Identifying Sources of Aeolian Mineral Dust: Present and Past - Mineral Dust: A Key Player in the Earth System - page 51

that are part of the geologic toolbox of provenance studies. Identification of most
dust sources of the past requires the use of physical, mineralogical, geochemical,
and isotopic analyses of dust deposits. Physical properties include systematic spatial
changes in dust deposit thickness and particle size away from a source. Mineralogy
and geochemistry can pinpoint dust sources by clay mineral ratios and Sc-Th-
La abundances, respectively. The most commonly used isotopic methods utilize
isotopes of Nd, Sr, and Pb and have been applied extensively in dust archives of
deep-sea cores, ice cores, and loess. All these methods have shown that dust sources
have changed over time, with far more abundant dust supplies existing during
glacial periods. Greater dust supplies in glacial periods are likely due to greater
production of glaciogenic dust particles from expanded ice sheets and mountain
glaciers, but could also include dust inputs from exposed continental and insular
shelves now submerged. Future dust sources are difficult to assess, but will likely
differ from those of the present because of global warming. Global warming could
bring about shifts in dust sources by changes in degree or type of vegetation cover,
changes in wind strength, and increases or decreases in the size of water bodies.
A major uncertainty in assessing dust sources of the future is related to changes in
human land use, which could affect land surface cover, particularly due to increased
agricultural endeavors and water usage.

Keywords Composition ￿ Mineralogy ￿ Chemistry ￿ Elements ￿ Isotopes ￿
Arid regions ￿ Semiarid regions ￿ Glaciated regions ￿ Satellite imagery ￿ Back-
trajectory analysis

3.1 Introduction

Aeolian mineral dust is an important component of the atmosphere, geosphere,
hydrosphere, and biosphere. Recent reviews (Kohfeld and Harrison 2001 ; Harrison
et al. 2001 ;Tegen 2003 ; Goudie and Middleton 2006 ; Kohfeld and Tegen 2007 ;
Maher et al. 2010 ;Shaoetal. 2011 ; Muhs 2013a , b ) summarize a number of
important aspects of aeolian mineral dust on the Earth-atmosphere system. Dust can
change the overall planetary radiation balance through direct effects on radiation
at both solar (shortwave) and terrestrial (longwave) portions of the electromagnetic
spectrum (Tegen 2003 ). Dust, acting as condensation and ice nuclei (Creamean et al.
2013 ; Karydis et al. 2011 ; Twohy et al. 2009 ), can affect climate and meteorology by
changing cloud lifetime, cloud fraction, and precipitation processes. Aeolian dust is
a significant carrier of Fe, a limiting nutrient in many ocean regions; dust deposition
can significantly increase ocean primary productivity and, consequently, impact the
global carbon cycle (Falkowski et al. 1998 ; Jickells et al. 2005 ; Mahowald et al.
2009 ). There are important effects that dust can have on the biogeochemical cycle
of terrestrial ecosystems, adding nutrients to soils and the vegetation they support
(Ravi et al. 2011 ).