27 research outputs found
Landschaftsentwicklung im Bereich des Tell Chuera - Geomorphologisch-sedimentologische Untersuchungen in Nord-Syrien
Holocene dust records from the West African Sahel and their implications for changes in climate and land surface conditions
We reconstructed aeolian dust accumulation during the Holocene from two radiocarbon-dated
lake-sediment sequences from the Manga Grasslands in northeastern Nigeria in order to investigate long-term
changes in the Harmattan dust system over West Africa and evaluate their possible causes. Flux values
were low in the early Holocene, decreasing further to a minimum at around 6.2 kyr B.P. after which time
they increased, steadily until around 2 kyr B.P. and then more sharply after this time. The long-term
variations in dust flux agree broadly with changes in the exposed area of the Lake Chad Basin to the
northeast of the study sites, which vary inversely with the volume of Paleolake Megachad. More proximal
sources of dust, including the fine fraction of local dune sand and floodplains of nearby rivers, have also
made a contribution to the total dust load during times of enhanced dune and fluvial activity. Sharp rises in
dust flux over the past century may be related to human activity. Broad patterns of change in dust flux
during the Holocene agree with other reconstructions over the same period. However,we see no evidence
for a stepped rise during the middle Holocene, as seen at some sites from the northeastern tropical
Atlantic, suggesting that controls on the Harmattan dust system have differed from those affecting dust
deposition elsewhere across northern Africa
Palaeoenvironmental changes and vegetation history of the northern Upper Rhine Graben (southwestern Germany) since the Lateglacial
The vegetation of the northern Upper Rhine Graben (southwestern Germany) is reconstructed for the end of the Lateglacial and the Holocene by means of palynological analyses in combination with AMS 14C dating. Analogous to adjacent lowland areas, the Younger Dryas climatic deterioration did not result in a complete deforestation of the area and open pine woodlands with locally birch stands and shrubs persisted. A subdivision of the Younger Dryas period, into a humid first phase, followed by a dry second phase was also reflected in our records. For the Holocene, the pollen diagrams show two regionally different vegetation developments, related to substrate and variations in annual precipitation: in the south the ‘classical’ succession of pine then hazel is followed by other deciduous trees, whereas in the northern part, pine kept its dominance far into the Subboreal