Ocean Circulation Deep Thermohaline currents. Density = mass/volume (gr/cm 3 ) D (ρ) ~(T, S)

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Ocean Circulation Deep Thermohaline currents
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Transcript of Ocean Circulation Deep Thermohaline currents. Density = mass/volume (gr/cm 3 ) D (ρ) ~(T, S)

Ocean Circulation Deep Thermohaline

currents

Density = mass/volume(gr/cm3)

D (ρ) ~(T, S)

Density Layered Ocean!

Surface layer – Ekman SpiralPycnocline Layer – Geostrophic curr.Deep Ocean – Thermohaline curr.

Ocean Circulation

1. Surface Circulation Wind Driven– Ekman Transport and Geostrophic

Currents– Surface layer and Picnocline zone – 0 – 50,100m / 50,100m - ~1000m– Affects ~25% of total water mass– Fast (1-2 m/s)

Surface Geostrophic and Deep Thermohaline

Circulation

Ocean Circulation1. Surface Circulation Wind Driven

– Ekman Transport and Geostrophic Currents

– Surface layer and Picnocline zone – 0 – 50,100m / 50,100m - ~1000m– Affects ~25% of total water mass– Fast (1-2 m/s)

2. Deep Circulation Density Driven– Thermohaline Circulation– Below Picnocline zone (>~1000m)– Affects ~75% of total water mass– Slow (~ m/day)

Deep Thermohaline Circulation

• T, S are CONSERVATIVE properties– TS properties attained at the surface– Change only by mixing

• (Non-Conservative Properties)– O2, Nutrients

• Oceans are layered according to water densities!!!

H20: Temperature and Density

Seawater: Temperature and Density

Seawater: Ice Formation

Seasonal changes of surface layer thermocline

•Surface seasonal thermocline•Deep permanent thermocline

Latitudinal changes of surface layer salinity

TS PlotsRepresent the influence of TS on density (iso-picnolines)

TS Plot example

Example: CTD Hydrographic Survey

Example: TS Diagram for CTD Line A

Deep Thermohaline Circulation

• So… where do Deep Waters Form?– TS properties attained at the surface– TS properties remain remarkably constant– TS properties only altered by water mixing

Deep Water Formation

Major Water Masses – Thermohaline Circulation

• Central Waters (0-1000m)• Intermediate Waters (1000-

2000m)• Deep Waters (2000-5000m)• Bottom Waters (over ocean

bottom)

Atlantic Deep Waters• AABW

• Antarctic Atlantic Bottom Water• -1.9 oC - 34.6 o/oo (cold & “fresh”)• Forms in the Weddell Sea, during southern

winter ice formation

• NADW• North Atlantic Deep Water• 4 oC - 34.9 o/oo (“warm” & saline)• Forms by cooling of saline Atlantic surface

waters during northern winters, in the Norwegian and Greenland Seas

Atlantic Deep Waters• AIW

• Antarctic Intermediate Water

• 2.2 oC - 33.8 o/oo (cold & “fresh”)

• Forms in sub-polar regions, in the Antarctic Convergence zone

• Extends Northward up to 25oN• (NAIW – North Atlantic Intermediate Water)

• MIW• Mediterranean Intermediate Water

• 11.9 oC - 35.5 o/oo (warm and very saline)

• Spills from Mediterrenan over the Gibraltar Sill• Forms a tongue in the Atlantic ~1000m deep

Atlantic Surface Waters

• NACW • North Atlantic Central Water

• 24 oC - 36 o/oo (very warm & very saline)

• Surface waters, low density

Atlantic Deep Water Masses

Atlantic Deep Water Masses

Weddell Sea – formation AABW

Weddell Sea

MediterraneanIntermidiate Water

Tracing Deep water masses TS Diagrams

Coriolis Effect on Thermohaline Circulation

North Atlantic Deep Conveyer belt – 1000 year

cycles

Conveyor Belt “engine”

North Atlantic Deep Conveyer belt – 1000 year

cycles

Pacific Ocean Thermohaline Circulation