Chemistry Reference
In-Depth Information
releases carbon dioxide that is collected and. The relative amounts of the
oxygen isotopes in the released carbon dioxide is then measured, usually
in a
mass spectrometer
(see Textbox 10). With this measurement at hand,
the temperature prevalent at the time of formation of the sediment can
be calculated with an accuracy within
+
1°C and occasionally even within
+
0.5°C.
The study of oxygen isotopes in water and in sediments also provides
information on other paleoclimatological fields, such as wind strength and
temperature divergences among different areas of the world. When air
moves from warm, equatorial regions toward colder areas near the poles, for
example, it loses water rich in oxygen-18 as rain and snow, while the water
vapor remaining in the air becomes richer in the lighter isotopes (Grootes
et al. 1993; Wilson and Hendy 1971). Determining the relative amounts of
oxygen isotopes in rain or snow at particular locations on the surface of the
earth makes it possible, therefore, to calculate temperature differences
between colder and hotter regions of the world.
Analyzing the oxygen isotopes in ice cores obtained from stratified,
frozen sheets in cold regions of the world may provide data on climatic
variations in the past, often extending back for many thousands of years.
Using hollow drills to cut through layers of sea sediments or the ice of gla-
ciers, for example, provides samples, generally referred to as
sea cores
, in
which the oxygen isotopes ratios can then be analyzed; the analysis of each
separate layer from a core provides information on the environmental con-
ditions at the time of formation of the sediments and/or the freezing of the
water.
6.2.
SOIL
Soil
is a relatively thin layer of unconsolidated matter on the surface of the
earth, in which there is biological activity. The bulk of most soil consists of
a mixture of extremely small, loose particles of minerals and organic matter:
the mineral particles are derived from the weathering of rocks; the organic
matter from the dead remains of living organisms (Rowell 1994; Limbrey
1975). The composition and texture of the soil are altered by human habita-
tion; humans change the natural flora and fauna of entire areas, their activ-
