A 30000 year record of physical and optical properties of microparticles from an East Antarctic ice core and implications for paleoclimate reconstruction models |
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| Authors: | A Royer M De Angelis J R Petit |
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| Institution: | 1. sr2, rue Très-Clo?tres, Laboratoire de Glaciologie et de Géophysique de I'Environment, 38031, Grenoble-Cedex, France
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| Abstract: | Ice samples from the 905 m deep Dome C core (East Antarctica) were studied in terms of insoluble microparticle contents. Various
techniques were used: right angle light scattering, nephelometer (multiangle light scattering), Coulter counter and microscope
analyses, in order to make a thorough study of the physical and optical properties of microparticles and their variations
over the last 30000 years. Because of the possible effect of atmospheric turbidity on the earth-atmosphere radiation balance,
optical parameters of climatic importance were estimated for insoluble microparticles.
The detailed profile of total microparticle mass concentrations shows a drastic (factor of 17 ± 13) difference between high
Last Glacial Maximum (LGM) and low Holocene concentrations. The optical scattering properties of 18000 BP continental dust
do not indicate a significant difference with respect to Holocene dust in terms of particle size distribution and complex
refractive index. The number to log radius size distribution of microparticles for the entire 30 000 yr period can be fitted
by a log-normal distribution with two parameters (modal radius 0.25 ± 0.08 μm; geometric standard deviation 2.2. ± 0.2). However,
for the smallest particles a better adjustment between experimental and theoretical scattering diagrams is obtained by adding
to the observed size distribution another log-normal distribution (modal radius = 0.025 μm, σ
g
= 2). The complex refractive index is 1.53 to 1.56 for the real part and 0.005 ± 0.005 for the imaginary part at the wavelength
used (λ= 546 nm).
During the LGM stage, over the whole of Antarctica, the change in the total optical depth due to the drastic change in the
insoluble aerosol loading is small because insoluble impurities are not the dominant aerosol component. It may have produced
a slight warming of the snow surface (≈ 2 K). In the dust source regions, the optical depth would have been a maximum of 2
to 4 times the present value. The possible warming of the atmosphere in these regions is estimated at 3 K per day and should
therefore be taken into account in paleoclimate reconstruction models. |
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