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

Abstract

Abstract. Cold glaciers at the highest locations of the European Alps have been investigated by drilling ice cores to retrieve their stratigraphic climate records. Findings like the Oetztal ice man have demonstrated that small ice bodies at summit locations of comparatively lower altitudes may also contain old ice if locally frozen to the underlying bedrock. In this case, constraining the maximum age of their lowermost ice part may help to identify past periods with minimum ice extent in the Alps. However, with recent warming and consequent glacier mass loss, these sites may not preserve their unique climate information for much longer. Here we utilized an existing ice cave at Chli Titlis (3030 m), central Switzerland, to perform a case study for investigating the maximum age of cold-based summit glaciers in the Alps. The cave offers direct access to the glacier stratigraphy without the logistical effort required in ice core drilling. In addition, a pioneering exploration had already demonstrated stagnant cold ice conditions at Chli Titlis, albeit more than 25 years ago. Our englacial temperature measurements and the analysis of the isotopic and physical properties of ice blocks sampled at three locations within the ice cave show that cold ice still exists fairly unchanged today. State-of-the-art micro-radiocarbon analysis constrains the maximum age of the ice at Chli Titlis to about 5000 years before present. By this means, the approach presented here will contribute to a future systematic investigation of cold-based summit glaciers, also in the Eastern Alps.

New glacier evidence for ice-free summits during the life of the Tyrolean Iceman

“…Measurements were performed at the Institute of Environmental Physics, Heidelberg University, using a cavity ring-down spectrometer. Measurement uncertainties range within ± 0.1 and ± 0.4‰ for δ 18 O and δD, respectively 12 . Calculating ordinary linear regression of δD against δ 18 O yields a slope of 7.5 at a correlation coefficient of r = 0.99 (Fig.…”

Dating glacier ice of the last millennium by quantum technology

“…The adjacent block below, block 1-2, is at least 170 years older, with a best-estimate argon age of 1126 +1286 −273 years before The wall in the cave shows a distinct horizontal layering, hence no evidence of layer folding. The 14 C age constraints reveal a strong vertical age gradient within the sampled depths [19]. The two uppermost blocks (1-1 and 1-2) have been analyzed for 39 Ar.…”

“…It is important to note that no macroscopic organic fragments were found at Chli Titlis, and all 14 C analyses had to be performed on microscopic particulate organic carbon, for which known biases towards older ages can exist. Following the discussion of potential reservoir effects in [3], the 14 C age is thus regarded as upper age limit [19]. Additionally, important relative age control is provided by the evident nearhorizontal layering, i.e.…”

“…The 14 C results revealed that age differences of several hundred years occur at close range, even between two adjacent blocks. The large age gradient in the lowermost ice layers is not necessarily connected to layer thinning by deformation but can instead result from past hiatuses in glacier growth or intermittent melting periods [19]. In this context, the 39 Ar ages perfectly match what is known to-date about the Chli Titlis glacier cave, namely (i) that age differences of up to several hundred years can occur even between two adjacent blocks of ∼ 20 cm height, (ii) the 39 Ar age of 1126 +1286 −273 years of block 1-2 is a match against the lower carbon age limit of 1246 years before 2018 CE.…”

“…For later direct comparison to 39 Ar, all calibrated radiocarbon ages have been adjusted to refer to the year 2018 CE as present. Further details regarding the sampling methods and the site characteristics of the Chli Titlis glacier cave can be found in [19]. Based on the 14 C age constraints, we selected the two youngest ice blocks for our comparison with 39 Ar, blocks 1-1 and 1-2.…”