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