# 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.

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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 3.6x10 12 kg salts are added to ocean each year from rivers Mass of the oceans is 1.4x10 21 kg IF only riverine inputs, increase in salinity is S ~ 1000 * 3.6x10 12 kg/y / 1.4x10 21 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 = 10 6 m 3 s -1 Why is the Atlantic so salty?

Material Budgets

Water Mass Budgeting Volume fluxes, V 1, are determined from mean velocities and cross-sectional areas V 1 = u 1 A 1 Mass fluxes, M 1, are determined from mean velocities and cross-sectional areas M 1 = 1 u 1 A 1 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 (V 1 in m 3 /s or Sverdrup) Volume Flow @ 1 + Input= Volume Flow 2 V 1 + F = V 2 F = river + air/sea exchange

Salinity Budgets Salt conservation (in kg/sec) Salt Flow @ 1=Salt Flow 2 S 1 V 1 = S 2 V 2 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 V1V1 V2V2 E-P-R

Mediterranean Outflow Example Can we use volume & salinity budgets to estimate flows & residence time?? We know... V 1 + F = V 2 S 1 V 1 = S 2 V 2 S 1 ~ 36.3 S 2 ~ 37.8 F ~ -7x10 4 m 3 /s V1V1 V2V2 F

Mediterranean Outflow Example We know V 1 + F = V 2 & S 1 V 1 = S 2 V 2 Rearranging… V 1 = S 2 V 2 / S 1 S 2 V 2 / S 1 + F = V 2 V 2 = F / (1 - (S 2 /S 1 )) V 1 = (S 2 /S 1 ) V 2

Mediterranean Outflow Example We know S 1 ~ 36.3, S 2 ~ 37.8 & F ~ -7x10 4 m 3 /s (= -0.07 Sverdrups) V 2 = F / (1 - (S 2 /S 1 )) = (-7x10 4 m 3 /s) / (1 - 37.8/36.3) = 1.69x10 6 m 3 /s or 1.69 Sverdrups V 1 = (S 2 /S 1 ) V 2 = (37.8/36.3) 1.69x10 6 m 3 /s = 1.76 Sverdrups V 1 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 = 3.8x10 6 km 3 Time = 3.8x10 15 m 3 / 1.76x10 6 m 3 /s = 2.2x10 9 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 AAEQ AABW

Abyssal Recipes – Munk [1966] Steady thermocline requires downward mixing of heat balancing upwelling of cool water AAEQ 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: M s = M i + M b Salt balance: S s M s = S i M i + S b M b M b / M i = (S s - S i ) / (S b - S s )

Abyssal Recipes – Munk [1966] From obs, S s = 34, S i = 4 & S b = 34.67 ppt Therefore M b / M i = (S s - S i ) / (S b - S s ) ~ 44!! M i = mass of ice produced each year [kg/y] Sea ice analyses in 1966 suggested – Area Seasonal AA ice = 16x10 12 m 2 – Thickness seasonal ice ~ 1 m => M i = 2.1x10 16 kg ice formed each year

Abyssal Recipes – Munk [1966] M b = mass of bottom water produced each year = 9 x10 17 kg / y What is the upwelling rate (w) ? – Upward mass flux => M b = w A – Upwelling velocity => w = M b / ( A) – About ½ bottom water enters the Pacific – A Pacific = 1.37x10 14 m 2 (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 M b / = [m 3 /y] – From before, V b = 4.4x10 14 m 3 /y = 14 Sverdrups – Volume Pacific = A Pacific D Pacific = (1.37x10 14 m 2 ) (5000 m) = 6.9x10 17 m 3 – Turnover Pacific = 6.9x10 17 m 3 / 4.4x10 14 m 3 /y ~ 1500 years (little on the low side)

Abyssal Recipes – Munk [1966] Bottom water formation drives global upwelling by convection AAEQ 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

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