A New Sample Preparation System for Micro-¹⁴C Dating of Glacier Ice with a First Application to a High Alpine Ice Core from Colle Gnifetti (Switzerland)

Abstract

ABSTRACT. Radiometric dating of glacier ice is an essential tool where stratigraphic dating methods cannot be applied. This study focuses on Alpine glacier ice and presents a new sample preparation system for dating of glacier ice samples via radiocarbon ( 14 C) dating of the microscopic particulate organic carbon (POC) fraction incorporated in the ice matrix. An adaptable, low-cost inline filtration-oxidation-unit (REFILOX) has been developed, which for the first time unifies all sample preparation steps from ice filtration to CO 2 quantification in one closed setup. A systematic 14 C investigation of modern European aerosol samples revealed that a POC combustion temperature of 340°C provides the best representation of the real sample age. A very low process blank of maximally 0.3 ± 0.1 µgC now enables 14 C dating of high Alpine ice samples, where POC concentrations are generally low (typically 10-50 µgC/kg), in an ice sample mass range of 300-500 g. In a first successful application, the method was used to obtain age constraints for an ice core from the cold, high Alpine firn saddle Colle Gnifetti (Switzerland). Analysis of the bottom ice core sections revealed a basal age of 4171-3923 cal yr BP but also a so far enigmatic discontinuity in the age-depth relationship.

Lead and Antimony in Basal Ice From Col du Dome (French Alps) Dated With Radiocarbon: A Record of Pollution During Antiquity

“…Radiocarbon sample preparations were performed at the Institute of Environmental Physics (Heidelberg, Germany) with the inline filtration‐oxidation‐unit REFILOX (Reinigungs‐Filtrations‐Oxidationssystem) and radiocarbon analysis at the accelerator mass spectrometer facility of the Curt‐Engelhorn‐Center Archaeometry in Mannheim, Germany (Hoffmann et al, ). POC trapped in the ice matrix was filtered, combusted at 340 °C, and analyzed for its 14 C content as described by Hoffmann et al (). Calibration of the single 14 C ages was performed using the IntCal13 atmospheric curve (Reimer et al, ) and OxCal 4.3 (Bronk Ramsey, ).…”

Temperature and mineral dust variability recorded in two low-accumulation Alpine ice cores over the last millennium

“…In order to obtain a reliable long-term chronology for the 2013 core, we utilize state-ofthe-art continuous flow analysis for ice core impurity profiling and, to identify even highly thinned annual layers, laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) at sub-millimetre depth resolution (Mayewski et al, 2014;Haines et al, 2016;Della Lunga et al, 2017;More et al, 2017). We combine annual layer counting in the resulting impurity profiles with absolute age constraints from radiocarbon analysis, taking advantage of recent progress in applying this technique to mountain ice cores Hoffmann et al, 2017b). Based on a refined long-term chronology, the time series of stable water isotopes and mineral dust proxies (Ca 2+ and insoluble particles) are investigated, with special emphasis on their relation to temperature.…”

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

“…The ice samples were melted, the POC was filtered, combusted into CO 2 and the radiocarbon content was measured via an accelerator mass spectrometer utilizing a gas ion source. Details on POC extraction and 14 C measurement can be found in Hoffmann et al (2017). Visible dark layers and sediment-contaminated parts were carefully avoided during sub-sampling.…”

“…Samples 2-3 and 2-6 were combusted at 340 • C. Samples 1-2, 1-9 and 3-5 were combusted at 800 • C. It is important to point out that due to different combustion temperatures of multiple organic species and increasing influences of aged and decomposed organic material (reservoir effect), higher combustion temperatures can lead to higher 14 C ages. In a separate investigation parallel to the work presented here, a combustion temperature of 340 • C for POC was determined as the best way to avoid reservoir effects caused by influences of already aged material incorporated into the sample and hence yields the best representation of the actual ice sample age (Hoffmann et al, 2017). Accordingly, the retrieved ages for the 800 • C combustion temperature samples are regarded as upper age limits only.…”

“…Since the stratigraphy of the expected glacier types (usually mostly made from congelation ice) cannot be expected to include layers of every single year, conventional dating methods like annual layer counting are severely hampered and, as a result, age constraints must be obtained mostly from radiometric methods (May, 2009). Novel developments in adapting and refining radiocarbon techniques for microscopic organic material from glacier ice (Hoffmann et al, 2017;Uglietti et al, 2016) are now available to offer an indispensable dating tool in this context. This is especially the case since the expected glacier age falls within the age range for the application of the radiocarbon technique, e.g., as indicated by the dating of the Oetztal ice man.…”