Presentation is loading. Please wait.

Presentation is loading. Please wait.

Oceanic Circulation Current = a moving mass of water OCEAN WATER MOVES IN CURRENTS CAUSED BY WIND AND DIFFERENCE IN WATER DENSITY (beneath surface zone)

Similar presentations


Presentation on theme: "Oceanic Circulation Current = a moving mass of water OCEAN WATER MOVES IN CURRENTS CAUSED BY WIND AND DIFFERENCE IN WATER DENSITY (beneath surface zone)"— Presentation transcript:

1 Oceanic Circulation Current = a moving mass of water OCEAN WATER MOVES IN CURRENTS CAUSED BY WIND AND DIFFERENCE IN WATER DENSITY (beneath surface zone)

2 Oceanic Circulation Surface Currents –horizontally flowing water in the uppermost 400m of the ocean –10% of water in Oceans moves this way –driven by thermal expansion & contraction and WIND friction

3 Oceanic Circulation Surface Currents –horizontally flowing water in the uppermost 400m of the ocean –driven by thermal expansion & contraction and wind friction Thermohaline Circulation –slower, deeper circulation

4 Oceanic Circulation Surface Currents –horizontally flowing water in the uppermost 400m of the ocean (above pycnocline) –driven by thermal expansion & contraction and wind friction Thermohaline Circulation –slower, deeper circulation (below pycnocline) –due to the action of gravity on water masses of different densities

5 Refresher From Ch. 6

6 “Thermocline” (refresher) Tropical and subtropical oceans are permanently layered with warm, less dense surface water separated from cold, dense deep water by a thermocline. –The thermocline is a layer in which water temperature and density change rapidly. Temperate regions have a seasonal thermocline and polar regions have none.

7 Thermocline, Halocline, and Pycnocline

8 Surface Currents Solar heating –water expands at equator and contracts near poles

9 Surface Currents Solar heating –water expands at equator and contracts near poles –water moves toward poles due to gravity

10 Surface Currents Solar heating –water expands at equator and contracts near poles –water moves toward poles due to gravity –water lags behind earth’s rotation & piles up on west sides of oceans

11 Surface Currents Wind –primary force responsible for surface currents Friction drags water along Coriolis effect The “piled up” water will move in direction the wind is blowing it UNTIL the coreolis determines final direction (right of wind direction in N. Hemisphere)

12 Surface Currents Continents prevent continuos flow and deflect water…

13 Surface Currents Continents prevent continuous flow and deflect water… Gyre –the circular flow around the periphery of an ocean basin

14 Fig 8-1, g Trade Winds = Easterlies Winds are Driven by Uneven Solar Heating and the earths spin

15 Fig 8-2, g Surface Winds, Sun’s heat, Coreolis Effect and Gravity = surface current = gyres

16 5 major ocean gyres

17 Six great current circuits North Atlantic Gyre South Atlantic Gyre North Pacific Gyre South Pacific Gyre West Wind drift or Antarctic Circumpolar Current

18 Sea Surface Temperatures Insolation and ocean-surface water temperature vary with the season. Ocean temperature is highest in the tropics (25 o C) and decreases poleward. Figure 5-9a Sea-Surface Temperature in August Using Thermocline Principles

19 Fig 8-3, g Northern Atlantic Gyre

20 Flow within Gyres Western Boundary Currents (ex: Gulf Stream) –narrow, fast, deep currents that carry warm water toward poles

21 Flow within Gyres Western Boundary Currents (ex: Gulf Stream) –narrow, fast, deep currents that carry warm water toward poles –westward intensification - more concentrated due to water piling up due to eastward rotation of earth

22 Fig 8-13b, g

23 Flow within Gyres Eastern Boundary Currents (ex: Canary Current) –broad, slow, shallow currents that carry cold water toward equator

24

25 Flow within Gyres Transverse Currents (ex: North Atlantic Current, North Equatorial current) –currents that flow from east to west or west to east

26 Flow within Gyres Currents affect climate: –North Atlantic current warms England –California current cools San Francisco in the summer

27 Fig 8-8, g

28 Fig. 8-9, g

29 …Gyres…a final word Gyres consist of currents that blend into 1 Flow is continuous Caused by combo of: wind energy, friction, the Coreolis effect and the pressure gradient

30 EKMAN SPIRAL Sum of water direction in (multi) layered Ocean Net motion of water (down to 100 meters) w/ ekman spiral included = ekman transport Each layer in “spiral” acts differently

31 Fig 8-5, g

32 Fig 8-5a, g

33 Fig 8-5b, g

34 Fig 8-5c, g

35

36 fnft

37 Figure fnft

38

39 Convergence & Divergence of Water Currents in the Northern Hemisphere

40

41 Eddy Formation Western boundary of Gulf Stream has distinct Temperature, Speed and Direction Meanders (EDDIES) form here Eddies pinch off and become isolated cells of either warm or cold water

42 Eddy

43 Gulf stream Viewed from Space 1=east coast off Fl. 2=warm eddy 3=cold eddy 4=mix of surface and surrounding waters

44

45 Wind- Induced Vertical Circulation Upwelling –upward movement of water Downwelling –downward movement of water

46 Fig 8-16, g

47 Principal regions of coastal upwelling and down-current areas of increased primary productivity

48 Wind- Induced Vertical Circulation Coastal Upwelling –cold, deeper water upwells to replace the surface water –leads to increased nutrients & productivity and cooler climates

49 Coastal upwelling in the Northern Hemisphere

50 Wind- Induced Vertical Circulation Equatorial Upwelling –westward flowing equatorial currents are deflected poleward –deeper water comes up to replace the surface water

51

52 Fig 8-14a, g

53 Wind- Induced Vertical Circulation Downwelling –water driven toward the coast will be forced down –Brings down dissolved gases

54 Deep Circulation Thermohaline Circulation Driven by density differences water masses do not mix easily but flow above or beneath each other

55 Fnft Classic thermohaline circulation

56 Cross-section of the South Atlantic Ocean

57 5 Common Water Masses Surface water –to 200m Central water –to bottom of thermocline Intermediate Water –to 1500m Deep water –below intermediate but not in contact with bottom Bottom water –in contact with bottom

58 Some Water Masses in the Deep Atlantic Antarctic Bottom Water North Atlantic Deep water Mediterranean Intermediate Water Antarctic Intermediate Water

59 Water layers and deep circulation of Atlantic

60

61 The water sinks to a density-appropriate level and then slowly flows equatorward across the basin. Deep water gradually mixes with other water masses and eventually rises to the surface.

62 Fig. 8-23, p. 190

63 Fig. 8-24, g

64 Thermohaline Circulation Sinking of water masses is offset by slow, gradual rising across warmer temperate and tropical zones

65 Thermohaline Circulation Much slower than surface circulation –hundreds of years (1500?) vs 1 year (North Atlantic Gyre)

66 Remember… From lecture #1 of the course – those 1 st “facts” are extremely important Let’s review…

67 Important Facts 81% of the Southern Hemisphere is covered by Ocean (remember that! It’ll become really important later…); while only 61% of the Northern Hemisphere is covered – WHY? The Oceans are 4X as deep as the Continents are high (average depth = 2.5 miles). The Pacific (Ocean) is so huge that it covers almost ½ of the Earth’s surface; it is also the Earth’s largest collection of water. We have 100X more “aquatic” habitats available on earth than terrestrial habitats (1.4 billion cubic kilometers).

68

69 A synthetic view of our ocean planet © digitalife/ShutterStock, Inc.

70 El Nino (if time permits)

71 ENSO events Surface winds generally move from East to West in Tropical (equator) Pacific but every 3-8 yrs. these pressure areas (typically high to low) change and you get a reversal of wind direction/atmospheric pressure (low to high) = southern oscillation El nino = water flow name (+ southern osc. = ENSO event) Still no one really knows why/how this occurs

72 El Nino “Current of the Christ Child” because Peru had an (unexpected) abundance of fishing 1 X-Mas.

73 Why 2 names? Southern oscillation (ENSO): Weather related name (pressure changes in wind patterns are clearly associated; these drive water change) El Nino: oceanographic name (associated w/ water and temp. patterns that change biological species’ productivity in the Pacific)

74 Fig 8-16a, g A non el nino year Thermocline rises Upwelling of cold water

75 What happens (non El Nino)? Warmest part of the Worlds’ ocean = western Pacific b/c warm water moves East to West and builds up there As a result you get a decreased thermocline (lower in water column, less upwelling)

76 Fig. 8-21, g

77 Fig 8-16d, g

78 What happens (El Nino)? Warm water (that usually moves East to West) shifts to West –> East movement Slows trade winds (southern oscillation) Pressure system shifts Warm water on other side, less where expected As a result you get an increased thermocline (higher in water column, more upwelling)

79 Fig. 8-22a, g

80 Fig 8-16b, g

81 Fig 8-16c, g El nino year Eastward Movement of Water, no upwelling

82 The opposite – La Nina “The Girl” When we “return to normal,” it is fast w/ a huge change and increased currents, increased upwelling (thus increased cold water upwards) result. Trade winds renewed

83 Fig. 8-22b, g

84 Fig 8-21b, g

85 60°N 30°N 30°S 0° 60°W North Pole South Pole 30°E 0°30°W 60°W 0° North Pole South Pole 60°N 30°N 30°S 0° North Pole South Pole Stepped Art Latitude Equator Longitude Prime meridien


Download ppt "Oceanic Circulation Current = a moving mass of water OCEAN WATER MOVES IN CURRENTS CAUSED BY WIND AND DIFFERENCE IN WATER DENSITY (beneath surface zone)"

Similar presentations


Ads by Google