Chapter 14 The Ocean Floor
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Transcript Chapter 14 The Ocean Floor
The Vast World Ocean
Ocean Floor Features
Seafloor Sediments
Resources from the Seafloor
The Vast World Ocean
The Blue Planet
Nearly 71% of Earth’s surface is covered by the global
ocean
The oceans haven’t really been a huge focus of study
until the late 1800’s
As technology becomes better, it allows us to study what
happens underneath the oceans
Oceanography a science that draws on the methods
and knowledge of geology, chemistry, physics, and
biology to study all aspects of the world ocean
Geography of the Oceans
The world ocean can be divided into four main ocean
basins
Pacific Ocean the largest of the four oceans; it covers
more than half of the ocean surface area on Earth
Atlantic Ocean about half the size of the Pacific and
not quite as deep
Indian Ocean slightly smaller than the Atlantic; it is
located almost entirely in the southern hemisphere
Arctic Ocean about 7% the size of the Pacific; only
one-quarter as deep as the other oceans
Mapping the Ocean Floor
The topography of the ocean floor is as diverse as that
of the continents
If the oceans were drained, we would find chains of
volcanoes, tall mountain ranges, trenches, and large
plateaus
The more the oceans were studied, the more
techniques were created to study the ocean floor
Bathymetry (bathos = depth, metry = measurement)
the measurement of ocean depths and the charting of
the shape/topography of the ocean floor
Current Technology
Today’s technology allows scientists to study the ocean
floor in a more efficient and precise manner than ever
before
Sonar (Sound Navigation and Ranging) using sound
waves to determine depth and features on the ocean
bottom
Satellites
Submersibles a small underwater craft used for deepsea research; allows for a human point of view under
water for long periods of time
Ocean Floor Features
Oceanographers studying the ocean floor have divided
it into three major regions
Continental Margins
Ocean Basin Floor
Mid-Ocean Ridge
Continental Margins
Continental Margin the zone of transition between
a continent and the adjacent ocean basin floor
In the Atlantic Ocean, thick layers of undisturbed
sediment cover the continental margin
This region has very little volcanic or earthquake activity
In the Pacific Ocean, oceanic crust is plunging beneath
continental crust
This force results in a narrow continental margin that
experiences both volcanoes and earthquake activity
Continental Shelf
Continental Shelf the gently sloping submerged
surface extending from the shoreline
The average steepness of the shelf is equal to a drop of
only about 2 meters per kilometer
Continental shelves contain important mineral deposits,
large reservoirs of oil and natural gas, and huge sand
and gravel deposits
Continental Slope
Continental Slope marking the seaward edge of the
continental shelf, this slope is steeper than the shelf
and marks the boundary between continental crust
and oceanic crust
Submarine Canyons deep, steep-sided valleys cut into
the continental slope
Turbidity Currents occasional movements of dense,
sediment-rich water down the continental slope
Continental Rise
Continental Rise in regions where trenches do not
exist, the steep continental slope merges into this
more gradual incline
Steepness of the slope drops to about 6 m per km
May be hundreds of km wide
Ocean Basin Floor
Ocean Basin Floor found between the continental
margin and mid-ocean ridge
Size of this region is almost 30% of Earth’s surface
Region includes:
Deep-ocean trenches
Abyssal Plains
Seamounts
Guyots
Deep-Ocean Trenches
Deep-Ocean Trenches long, narrow creases in the
ocean floor that form the deepest parts of the ocean
Most are located along the margins of the Pacific
Many exceed 10,000 meters in depth
Challenger Deep in the Mariana Trench
Trenches form at sites of plate convergence where one
moving plate descends beneath another and plunges
back into the mantle
Abyssal Plains
Abyssal Plains deep, extremely flat features; these
regions are quite possibly the most level places on
Earth
The sediments that make up abyssal plains are carried
there by turbidity currents or deposited as a result of
suspended sediments settling
Seamounts and Guyots
Seamounts the submerged volcanic peaks that dot
the ocean floor
They are volcanoes that have not reached the ocean
surface
Most found in the Pacific Ocean
As volcanoes break the surface, they form islands
The islands are eroded and eventually sink beneath the
ocean level
Guyots once active, now submerged, flat-topped
structures
Mid-Ocean Ridges
Mid-Ocean Ridge found near the center of most
ocean basins; an interconnected system of underwater
mountains that have developed on newly formed
ocean crust
Longest topographic feature on Earth’s surface
Exceeds 70,000 km in length
Think of it like seams on a baseball
Seafloor Spreading
A high amount of volcanic activity takes place along
the crest of the mid-ocean ridge
Seafloor Spreading occurs at divergent plate
boundaries where two lithospheric plates are moving
apart
New ocean floor is formed at mid-ocean ridges as
magma rises between the diverging plates and cools
Hydrothermal Vents
Hydrothermal Vents zones where mineral-rich
water, heated by the hot, newly-formed oceanic crust,
escapes through cracks in ocean crust
As the super-heated, mineral-rich water comes into
contact with the surrounding cold water, minerals
containing metals precipitate out and are deposited
Seafloor Sediments
Types of Seafloor Sediments
Ocean-floor sediments can be classified according to
their origin into three broad categories
Terrigenous Sediments
Biogenous Sediments
Hydrogenous Sediments
Terrigenous Sediment
Terrigenous Sediment sediment that originates on
land
Consist primarily of mineral grains that were eroded
from continental rocks and transported to the ocean
Larger particles (gravel/sand) settle near shore
Smaller particles (clay) are carried out to sea and can
take years to settle to the bottom
Biogenous Sediment
Biogenous Sediment sediment that is biological in
origin; consists of shells and skeletons of marine
animals and algae
Calcareous Ooze most common type of biogenous
sediment; it is produced from the calcium carbonate
shells of organisms
Siliceous Ooze composed primarily of the shells of
diatoms (single-celled algae) and radiolarians (singlecelled animals that have shells made out of silica
Hydrogenous Sediment
Hydrogenous Sediment consists of minerals that
crystallize directly form ocean water through various
chemical reactions
Make up a very small portion of ocean sediments
Most common types:
Manganese Nodules
Calcium Carbonates
Evaporites
Resources from the Seafloor
Energy Resources
Oil and natural gas are the main energy products
currently being obtained from the ocean floor
Gas Hydrates compact chemical structures made of
water and natural gas
Most oceanic gas hydrates are created when bacteria break
down organic matter trapped in ocean-floor sediments
Other Resources
Sand and Gravel
Used for landfill, to fill in recreational beaches, and to
make concrete
Manganese Nodules
Manganese Nodules hard lumps of manganese and
other metals that precipitate around a smaller object
Used in the creation of many metal alloys
Evaporative Salts
Table salt (halite), drying fabric, de-icing roads