Geoscience Reference
In-Depth Information
The principle of palynological methods is as follows: pollens are
extracted from the soil horizons; their species are determined; a pollen
diagram is constructed (Fig. 2.1).
Palynology
Soil surface
Interpretation
Period characterized by tree
species of temperate climate, thus
of relatively high temperature
A horizon
Pine
Lime-tree
B horizon
Transition period
Period characterized by
tree species of cold climate,
i.e. low temperature
Alder
Oak
C horizon
Relative abundance of pollens
Fig. 2.1
Pollen diagram and interpretation.
According to specialists, the pollens are deposited on the soil surface
and then, carried along by water, are stratified in the soil profile. In the
present case (Fig. 2.1) there would have been a cold period (pines and
birches) giving place gradually to a warmer period (oaks, lime-trees,
alders). The method is quite suitable for peats because the organic
materials are very well preserved in them. Above all, peats grow
upwards. Thus, the newly formed horizons can trap the pollens as and
when they are deposited. In other soils, the validity of the method is
less clear.
There are other methods of reconstructing ancient climates:
Other methods
study of isotopic ratios
18
O/
16
O and D/H in the ices of higher
latitudes; the heavier isotopes are less easily vaporized. The
lower the temperature the less abundant the heavier isotopes in
the clouds and snowfalls, and therefore in the ice formed;
study of Foraminifera of ocean bottoms because the abundance
of such or such species is also a function of the temperature;
correlation can be established with the conditions at the corre-
sponding period on the continents, that is, in the soils;
study of tree rings because these rings are broader or narrower
according to climatic conditions (Chap. 1);
