Restructing the geological past, therefore, requires con-sideration of natural processes, as well as the results of human activity and to separate them from each other.. This adds a weal
Trang 1W Lemke and J Harff, Baltic Sea Research Institute
Warnemu¨nde, Rostock, Germany
ß 2005, Elsevier Ltd All Rights Reserved.
Introduction
The Quaternary period comprises the shortest time
interval of all geological systems Compared to the
preceding climatically stable and warm Tertiary, it is
characterised by a multiple alternation of large-scale
glaciations and short warm intervals in between The
latest interglacial period, which is still ongoing, is
called Holocene after the Greek words ‘holos’ (entire)
and ‘ceno’ (new) According to recent understanding,
it began ca 11 600 calendar years before present In
contrast to other epochs of the Earth’s history, it is
not defined and subdivided by certain floral or faunal
assemblages but by climatic features Another basic
difference from former geological periods is the
in-creasing human impact on the geosphere In fact,
some authors claim that the properties of the ‘system
Earth’ have changed by human influence to an extent
that it cannot be called natural anymore
Restructing the geological past, therefore, requires
con-sideration of natural processes, as well as the results
of human activity and to separate them from each
other Thus, Holocene geology is intensely
inter-related not only with other natural sciences but also
with human history, archaeology, and further social
sciences This adds a wealth of additional
informa-tion to the data stored within geological archives On
the other hand, geological problems during the
Holo-cene are not only a matter of actualism in the classical
sense anymore Due to the increasingly closer
connec-tion between geological processes and the
develop-ment of the human society, forecasting of geological
trends becomes more and more important In this
way, Charles Lyell’s (see Famous Geologists: Lyell)
statement about the principle of actualism could be
extended to: ‘‘The knowledge about present and past
is the key to the future.’’
Dating
When aiming for an accurate reconstruction of the
geological past, dating becomes an essential issue
Looking back from recent times to the near past,
dating of geological events is simply done on a high
resolution by analysing the written historical archives
Further back in time, indirect methods (by using
so-called proxy data) have to be used Proxy data with a
yearly resolution are related to processes which result
in persistent and regularly successive yearly structures within sediments (e.g., varve sequences) or organic material like wood (dendrochronology) The latter is based on the study of tree ring patterns which are controlled mainly by climatic factors In Europe it was used particularly for oaks in central and western Europe and for pines in northern Europe Regionally generalised curves for these two tree species cover nearly all of the European Holocene
Dendrochronological dates are highly valuable for calibrating dating results produced by other methods This refers especially to isotopic dating by radiocar-bon, which is widely used as a standard method for the dating of organic material within the Holocene
By comparing dendrochronological or varve counting dates with radiocarbon dating, inconsistencies within the later ones, particularly within the early Holocene, became obvious Therefore, when looking at dates in the literature, it is crucial to consider if calibrated (calendar) years or radiocarbon years are referred
to Within this article calendar years before present (BP) are used (except forFigure 10) Other short-lived isotopes, such as210Pb are used to date processes and events in the more recent past on time-scales of decades and centuries
Once the environmental history of a specific region
is well known, assemblages of plants or animals might also help to assess the age of the deposits they are found in
Climate
One of the most intensively studied subjects of Holocene development is climate Ice and marine sediment cores have been used to assess climatic changes and they provide smoothed background data to more regional, or local and mostly more dramatic, climatic variations on the European contin-ent The onset of the Holocene is marked by a global drastic temperature increase of about 7C at the end
of the Younger Dryas, about 11 600 calendar years
BP This climate reorganisation happened during a period of not more than a few decades Since then, the Holocene climate has been stable by comparison with the preceding glacial period Nevertheless, minor climate fluctuations have been reconstructed Several periods with cooler and warmer temperatures than the last century have left their traces in the geological and biological archives and also in human history (Figure 1)
EUROPE/Holocene 147