Laser ablation ICP-MS on KCC microstructure - pilot study

In a two week pilot study at the Keck Laser Ice Facility at the Climate Change Institute in Orono, Maine, laser ablation ICP-MS experiments were conducted on samples from four depths of the Alpine ice core KCC from Colle Gnifetti that were selected based on available fabric and microstructure data. Impurity fractions of sodium, iron and calcium were measured with respect to the visible microstructure on the ice sample surface. The first assessment of the data suggests that sodium concentrations are increased in the grain bound- aries regardless of ice core depth and grain properties, while iron concentrations show no discernible spatial pattern. Althought the results cannot be interpreted conclusively – due to the pilot character of the study – the po- tential of this technique for high-resolution impurity measurements with regard to the local microstructure becomes evident and possible improvements for deeper studies could be identified

Investigating cold based summit glaciers through direct access to the glacier base: a case study constraining the maximum age of Chli Titlis glacier, Switzerland

Cold glaciers at the highest locations of the European Alps have been investigated by drilling ice cores to retrieve their stratigraphic climate records. Findings like the Oetztal ice man have demonstrated that small ice bodies at summit locations of comparatively lower altitudes may also contain old ice if locally frozen to the underlying bedrock. In this case, constraining the maximum age of their lowermost ice part may help to identify past periods with minimum ice extent in the Alps. However, with recent warming and consequent glacier mass loss, these sites may not preserve their unique climate information for much longer. Here we utilized an existing ice cave at Chli Titlis (3030 m), central Switzerland, to perform a case study for investigating the maximum age of cold-based summit glaciers in the Alps. The cave offers direct access to the glacier stratigraphy without the logistical effort required in ice core drilling. In addition, a pioneering exploration had already demonstrated stagnant cold ice conditions at Chli Titlis, albeit more than 25 years ago. Our englacial temperature measurements and the analysis of the isotopic and physical properties of ice blocks sampled at three locations within the ice cave show that cold ice still exists fairly unchanged today. State-of-the-art micro-radiocarbon analysis constrains the maximum age of the ice at Chli Titlis to about 5000 years before present. By this means, the approach presented here will contribute to a future systematic investigation of cold-based summit glaciers, also in the Eastern Alps

A full Stokes ice-flow model to assist the interpretation of millennial-scale ice cores at the high-Alpine drilling site Colle Gnifetti, Swiss/Italian Alps

The high-Alpine ice-core drilling site Colle Gnifetti (CG), Monte Rosa, Swiss/Italian Alps, provides climate records over the last millennium and beyond. However, the full exploitation of the oldest part of the existing ice cores requires complementary knowledge of the intricate glacio-meteorological settings, including glacier dynamics. Here, we present new ice-flow modeling studies of CG, focused on characterizing the flow at two neighboring drill sites in the eastern part of the glacier. The3-D full Stokes ice-flow model is thermo-mechanically coupled and includes firn rheology, firn densification and enthalpy transport, and is implemented using the finite element software Elmer/Ice. Measurements of surface velocities, accumulation, borehole inclination, density and englacial temperatures are used to validate the model output. We calculate backward trajectories and map the catchment areas. This constrains, for the first time at this site, the so-called upstream effects for the stable water isotope time series of the two ice cores drilled in 2005 and 2013. The model also provides a 3-D age field of the glacier and independent ice-core chronologies for five ice-core sites. Model results are a valuable addition to the existing glaciological and ice-core datasets. This especially concerns the quantitative estimate of upstream conditions affecting the interpretation of the deep ice-core layers

Ice Core Science Meets Computer Vision: Challenges and Perspectives

Polar ice cores play a central role in studies of the earth's climate system through natural archives. A pressing issue is the analysis of the oldest, highly thinned ice core sections, where the identification of paleoclimate signals is particularly challenging. For this, state-of-the-art imaging by laser-ablation inductively-coupled plasma mass spectrometry (LA-ICP-MS) has the potential to be revolutionary due to its combination of micron-scale 2D chemical information with visual features. However, the quantitative study of record preservation in chemical images raises new questions that call for the expertise of the computer vision community. To illustrate this new inter-disciplinary frontier, we describe a selected set of key questions. One critical task is to assess the paleoclimate significance of single line profiles along the main core axis, which we show is a scale-dependent problem for which advanced image analysis methods are critical. Another important issue is the evaluation of post-depositional layer changes, for which the chemical images provide rich information. Accordingly, the time is ripe to begin an intensified exchange between the two scientific communities of computer vision and ice core science. The collaborative building of a new framework for investigating high-resolution chemical images with automated image analysis techniques will also benefit the already wide-spread application of laser-ablation inductively-coupled plasma mass spectrometry chemical imaging in the geosciences

The new frontier of microstructural impurity research in polar ice

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 high- lighting recent progress in bringing together cryo-Raman spectroscopy and laser ablation induct- ively 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 under- standing 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

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

Impurities in polar ice play a critical role in ice flow, deformation, and the integrity of the ice core record. Especially cloudy bands, visible layers with high impurity concentrations are prominent features in ice from the last glacial. Their physical and chemical properties are poorly understood, highlighting the need to analyse them in more detail. We bridge the gap between decimetre and micrometre scales by combining the visual stratigraphy line scanner, fabric analyser, microstructure mapping, Raman spectroscopy, and laser ablation inductively coupled plasma mass spectrometry 2D impurity imaging. We classified almost 1300 cloudy bands from glacial ice from the East Greenland Ice-core Project (EGRIP) ice core into seven different types. We determine the localisation and mineralogy of more than 1000 micro-inclusions at 13 depths. The majority of the found minerals are related to terrestrial dust, such as quartz, feldspar, mica, and hematite. We further found carbonaceous particles, dolomite, and gypsum in high abundance. Rare minerals are e.g., rutile, anatase, epidote, titanite, and grossular. 2D impurity imaging with 20 &mu;m resolution revealed that Na, Mg and Sr are mainly at grain boundaries. Dust-related analytes, such as Al, Fe, and Ti, are also located in the grain interior forming clusters of insoluble impurities. Cloudy bands are thus clearly distinguishable in the chemical data. We present novel vast micron-resolution insights into cloudy bands and describe the differences within and outside these bands. Combining the visual and chemical data results in new insights into the formation of different cloudy band types and could be the starting point for future in-depth studies on impurity signal integrity and internal deformation.</p

A New Multielement Method for LA-ICP-MS Data Acquisition From Glacier Ice Cores

To answer pressing new research questions about the rate and timing of abrupt climate transitions, a robust system for ultrahigh-resolution sampling of glacier ice is needed. Here, we present a multielement method of LA-ICP-MS analysis wherein an array of chemical elements is simultaneously measured from the same ablation area. Although multielement techniques are commonplace for high-concentration materials, prior to the development of this method, all LA-ICP-MS analyses of glacier ice involved a single element per ablation pass or spot. This new method, developed using the LA-ICP-MS system at the W. M. Keck Laser Ice Facility at the University of Maine Climate Change Institute, has already been used to shed light on our flawed understanding of natural levels of Pb in Earth?s atmospherepublishersversionPeer reviewe

Full Stokes ice-flow modeling of the high-Alpine glacier saddle Colle Gnifetti, Monte Rosa

The high-Alpine glacier saddle Colle Gnifetti (CG), Monte Rosa massif, is a unique drilling site in the European Alps offering continuous ice-core records on the millennial time-scale. However, the full interpretation ofthe ice-core time series is challenging due to the highly irregular (spatial and temporal) snow deposition pattern and, together with a complex flow regime, upstream effects. In this context, we present results of a new three-dimensional full Stokes ice-flow model of the CG saddle. The main objectives of the modeling tool concern (a) the calculation of backward trajectories of existing ice-core drill sites, which is required in order to evaluate potential upstream effects, and (b) provide a reliable age–depth relation, in order to support experimental methods in ice-core dating.The established full Stokes model is fully thermo-mechanically coupled. The model includes firn rheology and firn densification. The temperature field is calculated using the enthalpy method, with consideration of atmospheric temperature changes of the last century, strain heating and surface meltwater refreezing. The simulations are performed using the state-of-the-art Finite Element software Elmer/Ice. The CG full Stokes model is validated by comparison with glaciological measurements of surface velocities, snow accumulation, borehole inclination angles, density and englacial temperatures. Using the calculated backwards trajectories, the locations on the glacier surface of the ice-core source points are identified with an uncertainty of∼10% of the distance to the corresponding drill site. Moreover, the three-dimensional age field of the glacier is calculated with an uncertainty of∼20%. The calculated ice-core chronologiesare consistent with experimental dating results, based among others on annual layer counting and 14C measurements

Investigating two possible schemes of Laser Ablation – Cavity Ring Down Spectrometry for water isotope measurements on ice cores

Thinning of the deep ice core layers must be considered when the water isotopic composition of the Oldest Ice Core is to be analyzed. From an experimental point of view, a novel instrument combining a micro-destructive cold femtosecond - Laser Ablation (LA) sampling system, that provides high spatial resolution together with minimal usage of ice sample, and a Cavity Ring Down Spectrometer is being built for high-quality water isotope measurements. Laser ablation results in crater formation and its morphology depends on the laser parameters used. Optical images that show crater morphology under different experimental conditions allow crater characterization towards an efficient cold LA sampling. An ablation chamber and a transfer line are both the connecting parts between the LA system and the CRDS instrument. They are to be designed and constructed in the optimal size and shape to collect the ablated mass and guarantee its smooth delivery to the CRDS analyzer with minimum disturbance. Coupling a Laser Ablation system with a CRDS analyzer has already been achieved using a laser operating at the nanosecond regime and a cryo-cell as the ablation chamber. Comparison of the two Laser Ablation systems, by the means of ice sampling and collection of the ablated material, will be of great importance to understand the ablation mechanism and post-ablation processes on ice and further develop a system dedicated to water isotope measurements