Microstructure, micro-inclusions, and mineralogy along the EGRIP (East Greenland Ice Core Project) ice core – Part 2: Implications for palaeo-mineralogy

Abstract

Abstract. Impurities in polar ice do not only allow the reconstruction of past atmospheric aerosol concentrations but also influence the physical properties of the ice. However, the localisation of impurities inside the microstructure is still under debate and little is known about the mineralogy of solid inclusions. In particular, the general mineralogical diversity throughout an ice core and the specific distribution inside the microstructure is poorly investigated; the impact of the mineralogy on the localisation of inclusions and other processes is thus hardly known. We use dust particle concentration, optical microscopy, and cryo-Raman spectroscopy to systematically locate and analyse the mineralogy of micro-inclusions in situ inside 11 solid ice samples from the upper 1340 m of the East Greenland Ice Core Project ice core. Micro-inclusions are more variable in mineralogy than previously observed and are mainly composed of mineral dust (quartz, mica, and feldspar) and sulfates (mainly gypsum). Inclusions of the same composition tend to cluster, but clustering frequency and mineralogy changes with depth. A variety of sulfates dominate the upper 900 m, while gypsum is the only sulfate in deeper samples, which however contain more mineral dust, nitrates, and dolomite. The analysed part of the core can thus be divided into two depth regimes of different mineralogy, and to a lesser degree of spatial distribution, which could originate from different chemical reactions in the ice or large-scale changes in ice cover in northeast Greenland during the mid-Holocene. The complexity of impurity mineralogy on the metre scale and centimetre scale in polar ice is still underestimated, and new methodological approaches are necessary to establish a comprehensive understanding of the role of impurities. Our results show that applying new methods to the mineralogy in ice cores and recognising its complexity, as well as the importance for localisation studies, open new avenues for understanding the role of impurities in ice cores.

Chemical and visual characterisation of EGRIP glacial ice and cloudy bands within

“…The presented data enable a detailed systematic overview of micro-inclusions over the, to date, entire EGRIP ice core extended by LA-ICP-MS 2D impurity imaging expanding the recent observations of micro-inclusions in the EGRIP ice core (Stoll et al, 2021a(Stoll et al, , 2022.…”

“…The remaining pieces of the fabric analyser samples were cut into cubes of ca. 2 x 2 cm (Table 2) and polished from two sides with a microtome to enable successful microstructure mapping (Stoll et al, 2021a) and Raman spectroscopy analyses (Stoll et al, 2022).…”

“…A Hg/Ar spectral calibration lamp was used to calibrate the system. Spectra were background corrected and identified using the RRUFF database (Lafuente et al, 2015) and reference spectra (e.g., Eichler et al, 2019;Stoll et al, 2022).…”

“…Recent methodological progress now enables state-of-the-art LA-ICP-MS 2D chemical imaging of the total impurity content at the scale of a few ten microns (Bohleber et al, 2020(Bohleber et al, , 2021, in particular when focusing also on dust-related elemental species (Bohleber et al, 2022). Furthermore, cryo-Raman spectroscopy coupled with microstructure-mapping was established as a powerful tool to localise and identify solid micro-inclusions in the microstructure of ice (Eichler et al, 2017(Eichler et al, , 2019Stoll et al, 2021aStoll et al, , 2022.…”

“…Hence, the mineralogy and localisation of micro-inclusions in the upper 1340 m, i.e. the Holocene, Younger Dryas, and the Bølling-Allerød, of the East Greenland Ice-core Project (EGRIP) ice core were recently analysed (Stoll et al, 2021a(Stoll et al, , 2022.…”