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The Nature of Oceans

The Nature of Oceans. Chapter 16. Global Ocean?. Separate but whole Divisions resulting from Continents Island arcs Straits Political boundaries. Salinity. Total dissolved salts (all dissolved ions). Oceans as buffers. Dissolved gasses CO2 and O2

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The Nature of Oceans

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  1. The Nature of Oceans Chapter 16

  2. Global Ocean? • Separate but whole • Divisions resulting from • Continents • Island arcs • Straits • Political boundaries

  3. Salinity • Total dissolved salts (all dissolved ions)

  4. Oceans as buffers • Dissolved gasses • CO2 and O2 • Atmospheric gasses and dissolved ocean gas concentrations

  5. Salinity and Latitude (in ppt)

  6. Other salinity factors • Coastlines • Fresh water inflow—rivers

  7. “Ogres…I mean, Oceans are like onions…” • Thermal layering—think oil/water Epipelagic zone—surface to 200-450 m Constant temp—stirring by wind/waves Thermocline—layer of rapidly decreasing temperature Here be strange critters—FRIGG’N COLD Polar seas—exception--no layering

  8. Ocean Currents • Surface currents in upper 400 m • Involve 10% of water in oceans • Driven by wind horizontally • Deep-sea currents caused by changes in density below 400 m • Vertical and horizontal changes • Driven by density

  9. Surface Currents • Benjamin Franklin and mail • Driving force • Friction between wind and water—circular ocean currents--gyres

  10. Notice Something Odd? • Currents do not always flow in direction of prevailing wind—why? • Coriolis Effect • All free standing objects in N. hemisphere are deflected to the right--opposite in S. hemisphere

  11. Effect on Oceans WIND Wind effect on Water with Depth Coriolis Effect and Water Depth (collectively named Ekman Transport)

  12. Surface Currents • Can also profoundly affect climate

  13. Deep-sea Currents • Caused by cooling temperature and rising salinity • Thermohaline circulation)

  14. Something cold with salt? • Wind near poles = cold • Wind causes evaporation • Water salinity increases • Water temp decreases • Density of water at poles = high • Water sinks at poles and rises near the equator

  15. Upwelling Elkman transport Nitrogen, phosphates and silica— Support plankton populations—base of Food chain Fishing industry

  16. Tides • Gravitational pull of moon and sun causes Earth’s oceans to swell at given times • Two tides per day—12 hours apart • Place directly beneath moon—strongest pull • Only part of story

  17. What Causes Tides? • Second tide—when moon on opposite side of Earth--Why? Actual E/M system Common conception of E/M system

  18. Tide Times • Tides do not occur at same time everyday • Tot offset by 53 minutes/day

  19. Types of tides Spring Tide ~ Seven Days Between… Neap Tide

  20. Who Cares? • Tides (whether high or low) can affect wave height/erosion • Especially in narrow inlets • Its an additive effect • Think about: • Waves • Storm surge

  21. Narrow inlets • Bay of Fundy, Canada • Shape of bay creates dramatic changes between normal and high tides LT HT

  22. Storm Surge • A low pressure effect • Stronger waves, more erosion • Decrease beach slope

  23. Coastlines

  24. Coasting along… • Coasts • Complex Interaction between • Atmosphere, hydrosphere, geosphere, biosphere

  25. Ocean Waves Waves don’t affect us past ½ the wavelength

  26. Nothing Like a Day at the Beach… • Beach • Accumulations of sand and gravel • Sediment for beaches • Sea cliff erosion • river transport

  27. Sea Cliff Erosion • Storms • Power of waves • Sea cliffs and spaceships—hydraulic fracture • Waves carry sand, gravel • Liquid sandpaper • Can create sea caves • Salt cracking

  28. Sediments Supplied by Rivers

  29. Constructive Waves SummerLeaves sandy beach Spilling Breaker Powerful Swash (pushes material up beach) Weak Backwash (little erosion)

  30. Destructive Waves WinterLeaves gravelly beach Crashing breaker AHHHHHHHHHHH! Weak swash (little material brought in) Powerful Backwash (lots of erosion)

  31. Wave Refraction

  32. 1 million m3/yr moved S just at Santa Monica, CA Longshore Current, Drift

  33. In the Old Days • Temporary shelters • Ramshackle cabins • By the 1700s: • Built behind barrier islands • Built houses on stilts • By the 1850s: • Resorts, bridges, summer homes, retirement homes

  34. Riprap and “Claptrap” • Changing the natural order • Boulders, seawalls • Requests to local government • An increase in sedimentation—”olde days” • wide deforestation • railroads • population increase • land cultivation • overgrazing • Beach enlargement

  35. Everything Has a Price: Seawalls • Act just like sea cliffs • Small sand is removed • Bigger waves approach closer to shore • With no beach, waves can undermine barrier

  36. A Decline In Beaches • Modern changes… • Dams as sediment traps • Mining sand from river bottoms—building material • Better land use practices • Beach erosion accelerated • Commonly 5-10 m/yr, up to 200 m/yr in Nile • Need to stop erosion…

  37. A “Kick” in the Groin • Recall longshore drift • Sand is carried along the beach by waves at angle to beach

  38. Good and Bad Results • Bad • Manasquan, NJ Argh, my beaches • Good

  39. Beach Replenishment • In areas already “screwed up” can’t we just dump more sand? • Dump truck = 10 m3 of sand • If person’s lot is 30 m wide with 65 m of beach (~2,000 m2) = 0.5 cm thick sand • 200 truck loads to raise the beach 1 m at a cost of $60,000 / home • Need to also dump sand offshore • Where do we get all this sand? Peter or Paul? • Inland finer-grained sand

  40. What else can we do? • Offshore dredging below wave base • Cost • Larger storms • Nourishment • Dumping sand offshore • Longshore drift • Inlets and dredging

  41. Barrier Islands • Offshore bars or barrier islands • Parallel to shoreline, migrate with waves • Common on East and Gulf coasts • 0.4 – 4 km wide, usually < 3 m asl • Lagoons act as quiet waterways for boats

  42. Island Migration • Migrate with gradual rise of sea level • Sea level rises about 30 cm (1 ft) a century • Migration inland by 100-150 m or more • Immediate danger during large “storms”

  43. Galveston, TX—Hurricane Ike

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