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

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 S ~ 1000 * 3.6x1012

kg/y / 1.4x1021 kg = 2.6x10-6 ppt per

year

• Undetectable, but not geologically…

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)

Global Salinity Distribution

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

1 Sverdrup = 106 m3 s-1

Why is the Atlantic so salty?

Material Budgets

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 = 1 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

Volume Budgets• Volume conservation (V1 in m3/s or Sverdrup)

Volume Flow @ 1 + Input = Volume Flow 2 V1 + F =

V2

• F = river + air/sea exchange

Salinity Budgets

• Salt conservation (in kg/sec) Salt Flow @ 1 = Salt

Flow 2 S1 V1 = S2 V2

• No exchanges of salinity, only freshwater

Mediterranean Outflow Example

• Saline water flows out of the Mediterranean Sea at depth & fresh water at the surface

• In the Med,

E-P-R > 0

• The Med is salty

V1

V2

E-P-R

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

V1

V2

F

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

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

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

Abyssal Recipes Example

• Seasonal sea ice formation drive

deep water production (namely

AABW & NADW)

Abyssal Recipes – Munk [1966]

• Bottom water formation drives global upwelling by convection

AA EQ

AABW

Abyssal Recipes – Munk [1966]

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

AA EQ

AABW

Heat

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

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)

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

=> Mi = 2.1x1016 kg ice formed each year

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 => Mb = w A

– Upwelling velocity => w = Mb / ( A)

– About ½ bottom water enters the Pacific

– APacific = 1.37x1014 m2 (excludes SO & marginal seas)

– w ~ 3 m / year ~ 1 cm / day

Abyssal Recipes – Munk [1966]

• How long will it take the Pacific to turnover?

– Turnover Time = Volume / Upward Volume flux

– Upward volume flux = ½ Mb / = [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)

Abyssal Recipes – Munk [1966]

• Bottom water formation drives global upwelling by convection

AA EQ

AABW

Global Conveyor Belt

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

Global Circulation

Global Heat Transport

Global Conveyor Belt

Global Heat Transport

Global Circulation