Oceanography
What is Oceanography
the scientific study of the oceans, with the goal of understanding the processes and phenomena that take place in the marine realm
Which are the natural sciences applied to the study of oceans within oceanography?
Geological Oceanography (study of rocks and sediments0
Physical Oceangraphy (how and why ocean currents flow)
Chemical Oceanography (composition of sea water and process altering it)
Biological Oceanography (organisms that live in the oceans)
Eratosthenes of Cyrene
introduced latitude and longitude
Hipparcus
150 BC- divided the surface of the Earth into 360 degrees
Ptolemy
150 ad- showed the world as a globe, with north at the top and east on the right
Why were accurate measurements of longitude difficult to obtain before the middle of the 18th century?
If you’re clock was off 1 minute you are off 15 miles? John Harrison made a more accurate time piece allowing you to measure time with the sun at noon
What are latitude and longitude?
Latitude Horizontal lines around earth 90N-90S equally spaced
Longitude- Vertical lines not parallel Prime Meridian 0
What information do you need to determine latitude and longitude
Time and the angle to the sun at noon
James Cook
Voyaged on Endeavor and Resolution creating charts of the Pacific still used by the Allies in World War II
Benjamin Franklin
Published the first chart of the gulf stream
Matthew Maury
created the first reliable wind and current charts
Charles Darwin
voyage on the HMS Beagle. Studied geology and biology o f the South American coastline
Charles(Wyville) Thompson and John Murray
Directed the first modern, deep-ocean, global sampling expedition on the HMS Challenger. They visited all oceans, covering 127,000 km
Fridtjof Nansen
allowed his ship to be trapped in the Artic ice pack. The fram and its crew drifted with the pack for almost four years and 1,650 km, exploring to 85’57 N proving that no Artic continent existed
Which expedition is considered the beginning of modern oceanography?
The Challenger
Why is the Glomar Challenger important?
It was the first drill-ship built, starting the JOIDES program
What are ROVs?
Remotely operated vehicle- an underwater vehicle that is operated remotely and not manned by humans. It can explore and sample hundreds of square kilometers of ocean floor per month.
What are the contributions of satellites to oceanography?
measure various ocean property such as temperature, ice cover, roughness of surface (waves), and water color (indicating plankton abundance)
When did the universe form
13.7 Billion years ago
Galaxies
huge rotating aggregation of stars, dust, gas and other debris held together by gravity
Nebulae
Clouds of dust adn gas within galaxies, from which stars form
Star
massive sphere of incandescent gases
How did the solar system form and when?
5 billions years ago
a. Cloud of gas and space dusts (nebula) began to contract
b. Nebula became a rotating flattened disk
c. Most of the material was gravitationally swept toward the center, producing the sun
d. the planets began to accrete from the material that was orbiting within the flattened disk
How did the Earth form and when?
4.6 bya through planetesimal accretion
What is the process of density stratification?
Gravity then causes Density Stratification
A. Heavy Atoms (Iron) gravitate towards the center of the earth
B. Lighter Atoms (Silicone) gravitate towards the surface of the earth
How did the ocean form?
Water vapor and other gases seperated out from the rocks that make up the bulk of the Earth and were outgassed on the surface, forming the atmosphere and the oceans
What is outgassing and why is it important?
A process, resulting form heating, by which gases and water vapor are released from molten rocks. It as produced Earth’s atmosphere and oceans.
What is the origin of water on Earth?
Water was formed after outgassing in the form of water vapor and then form droplets and eventually collecting water in basins before surface cooled down enough
What is the origin in evolution of the atmosphere?
First Atmo prior to 4.5 mil
Second (proto) Atmo gassed on through volcanoes
Earth’s present is third generation
Why did the Earth lose its initial atmosphere
Solar winds when the sun became a star swept it away
What is the oxygen revolution?
Organisms learned to do photosynthesis creating oxygen as a bi-product (and killing of most anaerobic bacteria)
What is the importance of photosynthesis for the Earth evolution?
It produced oxygen which is essential for aerobic respiration (which yields much more energy)
When did life begin?
In the ocean probably 3.5 (3.8) bya
HOw did the Challenger measure depth?
Lead lines with knots were lowered to find depth of ocean (had to stop boat)
What are lead lines?
ropes with something heavy (rock or weight) with knots same difference from each other and they count the knots as they lowered it to find depth of ocean (might take whole day).
What is Echo Sounding?
depth measured based on reflection of a sound impulse from the sea floor
-Depth = velocity x (1/2) Time (there and back)
What are the problems associated with the use of echo sounding (think of wide beam bathymetry)?
Sound beam spreads out and exagerates, meaning the depth you measure could be on an angle and not the actual depth of directly below you (just first sound you receive again)
What are the advantages of single focused sound beam bathymetry?
Beam is narrower, less margin for inaccurate measurements (more likely directly below you)
What is a multibeam echo sounder?
multiple sound beams are used
Larger area can be measured at once
Receivers on both sides of ship
What is side-scan sonar?
Scanner towed behind ship which can map a strip of ocean floor with a gap directly below the instrument
Gives photolike pictures, but no good at measuring depth because you have to account for distance beneath water
How does satellite bathymetry work?
Radar pulses measure from sea surface, surface is affected by mass of moutains attracting water
Difference between real height(what satellite measures)and actual height is sea surface anomally.
Why is it important to map the seafloor
Tsunami Runup Models, Habitat Restoration, Shoreline change Analysis, Analyzing Storm Impacts- Coastal Erosion, Fisheries management commerical fishing, marine rerve design.
How is the surface of the Earth distributed over continents and oceans?
Continental area = 207×10^6 km^2 (40.6%)
Oceanic area = 303×10^6km^2 (59.4%)
11.5% of Earth is continent below sea level
Name the major oceans and their main characteristics
Pacific Ocean- Largest, deepest, lots of islands and seamounts
Atlantic Ocean- long, narrow, parrallel sides 68% of freshwater runs into it
Indian Ocean- delivery of lots of sediments to the northern part
Arctic Ocean- very broad continental shelves
What is the hypsographic curve and what does it tell you?
It plots the amount of Earth’s surface at each elevation or depth
It shows that there is a bimodal distribution (two bumps one above sea level one below)
Where is the geological continent/ocean boundary?
2,000 m below sea level (mbsl)
What are continental margins and how are they subdivided?
Continental margins extend from the shoreline to the deep-ocean basin, include contiental shelf, continetal slope, and continental rise (can be passive or active)
Continental Shelf
gently sloping depositional surface extending from the low-water line to a marked increase in slope around the margin of a contient
Continental Slope
a relatively steeply sloping surface lying seaward of the continental shelf.
Continental Rise
A gently sloping depositional surface at the base of the continental slope.
Typical passive continental margin
[image][image][image]
How do submarine canyons form?
they cut into the continental shelf and slope, terminating in a fan-shaped wedge of sediment
Formed by turbidity currents
What is a turbidity current?
Underwater avalanches caused by earthquake or volcanic eruption
Made up of very find mud like sediments
What are deep sea trenches?
narrow steep-sided troughs as deep as 11 km, 50-200 km wide, and thousand of km long
Always occur in active margins, always occur together with volcanoes
Active Continental Margin
[image]
What is the difference between an atlantic-like and Pacific-like continental margin
Atlantic is passive with a continental rise
Pacific is active with a deep sea trench
What are the main features of the deep sea ocean basin?
abyssal plains, abyssal hills, seamounts, mid-oceanic ridges, and deep sea trenches.
Abyssal plains
flat portions of the ocean floor covered by sediments
Abyssal Hills
small extinct volcanoes or intrusions of once molten rock covered by sediments
Seamounts
under water volcanoes that rise abruptly and steeply from the ocean floor (flat topped are guyots)
Difference between abyssal hills and seamounts?
Seamounts are much higher than abysmal hills (up to 1 km) and tend to be active (volcanoes?)
How are guyots formed?
when seamounts are moved off the source of magma the tops eroded after a few million years.
Mid-ocean ridges
continuous system of mountain chans that runs through every ocean basin
Rift Valley
In middle of ridge there is rift valley (present in Atlantic and Indian not Pacific)
Transform faults
fractures that run perpendicular to Mid ocean ridge (area in between axis)
Fracture Zones
long, narrow regions of broken or disturbed seafloor
What is Density?
the ratio of mass to unit volume
What is an earthquake?
a phenomenon that results from the sudden release of stored energy in the form of low-frequency waves called seismic waves
How is seismology important for the study of the interior of the Earth?
By measuring the speed waves take to reach different parts of the earth we can find out the density and different layers of the earth
What are P-waves and S-waves
P-Waves (compressional waves) travel by squeezing and expanding the medium they travel through. They can travel though both sounds and liquids. (spring) twice as fast as S-waves
S- Waves (Shear waves)- travel by shearing the medium they pass through. S-waves can travel through only solids (whip)
What are the main difference between the behavior of P-waves and S-wave?
P-waves are faster and can go through liquids
WHy do S-waves disappear in the outer core?
They can’t travel through liquid?
How would you expect P-waves and S-waves to behave as they attempt to travel between 1) the mantle and the outer core: 2)the outer core and the inner core?
1) S-wave disappear and P-waves slow down due to change from solid to liquid
2) S-waves return and both waves speed up
How does density change inside the Earth, from the surface to the core?
Increases constantly, big jump between mantle and outer core (jumps at all)
Where are the largest contrasts in material properties (density, velocity of P- and S- waves) located inside the Earth
Large increase in density between mantle and Outer core and decrease (disappearance for S-waves) in velocity.
Describe the classification of the Earth’s interior based on chemical composition.
Crust- thin, light outermost layer
Mantle- made of oxygen and silicon with Fe and Mg
Core- consists mainly of Fe and Ni
What is the Moho?
The chemical boundary between the crust and mantle
What are the effects of increasing temperature and pressure on the physical properties of the rock material inside the Earth?
Increasing pressure- raises the melting point of a material
Increasing temperature- provides additional energy to the atoms and molecules of matter eventually causing the material to melt
Describe the classification of the Earth’s interior based on physical properties of the material inside the Earth?
Lithosphere- rigid outer layer, crust + uppermost mantle
Asthenosphere- deformable layer of upper mantle
Lower mantle- denser and less deformable layer of upper mantle
Lower mantle- denser and less deformable
Outer core: dense, viscous liquid
Inner core: solid, very dense~ 6,600 C (hotter than surface of sun)
What is the chemical composition of the Earth’s core?
Fe, Ni metal
What are the two kinds of crust of the Earth?
Continental and Oceanic crust
Difference between Continental and Oceanic Crust
Continetal Crust is granite, has low density, and rises high above the supporting mantle rocks
Oceanic Crust is basalt, has greater density, and does not rise as high above the mantle
What is isostacy?
the ability of an object to float in a liquid by displacing a volume of that fluid EQUAL in weight to the weight of the floating object
Why is continental crust thickest under the tallest mountains?
Because of isostasy it has to displace the mantle and stretches underneath??
Explain the distribution of elevated continents and depressed ocean basins?
Continents are less dense than oceanic crust so they rise while oceanic crust sinks.
What is isostatic adjustment and when does it occur?
adjustment of crustal material due to isotasy, (think mountains)
Who proposed the Theory of Continental Drift?
Alfred Wegener 1912, which proposed that continents are not stationary but drift around Earth’s surface, and that the ocean basins are the holes left behind
What are the four sets of evidence that Wegener cited to support his ideas about continental drift?
1. The fit of continents
2. Used to be continous mountain belt
3. Fossil evidence
4. Late Paleozoic Glaciations happens only in polar regions yet there is evidence of it in India
What is the mechanism of Continental Drift and why was it rejected?
heavy continents pulled toward the equator by centrifugal force and by effect of sun and moon
Problem- Centrifugal force is pretty weak, and they though whole earth was rigid
In the 1950s scientists started to accumulate new evidence that corroborated the Theory of Continental Drift. What are these data?
New seismic data
Improvements of radiometric dating (showed young crust)
Mapping of ocean floor-showed submerged mountain ranges
Wandering magnetic poles
Heat flow
Describe the pattern of earthquakes on the Earth’s surface?
Shallow earthquakes move along ridges
What is the difference in age between the seafloor and the continents?
Oldest seafloor is only 180 billion years old
What is paleomagnetism?
The study of Earth’s ancient magnetic field
Why do rocks have a magnetic field and how do they get it?
They contain iron rich magnetic materials, and record magnetic field as they cool through their Curie point
Where does the Earth’s Magnetic Field come from?
movements in liquid outer core cause magnetic field.
What are the positive and negative magnetic anomalies found on the seafloor? What is there significance
They are a repetitive pattern of positive and negative magnetic intensities arranged in a zebra stripe fashion, they show ancient reversals of Earth’s magnetic field
Describe the Age pattern of the seafloor
The seafloor has magnetic anomalies symmetrically distributed about ocean ridge axis progressively getting younger towards the middle
What is the apparent polar wandering? What is its significance?
The pole seems to move (in different directions)by looking at older rocks magnetic field, but if you move the continents back together it has one path (proving continental drift)
How do heat flow measurements and the thickness of marine sediments corroborate the Theory of Plate Tectonics?
Mid ocean ridge you have high heat flow, and along subduction zones you have very little or none. That goes together with the theory of plate tetoncis, asthenosphere bulges up and comes to surface very hot at divergent zones (mid ocean ridge)
Thickness of sediments- there is basically no sediment coverage on top of mid ocean ridge system, as you move away from axis, sediment coverage becomes thicker and thicker (new crust didn’t have time to accumulate sediments)
What are the three main assumptions of plate tectonics?
1. The lithosphere is broken into plates that move at rates of a few cm/yr and interact with each other at the plate
boundaries
2. Lithospheric plates move on the ductile asthenosphere
3. Plates consist of either oceanic lithosphere only or oceanic & continent lithosphe (boundaries have a high degree of activity)
What is a plate and what does it consist of?
Lithosphere that moves on a converyor belt (asthenosphere)
List and describe all the types of divergent, convergent, and transform boundaries?
Divergent boundaries- plates move apart (only in ocean there are ridges) Mid Ocean Ridges

Convergent boundaries- plates move toward each other (only in ocean does subduction occur) Deep Sea Trenches (subduction zones)

Transform boundaries- plates slide past one antoher (transform faults)

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Along which plate boundaries do you find only shallow earthquakes
Transform (can also have mid earthquakes) and divergent only has shallow
Where do deep earthquakes occur
Only at convergent boundaries because the sub ducted plate can sink lithosphere 340 km below
Describe the Various Stages of the formation of a new ocean basin like the Atlantic Ocean.
[image]
What is a spreading center? How is it expressed on earth?
At divergent boundaries, they are where new crust is being generated and the two plates move away from each other
What is the difference between oceanic ridges and rises? Where do you find them?
Oceanic rise is flater and spread faster
Oceanic ridge has rift valley, peaks,and spread slower, they both appear on the mid ocean ridge
What is a transform fault? What is a fracture zone? How are they formed?
Tranform Faults- where plates shear laterally past each other
Fracture Zone- See earlier definition
They are formed to accomodate spreading of a linear ridge system on spherical Earth
What is a subduction zone? How is it expressed on the surface of the Earth?
regions in which crust is recycled into the mantle, they are expressed in deep sea trenches.
Along which plate boundaries do you find the most of the world’s volcanoes?
Convergent Boundaries
How does and ocean close?
Convergent boundaries converge until all the oceanic crust is subducted
What factors determine which of the two colliding oceanic plates will be subducted?
The older (denser and colder) plate will be subducted
Why is continental lithosphere not subducted?
Because both have equal density that is to low in density to be pulled very far down into mantle, instead mountains are formed
What is the mechanism that drives plate tectonics?
Convection
What are hot spots? What do hot spots create on the Earth’s surface? Why are they useful in tracing the motions of plates?
Hot Spots- surface expressions of plumes of magma rising from stationary soruce of heat in the mantle
Give rise to linear island and volcanic chains
They are stationary so we see plates move with respect to them
How is an atoll formed?
Coral reef forms around active voclano island, as hot spot moves volcano cools and sinks until there is nothing atoll
How was Iceland formed?
Built by hotspot and mid ocean ridge system
What are the major events of the last spreading cycle?
180 mil Pangea Splits (ocean Panthalassa)
150 Laurasia and Gondwana
135 South atlantic forming
70 Atlantic devloped
50 mil Australia formed
40 India collided with asia
What are Marine Sediments?
Particles of various sizes derived from a variety of sources that are deposited on the ocean floor
How do you classify sediments based on their source?
Terrigenous- erosion of continents volcanic ash
Biogenous- formed biologically in the ocean
Hydrogenous- precipitate from seawater
Cosmogenous- dust from space
How do classify terrigenous sediments based on size?
By grain size (diameter) indicates hwo grains are transported where they accumulate
What is the Hjulstrom’s Diagram? What does it tell you?
describes the relationship between grain size and horizontal current velocity that result in erosion, transportation or sediment deposition
Erosion goes up for clay
Why are clay sized particles more difficult to erode than sand sized particles?
Clay’s stick to each other so you’re not dealing with a single grains but rather a wall.
What is sorting? Rounding? Sediment maturity?
Sorting- degree of uniformity of grain size
Rounding- gives us clues to the amount of time a sediment has been transported
How old sediment is based on previous descriptions
What are biogenous sediments
Particles produced directly by marine organisms
What are the major types of marine organisms whose shell remains result in the formation of carbonate (calcareous) and siliceous biogenous sediments?
Calcareous- Foraminifera- zooplankton and Coccolithophores- phytoplankton
Siliceous- Radiolaria (zooplankton) and Diatoms (phytoplankton)
What is an ooze?
30% of weight is biogenous (rarely happens on continental shelf)
What are hydrogenous sediments? Describe the different kinds them.
Precipitate (crystallize) directly from seawater.
Manganese (only found in middle of ocean away from margin) and phosphorite nodules (only on continental shelf-indicate high biological activity) , evaporites (warm climate isolated areas) , sulfides from black smokers, carbonates
What is a black smoker?
Hydrothermal vents that are hot springs discovered on oceanic ridges
What are cosmogenous sediments? What are their source?
derived mostly from interplanetary dust and impacts by large asteriods and comets
What are microketites and how do they form
Impact of large meteors or small asteroids on the crust of the earth form translucent oblong particles of glass (found around extinction of dinosaurs)
What are neritic sediments? Where do you find them?
terrigenous sediments whereas a greater proportion of deep-sea sediments is of biogenous origin they tend to be coarser
Found on continental shelf
What are pelagic sediments? Where do you find them?
deposits of sediment found on the deep ocean floor beyond the continental rise. They typically tend to be finer
How would you expect grain size to be distributed ideally along the continental shelf?
Coarse to fine
How do sea level changes affect the distribution of sediment grain size on the continental shelf?
Make is so they are multiple graded layers?
What are relict sediments?
A sediment deposited under a set of environmental conditions that still remains unchanged although the environment has changed and it reamins unburied by later sediments
How are sediments distributed according to latitude on the continental shelf?
Biogenic by equator then Terrigenous- then relict then glacial-marine
What is a turbidity current? What kind of deposits does it produce? How?
Graded, because it takes less energy to transport finer deposits farther
What does sediment distribution in the deep ocean depend on?
1. Latitude
2. Distance from landmasses
3. Calcium carbonate compensation depth (CCD)
What are the most common types of pelagic sediments?
Red Clay
What are red clays? Where do you find them? How do they accumulate and form?
fine grained reddish-brown terrigenous sediments that accumulate very slwolya nd cover the deepest abyssal basins. Produced by chemical weathering
Chlorite-high lat
Kaolonite- low lat
Illite- southern hemisphere
What controls the distribution of biogenous sediments?
1. Production in surface waters;
2. Dilution on the sea floor-
3. Dissolution in deep waters- more =less S
Why are fecal pellets important for the deposition of pelagic sediments
it would take 20 to 50 years for them to make it to the ocean floor, fecal pellets take 10-15 days, allow you to make assumption that what you study reflect the surface
How is dissolution different for calcareous and siliceous sediments?
Calcareous sediments dissappear after CCD
Siliceous particles dissolve more slowly (faster at warm waters) and don’t dissolve after a certain depth
What is the calcium carbonate compensation depth? What controls its formation and depth?
Depth at which the rate of supply of calcium carbonate (CaCO3) equals the rate of dissolution?
Affected by rate of productiona nd supply
Where in the ocean do you find calcareous oozes? Why?
Found in middle ocean (near mid ocean ridges) where you find calcium carbonate is where your mid ocean ridge is (shallower there)
Where in the ocean do you find siliceous oozes? Why?
high latitude and along equator, because these two locations are characterized by high productivity
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