Post on 26-Mar-2018
Deep Ocean CirculationDeep Ocean Circulation
Recall: Recall:
•• Surface currentsSurface currents–– Affect surface water above the main Affect surface water above the main
thermoclinethermocline (<10% of ocean water!)(<10% of ocean water!)–– Driven by major wind beltsDriven by major wind belts–– ““GeostrophicGeostrophic” circulation : balance of ” circulation : balance of
coriolis coriolis driven transport vs. gravitydriven transport vs. gravity
Surface
Deep
Recall: Recall:
The “Other” kind of Ocean currentsThe “Other” kind of Ocean currents
•• Deep currentsDeep currents–– Affect deep water below pycnocline Affect deep water below pycnocline
(90% of ocean water!)(90% of ocean water!)–– Driven by density differencesDriven by density differences–– Larger and Larger and slowerslower (way.. Way slower) (way.. Way slower)
than surface currentsthan surface currents–– Critical to overall longCritical to overall long--term circulation term circulation
of ocean of ocean –– Balance of HEAT Balance of HEAT
TRANSPORT..(climate..) TRANSPORT..(climate..)
Deep currentsDeep currents
•• DensityDensity--driven driven –– Factors affecting density of water:Factors affecting density of water:
•• Temperature (most important factor)Temperature (most important factor)•• SalinitySalinity
–– Thus, THERMOHALINE CirculationThus, THERMOHALINE Circulation
•• Two ProcessesTwo Processes–– Deep water Deep water formation formation (Vertical)(Vertical)
•• Surface water becomes dense Surface water becomes dense --> sinks> sinks
–– Deep water Deep water movementmovement (Horizontal)(Horizontal)•• Slow, along constant density strataSlow, 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 -Excess Evaporation
Indo-Pacific -Excess Rain
AnnualSea Surface Temperature
AnnualSea Surface Salinity
So where does ocean deep water actually form?
How would you predict?
KEY: Gulf Stream Current
Carries Salty and Warm
water to high latitude North
Atlantic
Gulf streamGulf stream
*
ICELAND SEA
Northern cold water deeps: North Atlantic Deep Water (NADW) formation
Is the main source of deep water to entire world ocean
*
LABRADOR SEA
NADW
One other place..
*WEDDELL SEA
Antarctic Bottom Water Formation
ANTARCTIC BOTTOM WATER FORMATIONWEDDELL SEA
Continental Shelf
Slope
0 m
250 m
Antarctica
Shelf water becomes salty and dense
ABW
Sea ice forms in winter
Freshwater used to form sea ice
Open ocean water is fresher and less dense
Atlantic Ocean Cross SectionN S
Deep “water masses”Deep “water masses”
SummarySummary
•• Two main sources of Deep WaterTwo main sources of Deep Water–– North Atlantic Deep WaterNorth Atlantic Deep Water
••Salty surface water cools as it reaches Salty surface water cools as it reaches high latitudeshigh latitudes
–– Antarctic Bottom WaterAntarctic Bottom Water••Cold water becomes salty as sea ice Cold water becomes salty as sea ice
forms on continental shelvesforms on continental shelves
•• NO SOURCES in North PacificNO SOURCES in North Pacific–– Too freshToo fresh
Main Paradigm: “the Global Conveyer Belt”
Global Ocean Conveyor BeltGlobal Ocean Conveyor Beltrepresents net ocean circulationrepresents net ocean circulation
Global Circulation (Net Flow)Global Circulation (Net Flow)•• NADW forms, and flows southNADW forms, and flows south•• joins the Antarctic Circumpolar Currentjoins the Antarctic Circumpolar Current•• flows north into Indian flows north into Indian OcOc. then Pacific . then Pacific
OcOc..•• returns to surface in Upwelling regions returns to surface in Upwelling regions
(spots all over the globe)(spots all over the globe)
Global Circulation (Net Flow)Global Circulation (Net Flow)•• Surface water flows from Pacific Surface water flows from Pacific
through Indonesiathrough Indonesia•• through Indian Oceanthrough Indian Ocean•• around tip of Africa and up to tropical around tip of Africa and up to tropical
AtlanticAtlantic•• Gulf Stream carries water to N Atlantic Gulf Stream carries water to N Atlantic
to start journey againto start journey again
Deep Cold Ocean
Surface Ocean
Global Conveyor BeltGlobal Conveyor Belttotal turnover time of ocean ~ 1000 yearstotal turnover time of ocean ~ 1000 years
Deep Cold Oceanresidence time = 1000 years
Surface Oceanresidence time = 100 years
DeepWaterFormation
Residence time is the average amount of time a substance (in this case water) spends in a reservoir
Upwelling
How we know this?How we know this?
Slight Slight SequeSeque……
How “old” is deep water? How “old” is deep water?
“EXTREME” deep sea water! “EXTREME” deep sea water!
Natural Energy Laboratory near Kona Natural Energy Laboratory near Kona Hawaii Hawaii
Pipelines 10 to 600 and 1000 meters, in central N Pacific ocean gyre-
What does “old” water even What does “old” water even mean? mean?
But how would you know But how would you know How “old” is water? How “old” is water?
•• Deepwater formed at surfaceDeepwater formed at surface–– NADW and AABWNADW and AABW
•• In equilibrium w/atm at surfaceIn equilibrium w/atm at surface
•• Background fact:Background fact:–– CO2 atm >> oceanCO2 atm >> ocean
•• CO2 most soluble gas in water CO2 most soluble gas in water
•• Once deepwater sinks, isolatedOnce deepwater sinks, isolated•• CO2 is isolated too!CO2 is isolated too!
How “old” is deep water? How “old” is deep water?
How’s it done?How’s it done?
•• Isolate CO2 from seawaterIsolate CO2 from seawater•• Some chemistry:Some chemistry:
Inorganic carbon in the oceanInorganic carbon in the oceanHH22O + COO + CO22 > H> H22COCO33 <> HCO<> HCO33
-- + H+ H++ <> CO<> CO33== + H+ H++
Acidify
How’s it done?How’s it done?
•• Carbon (awesome atom)Carbon (awesome atom)–– 1212C major isotopeC major isotope–– 1313C stable isotopeC stable isotope
•• ~1% of all C~1% of all C
–– 1414C radioisotopeC radioisotope••0.0000000001% (part per trillion)0.0000000001% (part per trillion)••Undergoes constant radioactive decayUndergoes constant radioactive decay
–– HalfHalf--life of 5730 yrslife of 5730 yrs
How’s it done?How’s it done?
•• Measure radiocarbon at startMeasure radiocarbon at start•• Measure radiocarbon at endMeasure radiocarbon at end
–– Difference due to decay (gives time)Difference due to decay (gives time)–– Calculate how long it tookCalculate how long it took
Into the labInto the lab
•• Isolate COIsolate CO22 (and anything else of interest)(and anything else of interest)
•• Bring to your neighborhood Bring to your neighborhood Linear Accelerator Mass SpectrometerLinear Accelerator Mass Spectrometer
1414CC-- (Radiocarbon): (Radiocarbon): CompoundCompound--Specific measurementsSpecific measurements--
Lawrence Livermore, CAMS
Start (Youngest)
EndEnd(Oldest)(Oldest)
RESULTRESULT
Sound like fun?Sound like fun?
ENDEND
THE CLIMATE LINK