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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.

New and more detailed investigations from the EGRIP physical properties dataset down to 1650m of the ice core will be presented. EGRIP is the first deep ice core through one of our Earth’s ice sheets partly motivated by ice dynamics’ research. It is drilled just downstream of the onset of the largest ice stream in Greenland (North East Greenland Ice Stream). Data processing of the collected ice core physical properties data was done at the Alfred Wegener Institute Helmholtz Centre for Marine and Polar Research. The two main findings regarding CPO (c-axes fabric) pattern, 1) a rapid evolution of c-axes anisotropy and 2) partly novel characteristics, were further, and in more detail, investigated. To gain a better understanding of the dominating deformation mechanisms of NEGIS, different approaches considering different length scales were chosen (1650m versus 0.55m and 0.09m scale), including several case studies. A large-scale statistical analysis of the entire dataset results in new information about the depth-dependent evolution of parameters as for example the strength of c-axes anisotropy and grain-size in the polycrystal. In general, mean grain-size decreases with depth as we drill through the Holocene ice and approach the Glacial material. The grain size variability with fine and coarse grain layers is extreme in the Holocene ice but decreases in the Glacial ice. Microstructure properties were examined, with the aim to investigate the relationship between the remarkable rapid evolution of CPO-pattern and grain properties evolution. Furthermore, the evolution of a grain-size dependent anisotropy, found in the first 350m of the ice core, is investigated and examined also in deeper sections of the core. The large-scale evolution of density distributions of c-axes orientations differ significantly from observations in deep ice cores made so far: A novel "hourglass shaped" girdle was observed, characterized by a high density of horizontally oriented c-axes within the vertical girdle. In some parts of the core, this shape develops into a "butterfly shaped" cross girdle, varying in intensity and strength. It is the first time that this cross girdle was observed in polar ice and by combining approaches considering different length scales, we aimed to verify one of our three hypotheses for its origin: a) activation of multiple dislocation slip systems (in analogy to quartz), b) a memory effect or reminiscent features from older deformation modes, further upstream or even outside of NEGIS or c) horizontal uniaxial extension causing an early onset of dynamic migration recrystallization. Small-scale high-resolution studies were carried out on several selected bags (0.55m long) from different depth regimes and were chosen as case studies to better understand the formation mechanisms of the novel CPO patterns found in the EGRIP ice core. One approach is the examination of thin sections (9 x 7 x 0.03cm) regarding the occurrence of patches of grains with similar orientations, which was observed in several samples from different depths. Small grains with similar orientations seem to cluster around large grains with a different orientation. High-resolution images (5 to 20µm/pix), derived with a Large Area Scan Macroscope (LASM), enable detailed investigations of grain shape, grain boundaries and sub-grain boundaries and therefore the possibility to find distinct features from deformation and recrystallisation in the microstructure. Grains are rarely horizontally aligned and usually show irregular, circular or rectangular shapes rather than elongated shapes. Characteristic for our case studies are also amoeboid grain shapes and sutured grain boundaries, typical features of grain boundary migration. Furthermore, layering, "sandwiched grains" and strong gradients in grain-size over distances of only a few centimetres were observed in several samples. Although still under progress, at the current state of investigation, combining fabric data and microstructure analysis, the novel CPO patterns found in the EGRIP ice core are strongly influenced by dynamic migration recrystallisation.

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.

Antifreeze proteins (AFPs) from polar and cold-tolerant organisms are able to control ice growth as a result of their adsorption on the ice crystal surface. The proteins bind to selected crystallographic planes, which are characteristic for each kind of AFP. As a consequence of the adsorption, the freezing point of the solution is locally lowered below the melting point, following the Gibbs-Thomson equation. Within the difference between the melting and the freezing point (hysteresis gap), the macroscopic growth of the crystals is arrested. Below the freezing point, crystals grow with a burst of determined shapes. Their habit is dominated by the crystallographic planes inhibited by the proteins, due to the geometric adsorption selectivity as well as to the adsorption rate of the proteins. Most of the well-studied fish AFPs do not bind to the basal plane, therefore crystals burst as needles parallel to the c-axis. At strong supercoolings the protein adsorption rate is not fast enough to balance radial growth due to heat dissipation, and crystals develop dendrites. However, data about the shape of the crystals after the burst, and well below the freezing point, are still scarce, resulting in an incomplete understanding of the growth inhibition mechanisms by the different AFP types. Here we present ice growth experiments in the presence of AFPs from the polar diatom Fragilariopsis cylindrus, a dominant microalga in sea ice assemblages. The protein was recombinantely expressed and purified from E. coli. Ice grain habit was observed at light microscopy in a dish, from the hysteresis gap until growth into a solid sample of polycrystalline ice. Crystals grew with an expansion of the basal plane area, but a suppressed development parallel to the c-axis compared to negative controls, resulting in thin ice “sheets”. A slow three- dimensional growth was revealed by the formation of characteristic features as pits and groves. Dendritic growth was limited, presumably among others an effect of the rapid heat dissipation through the thin sheet. The effect of the AFPs was still evident hours after the initial burst, as shown by analyses of the fully frozen polycrystalline block. Microtomed ice observed through crossed polarizers revealed marked microstructural features, which confirm a freezing history as a process of sheet after sheet freezing. Our results suggest that proteins bind, among others, to the basal plane of crystals, as also proposed in previous studies. Analyses of the habit showed a crystal shape relatively stable over time, and explain the microstructural features in the polycrystalline sample. Furthermore, the studies about this kind of AFP contribute to complete the puzzle of growth inhibition by AFPs.

Antifreeze proteins (AFPs) have evolved in cold-adapted organisms to control ice crystal growth when exposed to sub-zero temperature conditions. It has been suggested that the effect of the proteins results in small ice crystal size, thus avoiding in frozen tissues and cells the damage mechanically caused by large ice grains. Also the polar diatom Fragilariopsis cylindrus, a dominant species within sea-ice assemblages, produces AFPs. We expressed in E. coli a recombinant form of this protein and isolated it by affinity chromatography. We studied its effect on ice grain size after shock-freezing and subsequent annealing, and under slow freezing conditions. Shock-freezing (−40°C) produced small sized crystals, and during annealing at −4°C AFPs successfully inhibited recrystallization already at low concentrations (1.2 μM), as observed at light microscopy and using the Otago optical recrystallometer. However, slow ice growth at −5°C, more likely to resemble natural freezing conditions, surprisingly resulted in the formation of larger crystals in the presence of AFPs than in the negative controls. Further characteristic microstructural features, like among others gradual c-axis transition within individual grains and sublimation etching patterns, were observed under crossed polarizers and at light microscopy. These features are possibly due to the incorporation of proteins into the ice lattice during growth, causing local defects. Our observations remain to be clarified, but should be taken into account when considering the biological role of AFPs as well as potential industrial applications of the proteins.