Deep Ocean Circulation

Recall: • Surface currents – Affect surface water above the main thermocline ( 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)

IndoPacific Excess Rain

Atlantic Excess Evaporation

Annual Sea Surface Salinity

Annual Sea Surface Temperature

So where does ocean deep water actually form? How would you predict?

Gulf stream KEY: Gulf Stream Current Carries Salty and Warm water to high latitude North Atlantic

LABRADOR SEA

ICELAND SEA

* * W D NA

Northern cold water deeps: North Atlantic Deep Water (NADW) formation Is the main source of deep water to entire world ocean

One other place..

*

Antarctic Bottom Water Formation

WEDDELL SEA

ANTARCTIC BOTTOM WATER FORMATION WEDDELL SEA Sea ice forms in winter

0m

Freshwater used to form sea ice Shelf water becomes salty and dense

Open ocean water is fresher and less dense

250 m Continental Shelf Antarctica

Slope

ABW

N

Atlantic Ocean Cross Section

S

Deep “water masses”

Summary • Two main sources of Deep Water – North Atlantic Deep Water

• Salty surface water cools as it reaches high latitudes

– Antarctic Bottom Water

• Cold water becomes salty as sea ice forms on continental shelves

• NO SOURCES in North Pacific – Too fresh

Main Paradigm: “the Global Conveyer Belt”

Global Ocean Conveyor Belt

represents net ocean circulation

Global Circulation (Net Flow) • NADW forms, and flows south • joins the Antarctic Circumpolar Current • flows north into Indian Oc. then Pacific Oc. • returns to surface in Upwelling regions (spots all over the globe)

Global Circulation (Net Flow) • Surface water flows from Pacific

through Indonesia • through Indian Ocean • around tip of Africa and up to tropical Atlantic • Gulf Stream carries water to N Atlantic to start journey again

Global Conveyor Belt

total turnover time of ocean ~ 1000 years 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

How we know this?

Slight Seque…

How “old” is deep water?

“EXTREME” deep sea water!

Natural Energy Laboratory near Kona Hawaii

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

What does “old” water even mean?

But how would you know

How “old” is water?

• Deepwater formed at surface – NADW and AABW • In equilibrium w/atm at surface

• Background fact:

– CO2 atm >> ocean • CO2 most soluble gas in water

• Once deepwater sinks, isolated • CO2 is isolated too!

How “old” is deep water?

How’s it done? • Isolate CO2 from seawater • Some chemistry: Inorganic carbon in the ocean H2O + CO2 > H2CO3 HCO3- + H+ CO3= + H+

Acidify

How’s it done? • Carbon (awesome atom) – 12C major isotope – 13C stable isotope • ~1% of all C – 14C radioisotope • 0.0000000001% (part per trillion) • Undergoes constant radioactive decay – Half-life of 5730 yrs

How’s it done? • Measure radiocarbon at start • Measure radiocarbon at end – Difference due to decay (gives time) – Calculate how long it took

Into the lab • Isolate CO2 (and anything else of interest) • Bring to your neighborhood Linear Accelerator Mass Spectrometer

14C-

(Radiocarbon):

CompoundSpecific measurements-

Lawrence Livermore, CAMS

Start (Youngest)

RESULT End (Oldest)

Sound like fun?

END

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