Mineral dust aerosols recently collected at the high-altitude Jungfraujoch research station (
Polar ice core studies document enhanced atmospheric crustal dust transport during cold glacial periods, whereas dust archived in Alpine, Himalayan, and Antarctica ice cores reveals higher continental dust deposition during the 20th-century warming [
The Sahara is the world’s major source of mineral dust, which subsequently spreads across the Mediterranean and Caribbean seas into northern South America, Central America, North America, and Europe [
This study was performed with the samples collected from the following. The Colle Gnifetti glacier saddle (CG, 45°55′50′′N, 7°52′33′′E; 4455 m a.s.l.; Figure The high-alpine research station Jungfraujoch (JFJ, 46°33′51′′N, 7°59′06′′E; 3580 m a.s.l.; Figure Fine grained sediments (till or glaciogenic clay and silt) have been collected on the Grenz Glacier (45°57′54′′N, 7°48′18′′E; 2600 m a.s.l.) in the vicinity of the
(Top) Panorama from the south of the Monte Rosa Massif showing the location of the ice core site (Colle Gnifetti glacier, CG) and the Grenz Glacier. (Bottom) Geographical map showing the 315-hour backward trajectories arriving at Jungfraujoch (JFJ), reconstructed using the NOAA HYSPLIT model (
(Left Insert) Aerial view of the Jungfraujoch (JFJ) research station. The record of black carbon (BC) concentration and the associated
Samples from the ice core were prepared in the −20°C refrigerated room at the Paul Scherrer Institute (PSI) Villigen, Switzerland. Cutting of the ice core sections and removal of possibly contaminated outer layers were performed using a precleaned stainless steel band saw. The frozen samples were then rinsed with ultrapure water (Millipore, Milli-Q, 18 MW) in a clean laboratory to remove possible surface contamination by dust and fibers from clothes. Subsequently, the samples were weighted and stored in precleaned polyethylene containers and melted at room temperature before being filtered. Afterward, cellulose membrane filters were mounted on smear slides using Canada balsam, in order to analyze total aerosol surface and mineral grain size by image analysis (details about the method in [
The preparation of the samples for trace-element and mineral matter analyses performed in this study were done in a clean room at the Institute F. -A. Forel (University of Geneva, Switzerland) using pure acids in Teflon bombs. The cellulose membrane filters were retrieved from the smear slides (see above) and cut in two parts and placed in 1.5 mL of xylene in an ultrasonic bath for 10 minutes to dissolve the Canada balsam. Afterward, the original filter was removed, and 5 mL of Milli-Q water was added in each sample. The first half of the ice core sample was filtered on Ag filter for being analyzed by X-ray diffraction, whereas the second part was digested in 1 mL HNO3 (suprapur, 65%), 2 mL of HF (suprapur, 40%), and 1 mL of HCLO4 (suprapur, 70%). Following evaporation at 150°C, 1 mL of Milli-Q water and 1 mL of HNO3 (suprapur, 65%) were successively added, and the solution was left to complete evaporation between each step. The resulting solid was finally dissolved in 8 mL of 1% HNO3 solution for chemical analysis. About 2 mL was used for elemental and REE analysis by ICPMS, while the remainder was further analyzed for isotopic composition by mass spectrometry as described in Section
Twelve ambient daily PM10 aerosols samples enriched in atmospheric dust and collected between 2008 and 2009 at the high-altitude research station JFJ were selected. The quartz fiber filters (Whatman QMA and Pallflex Tissuquartz) were placed in an ultrasonic bath for 10 min. and prepared following the method described above. Gravimetric filter measurements (PM10) were done by the Swiss National Air Pollution Monitoring Network. When sufficient dust material was present, the mean grain-size was measured with a laser granulometer (Malvern Mastersizer) by laser diffraction, after removing the organic fraction using H2O2 treatment.
Bulk dust and clay mineral analyses were performed on Ag filter, with an X’TRA-ARL (Thermo Scientific) diffractometer, using a wavelength of
The concentration of trace elements (Sc, Ti, Cs, Ba, Hf, Ta, Pb, Th, U, La) in the digested solution was measured using quadrupole-based inductively coupled plasma mass spectrometry (ICP-MS) (HP 4500, Agilent), with internal calibration by a Rh/Re solution and multielement standard solutions at different concentrations (0, 0.02, 1, 5, 20, 100, and 200 ppb) which were used for the calibration. Elemental equations in the 4500 ICP-MS ChemStation software were used for element interference corrections according to manufacturer’s recommendations. Analytical precision of concentration measurements by ICP-MS in precise mode was typically <5% for all analyzed elements. Such precision is comparable to what was preliminarily observed for a large set of international standards certified reference materials (LKSD1-LKSD4) [
Sr and Nd separation from the solutions prepared as described above was carried out using cascade columns with Sr-spec, TRU-spec, and Ln-spec resins following a modified method after Pin et al. [
In the absence of the initial sample masses for the CG core dust and for the JFJ samples, the trace element concentrations (Pb, Ti, Ba, Cs, U, and La) were normalized to conservative crustal elements (Sc, Ta, Hf, or Th) which primarily derive from wind-borne soil and rock-dust sources and expressed in the form of crustal enrichment factors (EFs) after normalization to the mean concentration ratios in the upper continental crust [
Variations in crustal element ratios are primarily influenced by total aerosol surface. Indeed, the dusty layers (>30 mm2/kg highlighted on Figure
According to the geomorphology of the two high-altitude sites, surrounded by permanent glaciers, the mineral dust air concentration is known as very low and important interruptions of this background situation only occur by the advection of air masses transporting Saharan dust [
Mineral characterization of CG and JFJ samples reveals strong similarities between modern and ancient dust composition (Figures
Sample depth (meter water equivalent, m weq.) for the Colle Gnifetti (CG) ice-core samples (upper part), sample name for the Jungfraujoch (JFJ) samples (lower part), age of sample, 87Sr/86Sr and 143Nd/144Nd isotopic compositions with 2
Sample depth (m weq.) | Apparent agea | 87Sr/86Sr FCb | 2 | 143Nd/144Nd FCc | 2 | |
---|---|---|---|---|---|---|
10.93–10.47 | 1974-1975 | 0.719775 | 2 | 0.511998 | 21 | −12.5 |
11.82–10.93 | 1971–1974 | 0.713703 | 14 | 0.512335 | 199 | −5.9 |
12.25–11.82 | 1970-1971 | 0.709416 | 12 | 0.511623 | 262 | −19.8 |
12.71–12.25 | 1968–1970 | 0.717248 | 13 | 0.512081 | 68 | −10.9 |
13.16–12.71 | 1967-1968 | 0.714732 | 15 | 0.511865 | 203 | −15.1 |
17.05–15.52 | 1952–1958 | 0.716986 | 5 | 0.511993 | 19 | −12.6 |
18.03–17.05 | 1948–1952 | 0.712315 | 25 | 0.511908 | 74 | −14.2 |
20.09–18.03 | 1939–1948 | 0.712284 | 26 | 0.512069 | 197 | −11.1 |
21.12–20.09 | 1934–1939 | 0.718733 | 14 | 0.511986 | 25 | −12.7 |
22.74–21.12 | 1926–1934 | 0.712936 | 51 | 0.511722 | 139 | −17.9 |
23.92–22.74 | 1919–1926 | 0.720629 | 3 | 0.511957 | 51 | −13.3 |
24.52–23.92 | 1916–1919 | 0.716637 | 20 | 0.512135 | 103 | −9.8 |
26.18–24.52 | 1906–1916 | 0.709494 | 42 | — | — | — |
27.14–26.18 | 1900–1906 | 0.723513 | 7 | 0.511929 | 18 | −13.8 |
28.38–27.14 | 1893–1900 | 0.713982 | 20 | 0.512110 | 40 | −10.3 |
29.61–28.38 | 1884–1893 | 0.715272 | 12 | 0.511999 | 53 | −12.5 |
30.89–29.61 | 1874–1884 | 0.719117 | 2 | 0.512011 | 11 | −12.2 |
31.50–30.89 | 1869–1874 | 0.714151 | 21 | 0.511907 | 108 | −14.3 |
34.04–31.50 | 1847–1869 | 0.711404 | 18 | 0.512005 | 55 | −12.4 |
36.55–34.04 | 1821–1847 | 0.713235 | 9 | 0.512090 | 17 | −10.7 |
38.43–36.55 | 1798–1821 | 0.711326 | 10 | 0.511911 | 44 | −14.2 |
39.10–38.43 | 1789–1798 | 0.716228 | 15 | 0.511956 | 25 | −13.3 |
39.62–39.26 | 1782–1787 | 0.726190 | 4 | 0.511967 | 8 | −13.1 |
41.57–39.62 | 1751–1782 | 0.711900 | 15 | 0.511968 | 72 | −13.1 |
42.81–41.57 | 1729–1751 | 0.712842 | 6 | 0.512382 | 28 | −5.0 |
43.43–42.81 | 1717–1729 | 0.712277 | 20 | — | — | — |
44.06–43.43 | 1704–1717 | 0.710148 | 23 | 0.511809 | 118 | −16.2 |
44.70–44.06 | 1690–1704 | 0.711321 | 16 | 0.511950 | 43 | −13.4 |
45.33–44.70 | 1675–1690 | 0.712921 | 63 | 0.511975 | 53 | −12.9 |
45.93–45.33 | 1660–1675 | 0.716865 | 34 | 0.512066 | 46 | −11.2 |
46.59–45.93 | 1642–1660 | 0.715511 | 10 | 0.511990 | 31 | −12.6 |
47.20–46.59 | 1624–1642 | 0.709537 | 15 | 0.512169 | 99 | −9.1 |
47.81–47.20 | 1605–1624 | 0.712651 | 20 | 0.511995 | 66 | −12.6 |
48.42–47.81 | 1585–1605 | 0.712811 | 30 | 0.511856 | 62 | −15.2 |
49.04–48.42 | 1563–1585 | 0.715854 | 11 | 0.511964 | 57 | −13.2 |
50.20–49.04 | 1514–1563 | 0.712714 | 37 | 0.512184 | 245 | −8.9 |
50.62–50.20 | 1495–1514 | 0.714821 | 169 | 0.511771 | 43 | −16.9 |
51.91–50.62 | 1427–1495 | 0.715864 | 5 | 0.511949 | 35 | −13.4 |
54.92–53.73 | 1187–1300 | 0.717380 | 1 | 0.512051 | 14 | −11.5 |
A | 25.06.2008 | 0.710311 | 2 | 0.511958 | 22 | −13.3 |
B | 07.08.2008 | 0.713474 | 24 | 0.512088 | 75 | −10.7 |
C | 09.09.2008 | 0.710946 | 5 | 0.512012 | 10 | −12.2 |
D | 10.09.2008 | 0.710859 | 1 | 0.512042 | 4 | −11.6 |
E | 12.10.2009 | 0.710600 | 5 | 0.512063 | 19 | −11.2 |
F | 14.10.2009 | 0.710728 | 5 | 0.512008 | 9 | −12.3 |
G | 13.05.2009 | 0.710740 | 2 | 0.512088 | 27 | −10.7 |
H | 24.05.2009 | 0.710430 | 1 | 0.512064 | 33 | −11.2 |
I | 28.05.2008 | 0.709737 | 8 | 0.512040 | 8 | −11.7 |
J | 01.06.2008 | 0.710570 | 4 | 0.512057 | 21 | −11.3 |
K | 11.09.2008 | 0.711140 | 3 | 0.512018 | 6 | −12.1 |
L | 13.10.2008 | 0.712981 | 5 | 0.512036 | 20 | −11.7 |
aThe apparent age is calculated by the age model and used to plot the results. Difference between absolute and apparent ages is discussed in the text, based on ice core absolute date (e.g., Laki volcanic layer) and radiocarbon dating.
bAll values corrected for internal mass fractionation by normalizing to 86Sr/88Sr = 0.1194 and for external fractionation by normalizing the measured SRM987 values to a SRM987 nominal value of 0.710248.
cAll values corrected for internal mass fractionation by normalizing to 146Nd/144Nd = 0.7219 and for external fractionation by normalizing the measured Jndi-1 values to a Jndi-1 value of 0.512115 [
dCalculated for a present-day CHUR value of 143Nd/144Nd = 0.512638 [
Sample depth (meter water equivalent, m weq.) for the Colle Gnifetti (CG) ice-core samples (upper part), sample name for the Jungfraujoch (JFJ) samples (middle part), and X-ray mineral composition with K/C for kaolinite/chlorite ratio. The symbol plus (minus) shows the abundance (absence) of minerals. The composition of fine-grained sediment (till or glaciogenic clay and silt) collected on the Grenz Glacier is reported (lower part) for comparison.
Sample depth (m weq.) | Apparent age | % Mica | % Kaolinite | % Chlorite | K/C | Palygorskite | Paragonite | Quartz |
---|---|---|---|---|---|---|---|---|
10.93–10.47 | 1974-1975 | 41 | 38 | 12 | 3.22 | ++ | + | +++ |
12.25–11.82 | 1970-1971 | 46 | 16 | 21 | 0.73 | − | + | − |
12.71–12.25 | 1968–1970 | 44 | 19 | 10 | 1.86 | + | + | + |
13.16–12.71 | 1967-1968 | 50 | 11 | 11 | 1.00 | + | + | − |
17.05–15.52 | 1952–1958 | 41 | 25 | 17 | 1.49 | ++ | + | ++ |
21.12–20.09 | 1934–1939 | 45 | 18 | 12 | 1.50 | ++ | + | + |
23.92–22.74 | 1919–1926 | 55 | 25 | 20 | 1.21 | + | − | +++ |
24.52–23.92 | 1916–1919 | 57 | 23 | 20 | 1.13 | ++ | − | ++ |
30.89–29.61 | 1874–1884 | 57 | 19 | 11 | 1.76 | ++ | + | ++ |
39.26–39.10 | 1788–1791 | 83 | 4 | 7 | 0.58 | +++ | + | +++ |
39.62–39.26 | 1784–1788 | 46 | 23 | 13 | 1.80 | +++ | + | ++ |
49.04–48.42 | 1563–1585 | 62 | 16 | 22 | 0.73 | + | − | + |
J | 01.06.2008 | 47 | 30 | 23 | 1.31 | ++ | − | +++ |
A | 25.06.2008 | 34 | 22 | 45 | 0.48 | + | − | +++ |
B | 07.08.2008 | 39 | 28 | 33 | 0.85 | + | − | +++ |
C | 09.09.2008 | 52 | 23 | 25 | 0.93 | ++ | − | +++ |
D | 10.09.2008 | 51 | 31 | 18 | 1.67 | ++ | + | ++ |
K | 11.09.2008 | 45 | 28 | 28 | 1 | + | − | — |
E | 12.10.2009 | 44 | 30 | 25 | 1.19 | ++ | − | +++ |
Till of the Grenz Glacier | 70 | − | 22 | − | − | − | +++ |
Sr and Nd isotopic data from Jungfraujoch samples (JFJ, crosses) and from Colle Gnifetti ice core (CG, circles) as a function of the total aerosol surface, compared to dust values from Gobi desert, China loess, Greenland ice cores (empty circles: GISP2, filled circles: GRIP), <30
X-ray diffraction (XRD) spectra of a fine-grained sediment sample (till or glaciogenic clay and silt) collected on the Grenz Glacier, from a Jungfraujoch sample (JFJ) and from two Colle Gnifetti ice-core (CG) samples enriched in Saharan dust. The minerals and the Miller indices associated with the major peaks are indicated. P: paragonite, and Pk: palygorskite.
Kaolinite-mica-chlorite triangular diagram illustrating the clay mineralogy of samples from the Colle Gnifetti ice core (CG, circles), the Jungfraujoch Research Station (JFJ, crosses), and the Grenz Glacier sample (diamond).
It is remarkable that the greatest event of the CG ice record, which encompasses a quantity of dust almost equivalent to the total remaining dust accumulated in the ice record (about 40 meters water equivalent, m weq.), is located between 39.62 and 39.10 m weq. (Figure
The Sr and Nd isotopic similarity between CG ice core data and possible African dust sources analyzed in the literature [
Figure
87Sr/86Sr values as a function of the aerosol surface, the mica and chlorite contents, and the EF Pb for the Colle Gnifetti ice-core (CG, circles) and Jungfraujoch samples (JFJ, crosses). Pre-1910 CG samples are represented by empty squares, whereas post-1910 samples are represented by filled circles. Correlation coefficients are calculated over the entire dataset (CG record and JFJ samples), except for EF Pb (CG samples after 1910). The color-shaded areas correspond to the aerosol surface classes of Figure
In order to assess the environmental factor that may influence the low Sr isotopic ratios in the depleted aerosols samples (PM10 and <10 mm2/kg) before the industrialized period (before 1850), Figure
Air-mass back-trajectories were calculated for analogs using the HYSPLIT model [
The backward trajectory arrival date and source countries of the Sahara dust events collected at the Jungfraujoch (JFJ) Research Station, PM10 values and mean grain size.
Sample name |
Backward trajectory arrival date and origin (Figure | PM10 ( | Mean ( | ||
---|---|---|---|---|---|
I | 28.05.2008 | 20 h | Libya, Tunisia | 26.2 | — |
J | 01.06.2008 | 17 h | Morocco, Algeria, Tunisia | 12 | 4.0 |
A | 25.06.2008 | 23 h | Libya, Tunisia, Algeria | 45.1 | 3.9 |
B | 07.08.2008 | 3 h | Morocco | 9.8 | 4.0 |
C | 09.09.2008 | 18 h | Algeria | 27.9 | 3.9 |
D | 10.09.2008 | 18 h | Libya, Tunisia, Algeria | 58.7 | 3.4 |
K | 11.09.2008 | 15 h | Algeria | 46.9 | — |
L | 13.10.2008 | 21 h | Algeria, Mali | 38.7 | — |
G | 13.05.2009 | 20 h | Libya, Algeria | 19 | 3.8 |
H | 24.05.2009 | 23 h | Morocco, Algeria | 22.2 | 4.3 |
E | 12.10.2009 | 23 h | West via Greenland | 1.1 | — |
F | 14.10.2009 | 12 h | West via Greenland | 1.3 | — |
The 315 h back-trajectories reaching JFJ are reported in Figure
Former mineral isotope analysis from dust deposition sites in the Alps, as well as air-mass back-trajectories analysis, evidences Saharan mineral dust, but also China loess, transported during several days along a pathway across the eastern North Atlantic and approaching the Alps from northerly direction [
The comparison of the mineral dust records from three Northern Hemisphere ice cores (Alaska, Himalayas, and Greenland) with instrumental sea-level pressure series of spring over the last century reveals consistent relationship between atmospheric circulation patterns and the long-range transport of mineral dust [
Post-1850 increase in carbonaceous residues of combustion, or black carbon (BC), and in trace elements content, highlighted the anthropogenic atmospheric pollutant emissions since the European Industrial Revolution [
The mineral composition of the dust recovered in the high-altitude glaciers of Western Alps shows a relatively similar mineralogical composition (e.g., quartz and micas) as the local glaciogenic fine-grained sediments. However, the presence of kaolinite and palygorskite in the JFJ and CG samples clearly identify Saharan source, whereas these minerals were not observed in the silt and clay samples collected in the Grenz Glacier tills which show high amount of serpentines and amphibole. Saharan has been already identified as being the main source of the dust input over the high-altitude glaciers of the Western Alps during the last decades, and the isotopic signature of the insoluble aerosols transported to the Jungfraujoch research station and the Colle Gnifetti glacier further reveal (i) a Saharan-derived source for the higher fluxes of dust transported by southwesterly winds during last centuries and (ii) low radiogenic Sr values for the daily PM10 aerosols and for the ice deposited during periods of low dust deposition. These results suggest a physical and chemical weathering effect on isotopic and elemental fractionations that requires further investigation on granulometric and mineralogical aerosol fractions.
The comparison of the Sr and Nd isotopic signatures from CG with those from Greenland cannot exclude that the Saharan dust sources possibly contribute, together with the Asian sources, to the long-range aeolian mineral aerosols deposited over Greenland during the last glacial period. However, further work based on the dust mineralogy and geochemistry of the geological sources and weathering/transport history are needed to address this hypothesis. Crustal element enrichment, mineral composition, and Sr/Nd isotopic analyses demonstrate that North Africa was the most important supplier of mineral dust to the Western Alps throughout the last millennium. Highly resolved geochemical records of water soluble material from CG ice archive can therefore provide new perspectives on our understanding of interannual atmospheric circulation changes at this latitude and large-scale atmospheric interconnection patterns (e.g., NAO, MOC).
The Colle Gnifetti ice-core samples were provided while F. Thevenon was at the Geological Institute of ETH Zürich, with the support of Margit Schwikowski from the Paul Scherrer Institute and University of Bern (Switzerland). The drilling team, Paolo Gabrielli, Frederic Planchon, Beat Rufibach, Aurel Schwerzmann, Margit Schwikowski, and Dieter Stampfli is acknowledged for recovery of the Colle Gnifetti ice core. The coring was partly funded by the NCCR Climate project of the Swiss National Science Foundation (projects VITA and VIVALDI), the EU FP6 project MILLENNIUM (017008), the Istituto Nazionale per la Ricerca Scientifica e Tecnologica sulla Montagna (INRM) and the Agence de l'Environnement et de la Maîtrise de l'Energie (ADEME). The present research work was financially supported by a grant from the Swiss National Science Foundation (SNSF Ambizione fellowship PZ00P2_121994). The authors thank Martine Collaud Coen (MeteoSwiss, Payerne) for fruitful scientific exchanges on air-mass back-trajectories, Michèle Senn and Denis Fontignie (Department of Mineralogy, Geneva) for technical support in the sample preparation, and T. M. Jenk and M. Sigl for giving access to the age model of CG core. They thank anonymous reviewers for their constructive comments that led to a substantial improvement in the paper.