Post on 03-Jul-2020
transcript
Ocean Basins
The Alvin …
the most famous research submarine.
Like most research vessels, it is owned by the U.S. Navy and operated by a
research institution (in this case, the Woods Hole Oceanographic Institution).
Outline for Today
• Class schedule & review questions
• Features of margins, basins, and ridges
(Chapter 4)
• A tiny bit of material about sediments
(Chapter 5) – take note of where
sediments are important as we go through
the slides.
Class schedule
2/1: Sediments (Ch. 5)
Water and Ocean Structure (Ch. 6)
2/3: Water and Ocean Structure (Ch. 6)
2/8: Review of Chapters 1-6
2/10: Exam 1 (multiple-choice)
(if you arrive late to class, you will receive a
short-answer version of the exam)
I will post
all slides
and
some
review
materials
on a
website
around
this time.
Question
• Early life on Earth was highly dependent
on
a) Oxygen
b) Liquid water
c) Ozone
d) Sunlight
Question
• Early life on Earth was highly dependent
on
a) Oxygen
b) Liquid water
c) Ozone
d) Sunlight
Question
• When did our oceans form on Earth?
a) When the Earth first formed
b) Very early on in Earth’s history
c) About half-way through Earth’s history
d) Very recently
Question
• When did our oceans form on Earth?
a) When the Earth first formed
b) Very early on in Earth’s history
c) About half-way through Earth’s history
d) Very recently
Question
• Where did most of the liquid water on
Earth ‘likely’ come from?
a) Comets
b) Meteorites
c) Mars
d) Outgassing from its interior
Question
• Where did most of the liquid water on
Earth ‘likely’ come from?
a) Comets
b) Meteorites
c) Mars
d) Outgassing from its interior
Question
• Which of the following are reasons why
humans have explored the ocean?
a) To seek out food
b) To increase military power
c) To identify structures and life in the ocean
d) All of the above
Question
• Which of the following are reasons why
humans have explored the ocean?
a) To seek out food
b) To increase military power
c) To identify structures and life in the ocean
d) All of the above
Question
• Which one of the following types of
structures is the most common geological
structure on the planet?
a) Ocean basins
b) Ocean ridges
c) Volcanic arcs
d) Continental shelves and slopes
Question
• Which one of the following types of
structures is the most common geological
structure on the planet?
a) Ocean basins
b) Ocean ridges
c) Volcanic arcs
d) Continental shelves and slopes
Three major categories:
margin, basin, ridge
To review Earth’s structure & isostasy:
https://www.youtube.com/watch?v=ybd17tx4Tz4
How/why does crust
vary in elevation &
thickness over time?
Icebergs sink into water so that the
same proportion of their volume
(about 90%) is submerged. This
type of buoyancy is called isostasy.
To review Earth’s structure & isostasy:
https://www.youtube.com/watch?v=ybd17tx4Tz4
How/why does crust
vary in elevation &
thickness over time?
Icebergs sink into water so that the
same proportion of their volume
(about 90%) is submerged.
This type of buoyancy is called
isostasy.
Isostasy:
the crust "floats" at an elevation that
depends on its thickness and density of
underlying roots of the low density of the
mountain.
Features of
continental margins
Submarine canyon –
erosion of continental margin causes sediment to
accumulate on the ocean floor.
Submarine Canyons
• Narrow, deep, V-shaped in profile
• Steep to overhanging walls
• Extend to base of continental slope,
3500 meters (11,500 feet) below sea level
• Carved by turbidity currents
Turbidity Currents
• Underwater avalanches
mixed with rocks and
other debris
• Sediment from
continental shelf
• Moves under influence
of gravity
• Sediments deposited at
slope base
Turbidity currents – underwater avalanche of sediment
Usually triggered by earthquakes*
Can carve canyons far below surface
* What does this suggest about the type of margins (passive or active)
where you would be more likely to find submarine canyons?
Turbidity currents – underwater avalanche of sediment
Usually triggered by earthquakes*
Can carve canyons far below surface
* What does this suggest about the type of margins (passive or active)
where you would be more likely to find submarine canyons?
Active margin – faces convergent or transform boundary
Passive margin – faces spreading centers
Review: active and passive margins
How does isostasy influence the
elevation of land relative to ocean?
Example:
what might happen to
the height of the
Andes Mountains after
they erode?
Sea levels affect shelves
18,000 years ago, Florida was much wider.
Sea level is rising very quickly as polar ice caps melt
due to climate change
Sea level also affects the height (and amount) of land,
relative to the ocean.
Question
• Given the picture on the next page,
where would you NOT look for oil?
a) Continental shelf
b) Continental slope
c) Continental rise
Question
• Given the picture on the next page,
where would you NOT look for oil?
a) Continental shelf
b) Continental slope
c) Continental rise
Continental Slope
• Where deep ocean basins begin
• Topography similar to land mountain
ranges
• Greater slope than continental shelf
– Averages 4° but varies from 1–25° gradient
What was found?
The ocean basin did not
get deeper as you went
further from land.
Abyssal Plains
• Extend from base of continental rise
• Some of the deepest, flattest parts of Earth
• Suspension settling of very fine particles
• Sediments cover ocean crust irregularities
• Well-developed in Atlantic and Indian oceans
Abyssal Plains
Abyssal plains – flat, featureless expanse of ocean floor.
Abyssal hills – protrusions off abyssal plain.
Earth’s most common landform: basin floor
Sediments
accumulate
Hydrothermal
Vents: features of
mid-ocean ridges
(and which other type
of location?)
Warm water vents –
temperatures below 30°C (86°F)
White smokers –
temperatures from 30–350°C (86–662°F)
Black smokers –
temperatures above 350°C (662°F)
https://www.youtube.com/watch?v=D69hGvCsWgA
hotspots
Biology and geology are closely
linked in oceanography.Inside the bodies of these giant tube
worms, bacteria make energy from
chemicals like hydrogen sulfide
(chemosynthesis).
Dr. Colleen Cavanaugh (Professor at
Harvard University) was the first to propose
that bacteria living inside the worms
provided food for them. She made this
observation when she was a graduate
student.
• Mid-ocean ridges are the most prominent feature on the planet –
like the seam of a baseball
• Ocean basin covers the greatest surface)
Draw and label a cross-section that
extends from one continent to another.
Continent ends when granite ends and basalt starts
Continental margin – submerged portion of continent
Ocean basin – submerged region beyond margin
Continental shelf – shallow submerged continent extension
Continental slope – transition between shelf and ocean floor
Continental rise – accumulated sediment from continent
Ocean ridges – newly erupting basalt at spreading centers.