: Biogenous sediment

The shells (tests) and skeletons of marine animals and plants - Foraminifera and Radiolarians

Atlantic Ocean Basin

about half the size of the Pacific and not as deep; relatively narrow

Multibeam Sonar uses..

an array of sound sources and listening devices; scans areas 10+ km wide - Ships traveled very slow (6 - 12 mi/hr) which explains why only 5% of the ocean floor has been mapped in great detail.

Multibeam Sonar - was...

an improvement from the sidescan sonar and does provide depth

Seamount

an isolated submarine volcano that rises at least 1,000 m above the ocean floor.

Extracting Salt from Seawater

around 30% of the world's salt supply is extracted from seawater; shown here in shallow, evaporating ponds --solar energy

Submarine Canyons

deep, steep-sided valleys cut into the continental slope. - They are seaward extensions of river valleys that once were above sea level, but not flooded with ocean. - Most appear to have been further eroded by turbidity currents

Sidescan Sonar

developed after WWII

Deep Ocean trenches features are...

long, relatively narrow. - Trenches are the deepest parts of the ocean many exceed 10,000 m (33,000 feet)

Continental Slope is

the boundary between continental crust and oceanic crust

Continental Rise is located at the base of...

the continental slope, - Found in regions where subduction trenches are absent. - Where the continental slope merges into a more gradual incline(the continental rise)

Measuring the shape of the ocean surface from space -

these subtle ocean surface irregularities mimic the shape of the seafloor and can be seen from space

Coral

tiny animals (marine invertebrates) that appear in large numbers that link together to form colonies; most have a hard external skeleton made of calcium carbonate; structures link together to form reefs; prefer warm, shallow waters with average temp of 75 F

Mariana Trench is the deepest location anywhere in the ocean and is a result of...

two oceanic plates colliding together(subduction) - Challenger Deep is the deepest point in the trench at around 6.85 miles