SEGH Articles

Dust Deposition in snow from NorthEast Antarctica: mineralogical, morphological and chemical characterization

05 October 2014
Aubry Vanderstraeten is a PhD student and won the runner-up prize for best student poster at SEGH 2014.

 

Mineral dusts are a major source of micronutrients (e.g. Fe) that limit phytoplankton growth in the open ocean, in particular in the so-called “High Nutrient Low Chlorophyll” (HNLC) oceanic zones. The southern Ocean is by far the largest of all HNLC regions and thus has the potential to greatly enhance the biological CO2 pump at the global scale. As the aerosol fluxes and sources in the southern Ocean are not well constrained and the potential impact of anthropogenic airborne particles may be larger than expected, a multidisciplinary study is being carried out on dust-bearing snow samples collected in NE Antarctica. Our goals are multiple: (i) determine the mineralogy, morphology and chemical composition of these dusts and, (ii) quantify, by using heavy stable isotopic signatures, the origin and the relative contribution of desert-derived, volcanic and anthropogenic particles in the dust, (iii) estimate the bioavailable fraction of bio-essential elements such as Fe through chemical extraction.

Snow samples were collected at four sites: two a few kilometres from the sea, at the summit of the Derwael Ice Rise (about 200km North of the Belgian Princess Elisabeth Station) and two other locations in a continental area (~225km inland) around the Princess Elisabeth station in the Sør Rondane Mountains. Three litres of snow from each site were melted and filtrated on 0.2 µm poresize NucleporeÓ polycarbonate filters in an ISO 5-class clean room. Subsequently, a series of single particle analyses were performed by (i) FEG-SEM (Field Emission Gun-Scanning Electron Microscopy) to determine particles-size distribution of dust; (ii) automated-SEM-EDS (Energy Dispersive Spectroscopy) to estimate the chemical composition of individual dust particles; (iii) TEM-SAED analysis (Transmission Electron Microscopy Selected Area Electron Diffraction) to identify the minerals present. In addition, trace element compositions of the bulk samples were analyzed by high-resolution ICP-MS.

Preliminary data in elemental composition and mineralogy indicate similarities between dust samples and the rock-forming minerals from the Sør Rondane Mountains suggesting a local dust source. However, major distinctions can be made between coastal and inland dust samples: (i) mineralogical distributions are very distinct; (ii) a large proportion of the quartz and feldspath dust particles exhibit surprisingly enrichment in iron (less than 20% of particles for inland samples and up to 80% for coastal samples), which is probably due to surface Fe-rich coating/aggregates; (iii) coastal samples are heavily enriched (vs. upper continental crust reference values) in Pb and Ni. These Fe, Pb and Ni enrichment trends tend to suggest an external and distal source of dust at the coast, potentially impacted by anthropogenic activities.

To complement those preliminary results, new sampling campaign will take place in December 2014 at the same locations to acquire large quantity of snow. In addition, passive dust collectors will be placed for a period of one year along a transect connecting the Sør Rondane Mountains and the Derwael Ice Rise. The perspectives of this new sampling campaign aim to fulfil our analysis plan through isotopic analyses and chemical extractions.

This in-depth characterisation study will improve our knowledge and understanding of dusts reaching the coast of NE-Antarctica, which represent a proxy of the dust materials supplied to the Southern Ocean. 

by Aubry Vanderstraeten, PhD student

Keep up to date

Submit Content

Members can keep in touch with their colleagues through short news and events articles of interest to the SEGH community.

Science in the News

Latest on-line papers from the SEGH journal: Environmental Geochemistry and Health

  • Fertilizer usage and cadmium in soils, crops and food 2018-06-23

    Abstract

    Phosphate fertilizers were first implicated by Schroeder and Balassa (Science 140(3568):819–820, 1963) for increasing the Cd concentration in cultivated soils and crops. This suggestion has become a part of the accepted paradigm on soil toxicity. Consequently, stringent fertilizer control programs to monitor Cd have been launched. Attempts to link Cd toxicity and fertilizers to chronic diseases, sometimes with good evidence, but mostly on less certain data are frequent. A re-assessment of this “accepted” paradigm is timely, given the larger body of data available today. The data show that both the input and output of Cd per hectare from fertilizers are negligibly small compared to the total amount of Cd/hectare usually present in the soil itself. Calculations based on current agricultural practices are used to show that it will take centuries to double the ambient soil Cd level, even after neglecting leaching and other removal effects. The concern of long-term agriculture should be the depletion of available phosphate fertilizers, rather than the negligible contamination of the soil by trace metals from fertilizer inputs. This conclusion is confirmed by showing that the claimed correlations between fertilizer input and Cd accumulation in crops are not robust. Alternative scenarios that explain the data are presented. Thus, soil acidulation on fertilizer loading and the effect of Mg, Zn and F ions contained in fertilizers are considered using recent \(\hbox {Cd}^{2+}\) , \(\hbox {Mg}^{2+}\) and \(\hbox {F}^-\) ion-association theories. The protective role of ions like Zn, Se, Fe is emphasized, and the question of Cd toxicity in the presence of other ions is considered. These help to clarify difficulties in the standard point of view. This analysis does not modify the accepted views on Cd contamination by airborne delivery, smoking, and industrial activity, or algal blooms caused by phosphates.

  • Effects of conversion of mangroves into gei wai ponds on accumulation, speciation and risk of heavy metals in intertidal sediments 2018-06-23

    Abstract

    Mangroves are often converted into gei wai ponds for aquaculture, but how such conversion affects the accumulation and behavior of heavy metals in sediments is not clear. The present study aims to quantify the concentration and speciation of heavy metals in sediments in different habitats, including gei wai pond, mangrove marsh dominated by Avicennia marina and bare mudflat, in a mangrove nature reserve in South China. The results showed that gei wai pond acidified the sediment and reduced its electronic conductivity and total organic carbon (TOC) when compared to A. marina marsh and mudflat. The concentrations of Cd, Cu, Zn and Pb at all sediment depths in gei wai pond were lower than the other habitats, indicating gei wai pond reduced the fertility and the ability to retain heavy metals in sediment. Gei wai pond sediment also had a lower heavy metal pollution problem according to multiple evaluation methods, including potential ecological risk coefficient, potential ecological risk index, geo-accumulation index, mean PEL quotients, pollution load index, mean ERM quotients and total toxic unit. Heavy metal speciation analysis showed that gei wai pond increased the transfer of the immobilized fraction of Cd and Cr to the mobilized one. According to the acid-volatile sulfide (AVS) and simultaneously extracted metals (SEM) analysis, the conversion of mangroves into gei wai pond reduced values of ([SEM] − [AVS])/f oc , and the role of TOC in alleviating heavy metal toxicity in sediment. This study demonstrated the conversion of mangrove marsh into gei wai pond not only reduced the ecological purification capacity on heavy metal contamination, but also enhanced the transfer of heavy metals from gei wai pond sediment to nearby habitats.

  • Cytotoxicity induced by the mixture components of nickel and poly aromatic hydrocarbons 2018-06-22

    Abstract

    Although particulate matter (PM) is composed of various chemicals, investigations regarding the toxicity that results from mixing the substances in PM are insufficient. In this study, the effects of low levels of three PAHs (benz[a]anthracene, benzo[a]pyrene, and dibenz[a,h]anthracene) on Ni toxicity were investigated to assess the combined effect of Ni–PAHs on the environment. We compared the difference in cell mortality and total glutathione (tGSH) reduction between single Ni and Ni–PAHs co-exposure using A549 (human alveolar carcinoma). In addition, we measured the change in Ni solubility in chloroform that was triggered by PAHs to confirm the existence of cation–π interactions between Ni and PAHs. In the single Ni exposure, the dose–response curve of cell mortality and tGSH reduction were very similar, indicating that cell death was mediated by the oxidative stress. However, 10 μM PAHs induced a depleted tGSH reduction compared to single Ni without a change in cell mortality. The solubility of Ni in chloroform was greatly enhanced by the addition of benz[a]anthracene, which demonstrates the cation–π interactions between Ni and PAHs. Ni–PAH complexes can change the toxicity mechanisms of Ni from oxidative stress to others due to the reduction of Ni2+ bioavailability and the accumulation of Ni–PAH complexes on cell membranes. The abundant PAHs contained in PM have strong potential to interact with metals, which can affect the toxicity of the metal. Therefore, the mixture toxicity and interactions between diverse metals and PAHs in PM should be investigated in the future.