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We developed a novel laser melting sampler (LMS) for ice cores to measure the stable water isotope ratios (δ18O and δD) as temperature proxies at sub-centimeter depth resolutions. In this LMS system, a 2 mm diameter movable evacuation nozzle holds an optical fiber through which a laser beam irradiates the ice core. The movable nozzle intrudes into the ice core, the laser radiation meanwhile melts the ice cylindrically, and the meltwater is pumped away simultaneously through the same nozzle and transferred to a vial for analysis. To avoid isotopic fractionation of the ice through vaporization, the laser power is adjusted to ensure that the temperature of the meltwater is always kept well below its boiling point. A segment of a Dome Fuji shallow ice core (Antarctica), using the LMS, was then demonstrated to have been discretely sampled with a depth resolution as small as 3 mm: subsequent analysis of δ18O, δD, and deuterium excess (d) was consistent with results obtained by hand segmentation within measurement uncertainties. With system software to control sampling resolution, the LMS will enable us to identify temperature variations that may be detectable only at sub-centimeter resolutions in ice cores.

We developed a novel laser melting sampler (LMS) for ice cores to measure the stable water isotope ratios (δ18O and δD) as temperature proxies at sub-centimeter depth resolutions. In this LMS system, a 2 mm diameter movable evacuation nozzle holds an optical fiber through which a laser beam irradiates the ice core. The movable nozzle intrudes into the ice core, the laser radiation meanwhile melts the ice cylindrically, and the meltwater is pumped away simultaneously through the same nozzle and transferred to a vial for analysis. To avoid isotopic fractionation of the ice through vaporization, the laser power is adjusted to ensure that the temperature of the meltwater is always kept well below its boiling point. A segment of a Dome Fuji shallow ice core (Antarctica), using the LMS, was then demonstrated to have been discretely sampled with a depth resolution as small as 3 mm: subsequent analysis of δ18O, δD, and deuterium excess (d) was consistent with results obtained by hand segmentation within measurement uncertainties. With system software to control sampling resolution, the LMS will enable us to identify temperature variations that may be detectable only at sub-centimeter resolutions in ice cores. [ABSTRACT FROM AUTHOR]

Shallow firn cores, in addition to a near-basal ice core, were recovered in 2018 from the Quelccaya ice cap (5470 m a.s.l) in the Cordillera Vilcanota, Peru, and in 2017 from the Nevado Illimani glacier (6350 m a.s.l) in the Cordillera Real, Bolivia. The two sites are ~450 km apart. Despite meltwater percolation resulting from warming, particle-based trace element records (e.g. Fe, Mg, K) in the Quelccaya and Illimani shallow cores retain well-preserved signals. The firn core chronologies, established independently by annual layer counting, show a convincing overlap indicating the two records contain comparable signals and therefore capture similar regional scale climatology. Trace element records at a ~1–4 cm resolution provide past records of anthropogenic emissions, dust sources, volcanic emissions, evaporite salts and marine-sourced air masses. Using novel ultra-high-resolution (120 μm) laser technology, we identify annual layer thicknesses ranging from 0.3 to 0.8 cm in a section of 2000-year-old radiocarbon-dated near-basal ice which compared to the previous annual layer estimates suggests that Quelccaya ice cores drilled to bedrock may be older than previously suggested by depth-age models. With the information collected from this study in combination with past studies, we emphasize the importance of collecting new surface-to-bedrock ice cores from at least the Quelccaya ice cap, in particular, due to its projected disappearance as soon as the 2050s.

In recent decades, surface melting on the inland Greenland ice sheet has increased, leading to significant meltwater-refreezing in the snow and firn. Increased knowledge of the physical and chemical characteristics of these melt features (i.e., ice layers) is needed to help estimate future global sea-level rise. Here, using a combination of microscopy and spectroscopy, we investigate the size, shape, location, and chemical compositions of inclusions in 12 ice layers of the SIGMA-A ice core in the northwestern Greenland ice sheet (78°03′06″N, 67°37′42″W, 1490 m a.s.l.). In the ice layers, we found inclusions exceeding 30 μm diameter that could only be formed by melting–refreezing, which we classify into columnar-, particle-, and rod-like inclusions. We propose that the smaller columnar- and particle-like inclusions of solid Na2SO4⋅10H2O and CaSO4⋅2H2O form first, within the ice grains, followed by the larger rod-like inclusions of brines with mainly Na+ and Cl− in grain boundaries. Our results suggest a new proxy that may help identify past warm climates in deeper ice cores in Greenland and for studying future ice sheet melting behavior.

Deciphering the localisation of solid and dissolved impurities on the micron-scale in glacial ice remains a challenge, but is critical to understand the integrity of ice core records and internal deformation. Here we report on the state-of-the-art in microstructural impurity research by highlighting recent progress in bringing together cryo-Raman spectroscopy and laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS). We show the potential of both methods and discuss possibilities to improve inter-method approaches aiming for a more holistic understanding of the evolution of impurity localisation throughout the ice column, including post-depositional processes. In this framework, we elaborate on future research priorities such as LA-ICP-MS imaging on firn samples and integrating a large cryo-cell with imaging capabilities.

In recent decades, surface melting on the inland Greenland ice sheet has increased, leading to significant meltwater-refreezing in the snow and firn. Increased knowledge of the physical and chemical characteristics of these melt features (i.e., ice layers) is needed to help estimate future global sea-level rise. Here, using a combination of microscopy and spectroscopy, we investigate the size, shape, location, and chemical compositions of inclusions in 12 ice layers of the SIGMA-A ice core in the northwestern Greenland ice sheet (78°03′06″N, 67°37′42″W, 1490 m a.s.l.). In the ice layers, we found inclusions exceeding 30 μm diameter that could only be formed by melting–refreezing, which we classify into columnar-, particle-, and rod-like inclusions. We propose that the smaller columnar- and particle-like inclusions of solid Na2SO4⋅10H2O and CaSO4⋅2H2O form first, within the ice grains, followed by the larger rod-like inclusions of brines with mainly Na+ and Cl− in grain boundaries. Our results suggest a new proxy that may help identify past warm climates in deeper ice cores in Greenland and for studying future ice sheet melting behavior. [ABSTRACT FROM AUTHOR]

Shallow firn cores, in addition to a near-basal ice core, were recovered in 2018 from the Quelccaya ice cap (5470 m a.s.l) in the Cordillera Vilcanota, Peru, and in 2017 from the Nevado Illimani glacier (6350 m a.s.l) in the Cordillera Real, Bolivia. The two sites are ~450 km apart. Despite meltwater percolation resulting from warming, particle-based trace element records (e.g. Fe, Mg, K) in the Quelccaya and Illimani shallow cores retain well-preserved signals. The firn core chronologies, established independently by annual layer counting, show a convincing overlap indicating the two records contain comparable signals and therefore capture similar regional scale climatology. Trace element records at a ~1–4 cm resolution provide past records of anthropogenic emissions, dust sources, volcanic emissions, evaporite salts and marine-sourced air masses. Using novel ultra-high-resolution (120 μm) laser technology, we identify annual layer thicknesses ranging from 0.3 to 0.8 cm in a section of 2000-year-old radiocarbon-dated near-basal ice which compared to the previous annual layer estimates suggests that Quelccaya ice cores drilled to bedrock may be older than previously suggested by depth-age models. With the information collected from this study in combination with past studies, we emphasize the importance of collecting new surface-to-bedrock ice cores from at least the Quelccaya ice cap, in particular, due to its projected disappearance as soon as the 2050s. [ABSTRACT FROM AUTHOR]

Deciphering the localisation of solid and dissolved impurities on the micron-scale in glacial ice remains a challenge, but is critical to understand the integrity of ice core records and internal deformation. Here we report on the state-of-the-art in microstructural impurity research by highlighting recent progress in bringing together cryo-Raman spectroscopy and laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS). We show the potential of both methods and discuss possibilities to improve inter-method approaches aiming for a more holistic understanding of the evolution of impurity localisation throughout the ice column, including post-depositional processes. In this framework, we elaborate on future research priorities such as LA-ICP-MS imaging on firn samples and integrating a large cryo-cell with imaging capabilities. [ABSTRACT FROM AUTHOR]

Active rock glaciers—known as mixtures of unconsolidated debris with interstitial ice, ice lenses or a core of massive ice—are widespread indicators of mountain permafrost. The age of a frozen rock glacier core in the Central European Alps (Lazaun, Italy) was dated to about 10,000 years. Here we report on the chemical composition of the frozen Lazaun core. The ice containing part of the core extended from about 2.8 m down to 24 m depth and consisted of two lobes—both a mix of ice and debris, separated by more than 3 m thick almost ice-free layer. The two lobes of the core showed layers of high solute content and peak values of electrical conductivity exceeding 1,000 μS/cm, but they differed in acidity and metal concentration. High acidity (minimum pH of 4.15) and high levels of elements like nickel, cobalt, zinc, manganese, iron and aluminum characterized the upper lobe, while neutral to alkaline pH and low metal values prevailed in the bottom lobe. We attributed solutes accumulated in the ice matrix to the weathering of bedrock minerals, with peak values favored by the oxidation of pyrite, or by an enhanced reactive surface area in fine-grained sediment layers. The chemical composition of the ice core also revealed signals of prehistoric atmospheric deposition from different sources including wood combustion, metal ore mining, and large volcanic eruptions (Thera, Aniakchak II). To our knowledge, this is the first study that presents the chemical stratigraphy of an entire rock glacier ice core.

Predicting the isotopic modification of ice by melting processes is important for improving the accuracy in paleoclimate reconstruction. To this end, we present results from cold room laboratory observations of changes in the isotopic ratio (D/H and 18O/16O) of ice cubes by isotopic exchange between liquid water and ice in nearly isothermal conditions. A 1-D model was fit to the isotopic results by adjusting the values of two parameters, the isotopic exchange rate constant (kr) and the fraction of ice participating in the exchange (f). We found that the rate constant for hydrogen isotopic exchange between liquid water and ice may be greater (up to 40%) than that for the oxygen isotopic exchange. The range of the rate constant obtained from four melt experiments is from 0.21 to 0.82 h–1. The model results also suggest that f decreases with the increasing wetness of the ice. This is because with increasing water saturation in ice, water may be present only in the small pores or some of the water that was exchanged with ice may be bypassed, decreasing the effective surface area over which the isotopic exchange can occur. The relationship between the two water isotopes (δ18O vs δD) was observed and modeled and the slope was

Past atmospheric pollution can be reconstructed from ice core trace element records retrieved from mountain glaciers. However, the current global temperature increase can result in post-depositional melt processes, significantly altering the originally stored information. Here, we present a comprehensive study on the behaviour of 35 trace elements (TEs) during meltwater percolation in a high-Alpine ice core segment from upper Grenzgletscher, Switzerland. Some TEs revealed significant concentration depletion, whereas others were well preserved depending on their water solubility and location at the grain scale. TEs present in insoluble minerals, typically enriched at grain boundaries, were found to be mostly preserved because their insolubility in water results in immobility with meltwater percolation. Water-soluble TEs revealed a variable meltwater-mobility. Whereas ultra-TEs tend to be preserved, likely due to incorporation into the ice lattice, abundant TEs are prone to relocation from grain-boundary regions. We propose that at Alpine sites, Ag, Al, Bi, Cu, Cs, Fe, Li, Mo, Pb, Rb, Sb, Th, Tl, U, V, W, Zr and the rare-earth elements may still be applicable as robust environmental proxies even if partial melting occurred, whereas Ba, Ca, Cd Co, Mg, Mn, Na, Ni, Sr and Zn are prone to significant depletion.

Predicting the isotopic modification of ice by melting processes is important for improving the accuracy in paleoclimate reconstruction. To this end, we present results from cold room laboratory observations of changes in the isotopic ratio (D/H and 18O/16O) of ice cubes by isotopic exchange between liquid water and ice in nearly isothermal conditions. A 1-D model was fit to the isotopic results by adjusting the values of two parameters, the isotopic exchange rate constant (k r) and the fraction of ice participating in the exchange (f). We found that the rate constant for hydrogen isotopic exchange between liquid water and ice may be greater (up to 40%) than that for the oxygen isotopic exchange. The range of the rate constant obtained from four melt experiments is from 0.21 to 0.82 h–1. The model results also suggest that f decreases with the increasing wetness of the ice. This is because with increasing water saturation in ice, water may be present only in the small pores or some of the water that was exchanged with ice may be bypassed, decreasing the effective surface area over which the isotopic exchange can occur. The relationship between the two water isotopes (δ 18O vs δ D) was observed and modeled and the slope was <8, which is significantly different from the slope of the meteoric waterline. We note that these slopes were obtained without considering the sublimation process. [ABSTRACT FROM AUTHOR]

Two ice cores drilled to the bottom were recovered from Miaoergou flat-topped glacier (43°03'19“N, 94°19'21“E; 4512 ma.s.l.), eastern Tien Shan, central Asia, in 2005. A high–resolution record of cadmium was established by applying inductively coupled plasma mass spectrometry to one of the ice cores (57.6 m), covering a 228 year period from AD 1776 to 2004. The results showed long-term variations of atmospheric transport and deposition of cadmium at high altitudes. Trend analysis based on the sequential Mann-Kendall test and the analysis of crustal enrichment factors of the cadmium shows that natural contribution, mainly from rock and mineral dust, dominated the atmospheric cycles of cadmium during the period AD 1776–1957, which was confirmed by the significant correlation between the winter North Atlantic Oscillation (NAO) index and annual cadmium concentration. The concentration of cadmium increased sharply from AD 1957 to 2004, suggesting increasing influence from human activities, such as metals production. The ice–core record indicated increasing atmospheric cadmium pollution in response to rapid economic growth after AD 1957 in the region.

Past atmospheric pollution can be reconstructed from ice core trace element records retrieved from mountain glaciers. However, the current global temperature increase can result in post-depositional melt processes, significantly altering the originally stored information. Here, we present a comprehensive study on the behaviour of 35 trace elements (TEs) during meltwater percolation in a high-Alpine ice core segment from upper Grenzgletscher, Switzerland. Some TEs revealed significant concentration depletion, whereas others were well preserved depending on their water solubility and location at the grain scale. TEs present in insoluble minerals, typically enriched at grain boundaries, were found to be mostly preserved because their insolubility in water results in immobility with meltwater percolation. Water-soluble TEs revealed a variable meltwater-mobility. Whereas ultra-TEs tend to be preserved, likely due to incorporation into the ice lattice, abundant TEs are prone to relocation from grain-boundary regions. We propose that at Alpine sites, Ag, Al, Bi, Cu, Cs, Fe, Li, Mo, Pb, Rb, Sb, Th, Tl, U, V, W, Zr and the rare-earth elements may still be applicable as robust environmental proxies even if partial melting occurred, whereas Ba, Ca, Cd Co, Mg, Mn, Na, Ni, Sr and Zn are prone to significant depletion. [ABSTRACT FROM AUTHOR]

In polar ice sheets, the average grain size varies with depth. Ice grain size increases due to several factors including ice temperature and impurity content, which in turn varies with climate. The effect of impurities on grain growth is thought to be crucial but has never been observed experimentally. Using a methodology recently developed at Royal Holloway University of London, in situ chemical analysis of frozen ice at sub-ppm concentrations with unprecedented spatial resolution (~150 μm) is achievable using ultraviolet laser ablation inductively coupled plasma mass spectrometry (UV-LA-ICPMS) featuring a two-volume cryo-LA-cell. Following surface cleaning with a custom-built vice equipped with a ceramic blade, NGRIP ice slabs (~86 ka before AD 2000) have been analysed using a series of one-dimensional profiles and two-dimensional maps of laser spots at a resolution of 200-300 μm. Results demonstrate that cation impurities are not uniformly distributed in ice layers and show significant variations in concentration on a sub-millimetre scale. Furthermore, a different pattern of elemental distribution between clear ice and layers enriched in impurities (cloudy bands) has been identified: while concentration differences for cloudy bands are not resolvable between boundaries and inner grain domains, within clear ice, grain boundaries and junctions are significantly (up to 100 times) impurity-enriched relative to corresponding grain interiors. [ABSTRACT FROM AUTHOR]