Deep Ocean Circulation: Also Called Thermo-Haline Circulation

DeepDeep OceanOcean CirculationCirculation Recall:Recall:

•• SurfaceSurface currentscurrents –– AffectAffect surfacesurface waterwater aboveabove thethe mainmain thermoclinethermocline (<10%(<10% ofof oceanocean water!)water!) –– DrivenDriven byby majormajor windwind beltsbelts –– ““GeostrophicGeostrophic”” circulationcirculation :: balancebalance ofof corioliscoriolis drivendriven transporttransport vs.vs. gravitygravity Recall:Recall: Surface

Deep TheThe “Other”“Other” kindkind ofof OceanOcean currentscurrents •• DeepDeep currentscurrents ––AffectAffect deepdeep waterwater belowbelow pycnoclinepycnocline (90%(90% ofof oceanocean water!)water!) ––DrivenDriven byby densitydensity differencesdifferences ––LargerLarger andand slowerslower (way..(way.. WayWay slower)slower) thanthan surfacesurface currentscurrents ––CriticalCritical toto overalloverall longlong--termterm circulationcirculation ofof oceanocean –– BalanceBalance ofof HEATHEAT TRANSPORT..(climate..)TRANSPORT..(climate..) DeepDeep currentscurrents

•• DensityDensity--drivendriven – Factors affecting density of water: • Temperature (most important factor) • Salinity – Thus, THERMOHALINE Circulation •• TwoTwo ProcessesProcesses – Deep water formation (Vertical) • Surface water becomes dense -> sinks – Deep water movement (Horizontal) • Slow, along constant density strata Deep ocean circulation: Also called thermo-haline circulation

Temperature (T) Salinity (S)

Seawater Density depends on both T and S Annual Mean Precipitation Rate (Kg/m2/day)

Atlantic - Indo- Excess Pacific - Evaporation Excess Rain Annual Sea Surface Salinity

Annual Sea Surface Temperature So where does ocean deep water actually form?

How would you predict? GulfGulf streamstream

KEY: Gulf Stream Current Carries Salty and Warm water to high latitude North Atlantic ICELAND SEA LABRADOR SEA

* *

W D A N

Northern cold water deeps: North Atlantic Deep Water (NADW) formation Is the main source of deep water to entire world ocean One other place.. WEDDELL SEA *

Antarctic Bottom Water Formation ANTARCTIC BOTTOM WATER FORMATION WEDDELL SEA

Sea ice forms in winter 0 m

Freshwater used to form sea ice Shelf water becomes Open ocean salty and dense water is 250 m fresher and Continental Shelf less dense

Antarctica Slope

ABW N S Atlantic Ocean Cross Section DeepDeep “water“water masses”masses” SummarySummary

•• TwoTwo mainmain sourcessources ofof DeepDeep WaterWater ––NorthNorth AtlanticAtlantic DeepDeep WaterWater ••SaltySalty surfacesurface waterwater coolscools asas itit reachesreaches highhigh latitudeslatitudes ––AntarcticAntarctic BottomBottom WaterWater ••ColdCold waterwater becomesbecomes saltysalty asas seasea iceice formsforms onon continentalcontinental shelvesshelves •• NONO SOURCESSOURCES inin NorthNorth PacificPacific ––TooToo freshfresh Main Paradigm: “the Global Conveyer Belt” GlobalGlobal OceanOcean ConveyorConveyor BeltBelt representsrepresents netnet oceanocean circulationcirculation GlobalGlobal CirculationCirculation (Net(Net Flow)Flow) •• NADWNADW forms,forms, andand flowsflows southsouth •• joinsjoins thethe AntarcticAntarctic CircumpolarCircumpolar CurrentCurrent •• flowsflows northnorth intointo IndianIndian OcOc.. thenthen PacificPacific OcOc.. •• returnsreturns toto surfacesurface inin UpwellingUpwelling regionsregions (spots(spots allall overover thethe globe)globe) GlobalGlobal CirculationCirculation (Net(Net Flow)Flow) •• SurfaceSurface waterwater flowsflows fromfrom PacificPacific throughthrough IndonesiaIndonesia •• throughthrough IndianIndian OceanOcean •• aroundaround tiptip ofof AfricaAfrica andand upup toto tropicaltropical AtlanticAtlantic •• GulfGulf StreamStream carriescarries waterwater toto NN AtlanticAtlantic toto startstart journeyjourney againagain GlobalGlobal ConveyorConveyor BeltBelt totaltotal turnoverturnover timetime ofof oceanocean ~~ 10001000 yearsyears Surface Ocean residence time = 100 years

Upwelling Deep Water Formation

Deep Cold Ocean residence time = 1000 years Residence time is the average amount of time a substance (in this case water) spends in a reservoir HowHow wewe knowknow this?this? SlightSlight SequeSeque…… HowHow “old”“old” isis deepdeep water?water? “EXTREME”“EXTREME” deepdeep seasea water!water! NaturalNatural EnergyEnergy LaboratoryLaboratory nearnear KonaKona HawaiiHawaii

Pipelines 10 to 600 and 1000 meters, in central N Pacific ocean gyre-

WhatWhat doesdoes “old”“old” waterwater eveneven mean?mean? ButBut howhow wouldwould youyou knowknow HowHow “old”“old” isis water?water? •• DeepwaterDeepwater formedformed atat surfacesurface –– NADWNADW andand AABWAABW •• In equilibrium w/atm at surface •• BackgroundBackground fact:fact: –– CO2CO2 atmatm >>>> oceanocean •• CO2 most soluble gas in water •• OnceOnce deepwaterdeepwater sinks,sinks, isolatedisolated •• CO2 is isolated too! HowHow “old”“old” isis deepdeep water?water? How’sHow’s itit done?done?

•• IsolateIsolate CO2CO2 fromfrom seawaterseawater •• SomeSome chemistry:chemistry: Inorganic carbon in the ocean - + = + H2O + CO2 > H2CO3 <> HCO3 + H <> CO3 + H

Acidify How’sHow’s itit done?done?

•• CarbonCarbon (awesome(awesome atom)atom) –– 12CC majormajor isotopeisotope –– 13CC stablestable isotopeisotope •• ~1% of all C –– 14CC radioisotoperadioisotope ••0.0000000001% (part per trillion) ••Undergoes constant radioactive decay – Half-life of 5730 yrs How’sHow’s itit done?done?

•• MeasureMeasure radiocarbonradiocarbon atat startstart •• MeasureMeasure radiocarbonradiocarbon atat endend –– DifferenceDifference duedue toto decaydecay (gives(gives time)time) –– CalculateCalculate howhow longlong itit tooktook

IntoInto thethe lablab

•• IsolateIsolate COCO2 (and(and anythinganything elseelse ofof interest)interest)

•• BringBring toto youryour neighborhoodneighborhood LinearLinear AcceleratorAccelerator MassMass SpectrometerSpectrometer

14CC-- (Radiocarbon):(Radiocarbon): Compound- Specific measurements-

Lawrence Livermore, CAMS

Start (Youngest) RESULTRESULT

End (Oldest) SoundSound likelike fun?fun? ENDEND

THE CLIMATE LINK