Abstract
Abstract. In the 1950s and 1960s, specific radionuclides were released into the atmosphere as a result of nuclear weapons testing. This radioactive fallout left its signature on the accumulated layers of glaciers worldwide, thus providing a tracer for ice particles traveling within the gravitational ice flow and being released into the ablation zone. For surface ice dating purposes, we analyze here the activity of 239Pu, 240Pu and 236U radionuclides derived from more than 200 ice samples collected along five flowlines at the surface of Gauligletscher, Switzerland. It was found that contaminations appear band-wise along most of the sampled lines, revealing a V-shaped profile consistent with the ice flow field already observed. Similarities to activities found in ice cores permit the isochronal lines at the glacier from 1960 and 1963 to be identified. Hence this information is used to fine-tune an ice flow/mass balance model, and to accurately map the age of the entire glacier ice. Our results indicate the strong potential for combining radionuclide contamination and ice flow modeling in two different ways. First, such tracers provide unique information on the long-term ice motion of the entire glacier (and not only at its surface), and on the long-term mass balance, and therefore offer an extremely valuable data tool for calibrating ice flows within a model. Second, the dating of surface ice is highly relevant when conducting “horizontal ice core sampling”, i.e., when taking chronological samples of surface ice from the distant past, without having to perform expensive and logistically complex deep ice-core drilling. In conclusion, our results show that an airplane which crash-landed on the Gauligletscher in 1946 will likely soon be released from the ice close to the place where pieces have emerged in recent years, thus permitting the prognosis given in an earlier model to be revised considerably.
Highlights
Climate change is expected to bring about the massive retreat of glaciers worldwide (e.g., Marzeion et al, 2018) with important consequences for hydropower production (Schaefli et al, 2019), the tourism economy (Wiesmann et al, 2005) or in terms of sea level rise (Mengel et al, 2018)
We describe in order the methods we used to model the age of ice using both ice flow modeling and radionuclide contamination
We successfully used plutonium and uranium contamination in an Alpine glacier induced by the 1950s and 1960s atmospheric nuclear weapon tests to date the ice of its ablation zone
Summary
Climate change is expected to bring about the massive retreat of glaciers worldwide (e.g., Marzeion et al, 2018) with important consequences for hydropower production (Schaefli et al, 2019), the tourism economy (Wiesmann et al, 2005) or in terms of sea level rise (Mengel et al, 2018). A common difficulty in setting up sophisticated models is the lack of data to simultaneously constrain the key parameters that control the mass balance, the ice deformation and the basal conditions; this can be a source of major model uncertainties (Gillet-Chaulet et al, 2012). Both mass balance measurements and ice velocities observed at the glacier surface are generally available only for the ablation area and for the recent past. Another important limitation is that models rarely integrate data on the basal motion at the bedrock, for reasons of inaccessibility (Vincent and Moreau, 2016)
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