GEOF236 CHEMICAL OCEANOGRAPHY (HØST 2012)
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GEOF236 CHEMICAL OCEANOGRAPHY (HØST 2012) Christoph Heinze University of Bergen, Geophysical Institute and Bjerknes Centre for Climate Research Prof. in Global Carbon Cycle Modelling Allegaten 70, N-5007 Bergen, Norway Phone: +47 55 58 98 44 Fax: +47 55 58 98 83

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GEOF236 CHEMICAL OCEANOGRAPHY (HØST 2012) Christoph Heinze

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GEOF236 CHEMICAL OCEANOGRAPHY (HØST 2012)

ChristophHeinze

University of Bergen, Geophysical Institute and

Bjerknes Centre for Climate Research

Prof. in Global Carbon Cycle Modelling

Allegaten 70, N-5007 Bergen, Norway

Phone: +47 55 58 98 44 Fax: +47 55 58 98 83

Mobile phone: +47 975 57 119

Email: [email protected]

DEAR STUDENT AND COLLEAGUE:

”This presentation is for teaching/learning purposes only. Do not useany material ofthispresentation for any purpose outsidecourse GEOF236, ”Chemical Oceanography”, autumn 2012, Universityof Bergen. Thankyou for yourattention.”


Sarmiento&Gruber 2006 Chapter 2:

Tracer conservation and ocean transport, part 2


  • The tracer conservation equation expresses that changes of ocean water column tracer concentrations depend on the

  • 3-dimensional ocean velocity field

  • Biogeochemical sources and sinks

  • The 3-d velocity field includes a multitude of processes. In general, a quantification of the velocity field is based on a balance of forces and resulting momentum induced on water “parcels”. Advection – convection – mixing – turbulence – wave motion.

  • The velocity field includes:

  • Friction forces (windstress, internal friction, bottom and side wall friction)

  • Pressure gradient forces

  • Coriolis force (rotating coordinate frame)

  • Gravity force, buoyancy force

  • Forcings, drivers:

  • Wind, evaporation-precipitation, sea ice melt / freezing cooling-warming, tidal force, sea level pressure exerted by atmosphere

  • Equations/models:

  • Navier Stokes equations of motion, these are nonlinear and extremely complex

  • Solutions are provided numerically in ocean general circulation models OGCMs


The wind driven circulation – qualitative findings:

Gyres

Upwelling/downwelling regions


Surface winds, January:

COADS data set

Sarmiento & Gruber (2006)


Surface winds, July:

COADS data set

Sarmiento & Gruber (2006)


Surface winds, schematic pattern of latitudinal variation:

Original source: Book of Pond & Pickard, 1983.

Sarmiento & Gruber (2006)


Streamlines (isolines of equal velocity) in the upper 50 m of the ocean, “surface currents”:

ECCO project, Stammer et al. 2002, dark shades correspond to high velocity

Sarmiento & Gruber (2006)


Sea surface height (top) and thermocline currents (0-500m)(bottom):

ECCO project, Stammer et al. 2002

Sarmiento & Gruber (2006)


Coastal up and downwelling, southern hemisphere case:

Where would you find a typical coastal upwelling in the northern hemisphere?

Original: Thurman, 1990

Sarmiento & Gruber (2006)


Open ocean upwelling/downwelling at divergences/convergences:

Original: Thurman, 1990

Sarmiento & Gruber (2006)


Large-scale gyre structure of the ocean seen from top, left side shows schematic windstress pattern with latitude variations:

Note the westward intensification of ocean currents. Can you give examples for current systems in these west-side currents?

Original: Munk & Carrier, 1950

Sarmiento & Gruber (2006)


Sea surface phosphate (annual mean):

Original: World Ocean Atlas 2001, Conkright et al 2002


Sea surface nitrate (annual mean):

Original: World Ocean Atlas 2001, Conkright et al 2002


SOME THOUGHTS ABOUT THE MAJOR CATEGORIES OF OCEAN CORCULATION:

Wind driven circulation

Thermohaline circulation – does it exist as such?

(think also about continuity equation, conservation of volume)

Meridional overturning circulation (MOC)


Sea surface temperatures (annual mean):

Original: World Ocean Atlas 2001, Conkright et al 2002

Sarmiento & Gruber (2006)


Sea surface salinities (annual mean):

Original: World Ocean Atlas 2001, Conkright et al 2002

Sarmiento & Gruber (2006)


T-S diagram: The isolines indicate equal densities. What dominates density variations at high and low temperatures?

Sarmiento & Gruber (2006)


Definitions – thermocline and mixed layer depth:

Original: Knauss, 1997, Pickard & Emery 1990

Sarmiento & Gruber (2006)


Potential temperature – global section:

Why is the potential temperature shown and not the in situ temperature?

Original: WOCE data

Sarmiento & Gruber (2006)


Salinity – global section:

Original: WOCE data

Sarmiento & Gruber (2006)


Source functions of “transient tracers”:

Sarmiento & Gruber (2006)


Thermocline ventilation – concept and bomb tritium data:

Sarmiento & Gruber (2006)


Thermocline ventilation – formal ages through the “3H/3He tracer clock”:

Sarmiento & Gruber (2006)


Strong density variation across the Gulf stream (zonal section):

Original: WOCE data

Sarmiento & Gruber (2006)


Geostrophic equilibrium – a very much reduced version of the full set of equations of motion:


Radiocarbon age – global meridional cross section:

COLOURED VERSION AVAILABLE?

Original: GLODAP compilation, Key et al., 2004

Sarmiento & Gruber (2006)


Radiocarbon age – map at 3500 m depth:

Original: GLODAP compilation, Key et al., 2004

Sarmiento & Gruber (2006)


Schematic figure of cluster of 8 water molecules

Fraction of molecule aggergates as compared to single H2O molecule

Sea water T

From Dietrich&Kalle, ”Allgemeine Meereskunde”, 1965


Sea water temperature

Density maximum

From Dietrich&Kalle, ”Allgemeine Meereskunde”, 1965

Freezing point

Salinity


From Libes, ”An introduction to marine biogeochemistry”, 1992


What happens to the salt at formation of sea ice ?

From Eide, L.I., and S. Martin, The formation of brine drainage features in young sea ice,

J. Glaciology, 14(79), 137-154, 1975


From Eide, L.I., and S. Martin, The formation of brine drainage features in young sea ice,

J. Glaciology, 14(79), 137-154, 1975


From Eide, L.I., and S. Martin, The formation of brine drainage features in young sea ice, J. Glaciology, 14(79), 137-154, 1975


How to simulate convective overturning or

deep water production in models?

Non-hydrostatic models (often impractical, require high resolution).

Convective adjustment:

If shallower layer A gets heavier than layer B.

Alternatives:

- Homogenisation

- Swap vertical position of layers


Schlitzer, JPO (2007)


Schlitzer, JPO (2007)


Model intercomparison for CFC

GOSAC report

Orr et al., 2002


Model intercomparison for radiocarbon

GOSAC report

Orr et al., 2002


Meridional global water transport stream function [Sv] from an ocean model (PA2 OGCM, GFDL Princeton):

Sarmiento & Gruber (2006)


Meridional Atlantic water transport stream function [Sv] from an ocean model (PA2 OGCM, GFDL Princeton):

Sarmiento & Gruber (2006)


Meridional Indo-Pacific water transport stream function [Sv] from an ocean model (PA2 OGCM, GFDL Princeton):

Sarmiento & Gruber (2006)


Schematic of the meridional overturning circulation:

Original: Toggweiler & Samuals 1993

Sarmiento & Gruber (2006)


Schematic of the global ocean conveyor belt circulation:

Original following: Broecker, 1991 and Gnanadesikan&Hallberg, 2002

Sarmiento & Gruber (2006)


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