Project Details
Projekt
High resolution basal ice properties at sedimentary and non-sedimentary Alpine summit glaciers
Applicant
Dr. Pascal Bohleber
Subject Area
Mineralogy, Petrology and Geochemistry
Term
from 2014 to 2017
Project identifier
Deutsche Forschungsgemeinschaft (DFG) - Project number 249850554
Ice cores drilled at polar ice sheets and cold mountain glaciers allow to reconstruct past climate changes by deciphering temperature-related and bio-geochemical signals stored in cold glacier ice. However, for the lowermost and thus oldest ice it is so far not sufficiently understood to which extent ice deformation and ice-bedrock interaction can distort these meteoric signals. Here, cold basal layers of alpine glaciers are a promising target, since covering a broader spectrum of basal ice properties, while being much easier to access compared to their km-thick polar counterparts. Accordingly, this project aims at investigating a wide range of basal ice recovered from a high Alpine drilling site and lower cold based summit glaciers. Among ice core drilling sites in the Alps, Colle Gnifetti (4500 m asl, Monte Rosa massif) uniquely offers millennial ice core records, with the interesting paleo-climate period compressed into thinned bottom layers, however. The reconstruction of atmospheric signals beyond the instrumental era from Colle Gnifetti ice cores is so far hampered by dating uncertainties and interpretation deficits related to depositional noise and potentially distorted basal layer signals. These sub-cm basal layers are approached here by novel application of laser ablation ion coupled plasma mass spectrometry offering up to three orders of magnitude larger depth resolution than ever before. The results from laser ablation are compared to existing datasets, aimed at the identification of annual impurity layers beyond the resolution of state-of-the-art analyses. This is to assess the potential of laser ablation for dating highly thinned ice and to give a comprehensive picture on basal ice properties in relation to potentially biased ice core signals. The findings from the basal ice investigation at Colle Gnifetti will be compared to the respective results from lower summit glaciers that typically feature a different, non-sedimentary build-up process, hence not providing temporally continuous climatic records. The basal layers of these sites are explored for englacial ice temperature, as well as impurity and physical properties. This is to characterize their basal ice frozen-to-bedrock that is much closer to the melting point in comparison to Colle Gnifetti. In this respect, basal ice of these non-sedimentary summit sites may serve as an analogue for the today much colder sedimentary drilling sites under future climate warming.
DFG Programme
Research Fellowships
International Connection
Austria, USA
