Geoscience Reference
In-Depth Information
suggesting that deglaciation was rapid. Barrows et al. (
2001
) noted that the glacial
advances in the Snowy Mountains of Australia were more or less synchronous with
glacial advances in Tasmania, New Zealand and South America, indicating a common
response to cooler late Pleistocene climates in the Southern Hemisphere.
13.11 The glacial record from Antarctica
It is easy to forget that Antarctica is the driest continent on earth - it is simply too
cold for much precipitation. Australia is the second driest continent, and the contrasts
between these two continents could not be greater. On the surface of the Dry Valleys
of Antarctica, wind-abraded pebbles, or ventifacts, are common; they are identical
in form and origin to the better-known ventifacts of the Atacama, Namib, Gobi and
Sahara deserts. However, the Antarctic sedimentary record of past climatic events is
patchy and poorly dated, in contrast to the long and unrivalled record from ice cores
drilled to several kilometres depth into the central ice cap of East Antarctica, such
as the cores collected from near the scientific base at Vostok and jointly studied by
Russian and French glaciologists. These ice cores provide a million-year record of past
fluctuations in the global atmospheric concentration of methane and carbon dioxide
(pCO
2
), as well as the more regional temperature changes inferred from fluctuations
in deuterium, the heavy isotope of hydrogen. They also provide a detailed record of
past fluctuations in the atmospheric dust flux, discussed in
Chapter 9
.
What these records clearly indicate is that during times of minimum temperature
(i.e., glacial maxima), the pCO
2
levels hovered around 160-180 parts per million by
volume (ppmv), rising to 260-280 ppmv during the warmest times (i.e., interglacials).
These background records are sobering because they reveal that since the onset of
the Industrial Revolution around 1750 AD, the pCO
2
levels have been increasing at
an accelerating rate, and by April 2013 they exceeded 400 ppmv. Carbon dioxide
is a potent greenhouse gas, meaning that it has the capacity to allow the passage of
short wave solar radiation through to the earth's surface but will absorb a certain
proportion of the outgoing long wave, or terrestrial, radiation, thereby causing slow
but inexorable warming of the lower atmosphere (see
Chapter 25
).
The atmospheric concentration of two other greenhouse gases has also been increas-
ing exponentially during the last 200 years, namely, methane and nitrous oxide, adding
to the absorption of outgoing infrared radiation and hence enhancing the warming
of the lower atmosphere. We deal with some of the climatic, ecological and social
repercussions of these changes in atmospheric chemistry in Chapters
25
and
26
.
Another long-debated question was whether or not the Antarctic and Greenland ice
core records were in or out of phase. The issue was resolved in 2006 when an ice core
was obtained from Dronning Maud Land in Antarctica with a resolution comparable
to the Greenland ice core records (EPICA Community Members,
2006
). The results
showed a temporal correspondence between Antarctic warm events and Greenland
