Centre of Excellence
2013–2014
Deep Ocean
Circulation
Natália Tasso Signorelli
Mathew Kuttivadakkethil Avarachen
Helgoland
Feb. 2014
Outline
• What’s deep ocean circulation?
• Why is it important?
• Is it the same in all the oceans?
 Water masses and circulation
• How can we measure it?
 Mooring and floats
 Tracers
• Deep circulation and primary production
 Upwelling zones
• Deep ocean: a reservoir of CO2
• Deep circulation and age of water masses:
 Consequences: the carbon compensation depth (CCD)
• Deep ocean and the Ice Ages
 The role of the MOC shutdown
What’s deep ocean circulation?
The ocean surface layer
:
• Movement driven by wind;
• Ekman layer, Subtropical Gyres…
Below this layer:
• Deep ocean circulation
;
• Intermediate layer
;
• Driven by both wind and density driven.
Lumpkin & Speer (2007),
Speich, Blanke & Cai (2007),
Garzoli & Matano (2011).
What’s deep ocean circulation?
Many terms define it:
• Abyssal circulation;
• Thermohaline circulation;
• Meridional overturning circulation;
• Global conveyor.
Lumpkin & Speer (2007),
Speich, Blanke & Cai (2007),
Garzoli & Matano (2011).
What’s deep ocean circulation?
Many terms define it:
• Abyssal circulation;
• Thermohaline circulation;
• Meridional overturning circulation;
• Global conveyor.
Has disappeared almost entirely from the
oceanographic literature (Toggweiler and
Russell, 2008):
• Not only density driven;
Lumpkin & Speer (2007),
Speich, Blanke & Cai (2007),
Garzoli & Matano (2011).
What’s deep ocean circulation?
Many terms define it:
• Abyssal circulation;
• Thermohaline circulation;
• Meridional overturning circulation;
• Global conveyor.
It is better defined (Stewart, 2008):
• Includes also the influence of the wind.
Lumpkin & Speer (2007),
Speich, Blanke & Cai (2007),
Garzoli & Matano (2011).
Why is it important?
Cold waters in the deep ocean (Stewart, 2008):
• Stratification: influences its dynamics;
• Transports from high to lower latitudes:
 Influences Earth's heat budget and
climate.
• Reservoir of CO2.
Lumpkin & Speer (2007),
Speich, Blanke & Cai (2007),
Garzoli & Matano (2011).
Is it the same in all the basins?
The deep ocean in the different basins:
• Some differences:
 Water masses.
• Some similarities:
 Western boundary currents
Lumpkin & Speer (2007).
Western boundary currents
Conservation of potential
vorticity (Stommel & Arons, 1960).
Effect of the Earth rotation: −20˚
• Coriolis force (f);
−40˚
−60˚
−60˚
−30˚
0˚
m
Stramma & England (1999).
−6000
−4000
−2000
0
Western boundary currents
In the Atlantic Ocean:
• Deep Western Boundary
Current:
 NADW southward;
• Bottom Western Boundary
Current:
 AABW northward.
−20˚
−40˚
−60˚
−60˚
−30˚
0˚
m
Stramma & England (1999).
−6000
−4000
−2000
0
Atlantic Ocean
Potential temperature.
In the Atlantic Ocean (Stewart & Godfrey,
2003):
• North Atlantic Deep water (NADW):
 From Labrador Sea to Antarctic
Divergence.
• Antarctic Bottom Water (AABW):
 From Southern Ocean to Labrador
Basin.
Salinity.
Oxygen
Tomczak & Godfrey (2003).
AABW potential temperature
Atlantic Ocean
In the Atlantic Ocean (Stewart & Godfrey,
2003):
• North Atlantic Deep water (NADW):
 From Labrador Sea to Antarctic
Divergence.
• Antarctic Bottom Water (AABW):
 From Weddell Sea to Labrador
Basin.
Tomczak & Godfrey (2003).
Indian Ocean
Potential temperature
In the Indian Ocean (Stewart &
Godfrey, 2003):
• Indian Deep water (IDW):
 fraction of NADW not
converted into Intermediate
Water in the Atlantic sector
but carried with the upper
Circumpolar Current;
• Antarctic Bottom Water (AABW):
 Inflow from Atlantic and
Pacific;
Tomczak & Godfrey (2003).
Salinity
Oxygen
AABW potential temperature
Indian Ocean
In the Indian Ocean (Stewart &
Godfrey, 2003):
• Indian Deep water (IDW):
 fraction of NADW not
converted into Intermediate
Water in the Atlantic sector
but carried with the upper
Circumpolar Current;
• Antarctic Bottom Water (AABW):
 Inflow from Atlantic and
Pacific;
Tomczak & Godfrey (2003).
Pacific Ocean
Potential temperature
In the Pacific Ocean (Stewart &
Godfrey, 2003):
• Pacific Deep water (PDW):
 North Hemisphere;
 Oldest water mass;
 Does not participate much in
the circulation;
 Slow mixing process;
• Antarctic Bottom Water (AABW):
 Water formation in the Ross
Sea;
Tomczak & Godfrey (2003).
Salinity
Oxygen
Pacific Ocean
AABW potential temperature
In the Pacific Ocean (Stewart &
Godfrey, 2003):
• Pacific Deep water (PDW):
 North Hemisphere;
 Oldest water mass;
 Does not participate much in
the circulation;
 Slow mixing process;
• Antarctic Bottom Water (AABW):
 Water formation in the Ross
Sea;
Tomczak & Godfrey (2003).
How can we measure it?
Recent direct observations:
• Moored current meters;
• deep-drifting floats;
Some limitations:
• Short time series;
• Slow velocities: 1mm/s.
Indirect observations:
• Distribution of temperature,
salinity, oxygen, silicate,
tritium, fluorocarbons and
other tracers.
http://www.roatanmarinepark.com/.
How can we measure it?
Nitrate:
WOCE A16 section, Atlantic Ocean
How can we measure it?
Phosphate:
WOCE A16 section, Atlantic Ocean
How can we measure it?
CFC:
WOCE A16 section, Atlantic Ocean
Upwelling
http://www.greenseaupwelling.com/_images/EarthMap_upwelling_red.jpg
A reservoir of CO2
http://worldoceanreview.com/en/files/2010/10/k2_kompo_kohlenstoffkreislauf_e_en.jpg
Deep circulation and CaCO3
http://oceanservice.noaa.gov/education/tutorial_currents/05conveyor2.html
Deep circulation and CaCO3
http://oceanservice.noaa.gov/education/tutorial_currents/05conveyor2.html
http://oceanservice.noaa.gov/education/tutorial_currents/05conveyor2.html
Freely et al., 2004
Deep circulation modulating climate
•
•
•
•
•
•
The circulation will be more zonal.
The Sea ice will reduce – lowering of Albedo.
Increase in the Global Temperature and sea level rise.
More carbondioxide release and ocean acidification.
Leaches out carbondioxide from mollusc and calcite rocks.
More carbondioxide added to atmosphere, positive feedback for the global
temperature increase.
• Reduces the ocean productivity and the biodiversity up the higher trophic levels.
Deep circulation modulating climate
MOC transporting heat:
• http://www.youtube.com/watch?v=UT2Xy6dZXpQ
• Leads climate on Europe.
Deep circulation modulating climate
MOC slowdown or shutdown (IPCC, 5th Report):
• Reductions in runoff and water availability in southern
Europe;
• Major increase in snowmelt flooding in western Europe;
• Disruption to winter travel opportunities and increased icing
of northern ports and seas;
• Changes in temperature affecting ecosystems in western
Europe and the Mediterranean (e.g., affecting biodiversity,
forest products and food production);
• Movement of populations to southern Europe and a shift in
the centre of economic gravity;
• Reductions in crop production with consequent impacts on
food prices.
Deep circulation modulating climate
MOC on/off state drives Ice Ages.
http://theresilientearth.com/
Centre of Excellence
2013–2014
Deep Ocean
Circulation
Danke
Nhanni
Obrigada