Transient Changes in the Global Carbon Cycle During the Last Glacial/Interglacial Transition
Peter Köhler & Hubertus Fischer
Alfred Wegener Institute for Polar and Marine Research, P.O. Box 12 01 61, D-27515 Bremerhaven, Germany, email: pkoehler@awi-bremerhaven.de, hufischer@awi-bremerhaven.de
H0 H1 H2
H3
-7.0 -6.8 -6.6 -6.4 -6.2
13 C[o /oo]
13C
200 220 240 260 280
pCO2[ppmv] pCO2
Taylor Dome Dome C
-120 -100 -80 -60 -40 -20 0
sealevel[m]
sea level
-42-41 -40-39 -38-37 -36-35 -34
18 O[o /oo]
GISP2 18O
-450 -440 -430 -420 -410 -400 -390 -380
D[o /oo]
Dome C D
0 5 10 15 20 25 30
Time [kyr BP]
0 10 20 30 40 50 60 70 80
nss-Ca2+ [ppb]
Dome C nss-Ca2+
Box model of the Isotopic Carbon cYCLE
BICYCLE
100 m
1000 m
DEEP SURFACE
MEDIATE INTER-
Rock
carbon
water C3
FS SS
NW W D C4
Atmosphere
Atlantic IndoPazific
Sediment
40°N
50°N 40°S 40°S
SO
Biosphere
Processes pCO 2
Temperature -29 ppmv Sealevel +18 ppmv Gas exchange +4 ppmv Increased marine production -20 ppmv Ocean circulation -69 ppmv Terrestrial biosphere +26 ppmv Carbonate compensation -18 ppmv Sum of pCO2 changes -88 ppmv Simulated pCO2 change -85 ppmv Target -80 ppmv
180 200 220 240 260 280 300
pCO2[ppmv]
Simulated (C1a) vs measured data (EDC)
C1a
A
EDC Changes in ocean circulation too abrupt10 15
20 25
Time [kyr BP]
-7.0 -6.8 -6.6 -6.4 -6.2
13 C(atm)[o /oo]
B
1 Dating of (T) forcing not on EDC1 2 Terr. biosphere need stronger T forcing 3 GISP2 T altered: no sharp transition YD-H
-80 -60 -40 -20 0 20 40
pCO2[ppmv]
Changes caused by individual forcings
CaC TBio MBio THC Gas Seal T
A
10 15
20 25
Time [kyr BP]
-0.4 -0.2 0.0 0.2 0.4 0.6
13 C(atm)[o /oo]
B
Data
Time dependent driving forces of the model:
1. pCO2, dD (temperature proxy in the SO) and non sea salt Ca2+ (proxy for Fe input, controlling SO marine NPP) from EPICA Dome C on the EDC1 time scale (Jouzel et al., 2001;
Monnin et al., 2001;
Schwander et al., 2001;
Röthlisberger et al., 2002) 2. d13C measured in Taylor Dome ice (Smith et al., 1999) on the EDC1 time scale via pCO2 correlation 3. GISP2 d18O (tempe- rature proxy for the NH, Grootes and Stuiver, 1997) on the EDC1 time scale via CH4 synchronisation 4. sea level changes derived from coral reef terraces (Fairbanks, 1990) on an independent age scale
5. Heinrich events H0-H3 indicated by grey stripes Abstract
The global carbon cycle plays a significant role in glacial/interglacial transitions. On one hand because carbon reservoirs and exchange rates are subject to external climate conditions, on the other because changes in pCO2 lead to amplification and mediation of regional climate variations. Time slice experiments were so far unable to unambiguously explain the driving forces of the glacial/interglacial pCO2 change of about 80 ppmv. Additional information can be derived from the temporal evolution of the carbon cycle using transient model runs and from the carbon isotopic composition of CO2. Here, we use a coupled atmosphere/biosphere/ocean Box model of the Isotopic Carbon cYCLE (BICYCLE) to quantify changes in pCO2 and d13C in Antarctic ice cores. To this end the model is transiently driven by various proxy records over the last 26,000 years. The result shows that a breakdown in Southern Ocean (SO) stratification triggered by SO warming might explain the initial drop in atmospheric d13C by 0.5°/
°°. In addition, a significant role of the terrestrial biosphere on changes in d13C during the second half of the transition is supported. Carbonate compensation has to be considered as additional process to explain the observed increase in pCO2.
Keywords: 1827 Glaciology (1863), 4267 Paleoceanography, 4805 Biogeochemical Cycles (1615), 4806 Carbon Cycling
Session: Global Climate Change, Eos Trans. AGU, 84(46), Fall Meet. Suppl., Abstract GC12A- 0145,8.-12.12, 2003 San Francisco, Ca, USA, 2003
References
Fairbanks, R.G., Paleocanography, 5, 937-948, 1997 Grootes, P.M. & Stuiver, M., JGR, 102, 26455-26470, 1997 Jouzel, J. et al., GRL, 28, 3199-3202, 2001
Kaplan, J.O. et al., GRL, 29, 2074, doi: 10.1029/2002GL015230, 2002 Keshgi, H.S. & Jain, A.K., GBC, 17, 1047, doi: 10.1029/2001GB001842 Knorr, G. & Lohmann, G., Nature, 424, 532-536, 2003
Monnin, E. et al., Science, 291, 112-114, 2001
Munhoven, G., PhD thesis, Universite de Liege, Belgium, 1997 Röthlisberger, R. et al., GRL, 29, 1963, 10.1029/2002/GL015186, 2002 Schwander, J. et al., GRL, 28, 4243-4246, 2001
Smith, H. et al., Nature, 400, 248-250, 1999
Stephens, B.B. & Keeling, R.F., Nature, 404, 171-174, 2000
Conclusions
1. Glacial/interglacial changes in sea ice might induce pCO2 changes not primarily via gas exchange (Stephens & Keeling, 2000) but via increased mixing in the SO.
This can potentially explain the 0.5°/
drop in d13C at the beginning of the °°
termination.
2. Increased glacial marine export production via Fe fertilization depends on available macro-nutrients and thus oceanic transport processes.
3. SO processes as flywheel of THC kick- on (Knorr & Lohmann, 2003) are consistent with atmospheric carbon changes.
4. Dynamics in d13C in the 2nd half of the transition are dominated by terrestrial biosphere growth.
Model
Structure of BICYCLE (Box model of the Isotopic Carbon cYCLE) adopted from Munhoven (1997) and Keshgi & Jain (2003). The internal module of the terrestrial biosphere or other model output of DGVMs can be used. Arrows indicate
