Effects of atmospheric CO₂ variability of the past 800 kyr on the biomes of southeast Africa

Abstract

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.