ocean currents water masses

1. It all begins with the sun……

2. Resultant flow which gives rise to vertical motion in and below the Ekman layer -Upwelling -Downwelling

3. Ekman pumping

4. © 2011 Pearson Education, Inc. Geostrophic Flow Ekman transport piles up water within subtropical gyres. Surface water flows downhill and to the right. Geostrophic flow – balance of Coriolis Effect and gravitational forces Ideal geostrophic flow Friction generates actual geostrophic flow

5. Geostrophic flow and western intensification Geostrophic flow causes a hill to form in subtropical gyres The center of the gyre is shifted to the west because of Earth’s rotation Western boundary currents are intensified Figure 7-7

6. 30o 30o 60o 60o 90o 90o 0o Forces 1. Solar Heating (temp, density) 2. Winds 3. Coriolis Surface Currents

7. Factors Influencing Nature and Movement of Ocean Currents: 1. Factors related to the earth’s rotation: Gravitational force and force of deflection. 2. Factors originating within the sea: Atmospheric pressure, winds, precipitation, evaporation and insolation. 3. Factors originating within the sea: Pressure gradient, temperature difference, salinity, density and melting of ice. 4. Factors modifying the ocean currents: Direction and shape of the coast, seasonal variations and bottom topography.

8. Surface and Deep-Sea Current Interactions “Global Ocean Conveyor Belt”

9. Global ocean circulation that is driven by differences in the density of the sea water which is controlled by temperature and salinity.

10. White sections represent warm surface currents. Purple sections represent deep cold currents

11. Formation of Antarctic Bottom Water (AABW)

12. Weddel Sea (Flichner ice shelf) and Ross Sea (Ross Ice Shelf) Weddel Sea – partially isolated embayment -greatest contributor There is less entrainment than with NADW so AABW is densest water in ocean.

13. Cold wind blows ice offshore (polyna) allowing ice to continually form. During freezing, salts are left behind (brine formation) resulting in water that is more saline. Surface waters are chilled to temperature of ~ -1.9°C, salinity is 34.6 psu.  This cold dense water collects on the Antarctic shelf and sinks to the bottom of the adjacent deep-ocean basin. In the process of mixing, mixes with other waters and is warmed. Resulting water is ~ -0.4-1°C and 34.6 to 34.8 psu.

14. Formation of North Atlantic Bottom Water (NABW)

15. © 2011 Pearson Education, Inc. Antarctic CirculationAntarctic Circumpolar Current Also called West Wind Drift and Penguin Gyre Only current to completely encircle Earth Moves more water than any other current

16. © 2011 Pearson Education, Inc. Antarctic CirculationAntarctic Circumpolar Current Also called West Wind Drift and Penguin Gyre Only current to completely encircle Earth Moves more water than any other current

17. © 2011 Pearson Education, Inc. Antarctic Circulation Antarctic Convergence Cold, dense Antarctic waters converge with warmer, less dense sub-Antarctic waters Northernmost boundary of Antarctic Ocean East Wind Drift Polar Easterlies Creates surface divergence with opposite flowing Antarctic Circumpolar Current Antarctic Divergence Abundant marine life

18. © 2011 Pearson Education, Inc. Atlantic Ocean Circulation Equatorial Atlantic circulation At the Equator, Atlantic extends from 10° E to 45 ° W – 6000 km Main currents North equatorial counter current (NECC) flowing to east from 8° -3° N South Equatorial current (SEC) flowing west from 3°N to 8°S Equatorial undercurrent (EUC) flowing east at equator about 50-300m Brazil coastal current

19. © 2011 Pearson Education, Inc. Atlantic Ocean CirculationNorth Atlantic Subtropical Gyre Rotates clockwise – Coriolis effect Separated from South Atlantic gyre by Atlantic equatorial counter current

20. © 2011 Pearson Education, Inc. Atlantic Ocean CirculationNorth Atlantic Subtropical Gyre North Equatorial Current Gulf Stream North Atlantic Current Canary Current South Equatorial Current Atlantic Equatorial Counter Current

22. South Atlantic – upper water gyre – extends from surface to a depth of 200 m near the equator to 800m southern limits of gyre at Subtropical convergence Wind stress of South East trade winds between equator and 10-15° S – main driving force Acts on sea and forms South Equatorial current (SEC) – greatest strength just below equator – flows west towards American side of South Atlantic Spills by topographic interference by eastern prominence of Brazil. Part of SEC moves off northeastern coast of South America towards Caribbean and North Atlantic, rest is turns southwards as brazil current

23. Brazil current coming from the tropics is warm and saline, turns east and continues across Atlantic as Antarctic Circumpolar current (WWD) and moves eastward. The Brazil current is much smaller than the Northern Hemisphere counterpart i.e. the Gulf stream due to the splitting of SEC WWD than turns north up on African side as the Benguela Current which flows equatorward along Africa’s western coast Benguela current is slow drifting cold current because of the contribution of Subantartic water and of upwelling along the African coast Falkland current

24. Falkland current – is outside the South Atlantic gyre, but is a significant north bound flow of cold water. Current flows from Drake passage and moves along the western margin of South Atlantic up the coast of South America. Falkland current impart cold current that moves along the coast of Argentina as far as north as 30°S thus separating Brazil current from coast at this point. South Atlantic circulation is bounded on south by Subtropical Convergence.

25. © 2011 Pearson Education, Inc. Gulf Stream  Best studied of all ocean currents  Meanders and loops  Merges with Sargasso Sea  Circulates around center of North Atlantic Gyre  Unique biology – Sargassum

26. © 2011 Pearson Education, Inc. Gulf Stream Meanders or loops may cause loss of water volume and generate:  Warm-core rings – warmer Sargasso Sea water trapped in loop surrounded by cool water  Cold-core rings – cold water trapped in loop surrounded by warmer water  Unique biological populations

28. © 2011 Pearson Education, Inc. Climate Effects of North Atlantic Currents North-moving currents – warm Gulf Stream warms East coast of United States and northern Europe North Atlantic and Norwegian Currents warm northwestern Europe South-moving currents – cool Labrador Current cools eastern Canada Canary Current cools north African coast

29. © 2011 Pearson Education, Inc. Indian Ocean Circulation Monsoons – seasonal reversal of winds over northern Indian Ocean Heat Capacity Differential Northeast monsoon – winter Southwest monsoon – summer

34. © 2011 Pearson Education, Inc. Pacific Ocean Circulation South Pacific Subtropical Gyre East Australian Current Antarctic Circumpolar Current Peru Current South Equatorial Current Equatorial Counter Current

36. Upwelling and downwelling Vertical movement of water Upwelling = movement of deep water to surface  Hoists cold, nutrient-rich water to surface  Produces high productivities and abundant marine life Downwelling = movement of surface water down  Moves warm, nutrient-depleted surface water down  Not associated with high productivities or abundant marine life

37. upwelling downwelling

38. Upwelling Causes cold, nutrient rich water from the deep ocean to rise to the surface.

39. El Nino and La Nina El Nino is a change in water temperature in the Pacific ocean that produces a warm current. La Nina is a change in temperature in the Eastern Pacific that causes surface water temperature to be much colder than usual

40. BOTH El nino and La Nina can cause flooding (too much rain) and drought (too little rain) in different places on Earth. Upwelling does not occur where it normally would and this affects fish and sealife.

41. El Niño-Southern Oscillation (ENSO) El Niño = warm surface current in equatorial eastern Pacific that occurs periodically around December Southern Oscillation = change in atmospheric pressure over Pacific Ocean accompanying El Niño ENSO describes a combined oceanic-atmospheric disturbance

42. • Oceanic and atmospheric phenomenon in the Pacific Ocean • Occurs during December • 2 to 7 year cycle Sea Surface Temperature Atmospheric Winds Upwelling

43. El NiñoNon El Niño 1997

44. Non El Niño El Niño Thermocline – layer of ocean right beneath the “mixed layer” where temperatures decrease rapidly. upwelling

45. El Niño events over the last 55 years El Niño warmings (red) and La Niña coolings (blue) since 1950. Source: NOAA Climate Diagnostics Center

46. El Nino Animation World Wide Effects of El Niño • Weather patterns • Marine Life • Economic resources

47. Effects of severe El Niños

48. Coriolis Effect Because of the coriolis effect, winds appear to deflected to the east or west depending on the direction winds are traveling.

49. A buoy records data about surface ocean temperature and transmits (sends) the information to a satellite in space that then transmits(sends) the information to scientists.

50. Land breeze and sea breeze

51. Water has a much higher heat capacity (absorbs and lets go of heat more) slowly than land, water temperature will increase and decrease less than land temperature. e.g. during daytime, land temperatures might change by tens of degrees, water temperature change by less than half a degree.

52. i.e. coastal land temperatures don’t fluctuate (go up and down) extremely (a lot) because the ocean water nearby doesn’t fluctuate much.

53. © 2011 Pearson Education, Inc. Chapter Overview Ocean currents are moving loops of water. Surface currents are influenced by major wind belts. Currents redistribute global heat. Thermohaline circulation affects deep currents. Currents affect marine life.

54. © 2011 Pearson Education, Inc. Types of Ocean Currents Surface currents Wind-driven Primarily horizontal motion Deep currents Driven by differences in density caused by differences in temperature and salinity Vertical and horizontal motions

55. © 2011 Pearson Education, Inc. Measuring Surface CurrentsDirect methods Floating device tracked through time Fixed current meter Indirect methods Pressure gradients Radar altimeters Doppler flow meter

59. © 2011 Pearson Education, Inc. Surface CurrentsOccur above pycnocline Frictional drag between wind and ocean Generally follow wind belt pattern Other factors: Distribution of continents Gravity Friction Coriolis effect

60. © 2011 Pearson Education, Inc. Subtropical Gyres Large, circular loops of moving water Bounded by: Equatorial current Western Boundary currents Northern or Southern Boundary currents Eastern Boundary currents Centered around 30 degrees latitude

61. © 2011 Pearson Education, Inc. Five Subtropical Gyres North Atlantic – Columbus Gyre South Atlantic – Navigator Gyre North Pacific – Turtle Gyre South Pacific – Heyerdahl Gyre Indian Ocean – Majid Gyre

63. © 2011 Pearson Education, Inc. Subtropical Gyre CurrentsFour main currents flowing into one another: Equatorial Currents North or south Travel westward along equator Western Boundary Currents – warm waters Northern or Southern Boundary Currents – easterly water flow across ocean basin Eastern Boundary Currents – cool waters

65. © 2011 Pearson Education, Inc. Other Surface Currents Equatorial Countercurrents – eastward flow between North and South Equatorial Currents Subpolar Gyres Rotate opposite subtropical gyres Smaller and fewer than subtropical gyres

66. © 2011 Pearson Education, Inc. Western Intensification Top of hill of water displaced toward west due to Earth’s rotation Western boundary currents intensified in both hemispheres Faster Narrower Deeper Warm Coriolis Effect contributes to western intensification

69. © 2011 Pearson Education, Inc. Ocean Currents and ClimateWarm ocean currents warm the air at the coast. Warm, humid air Humid climate on adjoining landmass Cool ocean currents cool the air at the coast. Cool, dry air Dry climate on adjoining landmass

71. © 2011 Pearson Education, Inc. Upwelling and Downwelling Upwelling – Vertical movement of cold, nutrient-rich water to surface High biological productivity Downwelling – Vertical movement of surface water downward in water column

73. © 2011 Pearson Education, Inc. Coastal UpwellingEkman transport moves surface seawater offshore. Cool, nutrient-rich deep water comes up to replace displaced surface waters. Example: U.S. West Coast

77. © 2011 Pearson Education, Inc. Atmospheric-Ocean Connections in the Pacific OceanWalker Circulation Cell – normal conditions Air pressure across equatorial Pacific is higher in eastern Pacific Strong southeast trade winds Pacific warm pool on western side of ocean Thermocline deeper on western side Upwelling off the coast of Peru

79. © 2011 Pearson Education, Inc. El Niño – Southern Oscillation (ENSO) Walker Cell Circulation disrupted High pressure in eastern Pacific weakens Weaker trade winds Warm pool migrates eastward Thermocline deeper in eastern Pacific Downwelling Lower biological productivity Peruvian fishing suffers

81. © 2011 Pearson Education, Inc. La Niña – ENSO Cool Phase Increased pressure difference across equatorial Pacific Stronger trade winds Stronger upwelling in eastern Pacific Shallower thermocline Cooler than normal seawater Higher biological productivity

83. © 2011 Pearson Education, Inc. Occurrence of ENSO Events El Niño warm phase about every 2–10 years Highly irregular Phases usually last 12–18 months 10,000-year sediment record of events ENSO may be part of Pacific Decadal Oscillation (PDO) Long-term natural climate cycle Lasts 20–30 years

87. © 2011 Pearson Education, Inc. Predicting El Niño Events Tropical Ocean−Global Atmosphere (TOGA) program 1985 Monitors equatorial South Pacific System of buoys Tropical Atmosphere and Ocean (TOA) project Continues monitoring ENSO still not fully understood

88. © 2011 Pearson Education, Inc. Deep-Ocean Currents Thermohaline Circulation – deep ocean circulation driven by temperature and density differences in water Below the pycnocline 90% of all ocean water Slow velocity

89. © 2011 Pearson Education, Inc. Thermohaline Circulation Originates in high latitude surface ocean Cooled, now dense surface water sinks and changes little. Deep-water masses identified on temperature– salinity (T–S) diagram Identifies deep water masses based on temperature, salinity, and resulting density

92. © 2011 Pearson Education, Inc. Thermohaline Circulation Some deep-water masses Antarctic Bottom Water North Atlantic Deep Water Antarctic Intermediate Water Oceanic Common Water Cold surface seawater sinks at polar regions and moves equatorward

94. © 2011 Pearson Education, Inc. Power From Currents Currents carry more energy than winds Florida–Gulf Stream Current System Underwater turbines Expensive Difficult to maintain Hazard to boating

95. Measuring surface currents Direct methods Float meters  Intentional  Inadvertent Propeller meters Indirect methods Pressure gradients Satellites Doppler flow meters Figure 7B

96. Surface currents closely follow global wind belt pattern Trade winds at 0-30º blow surface currents to the east Prevailing westerlies at 30-60º blow currents to the west Figure 7-3

97. Figure 7-4

98. Current gyres Gyres are large circular-moving loops of water Subtropical gyres  Five main gyres (one in each ocean basin):  North Pacific  South Pacific  North Atlantic  South Atlantic  Indian  Generally 4 currents in each gyre  Centered at about 30º north or south latitude

99. Current gyres Gyres (continued) Subpolar gyres  Smaller and fewer than subtropical gyres  Generally 2 currents in each gyre  Centered at about 60º north or south latitude  Rotate in the opposite direction of adjoining subtropical gyres

100. Western intensification of subtropical gyres The western boundary currents of all subtropical gyres are: Fast Narrow Deep Western boundary currents are also warm Eastern boundary currents of subtropical gyres have opposite characteristics

101. Currents and climate Warm current warms air high water vapor humid coastal climate Cool current cools air low water vapor dry coastal climate Figure 7-8a

102. Upwelling and downwelling Vertical movement of water ( ) Upwelling = movement of deep water to surface  Hoists cold, nutrient-rich water to surface  Produces high productivities and abundant marine life Downwelling = movement of surface water down  Moves warm, nutrient-depleted surface water down  Not associated with high productivities or abundant marine life

103. Coastal upwelling and downwelling Ekman transport moves surface water away from shore, producing upwelling Ekman transport moves surface water towards shore, producing downwelling Figure 7-11

104. Other types of upwelling Equatorial upwelling Offshore wind Sea floor obstruction Sharp bend in coastal geometry Figure 7-9 Equatorial upwelling

105. Figure 7-13

106. Figure 7-14

107. Figure 7-15

108. The Gulf Stream and sea surface temperatures The Gulf Stream is a warm, western intensified current Meanders as it moves into the North Atlantic Creates warm and cold core rings Figure 7-16

109. Figure 7-17

110. El Niño-Southern Oscillation (ENSO) El Niño = warm surface current in equatorial eastern Pacific that occurs periodically around Christmastime Southern Oscillation = change in atmospheric pressure over Pacific Ocean accompanying El Niño ENSO describes a combined oceanic-atmospheric disturbance

111. Figure 7-18a

112. Figure 7-18b

113. Figure 7-18c

114. The 1997-98 El Niño Sea surface temperature anomaly map shows warming during severe 1997-98 El Niño Internet site for El Niño visualizations Current state of the tropical Pacific Figure 7-19a

115. El Niño recurrence interval Typical recurrence interval for El Niños = 2-12 years Pacific has alternated between El Niño and La Niña events since 1950 Figure 7-20

116. Figure 7-21

117. Figure 7-23 Northeast monsoon Southwest monsoon

118. Deep currents Deep currents: Form in subpolar regions at the surface Are created when high density surface water sinks Factors affecting density of surface water:  Temperature (most important factor)  Salinity Deep currents are also known as thermohaline circulation

119. Deep ocean characteristics Conditions of the deep ocean: Cold Still Dark Essentially no productivity Sparse life Extremely high pressure

120. Identification of deep currents Deep currents are identified by measuring temperature (T) and salinity (S), from which density can be determined Figure 7-24

121. Figure 7-25

122. Figure 7-27

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