Abstract
AbstractRadiometric 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 (14C) 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 CO2quantification in one closed setup. A systematic14C 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 enables14C 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.
Highlights
For every climate archive, the construction of a reliable age-depth relationship is a crucial step to enable paleoclimatic interpretation of the extracted proxy records
This study focuses on Alpine glacier ice and presents a new sample preparation system for dating of glacier ice samples via radiocarbon (14C) dating of the microscopic particulate organic carbon (POC) fraction incorporated in the ice matrix
We present the POC extraction system REFILOX (Reinigungs – Filtrations – Oxidationssystem) which is a simple and low cost alternative to the use of a commercial Sunset OC/elemental carbon (EC) analyzer, with the additional benefit of comprising all sample preparation steps of pre-cleaning, POC extraction from the ice and oxidation to CO2 in one closed and unique system
Summary
The construction of a reliable age-depth relationship is a crucial step to enable paleoclimatic interpretation of the extracted proxy records. Regarding ice cores drilled at polar ice sheets, conventional stratigraphic dating methods, i.e. annual layer counting in isotope and impurity profiles, have proven to be highly successful High Alpine stratified glaciers, characterized by complex bedrock geometry and highly variable accumulation regimes, previous attempts at annual layer counting were found to be limited to the last few hundred years (Wagenbach and Geis 1989; Wagenbach et al 2012; Bohleber et al 2013). The basal age determining the onset of formation of the ice body contains important climatic information itself. In this context, an alternative dating method delivering absolute ages is required. The main challenge of this method lies in the overall very small concentrations of organic material in high Alpine ice samples in the range of micrograms.
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