616
Climatic Geomorphology
been produced very rapidly. These important knowledge advances on climate change have
been developed mainly over the last three decades.
From drill cores made in ice sheets, it is possible to obtain paleoclimate records that
contain annual snow precipitation data. Records from the upper part of the core are
alternate layers coming from annual precipitation, whereas in lower layers the
identification of the alternation is not so simple and the records have to be dated by
indirect methods.
Valley glaciers and mountain icecaps have also been cored in Tibet, the Peruvian
Andes, and elsewhere, but the data only provide information on recent climate changes,
which is different from the results obtained from deep drilling in polar ice sheets. The first
deep core was drilled in 1963 to 1966, in Camp Century, Greenland (Dansgaard et al.,
1969). In Antarctica, the Vostok drill in 1983 (Jouzel et al., 1987) provided a climatic
record of the last 160,000 years, exceeding the ice of the last interglacial. The final section
of this core has reached back to 400,000 yr BP Recently the ice has been drilled at
Dome C, located 500 km away from Russian station Vostok, in the East Antarctic ice
sheet, by a consortium called the European Project for Ice Coring in Antarctica (EPICA).
A 740,000 years record is being researched in this project (EPICA, 2004). It is thought
that the final section could reach back to 900,000 years or even further (Walker, 2004).
Between 740,000 and 430,000 years ago, the climate was characterized by less pronounced
warmth in interglacial periods in Antarctica, but a higher proportion of each cycle was
spent in the warm mode (EPICA, 2004, McManus, 2004). The result of this research may
imply that without human intervention a climate similar to the present one would extend
well into the future (EPICA, 2004).
The drill cores, GRIP and GISP2, were carried out in the centre of Greenland, 28 km
apart. In the first one no horizontal movement in the ice was recognized, while in GISP2,
from 2750 m depth on, disagreements in the interpretation exist, due probably to ice flow.
This increases toward the boundaries of the ice sheet.
Oxygen atoms, which are constituents of the glacial ice, have three types of isotopes,
160, 170, and 180. The relative abundance in nature is 0.2, 0.04, and 99.76%, respectively.
During water evaporation on the surface of the sea, the heaviest isotope enriches mainly
in the liquid phase and decreases in the vapor phase. This process is called fractionating.
The resulting vapor has become impoverished in 180, compared to the former water.
Condensation depends on the temperature and the isotopic composition of the precipitation reflects the temperature of the condensation. Therefore, the isotopic composition of
the glacial ice can be used to reconstruct the temperature of the original precipitation. The
isotopes existing in the ice are determined by melting the ice in the laboratory and then
analysing it utilizing a mass spectrometer. The difference between 180/160 and a sample
of standard water (Standard Mean Ocean Water, SMOW) is expressed as ~ 180. If values
are small, the paleotemperatures were low, and vice versa. Because of this, detecting
global climate fluctuations is possible (Dawson, 1992; Ehlers, 1996; Benn and Evans,
1998). Figure 24.1 shows data obtained for GRIP, almost 3000 m depth. The table
represents the interglacial conditions at 130,000yr BP (Eemian or last interglacial),
several interstades (short warming phases) and the rapid termination of the glacial
conditions around 11,000 yr BP. Holocene climate changes have a poor representation,
according to Dansgaard et al. (1993), whereas in the later work of Bond et al. (1997)
a detailed subdivision has been carried out.
Climatic Geomorphology
been produced very rapidly. These important knowledge advances on climate change have
been developed mainly over the last three decades.
From drill cores made in ice sheets, it is possible to obtain paleoclimate records that
contain annual snow precipitation data. Records from the upper part of the core are
alternate layers coming from annual precipitation, whereas in lower layers the
identification of the alternation is not so simple and the records have to be dated by
indirect methods.
Valley glaciers and mountain icecaps have also been cored in Tibet, the Peruvian
Andes, and elsewhere, but the data only provide information on recent climate changes,
which is different from the results obtained from deep drilling in polar ice sheets. The first
deep core was drilled in 1963 to 1966, in Camp Century, Greenland (Dansgaard et al.,
1969). In Antarctica, the Vostok drill in 1983 (Jouzel et al., 1987) provided a climatic
record of the last 160,000 years, exceeding the ice of the last interglacial. The final section
of this core has reached back to 400,000 yr BP Recently the ice has been drilled at
Dome C, located 500 km away from Russian station Vostok, in the East Antarctic ice
sheet, by a consortium called the European Project for Ice Coring in Antarctica (EPICA).
A 740,000 years record is being researched in this project (EPICA, 2004). It is thought
that the final section could reach back to 900,000 years or even further (Walker, 2004).
Between 740,000 and 430,000 years ago, the climate was characterized by less pronounced
warmth in interglacial periods in Antarctica, but a higher proportion of each cycle was
spent in the warm mode (EPICA, 2004, McManus, 2004). The result of this research may
imply that without human intervention a climate similar to the present one would extend
well into the future (EPICA, 2004).
The drill cores, GRIP and GISP2, were carried out in the centre of Greenland, 28 km
apart. In the first one no horizontal movement in the ice was recognized, while in GISP2,
from 2750 m depth on, disagreements in the interpretation exist, due probably to ice flow.
This increases toward the boundaries of the ice sheet.
Oxygen atoms, which are constituents of the glacial ice, have three types of isotopes,
160, 170, and 180. The relative abundance in nature is 0.2, 0.04, and 99.76%, respectively.
During water evaporation on the surface of the sea, the heaviest isotope enriches mainly
in the liquid phase and decreases in the vapor phase. This process is called fractionating.
The resulting vapor has become impoverished in 180, compared to the former water.
Condensation depends on the temperature and the isotopic composition of the precipitation reflects the temperature of the condensation. Therefore, the isotopic composition of
the glacial ice can be used to reconstruct the temperature of the original precipitation. The
isotopes existing in the ice are determined by melting the ice in the laboratory and then
analysing it utilizing a mass spectrometer. The difference between 180/160 and a sample
of standard water (Standard Mean Ocean Water, SMOW) is expressed as ~ 180. If values
are small, the paleotemperatures were low, and vice versa. Because of this, detecting
global climate fluctuations is possible (Dawson, 1992; Ehlers, 1996; Benn and Evans,
1998). Figure 24.1 shows data obtained for GRIP, almost 3000 m depth. The table
represents the interglacial conditions at 130,000yr BP (Eemian or last interglacial),
several interstades (short warming phases) and the rapid termination of the glacial
conditions around 11,000 yr BP. Holocene climate changes have a poor representation,
according to Dansgaard et al. (1993), whereas in the later work of Bond et al. (1997)
a detailed subdivision has been carried out.