Ice Core Archives of Mineral Dust - Mineral Dust: A Key Player in the Earth System - page 457

The borehole is stabilized using a dense non-freezing liquid which may poten-
tially contaminate the dust record contained within the ice (Svensson et al. 2011 ).
The outer contaminated section of the ice core is removed to ensure accurate dust
measurements. This is done by various methods; mechanical scraping of the outer
layers using steel or ceramic chisels (Vallelonga et al. 2002a ); melting the outer
layers by dipping them into baths of particle-free purified water (Delmonte et al.
2002a ); or by continuously melting the ice on a hot surface that separates the inner
pristine ice from the outer contaminated section (Bigler et al. 2011 ).
Ice core chronologies are constructed from a variety of parameters; these include
ice flow models, absolute time markers and seasonal indicators (Wolff et al. 2010 ).
Seasonal indicators include Oxygen isotope ratios (• 18 O, related primarily to
precipitation temperature), sea salts (usually greater in winter) and dust fluxes
(spring peaks in Greenland ice). Seasonal indicators are difficult to measure in
deep ice as they are diffused or thinned by ice flow. Absolute time markers include
atmospheric nuclear bomb testing maxima in 1954 and 1963, as well as volcanic
eruption products such as sulphate, fluoride, chloride, ash and tephra. On longer
time scales, geomagnetic excursions and reversals can be detected by variability in
the production of cosmogenic nuclides ( 10 Be, 36 Cl, 81 Kr). All of these chronological
markers can then be incorporated into models of firn densification and ice flow, to
produce a complete ice core chronology (Parrenin et al. 2007 ). Ice flow models are
the bases for the longest Greenland and Antarctic ice core records.
Dust plays an important role in ice crystal structure, densification and possibly
glacial dynamics. Inaccuracies in firn densification models are likely due to the
absence of parameterizations for dust and impurity content. Recent observations
have shown a correlation between impurity content and densification, which
implies that impurities have an effect on the strength and/or structure of the ice
crystals formed (Hörhold et al. 2012 ). Firn modelling is valuable for constructing
age models for shallow and intermediate ice cores, and for interpreting gas records
from deep ice cores. The information that can be retrieved from a well-tuned firn
model include ice-gas age differences (age), past site elevation and temperature.
There is also indirect evidence that impurities have an effect on larger scale
dynamics of ice sheets; the Greenland NEEM deep ice drilling project has identified
that ice folding preferentially occurs at the interface of the early glacial ice and
late interglacial ice, which have different rheologies due to many factors including
impurity concentrations (NEEM Community Members 2013 ).
Dust plays an important role in the formation and growth of glaciers, as it both
affects and responds to climate changes and influences the formation and densifica-
tion of snow strata. The effects of dust deflation and atmospheric transport on cli-
mate have been covered in Chaps. 5 , 6 , 7 . The impacts of atmospheric dust loading
on insolation and albedo have also been discussed in detail in Chaps. 11 , 13 and 15 .
In this chapter we will discuss the methods used to produce dust records from ice
cores, outline the dust flux records produced, and synthesize the current understand-
ing of global variability in dust transport and deposition revealed by ice cores.