Modifications of natural minerals by irradiation with relativistic heavy ions with and without external pressure

Irradiations with swift heavy ions have been performed using different crystalline target materials and various pressure and irradiation conditions. Changes in the crystal lattice, e.g. the production of point defects and amorphisation, have been characterised by Raman spectroscopy. The cordierite lattice is very resistant against radiation-induced damage, while the amount of volatile phases in the structural channels is significantly changed. Furthermore, a direct conversion from CO2 to CO could be evidenced. Irradiations along the different crystallographic axes did not yield sytematic differences regarding the monitored parameters. In contrast to cordierite, apatite is substantially more sensitive to radiation damage. With increasing fluence, the overall amount of amorphisation increases. However, even for the highest fluences, complete amorphisation could not be achieved. Irradiations along the different crystallographic axes show larger amounts of damage for samples irradiated parallel (0001). The application of external pressure during irradiation stabilises the lattice and can prevent amorphisation. The suitability of large-volume Paris-Edinburgh presses for in-situ irradiation with swift heavy ions could be proven

Location and distribution of micro-inclusions in the EDML and NEEM ice cores using optical microscopy and in situ Raman spectroscopy

Impurities control a variety of physical properties of polar ice. Their impact can be observed at all scales – from the microstructure (e.g., grain size and orientation) to the ice sheet flow behavior (e.g., borehole tilting and closure). Most impurities in ice form micrometer-sized inclusions. It has been suggested that these μ inclusions control the grain size of polycrystalline ice by pinning of grain boundaries (Zener pinning), which should be reflected in their distribution with respect to the grain boundary network. We used an optical microscope to generate high-resolution large-scale maps (3 μm pix^-1, 8 x 2 cm^2) of the distribution of micro-inclusions in four polar ice samples: two from Antarctica (EDML, MIS 5.5) and two from Greenland (NEEM, Holocene). The in situ positions of more than 5000 μ inclusions have been determined. A Raman microscope was used to confirm the extrinsic nature of a sample proportion of the mapped inclusions. A superposition of the 2-D grain boundary network and μ-inclusion distributions shows no significant correlations between grain boundaries and μ inclusions. In particular, no signs of grain boundaries harvesting μ inclusions could be found and no evidence of μ inclusions inhibiting grain boundary migration by slow-mode pinning could be detected. Consequences for our understanding of the impurity effect on ice microstructure and rheology are discussed

Influence of ISPs from a polar sea-ice microalga on whipped cream detected by cryo-Raman microscopy

The occurrence of recrystallization and large ice areas after storage of frozen food products makes the use of ice-structuring proteins (ISPs) in food products meaningful. Food products are frozen to extend shelf-life during long storage periods while preservation of the overall sensoric quality. Recrystallisation processes alter and, in the worst case, damage the structure of the food, resulting in an unsightly thawed e.g. cream cake or cream puff product. Freezing and freeze storage behaviour of various food products should be investigated in order to optimize the manufacturing of frozen products and to maintain the product quality with appropriate storage until the consumers usage. We present a study on the influence of ice-structuring proteins, isolated from the sea-ice microalgae Fragilariopsis cylindrus (fcISP), on frozen whipped cream. The individual phases of the frozen cream foam have been detected by cryo-Raman spectroscopy and visualized. The advantage of the unique cryo-Raman spectroscopy system available at the AWI is that the individual components can be detected not only qualitatively, but also localized in the frozen sample. We show that the fat and ice structure in frozen cream, and their temperature-induced changes, are well detectable by cryo-Raman spectroscopy. Furthermore, the effect of fcISPs on the microstructure shows an inhibition of ice recrystallization, leading to smaller grain aggregates and a finer fat distribution than without fcISPs. We therefore suggest that fcISPs are an effective mean in controlling recrystallization processes in frozen goods

Location and composition of micro-inclusions in deep ice from the EDML ice core (Antarctica) using optical microscope and cryo-Raman spectroscopy

The impurity content in meteoric ice from polar regions is relatively low compared to other natural materials. However, it controls a variety of physical properties of ice - from dielectric response to its mechanical behaviour. Links between impurity concentration, changes in ice micro-structure and deformation rate have been reported on several scales. In order to approach the responsible mechanisms, a better understanding is needed regarding the in-situ form, location, and distribution of the different species within the polycrystal. We used an optical microscope to generate high-resolution 2D-maps of micro-inclusions in deep ice from the EDML ice core (Antarctica). Superposition of the grain boundary network and micro-inclusion distributions shows no significant correlations between grain boundaries and micro-inclusions. Implications for the relevance of Zener pinning during grain boundary migration and redistribution of impurities by grain boundary drag are discussed. Raman spectra of micro-inclusions in selected regions were obtained using a confocal cryo-Raman system. Comparison with ion chromatography shows that most of the available ions in ice precipitate in form of micro-inclusions. However, indications were found that some of the residual components could coexist in form of solid solution

Microparticles and crystal microstructure in polar ice sheets

The pollution input in polar ice sheets in Greenland and Antarctica is of atmospheric aeolian origin, just as all natural non-ice impurities as well. They thus provide potential information on the evolution of the atmospheric share of pollutants in the ocean. Aerosols found in ice are transported with atmospheric circulation and wind patterns and are deposited e.g. with precipitating snow. The impurity content in this so-called meteoric ice is relatively low compared to many other natural materials such as rocks (ppb to ppm range). The reason is that most aerosols in the atmosphere have been removed by fall-out or precipitation during transport from the impurities’ sources to the remote ice sheet. Non-ice constituents in polar ice cores have been studied in the last decades mainly for reconstructions of past atmospheric aerosol concentrations, with respect to questions conceding the global climate change. The fastest and easiest analytical way is chemical analysis of the melted water from ice cores. However despite the tiny concentrations, the interactions with and effects of impurities in the solid ice influence the physical properties of the material as a whole: e.g. electric as well as dielectric response and, in particular, mechanical behaviour thus “softness” of the material seems to be strongly controlled by impurities. Smaller concentrations of impurities (up to a few ‰) do soften the material as a whole, while larger concentrations of particles harden it, depending on the type of impurities of course. The underlying processes are partly hypothesised for decades, but not yet proven or understood satisfactorily as the quest for ppb to ppm concentrations in solid matrix material is a search for a “needle in a haystack”. To improve the data basis regarding the in-situ form of incorporation and spatial distribution of impurities in ice we used micro-cryo-Raman spectroscopy to identify the location, phase and composition of micrometer-sized inclusions in natural ice samples (NEEM ice core from Greenland and EPICA-DML ice core from Antarctica). The combination of Raman results with ice-microsctructure measurements and complementary impurity data provided by the standard analytical methods (IC, CFA, and DEP) allows for a more interdisciplinary approach interconnecting ice core chemistry and ice core physics. While the samples originating from interglacial times were dominated by sulfate salts—mainly gypsum, sodium sulfate (possibly thenardite) and iron–potassium sulfate (likely jarosite)—the glacial ice contained high numbers of mineral dust particles—in particular quartz, mica, feldspar, anatase, hematite and carbonaceous particles (black carbon). We cannot confirm cumulation of impurities in the grain boundary network as reported by other studies, neither micro-particles being dragged by migrating grain boundaries nor in form of liquid veins in triple junctions. We argue that mixing of impurities on the millimeter scale and chemical reactions are facilitated by the deforming ice matrix. Refs.: doi: 10.5194/tc-11-1075-2017 doi: 10.3389/feart.2019.00020 https://www.humboldt-foundation.de/web/trilateral-jagfos-2019.html http://www.nasonline.org/programs/kavli-frontiers-of-science/past-symposia/2019-jagfos.html Invited poster

Impurity Analysis and Microstructure Along the Climatic Transition From MIS 6 Into 5e in the EDML Ice Core Using Cryo-Raman Microscopy

Impurities in polar ice cores have been studied so far mainly for the purpose of reconstructions of past atmospheric aerosol concentrations. However, impurities also critically influence physical properties of the ice matrix itself. To improve the data basis regarding the in-situ form of incorporation and spatial distribution of impurities in ice we used micro-cryo-Raman spectroscopy to identify the location, phase and composition of micrometer-sized inclusions in natural ice samples around the transition from marine isotope stage (MIS) 6 into 5e in the EDML ice core. The combination of Raman results with ice-microsctructure measurements and complementary impurity data provided by the standard analytical methods (IC, CFA, and DEP) allows for a more interdisciplinary approach interconnecting ice core chemistry and ice core physics. While the interglacial samples were dominated by sulfate salts—mainly gypsum, sodium sulfate (possibly thenardite) and iron–potassium sulfate (likely jarosite)—the glacial ice contained high numbers of mineral dust particles—in particular quartz, mica, feldspar, anatase, hematite and carbonaceous particles (black carbon). We cannot confirm cumulation of impurities in the grain boundary network as reported by other studies, neither micro-particles being dragged by migrating grain boundaries nor in form of liquid veins in triple junctions. We argue that mixing of impurities on millimeter scale and chemical reactions are facilitated by the deforming ice matrix. We review possible effects of impurities on physical properties of ice, however the ultimate identification of the deformation agent and the mechanism behind remains challenging

A large impact crater beneath Hiawatha Glacier in northwest Greenland.

We report the discovery of a large impact crater beneath Hiawatha Glacier in northwest Greenland. From airborne radar surveys, we identify a 31-kilometer-wide, circular bedrock depression beneath up to a kilometer of ice. This depression has an elevated rim that cross-cuts tributary subglacial channels and a subdued central uplift that appears to be actively eroding. From ground investigations of the deglaciated foreland, we identify overprinted structures within Precambrian bedrock along the ice margin that strike tangent to the subglacial rim. Glaciofluvial sediment from the largest river draining the crater contains shocked quartz and other impact-related grains. Geochemical analysis of this sediment indicates that the impactor was a fractionated iron asteroid, which must have been more than a kilometer wide to produce the identified crater. Radiostratigraphy of the ice in the crater shows that the Holocene ice is continuous and conformable, but all deeper and older ice appears to be debris rich or heavily disturbed. The age of this impact crater is presently unknown, but from our geological and geophysical evidence, we conclude that it is unlikely to predate the Pleistocene inception of the Greenland Ice Sheet

Raman spectroscopy on ice cores from Greenland and Antarctica

Ice cores are invaluable archives for the reconstruction of the climatic history of the earth. Besides the analysis of various climatic processes from isotopes and chemical signatures they offer the unique possibility of directly extracting the past atmosphere from gaseous inclusions in the ice. Many aspects of the formation and alterations of these inclusions, e.g. the entrapment of air at the firn-ice-transition, the formation of crystalline gas hydrates (clathrates) from the bubbles or the structural relaxation during storage of the cores, need to be better understood to enable reliable interpretations of the obtained data. Modern micro Raman spectroscopy is an excellent tool to obtain high-quality data for all of these aspects. It has been productively used for phase identification of solid inclusions, investigation of air clathrates and high-resolution measurements of N2/O2 mixing ratios inside individual air bubbles. Detailed examples of the various uses of Raman spectroscopy will be presented along with practical information about the techniques required to obtain high-quality spectra. Retrieval and interpretation of quantitative data from the spectra will be explained. Future possibilities for advanced uses of Raman spectroscopy for ice core research will be discussed

Raman tomography of natural air hydrates

Ice cores are the only climate archives incorporating paleo-atmosphere as individual gas inclusions, enabling the extraction and analysis of the contained gasses. A firm understanding of the processes involved is mandatory for a reliable interpretation of the gas records. One prominent process is the transition from air bubbles to crystalline air hydrates, which is known to influence, at least temporarily, the gas mixing ratios by diffusion and fractionation. This transition is still not understood completely and the existing theories do not explain the large diversity of observed hydrate morphologies. Raman tomographic measurements using the AWI cryo-Raman system provide 3D reconstructions of air hydrate morphologies. The results show complex growth structures that emphasize the importance of crystallography, microstructure and ice rheology for the hydrate formation process. Accurate hydrate volumes can be calculated from the 3D objects, improving the estimates of total gas contents