Ice with everything - Antarctica: Global Science from a Frozen Continent - page 84

in temperature from mass spectrometry measurements of the light to heavy water
molecule ratio in Antarctic ice cores. These data also provide a tool to test the
realism of the water cycle simulated by atmospheric circulation models including the
representation of the cycle of the different isotopic forms of water molecules. Such
models have conversely been used to test the hypothesis that the present-day
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applies for past climates.
The dating of deep ice cores also relies on stable isotopes. Glaciological
models require assumptions on the relationships between stable isotopes in the
ice, temperature and the accumulation rate (due to the saturation vapour
pressure of the atmosphere). Glaciological age scales and independent age
markers agree, supporting the use of stable isotope-derived temperature and
accumulation estimates. Changes in snowfall patterns, deposition of

isotopic thermometer '

' diamond

dust and the strength of the temperature gradient up from the ground can all

bias the relationship between snow isotopic composition and annual mean
temperature. A conservative estimate is that past temperatures can be estimated
using water stable isotopes with an accuracy of 20 to 30%, which represents an
error of 2 to 3 C for the magnitude of glacial

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- interglacial changes, reaching

around 10 C in central Antarctica.
Stable isotopes can also provide information on the evaporation conditions
at the sea surface. Variations in deuterium excess are expected to be mostly
controlled by the kinetic fractionation processes occurring both during
evaporation and during snow crystal cloud formation. Thus precise measurements
of both deuterium and oxygen 18 ratios of the same snow

akeorthesamepieceof
ice provide information on the evaporation conditions, in particular, the relative
humidity at the ocean surface and the sea surface temperature. Data on deuterium
excess from central Antarctic sites suggest a long distance, high altitude transport
of moisture from the subtropics to inland Antarctica, while coastal locations
receivemoistureoriginatinglocallyfromtheSouthernOcean.Icecoredata
therefore provide an integrated view of the water cycle, not only restricted to
the deposition of snowfall inland on Antarctica, but also re ecting changes at

the ocean surface much further north.
Together with snowfall, aerosols are deposited on the snow surface. These aerosols
can be formed at the surface of our planet, through marine sea salt spray and salt

flowers deposited on sea ice, by phytoplankton biogenic sulfur production, or uplift
of continental dust all transported towards the polar atmosphere. Ice cores can
therefore provide clues about environmental changes in remote areas, especially
about sea ice extent or turbulence/windiness at the ocean surface. Detailed
elementary and chemical analyses suggest that most Antarctic dust comes from
Patagonia. Ice cores are thus truly an archive of many types of information: local