Methods:
The flowering
vegetation produces pollen (fig.1). This pollen dust is dispersed over long
distances by wind, insects, birds etc.
The inner core of the pollen grain is protected by a durable outer shell made
up of sporopollenin. Sporopollenin is an extremely resilient substance, which
resists a large number of chemical processes. In this way, under the right
conditions (mainly anaerobic milieu), pollen grains can be preserved over
thousands of years.
To be able to carry out palynological work, first a suitable location for sampling has to be found. In general, the pollen's richest and best records can be gathered from peat or lake deposits. In this kind of environment an anaerobic milieu prevails. This prevents bacterial growth and subsequent feeding, as well as oxidation, which both would destroy the pollen grains (fig.2).
Normally
a 'peat sampler' is used to extract the sediment sequences that are usually
of a few meters in length. Afterwards, the sediment cores are sampled for
pollen analyses. In most cases an amount of only 0.3 cm³ sediment is
enough material (fig.3).
Before the analysis can start, however, the sediment samples have to undergo
chemical treatment, during which most 'non-pollen' material is dissolved.
Pollen grains have a size from only a few microns (µm) to about 100
µm (= 0.1 mm), which means that they cannot be detected with the naked
eye, but can only be examined under the microscope (fig.4).
Different plant taxa produce pollen grains of different shapes. Using these
morphological characteristics, they can be identified in most cases to family
level, sometimes even to species level.
In this manner, the vegetation, that grew when the sediment was deposited,
can be inferred.
From longer records the vegetation cover of a landscape and its changes over
thousands of years can be reconstructed.
Although,
it seemed impossible to retrieve pollen bearing material from the semiarid
Syrian steppe, during the course of the current project, a number of pollen
sequences could be extracted. These are currently analysed in the J. - W.
Goethe University in Frankfurt/Main.
For more detailed information on pollen analyses refer for example to:
FAEGRI, K. UND IVERSEN, J.:- (1989) Textbook of Pollenanalysis. 4. edition.;
Chichester (John Wiley & Sons).
MOORE, P.H., WEBB, J.A. & COLLINSON, M.E. (1991) Pollen Analysis; Oxford
(Blackwell Scientific Publications).