Lecture 5.1 Surface Ocean Circulation. Image from Daily Mail Newspaper, UK

Transcription

1 Lecture 5.1 Surface Ocean Circulation Image from Daily Mail Newspaper, UK

2 Announcements Midterm is Thursday, consists of 25 multiple choice, 3 pages short answer questions No Scantron needed Calculators, cell phones, other electronics, etc not allowed 1 side of a 3x5 card is permitted for notes - Write your name and ID# on the blank side anything larger than 3x5 inches is academic dishonesty Bring pen/pencil Today s assignment will be due on Tuesday, 8/29 Midterm evaluations are open until 5PM on Friday, 8/25 you will receive 1% extra credit for completing both the midterm and final evaluations Quiz 3 will open as usual on Thursday at noon

3 Announcements Would you prefer to take the midterm: a) From 9:00-9:50 AM b) From 11:00-11:50 AM

4 Quiz 2 Review The salinity of the Great Salt Lake in Utah is 260. What mass of salt would remain if you evaporate 1kg of lake water? a) 0.26g b) 2.6g c) 26g d) 260g e) 2600g

5 Quiz 2 Review Which of the following elements has the lowest concentration in seawater? a) Zinc b) Nitrogen c) Magnesium d) Oxygen e) Bromine

6 Quiz 2 Review What type of sediment would you likely find on the seafloor if you are a long way from land, the surface waters are warm, the surface waters are low in nutrients, and the seafloor is 6,000m deep (below the CCD)? a) Abyssal clay b) Siliceous ooze c) Calcareous ooze d) Sand and gravel e) None of the above

7 Quiz 2 Review Which of the following would cause an increase in ocean salinity? a) Decreased evaporation rates worldwide b) A decrease in the amount of weathering and material transported to the ocean c) The formation of a lot of shells by ocean organisms which then sink to form ocean sediments d) Faster melting of ice on Greenland and Antarctica e) A decrease in ph at all ocean depths (acidification)

8 Quiz 2 Review At what latitudes do we get consistently clear skies and sunny conditions according to the 3-cell model of atmospheric circulation? (Clear skies and sunny conditions are associated with air subsiding to the surface from higher in the troposphere.) a) 0 and 30 b) 30 and 60 c) 0 and 60 d) 30 and 90 e) 60 and 90

9 Quiz 2 Review A wind in the southern hemisphere is blowing from the Equator towards the South Pole. Due to the Coriolis effect, which direction will the wind actually blow?

10 Quiz 2 Review Which of the following processes changes salinity by changing the amount of dissolved material in the ocean? a) Evaporation b) Precipitation c) Sea spray d) Formation of sea ice e) All of the above

11 Learning Outcomes Be able to draw out the 3-cell conceptual model and explain how it affects ocean salinity and surface winds Be able to describe the direct and indirect methods of measuring ocean circulation Be able to describe/draw diagrams to explain Ekman spirals and Ekman transport Be able to describe/explain/draw diagrams to illustrate the formation, location, and direction of flow of the subtropical gyres in the Northern and Southern hemispheres

12 Atmospheric circulation: 3-cell model Atmosphere and oceans move due to unequal heating (day/night, Equator vs Poles, etc)

13 Atmospheric circulation: Reality Differs from 3-cell conceptual model due to: - Tilt of Earth s axis which generates seasons - Uneven distribution and heating of land and oceans due to different specific heats

14 Surface ocean temperatures and salinity

15 Review: Surface salinity of ocean

16 Atmospheric circulation: 3-cell model Watch this video and make at least: - 3 observations which can be explained using our 3-cell model - 2 observations which can t be explained using our 3-cell model

17 Ocean circulation Just like atmosphere, our oceans are constantly in motion: - Transfer heat from warmer to colder areas - Affected how prehistoric (and historic peoples) travelled around world - Influences abundance of life in surface waters by affecting nutrients Two types of ocean circulation: 1. Surface circulation (above 400m) driven by winds 2. Deep circulation (below 400m) driven by density

18 Measuring ocean circulation Direct methods: - Floating devices released and tracked through time - Fixed propeller flow meter Indirect methods: - Satellite measurements of sea surface height - Doppler flow meters - Tracking T, S or other chemical tracers

19 Measuring ocean circulation: Accidental experiments!

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21 Measuring ocean circulation: Scientific equipment

22 Measuring ocean circulation: Scientific equipment

23 Ocean circulation: Surface currents Winds drive surface circulation but not in a simple way!

24 Ocean circulation: Ekman Transport Wind drags water Ekman Spiral looking vertically down at the currents, they seem to spiral Ekman transport average flow of water throughout the spiral is ~90 o to the right/left of the surface wind in the northern/southern hemisphere

25 Surface Currents: Ekman Transport 1. Winds exert a force on the surface. 2. Friction translates this force down into the water column. 3. Without Coriolis, surface water would flow with the applied winds. Coriolis effect acts at 90 o to the direction of movement so surface water actually flows at o 4. Water in the layer beneath feels friction/drag from the layer moving above. 5. Coriolis effect again acts at 90 o to movement so this layer moves at even more of an angle compared to wind. 6. Process repeats with each layer feeling less force. Layers seem to spiral but NET (average) direction of motion is 90 o at angle to the wind.

26 Surface Currents: Ekman Transport iclicker question which diagram shows what would happen in the southern hemisphere? A B

27 Surface Currents: Ekman Transport iclicker question which diagram shows what would happen in the southern hemisphere? A B

28 Surface ocean circulation: Gyres Gyres form due to continent positions and wind patterns

29 Surface ocean circulation: Subtropical gyres Gyres form due to continent positions and wind patterns

30 Great Pacific Garbage Patch

31 Which hemisphere is the below subtropical gyre in? a) Northern b) Southern c) Trick question - neither Land Land

32 Which hemisphere is the below subtropical gyre in? a) Northern b) Southern c) Trick question - neither Land Land

33 Lecture 5.2 Surface Ocean Circulation Continued

34 Learning Outcomes Be able to describe/explain/or draw diagrams to illustrate the formation of subtropical gyres, subpolar gyres, and Equatorial currents Be able to predict whether a coastline will be warm/humid or cold/dry based on patterns of ocean currents Be able to describe/explain why upwelling or downwelling affect the amount of life in the surface ocean Be able to explain/draw labelled diagrams showing the different mechanisms which can cause upwelling or downwelling to occur Be able to interpret/explain the patterns in the abundance of life in the surface ocean

35 Ocean circulation: Surface currents Winds drive surface circulation but not in a simple way!

36 Ocean circulation: Ekman Transport Wind drags water Ekman Spiral looking vertically down at the currents, they seem to spiral Ekman transport average flow of water throughout the spiral is ~90 o to the right/left of the surface wind in the northern/southern hemisphere

37 Surface ocean circulation: Gyres Gyres form due to continent positions and wind patterns

38 Surface ocean circulation: Geostrophic flow Geostrophic currents occur where the Coriolis effect and gravity balance out

39 Surface ocean circulation: Western boundary currents Western boundary currents are intensified due to the rotation of the Earth

40 Surface ocean circulation: Western boundary currents

41 Surface ocean circulation: Coastal climate Warm currents = warmer and more humid climates Cold currents = cooler and drier climates

42 Surface ocean circulation: Coastal climate Will the climate of eastern Australia or western South America be more humid at 20 o S? a) Eastern Australia b) Western South America

43 Surface ocean circulation: Coastal climate Will the climate of eastern Australia or western South America be more humid at 20 o S? a) Eastern Australia b) Western South America

44 Surface ocean circulation: Coastal climate California Current vs Gulf Stream

45 Surface ocean circulation: Subpolar gyres Less common and smaller than subtropical gyres

46 Do subpolar gyres circulate around an area of high or low sea level? a) High b) Low c) Neither

47 Do subpolar gyres circulate around an area of high or low sea level? a) High b) Low c) Neither

48 Surface ocean circulation: Other currents Equatorial Currents water moves with easterly trade winds Equatorial Counter Currents move against wind to balance flows Southern Ocean currents no continent to interrupt flow

49 Upwelling and Downwelling Upwelling = movement of deeper water to surface Downwelling = movement of surface water to deeper ocean Can happen due to: 1. Diverging/converging surface waters 2. Interaction of winds and coastlines 3. Bends in coastlines 4. Shape of sea floor 5. Lack of pycnocline Why do we care?

50 Oceans: Life What will life be limited by in the surface ocean? a) CO 2 b) H 2 O c) nutrients d) light Photosynthesis: CO 2 and nutrients are consumed in the surface layer CO 2 + H 2 O + nutrients light Organic Matter + O 2 (+ shells)

51 Oceans: Life What will life be limited by in the surface ocean? a) CO 2 b) H 2 O c) nutrients d) light Photosynthesis: CO 2 and nutrients are consumed in the surface layer CO 2 + H 2 O + nutrients light Organic Matter + O 2 (+ shells)

52 ~0.1 % of material is buried as sediment on the ocean floor Oceans: Life Upwelling brings nutrient-rich water to the surface for life! Photosynthesis: CO 2 and nutrients are consumed in the surface layer CO 2 + H 2 O + nutrients light Organic Matter + O 2 (+ shells) Upwelling Respiration: CO 2 + H 2 O + nutrients Organic Matter + O 2 (+ shells)

53 Oceans: Life Where is there the most life in the surface ocean? Where is there the least?

54 Upwelling and Downwelling 1. Diverging/converging surface waters

55 Upwelling and Downwelling 2. Interaction of winds and coastlines

56 iclicker question Does upwelling or downwelling happen off California? Wind direction A)Downwelling B)Upwelling

57 iclicker question Does upwelling or downwelling happen off California? Wind direction A)Downwelling B)Upwelling

58 California Upwelling Upwelled water is colder, saltier and contains more nutrients so fertilizes the ocean off California Also lowers ocean temperatures and makes fog more likely

59 Upwelling and Downwelling 3. Bends in coastlines What would happen if the surface currents were flowing the other way?

60 Upwelling and Downwelling 4. Shape of the seafloor

61 Upwelling and Downwelling 5. Lack of pycnocline Lack of pycnocline makes it easier for surface and deeper waters to mix at high latitudes

62 Oceans: Life Where is there the most life in the surface ocean? Where is there the least?

63 On Thursday Deep Ocean Circulation, Ocean- Atmosphere Interactions Reading 6.5 (How does the ocean influence global weather patterns? Tropical Cyclones), 7.4 (What are the main surface circulation patterns in each ocean basin? Pacific Ocean Circulation), and 7.5 (How do deep-ocean currents form?)