OCEANOGRAPHY: COMPLETED EXAM 1 STUDY GUIDE 9.15.16
OCEANOGRAPHY: COMPLETED EXAM 1 STUDY GUIDE 9.15.16 OCNG 251
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This 17 page Study Guide was uploaded by Anna Notetaker on Thursday September 15, 2016. The Study Guide belongs to OCNG 251 at Texas A&M University taught by Dr. Benjamin Giese in Fall 2016. Since its upload, it has received 375 views. For similar materials see Oceanography in Science at Texas A&M University.
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Date Created: 09/15/16
Oceanography 251 – EXAM 1 Study Guide 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 water • Oceanic Crust: o Basalt (created from volcanic material, as a result of Earth’s interior) 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 • 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) 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) 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) • Extremely high temperatures: 400 degrees (F) • Doesn’t boil because of pressure • Immense pressure • Spreading centers • Magma results in very high temperature 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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