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INTRODUCTION TO OCEANOGRAPHY Instructor: Prof. ANAMARIJA FRANKIĆ Office Number: S-1-061 Office Hours: Posted on office door or by appointment Telephone: 617-287-4415 Email Address: [email protected] Web Page: http://alpha.es.umb.edu/faculty/af/frankic.hml Department Website: http://www.es.umb.edu/ Oceanography is an observationally driven field! What are the independent variables/parameters for the ocean? What do they measure and what is there use? Geology: coastlines, bathymetry, movement of tectonic plates Chemistry: Carbon, Nitrogen, Iron, Oxygen… Physics: T, U, V, S, SSH Biology: Chl-a, Productivity, Zooplankton, Phytoplankton, Fish and Egg counts, etc… How was the ocean observed so far? Lots of historical account of early explorations – (see book). HMS Challenger http://www.amazon.com/gp/reader/0393317552/ref=sib_dp_pt/1 03-3317661-1512644#reader-page International Observational Programs Deep Sea Drilling Project - DSDP 1968, Glomar Challenger Theory of Plate Tectonics and much more… 1985, Joides Resolution Replace G. Challenger International Observational Programs The Joint Global Ocean Flux Study (JGOFS) (launched in 1987 at a planning meeting in Paris) The Operational Goal of JGOFS : Spatial Scale: regional to global Temporal Scale: seasonal to interannual 1) Fluxes of carbon between the atmosphere-surface ocean-ocean interior. 2) Sensitivity to climate changes International Observational Programs The World Ocean Circulation Experiment 1990-1998 http://woce.nodc.noaa.gov/wdiu/ International Programme on Climate Variability and Predictability, 1995-present http://www.clivar.org/index.htm http://www.clivar.org/publications/other_pubs/clivar_transp/index.htm World Climate Research Programme http://www.wmo.ch/web/wcrp/wcrp-home.html US Programs sponsors: http://www.nsf.gov/ e.g. GLOBEC http://www.pml.ac.uk/globec/ http://www.noaa.gov/ http://science.hq.nasa.gov/oceans/ http://www.onr.navy.mil/focus/ocean/habitats/default.htm U.S. Coastal Observing Systems http://www.csc.noaa.gov/coos/ Technologies for ocean observing Remote Sensing/Satellite Imagery: Geostationary Server -http://www.goes.noaa.gov/ Satellite significant events: http://www.osei.noaa.gov/ National Geophysical Data Center: http://www.ngdc.noaa.gov/ngdc.html Floating devices in the ocean: Argo FLoats - http://www.argo.ucsd.edu/ Drifter Programs: http://www.aoml.noaa.gov/phod/graphics/pacifictraj.gif Remotely Operated Vehicles (ROVs) : Amazing discoveries… http://oceanexplorer.noaa.gov/technology/subs/rov /rov.html Automated Underwater Vehicles (AUVs) : How do we define the science of Oceanography? WHAT PEOPLE NEED TO KNOW ABOUT OCEAN SCIENCES • • • • • • • • Ways of knowing – “Reflection on how we know what we believe will help our understanding” Human interactions – “Currently, the human species is significantly affecting earth systems, but has the ability to choose its relationship with the environment” Ecosystems – “The survival and health of individuals and groups of organisms are intimately coupled to their environment” Earth system science – “The Earth as a whole acts as a complex set of interacting systems with emergent properties” Evolution & Biodiversity – “Evolution explains both the unity and diversity of life” Energy flow and transformation – “Energy transformation drive physical, chemical, and biological processes. Total energy is conserved and flows to more diffuse forms” Conservation of mass – “Mass is conserved as it is transferred from one pool to another” Spatio-temporal relationships – “Choosing the appropriate reference frame is the key to understanding one’s environment” Beginnings 1. Earth’s formation 2. Earth’s timeline Earth’s Formation The Universe - formed 10-15 billion years ago Currently referred to as the ‘Big Bang‘ • • current theory is that the universe was formed from something smaller than an atom the atom exploded and everything was blown outward with great heat and speed Earth’s Formation Our Solar System was formed 4.6 billion years ago The Earth is assumed to be the same age • • At this time, Earth had a surface ~ known from radiometric dating of meteorites (uranium and potassium) We think water condensed on the planet 3.9 billion years ago ~ known from radiometric dating of sedimentary rocks that formed by processes requiring water Earth’s Formation Where did oceans come from? Old Theory: a) H2O came from big comets during period of heavy bombardment a) H2O locked up in minerals released from differentiation and heating Earth’s Formation Where did oceans come from? (cont’d) New Theory: a) Oceans still forming and H2O comes from many small cometessimals that continually bombard the Earth a) H2O came from big comets during period of heavy bombardment a) H2O locked up in minerals released from differentiation and heating Earth’s Timeline Mother Earth formed 4.6 billion years ago.. What has happened during this time? Earth’s Timeline (cont’d) Divide by 4.6 billion by 100 million years - makes Earth 46 years old 0-3 yrs 3 yrs 8-11 yrs 22-23 yrs 31 yrs 39th yr 41rst yr no record dated from rocks in Canada, Africa and Greenland 1st living cells - primitive bacteria oxygen production by cells begins atmosphere has enough oxygen to support life first invertebrates-hard shelled fossils primitive fish and corals Earth’s Timeline (cont’d) 41-42 yrs 43 yr 44 yr 45 yr land plants, fish reptiles, dinosaurs, sharks dinosaurs dominate dinosaurs die 1 yr ago plants and flowers proliferate 7 mos. ago 25 days ago 6 days ago 1/2 hour ago 1 minute ago insects, mammals, birds proliferate first humans homosapiens 1st recorded civilization industrial revolution change Earth and relationship with Earth for all time… Earth 1. Coordinates 2. Earth’s Water 3. Earth’s Structure Coordinates Earth • • Highest mountain is Mt. Everest at 8840m above sea level Lowest trench is the Mariana Trench (Pacific) at 11,000m below sea level Think of earth like a basketball - the bumps would be the mountains and the dimples would be the trenches. Earth has a huge mass!!! Coordinates (cont’d) Latitude and Longitude Latitude • Parallel to the equator • Expressed as degrees N or S of the equator where equator = 0 Coordinates (cont’d) Latitude and Longitude (cont’d) Longitude • • • Lines of longitude are meridians Longitudinal lines are at a right angle to latitudinal grid 0° longitude is known as the prime meridian Goes right through Royal Observatory in Greenwich, England Greenwich Mean Time = ‘Universal Time’, when sun is directly above 0 longitude • Expressed as degrees E or W of prime meridian where prime meridian = 0 Earth’s Water How Earth's water reservoirs are connected Connected by 2 processes: evaporation and precipitation See fig 1.18 (Intro 7e) or 2.13 (Fund. 4e) Earth’s water reservoirs: Oceans 97.2% Lakes, rivers and inland seas 0.017% Glaciers 2.14% Atmosphere 0.001% Ground H20 0.61% Biosphere 0.005% WORLDS WATER SOURCES: Earth’s Structure • Layered system (like an onion, concentric regions) ~ differentiation of mineral material Not only Earth’s mineral material, but also: 1. hydrosphere 2. biosphere 3. atmosphere Earth’s Structure (cont’d.) Classification according to chemical composition 4 concentric regions of mineral material: 1. crust 2. mantle 3. outer core - molten 4. inner core - solid Earth’s Structure (cont’d.) Classification according to chemical composition 1. Crust Two types: continental g granite – composed of silicates rich in Na, K & Al ocean g basalt – composed of silicates rich in Ca, Mg & Fe • represents 0.4% of Earth’s mass • extends down to 75 km Earth’s Structure (cont’d.) Classification according to chemical composition 2. Mantle Three parts: uppermost/middle/innermost • Composed of Mg-Fe silicates • represents 68% of Earth’s mass • extends down from base of crust to ~2,900 km Earth’s Structure (cont’d.) Classification according to chemical composition 3. Core Two parts: Outer Inner • Composed of Fe & Ni • Represents 28% of Earth’s mass • Extends down from base of mantle ~ 6400km Earth’s Structure (cont’d.) Classification according to physical properties (factor in temperature and pressure) 4 concentric regions: 1. lithosphere - rigid outer shell (crust & uppermost mantle) • 100 - 150km thick • does not change shape Earth’s Structure (cont’d.) 2. Asthenosphere - soft, flows over geologic time under the weight of the lithosphere (small fraction of middle mantle) • lithosphere ‘floats on top’ • zone where magma formed • 200 – 350km thick • easily deformed, can be pushed down by overlying lithosphere – “plastic” – tar or asphalt Earth’s Structure (cont’d.) Classification according to physical properties 3. Mesosphere - rigid but not as hard as lithosphere • higher temp than asthenosphere, but not molten because of compression pressure • 4950km thick Earth’s Structure (cont’d.) Classification according to physical properties 4. Core - outer is molten, inner is solid Earth’s Structure (cont’d.) Isostacy Principle that dictates how different parts of the lithosphere stand in relation to each other in the vertical direction • Continental crust less dense (granitic) therefore rises higher relative to ocean crust (basaltic) • Continents move up and down depending on weight on top (i.e. from glaciers - ‘isostatic rebound’) ~ Continents pop up after glaciers melt ~ Canada and Scandinavia rising at a rate of 1m/100yrs because the glaciers are receding Earth’s Water (cont’d.) Five oceans: 1. Atlantic – shallowest, greatest number of adjacent seasregional seas: i.e. Gulf of Mexico, Caribbean, Mediterranean, North), has the largest freshwater input (i.e. Amazon, Congo, Mississippi) 2. Pacific – largest, deepest 3. Indian – smallest, muddiest 4. Arctic – covers N. Pole, saltiest 5. Southern Ocean – coldest, most productive (Some) OCEANS’ related FACTS: Our planet is actually the Ocean Planet - 77% of the Earth’s surface is covered by oceans and seas. However, less than 10% has been investigated. Oceans provide more than 70% of oxygen we breathe 80% of world’s plant and animal species live in oceans More than 60% of the current human population (5.8 billion) lives in the coastal zones (~60 km wide), the areas representing only 8% of the Earth surface! ‘Poorest of the poor’ - 1.1 billion people ‘survive’ on less than 1$/day 1 billion people rely on fish as the only daily source of protein Global climate change and the humans’ well being depend on the conditions and health of the oceans; Poverty, hunger, diseases as well as casualties from natural disasters can be alleviated by improving the health of the environment and by sustainable use and management of the coasts and oceans! Plate Tectonics Horizontal Movement of Earth’s Lithosphere Plate Tectonics 1. The Theory of Plate Tectonics 2. Plate Boundaries a) Spreading Centers b) Subduction Zones c) Transform Faults 3. Plate Movement The Theory of Plate Tectonics “Continental Drift” - theory* proposed by Alfred Wagner, a German meteorologist (1915) Explained by: • geologic fit • fossils * Not accepted by scientific community - no mechanism to explain plate movement The Theory of Plate Tectonics (cont’d.) Plate Tectonics - evidence for theory of continental drift Hess, Heezen and Tharp (1960’s) found lithospheres plate boundaries, 3 types: 1) ridges (spreading centers) 2) trenches (subduction zones) 3) transform faults (plates sliding past one another) The Theory of Plate Tectonics (cont’d.) Lithospheric Plates major plates: 1. 2. 3. 4. 5. 6. 7. Pacific – 105 x106 km2 Eurasian - 70 x106 km2 Antarctic - 60 x106 km2 Australian - 45 x106 km2 S. American - 45 x106 km2 African - 80 x106 km2 N. American - 60 x106 km2 From Fundamentals of Oceanography, 5h edition, Duxbury Duxbury, and Sverdup. The McGraw-Hill Companies minor plates: 1. 2. 3. 4. 5. 6. 7. 8. Cocos - 5 x106 km2 Phillipine - 6 x106 km2 Caribbean - 5 x106 km2 Nazca - 15 x106 km2 Arabian - 8 x106 km2 Indian - 10 x106 km2 Scotia - 5 x106 km2 Juan de Fuca - 2 x106 km2 Plate Boundaries a) Spreading centers - ‘rift zones’ (cont’d.) 1) Convection cells form • Density differences – cool vs. hot 2) Convection cells cause frictional drag on lithosphere 3) Lithosphere stretches due to convective movement 4) Lithospheric crust weakens Plate Boundaries (cont’d.) a) Spreading centers - ‘rift zones’ (cont’d.) 5) Faulting – break in overlying lithosphere 6) Magma flows upward 7) New lithospheric crust formed Plate Boundaries (cont’d.) a) Spreading centers - ‘rift zones’ (cont’d.) • • Plates split apart -‘divergent plate’ boundary New crust formed - ‘constructive’ plate boundary Evolution of a mid-ocean ridge system 1. Upwarping 2. Rift valley 3. Linear sea 4. Mid-ocean ridge system Ex. 1 - oceans: mid Atlantic Ridge east Pacific Rise Ex. 2 - continents: E. Africa Rift Valley Baikal Rift Valley Plate Boundaries (cont’d.) b) Subduction zones • • • Lithospheric Plates collide - ‘convergent’ plate boundary Crust destroyed - ‘destructive’ plate boundary Forms trenches and mountains Plate Boundaries (cont’d.) b) Subduction zones (cont’d.) 3 types of subduction zones: 1. Ocean crust into continental crust – form trenches and mountain ranges Ex. a): Juan de Fuca plate into the N. American plate - forms Cascade Mtn. Range Ex. b): Nazca plate into the S. American plate - forms Peru-Chile Trench and the Andes Mtn. Range Plate Boundaries (cont’d.) b) Subduction zones (cont’d.) 2. Ocean crust into ocean crust – forms trenches and island arcs Ex. A): Philippine plate into the Pacific plate – formed the Marianna Trench and the Marianna Island Arc system Ex. B): N. American plate into the Caribbean plate and then the N. American plate into the S. American plate – formed the Isthmus of Panama Plate Boundaries (cont’d.) b) Subduction zones (cont’d.) 3. Continental crust into continental crust – form mountain ranges Ex. A): Indian plate into the Eurasian plate – formed the Himalayas Ex. B): Eurasian plate into the African plate - closing up of the Mediterranean sea Plate Boundaries (cont’d.) c) Transform faults • • Plates slide past one another Lithospheric crust neither created nor destroyed - ‘conservative’ plate boundary Ex. A) Pacific plate sliding past N. American plate – forms the San Andreas Fault Plate Movement • • New crust is created at spreading centers at a rate of approximately 1-10cm per year Old crust is destroyed at the same rate at subduction zones How do we know these rates? (Rate=distance/time) Plate Movement • (cont’d.) Magnetic anomalies in ocean crust...look at spreading centers paleomagnetism every so often Earth’s magnetic field flips (every 300K-500K years) magnetic signal recorded in crust at spreading center as it’s formed, forms bands of crust with either a weak or strong magnetic signal determine rate of plate movement by distance of band from spreading center divided by age of rock in band (r=d/t) Plate Movement (cont’d.) Hot spots Emperor Sea Mount chain islands or sea mountains formed over hotspots (fixed area where magma comes up) lithosphere moves over hotspot and end up have volcanic mountain over hotspot as well as a series of mountains in ‘front’ of hotspot determine rate of plate movement by distance of mountain from hotspot divided by age of rock in mountain (r=d/t) Learning Objectives Understand the processes that are continuously changing Earth’s surface as lithospheric plates move relative to one another. Identify the role of oceanic ridges, transform faults and deep-sea trenches in defining the edges of lithospheric plates. Understand the importance of asthenospheric thermal convection in plate tectonics and the resulting compression or tensional forces at the plate boundaries. Explain the distribution of magnetic anomaly stripes, seismicity, and volcanism in terms of the concept of global plate tectonics. Calculate spreading rates of ocean basins. Age of Ocean Crust http://www.ngdc.noaa.gov/mgg/geology/geology.html Creating new ocean crust More evidence of plate moving.. Oceanic crust moves away from MOR (Mid Oceanic Ridge) and cools and subsides 3-3 Destructive margins Subduction zones Constructive margins Midocean ridges Driving Mechanisms for Plate Motions Type of boundary between plates: Constructive margins Mid ocean ridges Destructive margins Subduction zones Conservative margins Transform faults Conservative margins Transform faults Conservative margins Transform faults The San Andreas fault in southern California Hot Spots ? 3-3 • Mantle plumes originate deep within the asthenosphere as molten rock which rises and melts through the lithospheric plate forming a large volcanic mass at a “hot spot”. Mantle Plume Coral Reefs Air view Spreading rates Geological Periods Geological Periods Precambrian Cambrian Ordovician Silurian Devonian Early Carboniferous Late Carboniferous Permian Triassic Jurassic Late Jurassic Cretaceous K/T extinction Eocene Miocene Modern Future World Future Future 4.6 B 514 Ma 458 Ma 425 Ma 390 Ma 356 Ma 306 Ma 255 Ma 237 Ma 195 Ma 152 Ma 94 Ma 66 Ma 50.2 Ma 14 Ma 570 Ma solidification Gondwana, hard shell anim. separation, coldest Laurentia collides with Baltica pre-Pangea, equatorial forests western Pangea is complete deserts, reptiles, major ext. Life begins to rediversify,Pangea Dinosaurs, Pangea starts to break Pangea rifts apart, Atlantic New oceans, India end of dinosaurs India collides with Asia Modern look +50 Ma N. Atlantic widens, Med. vanish +100 Ma new subduction +250 Ma new Pangea Precambrian break-up of the supercontinent, Rodinia, which formed 1100 million years ago. The Late Precambrian was an "Ice House" World, much like the present-day. Source: www.scotese.com Cambrian Animals with hard-shells appeared in great numbers for the first time during the Cambrian. The continents were flooded by shallow seas. The supercontinent of Gondwana had just formed and was located near the South Pole. Ordovician During the Ordovician ancient oceans separated the barren continents of Laurentia, Baltica, Siberia and Gondwana. The end of the Ordovician was one of the coldest times in Earth history. Ice covered much of the southern region of Gondwana. Silurian Laurentia collides with Baltica closing the northen branch of the Iapetus Ocean and forming the "Old Red Sandstone" continent. Coral reefs expand and land plants begin to colonize the barren continents. Devonian By the Devonian the early Paleozoic oceans were closing, forming a "prePangea". Freshwater fish were able to migrate from the southern hemisphere continents to North America and Europe. Forests grew for the first time in the equatorial regions of Artic Canada. Early Carboniferous During the Early Carboniferous the Paleozoic oceans between Euramerica and Gondwana began to close, forming the Appalachian and Variscan mountains. An ice cap grew at the South Pole as fourlegged vertebrates evolved in the coal swamps near the Equator. Late Carboniferous By the Late Carboniferous the continents that make up modern North America and Europe had collided with the southern continents of Gondwana to form the western half of Pangea. Ice covered much of the southern hemisphere and vast coal swamps formed along the equator. Permian Vast deserts covered western Pangea during the Permian as reptiles spread across the face of the supercontinent. Triassic The supercontinent of Pangea, mostly assembled by the Triassic, allowed land animals to migrate from the South Pole to the North Pole; and warm-water faunas spread across Tethys. The first mammals and dinosaurs appeared; Jurassic By the Early Jurassic, southcentral Asia had assembled. A wide Tethys ocean separated the northern continents from Gondwana. Subduction zone Rocky Mountains Formation of the Rocky Mountains http://wrgis.wr.usgs.gov/docs/parks/province/rockymtn.html Late Jurassic In the Late Jurassic the Central Atlantic Ocean was a narrow ocean separating Africa from eastern North America. Cretaceous During the Cretaceous the South Atlantic Ocean opened. India separated from Madagascar and raced northward on a collision course with Eurasia. Notice that North America was connected to Europe, and that Australia was still joined to Antarctica. K/T extinction The bull's eye marks the location of impact site of a 10 mile wide comet caused global climate changes that killed the dinosaurs and many other forms of life. By the Late Cretaceous the oceans had widened, and India approached the southern margin of Asia. Eocene 50 - 55 million years ago India began to collide with Asia forming the Tibetan plateau and Himalayas (destroying the last of Tethys ocean). Australia, which was attached to Antarctica, began to move rapidly northward. Collision of continental crust 3-2 • Whereas oceanic ridges indicate tension, continental mountains indicate compressional forces are squeezing the land together. Sedimentary Rocks Squeezed by Compression Miocene 20 million years ago, Antarctica was covered by ice and the northern continents were cooling rapidly. The world has taken on a "modern" look, but notice that Florida and parts of Asia were flooded by the sea. Arabia moved away from Africa forming Gulf of Aden and Red Sea; Last Ice Age When the Earth is in its "Ice House" climate mode, there is ice at the poles. The polar ice sheet expands and contacts because of variations in the Earth's orbit (Milankovitch cycles). The last expansion of the polar ice sheets took place about 18,000 years ago. Modern World If we continue present-day plate motions the Atlantic will widen, Africa will collide with Europe closing the Mediterranean, Australia will collide with S.E. Asia, and California will slide northward up the coast to Alaska. Future +100 Earth is ~ 4.6 bill years old – suggested cyclic of 500 mill year pattern of assembling and disassembling the land masses; Future +250 The Wilson Cycle The Wilson Cycle