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| Titel |
Stable isotope and modelling evidence for CO2 as a driver of glacial–interglacial vegetation shifts in southern Africa |
| VerfasserIn |
F. J. Bragg, I. C. Prentice, S. P. Harrison, G. Eglinton, P. N. Foster, F. Rommerskirchen, J. Rullkötter |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1726-4170
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| Digitales Dokument |
URL |
| Erschienen |
In: Biogeosciences ; 10, no. 3 ; Nr. 10, no. 3 (2013-03-22), S.2001-2010 |
| Datensatznummer |
250018168
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| Publikation (Nr.) |
 copernicus.org/bg-10-2001-2013.pdf |
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| Zusammenfassung |
Atmospheric CO2 concentration is hypothesized to influence vegetation
distribution via tree–grass competition, with higher CO2 concentrations
favouring trees. The stable carbon isotope (δ13C) signature of
vegetation is influenced by the relative importance of C4 plants
(including most tropical grasses) and C3 plants (including nearly all
trees), and the degree of stomatal closure – a response to aridity – in
C3 plants. Compound-specific δ13C analyses of leaf-wax
biomarkers in sediment cores of an offshore South Atlantic transect are used
here as a record of vegetation changes in subequatorial Africa. These data
suggest a large increase in C3 relative to C4 plant dominance
after the Last Glacial Maximum. Using a process-based biogeography model
that explicitly simulates 13C discrimination, it is shown that
precipitation and temperature changes cannot explain the observed shift in
δ13C values. The physiological effect of increasing CO2
concentration is decisive, altering the C3/C4 balance and bringing
the simulated and observed δ13C values into line.
It is concluded that CO2 concentration itself was a key agent of
vegetation change in tropical southern Africa during the last
glacial–interglacial transition. Two additional inferences follow. First,
long-term variations in terrestrial δ13Cvalues are not simply
a proxy for regional rainfall, as has sometimes been assumed. Although
precipitation and temperature changes have had major effects on vegetation
in many regions of the world during the period between the Last Glacial
Maximum and recent times, CO2 effects must also be taken into account,
especially when reconstructing changes in climate between glacial and
interglacial states. Second, rising CO2 concentration today is likely
to be influencing tree–grass competition in a similar way, and thus
contributing to the "woody thickening" observed in savannas worldwide.
This second inference points to the importance of experiments to determine
how vegetation composition in savannas is likely to be influenced by the
continuing rise of CO2 concentration. |
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