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

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