A comprehensive interpretation of the NEEM basal ice build-up using a multi parametric approach

• Main Authors: Goossens, Thomas, Sapart, Célia, Dahl-Jensen, Dorthe, Popp, T., El Amri, Saïda, Tison, Jean-Louis
• Format: Article in Journal/Newspaper
• Language: English
• Published: 2016
• Subjects: Glaciologie; Climatologie; Greenland; Greenland ice core; Greenland Ice core Project; GRIP; ice core; Ice Sheet; North Greenland; The Cryosphere
• Online Access: http://hdl.handle.net/2013/ULB-DIPOT:oai:dipot.ulb.ac.be:2013/206986; https://dipot.ulb.ac.be/dspace/bitstream/2013/206986/3/doi_190613.pdf

Basal ice is a common expression to describe debris-laden ice layers found close to the ice-bedrock interface under glaciers and ice sheets. The study of basal ice properties provides a unique opportunity to improve our understanding of subglacial environments and processes and to refine ice sheet behaviour modelling. Here, we present and discuss the results of water stable isotopes (δ18O and δD), ice fabrics, debris weight and gas content of the basal part of the NEEM (North Greenland Eemian Ice Drilling Project) ice core. Below a depth of 2533.85 m, almost 10 m of basal debris-rich material were retrieved from the borehole. The sequence is composed of an alternation of three visually contrasting types of ice :clear ice with specks of particulate inclusions, stratified debris-rich layers, and ice containing dispersed debris. The use of water stable isotope signatures (δ18O and δD) together with other parameters, allows discrimination between the different types of ice and to unravel the processes involved in their formation and transformation. The basal debris-rich material presents δ18O values [-39.9 ‰; -34.4 ‰] within the range of the above last 300 m of unaltered meteoric ice [-44.9 ‰; -30.6 ‰] spanning a glacial-interglacial range of values. This rules out the hypothesis of a basal ice layer originating from pre-ice sheet ice overridden by the growing ice sheet, as previously suggested e.g. in the case of GRIP (Greenland Ice Core Project). We show that clear basal ice with specks corresponds to altered meteoric glacial ice where a climatic signal is preserved. On the other hand, both stratified debris-rich layers and ice containing dispersed debris layers express an “open” or “closed” system melting/refreezing signature, somewhat blurred by mixing processes. Climatic reconstruction is therefore prohibited from these ice types. We propose a first interpretative framework for the build-up of the NEEM basal ice sequence, based on the origin of the various ice types. SCOPUS: ar.j ...