Sr‐Nd‐Hf Isotopic Analysis of <10 mg Dust Samples: Implications for Ice Core Dust Source Fingerprinting

Abstract

Combined Sr‐Nd‐Hf isotopic data of two reference materials (AGV‐1/BCR2) and 50, 10, and 5 mg aliquots of carbonate‐free fine grain (<10 μm) separates of three loess samples (Central Europe/NUS, China/BEI, USA/JUD) are presented. Good agreement between measured and reference Sr‐Nd‐Hf isotopic compositions (ICs) demonstrate that robust isotopic ratios can be obtained from 5 to 10 mg size rock samples using the ion exchange/mass spectrometry techniques applied. While 87Sr/86Sr ratios of dust aluminosilicate fractions are affected by even small changes in pretreatments, Nd isotopic ratios are found to be insensitive to acid leaching, grain‐size or weathering effects. However, the Nd isotopic tracer is sometimes inconclusive in dust source fingerprinting (BEI and NUS both close to ɛNd(0) –10). Hafnium isotopic values (<10 μm fractions) are homogenous for NUS, while highly variable for BEI. This heterogeneity and vertical arrays of Hf isotopic data suggest zircon depletion effects toward the clay fractions (<2 μm). Monte Carlo simulations demonstrate that the Hf IC of the dust <10 μm fraction is influenced by both the abundance of zircons present and maturity of crustal rocks supplying this heavy mineral, while the <2 μm fraction is almost unaffected. Thus, ɛHf(0) variations in the clay fraction are largely controlled by the Hf IC of clays/heavy minerals having high Lu/Hf and radiogenic 176Hf/177Hf IC. Future work should be focused on Hf IC of both the <10 and <2 μm fractions of dust from potential source areas to gain more insight into the origin of last glacial dust in Greenland ice cores.

Greenland Ice Core Record of Last Glacial Dust Sources and Atmospheric Circulation

“…Hafnium isotope ratios have only been used once, to our knowledge, in ice core dust source discrimination on the Dye‐3 ice core (Lupker et al., 2010), partly because of analytical issues, low amount of ice core dust available and the scarcity of 176 Hf/ 177 Hf data from the fine fractions of PSA samples. Bulk samples of wind‐blown sediments are dominated by zircons having extremely high Hf contents (Hoskin & Schaltegger, 2003) and unradiogenic 176 Hf/ 177 Hf ratios (Újvári & Klötzli, 2015), while the clay fractions contain little zircon (Újvári et al., 2018). This is further evidenced in Figure S16 of Supporting Information (Text S8 in Supporting Information ), where zircon depletion toward the finer grain size fractions of Quaternary aeolian loess, paleosol and red clay samples is clearly visible in the Zr, Hf concentration and Nd–Hf isotope data sets.…”

“…Nd and Hf isotopic ratios are also reported as ε Nd(0) = (( 143 Nd/ 144 Nd sample / 143 Nd/ 144 Nd CHUR ) −1) × 10 4 and ε Hf(0) = (( 176 Hf/ 177 Hf sample / 176 Hf/ 177 Hf CHUR ) −1) × 10 4 in this study using the present‐day chondritic uniform reservoir (CHUR) values of 0.512630 ± 0.000011 and 0.282785 ± 0.000011 (Bouvier et al., 2008). Uncertainties of ε Nd(0) and ε Hf(0) values were propagated as $$\sqrt{{\left((\partial \varepsilon /\partial x){\sigma }_{x}\right)}^{2}+{\left((\partial \varepsilon /\partial y){\sigma }_{y}\right)}^{2}}=\sqrt{{\left((1/y)10000{\sigma }_{x}\right)}^{2}+{\left(\left(-x/{y}^{2}\right)10000{\sigma }_{y}\right)}^{2}}$$, where ε = ε Nd(0) or ε Hf(0), x = 143 Nd/ 144 Nd sample or 176 Hf/ 177 Hf sample , y = 143 Nd/ 144 Nd CHUR or 176 Hf/ 177 Hf CHUR , σ x and σ y are uncertainties of x and y (Újvári et al., 2018). Further information on reproducibility of Sr–Nd–Hf isotope measurements can be found in Text S3 and Figures S3‐S4 of Supporting Information .…”

Three North African dust source areas and their geochemical fingerprint

“…Although there appears to be a wide acceptance in the literature (e.g. Feng et al, 2009;Grousset et al, 1992;Meyer et al, 2011;Újvári et al, 2018) that Nd isotopes do not fractionate with increased weathering and decreasing grain size, this perception stems from data reported on only one or two samples (Goldstein et al, 1984;Grousset et al, 1998).…”

Saharan dust and giant quartz particle transport towards Iceland

“…Pleistocene glacial dust deposition in the Arctic has been extensively studied in ice cores from Greenland, and potential dust sources have been reported for Asia, North America, and the Sahara 63 – 67 . Several studies have eliminated North Africa as a probable dust source region based on clay mineralogical and Sr/Nd isotopic considerations 63 , 64 .…”