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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.