oceanography. suppose that all of the water were drained from the oceans. what would we see? plains?...
TRANSCRIPT
The Vast World OceanSuppose that all of the water were drained from the oceans. What would we see? Plains?Mountains?Canyons?Plateaus?
The Blue PlanetIt has only been since the
late 1800s that the ocean became an important focus of study.
The Blue PlanetOceanography is a science
that draws on the methods and knowledge of geology, chemistry, physics, and biology to study the world ocean.
Pacific OceanLargest ocean
Largest single geographic feature on Earth
Deepest oceanavg. depth:3940 meters.
Indian OceanSlightly smaller than the
Atlantic Ocean, but about the same average depth.
Located almost entirely in the southernhemisphere.
Arctic OceanAbout 7% the size of the
Pacific.Only a little more than one-
quarter as deep as the rest of the oceans.
Mapping the Ocean FloorIf all the water were drained
from the ocean basins, a variety of features would be seen.
Mapping the Ocean FloorBathymetry is the
measurement of ocean depths and the charting of the shape or topography of the ocean floor.
Mapping the Ocean FloorThe first understanding of
the ocean floor’s varied topography did not unfold until the 3.5 year voyage of the HMS Challenger.
HMS Challenger—1872-1876127,500 km tripWent to every ocean
except the Arctic.Sampled various ocean
properties.Measured depth by lowering a
long, weighted line overboard.
Mapping the Ocean FloorToday’s technology—
particularly sonar, satellites, and submersibles—allow scientists to study the ocean floor in a more efficient and precise manner than ever before.
SONARInvented in the 1920sA type of electronic depth-
sounding equipment.Also referred to as echo
sounding.
SONARTransmits sound
waves toward the ocean bottom.
A sensitive receiver intercepts the echo reflected from the bottom.
SONARA clock precisely measures the
time interval from sent to received.
Depth can be calculated from the speed of sound in water—about 1500 m/s—and the time required for the sound wave to reach the bottom and return.
SONARThe depths determined from
continuous monitoring of these echoes are plotted, and a map of the ocean floor is obtained.
SONARTechnology today allows to
plot a narrow strip of ocean floor instead of a single point at a time.
SONARWhen a ship uses multibeam
sonar to make a map, the ship travels through the areain a regularlyspaced back-and-forth pattern.
SatellitesAfter compensating for
waves, tides, currents, and atmospheric effects, scientists discovered that the ocean surface is not perfectly flat.
SatellitesThe differences in ocean-
surface height cannot be seen with the naked eye, satellites, however, can detect the small differences.
SatellitesUsing a system similar to
SONAR, instead using RADAR, radio waves, they can map the surface height differences as small as 3 to 6 cm difference.
SubmersibleThey collect data, record
video, use SONAR, and collect sample organisms with remotely operated arms.
SubmersibleAnother unmanned
submersible is being built with a goal to collect long-term data without interruption.
Ocean Floor FeaturesThe ocean floor features are
the continental margins, the ocean basin floor, and the mid-ocean ridge.
Continental MarginIn the Atlantic Ocean, thick
layers of undisturbed sediment cover the continental margin, which experiences little earthquake/volcanic activity
Continental MarginIn the Pacific, oceanic crust is
plunging beneath continental crust, which results in a narrow continental margin which results in earthquake/volcanic activity.
Continental MarginSome features common to
the continental margin include: the continental shelf, the continental slope, and the continental rise.
Continental ShelfThe shelf is almost
nonexsitant along some coastlines, and may extend 1500 km along others.
Continental ShelfContinental shelves contain
important mineral deposits, large reservoirs of oil and natural gas, and huge sand and gravel deposits.
Continental ShelfThe waters here also contain
important fishing grounds, which are significant sources of food.
Continental SlopeSteeper than the shelf, it
marks the boundary between continental crust and oceanic crust.
Continental SlopeDeep, steep-sided valleys
known as submarine canyons are cut into the continental slope.
Continental SlopeMost information suggests
that the submarine canyons have been eroded by turbidity currents.
Continental SlopeTurbidity currents are
occasional movements of dense, sediment-rich water down the continental slope.
Ocean Basin FloorThis region includes deep-
ocean trenches, very flat areas known as abyssal plains, and tall volcanic peaks called seamounts and guyots.
Deep-Ocean TrenchesLong, narrow creases in the
ocean floor that form the deepest parts of the ocean.
Deep-Ocean TrenchesTrenches form at sites of
plate convergence where one moving plate descends beneath another and plunges back into the mantle.
Deep-Ocean TrenchesA portion of one
trench—the Challenger Deep in the Mariana Trench—has been measured at a record 11,022 meters below sea level.
Abyssal PlainsDeep, extremely flat features
where thick accumulations of fine sediment have covered an otherwise rugged ocean floor.
Abyssal PlainsThe sediments that make up
the abyssal plains are carried there by turbidity currents or deposited as a result of suspended sediments settling.
Seamounts and GuyotsSubmerged volcanic peaks
that dot the ocean floor, which have not reached the ocean surface.
Seamounts and GuyotsWhen a volcano reaches the
surface it starts being eroded and may sink back into the ocean.
Mid-Ocean RidgesFound near the center of
most oceans, interconnected system of underwater mountains that have developed on new ocean crust.
Mid-Ocean RidgesSeafloor spreading occurs at
divergent plate boundaries where two lithospheric plates are moving apart.
Mid-Ocean RidgesNew ocean floor is formed at
mid-ocean ridges as magma rises between the diverging plates and cool.
Mid-Ocean RidgesHydrothermal vents are
zones of mineral-rich water, heated by the hot, newly-formed oceanic crust.
Mid-Ocean RidgesAs the super-heated, mineral-
rich water comes in contact with the surrounding cold water, minerals and metals precipitate out and are deposited.
Seafloor SedimentsExcept for steep areas of the
continental slope and the crest of the mid-ocean ridge, most of the seafloor is covered with sediments
Seafloor SedimentsThe thickness of the
sediments varies from sparse coverage up to 10 km in some areas.
Seafloor SedimentsOcean-floor sediments can be
classified according to their origin into three broad categories.
Terrigenous SedimentsConsists primarily of mineral
grains that were eroded from continental rocks and transported to the ocean.
Biogenous SedimentsCalcareous ooze, produced
from the calcium carbonate shells of organisms, is the most common biogenous sediment.
Biogenous SedimentSiliceous ooze, composed
primarily of the shells of single-cell organisms with shells of silicon, along with phosphate- rich material, make up the other biogenous sediments.
Hydrogenous SedimentHydrogenous sediment
consists of minerals that crystallize from ocean water through various chemical reactions.
Hydrogenous SedimentsManganese Nodules,
rounded, hard lumps of manganese, iron, and other metals, are often scattered across large areas of the deep ocean.
Hydrogenous SedimentsCalcium Carbonates form by
precipitation directly by ocean water in warm climates.
Hydrogenous SedimentsEvaporites, formed in high
evaporation rates and areas of restricted open-ocean circulation.
Energy ResourcesOil and natural gas are the
main energy products currently being obtained from the ocean floor.
Energy ResourcesPercentage of world oil
production from off-shore rigs has increased from sparse amounts in the 1930s to more than 30% today.
Energy ResourcesThere are rigs in Persian
Gulf, Gulf of Mexico, off southern California, in the North Sea, and East Indies.
Energy ResourcesOne environmental concern
about offshore petroleum exploration is the possibility of oil spills.
Energy ResourcesMost oceanic gas hydrates
are created when bacteria break down organic matter trapped in ocean-floor sediments.
Energy ResourcesAn estimated 20 quadrillion
cubic meters of methane are locked up in sediments containing gas hydrates.
Energy ResourcesThe amount of methane is
double the amount of Earth’s known coal, oil, and natural gas reserves combined.
Other ResourcesOther major resources from
the ocean floor include sand and gravel, evaporative salts, and manganese nodules.
Sand and GravelThe offshore sand-and-gravel
industry is second in economic value only to the petroleum industry.
Sand and GravelIn some cases, materials of
high value, such as diamonds, can be found in the gravel.
Manganese NodulesHard lumps of manganese
and other metals that precipitate around a smaller object, such as sand.
Manganese NodulesContain high concentration
of manganese, iron, and smaller concentrations of copper, nickel, and cobalt.
Manganese NodulesWith current technology,
mining the deep-ocean floor for manganese nodules is possible but not economically profitable.
Evaporative SaltsWhen seawater evaporates,
the salts increase in concentration until they can no longer be dissolved.
Evaporative SaltsWhen the concentration
becomes high enough, the salts precipitate out and form salt deposits.