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We will present the EGRIP CPO (c-axes fabric) dataset and give preliminary interpretations concerning the processes leading to its evolution. 120 bags were selected, with a minimum depth resolution of 15m. Bags were mostly measured continuously, and in total 778 thin sections were prepared, measured and pre-processed on site. Thus, c-axes distribution CPO data are already available, while other parameters on grain stereology are still to be processed at this stage. The CPO patterns found in the upper 1650m at EGRIP show (1) a rapid evolution of c-axes anisotropy compared to lower dynamics sites and (2) partly novel characteristics in the CPO patterns. (1) Starting the measurements at 118m of depth we find a very broad single maximum distribution. The c-axes align with depth in the upper 400m much more rapidly than seen in ice cores from divides or domes. Down to only 140m depth the almost random CPO develops into a very broad single maximum which is similar to those CPOs found in the shallowest samples of other ice cores. Possible interpretations of these distributions are deformation by vertical compression from overlying layers, or alternatively a temperature-gradient snow metamorphosis. This weak CPO pattern is, however, quickly overprinted in the depth zone below 140m where a progressive evolution towards a vertical girdle distribution is observed. As vertical girdles are produced by extension along flow, the observed distribution indicates that the ice at this depth is deforming rather than just being translated by rigid block movement. From approximately 600m of depth downward we observe crystal orientation anisotropy of a strength comparable to samples from ~1400m of depth at divides (NEEM and EDML). This strong girdle CPO remains rather stable down to approximately 1300m depth, where we reach the ice deposited during the last glacial period. A novel pattern, not observed before in natural ice, is a higher densities of c-axes horizontally oriented within the vertical girdle. (2) The early onset of deformation seems further supported by the observation of a broad “hourglass shaped” girdle, which seems to develop in some depths into a “butterfly shaped” cross girdle. Another characteristic deserves attention: the distribution density within the girdle. In contrast to observations in deep ice cores so far, the highest density seems to deviate from the vertical direction being (sub-)parallel to the horizontal. The origin of this may lay in the main deformation modes, e.g. a combination of along flow extension with additional deformation modes. Especially interesting is the cross girdle, which has not yet been observed in polar ice cores so far. We suggest three possible interpretations for its origin: a) In other materials, such as quartz, cross girdles can be interpreted as activation of multiple dislocation slip systems. b) Alternatively, the CPO pattern may reflect reminiscent features from previous deformation modes, which the ice experienced upstream or possibly even outside of the ice stream. This memory effect would point to a relevance of strain dependence of the CPO. c) The cross- /double-girdle might be caused by the early onset of dynamic migration recrystallization under horizontal uniaxial extension.

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.

Behavior of Earth’s ice sheets is intensely monitored via surface and remote sensing techniques to improve predictions of sea level evolution. Radio echo sounding along with drilling ice cores are currently used to monitor the Earth’s ice sheets behaviour not only from the surface but in the 3rd dimension. Particularly the ice material properties can only be accessed via ice drilling. These properties control the deformation in general, and particularly strain localization such as observed in ice streams, which supply the major discharges into the oceans. Currently the first ice core on an active ice stream, the North-East Greenland Ice Stream (NEGIS) is being drilled. EastGRIP (East Greenland Ice-Core Project, http://eastgrip.org) drilling started in 2016 and will be ongoing until 2019. This is the first chance to study ice microstructure from a dynamically active region (www.awi.de/en/focus/eisschilde/eis-ist-ein-heisses-material.html), with a deformation regime differing from the usual locations of previous long ice cores. Those were usually placed on domes or on ice divides due to straightforward kinematics and deformation rates which is advantageous for paleo-climate reconstruction from ice core records. We present CPO (c-axes fabric) and the grain size measurements of the uppermost 350m, the depth to which the ice core has been processed for analysis so far (275 thin sections discontinuous with 10m depth resolution). The CPO patterns found in the upper 350m at EastGRIP show (1) a more rapid evolution of c-axes anisotropy with depth compared to other ice cores and (2) partly novel characteristics in the caxes distributions. (Remark: This is an invited poster.)

The aim of this study was to determine relations between the impurity content and the microstructural features of natural ice using Raman spectroscopy. It should be investigated whether certain chemical species can be related to microstructural features, such as grain boundaries. The method of Raman spectroscopy enables to measure the particles in situ without melting the ice samples. Fourteen bags of the NEEM ice core (North Greenland Eemian Ice Drilling), drilled from different depths, were chosen. As a first step, data from fabric analysis (mean grain size and eigenvalue 3) were plotted together with data for the major ions obtained from continuous flow analysis and correlation coefficients between those parameters were calculated. The statistically significant correlations between the chemical and physical parameters remained sporadic. For a case study, two sections from Holocene ice from a depth of 739,75 m to 740,30 m were chosen. After mapping the microstructure of the sections, particles were labelled and counted (from a layer with a focal depth of approximately 500 μm). Using Raman spectroscopy the particles were measured in-situ and the chemical species of most of the compounds could be identified. The major components were sulfate, silica particles, TiO2, some organic species and black carbon, which mostly appeared as a mixed signal. No carbonates were found and no Raman spectra could be obtained from grain boundaries or triple junctions. The particles often appeared to be in clusters or conglomerates. The location of the particles in relation to grain boundaries was difficult to assess due to relaxation of the ice.

Predicting future climate requires deep understanding of past climatic processes. Deep ice cores drilled in Greenland and Antarctica provide an excellent archive for climate proxies, which can be extracted by several methods. Flow properties of ice sheets can be derived by measuring c-axes orientations; furthermore trace elements and impurities can help to reconstruct atmospheric circulation patterns and provide information about the paleo-temperature. It is assumed that the impurity content of the ice does influence the grain size as well as c-axes orientations. The aim of this thesis is to investigate the relations between impurities and ice microstructure statistically. This was done by calculating correlations (Pearson and Spearman) and cross-correlations between mean grain sizes, c-axes orientations and chemical components. The data for the calculations was taken from four bags of the NEEM ice core (North Greenland Eemian Ice Drilling), drilled at depths of approximately 1845 m to 2202 m. The correlation coefficients showed only very weak statistical relations between the parameters. However, during preparation and measurement of the samples as well as during processing of the data, several error sources could be detected, possibly causing slight distortions of the results.