Report of the JARE-54 and BELARE 2012-2013 joint expedition to collect meteorites on the Nansen Ice Field, Antarctica

第54次日本南極地域観測隊員4名とベルギー南極観測隊員6 名の合計10名から構成される隕石探査隊は，2012年12月から2013年2月まで，セール・ロンダーネ山地南部に広がるナンセン氷原（南緯72°30′-73°，東経23°-25°，標高約2900-3000m）において隕石探査を実施した．ナンセン氷原には2012年12月26日から2013年2月2日まで39日間滞在した．今回の探査域は第29次日本南極地域観測隊以降探査が行われていない．探査の結果，採集した隕石の総数は424個，合計重量は約70kgであった．隕石発見地点は携帯GPSに記録されたので，探査域における隕石の分布が明確になった．これは隕石集積機構解明のための基礎データだけでなく，今後の探査計画に活用できる．本稿は主に日本隊による準備期間を含む実施報告書である．This paper reports on a joint expedition (JARE-54 and BELARE 2012-2013) that conducted a search for meteorites on the Nansen Ice Field, Antarctica, in an area south of the Sor Rondane Mountains (72°30′-73°S, 23°-25°E; elevation 2900-3000 m). The expedition took place over a period of 39 days during the austral summer, between 26 December 2012 and 2 February 2013. The team consisted of ten members: three researchers and one field assistant from the 54th Japanese Antarctic Research Expedition (JARE-54), and five researchers and one field assistant from the Belgian Antarctic Expedition (BELARE) 2012-2013. Previously, this area had only been searched by JARE-29. The team collected 424 meteorites, which had a total weight of about 70 kg. The search tracks of the ten members of the expedition were recorded using hand-held GPS units, and this allowed the distribution of meteorites within the searched area to be mapped. The resultant data will be useful for planning future expeditions and can be used to clarify the meteorite concentration mechanism on the ice field. This paper focuses on the activities of JARE-54 during the joint expedition

Archean lithospheric differentiation: Insights from Fe and Zn isotopes

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Archean Lithospheric differentiation: Insights from Fe and Zn isotopes

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First Multi-Isotopic (Pb-Nd-Sr-Zn-Cu-Fe) Characterisation of Dust Reference Materials (ATD and BCR-723): A Multi-Column Chromatographic Method Optimised to Trace Mineral and Anthropogenic Dust Sources

Atmospheric dust is an integral component of the Earth system with major implications for the climate, biosphere and public health. In this context, identifying and quantifying the provenance and the processes generating the various types of dust found in the atmosphere is paramount. Isotopic signatures of Pb, Nd, Sr, Zn, Cu and Fe are commonly used as sensitive geochemical tracers. However, their combined use is limited by the lack of (a) a dedicated chromatographic protocol to separate the six elements of interest for low-mass samples and (b) specific reference materials for dust. Indeed, our work shows that USGS rock reference materials BHVO-2, AGV-2 and G-2 are not applicable as substitute reference materials for dust. We characterised the isotopic signatures of these six elements in dust reference materials ATD and BCR-723, representatives of natural and urban environments, respectively. To achieve this, we developed a specific procedure for dust, applicable in the 4–25 mg mass range, to separate the six elements using a multi-column ion-exchange chromatographic method and MC-ICP-MS measurements.SCOPUS: ar.jinfo:eu-repo/semantics/publishe

Successful Joint Field Campaigns for Collecting Meteorites in Antarctica: An Efficient Collaboration between Japan and Belgium

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Mineralogical and geochemical characterization of Saharan dust sources based on an approach combining field measurements and remote sensing data

International audienceMineral dust is an active component of the climate system. Dust can absorb and/or scatter solar and terrestrial radiations and may act as condensation or ice nuclei in the atmosphere. Eolian mineral particles therefore have an impact on the radiative balance of the earth surface-atmosphere system and on the hydrological cycle. Dust plays an additional role as a fertilizer by supplying iron and phosphorous, among other micronutrients, to oceanic and terrestrial ecosystems, potentially boosting the biological productivity in some regions. Besides, mineral dust has also an impact on air quality. The optical and hygroscopic properties of the dust, as well as its biogeochemical and health impact, depend on its mineralogical and chemical composition as well as on its grain size. The Sahara/Sahel is by far the most important dust source region in the world ; it is estimated that several hundreds of Tg of Saharan dust is injected in the atmosphere every year, most of which in the direction of the North-eastern Tropical Atlantic Ocean (Yu et al. 2015). Considering the vastness of the Saharan desert and the intermittency of dust emission, however, Saharan dust geochemical composition is poorly constrained. The main objective of this work is to improve our knowledge of the mineralogical and geochemical composition of the Saharan dust sources, particularly those responsible for long-range transport over the Atlantic Ocean (see joint presentation by Aloys Bory et al.).This study combines remote sensing data and field measurements. First, we use the IDDI (Infrared Difference Dust Index) satellite product to identify the geographical location of Saharan dust sources (Legrand, Plana-Fattori, and N’doumé 2001). This satellite product takes advantage of Meteosat Infrared imagery and is based on the impact of aerosols on thermic infrared radiance. The difference of brightness temperature is calculated using a reference value given by the maximal brightness temperature during a period of 15 days centred on the day of interest. Indeed, ground brightness temperature can be up to 15-to-20°C lower with dust than without. A database of 24 years of IDDI images (1982-2006) is available for this study. This time series enables us to establish a new mapping of dust emission in the Sahara-Sahel region and its temporal variability throughout the year. IDDI monthly means will be discussed in the light of other available satellite products such as TOMS/OMI (Prospero 2002) or BMDI/DSA (Schepanski et al. 2007).The mineralogical and geochemical characterization of Saharan dust is based on a time series of dust samples collected at M’bour in Senegal (80 km south of Dakar) since 2006 on the premises of the Institut de la Recherche et du Développement (IRD) ecological center. Total dust deposition has been collected using a Capyr-type reversed pyramid-shaped PVC passive collector installed at about 12 m above ground on a sampling tower facing the Atlantic Ocean. We will present results from a selection of samples collected during major Saharan dust outbreaks originating from various sectors of West Africa. These samples are currently being characterized mineralogically (clay mineral assemblages) and geochemically (major and trace elements, including REE, as well as Sr and Nd isotopes). The observed mineralogical and geochemical differences observed at M’bour will be tracked as precisely as possible to the likely sources, on the basis of back trajectories computed with the HYSPLIT model and the IDDI source map. This study complements earlier work from Skoniecnzy et al. (Skonieczny et al. 2013) and should enable us to provide a preliminary characterization of the mineralogical and chemical signatures of several important sources in West Africa.AcknowledgementsWe gratefully thank Kristin Schepanski for grating us access to her BMDI/DSA data. ReferencesLegrand, M., A. Plana-Fattori, and C. N’doumé. 2001. “Satellite Detection of Dust Using the IR Imagery of Meteosat: 1. Infrared Difference Dust Index.” Journal of Geophysical Research: Atmospheres 106 (D16): 18251–74. https://doi.org/10.1029/2000JD900749.Prospero, Joseph M. 2002. “Environmental Characterization of Global Sources of Atmospheric Soil Dust Identified with the NIMBUS 7 Total Ozone Mapping Spectrometer (TOMS) Absorbing Aerosol Product.” Reviews of Geophysics 40 (1). https://doi.org/10.1029/2000RG000095.Schepanski, K., I. Tegen, B. Laurent, B. Heinold, and A. Macke. 2007. “A New Saharan Dust Source Activation Frequency Map Derived from MSG-SEVIRI IR-Channels.” Geophysical Research Letters 34 (18). https://doi.org/10.1029/2007GL030168.Skonieczny, C., A. Bory, V. Bout-Roumazeilles, W. Abouchami, S.J.G. Galer, X. Crosta, A. Diallo, and T. Ndiaye. 2013. “A Three-Year Time Series of Mineral Dust Deposits on the West African Margin: Sedimentological and Geochemical Signatures and Implications for Interpretation of Marine Paleo-Dust Records.” Earth and Planetary Science Letters 364 (February): 145–56. https://doi.org/10.1016/j.epsl.2012.12.039.Yu, Hongbin, Mian Chin, Huisheng Bian, Tianle Yuan, Joseph M. Prospero, Ali H. Omar, Lorraine A. Remer, et al. 2015. “Quantification of Trans-Atlantic Dust Transport from Seven-Year (2007–2013) Record of CALIPSO Lidar Measurements.” Remote Sensing of Environment 159 (March): 232–49. https://doi.org/10.1016/j.rse.2014.12.010.</ul

Elemental and isotopic (Sr and Nd) characterization of deposited dust on the Senegalese margin and implications for Saharan dust source geochemical fingerprinting

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Zn isotope heterogeneity in the continental lithosphere: New evidence from Archean granitoids of the northern Kaapvaal craton, South Africa

The Zn isotope data (expressed as δ66Zn) of 25 Archean crustal rocks (3.4–2.7 Ga) from the Pietersburg block in the northern part of the Kaapvaal craton (South Africa) exhibit a range from + 0.26 ± 0.04‰ to + 0.46 ± 0.04‰. This indicates the existence of resolvable Zn isotope heterogeneity in the continental lithosphere. Because the samples are representative of the processes of continental crust formation and evolution in the Archean, we propose that such Zn isotope heterogeneity is linked to early continental lithosphere formation and stabilisation. Among the crustal rock samples, two samples from the 2.97 Ga-old Rooiwater layered intrusion show indistinguishable δ66Zn of ca. + 0.28‰, which suggests that the Archean mafic mantle-derived rocks had the same isotopic composition as modern basalts (ca. + 0.22 to + 0.36‰) and the Earth's mantle (ca. + 0.30‰). Tonalite-trondhjemite-granodiorite (TTG) samples with ages of 3.43, 2.95 and 2.78 Ga, representing the first felsic continental crust formed in the studied area, have similar δ66Zn composition as the Earth's mantle (ca. + 0.30‰), irrespective of their ages, tectonic setting and petrogenesis. This indicates that formation of early, juvenile felsic crust either by melting or crystallization of basalts did not significantly fractionate Zn isotopes, or at least was associated with an equilibrium Zn fractionation process. The biotite-granites (2.85–2.75 Ga) have homogenous Zn isotope compositions with an average of δ66Zn = + 0.44 ± 0.04‰. The biotite-granites in Archean terranes are interpreted as partial melts from pre-existing TTGs. This suggests that reworking of the early felsic crust through partial melting does fractionate Zn isotopes up to + 0.15‰. This presumably results from disequilibrium kinetic fractionation during partial melting process, rather than an influence from the source component-related signature. Enriched mantle-derived sanukitoids have δ66Zn identical to that of the mantle (ca. + 0.30‰), indicating that Zn isotope fractionation would be relatively insensitive to mantle metasomatism and indicate the ultimate mantle origin of mafic sanukitoids rocks. Zinc isotopic compositions are useful to clarify the complex petrogenesis of intermediate, felsic sanukitoids and high-K cac-alkaline granites, especially to discriminate differentiation processes from the influence of interactions with the local felsic crust and its melting products at the time of magma emplacement