Two-dimensional impurity imaging in deep Antarctic ice cores: Snapshots of three climatic periods and implications for high-resolution signal interpretation

Abstract

Abstract. Due to its micron-scale resolution and micro-destructiveness, laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) is especially suited for exploring closely spaced layers in the oldest and highly thinned sections of polar ice cores. Recent adaptions of the LA-ICP-MS technique have achieved fast washout times as the basis for introducing state-of-the-art 2D imaging to ice core analysis. This new method has great potential in its application for investigating the localization of impurities on the ice sample, crucial to avoid misinterpretation of ultra-fine resolution signals. Here first results are presented from applying LA-ICP-MS elemental imaging to selected glacial and interglacial samples of the Talos Dome and EPICA Dome C ice cores from central Antarctica. The localization of impurities with both marine and terrestrial sources is discussed, revealing generally a strong connection with the network of grain boundaries but also distinct differences among climatic periods. Scale-dependent image analysis shows that the spatial significance of a single line profile along the main core axis increases systematically as the imprint of grain boundaries weakens. With this, it is demonstrated how instrumental settings can be adapted specifically fit-for-purpose, i.e. either to employ LA-ICP-MS to study the impurity-microstructure interplay or to investigate highly thinned climate proxy signals in deep polar ice.

Geochemical Characterization of Insoluble Particle Clusters in Ice Cores Using Two‐Dimensional Impurity Imaging

“…Al, Fe, and Sr feature substantial correlation, in particular Al and Fe, and Sr showing good correlation additionally with Mg. The correlation coefficient is a simple metric, however, and applying it to the entire data sets can only serve as a first indication, not least because it disregards important details regarding the relative spatial distribution among the elements (Bohleber, Roman, Šala, et al., 2021). This becomes evident in elemental maps with separate color channels for individual elements, providing an improved visual colocalization analysis.…”

“…This extraction of patterns from an image is referred to here as image segmentation. With a watershed algorithm, for example, by using an integrated function of the imaging processing within the software HDIP, it is possible to detect the grain boundary network in the Na maps (Bohleber, Roman, Šala, et al., 2021). In order to separate the pixel locations of the dispersed spots we considered the Al channel since it is showing the clearest signal for these features and generally has little or no association with the grain boundary network.…”

“…In comparison to the previously analyzed Antarctic ice core samples (Bohleber, Roman, Šala, et al., 2021), the higher impurity content of the EGRIP S10 sample allowed us to add further analytes to the previous used three to four chemical channels per elemental map (mainly 23 Na, 24 Mg, and 88 Sr). Analytes with predominant insoluble components in the ice were selected, with special focus on 27 Al but including also the exploration of 29 Si, 43 Ca, and 56 Fe.…”

“…LA‐ICP‐MS has recently been refined for two‐dimensional high‐resolution impurity imaging of ice cores (Bohleber et al., 2020). This new approach revealed a high degree of localization at grain boundaries of mostly soluble chemical species such as Na, but also clear differences among ice from glacial and interglacial periods (Bohleber, Roman, Šala, et al., 2021). As a result of these developments, LA‐ICP‐MS chemical imaging has become an important additional technique for investigating the localization of impurities in the ice matrix, supplementing methods such as energy‐dispersive X‐ray spectroscopy (e.g., Barnes et al., 2003), X‐ray spectroscopy coupled with scanning electron microscopy (e.g., Barnes & Wolff, 2004), and cryo‐Raman microscopy (e.g., Eichler et al., 2017).…”

Ice Core Science Meets Computer Vision: Challenges and Perspectives

“…The LA-ICP-MS image shown in Figure 1 has been obtained from the EPICA Dome C deep Antarctic ice core, on a sample from a glacial period of about 27.8 thousand years ago. Additional images are presented elsewhere [11]. From a conceptual point of view, Figure 1 is a representative example of the following general image characteristics: i) Small bright spots of a few ten microns occurring within grains as single spots or in small clusters.…”