Chemical impurity distribtion (Na, Mg, Sr) in the EPICA Dome C ice core bags 1065 and 3092 and Talos Dome ice core bag 375-B1 obtained from 2D imaging with LA-ICP-MS

Laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) offers micron-resolution 2D chemical imaging, which has been adapted recently to ice core analysis. Measurements were performed in 2020 at the Ca'Foscari University of Venice, in order to investigate the localization of impurities in the ice samples. Here images are presented from applying LA-ICP-MS elemental imaging to a samples of the EPICA Dome C ice core and the Talos Dome ice core from Antarctica. Lateral resolution is 35 microns both along and perpendicular to the scan direction. Considered as analytes are Na, Mg and Sr. Background and drift correction as well as image construction were performed using the software HDIP (Teledyne Photon Machines, Bozeman, MT, USA). Impurity images are acquired as a pattern of lines, without overlap in the direction perpendicular to that of the scan, and without any further spatial interpolation. Each pixel in an ice core chemical image has a size of 35 μm x 35 μm. For each chemical element the datasets comprise a numerical matrix which contains rows and columns according to the physical size of the image: an image of 7 mm x 35 mm in size has 200 rows and 1000 columns. The numerical entries in this matrix refer to the recorded intensity (e.g. in counts). Values lower than the detection limit are set to zero. Due to the careful synchronization, the individual pixels of the different chemical channels can be considered to be almost perfectly spatially aligned. In contrast, the mosaic of visual images obtained from the laser camera is not a-priori aligned with the chemical images. The visual images are generally characterized by air bubbles (dark blobs), grain boundaries (dark lines) and occasional sub-grain boundaries (thin dark lines).