On the interactions between airflow and ice melting in ice caves: A novel methodology based on computational fluid dynamics modeling.

Motivated by progressive climate-change influence on ice degradation in caves, in this paper we present a novel methodology to investigate the link between air dynamics and ice melting. Specifically, we use surveys available for the Leupa ice cave (LIC), located in the Canin-Kanin group in the southeastern Alps and a general purpose computational fluid dynamics model (CFD). Detailed numerical simulations are evaluated on the basis of well-established approaches that consider domain, grid, boundary-conditions, turbulence closure models, buoyancy effects, porous media properties and verification with measured data. External atmospheric conditions are the main trigger for internal circulation but morphology and thermal characteristics of ice and bedrock induce a dynamical process of heat exchange ultimately responsible for ice melting. This process is generally poorly documented in real conditions. Using CFD analyses we show that both in summer and winter, warm and cold air currents within the cave are "disturbed" by several vortices and stagnation zones which locally modify the energy balance. To account for this we introduce a macroscopic physical model based on energy balance between ice surfaces and the inner ice cave airflow to determine the heat exchanged between ice and air. Using this model, a prediction of ice thickness decay over time is obtained. In the case of LIC a reduction of initial 4 cm per year is first obtained with projection of a much faster increase. The methodology is general and easily extendable to other sites, proving to be a powerful method to estimate ice evolution in caves induced by external and internal forcing.

Interplay of grounding-line dynamics and sub-shelf melting during retreat of the Bjørnøyrenna Ice Stream.

The Barents Sea Ice Sheet was a marine-based ice sheet, i.e., it rested on the Barents Sea floor during the Last Glacial Maximum (21 ky BP). The Bjørnøyrenna Ice Stream was the largest ice stream draining the Barents Sea Ice Sheet and is regarded as an analogue for contemporary ice streams in West Antarctica. Here, the retreat of the Bjørnøyrenna Ice Stream is simulated by means of two numerical ice sheet models and results assessed against geological data. We investigate the sensitivity of the ice stream to changes in ocean temperature and the impact of grounding-line physics on ice stream retreat. Our results suggest that the role played by sub-shelf melting depends on how the grounding-line physics is represented in the models. When an analytic constraint on the ice flux across the grounding line is applied, the retreat of Bjørnøyrenna Ice Stream is primarily driven by internal ice dynamics rather than by oceanic forcing. This suggests that implementations of grounding-line physics need to be carefully assessed when evaluating and predicting the response of contemporary marine-based ice sheets and individual ice streams to ongoing and future ocean warming.

Author Correction: Interplay of grounding-line dynamics and sub-shelf melting during retreat of the Bjørnøyrenna Ice Stream.

A correction to this article has been published and is linked from the HTML and PDF versions of this paper. The error has not been fixed in the paper.

Unprecedented heat wave in December 2015 and potential for winter glacier ablation in the eastern Alps.

We document the occurrence in December 2015 of unprecedented high monthly mean temperatures in the observational record of mountain sites in the eastern Alps. For the first time in the last 150 years mean December temperature exceeded 0 °C at elevations between 2100 and 2500 m, with December mean anomalies exceeding 6.5 °C with respect to the 1971-2000 mean. Along with the absence of snow cover, such temperatures might have lead to unprecedented winter ablation of glaciers in this elevation range. Smaller temperature anomalies occurred in surrounding low elevation sites, highlighting the key role of topography in this event. Specifically, strong inversions associated with the very stable synoptic conditions during the month amplified the anomalies at the high elevations of the mountain glacier sites. We analyze the processes underlying this exceptional event and place this anomaly within the context of future warming scenarios over the region.