Prelim 1 STUDY GUIDE (Week 5)
Prelim 1 STUDY GUIDE (Week 5) BIOEE 1540
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This 16 page Study Guide was uploaded by Erica on Thursday September 24, 2015. The Study Guide belongs to BIOEE 1540 at Cornell University taught by Bruce C. Monger in Fall 2015. Since its upload, it has received 764 views.
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Date Created: 09/24/15
Oceanography Lecture Notes For Prelim 1 Geological Oceanograpay Paydical Oceanography a a a I v v H v v quotU c v c v S 1 Week12 Summary of Universe Galaxy Star Formation 1 Big Bang happened about 15 billion years ago All mass contained in a single point explodes outward 2 Temperatures in the core of large masses increase due to compressional heating I When core temperatures reach 10 million degrees Kelvin nuclear fusion of H into He is ignited thermonuclearfusion reaction to form heat and visible light among other types of radiation 3 Every single carbon nitrogen and phosphorous atom making up our physical body today was at one point in the past sitting in the center of a boiling hot star We very truly are made of star dust Summary of Solar System Earth Formation 1 46 billion years ago rockforming elements condensed into small solid grains as the nebula cooled Formation of the Moon The moon formed when earth was hit by a Marsized object Earth s Atmosphere 1 Early atmosphere consisted of hydrogen and helium 2 Volcano releases H20 C02 302 N2 H2 CL2 into Atmosphere 3 Photosynthetic life evolves and this produces a modern 02rich atmosphere Basic Physiography of Modern Oceans Officially 5 named oceans Pacific Atlantic Indian Arctic and Southern Oceanography Lecture Notes Average depth 4 km 3A of atmosphere s mass is within 12 km of the planet s surface The earth and Sun are middle aged in 4 billion more years the sun and earth will ABSOLUTELYnot be here anymore Basic Morphology of the Sea oor 1 Bathymetry 9 measuring topography of ocean surface 2 Main Sea Floor Features a Continental Shelf highest oor surface b Abyssal Plain lowest oor surface Plate Tectonic Theory Development 0 Main points 0 Alfred Wegener s proposal of the Theory of Continental Drift in 1915 was not well accepted because his proposed forcing mechanism tidal action of the moon was incorrect 0 Plate Tectonic Theory was accepted after SeaFloor Spreading and Sea Floor Subduction were discovered postWWII Part I Continental Drift 11 Fit of Continents 0 There was noticeably a n apparent fit of the continents 12 Paleobiology o 1915 9 Alfred Wegner the distribution of fossils and mineral belts was good evidence regarding the fit of the continents in the past 0 Compared to pieces of torn newspaper placed back together where the letters lined up Part II Sea oor Spreading Evidence of Sea oor Spreading was provided by magnetic anomaly patterns in ocean crust along the ridge 21 MidOcean Ridges o Discovered with WWII Sonar Oceanography Lecture Notes 22 Extensional Faulting o Indication of sea oor spreading at midocean ridges was inferred based on observed morphology of the faulting patterns along ridge axis 0 Faulting movement which produces displacement of adjacent rock masses along a fracture in the rock 23 Magnetic Anomalies that are Symmetric Across the Midocean Ridge 0 Magnetic anomalies are a substitute measure of geologic time 9 each anomaly can be assigned a specific date 0 Observing symmetric magnetic banding is a roundabout way of observing the rock getting older as you move away from the ridge axis This is strong evidence that the ridge is slowly spreading away from the ridge axis in opposite directions Age of Ocean Crust is youngest at ridges and symmetrically older offaxis Part III Sea oor Subduction 31 Discovery of deepsea trenches and seismic activity 0 This helped to explain the eventual loss of ocean crust that was formed originally at midocean ridges Finally Seismic Activity explains plate boundaries Oceanography Lecture Notes Details of Plate Boundaries 2 The driving mechanism Convection in the mantle amp slab pull I Molten rock rises to surface at divergent boundaries 9 spreads 9 cools 9 gets more dense 9 sinks 9 pulled back into mantle at subduction boundaries 3 Plate Tectonic Movement I Earth s crust composed of individual crustal plates tectonic plates that move to one another I Plates can be composed of ocean crust and continental crust I When plates move the continent moves as well I Original supercontinent Pangaea 9 split to form current continents Plate DivergenceConvergence Oceanic Crust is thin with a higher density mostly consists of basalt Continental Crust is thicker with lower density mostly granite Divergent Boundary 9 where plates are moving APART I Mostly midridges 0 New East Africa Rift Zone I ContinentContinent I OceanOcean Convergent Boundary 9 where plates are moving TOGETHER I OceanContinent Ocean crust subducted under continental more dense Creates deep ocean trench forms explosive volcanoes EX Andes Mountains in Chile I OceanOcean Older plate is pulled under colder and more dense I ContinentContinent Neither wants to go under the other 9 Mountainbuilding Oceanography Lecture Notes Transform Boundary 9 Plates slide laterally relative to one another I San Andreas Fault Mantle Hot Spots Hawaiian hotspots Marine Sediments SedimentAccumulation 1 Wide range of material raining down Continental dust biological material riverborn sediments 2 Sediment thickness is high near coast 0 Due to river runoff of terrigenous sediment and high productivity that leads to high rain rate of biological material 3 Red Clays found in openocean 0 Slow rain of continental dust and very low biological addition creates red clays 4 Calcareous or Siliceous Sediments found In high biological productivity regions and in absence of river out ows containing terrigenous material 0 Downward rain of biological material cause red clays to be ooded diluted by biologicallyderived calcareous or siliceous material 5 Rate of accumulation very slow and a 10m sediment core can represent a record of up to a million years of earth history Oceanography Lecture Notes Week 3 Ocean Waves 0 v Wavelength crest to crest distance 0 v Wave Speed distance a wave crest travels per unit time 1 Wave speed propagation is a function of wavelength and bottom depth 2 Wave Speeds 0 Deep Water Waves bottom depth is deeper than 12 the wavelength I Speed is a function of wavelength only I Longer wavelength 9 waves move faster 0 Shallow Water Waves bottom depth is shallower than 1 20 the wavelength I Speed is a function of depth only I All waves in shallower water move slower 0 Intermediate Waves L 20 lt Depth lt LZ I Wave speed is a function of both wavelength and depth Wave Dispersion Selfsorting of deep water waves based on wavelength 0 Occurs because longer wavelength waves travel faster Wave Refraction the bending of shallow water wave fronts o Occurs because of a change in bottom depth 0 Consequence focusing and defocusing of wave energy on headlands and bays Summer Creates wide and gently sloping sandy summer beach Winter Results in a rocky winter beach Ripe Currents 1 Initiated when large waves push water onto an elevated beach face 2 Rip currents are seldom wider than about 10 meters What Determines Wave Height Determined by Wind s speed duration and fetch Wind Speed Oceanography Lecture Notes 0 Sets the upper possible limit on wave height for a fully developed sea Duration of Wind Event 0 Modulates the upper possible limit on wave height The distance over which wind can blow without obstruction Modulates the upper possible limit on wave height Limited by the size of the storm system in the open ocean Larger fetch effectively gives the storm more time to increase in size of a given wave before the wave propagates out from under the storm center Fetch O O O O 20 E 15 G E 3 10 D I gt m 5 E 0 Tsunami Waves 3 45 feet 20 I I I 5 10 15 Wind Speed meters secquot 25 3 60 mph Tsunami wave generation at a convergent plate boundary Indonesian Earthquake December26 2004 japanese Tsunami March 11 2011 Internal Waves Travel along density discontinuities in the ocean interior Ocean Tides Oceanography Lecture Notes Equilibrium Theory of Tides Highly idealized but very instructive Equilibrium Tide Theory Daily Patterns diurnal semidiurnal and mixed semidiurnal tidal patterns Monthly Patterns springneap tidal pattern 1 Tide wave is treaded as a deepwater wave in equilibrium with lunar solar forcing 2 No interference of the tide wave s propagation by continents 3 Daily Tidal Patterns 0 Diurnal 1 high amp 1 low tide per day 0 Semidiurnal 2 equal high tides amp 2 equal low tides per day 0 Mixed Semidiurnal 2 unequal high tides amp 2 unequal low tides per day quotTidal Buldges on opposite sides of earth cause the normal risefall of tides over a 1 day period Monthly Tidal Patterns 0 The tidal force that the sun exerts on the earth is about 46 of the tital force that the moon exerts on the earth 0 Spring Tides occur when the moon and sun pull along the same line New and full moon 0 Neap Tides occur when the moon pulls at 90 degrees to the sun First and last quarter moon Dynamic Theory of Tides 1 Tide wave treated as a forced shallowwater wave 0 Not in equilibrium with lunar solar forcing 0 Tide waves are shallowwater waves Considered a shallowwater wave for depths ltL 20 or bottom depths lt 1000 km 0 Under ideal conditions the tide wave speed would be determined only by ocean bottom depth but this would only be the case if it were a freely Oceanography Lecture Notes propagating wave which it is not 0 Frictional drag slows the tide wave down so the earth spins out from directly under the moon before the tide crest can catch up 0 Result of this the high tide occurs at a time after the moon appears to pass overhead 2 Affected by the Coriolis Force 0 Since tidal waves have the same length scale as the earth and motions are on the order of a day the Coriolis Force has significant effect on the direction of wave propagation Acts exactly to the right of the direction of motion in the northern hemisphere Acts exactly to the left of the direction of motion in the southern hemisphere 3 Coriolis Force causes a rotary motion of a tide wave in a closed ocean basin Special Cases Tidal ranges can be exaggerated by 0 Forcing ocean water into a narrow embayment o Tidal forcing that is in resonance with the tide wave Oceanography Lecture Notes Week 4 Climate Change Atmospheric C02 concentration 0 Since the industrial era it s increased 35 0 Increasing by about 23 ppm each year So in about 10 years it will be 420430 ppm The increased C02 in the atmosphere created a persistent energy imbalance in the earth system that accumulates heat energy over time like rolling up the window on your car a little further Goal to limit global warming to 2 degrees Celsius above preindustrial levels Humans are now the trigger that moves C02 into the atmosphere We are now more certain of human caused global warming than we are that smoking causes cancer Greenhouse Gas E ect 1 Sunlight passes through the glass window short wavelength radiation 2 This energy is absorbed into car heat energy is radiated as long wave length radiation infrared 3 The window that let short wavelength radiation through then absorbs the long wavelength radiation and prevents heat from leaving the car The car heats because more energy enters the car than leaves it The inside of the car heats until the glass gets so hot that it radiates heat energy out at the same rate as sunlight enters 9149 Same amount of sunlight energy is coming into earth but less infrared energy is leaving 9 now we have more energy coming in than out so the earth warms Atmospheric C02 has a lifetime of 10000 years We have 500 Gt of C02 remaining that can be put into the atmosphere We currently emit about 50 Gt a year 9 do we keep emitting at 50 Gt per year for 20 years 9 do we slow down emissions starting now and make the 500 Gt last longer At some point we will absolutely need to transform our living to a zero Oceanography Lecture Notes carbon emission society but what path do we take Accumulation of Heat Energy in the Earth System Global warming isn t evenly distributed and the polar regions are very sensitive Atmosphere now has a C02 concentration of 400ppm humans didn t exist the last time this happened 9 the last time temperatures were 510 degrees Fahrenheit higher than today sea level was about 75120 feet higher Natural Climate Forcing Factors small compared to current human forcing o The timing of the ups and downs in C02 concentrations in the atmosphere coincide with the frequency of orbital forcing o Triggering mechanism on a time scale of 10000 years small variations in 3 orbital parameters produce small variations in the pattern of solar energy reaching the earth 0 Affect causes C02 to redistribute most likely moving C02 from deep ocean into atmosphere 0 Increased C02 in atmosphere green house effect warming 0 Orbital Variations the principle trigger mechanism of temperature change at large time scales with atmospheric C02 acting as the actual forcing mechanism Ocean Circulation I Ocean Surface Currents 1 Large subtropical gyres rotating clockwise in N hemisphere and counter clockwise in S hemisphere 2 Subpolar gyres rotating counter clockwise in the N clockwise in the S 3 Antarctic Circumpolar Current moving eastward around the Antarctic continent Deep Circulation in Oceans 1 Cold surface water sinks at high latitudes amp moves to lower latitudes at depth 2 Deepwater returned to the surface layer through broad diffusive upward vertical mixing Coriolis Force Oceanography Lecture Notes It arises from real physics related to the conservation of angular moment In the northern hemisphere the Coriolis Force is always directed to the right of the water parcel motion In the southern hemisphere the Coriolis Force is always directed to the left of the water parcel motion The Basic Rule to determine the direction of the Coriolis Force is to 1 point your nose in the direction of the ocean current or wind is moving and then 2 stick your hand directly out from your side to get the direction of the Coriolis force right hand for the northern hemisphere or left hand for the southern hemisphere Atmospheric Circulation 0 Material is warmed when it absorbs radiant energy Much of the visible radiant energy from the sun Short wavelength radiation passes right through the atmosphere without being absorbed and consequently without much direct heating of the atmosphere from the sun The earth s surface absorbs a lot of the sunlight energy and so it becomes warm The warm earth surface radiates infrared radiation long wavelength radiation from its surface and this energy is absorbed by the atmosphere and consequently warms the atmosphere So the atmosphere is heated from below by absorbing long wavelength radiation emitted from the warm earth surface Atmospheric Convection O The warm ocean surface heats the atmosphere from below Warm surface air is able to hold a lot of water vapor and so it becomes moist Warm moist surface air has low density so it rises like a hot air balloon and as it moves aloft it expands and cools Cooling of air aloft causes water vapor to condense and precipitate Condensation releases latent heat that drives the upward convection even higher Solar Heating of the Earth 5 Surface Oceanography Lecture Notes 0 Solar heating of the earth surface is most intense at the equator where the solar radiation is most direct 0 So atmospheric convection and precipitation is strongest along the equator Vertical Distribution of Seawa ter Density Vertical distribution of density directly in uences the vertical movement of water in the ocean Salt concentration and water temperature jointly determine seawater density I Surface ocean temperature is determined by the exchange of heat between ocean surface and the atmosphere Adding heat to the ocean is sunlight being absorbed 9 surface is warmed by gaining more heat than losing I Sunlight doesn t penetrate to the bottom of the ocean it is relatively shallow I 9 most heat energy is absorbed O30m of water Permanent thermocline uniformly cold to abrupt change in temperature Seasonal thermocline temporary thermocline above subtropical gyres Pycnocline strong change in density with depth change Adding more heat amp mixing summer it s hard for mixing when it isn t too warm the winds easily get water mixed in to about 70 m Spring 9 summer hotter and hotter less mixing Warm water 9 blown up beach ball cold water 9 Shriveled up beach ball Winds mix cold beach ball easily 1 Ekman Transport A slab of surface ocean water moved by wind forcing I This slab moves at 90 degrees to the direction of the wind forcing Exactly to the right northern hemisphere Exactly to the left southern hemisphere Due to Wind force Friction force Coriolis Force Ekamn Spiral spiraling of thin ocean currents within Ekman layer It is the rate of total water transported in the layer About 50100m thick Oceanography Lecture Notes 2 Geostrophic Currents Currents move along lines of constant pressure I Coriolis force always pushes the uid to the right of its present direction of travel I The point at which currents move with steady speed with Coriolis and pressure gradient forces in prefect opposition is referred to as geostrophic balance and the resulting current is referred to as a geostrophic current I fully developed geostrophic currents move along lines of constant pressure Formation of Subtropical Gyres Q If a mound of water builds up at the surface of the ocean a central high pressure develops under the mound and circular geostrophic currents develop Development of the Subtropical Gyre in Response to Forcing by the Westerly and Trade Wind Belts Westerly and Trade Winds drive the Ekman Layer to the center of the gyre to create a mound of surface water The uid initially moves away from the center of high pressure The push of Coriolis turns the uid until it travels along concentric lines of constant pressure 9 geostrophic balance Currents on western side of all subtropical gyres are called western boundary currents 0 they are very swift and narrow jets that bring warm water from the tropics to high latitudes Currents on eastern side of all subtropical gyres are called eastern boundary currents 0 they are broad and slow and bring cold water from the high latitudes toward the tropics Equatorial Upwelling 0 North East Trade Winds drive Ekman Transport of the surface layer to the north 0 South East Trade Winds drive Ekman Transport of the surface layer to the south 0 Surface water also piles up on the western side of the ocean basin forcing a downward tilt to the thermocline Oceanography Lecture Notes 0 Eastern Equatorial Pacific Cold Tongue due to equatorial upwelling AND the close proximity of the thermocline to surface Ekman Depth 0 Western Equatorial Pacific Warm Pool upwelling still occurs but the thermocline is much deeper than the surface Ekman Depth so upwelling just draws more warm water to the surface with no effective cooling Deep Ocean Abyssal Circulation Atlantic Ocean Temperature at Depth 0 Warm thin surface layer 0 Cold thick deep layer 0 Thermocline separates the warm and cold layers Atlantic Ocean Salinity at Depth 0 High salinity in surface layer in subtropics o Deepocean salinity more uniform and generally matches the surface salinity at higher latitude especially northern high latitudes TemperatureSalinity Signatures of the 3 makor water masses 1 NADW North Atlantic Deep Water 2 AABW Antarctic Bottom Water 3 AAIW Antarctic Intermediate Water Circulation of Deep Water in Global Ocean 0 Cold dense water sinks in the North Atlantic and around Antarctica to form deep water 0 North Pacific salinity is too low to sink even though temperatures are just as cold as the North Atlantic 0 Deep water in the North Atlantic moves south and mergers with Antarctic water in the Southern Ocean as they both swing around Antarctica and up into the Indian and Pacific Ocean basin Conveyor Belt Circulation Schematic of Heat Transport by the Global CBC Oceanography Lecture Notes 0 Heat is gained by the surface ocean at low latitudes and transported via the winddriven surface circulation western boundary currentsto higher latitudes 0 Heat is given up by the ocean to the atmosphere at higher latitudes to warm these regions 0 After giving up heat at high latitudes surface water sinks and enters the thermohaline deep circulation and eventually is returned to the surface to pick up more heat and start the journey all over again Most Heat Transport to High Latitudes is Done by Strong Western Boundary Currents
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