Ocean Circulation
Deep Thermohaline currents
Density = mass/volume
(gr/cm3)
D (ρ) ~(T, S)
Density Layered Ocean!
Surface layer – Ekman Spiral
Pycnocline Layer – Geostrophic curr.
Deep Ocean – Thermohaline curr.
Ocean Circulation
1. Surface Circulation  Wind Driven
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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 Circulation
1. Surface Circulation  Wind Driven
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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
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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 Plots
Represent the influence of TS on density (iso-picnolines)
TS Plot example
Example: CTD Hydrographic Survey
Example: CTD Casts Line ‘A’
T
S
D
http://tabs.gerg.tamu.edu/gomoms/ctddata.html
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
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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
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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
Mediterranean
Intermidiate
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