Geoscience Reference
In-Depth Information
3
Ice core methodology
3.1 HISTORY OF ICE CORE RESEARCH
Willi Dansgaard is a Danish scientist who is credited with the original idea of
using ice cores to probe temperature changes over the past thousands of years.
His book provides a very interesting history of
the early evolution of
this
technique (Dansgaard, 2005).
There are different isotopic forms of water (hydrogen can either be H or D,
and oxygen can either be
16
O,
17
O, or
18
O). While 99.99% of water is H
2
16
O,
other forms (particularly H
2
18
O and the HD
16
O) occur in concentrations of
about 2,000 and 320 ppm (parts per million), respectively. When water evaporates
a higher concentration of the lighter form of water appears in water vapor and,
conversely, when water vapor condenses there is an increase in the
concentration of the heavier form in the product liquid compared with the original
vapor.
The concentrations of the heavy water components H
2
18
O and HD
16
Oin
water samples were originally expressed in parts per million. However, the isotopic
composition of water is now presented as deviations of the concentrations of its
heavy components from the composition of an international standard reference
called SMOW (standard mean ocean water) and is designated by the symbol delta
(
d
). In common use,
d
18
O indicates
d
(H
2
18
O), whereas
d
(D) indicates
d
(HD
16
O).
The definition of
d
18
O is:
0
!
1
18
O
16
O
@
A
Sample
d
18
O
!
1
1,000
18
O
16
O
Reference
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