Geoscience Reference
In-Depth Information
A
B
C
Figure 3-30.
Collecting a peat/sediment core from Skansen Bog on Askøy Island, near Bergen, Norway. A. Peat
drill. The cutting and sampling part is 1 m long (to left) with extension poles added in 1-m sections to right. B.
Pulling up the drill. Note the risk of sinking into the soft turf. C. Inge Aarseth examines the resulting core sections
laid out for inspection. Such peat cores may be collected up to 10-12 m deep. Photos by J.S. Aber.
accelerator mass spectrometry (AMS). Each type
of sample must be prepared in special ways,
which is best done by a dedicated radiometric-
dating laboratory. In any case, all radiocarbon
dates are given with a standard deviation, for
example 10,000
3.4.2 Subsurface methods
Learning about the subsurface characteristics of
wetlands usually involves test drilling and geo-
physical prospecting. Wetland soils and underly-
ing sediments are generally unconsolidated
materials that are relatively easy to penetrate
with manual or powered drilling equipment. For
the study of peat deposits, manual drilling
equipment is usually sufi cient to recover con-
tinuous core samples (Fig. 3-30). When doing
any type of sampling or measuring work in a
bog, fen or swamp, the soft turf and watery
surface may not fully support the weight of
people and equipment. It may be necessary to
lay down a temporary wooden platform, or in
some cases permanent platforms are constructed
for research purposes (Fig. 3-31). The recovered
samples may be subjected to various types of
laboratory analysis for clay mineralogy, pollen
content, radiocarbon age, etc.
Radiocarbon (
14
C) is undoubtedly the most
important radioactive isotope for dating organic
materials of the late Pleistocene and Holocene.
Wood, charcoal, peat, shell, bone, and other
organic remains are suitable sample materials
(Fig. 3-32). Several analytical techniques are in
use for radiocarbon dating
-
proportional gas
counting, liquid scintillation, and negative-ion
±
200 years BP. This indicates
the dated age likely lies between 9,800 and
10,200 years ago; BP means before present.
Radiocarbon dates may be calibrated by com-
parison with the tree-ring record established by
dendrochronology.
Palynology is the study of pollen. Pollen is
well preserved as a record of ancient land veg-
etation and hence is useful for reconstructing
past environmental and climatic conditions.
Pollen is the resistant, dust-sized (0.01-0.1 mm)
male reproductive apparatus of plants. Pollen
grains can usually be identii ed on the basis of
size, shape and ornamentation to the generic
and sometimes specii c level of classii cation.
Most common trees and grasses are wind pol-
linated, and their pollen grains are widely scat-
tered and preserved in lake and mire sediments.
The science of palynology began in Scandinavia,
where a classic late glacial/Holocene pollen
sequence has been established (Fig. 3-33). The
major periods correspond to climatic conditions
that controlled vegetation. Additional factors
include soil development, depletion of nutrients,
