Geoscience Reference
In-Depth Information
Manitoba, Canada. For the most part, still, our
knowledge of pre-late Wisconsin wetland veg-
etation and paleoclimate is quite fragmented in
time and space. Following is a short review of
climatic conditions for the latest Pleistocene and
Holocene from selected regions of the world.
During the twentieth century, pollen analysis
of peat and lacustrine sediment became a stand-
ard approach (see Fig. 3-33), and all kinds of
paleoclimatic proxies have since been investi-
gated ranging from oxygen isotopes (e.g. St.
Amour et al. 2010) to growth patterns in pearl
mussels (e.g. Helama et al. 2010). Various dating
techniques have become quite sophisticated
in order to provide high-resolution temporal
control (e.g. Snowball et al. 2010). Any convinc-
ing reconstruction of paleoclimate depends
upon multiple techniques that are complemen-
tary to each other yet independent in their
sample materials and methods. For the Nordic
region, “the main biological and physical proxy
techniques show a remarkably consistent signal
for Holocene temperature trend” (Seppä et al.
2010, p. 651). Three main climatic phases are
well documented (Fig. 9-12):
9.4.1 Nordic region
Much of what we know about paleoclimate and
environmental conditions of the latest Pleis-
tocene and Holocene was i rst discovered in the
Nordic countries of northern Europe based on
wetland deposits and fossils, and this region
continues to be at the forefront of paleoclimate
research (Seppä et al. 2010). Fennoscandia has
abundant lakes and mires of many sizes and
types, and the region experiences unusually
warm and remarkably variable climate for its
latitude due to inl uence from the North Atlan-
tic. Fundamental discoveries, beginning in the
late nineteenth and early twentieth centuries,
include the Blytt-Sernander scheme for late
glacial and postglacial climate change (Boreal,
Atlantic, Sub-boreal, Sub-atlantic), recognition
of the Holocene thermal maximum (HTM) by
Gunnar Andersson, and establishment of modern
pollen analysis by Lennart von Post (Fig. 9-11).
Already in these early studies, an attempt was
made to link vegetation and climate with phases
of the Baltic Sea and the archaeological record
of early humans (Birks and Seppä 2010).
• Late-glacial/early Holocene climatic amelio-
ration (
c
. 11,000 to 8000 years ago) - rising
temperature, high lake levels, and ice sheets
shrinking into alpine glaciers.
• Holocene thermal maximum (
c.
8000 to
4000 years ago) - high temperature, pro-
nounced drought, low to dry lakes, and
alpine glaciers disappeared (Nesje and
Kvamme 1991).
• Neoglaciation of late Holocene (last 4000
years) - general cooling, high lake levels, and
renewed or expanded alpine glaciation.
Sub-atlantic
Subatlantikum
Subboreal
Sub-boreal
Atlantikum
Atlantic
Boreal
Boreal
Late glacial
Fresh
Sphagnum
peat
Pine bog
peat
Sedge peat
Woodland
humus
Deciduous
fen-wood peat
Amorphous
fen peat
Glacial
river sand
Figure 9-11.
Schematic illustration of peat layers from a bog in Närke, central Sweden. Tree stumps occur in two
dark peat layers (Boreal and Sub-boreal), and tree remains are absent from two light peat layers (Atlantic and
Sub-atlantic). Modii ed from Birks, H.J.B. and Seppä, H. 2010. Late-Quaternary palaeoclimatic research in
Fennoscandia - A historical review.
Boreas
39/4, p. 655-673, Fig. 1; adapted from von Post (1946).
