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| Titel |
Radiogenic isotope evidence for transatlantic atmospheric dust transport |
| VerfasserIn |
Ashwini Kumar, Wafa Abouchami, Virginia H. Garrison, Stephen J. G. Galer, Meinrat O. Andreae |
| Konferenz |
EGU General Assembly 2013
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 15 (2013) |
| Datensatznummer |
250073006
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| Zusammenfassung |
| Early studies by Prospero and colleagues [1] have shown that African dust reaches all across
the Atlantic and into the Caribbean. It may contribute to fertilizing the Amazon rainforest
[2,3,4], in addition to enhancing the ocean biological productivity via delivery of iron, a key
nutrient element[5]. Radiogenic isotope ratios (Sr, Nd, Pb) are robust tracers of dust sources
and can thus provide information on provenance and pathways of dust transport. Here
we report Sr, Nd and Pb isotope data on atmospheric aerosols, collected in 2008
on quartz filters, from three different locations in Mali (12.6Ë N, 8.0Ë W; 555 m
a.s.l.), Tobago (11.3Ë N, 60.5Ë W; 329 m a.s.l.) and the U.S. Virgin Islands (17.7Ë
N, 64.6Ë W; 27 m a.s.l.) to investigate the hypothesis of dust transport across the
Atlantic.
About 2 cm2 of filter were acid-leached in 0.5 N HBr for selective removal of the
anthropogenic labile Pb component (leachate) and possibly the fine soluble particle fraction.
The remainder of the filter was subsequently dissolved using a mixture of HF and HNO3
acids, and should be representative of the silicate fraction. Isotopic compositions were
measured by TIMS on a ThermoFisher Triton at MPIC, with Pb isotope ratios determined
using the triple-spike method.
Significant Pb isotope differences between leachates and residues were observed. The
variability in Pb isotopic composition among leachates may be attributed to variable and
distinct anthropogenic local Pb sources from Africa and South America [6], however,
residues are imprinted by filter blank contribution suggesting to avoid the quartz fiber filter
for isotopic study of aerosols. The Nd and Sr isotope ratios of aerosol leachates show similar
signatures at all three locations investigated. The nearly identical Nd and Sr isotopic
compositions in the Mali, Tobago and Virgin islands leachates are comparable to those
obtained on samples from the Bodélé depression, Northern Chad [7] and suggest a possible
common source origin.
These results identify an African source signal, in aerosols from the Virgin Islands and
Tobago collected during African dusts incursion, and thus provides evidence for transatlantic
dust transport during the spring/summer season. This, in turn, is entirely consistent with
7-day back-trajectory analysis at these locations as well as recent seasonal AOD maps
[8].
[1] Prospero et al. (1970) Earth Planet. Sci. Lett. 9, 287-293. [2] Swap et al. (1992) Tellus
44, 133-149. [3] Koren et al. (2006) Environ. Res. Lett. 1, 014005. [4] Ben-Ami et al. (2010)
Atmos. Chem. Phys. 10, 7533-7544. [5] Duce & Tindale (1991) Lim Ocean., 36, 1715-1726.
[6] Bollhöfer & Rosman (2000) Geochim. Cosmochim. Acta 64, 3251-3262. [7]
Abouchami et al. (in prep.) [8] Ridley et al. (2012) J. Geophys. Res. 117, D02202. |
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