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TEXAS A&M / Science / Sci 251 / what is paleomagnetism?

what is paleomagnetism?

what is paleomagnetism?

Description

School: Texas A&M University
Department: Science
Course: Oceanography
Professor: Benjamin giese
Term: Fall 2016
Tags: Oceanography
Cost: 50
Name: OCEANOGRAPHY: COMPLETED EXAM 1 STUDY GUIDE 9.15.16
Description: A completed study guide outlined by Dr. Giese for EXAM 1 Contains all EXAM 1 Chapters: Chapter 2 Chapter 4 Chapter 5
Uploaded: 09/16/2016
17 Pages 8 Views 19 Unlocks
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Oceanography 251 – EXAM 1 Study Guide


what is paleomagnetism?



EXAM 1:  

CHAPTER 2: Plate Tectonics and Ocean Floor

CHAPTER 4: Marine Sediments

CHAPTER 5: Seawater Properties

Chapter 2: Plate Tectonics and Ocean Floor

Width and depth of an ocean basin:

• Depth: 4000m

• Width: 5000-10000km

> Depth Vs. Width = Ratio of the Oceans, AKA:

• Hyposgraphic Curve:

o Provides information about elevation of the ocean

o Distribution between land/oceanography

o Proves majority of land sits near sea level

o Proves when sea level changes in small amounts it reduces  the land’s surface area by a lot  

???? Ex. Exponential Decay

Continental Crust Vs. Oceanic Crust:

• Continental Crust:

o Granitic

o Density = 2.7 gm/cm^3

o Older (than oceanic crust) – 4 Billion Years

???? Tangible example = “cork,” and how it floats on top of  


what are the types of convergant boundaries?



water

• Oceanic Crust:

o Basalt (created from volcanic material, as a result of Earth’s  interior) Don't forget about the age old question of the part of the brain that maintains balance and motor coordination grows fastest

o Density = 3gm/cm^3, AKA: thinner/deeper than continental  crust – (this is the biggest difference between oceanic crust  and continental crust)

o Relatively young – 200 Million Years

o Lower horizon

• ^^ The Relationship between Continental Crust and Oceanic Crust  provides for the “WHY” behind the existence of Oceanic Basins o Ex: “The summit of Mt. Everest is marine limestone”

- John McPhee, Basin and Range

???? AKA: the material at the absolute bottom of the ocean,  can be found at the highest point on Earth, as a result  

of Plate Tectonics (Continental Drift)

Evidence that supports Continental Drift:

• Alfred Wegener proposed Pangaea – one large continent that  existed 200 million years ago


which sediments has a macrosopic meteor debris?



If you want to learn more check out ∙ People act differently in the presence of others, but why?

• Panthalassa = one large ocean that also existed at that time • Noted the puzzle-like fit of modern continents

• Matching sequences of rocks/mountain chains

• Similar rock on different continents (Includes Fossils!) • Glaciation in regions that are now deemed ‘tropical’

• Direction of glacial flow/rock scouring

• Plant and animal fossils indicate different climate then today: o Distribution of organisms

o Same fossils found on continents that are widely separate  today

o Modern organisms with similar ancestries

• Earthquake patterns

o Most large earthquakes occur at subduction zones

o Earthquake activity mirrors plate tectonic boundaries

???? Where subduction/separation occurs

o Global distribution of earthquakes – allows one to see where  plate tectonics are/initially were (Global Plate Boundaries)

• Plate Motion Today – can be measured with satellites – measure  very small changes in distances and allows one to see that one  plate can move in multiple directions – (results in fissuring) We also discuss several other topics like to tartarus with you elpenor

Earth’s Changing Magnetic Field and Plate Tectonic Processes: (Magnetometer: provides magnetic/gravitational evidence of plate  tectonics and…)

Paleomagnetism: Study of Earth’s history/interaction of magnetic field • Earth has magnetic polarity

o AKA: North and South Polarities

o North Pole:  

???? Axis of Rotation – tiled 23.5 degrees (approx. 24) from  the Sun – Fairly stationary

• Magnetic Pole: create magnetic field lines that run from the north  pole to the south pole (and vise versa) – as opposed to Axis of  Rotation, the Magnetic Pole frequently changes: 

o Pole flips/Reverses sporadically – results in the  

orientation of Earth’s rocks to flip/reverse as well

???? Reversals occur over hundred thousands of years  

(chaotic/unique behavior)

???? These anomalies allow for one to detect the timing in  

regards to the existence of various rocks

???? Magnetic Polarity recorded in igneous rocks

✂ Magnetite in basalt

Plate Tectonics Processes:

Earth’s interior – heat – makes material fluid like and able to move around • Results in a Convection Cycle in the Asthenosphere: o The heat (as a result molecular motion as molecules are  bouncing off of each other) – results in expansion, and causes  the heat to rise (upward movement) If you want to learn more check out scad estar

o Lifted magma then generates convection cells – as it rises  and pushes against the solid, basaltic rock on surface, it  

creates stress

o Stress – physically pulls apart (fissures,) that basaltic rock. o Results in:

???? Subduction: when fluid material is forced under solid  

rock (at the edge of ocean) – causes friction:

✂ Creates new basaltic forms (reintegration)

• Ex. Andes Mts., mountain ranges

???? Sea Floor Spreading: when ocean splits (middle of the  ocean)  

✂ Ex. Mariana Trench, mid-ocean ridges

✂ Evidence of Sea Floor Spreading:

• Frederick Vine and Drummod Mathews  

(1963)

• Sea Floor Stripes – Records Earth’s  

magnetic polarity

o Results in those sporadic  

flips/reverses of orientation of rocks  

present  

• Symmetry of Sea Floor Stripes: as a  

result of the constant/consistent convection  

cycles, as hard rock is split and magma  

constantly rises to “fill that gap”

✂ ** Oldest ocean floor = only 180 million years old ???? Types of Spreading Centers:

✂ Discovery:

• Mid 1970s – Scientists visit Mid-Atlantic  

Ridge

• DSV Alvin (Allyn Vine)  

• Spherical submarine – distributes pressure  to withstand the immense pressure present  

at the bottom of the sea floor

✂ What they found:

• 4000 meters deep

• No light beginning at 100m deep (water  absorbs light)

• AKA: no photosynthesis, (initial belief: no  way to create food/life) Don't forget about the age old question of what is the simplest unit of an element that maintains all the characteristics of the element?

• Extremely high temperatures: 400 degrees  (F)

• Doesn’t boil because of pressure

• Immense pressure

• Spreading centers

• Magma results in very high temperature  We also discuss several other topics like sebastien robidoux concordia

waters, results in plumes “letting out,” into  

surround cold water

• The minerals initially found in extremely hot  water are no longer able to remain because  

of fast temperature change and are  

released

• Results in “black smoke”

o Results in Photosynthesis  

Equivalent:

???? Chemosynthesis

???? CHEMOSYNTHESIS: 

???? Magma (convection cycle) produces high heat energy

???? Results in high temperature waters

???? High temperature waters interact with surrounding cold  waters

???? Creates “plumes,” with “black smoke”

???? Black smoke is filled with minerals (sulfide)

???? Surrounding bacteria takes in those minerals

???? Bacteria converts those minerals into SULFIDE energy

???? Results in reduced Carbon Compounds

???? Allows sustained life

✂ EX: Thermal Vent Ecosytems:

• “tube worms”

• clams with hemoglobin  

• crabs/shrimp (without eyes b/c not  

necessary with lack of light anyways)

Types of Plate Boundaries:

• Divergent 

o Plates split, moving in opposite directions

o “plates move apart”

o Creates ocean basins

???? Ex. Mid-ocean ridge: Mid-Atlantic Ridge

???? Ex. Rift Valleys: East African Rift Valley

o new ocean floor (ocean basin) is created (goes back to cycle  form Week 1 Notes) – continued stress from convection cycle • Convergent 

o Plates collide, (subduction occurs)

o “plates move towards each other”

o Destroys ocean basins

???? Ex. Ocean trench

???? Ex. Volcanic Arc

???? Results in Deep Focus Earthquakes

o 3 Types of Convergent Boundaries:

???? Ocean Vs. Continental

✂ Ocean plate is subducted

✂ Ex. continental arcs

✂ Ex. Explosive andesitic volcanic eruptions

???? Ocean Vs. Ocean

✂ “Density vs. density”

✂ The more dense (older) ocean plate is subducted

✂ Ex. Island Arcs

???? Continental Vs. Continental

✂ Subduction doesn’t really occur

✂ More of collision/”uplifting”

• Ex. Tall mountains

✂ “light material vs. light material”

• Transform 

o Plates “slide past each other,” one moves north, one moves  south

o Offsets oriented perpendicular to mid-ocean ridge o Offsets permit mid-ocean ridge to move apart at different  rates

o Results in shallow but strong earthquakes

o Faulting occurs

???? Oceanic transform fault – ocean floor only

Hotspots, ocean islands, coral reefs

Applications of Plate Tectonics:

• Mantle plumes and hotspots

o Hotspots – as a result of mantle plume

???? Interpolate features

✂ Volcanic islands within a plate

✂ Island chains

✂ Records ancient plate movement

✂ Nematah – hotspot track

• Global hotspot locations:

o Yellowstone

o Hawaiian Island – Emperor Seamount  

Nematath

o As islands sink (contraction) they  

seem to be getting smaller – and if  

they sink enough, it seems as if  

islands no longer exist because  

they’re completely submerged

• Coral Reef Development

• Fringing reefs – develop along margin of landmass

• Physically attached to the shoreline

• Barrier reefs – separated from landmass by lagoon

• Atolls – reefs continue to grow after volcanoes are submerged o Reefs – living organisms

???? Can accommodate for change of geology

END OF CHAPTER 2

CHAPTER 4: Marine Sediments

“Why are sediments important?”

• “The Earth has warmed 1 degree ‘C over the past 100 years” o As a result of humans?

o As a result of naturally variability?

o Osculation of the climate?

• Sediments – “rained down” on top of hard rock developed by heat  convection/magma

PALEO-OCEANOGRAPHY!

The ability to detect signals in sediments on the sea floor using  phytoplankton and oxygen isotopes:

o Allows one to learn about timing/history

o Variability – provides history of when/why/how, behind  sedimentary deposits – provides evidence of climate  

change/ocean change

• Sediment accumulation – representation of what happens at the  surface

o Factors include:

???? Light

???? Organisms

???? Nutrients

✂ -- these shells sink down the water column and  

accumulate and provide for the sedimentary  

record  

???? ex. phytoplankton – small (microscopic) organisms that  use photosynthesis to survive

???? ex. plankton – anything that can’t swim faster than the  current – relative in size – largest accumulation of  

anything in the world – most of the biomass on earth is  

phytoplankton

✂ draws down CO2

✂ releases oxygen

• = small enough that they remain at the  

surface

• isotopes of oxygen – ratio of o18/o16 tells  

us about climate  

• o18 = heavier than o16, more neutrons =  

heavier

• AKA: o16 evaporates more readily than o18  

because it is lighter

• shells = hard, rigid

o ex. calcium (carbonate?)

o ex. silica  

o ^ both contain oxygen

o allows scientists to see temperature  

record, aka: the possibility to recreate  

climate from over 180million years

???? not exact, but gives a sense of  

boundaries  

Marine Sediment Classification

Classified by origin:

• Lithogenous – derived from land

o “litho” = rock, aka land

o as a result of erosion/weathering of land rock that is  

transported somehow to the ocean to the seafloor

• Biogenous – derived from organisms

o Remains of living organisms

o When they die shells sink down to the sea floor and  

accumulate and high pressure compresses that sediment into  rock

o ^^majority of sediment

• Hydrogenous or “authigenic” – derived from water

o Comes from mineralization (salt) – only sediments that  emanate from the ocean itself – everything else is  

transported. – very small percentage

o Cosmogenous – derived from outer space

o Smallest percentage  

o Rains down

o Virtually no mass associated

Lithogenous Sediments (cont.) 

• Eroded rock fragments from land (weathering, fracturing, etc. AKA  “breaking of rocks into smaller pieces”)

• Reflect composition of rock from which derived

• Small particles eroded and transported:

o Carried to ocean through:

???? Streams

???? Wind

???? Glaciers

???? Gravity

o Grain size – proportional to energy of transportation and  deposition

o Greatest quantity can be found around continental margins Sediment Distribution:

• Neritic - coastal

o Shallow water deposits

o Close to land

o Dominantly lithogenous

o Typically deposited quickly

• Pelagic – open ocean

o Deeper water deposits

o Finer grained sediments

o Deposited slowly

Biogenous Sediment (cont.) 

- Largest proportion of sediment

• Two most common chemical compounds:

o Calcium Carbonate (CaCo3)

???? Ex. Chalk  

???? “Calcareous seafloor sediments”

o Silica (SiO2 or SiO2XnH2O)

???? “Siliceous sediments”

✂ Diatoms (plants)

• Photosynthetic algae

• Diatomaceous earth

✂ Radiolarians

• Protozoans

• Use external food

???? Shells sink down to the seafloor when they die – where  they accumulate and generate siliceous ooze

o Siliceous Ooze

???? The siliceous ooze then solidifies and becomes  

diatomaceous earth

???? Siliceous ooze = cold, nutrient rich water that can  

accumulate in great depths (aka: if its found in very  

deep water along the floor, its siliceous)

???? As warm surface water is pushed away, siliceous ooze  

fills in that space

✂ Can be found at some coastlines, but most  

importantly at the equator and high latitudes 

Calcareous Ooze

• Coccolithophores – produces a lot of ooze

o Nannoplankton

o Photosynthetic algae

• Foraminifera

o Protozoans

o Use external food

o Calcareous ooze

• CCD – Calcite Compensation Depth (PRESSURE!!)

o Depth where CaCO3 readily dissolves into a solution, AKA:  cannot accumulate! 

o Can’t go much deeper than 5000m

o Rate of supply = rate at which the shells dissolve

o Warm, shallow ocean saturated with calcium carbonate

o Cool, deep ocean under saturated with calcium carbonate o Ancient calcareous oozes at greater depths of moved by sea  floor spreading (as a result of plate tectonics)

Distribution of Biogenous Sediments:

• Depends on 3 factors:

o Productivity

o Destruction

o Dilution

Hydrogenous Marine Sediments (cont.) 

• Minerals precipitate directly from seawater

o Manganese nodules

???? Fist-sized lumps of manganese, iron, and other metals

???? Very slow accumulation rates

???? Many commercial uses – but mining operations are hard  at great depths

???? Unsure why they are buried by seafloor sediments and  

remain at surface of the seafloor

o Phosphates

o Carbonates

o Metal sulfides

• Small portion of marine sediments

• Distributed in diverse environments

Cosmogenous Marine Sediments: “Space Marine Sediments” (cont.) • Macroscopic meteor debris

• Microscopic iron-nickel and silicate spherules (small globular  masses)

o Tektites

o Space dust

• Insignificant proportion of marine sediments

o ^ “Then why are they important?”

???? When looking at extinction rates – cosmogenous  

sediments are able to provide a timeline of extinction  

and potential reasoning as to the “why” behind the  

extinction of dinosaurs

✂ Ex. Walter Alvarez found a layer enriched in  

iridium (which is very rare on Earth)

• Knew iridium was present in asteroids

• Proposed the theory that a massive  

object(s) containing iridium struck the  

Earth, causing extinction of the dinosaurs

• Created a large fireball – ejected a huge  

amount of mass into atmosphere– created  

quartz material – rained down – created  

approx. 4 hours of intense heat

END OF CHAPTER 4

CHAPTER 5: Seawater Properties

The water molecule is dipolar: 2 hydrogens. 1 oxygen, results in…: Hydrogen Bonding:

• Polarity means small negative charge at  

O end

• Small positive charge at H end

• Attraction is present:

o Between positive and negative ends of water  

o With molecules to each other or other ions

???? Hydrogen bonds are weaker than covalent bonds but  

still strong enough to result in

✂ High water surface tension

✂ High solubility of chemical compounds in water

✂ Unusual thermal properties of water

✂ Unusual density of water

• Heat capacity of the air: 1005 J/kg/K

• Heat capacity of the ocean water: 3993  

J/kg/K

Unique Properties of Water:

• Water molecules stick to other polar molecules

• Electrostatic attraction – produces ionic bond

• Surface Tension (water is solid, liquid, and gas at Earth’s surface) o Influences Earth’s heat budget

• High Heat Capacity (3993 J/kg/K)

o Created by the energy of moving molecules

o AKA: Because water has such a high heat capacity, it can  take in or lose a lot of heat without changing temperature

???? Calorie – amount of heat needed to raise temperature  of 1 gram of water by 1 C

???? Temperature – a measurement of average kinetic  

energy

✂ Thermocline = abrupt change of temperature with  

depth

• Heat Capacity – amount of heat required  

to raise temperature of 1 gram of any  

substance by 1 C

• Specific Heat – heat capacity per unit  

mass

• High Latent Heats:

o Vaporization/condensation

o Melting/freezing

o Evaporation

• Water’s ability dissolve salt

• Water’s Density: 

o Increasing pressure or adding salt decrease the maximum  density temperature

o Dissolved solids also reduce the freezing point of water o Pycnocline = abrupt change of density with depth

???? Seawater Density:

✂ Density increases with decreasing temperature (=  greatest influence on density)

✂ Density increases with increasing salinity

✂ Density increases with increasing pressure

• Does not affect surface waters

✂ Most seawater never freezes

???? Freshwater Density:

✂ = 1000 g’cm^3

o The ocean is layered according to density

???? 3 Distinct water masses:

✂ Mixed surface layer – above thermocline

✂ Upper water – thermocline and pycnocline

✂ Deep water – below thermocline to ocean floor

• High latitude oceans: thermocline and  

pycnocline rarely develop

o > isothermal, isopycnal

• Water’s Salinity: 

o Total amount of dissolved solids in water including dissolved  gases 

o Ratio of mass of dissolved substances to mass of water  sample

???? Ex. typical ocean salinity is 35 ppt (approx. 33-38)

✂ In coastal areas salinity varies more widely  

• Influx of freshwater lowers salinity or  

creates brackish conditions

o Ex. run off, melting icebergs, melting  

sea ice

o Precipitation 

• A greater rate of evaporation raises salinity  

or creates hypersaline conditions

o Ex. sea ice formation

o Evaporation 

• High latitudes:

o Low salinity (except where ice is  

formed!)

o Abundant sea ice melting,  

precipitation, and runoff  

• Low latitudes near equator:

o Low salinity

o High precipitation and runoff

• Mid latitudes:

o High salinity

o Warm, dry descending air increases  evaporation

✂ Salinity can also vary with seasons (dry vs. rain) ✂ Halocline – separates ocean layers of different  salinity

9/15/16 8:24 PM

9/15/16 8:24 PM

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