Effects of atmospheric CO<sub>2</sub> variability of the past 800 kyr on the biomes of southeast Africa
Very little is known about the impact of atmospheric
carbon dioxide pressure (pCO2) on the shaping of biomes. The development
of pCO2 throughout the Brunhes Chron may be considered a natural
experiment to elucidate relationships between vegetation and pCO2. While
the glacial periods show low to very low values (∼220 to
∼190 ppmv, respectively), the pCO2 levels of the
interglacial periods vary from intermediate to relatively high
(∼250 to more than 270 ppmv, respectively). To study the influence
of pCO2 on the Pleistocene development of SE African vegetation, we used
the pollen record of a marine core (MD96-2048) retrieved from Delagoa Bight
south of the Limpopo River mouth in combination with stable isotopes and
geochemical proxies. Applying endmember analysis, four pollen assemblages
could be distinguished representing different biomes: heathland, mountain
forest, shrubland and woodland. We find that the vegetation of the Limpopo
River catchment and the coastal region of southern Mozambique is
influenced not only by hydroclimate but also by temperature and atmospheric
pCO2. Our results suggest that the extension of mountain forest occurred
during those parts of the glacials when pCO2 and temperatures were
moderate and that only during the colder periods when atmospheric
pCO2 was low (less than 220 ppmv) open ericaceous vegetation including
C4 sedges extended. The main development of woodlands in the area took place
after the Mid-Brunhes Event (∼430 ka) when interglacial
pCO2 levels regularly rose over 270 ppmv.
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