What is oceanography?

The study of the ocean

Both the water and the rock below it

Extremely broad topic - easily a full year class

What we will cover - a look ahead

Basically only 2 elevations to the earth

Above and below sea level


Water, water everywhere... a short review

What is water ­ H2O

A "polar" molecule - explain

Universal solvent - HOH

Neutrality between acids and bases

Origin of water

Volcanic vs. cosmic sources

Water is stuff: therefore follows laws of physics

Runs downhill due to gravity

Fills up the low elevations - Ocean basins

Hydro cycle

Review the process

Recycles water between different reservoirs

Oceans	        1,300,000,000 km3      97.2%
Ice               29,300,000 km3       2.15%
Groundwater        8,400,000 km3       0.625%
Freshwater Lakes     230,000 km3       0.017%
Atmosphere            13,000 km3       0.001%
Streams                1,250 km3       0.0001%

The ocean is clearly the largest of these temporary holding facilities

Holds a huge volume of water


Water is stuff, has mass, and occupies space

One cubic foot of pure water weighs 62.4 pounds

Would salt water be higher or lower (higher)?

Therefore, pressure rises by 650 pounds for each 100 feet of depth

Results in some pretty interesting aspects to things which live (or work) in ocean

Ammonite sutures

Rock cod

The "bends"


Water: suspension vs. solution

Water is water

And has always (?) been water

But seawater isn't just molecular water (H2O)

Seawater (as well as freshwater) contains other materials

Called "salts" - but not all is NaCl (See fig. 11-3, page 284)


Little pieces of sediment in the water

Can result from mechanical or chemical weathering

Not in contact with the bottom or sides

Usually VERY small - mud, silt, and clay size particles

Held in suspension by the energy of the water

Related to velocity - review Q=AV

You can see this stuff

Makes the water cloudy, dirty, etc.

The look of the water reflects composition of material held in suspension

These sediments can settle out to form sedimentary layers

Lead to the formation of sedimentary rocks


Material dissolved in water

You cannot see this stuff - water remains "clear"

Particle size is not relevant in this case

Nor is the energy or velocity of the water

A chemical weathering process

The materials will remain in solution until

Change in chemistry causes fluid to loose its capacity to hold material

Related to "saturation"

Related to amount of water and its temperature

Some other process extracts the material directly from the water

Biological processes - animals extract CaCO3 or SiO2 to use as shells

Once extracted from the water, the minerals can become "sediments"

And can then settle to the bottom as sedimentary debris

Fresh water is in short supply (especially the unpolluted kind)

Why can't we drink seawater?

Desalinization of seawater - see page 285

Relatively easy to "filter out" suspended load

Dissolved load - extracted by more complex (expensive) methods


Moving water

Several forces combine to keep the ocean's water in motion

Wind, density differences, thermal differences, and Coriolis effect

The Coriolis effect

Need to cover first - affects all fluids in motion

As well as solids not in contact with the earth

Result of the rotation of the earth (DESCRIBE in detail)

Surface currents

Affect upper few hundred meters of the water only

Most caused by wind

Have a major climatic effect on the lands they pass by

East vs. west coast of North America

Density Currents

Deeper currents

Move due to density differences in the sea water

Causes of density differences


Cold polar waters are denser

Sink and move towards the equator as very deep currents

Warm equatorial waters flow nearer to surface to replace the polar waters

Salinity - also related to latitude

Seawater freezes at the poles

Remaining water has high salinity

These cold, saline waters travel towards the equator at depth

Additional Thermal Effects

Strong surface winds "blow water away" from an area

Deeper, colder waters rise to "fill the hole"

Called upwelling

Bring nutrients to the surface (remains of dead plants and animals)

Make excellent fishing areas



Show film "Tides of the Ocean" (FK850; 17 min.; 6-12)

What is sea level?

Not a constant level around the globe

Actually higher in some places than in others

There are also daily variations in sea level - called "tides"

Actual bulge of sea level

Related to the gravitational attraction of moon and sun

Review Law of Gravity

Moon is smaller, but much closer

Therefore has the greatest affect on the tides

Actually pulls the water closer to the moon (and sun)

There are approx. 2 high and 2 low tides per day

Due to earth's rotation relative to the moon and sun

Diagram on board or overhead

Because the moon is also revolving around earth, each day's tides are 50 min. later than the day before

Spring tides - sun and moon lined up (full and new moon)

Neap tides - sun and moon at right angles (1st & 3rd quarters)


Swells and Waves

Show video "Waves in the Ocean" (VK1404; 23 min.; 11-12)


Morphology of the Seafloor

Liquids conform to the shape of the container

Two main elevations on the earth's surface

Above and below sea level

Correspond to continental and oceanic plates

The shoreline does not mark the boundary between the two

Was the cause of some of the initial problems with Continental Drift

Three distinct regions

Continental Shelf - Portions of continental crust below sea level

Abyssal Plain - Deep ocean basins underlain by oceanic crust

Continental Slope - The transition between the two main levels (crustal types)

Continental Shelves

The relatively low-relief platform seaward from the shore

Usually fairly shallow water

Surrounds most of the continents

Not uniformly wide - vary quite a bit

Local relief can be somewhat steep

Especially in areas subjected to glaciation

Or to stream erosion at times of lower sea level

Continental Slopes

Connects the two major levels of the earths surface

The major continental land masses at just above sea level (average!)

And the abyssal depths at 12,000' below sea level

Actually a fairly gentle gradient

Looks steep on most X-sections due to vertical exaggeration

Average slope 4°

Submarine Canyons

Characteristic features of the continental slopes

The formation of these is difficult to explain

Most now agree that Turbidity Currents are primarily responsible

Density currents of debris-laden water

Can move fast and far

Up to 100 kph for distances of up to 700 km

Can be set off by seismic or other disturbances

Example: Grand Banks - off Newfoundland 1929

Earthquake set off a large turbidity current

Severed Trans-Atlantic phone lines

Many cables over 13 hours

Speed of the current 66 ft/sec. (75 kph)

Anyway, all this debris piles up at the mouth of the canyons

Submarine fans - Like alluvial fans in an arid landscape

Called the Continental Rise

Continental rise

Coalesced fans (like a bajada in an arid landscape)

Forms the boundary between the slope and the abyssal plain

The abyss - the basic oceanic depths

Primarily basalt

Less than 200 m.y. old

Generated at spreading centers - Consumed at subduction zones

Features include

Abyssal Plains - Cover large portions of the ocean floor

Generally fairly low-relief

Most have at least a thin veneer of sediments (or oozes) covering them

Abyssal Hills

Topographic mounds on the abyssal plain

Remain well below sea level - Mere "pimples" on the sea floor

Oceanic Ridge systems

Spreading centers for the earth's tectonic plates

Median valley

The actual rift at the crest of the ridge/rise system


Increased depths below the main level of the abyssal plains

Generally long and narrow features - like the ridges

Associated with island arc chains

Represent zones of oceanic plate subduction

These are the lowest elevations on earth!

Mariana Trench @ -35,785'

Tonga Trench @ -35,326'


Depositional Environments and Sediments

Different types of sediments cover most of the ocean floor

Primary differences related to energy differences in the different depositional sites

Near shore - mostly terrigenous sediments

Sand and silt predominate on the beaches and Continental Shelf

Claystone and shale farther out

Facies changes with distance from shore reflect energy of environment

Describe in detail


In canyons and at base of continental slope (rise)

Ooze: Descriptive term which characterizes the majority of deep ocean sediments

Usually microscopic marine organisms

Lack of terrestrial sediments causes them to be concentrated in the deep ocean

Ooze composition varies systematically across the ocean floor

Calcareous oozes

Form in shallow, tropical and temperate seas

Single-celled calcium based creatures

Reproduce by dividing into two individual creatures

The vacated shells sink to the bottom

Also sink when organism dies

If too deep, or too cold, the calcium re-dissolves

Siliceous oozes

Single-celled silica based organisms

Deposits form in deeper water where calcium can't remain stable

Also has a depth/pressure limit

Red/Brown clays - occur in the deepest oceanic basins

Most widespread of all sedimentary deposits on the earth

Almost totally inorganic

Accumulate at a very slow rate

Only thing which can survive the pressure of the deepest basins


Shoreline Processes

The Beach

Oregon Dunes Nat. Park


Plate Tectonics and the ocean floor

Already touched on this quite a bit

Spreading Centers


Passive continental margin (Fig. 7-14 pg. 156 & Fig. 7-15 pg. 157)

Both sides of the Atlantic

Trailing edge of Continental plate

Minimal tectonic activity

Wide Continental Shelf

Active continental margin (Fig, 7-17 pg. 159)

West coast of North & South America

Leading edge of continental plate

Extensive tectonics

Narrow Continental Shelf

Subduction Zone/Trench

Island Arcs

Common where two oceanic plates collide

Japanese Islands, and many others in western Pacific

Similar volcanism occurs at Oceanic/continental margins

Andes, Cascades