2 Ocean Intro KD

7/29/2019 2 Ocean Intro KD

1/17

1/9/2013

1

OceanographyGEO 009

Kirk Domke

Winter 2013

Lecture 2:An Introduction to

Oceans Ocean Properties

History of Marine Science

Anatomy of the Ocean Floor

Ocean Formation Ocean Exploration

Here is some water.

Why doesnt the ocean

look like this (a great bigball of water hangin out

there above land)?

Is the ocean a solid, a liquid, or gas?

How do we define a liquid?

A liquid maintains its volume, but takes the shapeof its container

Ocean Properties

Why does the ocean look like this instead?

Gravity!!!

Ocean Properties


2/17

1/9/2013

2

Gravity always pulls you (and water)

towards the center of the Earth.

Ocean Properties

The surface of the ocean defines a gravity

equipotential (a surface on which the forceof gravity is equal everywhere).

This surface is (almost) a perfect sphere.

Ocean Properties

So, weve got the shape of the top surface of

the ocean covered

The top of the ocean is defined by a

surface of equal gravitational force.

What about the bottom (the container)?

Ocean Properties

What do you think is the shape of the ocean

bottom?

Ocean Properties


3/17

1/9/2013

3

Actually, to answer that question, we need to

dig a bit into the dusty archives of historyand see how others have answered it


At least since 4000 B.C., the ocean was

used for trade


A drive for exploration led to the dispersal of

the Polynesian people.

Initially Indonesia to

New Guinea and

Phillipines 20,000

years ago

Hawaii by A.D.

450-600 *



4/17

1/9/2013

4

It was always nice to be able to return to a

place you went before (or back to home!), sothe earliest traders and explorers had to

make charts*

A map is of land,

a chartis of the

ocean.

Never ask for a

map of the ocean!


Eratosthenes, 3rd century B.C.

However, early travelers needed

a way to locate themselves onthe surface.

Observations of certain stars

allowed them to determine latitude

Latitude - how far north or south of

the equator you are


Longitude (how far east or west you are

from a reference line) is more difficult

Earth is rotating, so you need to know theangle to the star AND the time difference

between your location and the PrimeMeridian.


The angle changeswith time of day

(15 /hr).

The Egyptians (230 B.C.) not only figuredout that the Earth was round, but they also

developed the system of latitude and

longitude.



5/17

1/9/2013

5

Question:What is latitude and longitude of

Riverside?:

a) 74oN, 17oW

b) 34oN, 17oW

c) 34oS, 117oW

d) 34oN, 117oW

Question:So, if Riverside is 34oN, 117oW, what

is latitude and longitude of New York

City?

a) 34oN, 102oW

b) 47oN, 122oW

c) 41oN, 74oW

d) 25oN, 80oW

Once people had charts, there was another

minor detail they needed to know

Depth!


Doh!

The earliest widely made measurements of

the ocean were of its depth

Depth Sounding - using

a weighted line that

has distances marked



6/17

1/9/2013

6

18th century chart of Scotland shows how

few soundings were made


units in fathoms (6 feet)

North Sea

Not until the 19th Century did people make

soundings deeper than a few hundredmeters

Sir John Ross (of the Ross Ice Sheet fame)

early 1800s - S. Atlantic depth of 4893 m

Matthew Maury

1840s - discovered mid Atlantic ridge

Known as father of physical oceanography

Discovered patterns of surface wind/currents


Advent of submarines really kicked

bathymetric studies into high gear

Where were they??


It was the need for submarine detection

tools that led to the major tools of modern

oceanography after WWII. In addition to waves bouncing off the

submarine, they bounced off the seafloor

We can use that information - echo sounding



7/17

1/9/2013

7

It was the need for submarine detection

tools that led to the major tools of modernoceanography after WWII.

History of Marine Science History of Marine Science

V = sound wave velocity

T = round-trip time

SONAR

Question:An echo sounder on the bottom of a ship

emits a sonar pulse and detects the reflected

pulse exactly 4 seconds later. What is thedepth of the seafloor beneath the ship?

(Use the speed of sound in the ocean as 1600m/s).

a. 200 m

b. 400 m

c. 1600 m

d. 3200 m

e. 6400 m

Today, we use a multibeam array with manyreceivers in order to eliminate the problem of

canyons and narrow features scattering the

sound waves.

Like a CAT scan of the

ocean floor!


121 beams - 120o arc Only 125 more years until wevecovered the ocean floor completely!


8/17

1/9/2013

8

We use satellites bouncing radar off the

ocean surface to measure its height to within1 inch

Jason-1 launched

by NASA in 2001

Jason-2 launched

in 2008

Used in tandem


Small variations (up to 200 m) of the oceans

height are created by gravitational attractionof local topographic variations

Satellite altimetry uses radar(microwave

and radio waves)


Geosat

Orbit

h

Sea Surface

Ocean

Crust


From these variations,we can calculate the

sea bed topography

And we discovered

that the ocean was

not deepest in the

middle!


9/17

1/9/2013

9


Mid- Atlantic Ridge

The ocean floor

has greater relief

than the continents!


The deepest part of the

ocean is NOT in themiddle but in some

places at the edges by

the continents

subduction zones

(stay tuned)

Japan Trench in purple


The highest elevation

Mt. Everest is NOT as

high as the ocean isdeep.

We also learn that the

oceans cover about

70%of the Earths

surface


Continental margin - part of continent, not

ocean (slope + shelf)


10/17

1/9/2013

10


Ocean basin

Ocean ridge - usually in center whereoceanic crust is created


Ocean basin

Abyssal plain - broad, flat, bounded bycontinental shelves, ridges, trenches


Ocean basin

Trench - usually at margin where oceaniccrust returns to the mantle


Active margins are coincident with plate

boundaries

Have volcanic and earthquake activity Pacific-type


11/17

1/9/2013

11


Passive margins do not coincide with plate

boundaries Geologically speaking, theyre more boring

Atlantic type

Summary

Lets summarize what we have learned

about the oceans shape:1. We know the top of the ocean container is a

gravitational equipotential.

2. We know the bottom and sides of the container

are controlled by the Earths crust and the shape

is complicated with continental shelves, abyssal

plains, ridges, and trenches

Summary

Now we know the top, bottom, and sides of

a container are holding the fluid

What can we calculate about the fluid??

VOLUME!1.37 billion cubic kilometers

(0.13% of Earths volume)

AREA: 361 million square kilometers

(70% of Earths surface)

AVERAGE DEPTH:

(higher than the San Gabriel mountains)

AVERAGE TEMPERATURE: 3.9C(about 40F)

(this has an enormous effect on our climate)

kmkmX

kmX8.3

10361

1037.1

26

39

Summary

Vol.Area

=


12/17

1/9/2013

12

But WHY is the ocean floor shaped the way

it is? Tectonic plate creation and destruction

controls the shape of the ocean floor

Provides coupling between the hydrosphere(water surface) and lithosphere (rock

surface).

Well dive into this further next week

Important Questions

Where did the water come from?

1. Mutual gravitational attraction

of particles causes planet to grow.

2. Gravitational attraction causes

pressure inside, melting rock and

light stuff rises, dense stuff sinks.

3. Core, mantle, crust forms.

Important Questions

Earth formed 4.6 billion yrs ago

Water vapor was an original component of

the Earth

Outgassing of lightest fraction (water, carbondioxide, other gases)

Ocean Formation


the Earth

Early earth resembled Venus

Ocean Formation

/ /


13/17

1/9/2013

13


the Earth The Earths surface eventually cooled enough

that rains fell due to gravitational attraction

and led to the oceans

Ocean Formation

Alternative suggestion:

Icy comets hit Earth

Ocean Formation

How do we know that there was an ocean 4

billion years ago, only 0.6 BY after the

formation of the Earth?

Types of sediments found today at the bottom

of oceans are also found in 3.8 BY old rocks(dated in labs), so the ocean must have been

there to deposit those sediments.

Ocean Formation

What assumption are we making when we

state that the sediments in the 4 Gyr old

rocks were formed at the ocean bottombecause they look like sediments we see at

the ocean bottom today?

UniformitarianismThe present is the key to the past.

Assumptions

1/9/2013


14/17

1/9/2013

14

Physical and chemical processes in the

past behaved as they do in modern systems

Physical laws of nature havent changed

through time

Assumptions

Oldest sedimentary rocks from Isua,

Greenland 3.8 billion years old (3,800million years)

a. Pillow lava

b. Banded iron

c. Red beds

d. Uraninite

Ocean Formation

Zircon crystals record oxygen isotopes

indicative of ocean existence

These minerals are

> 4.3 billion years old

Composition suggests

these were in contact

with liquid water

Ocean Formation

How do we know that there are sediments at

the bottom of the ocean and what they look

like?

We have samples!

Ocean Exploration

Clamshellsampler

1/9/2013


15/17

1/9/2013

15

Gravity corer - used for deep sediment cores

Provides a temporal

(time) record of climate

& environmental change

(oldest sediments are

deepest, youngest are

shallow)

Ocean Exploration

We have also used deep diving

submersibles to look at the ocean bottom

Ocean Exploration

Window for

viewing

Kaiko

Small ROV

Remote Operated Vehicle

New ROVs can reach

> 10 km depths

Ocean Exploration

We need specialized vehicles like these

because the pressure is so great at the

bottom of the ocean

Pressure is the weight

(gravity pulling on the

mass) of the water

above us/unit area

10 m of water is equivalent to the weight of theentire atmosphere on us (1 atm pressure)

Ocean Exploration

1/9/2013


16/17

1/9/2013

16

1101 atm

pressure!!

500 m - maximumdepth for divers

with special gearAlvinmax.depth

Satellite Oceanography

Hurricane

Katrina

Data from NASA satellite, Aura, launched in 2002

Also, GPS receivers are cheap and used for positioning

Ocean Exploration

Most of our information about the ocean

has come from sampling of sediments,

water, fish, . NOT DIRECT OBSERVATION!

Ships are

needed!

Expensive to buy and operate

Ocean Exploration

Much oceanographic research is done by

governments and oceanographic institutes

Expensive equipment Scientific research requires different

specialties working together

What scientific disciplines have we

discussed today?

Ocean Exploration

1/9/2013


17/17

1/9/2013

17

Geologistsrocks, sediments, history of Earths ocean, continent, climate

Physical oceanographerswaves, currents, coupling to lithosphere,atmosphere

Marine engineersbuild structures and specialized equipment

Marine biologistsstudy marine organisms

Chemical oceanographersstudy dissolved solids and gases

Space scientistssea surface, GPS, satellites

Documents

2 Ocean Intro KD