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
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This region has very little volcanic or earthquake activity
 In the Pacific Ocean, oceanic crust is plunging beneath
continental crust
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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:
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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
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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:
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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