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measurements using visual stratigraphy, the electrical conductivity method (ECM),
laser light scattering from dust (LLS), oxygen isotopic ratios of ice ( d 18 O), major
ion chemistry, and analysis of glass shards and ash from volcanic eruptions. Each
of these parameters (with the exception of volcanic matter) exhibits a distinct
seasonal signal. The definitive summer stratigraphic signal at the GISP2 site
occurs in the form of coarse-grained depth hoar layers formed by summer solar
irradiance. The depth-age relationship for GISP2 is shown in Figure 3.12 . In the
region around the GISP2 site the relief of the snow surface is remarkably flat.
Sastrugi (surface irregularities resulting from wind erosion) several centimeters in
height may be produced by storms, but subsequent deposition, sublimation, and
densification tend to level the surface (Meese et al. 1997). Visual stratigraphy was
the principal method, augmented by a variety of other techniques, used to eluci-
date yearly sequences in the ice core. Stratigraphy in the form of depth-hoar layer
sequences remained continuous through the Holocene and into the glacial transi-
tion. At the height of the Ice Age, the stratigraphic signal was not the
characteristic depth-hoar sequence, but rather cloudy bands resulting from signifi-
cant changes in seasonal dust concentration in the ice. The ECM technique
provided an excellent seasonal indicator.
During the late spring and summer in Greenland, there is an influx of dust
resulting in part from dust storms that occur in both hemispheres during this
period. A laser light scattering (LLS) technique was used in conjunction with
other methods to discern annual layers in the core. It was claimed that the
method can be used as an annual layer indicator in the Holocene and glacial
periods even though the signal changes from one of depth hoar to layers of
Figure 3.12. Depth-age relationship in GISP2.
 
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