Article (Scientific journals)
Biospheric carbon stocks reconstructed at the Last Glacial Maximum: comparison between general circulation models using prescribed and computed sea surface temperatures
Otto, D.; Rasse, Daniel; Kaplan, J. et al.
2002In Global and Planetary Change, 33 (1-2), p. 117-138
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Keywords :
Last Glacial Maximum; vegetation distribution; continental carbon stocks; climate and vegetation models; asynchronous coupling; prescribed and computed sea surface temperatures
Abstract :
[en] The terrestrial biosphere model Carbon Assimilation in the Biosphere (CARAIB) was improved by introducing two vegetation storeys and implementing a new module which simulates the equilibrium distribution of the vegetation inferred from physiological processes and climatic constraints. In this fourth version of CARAIB, we differentiate ground-level grasses from tree canopies, which allows us to determine the light available to grasses as a direct function of the leaf area index (LAI) of the forest canopy. Both of these storeys are potentially composed of several plant functional types (PFT). The cover fraction of each PFT within each storey is estimated according to its respective net primary productivity (NPP). A biome is assigned to each grid cell on the basis of three physiological criteria: (1) the cover fraction, (2) the NPP, and (3) the LAI; and two climatic constraints: (1) the growing degree-days (GDD) and (2) the lowest temperature reached during the cold season (T-min), which are well-known indices of vegetation expansion boundaries. Total biospheric carbon stocks (vegetation + soil) are reconstructed by forcing the model with eight climatic scenarios of the Last Glacial Maximum (LGM, 21 ka BP), which were obtained from the Palco-Modelling Intercomparison Project (PMIP) from four general circulation models (MRI2, UGAMP, LMD4, and GEN2) using prescribed and computed sea surface temperatures (SSTs). The model was also forced with a current climate together with a preindustrial atmospheric CO2 level of 280 ppm as reference simulation, To validate the model, current biome distribution is reconstructed and compared, for the modem climate, with two distributions of potential vegetation and, for the LGM, with pollen data. The model simulations are in good agreement with broad-scale patterns of vegetation distribution, The results indicate an increase in the total biospheric carbon stock of 827.8-1106.1 Gt C since the LGM. Sensitivity analyses were performed to discriminate the relative effects of the atmospheric CO, level ("fertilization effect"), the climate (present or LGM), and the sea level. Our results suggest that the CO, fertilization effect is mostly responsible for the total increase in vegetation and soil carbon stocks. The four GCMs diverged in their predicted responses of continental climate to calculated SSTs. Only one of them, i.e., MRI2, predicted a marked decline of the continental temperatures in response to lower calculated SSTs. For this GCM, the effect of reduced SSTs on continental biospheric carbon stocks was a decrease of 544.1 Gt for the soil carbon stock and of 283.7.
Disciplines :
Physical, chemical, mathematical & earth Sciences: Multidisciplinary, general & others
Earth sciences & physical geography
Author, co-author :
Otto, D.;  Université de Liège - ULiège > LPAP
Rasse, Daniel;  Université de Liège - ULiège > LPAP
Kaplan, J.;  Max-Planck-Gesellschaft zur Förderung der Wissenschaften - MPG > Max-Planck für Biogeochemie, Jena
Warnant, Pierre ;  Université de Liège - ULiège > Département d'astrophys., géophysique et océanographie (AGO) > Modélisation du climat et des cycles biogéochimiques
François, Louis  ;  Université de Liège - ULiège > Département d'astrophys., géophysique et océanographie (AGO) > Modélisation du climat et des cycles biogéochimiques
Language :
English
Title :
Biospheric carbon stocks reconstructed at the Last Glacial Maximum: comparison between general circulation models using prescribed and computed sea surface temperatures
Publication date :
2002
Journal title :
Global and Planetary Change
ISSN :
0921-8181
Publisher :
Elsevier Science, Amsterdam, Netherlands
Volume :
33
Issue :
1-2
Pages :
117-138
Peer reviewed :
Peer Reviewed verified by ORBi
Available on ORBi :
since 13 May 2010

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