1. Properties of Seawater (Part II)
Lecture 5 (Ch. 5 of text)
Properties of Seawater (Part II)
Density and Pressure

2. Why is the deep ocean cold?

3. Vertical Structure of Temperature
Thermocline
Hydrographic:水文
Thermocline is a permanent hydrographic feature of temperate and tropical oceans.

4. Seasonal evolution of thermocline at the mid-latitudes
Growing period
Downward heat transport from Sep. to Jan.
Decaying period

5. Vertical Structure of Temperature
Outstanding question:
what sets the depth of the thermocline?

6. Transfer of Heat to the Ocean (heat flux)
Absorption of solar radiation decreases rapidly with depth

7. What controls the ocean’s salinity?
Salinity variations are determined by the addition or removal of H2O from seawater
Processes such as evaporation and sea ice formation will increase the salinity
Processes such as rainfall, runoff, and ice melting will decrease the salinity
Why not plot the salinity in the polar seas?

8. How do the water masses move?
halocline
Salinity
Become unchanged with time
How do the water masses move?
c.f. Fig.5.13b
Temperature

9. Pressure in the Ocean (water is not absolutely incompressible)
Hydrostatic Equation
Hydrostatic Balance

10. Seawater density is a function of both temperature and salinity (so-called TS diagram)
ρA < ρB
ρB < ρC B C

11. OCEAN
WATER
MASSES

12. Vertical profiles
DENSITY: controls the movement and stability of the ocean water masses

13.  Thermohaline Circulation
Vertical circulation driven by density
 Thermohaline Circulation
Density stratification
(18%)
Tropical oceans: pycnocline ≈ thermocline
Mid-latitudes: pycnocline ≈ halocline
High latitudes: no pycnocline formation
Why? (important)

14. More on the DENSITY Density: amount of mass per unit volume
Units: kg m-3
Linear Equation for “in situ” Density

15. But water is slightly compressible

16. Density is actually a non-linear function of Temperature, Salinity and Pressure !
Kg m-3

18. Taking into account compressibility effects
Potential Temperature

19. Taking into account compressibility effects
Potential Density

20. HW#1: Application of Isostasy/Buoyancy Concept (Due date: 17 April)
There is a huge lake with constant depth 100 cm and extension of 500 km. The water surface is still and undisturbed, that is, nothing moves. Now objects A, B, and C (see below for their configurations) are dropped separately and we wait until everything is quiet again. How many cm will the objects be sticking out above or beneath the water surface, if
(a) density of the water is constant at 1.03 g/cm3,
(b) density of the water, for some reasons, increases linearly with depth from 1.03 g/cm3 at the surface to 1.43 g/cm3 at the bottom

21. Potential Temperature
In situ Temperature
Temperature of a particle of water measured at a particular depth and pressure (no correction for compressibility effects)
Surface
Deep ocean T1 T2
Potential Temperature
Temperature that a particle would have if raised adiabatically to the surface of the ocean (corrects for the effects of compression occurring at great depth  make the particle warmer)
T1=θ1
T2≠θ1
At the ocean surface In Situ and Potential Temperature are the same! θ1

22. In situ Density
Potential Density

23. Histograms of Temp. and Salinity in the Oceans
Temperature
Natural thermostate mechanism
tropical cirrus clouds resulting from deep convection contribute to long-wave radiative heating of the tropospheric column, and at the same time reduce solar insolation at the sea surface, in this way cooling the ocean. This dual tropospheric, long-wave radiative heating and surface, short-wave radiative cooling role of cirrus is called the thermostat mechanism.
The deep convection occurs only when the SST exceeds 27 C, which is associated with the so-called super-greenhouse effect
Salinity

24. TS Diagram
Kg m-3
Temperature
Salinity

25. Distribution of T and S in the Ocean

26. Tracking Water Masses on TS diagrams
AABW: Antarctic Bottom Water
NADW: North Atlantic Deep Water
AAIW: Antarctic Intermediate Water

27. Tracking Water Masses on TS diagrams

28. Worlds ocean
Water Masses

29. Mixing (supplements of Ch.5.6)
Properties of Seawater
Mixing (supplements of Ch.5.6)

30. How to mix water masses in the ocean?
Molecular diffusion
Turbulent diffusion

31. Horizontal Stirring and Mixing

32. Horizontal Stirring and Mixing

33. Vertical Stirring and Mixing
Mixing of two water masses with same Density
O1T1 S1
O2T2 S2
Object1; object2

34. + _ Mixing along surfaces of Constant Density y z Surfaces of
(i.e. isopycnal) _

35. + _ Mixing along surfaces of Constant Density y z Surfaces of
Along - Isopycnal diffusive mixing _

36. + _ Mixing across surfaces of Constant Density y z Surfaces of
Along - Isopycnal diffusive mixing
Across - Isopycnal diffusive mixing _

37. + _ Definitions of Mixing y z the “skew flux” Diapycnal Mixing
Surfaces of
constant density
the “skew flux”
Diapycnal Mixing _

38. + _ Definitions of Mixing y z the “skew flux” advection
Surfaces of
constant density
the “skew flux”
advection
Diapycnal Mixing
turbulent diffusion _

39. Diabatic exchanges with the atmosphere at the surface
非絕熱
Diabatic exchanges with the atmosphere at the surface
T1 S1
T2 S2
Adiabatic changes and Mixing in ocean interior 絕熱

40. Summary of major mixing processes in the Ocean
Surface:
Wind stirring and vertical mixing in the surface layer
Surface fluxes of heat and salt  buoyancy fluxes
Surface Waves
Interior:
Along Isopycnal
eddies and fronts
Across Isopycnal
internal wave breaking
Bottom:
Breaking internal waves over rough topography
(Important concepts)

41. Ocean Circulation and Climate Mixing energy and dissipation of tides
Mixing rates in the ocean govern the rate at which the ocean absorbs heat and greenhouse gases, mitigating climate. Global climate change forecasts are uncertain in part due to uncertainty in the global average ocean mixing rate. Mixing rates in the ocean vary geographically depending on bottom roughness. Shown are mixing rates observed during an oceanographic survey across the Brazil Basin in the South Atlantic Ocean. Low mixing rates (purple) were found over the smooth topography to the west, and higher mixing rates (colors) over the rough topography to the east (Mauritzen et al. 2002, JGR)

42. Properties of Seawater
Dissolved Gases (Ch.5.6)
(focus on O2 and CO2)

43. Dissolved Gases (ml l-1) Air Seawater
Total pressure = sum of partial pressures
Seawater
Note the log scale of figs

44. Oxygen
Saturation curve
Metabolic:新陳代謝的

45. Main regulator is the activity of organisms (biological oceanography later)

46. Dissolved Gases in the Ocean
Oxygen profile
compensation depth
Respiration:
Animal, plants and microbial decomposition
Anoxic environment

47. Main sources of O2 in the surface layer: photosynthesis and diffusion across the air-sea interface
Why does the O2-minimum layer coincide with the pycnocline layer? (important)
Why does the concentration increase with depth toward the deep seas? (important)

48. Why is the pH of seawater close to neutral?
(Seawater pH= )
Hydrochloric:氯化氫的
Acetic:醋的,酸的 vinegar
Borax:硼砂
Magnesia:苦土,氧化鎂
Lye:灰汁;灰水;洗濯用鹼水
Sodium:鈉
Hydroxide:氫氧化物
pOH ?

49. Carbon Dioxide and Carbonate system
Why is this important (important)?
Regulates temperature of our planet
2. Important for the ocean biota
3. Regulates the acidity of sea water
The pH of water is directly linked to the CO2 system

50. Carbon Dioxide and Carbonate system
Sources for acidity in the ocean
Carbonic Acid
Carbonate (碳酸鹽)
Bicarbonate Ion

51. At the pH of normal seawater, HCO3- makes up about 80% of the carbon species
less H+ ions need to be released
More H+ ions need to be released

52. (b) Photosynthesis and respiration

53. Why are the CaCO3 shells dissolved in the cold, deep water, but not in the warm, shallow water (important) ?
Carbonate Buffer self-regulating system

54. As temperature is low,
The cold water has a higher gas-saturation value
As the water becomes deeper,
The higher pressure also has a higher gas-saturation value
Thus, the dissolved CO2 amount increases and makes the water acidic, and melts the CaCO3 shells that sink to the deep-sea floor.
→NO Calcareous oozes at high latitudes

56. Carbon Dioxide and Carbonate system
Why is it important?
Regulates temperature of our planet
Important for ocean biota
Regulates the pH value of sea water

57. CO2
70 ppm
Temperature
Deuterium:重氫;氫的同位素

58. CO2
changes in the last 300 yr
70 ppm
Industrial Revolution

59. CO2
changes in the last 50 yr
Oceans
Biosphere
Rock Weathering

60. How much CO2 can be dissolved by the ocean (role of ocean uptake in regulating the global climate)?
Chemical
Biological
Physical
Process that control CO2
absorption in the ocean
Carbon Cycle

61. Grand Carbon Cycle

62. The Carbonate System sources of inorganic carbon
from dissolved CO2 gas
from dissolution of Calcium Carbonate
NOTE:
Biology and Physics participate in the equilibrium of the carbonate system

63. Total dissolved inorganic carbon
this is very small
not found in this form

64. (1) Total dissolved inorganic carbon (2)
formation and decomposition of organic matter
(1)
from dissolution of Calcium Carbonate
(2)
Total dissolved
inorganic carbon

65. Carbon Dioxide and Carbonate system+
High pH -
Low pH

66. Distribution of Carbon species in water+ -

67. Control of pH very rapid reaction in seawater at equilibrium
Equilibrium constant
hydrogen ion concentration

68. hydrogen ion concentration+ -

69. Concept of Alkalinity (鹼度)

70. Alkalinity

73. Why is the pH of seawater close to neutral?

74. So you want the day off :
Lets take a look at what you are asking for :
There are 365 days in the year available for work. There are 52 weeks in the year, in which you already have 2 days off per week, leaving 261 (365 − 52x2) days available for work. Since you spend 16 hours each day away from work, you have used up 170 days (16 x 261 / 24), leaving only 91 days available. You spend 50 minutes each day in coffee breaks which accounts for 27 days {[91 x (8 – 50/60)]/24} per year, leaving only 64 (91-27) days available. With 1 hour lunch period each day, you have used up another 46 days, leaving only 18 (64-46) days available for work. You normally spend 2 days per year on sick leave. This leaves only 16 days available for work. Normally, we are off for 5 holidays per year, so your available working time is down to 11 days. I generously give you 10 days vacation per year, which leaves ONLY 1 DAY available for work, and I'll be damned if I'm going to let you take that very day off.