Ice Core Archives of Mineral Dust - Mineral Dust: A Key Player in the Earth System - page 459

possibly due to the microsecond-long delay time between LPD measurements. CC
remains the reference technique for dust particle determination in ice core samples.

18.2.3 Elemental Dust Proxies

Elements with a high crustal abundance are often used as a proxy for total
dust flux when CC or LPD instruments are unavailable (see also Chap. 2 ) .
Calcium (measured as the soluble Ca 2C ion) is commonly used because it can
be determined routinely using Ion Chromatography or Continuous Flow Analysis
(CFA) techniques. Calcium is also present in seawater and marine inputs may
disturb the dust-Ca signal in coastal ice core records; these can be corrected by
determining the input of marine salts, usually from sodium (Na C ). The non-sea
salt Ca 2C (nssCa 2C ) concentration is then determined by substracting the sea salt
(ssCa 2C ) input as determined from the marine Ca 2C /Na C ratio, employing the
following equations:

R m Ca 2C

R m Na C

R t
R t

nssCa 2C D

R m Ca 2C

R m Na C

1
R t

ssNa C D Na C

where R m and R t are the respective Ca 2C /Na C ratios in seawater (0.038 by mass) and
crustal (1.78) sources (Fischer et al. 2007b ). For inland sites, the sea salt correction
is usually negligible. A detailed study of dust and marine salts and sources in EDC
ice has been reported by Bigler et al. ( 2006 ).
Aluminium (Al), Iron (Fe), Scandium (Sc), Thallium (Tl) and Barium (Ba) are
also used as dust proxies, and have been determined using Inductively-Coupled
Plasma Mass Spectrometer (ICP-MS) and/or Thermal Ionization Mass Spectrom-
eter (TIMS) instruments. Contamination controls are required in the preparation
and analysis of these elements. As for Ca, a limitation of using single elements
for dust proxies is the possible range of elemental abundances in different dust
sources. Using a suite of elements as proxies can minimize this. Ruth et al. ( 2008 )
compared CC and LPD data with elemental proxies such as Al and Fe. In all
cases, good agreement was found between the techniques, although ratios of glacial-
interglacial concentrations varied by up to a factor of two between the techniques.
Sample preparation is also an important consideration; elemental recoveries will
vary depending on the duration and type of sample acidification. In the case of Fe,
acidification at pH1 for 24 h will recover 40-80 % of the total Fe in dust particles,
but acidification periods of up to a month using concentrated HCl are required to
recover total Fe concentrations (Edwards et al. 2006 ). Traversi et al. ( 2004 )also
demonstrated that the recovery of Fe and Al is much greater for ICP-MS compared
to CFA, on account of the brief acidification time (2-3 min) used in CFA analyses.