Firn changes at Colle Gnifetti revealed with a high-resolution process-based physical model approach

Abstract

Abstract. Our changing climate is expected to affect ice core records as cold firn progressively transitions to a temperate state. Thus, there is a need to improve our understanding and to further develop quantitative process modeling, to better predict cold firn evolution under a range of climate scenarios. Here we present the application of a distributed, fully coupled energy balance model, to simulate cold firn at the high-alpine glaciated saddle of Colle Gnifetti (Swiss–Italian Alps) over the period 2003–2018. We force the model with high-resolution, long-term, and extensively quality-checked meteorological data measured in the closest vicinity of the firn site, at the highest automatic weather station in Europe (Capanna Margherita, 4560 m a.s.l.). The model incorporates the spatial variability of snow accumulation rates and is calibrated using several partly unpublished high-altitude measurements from the Monte Rosa area. The simulation reveals a very good overall agreement in the comparison with a large archive of firn temperature profiles. Our results show that surface melt over the glaciated saddle is increasing by 3–4 mm w.e. yr−2 depending on the location (29 %–36 % in 16 years), although with large inter-annual variability. Analysis of modeled melt indicates the frequent occurrence of small melt events (<4 mm w.e.), which collectively represent a significant fraction of the melt totals. Modeled firn warming rates at 20 m depth are relatively uniform above 4450 m a.s.l. (0.4–0.5 ∘C per decade). They become highly variable at lower elevations, with a marked dependence on surface aspect and absolute values up to 2.5 times the local rate of atmospheric warming. Our distributed simulation contributes to the understanding of the thermal regime and evolution of a prominent site for alpine ice cores and may support the planning of future core drilling efforts. Moreover, thanks to an extensive archive of measurements available for comparison, we also highlight the possibilities of model improvement most relevant to the investigation of future scenarios, such as the fixed-depth parametrized routine of deep preferential percolation.

Regime Shifts in Glacier and Ice Sheet Response to Climate Change: Examples From the Northern Hemisphere

“…Firn temperature observations on Lomonosovfonna, Svalbard (Marchenko et al, 2021) indicate that temperatures at ∼12m depth may have shifted from sub-freezing to temperate conditions over the past two decades. Such a transition may also be close at high elevations in the European Alps, where warming of cold firn has been measured over the last two decades (e.g., Hoelzle et al, 2011;Mattea et al, 2021; Colle Gnifetti on Monte Rosa). Climate change trends are strong at high latitudes (e.g., Zhang et al, 2019) and high elevations (Pepin et al, 2015;Williamson S. et al, 2020), which is likely to accelerate regime changes from polythermal to temperate ice.…”

Long-term firn and mass balance modelling for Abramov Glacier in the data-scarce Pamir Alay

“…We can speculate that Abramov Glacier might be affected by the same changes in precipitation patterns that could be partly responsible for the mass balance anomaly in western HMA (e.g. Miles et al, 2021). Barandun et al (2015) furthermore 1b describe a tendency towards more ablation during recent decades.…”

“…The model has participated in the firn meltwater Retention Model Intercomparison Project (RetMIP) as "UppsalaUniDeepPerc" (Vandecrux et al, 2020), and it has been applied to several other glaciers located in the Arctic and the Alps (e.g. van Pelt and Kohler, 2015;van Pelt et al, 2021;Mattea et al, 2021). Here, we use the model version described by van Pelt et al (2019), and we include an updated parametrization for seasonal snow densification after van Kampenhout et al (2017).…”

“…Kääb et al, 2012;Brun et al, 2017;Shean et al, 2020;Jakob et al, 2021). Topographical effects in combination with precipitation increases are suggested as reasons for balanced or positive mass changes for numerous glaciers in the Karakoram, Kunlun Shan, Pamir, Pamir Alay and Tibetan Plateau subregions (Miles et al, 2021). Whereas reliable precipitation data from in situ measurements are very scarce for the region (Pohl et al, 2015), the analysis of the gridded Global Precipitation Climatology Project over 30 years has indicated a precipitation increase in the western part of HMA due to largescale atmospheric circulation patterns (strengthening westerlies) (Yao et al, 2012).…”

Long-term firn and mass balance modelling for Abramov glacier, Pamir Alay

“…The model has participated in the firn meltwater Retention Model Intercomparison Project (RetMIP) as "UppsalaUniDeepPerc" (Vandecrux et al, 2020) and it has been applied to several other glaciers located in the Arctic and the Alps (e.g. van Pelt and Kohler, 2015;van Pelt et al, 2021;Mattea et al, 2021).…”