Ocean Basins
Bathymetry 
•	Originally measured by lowering lines overboard
•	Sonar invented in the 1920s 
•	Reflects sound waves off the ocean floor  

1) Major provinces of the ocean floor 
•	Continental margins
•	Deep-ocean basins 
•	Oceanic (mid-ocean) ridges 

a) Continental margins
•	Contains continental shelf, slope, and rise, and submarine canyons
•	Width varies: 	passive margins wider, 								active margins narrower
•	Continental processes
•	Submerged edge of continent

Continental shelf
•	Submerged extension of continent
•	Low relief: usually less than 1 degree.  
•	Average is one tenth of one degree.
•	Continental resources: oil and gas, sand and gravel etc.
•	Submarine canyons
Processes: beaches, deltas, carbonates (coral reefs)

Continental slope
•	Marks the seaward edge of the continental shelf 
•	Boundary between continental crust and oceanic crust 
•	The steepest slope. Range 1 to 25 degrees, average is 4 degrees. 
•	Pacific (active margin) average >5 degrees.  
•	Atlantic (passive margin) average about 3 degrees
•	Submarine canyons
Processes: turbidites

Continental rise
•	Found on passive margins where trenches are absent 
•	Accumulation of sediment from turbidites at the foot of the continental slope
•	Turbidites are like underwater landslides.  More later.
Processes: turbidites

Active continental margins
•	Found on mostly convergent plate boundaries
•	Continental slope descends abruptly into a deep-ocean trench
•	No continental rise
•	Located primarily around the Pacific Ocean 

2) Deep-ocean basins
a) Trenches
•	Long, relatively narrow features 
•	Parallel to continents
•	Deepest parts of ocean basins
•	Most are located in the Pacific Ocean 
•	Mobile lithospheric plates plunge into the mantle 
•	Associated with intense volcanic activity 

b) Submarine Canyons
•	Generally form perpendicular to coastline
•	Form from zones of weakness such as a fault or a “drowned” river valley
•	Turbidites transport sediment to deep ocean basin using submarine canyons
•	Start on continental shelf and cut into (erode) shelf and upper slope
•	Deposit in lower slope and continental rise
Ex: La Jolla Submarine Canyon

c) Abyssal plains 
•	Large horizontal seafloor regions
•	One of the flattest places on earth
•	Average 4500 to 6000 meters deep
•	Very slow sedimentation rates.  Some places less than 1 cm per 1000 years.
Processes: "Planktonic rain" which blankets seafloor

d) Seamounts and Guyots
•	Isolated volcanic peaks rising off seafloor 
•	Many form near oceanic ridges 
•	May emerge as an island 
•	May sink and form flat-topped seamounts called guyots 

e) Oceanic (mid-ocean) ridges and rises
•	Broad, linear swells along divergent plate boundaries are called oceanic ridges 
•	Extensive faulting and small earthquakes 
•	High heat flow  
•	Present in all ocean basins  
•	The shallowest and youngest parts of deep ocean basins
•	Sediments thicken away from the MOR
Features: vulcanism, hydrothermal vents, rift valley.

Why are ridges and rises so high?
•	Newly created oceanic lithosphere is hot and occupies more volume than cooler rocks 
•	As the oceanic crust travels away from the ridge crest it cools and becomes more dense and sinks

Spreading rates and ridge topography 
•	Topographic differences are controlled by spreading rates 
•	Ridges: steeper with slow spreading rates (1-5 centimeters per year) 
Ex: Mid-Atlantic Ridge
•	Rise: flatter with fast spreading rates (greater than 9 centimeters per year) 
Ex: East Pacific Rise

3)Oceanic lithosphere and basins
a) Origin of oceanic lithosphere 
•	Concept formulated in the early 1960s by Harry Hess 
•	At MOR plates move apart, lava wells up into the newly created fractures and generates new oceanic lithosphere 
•	New lithosphere moves away from the ridge crest  
•	Zones of active rifting are 20 to 30 km wide 

b) Structure of the oceanic lithosphere 
Four distinct layers 
•	Layer 1: sequence of unconsolidated sediments
•	Layer 2: consisting of pillow lavas 
•	Layer 3: interconnected dikes called sheet dikes 
•	Layer 4:gabbro (like basalt but slowly cooled at depth) 

Formation of oceanic lithosphere 
•	Magma (liquid with crystals) originates from partially melted mantle forms layer 4 
•	Magma injected into fractures above the magma chambers creates the sheeted dike complex layer 3 
•	Pillow basalts are from basaltic lava that is flash cooled in seawater
•	Sediments deposit on top of pillow basalts 

c) Continental rifting: The birth of a new ocean basin 
•	A new ocean basin begins with a continental rift 
•	The Red Sea is an example of a rift valley that has lengthened and deepened in a narrow linear sea 
•	If spreading continues the Red Sea will grow wider and develop an oceanic ridge similar to the Atlantic Ocean 

d) Destruction of oceanic lithosphere 
•	Oceanic lithosphere subducts because its overall density is greater than the underlying mantle
•	Subduction of older, colder lithosphere results in STEEP descending angles 
•	Younger, warmer oceanic lithosphere is more buoyant and angles of descent are SHALLOW
•	Research indicates that parts, or even entire oceanic basins, have been destroyed along subduction zones 

Marine Sediments
Definitions
•	Sediment: Solid material that has settled from a state of suspension.  When lithified (consolidated or cemented)  becomes a rock.

Rocks and the rock cycle: 
Process and path as earth materials change both on the surface and inside the Earth

Basic rock types
Metamorphic rocks (least important)
•	Formed by “changing” pre-existing igneous, sedimentary or other metamorphic rocks
•	Driving forces are increased heat and pressure 
•	Typically develop a fabric or texture
Ex: gneiss and marble

Igneous Rocks
•	A rock or mineral that has solidified from molten material (from a magma).
•	Slower cooling times have bigger crystals.
•	Extruded to surface or intruded into existing rock
Ex:
Volcanic (extrusive): Hawaii (basalt) and (Cascades) andesite
Plutonic (intrusive): Sierra Nevada (granites)
Sedimentary rocks: 
Sediment: Solid material that has settled from a state of suspension in a fluid
•	When lithified (consolidated or cemented) becomes a sedimentary rock
•	Derived from weathering of pre-existing rocks
•	Can tell the geologic history of an area.
•	Classified by grain size and source
Ex: sandstone and limestone

i) Grain size

ii) Source
a) Cosmogenous
b) Hydrogenous
c) Lithogenous
d) Biogenous

a) Cosmogenous
•	Originated from outer space
•	Evidence for extinction of dinosaurs
Example:
•	Tektites (silica glass)
•	Iron-nickel meteorites
•	Iridium

b) Hydrogenous
•	Precipitated from water
Example:
•	Manganese nodules: most in Pacific, grow very slowly 
•	Evaporite: salt NaCl 

c) Lithogenous (terrigenous)(clastics)
•	Small pieces of broken rock transported to ocean from the land (wind, rivers, glaciers, coastal erosion, turbidity currents etc.) 
•	Generally form rapidly
•	Can have high energy environments and coarse grain sizes.
•	Mostly composed of quartz, very resistant to weathering
•	Some deep ocean, very fine wind blown clays

Most lithogenous sediments are on or near a landmass 
•	Coarser sediments closer to shore, 
•	Finer sediments farther from shore

As transportation distance increases, sediment becomes more mature and 
•	Clay content decreases 
•	Sorting increases 
•	Non-quartz minerals decrease 
•	Grains become more rounded

Examples:
Delta, Beach, and Turbidite deposits
Fine wind-blown clays

d) Biogenous
•	Skeletal remains of organisms 
Examples:
•	Oozes (calcareous and siliceous)
•	Carbonate (coral) reefs

i) Oozes
•	>30% biogenous material
•	Oozes form slowly 1/2 to 2 1/2 inch per 1000 yrs
•	Oozes are soft and mushy.
•	Low energy environments, very fine grained (clay sized)
•	From phytoplankton and zooplankton

Calcareous oozes
•	Made of CaCO3  

Primarily from 
•	Foraminifera (forams), zooplankton
•	Coccoliths: phytoplankton
•	Fairly evenly distributed in oceans
Calcium carbonate compensation depth (CCD)
•	No CaCO3  beneath about 15,000 feet (4500 meters)
•	Lysocline: depth at which CaCO3 begins to dissolve rapidly

Siliceous oozes
•	Made of SiO2

Diatoms: most common plankton
•	Phytoplankton 
•	Common in polar regions
•	Very important for upwelling nutrients.
•	Many uses beer filters, optical glass.  

Radiolarians: 
•	zooplankton, 
•	more common in equatorial regions

ii) Carbonate (coral) reefs
•	Must have clear, warm shallow water
•	Contain the world's largest petroleum reserves
•	Comprised of dead animal and plant skeletons
•	Mostly of calcium carbonate-called "carbonates" 
•	Grow at rates of 10-30 feet per thousand years

Three main stages proposed by Charles Darwin. 
i) fringing reef (Hawaii),
ii) barrier reef (Great Barrier Reef)
iii) atoll (many Pacific atolls)

e) Distribution of sediments
•	Neritic sediments cover about ¼ of sea floor and are near landmasses
•	Pelagic sediments cover about ¾ of seafloor and are mostly in deepwater
•	Distribution controlled by proximity to sources of lithogenous sediments, ie: landmasses
•	Productivity of microscopic marine organisms

Neritic sediments are generally:
•	Shallow water deposits
•	Close to land
•	Dominated by lithogenous sources
•	Typically deposited quickly

Pelagic sediments are generally:
•	Deepwater deposits mostly oozes and windblown clays
•	Finer-grained sediments
•	Deposited slowly
•	Less lithogenous and more biogenous depending on biologic productivity

Properties of Seawater
1) Components
•	Water
•	Dissolved matter: solids and gas
•	Suspended matter

2) Properties:
•	Cohesion: high surface tension
•	Adhesion: water "sticks" to things
•	High capillary action: 
•	Powerful solvent
•	Polar substance
•	pH is about 8.1, where 1 is acidic and 14 is basic and 7 is neutral
•	Carbonate buffering keeps pH stable by precipitation (increase pH)  or dissolution (decrease pH) of calcium carbonate CaCO3 

High latent heat: 
•	Evaporation/vaporization takes a large amount of energy (to break hydrogen bonds). Ex: water absorbing energy as it evaporates on your skin
•	Condensation releases a large amount of energy. Ex: steam burning you as it releases energy on your skin

High heat capacity: energy required to heat 1gram of substance 1 degree C. Ex: local coastal winds
3) Ions in Seawater
•	Major Na, Mg, Ca, K, Cl, SO4
•	Minor Fe, S, I, F
•	Trace: almost everything!

4) Salinity
The total amount of solid material (salts) dissolved in water 

Salinity = Weight (mass) of salt
                 Weight (mass) of water

a) Units 
•	%  is part per hundred (pph)
•	%o is parts per thousand (ppt)

•	Open ocean range is 33 to 37 %o  ppt 
•	Average is 35 %o  ppt

Examples:
•	Baltic Sea 		10 %o  ppt (Brackish)
•	Red Sea 		42 %o  ppt (hypersaline)
•	Great Salt Lake	280 %o  ppt (hypersaline)
•	Dead Sea		330 %o  ppt (hypersaline)
•	Tap water		0.7 %o  ppt (fresh)
•	Spring 		0.3 %o  ppt (fresh)

b) Measured by 
•	electrical conductance or 
•	density 

c) Variability of salinity
•	Stable at depth variable on surface

Decrease salinity
•	Precipitation 
•	Runoff 
•	Melting icebergs/sea ice 

Increase salinity
•	Evaporation
•	Freezing sea ice

d) Salinity and latitude

5) Relation ship of Salinity, Density and Temperature
Assuming a closed system
•	Temperature and Density>>>>>>>Inverse
•	Salinity	and Density>>>>>>>>>Proportional
•	Temperature and Salinity>>>>>>>None

6) The "cline curves" changes with depth
•	Thermocline: temperature
•	Halocline: salinity
•	Pycnocline: density

Mixing (surface) zone
Uppermost water where mixing from currents make temp/salinity/density mostly constant.

Vertical changes in temperature with latitude
•	Polar: almost no thermocline
•	Temperate: weak thermocline
•	Tropical: strong thermocline

Locally 
•	We have a temperate thermocline, which is weak in the winter and strong in the summer. 
•	During El Nino years we may get a strong thermocline all year.

ATMOSPHERIC CIRCULATION

•	Outermost sphere of earth
•	Density stratified
•	About 100 kilometers thick

Composition
•	N2		78%
•	O2		21%
•	CO2		0.036%
•	Others		< 1 %

•	Also contains water vapor
    	
	 Warm air			 Cool air

1. Atmospheric pressure 
•	Pressure = Force/Area     
•	Units:	PSI  or  Millibars
•	Atmospheric Pressure changes with height/elevation

•	elevation  AP (inverse)

Weight/pressure of air molecules greater at A less at B

2) Pressure Systems: 
•	Surface winds blow from high to low pressure
•	High pressure systems have dry conditions with sinking air masses
•	Low pressure systems have wetter conditions with rising air masses 

Northern Hemisphere:  
•	High pressure turns clockwise
•	Low pressure turns counter-clockwise

Southern Hemisphere:  opposite of N.H.
•	High pressure turns counter-clockwise
•	Low pressure turns clockwise

3)  Convection 
•	Circulation of fluid due to density differences
•	Like a pot of boiling soup, warm fluid rising (in middle) and cool fluid falling (on sides)

4) Atmospheric Circulation
Two major forces
•	Uneven heating of earth
•	Rotation of earth

a) Uneven heating of earth
•	More energy per unit area is delivered to the equator than near the poles
•	The equatorial regions are warmer than the poles

b) Rotation of Earth
Coriolis effect: fluids (air, water) move to the
•	Right in Northern Hemisphere
•	Left in Southern Hemisphere
•	Influences all moving objects, especially ones moving over large distances
•	Changes direction not speed
•	Maximum Coriolis effect at poles
•	No Coriolis effect at equator

c) Circulation cells
Hadley cells (0o to 30o N and S of equator)
•	Trade winds, NE in N.Hemisphere and SE in S. Hemisphere

Ferrel cells (30o to 60o N and S of equator)
•	Prevailing westerlies in both hemispheres

Polar cells (60o to 90o N and S)
•	Polar easterlies in both hemispheres

The equatiorial doldrums (ITCZ)
•	Located on equator
•	Where tradewinds converge
•	Area of low atmospheric pressure
•	Low wind area
•	Lots of rain
 
Horse latitudes
•	30 degrees North and South of equator
•	Separate the Hadley and Ferrel Cells
•	Area of high atmospheric pressure, also called the subtropical high
•	Very dry because of high pressure, little rain
•	Dangerous for sailors

5) Tropical Cyclones

“Spinning air currents above low pressure systems.”

								Northern
								Hemisphere
								Example

•	Intensify over warm water (>77 degrees F), provides water vapor
•	Water vapor provides fuel for storm in the form of latent heat energy as water vapor condenses
•	Die over land and cool water
•	High winds, tornados near storm center
•	Sea level can rise in front of storm called a “storm surge”

Ratings (by windspeed) 
•	Tropical depression (<38 mph)
•	Tropical storm (between 38 and 74 mph)
•	Tropical cyclone (>74 mph)
•	Tropical cyclones are called Hurricanes (N or S America) or Typhoons (Western Pacific)

Saffir-Simpson Scale: 5 categories of hurricane intensity based upon wind speed
•	Category 1 is from 74 to 96 mph
•	Category 5 is >155 mph

Examples
•	Andrew 
•	Katrina