Doktoranden der Forschungsgruppe Grenzflächen-Geochemie werden halbjährlich über ihre bisherige Forschung berichten. Forschungs-Updates werden hier gepostet, sobald sie verfügbar sind. Updates werden nach Projekten kategorisiert.
Ruth Esther Delina, September 2021: To optimize a sequential extraction procedure tailored for Cr partitioning in tropical Fe-rich soils and sediments, I performed a series of dissolution experiments using reference Cr-bearing Fe phases. Here, I used several reagents of varying concentrations and in different conditions (e.g. time, temperature) to find the most suitable extractant for my optimized method. For example, the figure shows the mineral references reacted with hydrochloric acid (a), highlighting their dissolution at different time frames: after 10 mins (b) and after 48 h (c). Compared to previous dissolution studies of Fe minerals using this acid, I have increased the dissolution extent and drastically reduced the dissolution time of pure and metal-substituted Fe phases.
Ruth Esther Delina, März 2021: In my first six months, I focused on the syntheses of pure Fe-bearing phases (Fig. A) and metal-substituted (e.g. Cr) varieties (Fig. C) through different pathways such as transformation of ferrihydrite (Fig. B), forced hydrolysis of Fe(III) solutions, and partial oxidation of Fe(II) solutions (Fig. D-E). I characterized them using x-ray diffraction and infrared spectroscopy and prepared them for elemental analysis. During this period, I learned the effects of different physicochemical parameters such as temperature, pH, redox environment, substituting cation, etc. to the formation of Fe-oxyhydroxides. Several attempts of synthesizing Cr-hematite, for example, exhibited how Cr substitution inhibits its formation.
Zhengzheng Chen: During the first six months, I completed the first draft of the literature review and started co-precipitation experiments with different concentrations of organophosphorus and ferrihydrite, completing the adsorption of ferrihydrite on organophosphorus. The structural properties of the samples were characterized using XRD and IR. The surface area of the samples was determined by BET and so far, it appears that the surface area decreases with increasing organic concentrations.
Alice Paskin: In my research work I mainly focus on the geological relevance and phosphate recovery potential of Fe(II) based phosphate mineral vivianite, which is found widely in anoxic water bodies and soils. The broader purpose of this project is to optimize vivianite formation and the effect of various physical (pH, temperature) and chemical (organic and inorganic additives) parameters towards its formation. The analytical methods I frequently employ for my research work are pH-based kinetics, IR, powder XRD, SEM, TEM and UV-vis spectrophotometry.
Elisa Katharina Peter, August 2021: During my 2021 summer fieldwork season on the Greenland Ice Sheet I aimed to investigate the biotic and abiotic factors influencing the formation of pigments and their precursors in ice algae. Pigmented deep purple ice algae inhabit the Greenland Ice Sheet, darkening the surface, decreasing albedo and thus contributing to the acceleration of the ice melt. We presume that factors such as light, temperature, microbial community composition and cell density may influence the formation of pigments in these algae. I therefore collected samples from various habitats, throughout 24-cycles and tested processing at different temperatures. The picture above shows a collection of samples from ice-patches with distinct coloration intensities, which -after processing and analysis in our labs at GFZ- will help us better understand the darkening of the Greenland Ice Sheet.
Elisa Katharina Peter, März 2021: Within the Deep Purple project, we investigate pigmented microorganisms which inhabit the Greenland Ice Sheet and accelerate the ice melt due to surface darkening. We aim to improve our understanding of the processes governing pigment formation by investigating the metabolome of purple-brown ice algae (1) as well as red (2) and green snow algae. The picture above shows polar (1A, 2A) and non-polar (1B, 2B) intracellular metabolite extracts of ice and snow samples from our summer 2020 fieldwork. We are excited to see indications of a high abundance of water-soluble purple pigments such as purpurogallin in the ice algae and the prevalence of less polar orange and red pigments such as carotenoids in the red snow algae and look forward to the LC- and GC-MS results of our untargeted metabolome study.
Rey Mourot, September 2021: Glacier microbial communities are composed of diverse taxa from different kingdoms: archaea, bacteria, eukaryotes – especially the snow and ice algae that are the focus of Deep Purple, and viruses. To understand the state of these communities, their diversity and the inter-specific interactions at their base, my PhD project is based on the analysis of environmental samples. I was lucky to engage in several fieldwork campaigns in Svalbard and Greenland this year. On glaciers or directly on the ice sheet, snow and ice are collected following sterility procedures; brought to the field-lab and processed – most of the time filtered - to perform DNA, RNA, metabolic and chemical analyses. Filters are preserved at cold temperatures from -80°C to 4°C until arrival in the homelab at GFZ, where they are extracted, sequenced, and the data analyzed. The picture was taken during the processing of a green snow sample taken on the Feiringsbreen glacier in Svalbard, NyAlesund, in August 2021. The 0.2 micron filter retains the majority of cells, and here took the green color of the sample. On the back, a red and green snow samples are melted and ready to be processed.
Rey Mourot, März 2021: My research currently focuses on analysing the 3D structure of snow and ice in relation to the microbial communities and the amount of particles – minerals or cryoconite granules - present in the arrangement. The image presented here was obtained by computed-tomography of the snow-ice transition in an ice core taken in Greenland during summer 2020, in collaboration with Dr. John Maximilian Köhne, researcher at UFZ, Halle.
Rebecca Volkmann: To evaluate nucleation and growth processes of the mineral struvite, we conducted synthesis experiments of pure solutions of different initial concentrations at standard conditions. The crystal formation has been followed by UV-Vis spectrometry to monitor changes in turbidity that occur during crystallization. Precipitates have been imaged with the (cryo-) SEM. The next steps will include syntheses under a temperature range from approximately 5 to 50 °C as well as sample analysis and imaging to see changes in formation depending on temperature.
The image shows a turbidity [%] vs. time [s] plot of struvite formation at different solution concentrations. The first rise in turbidity refers to the induction time of crystal formation, which presents the time window until the first mineral nucleates are created. The induction time increases from 20 to 350 s with decreasing concentrations of the struvite solutions.