Oceanography

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Oceanography

  1. 1. Earth Science “ The Oceans”
  2. 2. The Oceans <ul><li>Since prehistoric times, people have used Earth’s oceans for travel, recreation, and to obtain food. </li></ul><ul><li>In the late 1800’s the British Challenger became the 1st research ship to explore under the ocean’s surface. </li></ul>
  3. 3. The Oceans <ul><li>Oceanography - The study of the Earth’s oceans. </li></ul><ul><li>The discipline of oceanography is usually considered to have started with the Challenger . </li></ul>
  4. 4. Modern Oceanography <ul><li>The Challenger investigated: </li></ul><ul><ul><li>ocean currents </li></ul></ul><ul><ul><li>water temperature and chemical composition </li></ul></ul><ul><ul><li>seafloor sediments and topography </li></ul></ul><ul><ul><li>marine life </li></ul></ul>
  5. 5. Modern Oceanography <ul><li>1920’s German research ship Meteor used sonar to map the seafloor features </li></ul><ul><li>Sonar stands for so und na vigation and r anging. </li></ul><ul><ul><li>Uses the return time of an echo, multiplied by 1500 m/s, divided by 2 </li></ul></ul><ul><ul><li>The answer gives you the distance to the ocean floor in meters </li></ul></ul>
  6. 6. Advanced Technology <ul><li>Advanced technology has greatly expanded scientific knowledge of the oceans. </li></ul><ul><li>Satellites Topex/Poseidon monitor the ocean’s surface temperatures, currents, and wave conditions. </li></ul>
  7. 7. Advanced Technology <ul><li>Side-scan sonar - a technique that directs sound waves to the seafloor at an angle, so that the sides of underwater hills can be mapped. </li></ul>
  8. 8. Origins of the Oceans <ul><li>Has Earth always had oceans? </li></ul><ul><li>Several geological clues indicate that we have had oceans since the beginning of geological history. </li></ul><ul><li>Earth is 4.6 billion years old. </li></ul>
  9. 9. Origins of the Oceans <ul><li>Scientists have found rocks made of sediments deposited in water that are nearly 4.6 billion years old. </li></ul><ul><li>Radioactive studies and lava flows offer evidence that there has been abundant water throughout Earth’s geologic history. </li></ul>
  10. 10. Where did the water come from? <ul><li>Scientists hypothesize that water could have come from 2 sources: </li></ul><ul><ul><li>Comets that collide with Earth release water on impact, over time these impacts filled the oceans </li></ul></ul><ul><ul><li>Volcanism </li></ul></ul>
  11. 11. Volcanism <ul><li>During volcanic eruptions, significant quantities of gases are emitted. </li></ul><ul><li>These gases consist mostly of water vapor and carbon dioxide. </li></ul><ul><li>At the beginning of the Earth, a massive episode of violent volcanism took place </li></ul>
  12. 12. Volcanism <ul><li>This took place over hundreds of million years </li></ul><ul><li>This episode created massive amounts of water vapor and carbon dioxide thus creating our oceans and our atmosphere </li></ul>
  13. 13. Volcanism <ul><li>Volcanoes still produce water that adds to our hydrosphere but, </li></ul><ul><li>Ultraviolet radiation from the Sun destroys water molecules so these two processes balance each other. </li></ul><ul><li>What would happen over geological time if they didn’t? </li></ul>
  14. 14. Distribution of Earth’s Water <ul><li>97% salt water </li></ul><ul><li>3% freshwater </li></ul><ul><li>Percentage of ice has varied on Earth from near 0 to 10 percent of the hydrosphere </li></ul><ul><li>Sea level - the level of the ocean’s surface. </li></ul>
  15. 15. Distribution of Earth’s Water <ul><li>Sea level has risen and fallen by hundreds of meters in response to melting ice and expanding glaciers. </li></ul><ul><li>Tectonic forces that lift and lower the seafloor also account for variations in sea level. </li></ul><ul><li>Global sea level rises at 1 to 2 mm per year because of melting glaciers. </li></ul>
  16. 16. The Blue Planet <ul><li>Approximately 71% of Earth’s surface is covered by oceans. </li></ul><ul><li>Average depth 3800 m. </li></ul><ul><li>Most land is in the northern hemisphere where oceans account for 61% </li></ul><ul><li>Southern hemisphere has 81% oceans </li></ul><ul><li>All oceans are connected into one vast body of water. </li></ul>
  17. 17. Major Oceans <ul><li>Three major oceans: Pacific, Atlantic, and Indian </li></ul><ul><li>Pacific is largest - roughly half of Earth’s seawater </li></ul><ul><li>Atlantic - 2nd largest </li></ul><ul><li>Indian - 3rd largest </li></ul>
  18. 18. Sea Ice <ul><li>The Arctic and Antarctic Oceans are covered by vast expanses of sea ice </li></ul><ul><li>In the summer ice breaks up </li></ul><ul><li>When sea-ice crystals form, it starts as slush on the surface </li></ul><ul><li>Eventually solidifying into pancake ice </li></ul><ul><li>Eventually these pieces thicken and freeze into continuous ice cover called pack ice. </li></ul>
  19. 19. Sea Ice <ul><li>In the coldest part of the Arctic and Antarctic oceans there is no summer thaw and ice is generally several meters thick and can be more than 1000 km wide. </li></ul>
  20. 20. Earth Science “ Seawater”
  21. 21. Seawater <ul><li>96.5% water </li></ul><ul><li>3.5% salts </li></ul><ul><li>Most abundant salt in the sea is sodium chloride (NaCl) </li></ul><ul><li>Most elements on Earth are found in seawater </li></ul><ul><li>Because these substances are dissolved they are in ion form </li></ul>
  22. 22. Chemical Properties of Seawater <ul><li>Salinity - measure of the amount of dissolved salts in seawater </li></ul><ul><li>Oceanographers express salinity as grams of salt per kilogram of water, (ppt) </li></ul><ul><li>Total salt content 35ppt or 35% </li></ul><ul><li>Nutrients and dissolved gases in seawater greatly affect life in the oceans </li></ul>
  23. 23. Variations in Salinity <ul><li>Although average salinity is 35 ppt, actual salinities vary from place to place </li></ul><ul><li>Subtropical regions have higher salinity (37 ppt). Why? </li></ul><ul><li>Equatorial where precipitation is abundant, salinities are lower. </li></ul><ul><li>Polar regions 32-33 ppt due to melting sea ice </li></ul><ul><li>Lowest salinity is found at river outlets </li></ul>
  24. 24. Sources of Sea Salt <ul><li>Geological evidence indicates that the salinity of ancient seas was not much different from that of today’s oceans. </li></ul><ul><ul><li>Proportion of sea salts - magnesium in calcium-carbonate shells </li></ul></ul><ul><ul><li>Sources of sea salts - weathering of rocks and minerals that wash into the rivers and carried to the ocean and seas. </li></ul></ul>
  25. 25. Removal of Sea Salts <ul><li>Salt ions are constantly being added to seawater </li></ul><ul><li>Salinity does not increase due to removal of salts by: </li></ul><ul><ul><li>Precipitate </li></ul></ul><ul><ul><li>Wind carries salt from waves </li></ul></ul><ul><ul><li>Marine organisms also remove ions </li></ul></ul>
  26. 26. Removal of Sea Salts <ul><li>As organisms die their solid parts accumulate on the seafloor. </li></ul><ul><li>All processes remove immense quantities of salt ions from the ocean </li></ul><ul><li>The existing salinity of seawater represents a balance between the processes that remove and add salts </li></ul>
  27. 27. Physical Properties of Seawater <ul><li>The presence of various salts causes the physical properties of seawater to be different than freshwater. </li></ul><ul><ul><li>Seawater is denser than freshwater </li></ul></ul><ul><ul><li>Temperature affects density, colder water is more dense </li></ul></ul><ul><ul><li>Range of seawater is 1.02 to 1.03 grams per centimeter cubed </li></ul></ul>
  28. 28. Physical Properties of Seawater <ul><li>These variations are small but vary significant. </li></ul><ul><li>They affect many oceanic processes </li></ul><ul><li>Difference in salinity also changes causes freezing point to lower compared with freshwater </li></ul><ul><li>Freshwater is 0°C, seawater is -2°C </li></ul>
  29. 29. Absorption of Light <ul><li>Intensity of light decreases with depth </li></ul><ul><li>Water absorbs light, so oceans are dark </li></ul><ul><li>Red light penetrates less than blue light </li></ul><ul><li>Light sufficient for photosynthesis only exists in the top 100 m of the ocean </li></ul>
  30. 30. Ocean Layering <ul><li>Temperatures range from -2°C to 30°C </li></ul><ul><li>Average temp. 15°C </li></ul><ul><li>Temperature dramatically decreases with depth </li></ul><ul><li>Temperature profile - plots changing water temp with depth </li></ul><ul><li>Dark waters below 1km have fairly uniform temp of less than 4ºC </li></ul>
  31. 31. Ocean Layering <ul><li>Three layers: </li></ul><ul><ul><li>Surface layers - first 100 m </li></ul></ul><ul><ul><li>Thermocline - 100 - 1000 m, characterized by rapidly decreasing temp with depth </li></ul></ul><ul><ul><li>Bottom layer - 1000m and below, cold and dark temps near freezing </li></ul></ul><ul><ul><li>Cold water sinks so the bottom because it is more dense </li></ul></ul>
  32. 32. Water Masses <ul><li>High salinity and and cold temps cause seawater to become more dense </li></ul><ul><li>Seawater freezes during arctic and Antarctic winter </li></ul><ul><li>Salt ions aren’t incorporated into the growing ice crystals and accumulate beneath the ice. </li></ul><ul><li>Cold water beneath the ice becomes saltier and denser so it sinks </li></ul>
  33. 33. <ul><li>This salty water migrates toward the equator as a cold, deep water mass along the ocean floor. </li></ul><ul><li>Three water masses account for most of the deep water in the Atlantic ocean. </li></ul><ul><ul><li>Antarctic Bottom Water </li></ul></ul><ul><ul><li>North Atlantic Deep Water </li></ul></ul><ul><ul><li>Antarctic Intermediate Water </li></ul></ul>
  34. 34. <ul><li>While the Atlantic contains all three major deep water masses </li></ul><ul><li>Indian and Pacific contain only two deep water masses </li></ul>
  35. 35. Earth Science “ Ocean Movements”
  36. 36. Ocean Movements <ul><li>Wave - a rhythmic movement that carries energy through space or matter - in this case, ocean water </li></ul><ul><li>Generated by wind over the water’s surface. </li></ul><ul><li>Energy moves forward </li></ul><ul><li>Water itself moves in circles until the energy passes, but it does not move forward. </li></ul>
  37. 37. Wave Characteristics <ul><li>Highest point of wave is the crest. </li></ul><ul><li>Lowest point of wave is the trough. </li></ul><ul><li>Vertical distance between crest and trough is the wave height </li></ul><ul><li>Crest to crest is the wavelength </li></ul>
  38. 38. Wave Characteristics <ul><li>The wavelength determines the depth to which the wave disturbs the water. </li></ul><ul><li>The depth, called the wave base, is equal to half the wavelength </li></ul><ul><li>Wavelength also determines speed; wave speed increases with wavelength </li></ul>
  39. 39. Wave Height <ul><li>Wave height depends on three things: </li></ul><ul><ul><li>Wind speed </li></ul></ul><ul><ul><li>Wind duration </li></ul></ul><ul><ul><li>Fetch - refers to the expanse of water that the wind blows across </li></ul></ul><ul><ul><li>Largest wave ever recorded was more than 30 meters - in the North Pacific </li></ul></ul>
  40. 40. Breaking Waves <ul><li>Waves lose energy as they approach the shore due to friction with the ocean bottom </li></ul><ul><li>Waves slow down </li></ul><ul><li>Crest-to-crest wavelengths decrease </li></ul><ul><li>Incoming waves become higher, steeper, and unstable collapsing their crest </li></ul>
  41. 41. <ul><li>Breakers - Collapsing waves </li></ul><ul><li>Major role in shaping shorelines </li></ul>
  42. 42. Tides <ul><li>Tides are the periodic rise and fall of sea level; cycles every 24h and 50 min </li></ul><ul><li>Difference in high and low tide varies from place to place </li></ul><ul><ul><li>Gulf of Mexico tidal range is less than 1 m </li></ul></ul><ul><ul><li>New England can be as high as 6 m </li></ul></ul><ul><ul><li>Highest range 15 m is in the Bay of Fundy off of Nova Scotia </li></ul></ul>
  43. 43. Problem - Solving Lab <ul><li>Analyze a tidal record </li></ul><ul><li>Page 401 </li></ul><ul><li>Individually create your graph </li></ul><ul><li>Complete “Thinking Critically” </li></ul>
  44. 44. Causes of Tides <ul><li>Basic cause of tides are the gravitational attraction among the Earth, the Moon, and the Sun </li></ul><ul><li>Gravitational attraction decreases with distance </li></ul><ul><li>Earth and Moon experience differing gravitational forces </li></ul><ul><li>Unbalanced forces generate tidal bulges on opposite sides of the Earth. </li></ul>
  45. 45. <ul><li>The gravitational effect on Earth’s oceans is similar to coffee in a cup going around a corner </li></ul><ul><li>Spring tides occur when the Moon is either full or new; when Sun, Moon and Earth are aligned; large tidal ranges </li></ul><ul><li>Small tidal ranges caused by neap tides, moon is either first or third quarter </li></ul><ul><li>Spring and neap tides alternate every 2 weeks; spring tides 3x higher than neap. </li></ul>
  46. 46. Ocean Currents <ul><li>Density current - caused by differences in the temperature and salinity of ocean water, which in turn affect density </li></ul><ul><li>Density currents move slowly in deep ocean waters </li></ul><ul><li>Surface currents - affect mainly the upper few hundred meters of the ocean </li></ul><ul><li>Surface currents move fast, 100km/day </li></ul>
  47. 47. Gyres <ul><li>Continents deflect ocean currents to the north and south so that closed circular current systems, called gyres, develop. </li></ul><ul><li>Five major gyres: </li></ul><ul><ul><li>North Pacific </li></ul></ul><ul><ul><li>South Pacific </li></ul></ul><ul><ul><li>North Atlantic </li></ul></ul><ul><ul><li>South Atlantic </li></ul></ul><ul><ul><li>Indian Ocean </li></ul></ul>
  48. 48. <ul><li>Gyres in the northern hemisphere circulate clockwise, southern hemisphere counter-clockwise. </li></ul>
  49. 49. Upwelling <ul><li>The upward motion of ocean water is upwelling. </li></ul><ul><li>Originate from the bottom of the ocean, so they are cold. </li></ul><ul><li>Rich in nutrients </li></ul>

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