G163S06L19 salt and abyssal recipes

The Global Salinity Budget: 

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: 

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…

The Global Salinity Budget: 

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: 

Global Salinity Distribution

The Global Salinity Budget: 

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

Why is the Atlantic so salty?: 

1 Sverdrup = 106 m3 s-1 Why is the Atlantic so salty?

Material Budgets: 

Material Budgets

Water Mass Budgeting: 

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

Volume Budgets: 

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: 

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: 

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: 

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: 

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: 

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: 

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: 

Abyssal Recipes Example Seasonal sea ice formation drive deep water production (namely AABW & NADW)

Abyssal Recipes – Munk [1966]: 

Abyssal Recipes – Munk [1966] Bottom water formation drives global upwelling by convection AA EQ AABW

Abyssal Recipes – Munk [1966]: 

Abyssal Recipes – Munk [1966] Steady thermocline requires downward mixing of heat balancing upwelling of cool water AA EQ AABW

Abyssal Recipes – Munk [1966]: 

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]: 

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]: 

Abyssal Recipes – Munk [1966] From obs, Ss = 34, Si = 4 & Sb = 34.67 ppt 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]: 

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 = r w A Upwelling velocity = 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

Abyssal Recipes – Munk [1966]: 

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)

Abyssal Recipes – Munk [1966]: 

Abyssal Recipes – Munk [1966] Bottom water formation drives global upwelling by convection AA EQ AABW

Global Conveyor Belt: 

Global Conveyor Belt

Hydrographic Inverse Models: 

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 Circulation

Global Heat Transport: 

Global Heat Transport

Global Conveyor Belt: 

Global Conveyor Belt

Global Heat Transport: 

Global Heat Transport

Global Circulation: 

Global Circulation