Deep Thermohaline currents 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 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 Circulation 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) 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 Plots Represent the influence of TS on density (iso-picnolines)

TS Plot example

Example: CTD Hydrographic Survey

Example: CTD Casts Line ‘A’ 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 Central Waters (0-1000m) Intermediate Waters (1000-2000m) Deep Waters (2000-5000m) Bottom Waters (over ocean bottom)

Atlantic Deep Waters AABW NADW 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 MIW 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

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