The Global Salinity Budget

1
The Global Salinity Budget

• From before, salinity is mass salts per mass
  seawater (S 1000 kg salts / kg SW)
• There is a riverine source BUT salinity of the
  ocean is nearly constant
• Salinity is altered by air-sea exchanges sea
  ice formation
• Useful for budgeting water mass

2
The Global Salinity Budget

• 3.6x1012 kg salts are added to ocean each year
  from rivers
• Mass of the oceans is 1.4x1021 kg
• IF only riverine inputs, increase in salinity is
  DS 1000 3.6x1012 kg/y / 1.4x1021 kg
  2.6x10-6 ppt per year
• Undetectable, but not geologically

3
The Global Salinity Budget

• In reality, loss of salts in sediments is thought
  to balance the riverine input
• Salinity is therefore constant (at least on
  oceanographic time scales)

4
Global Salinity Distribution
5
The Global Salinity Budget

• Salinity follows E-P to high degree through
  tropics and subtropics
• Degree of correspondence falls off towards the
  poles (sea ice)
• Atlantic salinities are much higher than Pacific
  or Indian Oceans

6
Why is the Atlantic so salty?

• 1 Sverdrup 106 m3 s-1

7
Material Budgets
8
Water Mass Budgeting

• Volume fluxes, V1, are determined from mean
  velocities and cross-sectional areas V1 u1
  A1
• Mass fluxes, M1, are determined from mean
  velocities and cross-sectional areas M1 r1
  u1 A1
• Velocities can also come from geostrophy with
  care deciding on level of no motion
• Provides way of solving for flows/exchanges
  knowing water properties

9
Volume Budgets

• Volume conservation (V1 in m3/s or Sverdrup)
• Volume Flow _at_ 1 Input Volume Flow 2 V1
  F V2
• F river air/sea exchange

10
Salinity Budgets

• Salt conservation (in kg/sec) Salt Flow _at_
  1 Salt Flow 2 S1 V1 S2 V2
• No exchanges of salinity, only
  freshwater

11
Mediterranean Outflow Example

• Saline water flows out of the Mediterranean Sea
  at depth fresh water at the surface
• In the Med, E-P-R gt 0
• The Med is salty

E-P-R
V1
V2
12
Mediterranean Outflow Example

• Can we use volume salinity budgets to estimate
  flows residence time??
• We know... V1 F V2 S1 V1 S2
  V2
• S1 36.3 S2 37.8
  F -7x104 m3/s

F
V1
V2
13
Mediterranean Outflow Example

• We know V1 F V2 S1 V1 S2 V2
• Rearranging V1 S2 V2 / S1 S2 V2
  / S1 F V2
• V2 F / (1 - (S2/S1))
• V1 (S2/S1) V2

14
Mediterranean Outflow Example

• We know S1 36.3, S2 37.8 F -7x104 m3/s
  ( -0.07 Sverdrups)
• V2 F / (1 - (S2/S1)) (-7x104 m3/s) / (1
  - 37.8/36.3) 1.69x106 m3/s or 1.69 Sverdrups
• V1 (S2/S1) V2 (37.8/36.3) 1.69x106 m3/s
  1.76 Sverdrups
• V1 observed 1.75 Sv

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Mediterranean Outflow Example

• Residence time is the time required for all of
  the water in the Mediterranean to turnover
• Residence Time Volume / Inflow
• Volume of Mediterranean Sea 3.8x106 km3
• Time 3.8x1015 m3 / 1.76x106 m3/s 2.2x109
  s 70 years

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Abyssal Recipes Example

• Seasonal sea ice formation drive deep water
  production (namely AABW NADW)

17
Abyssal Recipes Munk 1966

• Bottom water formation drives global upwelling by
  convection

AABW
AA
EQ
18
Abyssal Recipes Munk 1966

• Steady thermocline requires downward mixing of
  heat balancing upwelling of cool water

AABW
AA
EQ
19
Abyssal Recipes Munk 1966

• Abyssal recipes theory of thermocline
• AABW formation is estimated knowing area of
  seasonal ice formation, seasonal sea ice
  thickness, salinity of sea ice ambient ocean
• Knowing area of ocean, gave a global upwelling
  rate of 1 cm/day

20
Abyssal Recipes Munk 1966

• Mass salt balances for where bottom water is
  formed
• Mass flux balance Ms Mi Mb
• Salt balance Ss Ms Si Mi Sb Mb
• Mb / Mi (Ss - Si) / (Sb - Ss)

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Abyssal Recipes Munk 1966

• From obs, Ss 34, Si 4 Sb 34.67 ppt
• Therefore Mb / Mi (Ss - Si) / (Sb - Ss) 44!!
• Mi mass of ice produced each year kg/y
• Sea ice analyses in 1966 suggested
• Area Seasonal AA ice 16x1012 m2
• Thickness seasonal ice 1 m
• gt Mi 2.1x1016 kg ice formed each year

22
Abyssal Recipes Munk 1966

• Mb mass of bottom water produced each year 9
  x1017 kg / y
• What is the upwelling rate (w) ?
• Upward mass flux gt Mb r w A
• Upwelling velocity gt w Mb / (r A)
• About ½ bottom water enters the Pacific
• APacific 1.37x1014 m2 (excludes SO marginal
  seas)
• w 3 m / year 1 cm / day

23
Abyssal Recipes Munk 1966

• How long will it take the Pacific to turnover?
• Turnover Time Volume / Upward Volume flux
• Upward volume flux ½ Mb / r m3/y
• From before, Vb 4.4x1014 m3/y 14 Sverdrups
• VolumePacific APacific DPacific
  (1.37x1014 m2) (5000 m) 6.9x1017 m3
• TurnoverPacific 6.9x1017 m3 / 4.4x1014 m3/y
  1500 years (little on the low side)

24
Abyssal Recipes Munk 1966

• Bottom water formation drives global upwelling by
  convection

AABW
AA
EQ
25
Global Conveyor Belt
26
Hydrographic Inverse Models

• WOCE hydrographic sections are used to estimate
  global circulation material transport
• Mass, heat, salt other properties are conserved
  
• Air-sea exchanges removal processes are
  considered
• Provides estimates of basin scale circulation,
  heat freshwater transports

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Global Circulation
28
Global Heat Transport
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Global Conveyor Belt
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Global Heat Transport
31
Global Circulation