Oceanography 251 Week 2 Notes COMPLETE 9/5-9/9
Oceanography 251 Week 2 Notes COMPLETE 9/5-9/9 OCNG 251
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This 9 page Class Notes was uploaded by Anna Notetaker on Monday September 12, 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 129 views. For similar materials see Oceanography in Science at Texas A&M University.
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Date Created: 09/12/16
Oceanography 251-504 9/12/16 8:34 AM 9/5/16 CHAPTER 2 CONT. Types of Plate Boundaries: • Divergent o Plates split, moving in opposite directions o “Plates move apart” o Creates ocean basins ▯ Ex. Mid-Ocean ridge ▯ Ex. Mid-Atlantic Ridge ▯ Ex. Rift Valleys ▯ Ex. East African Rift Valley o New ocean floor (ocean basin) is created (goes back to cycle from Week 1 Notes!) – continued stress from convection cycle • Convergent o Plates collide, (subduction occurs) moving 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 ▯ 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 ▯ Continental Transform Fault – cuts across continent o ALL transform faults occur between mid-ocean ridge segments (Divergent Boundaries Continued: Types of Spreading Centers) Discovery: • Mid 1970s – Scientists visit Mid-Atlantic Ridge o DSV Alvin (Allyn Vine) ▯ Spherical submarine – distributes pressure to withstand the immense pressure present at the bottom of the sea floor o 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” ▯ 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 o EX: Thermal Vent Ecosytems: ▯ “tube worms” ▯ clams with hemoglobin ▯ crabs/shrimp (without eyes b/c not necessary with lack of light anyways) 9/6/16 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 o Nematah – hotspot track • Global hotspot locations: o Yellowstone o Hawaiian Island – Emperor Seamount Nematath ▯ 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 o Fringing reefs – develop along margin of landmass ▯ Physically attached to the shoreline o Barrier reefs – separated from landmass by lagoon o Atolls – reefs continue to grow after volcanoes are submerged ▯ Reefs – living organisms ▯ Can accommodate for change of geology CLICKER QUESTION: • The mid-atlantic ridge is an example of a ______ boundary. o A. convergent – cont. cont. o B. convergent – cont. ocean o C. convergent – ocean ocean o D. divergent o E. transform fault END OF CHAPTER 2 CHAPTER 4 – MARINE SEDIMENTS • “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 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 (microscropic) 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 • isoptopes 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 temperatute record, aka: the possibility to recreate climate from over 180million years ▯ not exact, but gives a sense of boundaries 9/9/16 What is the relation between CO2 and temperature? Today’s CO2 concentration: o about 400 parts per million – unprecedented compared to past ▯ unusually stable/warm o CO2-Temp curve – very highly correlated ▯ However, correlation does not provide for causation, AKA: there is no evidence that one causes the other ▯ “greenhouse mechanism” – with CO2 increases, temperature increases – could be reversed to say as temperature increases, CO2 increases ▯ we have added 100 parts per million NSF Sponsored program – ODP: Ocean Drilling Program (operated by Texas A&M) • The JOIDES Resolution 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 eminate from the ocean itself – everything else is transported. – very small percentage • Cosmogenous – derived from outerspace 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 CLICKER QUESTION: • We expect that most pelagic lithogenous sediment will be: o A. formed at the spreading center o B. composed of basalt o C. coarse grained o D. fine grained o E. composed of the shells of phytoplankton 9/12/16 8:34 AM 9/12/16 8:34 AM
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