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
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
Pressure
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 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)
Suspension
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
Solution
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
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
Temperature
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)
Show video "Waves in the Ocean" (VK1404; 23 min.; 11-12)
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
Trenches
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'
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
Turbidites
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
The Beach
Oregon Dunes Nat. Park
Already touched on this quite a bit
Spreading Centers
Ophiolites
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