Oceanography 251 Week 1 Notes COMPLETE 8/29-9/2
Oceanography 251 Week 1 Notes COMPLETE 8/29-9/2 OCNG 251
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This 8 page Class Notes was uploaded by Anna Notetaker on Monday September 5, 2016. The Class Notes belongs to OCNG 251 at Texas A&M University taught by Dr. Benjamin Giese in Fall 2016. Since its upload, it has received 146 views. For similar materials see Oceanography in Science at Texas A&M University.
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Date Created: 09/05/16
Oceanography 251-504 9/5/16 11:29 AM 8/29/16 Why study the Oceans? • S: climate change? • S: oil spills? – P: ocean pollution – plastics, micro-plastics • P: overfishing, ocean acidification (fossil fuel, hydrocarbons, releases CO2 -> dissolves into ocean, most CO2 end up in ocean, creates carbonic acid, causes PH to go down) ecosystem destruction (coral reefs, dead zones -> coral bleaching) pollution (ocean pollution, head pollution, plastics, chemicals, fertilizers -> alter ecosystems) climate (ex. 2011) • Climate: o A. Was 2011 dry because it was hot? o B. Was it hot because it was dry? o C. Both? o D. Neither? ▯ 2011 was a La Nina year 8/31/16 HBDD • Pacific ocean = largest/deepest ocean • Atlantic ocean = 2ndlargest/expanding at the expense of the pacific ocean – as a result of plate tectonics • Indian ocean = 3 rdlargest/unique because it’s mostly in the southern hemisphere > relevant to the ocean current/geology • arctic ocean = smallest/shallowest ocean – largely covered by ice > very highly reflective surface > relevant to climate change – contracting/shrinking rapidly > ex. polar bear picture • ‘Southern ocean’ – marginal region that goes around the coast of Antarctica – where water sinks o CLICKER QUESTION: How deep is the ocean (on average?) A. 40m B. 400m C. 4000m D. 40000m E. 400000m CLICKER QUESTION: How wide is an ocean basin? A. 500-1000km B. 5000-10000km C. 500000-1000000 D. 500000-10000000 E. None of the above • The aspect of ratio of the oceans: o Depth vs. width o Hypsographic Curve: ▯ Provides information about elevation of ocean ▯ /distribution between land/oceanography ▯ majority of land sits near sea level ▯ change sea level by small amounts > it reduces surface area by a lot (shrinks amount of land) • ex. exponential decay o oceanic crust vs. continental crust ▯ ALL crust = rough, rigid material o Continental crust: ▯ Granitic ▯ Density = 2.7 gm/cm^3 ▯ Older – 4 Billion Years (Earth assumed to be c. 5 billion) ▯ Ex. cork o Oceanic crust: ▯ Basalt (created from volcanic material, as a result of Earth’s interior) ▯ Density = 3 gm/cm^3 AKA: Thinner, and deeper AKA: biggest difference between O. crust and C. crust ▯ Relatively young – 200 million years ▯ Lower horizon o ^^ = the “WHY” behind oceanic basins • “The summit of Mt. Everest is marine limestone” o – John McPhee, Basin and Range o 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 o the why behind all formations on Earth o what makes the Earth so dynamic o Pangea ▯ Plates are continuing to move ▯ Continental motion is extremely slow ▯ Ex. finger nails growth ▯ Evidence claims there have been 5 cycles of coming together/separating ▯ 1. Permian 225 million years ago ▯ 2. Triassic 200 million years ago ▯ 3. Jurassic 135 million years ago ▯ 4. Cretaceous 65 million years ago ▯ 5. Present Day ▯ Every time a cycle occurs: ▯ the basalt material is re-integrated into the mantle/next cycle – constantly being recycled ▯ the granitic material always stays at the surface • History of Discovery of Plate Tectonics: st o Alfred Wegener = 1 to propose concept in 1912 o Called it “continental drift” o Concept was resisted up until the 1950’s/accepted by scientific community o Evidence from oceans finally provided for acceptance ▯ Evidence: ▯ Wegener proposed Pangaea – one large continent that existed 200 million years ago ▯ Panthalassa – one large ocean ▯ Noted puzzle-like fit of modern continents ▯ Matching sequences of rocks/mountain chains ▯ Similar rock on different continents (fossils??) ▯ Glacial ages and other climate evidence ▯ Evidence of glaciation in now tropical regions ▯ Direction of glacial flow and rock scouring ▯ Plant and animal fossils indicate different climate then today • Distribution of organisms • Same fossils found on continents that today are widely separated • Modern organisms with similar ancestries ▯ Objections: ▯ Hostile criticism and open ridicule • “what is pushing these continents?” • “would take too much energy that just doesn’t exist” ▯ Continents cannot plow through ocean basins ▯ Tidal gravitational attractions too small 9/2/16 Plate Tectonics (cont.) • Magnetometer – provides magnetic/gravitational evidence of plate tectonics o Paleomagnetism: Study of Earth’s history/interaction of magnetic field ▯ Earth has magnetic polarity ▯ North and South polarities ▯ North pole: axis of rotation – tilted 23.5 degrees (approx. 24) from the Sun – fairly stationary ▯ Magnetic pole: creates magnetic field lines that run from the north pole to the south pole and vis versa – as opposed to axis of rotation, the magnetic pole frequently changes and even flips/reverses sporadically – results in the orientation of 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 of various rocks • Earth’s magnetic polarity reverses periodically • Magnetic polarity recorded in igneous rocks o Magnetite in basalt o Paleomagnetism and the Ocean Floor: ▯ 1955 – deep water rock mapping ▯ Magnetic anomalies – regular pattern of north-south magnetism “stripes” ▯ Stripes were symmetrical about long underwater mountain range Plate tectonic processes: • Earth’s interior – heat – makes material fluid like and able to move around o Results in a convection cycle: ▯ The heat (molecular motion (molecules are bouncing off each other)) – results in expansion, and for the heat to rise and cause that movement ▯ Lifted magma generates convection cells – as it rises and pushed against the solid, basaltic rock on surface, it creates stress ▯ Stress – physically pulls apart (fissures,) the basaltic rock. Results in: mountain ranges, mid-ocean ridges, subduction zones, volcanoes, etc. ▯ Subduction: when fluid material is forced under solid rock (at edge of ocean) – causes friction • New basaltic rock forms (reintegration) o Ex. Andes Mountains ▯ Sea Floor Spreading: when ocean splits (middle of the ocean) • Ex. Mariana Trench, mid-ocean ridges ▯ Sea Floor Spreading Evidence: • Frederick Vine and Drummond Mathews (1963) • Sea floor stripes record Earth’s magnetic polarity Age of Ocean Floor: • Late 1960’s deep-sea drilling – began to try to date age of rocks – used radiometric dating of ocean rocks (found concentration of decayed material vs. non-decayed material) • Symmetric patterns of age distribution about mid-ocean ridges o Symmetry is as a result of the constant/consistent convection cycles, as hard rock is split and magma constantly rises to “fill that gap” ▯ And though the “stripes” are symmetric and consistently periodic, the orientation of these rocks is still sporadic and tend to flip “randomly” • Oldest ocean floor only 180 million years old • Earthquakes as evidence: o Most large earthquakes occur at subduction zones o Earthquake activity mirrors plate tectonic boundaries ▯ Subduction/separation occurs o Global distribution of Earthquakes – allow one to see where plate tectonics are/initially were ▯ Global Plate Boundaries: ▯ North American Plate - West ▯ South American Plate - West ▯ African Plate – East ▯ Eurasian Plate – East ▯ Pacific Plate – Northwest o Detecting Plate Motion with Satellites: ▯ Provides for the ability to measure very small changes in distances (plate motion) ▯ Allows one to see that one plate can move in multiple directions – results in fissuring o CLICKER QUESTION: o If you traveled to another earthlike planet with an ocean, how could you determine if tectonic plates and plate tectonic movement existed? A. Look for mountain ranges, oceanic ridges, oceanic trenches, and volcanoes B. From satellite imaging, observe a jigsaw fit of the continental edges C. Check seismic readings for earthquake activity D. All the above 9/5/16 11:29 AM 9/5/16 11:29 AM