ocean circulation changes 13-c fractionation palaeoclimate gerrit lohmann carbon course 16. january...
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Ocean Circulation Changes13-C Fractionation
Palaeoclimate
Gerrit Lohmann
Carbon Course16. January 2006
@PEP, University of Bremen, Germany
Ocean Circulation Methaphor
surfacedeep
conversion
Heat, freshwater surface fluxes
Tropical Box T2 S2
High Latitude
Box T1 S1q > 0
Z: Depth
Y: meridional direction
Stommel (1961) Box Model
Salinity loop
• S1 low
• q low
• q S2 low
• S1 low
T2 S2 T1 S1q > 0
Positive feedback
Flow in the direction of density
Tropical Box T2 S2
NorthernHigh
Latitude Box T1 S1
Southern High
Latitude Box
T3 S3
Rooth (1982) box model: Interhemispheric flow
q > 0
S NS+ N
Red arrows: motion of objects fixed to the globe
Yellow and green arrows: not fixed, northern velocity
Yellow arrows arrives ahead of a fixed object, green arrives behind
Rotation in
• The direction of rotation in draining sinks and toilets is NOT determined by the rotation of the Earth, but by rotation that was introduced earlier when it was being filled or subsequently being disturbed (say by washing).
• The rotation of the Earth does influence the direction of rotation of large weather systems and large vortices in the oceans
Ocean Circulation Methaphor
surfacedeep
conversion
Conveyor belt
Warm water route
Conveyor belt
Cold water route
Present
Glacial
S1 > S2
S1 < S2
South- Equator North- Atlantic
Conceptual Model of the THC (~ Rooth)
Cold & Warm water route
Cold water route
Signature at the end of a meltwater pertubation SST
deg°C
0 10000 20000 30000A ge (Calendar Y ears )
9
11
13
15
17
19
T (
°C)
2 4
2 6
2 8
T (
°C)
0 10000 20000 30000
North Atlantic (SU 81-18)(Bard et al. 2000)
YD H1 H2
Bard et al. 2000
SU81-18
NS
interhemispheric seesaw
Knorr and Lohmann 2005
Physical System is important for the marine carbon cycle
13-C Fractionation
• The photosynthetic activity in the oceans (limited to the photic zone) results in a very strong depletion of the surface waters in 12C (captured in organic matter), strong enrichment in 13C.
• Planktonic organisms living in the photic zone, and forming calcareous tests from dissolved inorganic carbon (largely HCO3
- ) in these surface layers, thus use carbon that is enriched in 13C (isotopically heavy) for the formation.
Organic Carbon cycle
Photosynthesis -> low PO4,
organic matter with 12-C,
residual water high 13-C
Organic Carbon cycle
oxidation
13-C oxidation
• 13-C provides a measure of oxidation of organic carbon:
• CH2O + O2 --> CO2 + H2O
The 13-C values of dissolved inorganic carbon at greater depths (and thus of benthic foraminifera) are quite different from those in surface waters, because carbon dioxide derived from oxidized organic material (thus isotopically light) is added to the deep waters.
http://ethomas.web.wesleyan.edu/wescourses/2004s/ees227/01/229lab6.htm
``13-C conveyor belt´´
13-C
• To complicate factors, there is a difference in d13C of total dissolved inorganic carbon (TDIC) in deep waters with a different "age":
waters that have been out of contact with the surface ocean for a long time, have accumulated much carbon derived from oxidation of organic material, thus their total dissolved inorganic carbon is isotopically light.
13-C: climate changes
Paleoclimate
Paleoclimate
Eccentricity
Precession of the axis of the earthYear:
A holy grail
Theory of ice ages
External:
Increased eccentricity of the earth's orbit
Changes in the intensity of solar radiation
The earth passing through cold regions of space
Internal: ice sheet, CO2, stochastic
Amplifiers: thresholds, rectification