The Global Salinity BudgetSlide 2Slide 3Global Salinity DistributionSlide 5Why is the Atlantic so salty?Material BudgetsWater Mass BudgetingVolume BudgetsSalinity BudgetsMediterranean Outflow ExampleSlide 12Slide 13Slide 14Slide 15Abyssal Recipes ExampleAbyssal Recipes – Munk [1966]Slide 18Slide 19Slide 20Slide 21Slide 22Slide 23Slide 24Global Conveyor BeltHydrographic Inverse ModelsGlobal CirculationGlobal Heat TransportSlide 29Slide 30Slide 31The 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 massThe 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 DistributionThe 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 Oceans1 Sverdrup = 106 m3 s-1Why is the Atlantic so salty?Material BudgetsWater 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 propertiesVolume Budgets•Volume conservation (V1 in m3/s or Sverdrup)Volume Flow @ 1 + Input = Volume Flow 2 V1 + F = V2•F = river + air/sea exchangeSalinity Budgets•Salt conservation (in kg/sec) Salt Flow @ 1 = Salt Flow 2 S1 V1 = S2 V2•No exchanges of salinity, only freshwaterMediterranean 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 saltyV1V2E-P-RMediterranean 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/sV1V2FMediterranean Outflow Example•We know V1 + F = V2 & S1 V1 = S2 V2•Rearranging… V1 = S2 V2 / S1S2 V2 / S1 + F = V2V2 = F / (1 - (S2/S1)) V1 = (S2/S1) V2Mediterranean 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 SvMediterranean 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 yearsAbyssal Recipes Example•Seasonal sea ice formation drive deep water production (namely AABW & NADW)Abyssal Recipes – Munk [1966]•Bottom water formation drives global upwelling by convectionAA EQAABWAbyssal Recipes – Munk [1966]•Steady thermocline requires downward mixing of heat balancing upwelling of cool waterAA EQAABWHeatAbyssal 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/dayAbyssal 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 MbMb / 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 yearAbyssal 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 / dayAbyssal 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 convectionAA EQAABWGlobal Conveyor BeltHydrographic 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 transportsGlobal CirculationGlobal Heat TransportGlobal Conveyor BeltGlobal Heat TransportGlobal