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Overview of the Morteratsch glacier complex and stakes for SMB measurements in the ablation area. The eight stakes used in the multiple linear regression analysis (MLRA) are shown in blue (Vadret da Morteratsch) and red (Vadret Pers), the other stakes are represented in light grey. The terminus is at ∼2100 m a.s.l., while the highest mountain peaks are ∼4000 m. The SwissTopo Digital Elevation Model (DEM) used to produce this figure is from 2001 (i.e. start of the field campaign). Figure created with TopoZeko toolbox (Zekollari, 2017).
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In this study we analyse a 15-year long time series of surface mass-balance (SMB) measurements performed between 2001 and 2016 in the ablation zone of the Morteratsch glacier complex (Engadine, Switzerland). For a better understanding of the SMB variability and its causes, multiple linear regressions analyses are performed with temperature and prec...
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... Morteratsch glacier complex is situated on the southern side of the European Alps (Engadine, SE Switzerland) and consists of two glaciers, the Morteratsch glacier (Vadret da Morteratsch) and the Pers glacier (Vadret Pers) (Fig. 1). Until 2015, Vadret Pers was the main tributary of the Vadret da Morteratsch ( Zekollari and Huybrechts, 2015), but now both glaciers have disconnected and act as inde- pendent ice bodies. At present, the glacier complex covers an area of ∼16 km 2 and has a volume of ∼1.1 km 3 (Zekollari and others, ...
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... the 15-year period, a total of 232 annual mass-balance point measurements are available for the ablation area and around the Equilibrium Line Altitude (ELA) of the Morteratsch glacier complex (Fig. 3). These readings result from annual visits to the glacier, which occur at the very end of September -beginning of October, corresponding to a floating-date system that is very close to the fixed-date system (Cogley and others, 2011). Of the 232 readings, eight have a positive mass balance (up to +0.6 m ice eq a −1 ) (Fig. 3). A total of 128 readings were performed on Vadret da Morteratsch and 104 on Vadret Pers (see Fig. 1). These readings were obtained from 31 separate stakes (17 on Vadret da Morteratsch, 14 on Vadret Pers), of which 12 stakes have a series of at least 10 years and eight stakes cover the full 15-year period. The entire dataset is available as Supplementary material. For Vadret da Morteratsch, the ele- vation of the stakes ranges from the front (∼2030-2100 m a.s.l. over this period) to ∼2600 m a.s.l. (just underneath the icefall, the 'labyrinth'). Most of this range is covered with stakes, roughly at 100 m height intervals (see also Fig. 1). For Vadret Pers, two SMB observations were taken at the front (∼2450 m a.s.l.), but all other measurements are situated between 2600 and 3050 m a.s.l. (∼ the ELA). The SMB is sig- nificantly lower on Vadret Pers compared with Vadret da Morteratsch (Fig. 3), which is likely related to the orientation and resulting daily insolation cycle for both glaciers. The abla- tion area of the Pers glacier is oriented towards the WNW (tongue)-NW (upper ablation area) and is more exposed to direct insolation than the Morteratsch glacier, which is exposed to the N and strongly shielded by the high mountain peaks (see also Fig. 1). A simple approach in which a best linear fit (i.e. linear regression) through all stakes is taken clearly illustrates the higher SMB for Morteratsch in the 2000-3000 m elevation range (ablation area): ...
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... the 15-year period, a total of 232 annual mass-balance point measurements are available for the ablation area and around the Equilibrium Line Altitude (ELA) of the Morteratsch glacier complex (Fig. 3). These readings result from annual visits to the glacier, which occur at the very end of September -beginning of October, corresponding to a floating-date system that is very close to the fixed-date system (Cogley and others, 2011). Of the 232 readings, eight have a positive mass balance (up to +0.6 m ice eq a −1 ) (Fig. 3). A total of 128 readings were performed on Vadret da Morteratsch and 104 on Vadret Pers (see Fig. 1). These readings were obtained from 31 separate stakes (17 on Vadret da Morteratsch, 14 on Vadret Pers), of which 12 stakes have a series of at least 10 years and eight stakes cover the full 15-year period. The entire dataset is available as Supplementary material. For Vadret da Morteratsch, the ele- vation of the stakes ranges from the front (∼2030-2100 m a.s.l. over this period) to ∼2600 m a.s.l. (just underneath the icefall, the 'labyrinth'). Most of this range is covered with stakes, roughly at 100 m height intervals (see also Fig. 1). For Vadret Pers, two SMB observations were taken at the front (∼2450 m a.s.l.), but all other measurements are situated between 2600 and 3050 m a.s.l. (∼ the ELA). The SMB is sig- nificantly lower on Vadret Pers compared with Vadret da Morteratsch (Fig. 3), which is likely related to the orientation and resulting daily insolation cycle for both glaciers. The abla- tion area of the Pers glacier is oriented towards the WNW (tongue)-NW (upper ablation area) and is more exposed to direct insolation than the Morteratsch glacier, which is exposed to the N and strongly shielded by the high mountain peaks (see also Fig. 1). A simple approach in which a best linear fit (i.e. linear regression) through all stakes is taken clearly illustrates the higher SMB for Morteratsch in the 2000-3000 m elevation range (ablation area): ...
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... the 15-year period, a total of 232 annual mass-balance point measurements are available for the ablation area and around the Equilibrium Line Altitude (ELA) of the Morteratsch glacier complex (Fig. 3). These readings result from annual visits to the glacier, which occur at the very end of September -beginning of October, corresponding to a floating-date system that is very close to the fixed-date system (Cogley and others, 2011). Of the 232 readings, eight have a positive mass balance (up to +0.6 m ice eq a −1 ) (Fig. 3). A total of 128 readings were performed on Vadret da Morteratsch and 104 on Vadret Pers (see Fig. 1). These readings were obtained from 31 separate stakes (17 on Vadret da Morteratsch, 14 on Vadret Pers), of which 12 stakes have a series of at least 10 years and eight stakes cover the full 15-year period. The entire dataset is available as Supplementary material. For Vadret da Morteratsch, the ele- vation of the stakes ranges from the front (∼2030-2100 m a.s.l. over this period) to ∼2600 m a.s.l. (just underneath the icefall, the 'labyrinth'). Most of this range is covered with stakes, roughly at 100 m height intervals (see also Fig. 1). For Vadret Pers, two SMB observations were taken at the front (∼2450 m a.s.l.), but all other measurements are situated between 2600 and 3050 m a.s.l. (∼ the ELA). The SMB is sig- nificantly lower on Vadret Pers compared with Vadret da Morteratsch (Fig. 3), which is likely related to the orientation and resulting daily insolation cycle for both glaciers. The abla- tion area of the Pers glacier is oriented towards the WNW (tongue)-NW (upper ablation area) and is more exposed to direct insolation than the Morteratsch glacier, which is exposed to the N and strongly shielded by the high mountain peaks (see also Fig. 1). A simple approach in which a best linear fit (i.e. linear regression) through all stakes is taken clearly illustrates the higher SMB for Morteratsch in the 2000-3000 m elevation range (ablation area): ...
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... the MLRA, 120 SMB measurements are considered, which correspond to the eight stakes that cover the whole observational period (i.e. the 15-year record). All eight stakes are in the ablation zone and are in debris-poor areas. Four of these stakes are located on Vadret da Morteratsch and four on Vadret Pers (see Fig. 1). Including SMB measurements from stakes that do not cover this entire period would introduce bias in the anomalies due to the gap in their data record. Since SMB data from the eight stakes covering the full period would be needed to solve these biases, this approach would not add information about total SMB ...
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... Morteratsch glacier complex is situated on the southern side of the European Alps (Engadine, SE Switzerland) and consists of two glaciers, the Morteratsch glacier (Vadret da Morteratsch) and the Pers glacier (Vadret Pers) (Fig. 1). Until 2015, Vadret Pers was the main tributary of the Vadret da Morteratsch ( Zekollari and Huybrechts, 2015), but now both glaciers have disconnected and act as inde- pendent ice bodies. At present, the glacier complex covers an area of ∼16 km 2 and has a volume of ∼1.1 km 3 (Zekollari and others, ...
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... at the very end of September -beginning of October, corresponding to a floating-date system that is very close to the fixed-date system (Cogley and others, 2011). Of the 232 readings, eight have a positive mass balance (up to +0.6 m ice eq a −1 ) (Fig. 3). A total of 128 readings were performed on Vadret da Morteratsch and 104 on Vadret Pers (see Fig. 1). These readings were obtained from 31 separate stakes (17 on Vadret da Morteratsch, 14 on Vadret Pers), of which 12 stakes have a series of at least 10 years and eight stakes cover the full 15-year period. The entire dataset is available as Supplementary material. For Vadret da Morteratsch, the ele- vation of the stakes ranges from ...
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... 15-year period. The entire dataset is available as Supplementary material. For Vadret da Morteratsch, the ele- vation of the stakes ranges from the front (∼2030-2100 m a.s.l. over this period) to ∼2600 m a.s.l. (just underneath the icefall, the 'labyrinth'). Most of this range is covered with stakes, roughly at 100 m height intervals (see also Fig. 1). For Vadret Pers, two SMB observations were taken at the front (∼2450 m a.s.l.), but all other measurements are situated between 2600 and 3050 m a.s.l. (∼ the ELA). The SMB is sig- nificantly lower on Vadret Pers compared with Vadret da Morteratsch (Fig. 3), which is likely related to the orientation and resulting daily insolation ...
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... likely related to the orientation and resulting daily insolation cycle for both glaciers. The abla- tion area of the Pers glacier is oriented towards the WNW (tongue)-NW (upper ablation area) and is more exposed to direct insolation than the Morteratsch glacier, which is exposed to the N and strongly shielded by the high mountain peaks (see also Fig. 1). A simple approach in which a best linear fit (i.e. linear regression) through all stakes is taken clearly illustrates the higher SMB for Morteratsch in the 2000-3000 m elevation range (ablation area): ...
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... the MLRA, 120 SMB measurements are considered, which correspond to the eight stakes that cover the whole observational period (i.e. the 15-year record). All eight stakes are in the ablation zone and are in debris-poor areas. Four of these stakes are located on Vadret da Morteratsch and four on Vadret Pers (see Fig. 1). Including SMB measurements from stakes that do not cover this entire period would introduce bias in the anomalies due to the gap in their data record. Since SMB data from the eight stakes covering the full period would be needed to solve these biases, this approach would not add information about total SMB ...
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Citations
... Continuous seasonal monitoring at a dense stake network is performed since 1991 on Ghiacciaio del Basòdino, southern Switzerland (Fig. 6). On Vadret Pers, southeastern Switzerland, a network of stakes in the ablation area has been 370 observed since 20 years (Zekollari and Huybrechts, 2018). ...
Glacier monitoring in Switzerland has resulted in some of the longest and most complete data series globally. Mass balance observations at individual locations, starting in the 19th century, are the backbone of the monitoring as they represent the raw and original glaciological data demonstrating the response of snow accumulation and snow/ice melt to changes in climate forcing. So far, however, the variety of sources of historic measurements has not been systematically processed and documented. Here, we present a new complete and extensive point glacier mass balance dataset for the Swiss Alps that provides attributes for data quality and corresponding uncertainties. Original sources were digitized or re-assessed to validate or to correct existing entries and to identify metadata. The sources of data are highly diverse and stem from almost 140 years of records, originating from handwritten field notes, unpublished project documents, various digital sources, published reports, and meta-knowledge of the observers. The project resulted in data series with metadata for 63 individual Swiss glaciers, including more than 60 000 point observations of mass balance. Data were systematically analysed and homogenized, e.g. by supplementing partly missing information based on correlations inferred from direct measurements. A system to estimate uncertainty in all individual observations was developed indicating that annual point balance is measured with a typical error of 0.07 m water equivalent (w.e.), while the average error in winter snow measurements is 0.20 m w.e. Our dataset permits further investigating the climate change impacts on Swiss glaciers. Results show an absence of long-term trends in snow accumulation over glaciers while melt rates have substantially increased over the last 3 decades. The complete dataset is available at DOI 10.18750/massbalance.point.2021.r2021 (GLAMOS, 2021).
... In contrast to MM, retreat at MOR since the late 1800s has only been interrupted by a standstill in the 1980s but not by any significant advances, highlighting a longer volume response time at MOR of c. 32 years (Zekollari et al., 2014). MOR is a benchmark site for glaciological research (Klok and Oerlemans, 2002;Nemec et al., 2009;Zekollari and Huybrechts, 2018) and has more recently also become a key site for geoengineering investigations (Oerlemans et al., 2017). Recent mass balance measurements, available for the period 2001/02 to 2019/20, document a mean mass loss of 0.956 m w.e. per year (GLAMOS, 1881(GLAMOS, -2019. ...
The term ‘Little Ice Age’ (LIA) is classically used to define a period of repeated and extensive glacier advances during the last millennium. In the meanwhile, this term is also used to address the period of relatively low temperatures between the Medieval Climate Anomaly (MCA), or Medieval Warm Period, and present-day warming. The end of the LIA is generally set to the mid or late 1800s CE, however, the published onset dates of the LIA are more variable from the mid 1200s to the late 1500s. At Mont Miné and Morteratsch glaciers, Swiss Alps, we sampled and subsequently analysed detrital as well as in situ tree remnants from the early LIA period. At both glaciers, trees with lifespans of up to about 400 years were buried at various lateral moraine sites. The corresponding advance of both glaciers can be traced from the 1280s until the 1310s. At Morteratsch glacier, this early LIA advance phase culminated likely around 1375 CE. Evidence collected at both glaciers indicates that the ice surfaces were at least c. 12–15 m from the lateral moraine crests deposited during the maximum extent of the LIA. This suggests a similar (though very slightly weaker) magnitude than later LIA advances at our sites. The advances of Mont Miné and Morteratsch glaciers coincide with relatively cool summer temperatures from the late 1200s to the late 1300s. Taken together, the onset of the Little Ice Age in the Alps can be considered to be c. 1260 CE. The Little Ice Age was not a uniform period, but had several phases as can be derived from the records of Alpine glaciers and summer temperatures. We propose a subdivision of the LIA in the European Alps into an early (1260–1380 CE), an intermediate (1380–1575 CE) and a main (1575–1860 CE) phase.
... Continuous seasonal monitoring at a dense stake network is performed since 1991 on Ghiacciaio del Basòdino, southern Switzerland (Fig. 6). On Vadret Pers, southeastern Switzerland, a network of stakes in the ablation area has been 370 observed since 20 years (Zekollari and Huybrechts, 2018). ...
Glacier monitoring in Switzerland has resulted in some of the longest and most complete data series globally. Mass balance observations at individual locations, starting in the 19th century, are the backbone of the monitoring as they represent the raw and original glaciological data demonstrating the response of snow accumulation and snow/ice melt to changes in climate forcing. So far, however, the variety of sources of historic measurements has not been systematically processed and documented. Here, we present a new complete and extensive point glacier mass balance dataset for the Swiss Alps that provides attributes for data quality and corresponding uncertainties. Original sources were digitized or re-assessed to validate or to correct existing entries and to identify metadata. The sources of data are highly diverse and stem from almost 140 years of records, originating from handwritten field notes, unpublished project documents, various digital sources, published reports, as well as meta-knowledge of the observers. The project resulted in data series with metadata for 63 individual Swiss glaciers, including more than 60'000 point observations of mass balance. Data were systematically analyzed and homogenized, e.g. by supplementing partly missing information based on correlations inferred from direct measurements. A system to estimate uncertainty in all individual observations was developed indicating that annual point balance is measured with a typical error of 0.07 m water equivalent (w.e.), while the average error in winter snow measurements is 0.20 m w.e. Our dataset permits further investigating the climate change impacts on Swiss glaciers. Results show an absence of long-term trends in snow accumulation over glaciers, while melt rates have substantially increased over the last three decades.
... These local elevation changes result from an interaction between mass balance and ice flow processes and therefore do not allow the mass balance distribution to be directly determined over glaciers (Berthier and Vincent, 2012). However, having such a mass balance distribution over glaciers is of large interest as this can be used to accurately calibrate mass balance models used in large-scale glacier modelling efforts to allow for example for an accurate calibration of mass balance gradients (Zekollari and Huybrechts, 2018;Marzeion et al., 2020). ...
... Vadret da Morteratsch, with a current length of approximately 6 km, is the main glacier and flows from the south to the north. Vadret Pers, which flows towards Vadret da Morteratsch from the south-east, became a separate glacier in 2015, when the glaciers disconnected (Zekollari and Huybrechts, 2018). At present, the two glaciers cover an area of about 15 km 2 with a volume of ca. 1 km 3 , making it the largest continuous ice area in the Bernina region. ...
... The upper parts of the glacier complex reach 4000 m a.s.l., originating at peaks such as Piz Bernina and Bellavista (Fig. 1). The glacier complex has been studied and monitored intensively with SMB stake measurements performed annually at the end of the ablation season since 2001 (Zekollari and Huybrechts, 2018). In addition, the geodetic mass balance of the 1980-2010 period was determined to be between −0.7 and Figure 1. ...
The surface mass balance (SMB) of a glacier provides the link between the glacier and the local climate. For this reason, it is intensively studied and monitored. However, major efforts are required to determine the point SMB at a sufficient number of locations to capture the heterogeneity of the SMB pattern. Furthermore, because of the time-consuming and costly nature of these measurements, detailed SMB measurements are carried out on only a limited number of glaciers. In this study, we investigate how to accurately determine the SMB in the ablation zone of Vadret da Morteratsch and Vadret Pers (Engadin, Switzerland) using the continuity equation method, based on the expression of conservation of mass for glacier flow with constant density. An elaborate dataset (spanning the 2017–2020 period) of high-resolution data derived from unoccupied aerial vehicle (UAV) measurements (surface elevation changes and surface velocities) is combined with reconstructed ice thickness fields (based on radar measurements). To determine the performance of the method, we compare modelled SMB with measured SMB values at the position of stakes. Our results indicate that with annual UAV surveys, it is possible to obtain SMB estimates with a mean absolute error smaller than 0.5 m of ice equivalent per year. Yet, our study demonstrates that to obtain these accuracies, it is necessary to consider the ice flow over spatial scales of several times the local ice thickness, accomplished in this study by applying an exponential decay filter. Furthermore, our study highlights the crucial importance of the ice thickness, which must be sufficiently well known in order to accurately apply the method. The latter currently seems to complicate the application of the continuity equation method to derive detailed SMB patterns on regional to global scales.
... Depuis, les modèles explicatifs ont été largement utilisés et adaptés dans leur forme et leur application géographique comme le Canada ouest (Letréguilly 1988), le Svalbard (Lefauconnier et Hagen 1990 ;Lefauconnier et al. 1999), la Norvège (Trachsel & Nesje 2015) et les Alpes (Vincent et Vallon 1997;Torinesi et al. 2002;Zekollari et Huybrechts 2018 ...
La Terre connaît depuis le milieu du XIXe siècle un bouleversement climatique marqué par une hausse importante des températures (+ 0.85°C sur la période 1880-2012). L’Arctique est la région du monde qui se réchauffe le plus rapidement soit 2 à 3 fois plus vite que la moyenne du globe. Dans ce contexte, tous les composants de la cryosphère arctique connaissent une modification de leur dynamique. En raison de leurs liens directs avec l’atmosphère, les glaciers comptent parmi les meilleurs indicateurs de ces variations climatiques. À l’image des autres glaciers du globe, les glaciers du Spitsberg qui couvrent 60% de la surface de l’île, sont dans une dynamique de retrait depuis la fin du Petit Âge Glaciaire. Ce retrait, évalué par des mesures de bilan de masse glaciaires s’est accéléré à partir des années 1980.Dans le cadre de cette thèse, nous avons cherché à participer à l’amélioration de la justesse et de la fiabilité des projections passées et futures des écoulements d’un bassin glaciaire arctique en comprenant également leur origine. En nous appuyant sur les nombreuses données acquises depuis plus de dix ans sur le glacier observatoire Austre Lovén au Spitsberg (78 °N), nous avons dans un premier temps identifié les facteurs nivo-météorologiques influençant le bilan de masse annuel de ce glacier (2008-2017). Après avoir appliqué un protocole rigoureux de traitement des données acquises in situ, nous avons utilisé la modélisation statistique explicative pour mettre en exergue non pas le rôle d’un facteur systématiquement prépondérant mais plutôt l’influence d’une combinaison de facteurs nivo-météorologiques sur les dynamiques glaciaires. Bien que l’enneigement hivernal joue un rôle majeur, l’amplitude de son influence sur le bilan glaciaire est en partie conditionnée par les facteurs de températures et précipitations. Par ailleurs, au regard de la surface du bassin glaciaire occupée par les versants (34%), nous avons évalué leur contribution au bilan hydro-glaciologique mesuré à l’exutoire. Grâce à des relevés à très haute résolution par LiDAR terrestre, la profondeur du manteau neigeux a été mesurée sur un échantillon représentatif des versants (2013 et 2014). La modélisation statistique a ici aussi permis de mettre en exergue le rôle de la pente et de l’orientation dans la distribution du manteau neigeux dans ces versants. A partir de ce constat, nous avons pu évaluer la contribution en eau non négligeable des versants au bilan hydro-glaciologique annuel lors de la période de fonte.
... www.nature.com/scientificreports/ The stake's elevation changes with time due to the melting of ice and glacial downward flow [56][57][58] . During seven years, the total elevation change is around 253 m for stake 1, 210 m for stake 2, and 183 m for stake 3 (kindly refer Statistical Analysis under Results and Discussion for Stake 1, 2 and 3 description). ...
... MLRA does not include the surface mass balance measurements from the stakes that could not survive for the whole study period. The involvement of these kinds of measurements will surely raise the biases due to the gap in their data record 56 . ...
... Here, x 1 andx 2 is represented by the z-score of the meteorological parameters, i.e., temperature and precipitation. The monthly temperature and precipitation data show a weak correlation (R 2 = 0.3), and this non-dependency is a common approach for MLRA performed on surface mass balance series e.g., 56,78,79 . We have converted the meteorological data to a z-score. ...
In the present study, we analyze a field-based seven-year data series of surface mass-balance measurements collected during 2011/12 to 2017/18 on Naradu Glacier, western Himalaya, India. The average annual specific mass balance for the said period is − 0.85 m w.e. with the maximum ablation of − 1.15 m w.e. The analysis shows that the topographic features, south and southeast aspects and slopes between 7 to 24 degrees are the reasons behind the maximum ablation from a particular zone. The causes of surface mass balance variability have been analyzed through multiple linear regression analyses (MLRA) by taking temperature and precipitation as predictors. The MLRA demonstrates that 71% of the observed surface mass balance variance can be explained by temperature and precipitation. It clearly illustrates the importance of summer temperature, which alone explains 64% variance of surface mass balance. The seasonal analysis shows that most of the surface mass balance variability is described by summer temperature and winter precipitation as two predictor variables. Among monthly combinations, surface mass balance variance is best characterized by June temperature and September precipitation.
... MLRA does not include those SMB measurements which are from the stakes that were not able 147 to survive for the whole study period. The involvement of these kinds of measurements will surely 148 raise the biases due to the gap in their dada record [55]. ...
... The stakes elevation change with time due to glacier flow and changes in local ice thickness [55][56][57] ...
... To find the relation between meteorological data and SMB perturbation, the MLRA approach has 168 been used [55,62] by considering below equation 2. This correlation analysis required the abandon 169 of the effect of measurement of different meteorological parameters in different units (here, the 170 temperature in degree C and precipitation in mm w.e.) and hence these parameters have been 171 standardised by converting the data to z-score. ...
In view of climate change, Himalayan glaciers are losing its mass. In present study we analyzed 7 year long field based data series of surface mass-balance measurements performed between 2011/12 and 2017/18 at Naradu glacier, western Himalaya. The average specific mass balance for the studied period was 0.83 m w.e. with a highest melting of 1.15 m w.e. The analysis of topographic features showed that south and southeast aspect along with the presence of debris cover area and the slope between 18 to 36 degree are the major factors which causes highest melting from a particular zone. For better understanding of SMB variability and its causes, multiple linear regression analyses (MLRA) was performed by taking temperature and precipitation as predictors. The temperature and precipitation records were taken from NASA GIOVANNI website. The MLRA shows that 71% of the variance of observed SMB can be explained by temperature and precipitation. The MLRA shows the importance of summer half-year temperature. This variable alone explains the 64% variance of observed SMB. The seasonal period analysis showed that with two predictor variables most of the SMB variability is described by summer temperature and winter precipitation. All monthly combinations show that SMB variance is best described by June temperature and September precipitation.
... We addressed these objectives with data collected during a survey at the Vadret da Morteratsch Glacier in the Swiss Alps. This glacier has been the focus of numerous studies in recent decades 4,21,45,46 . In particular, Oerlemans et al. ...
... summers. This glacier has been extensively studied in recent years 4,21,45,46 . Morteratsch Glacier has been rapidly retreating 21 , and it represents the perfect test bed for studying the impact of glacier algae in the European Alps. ...
The melting of glaciers and ice sheets is nowadays considered a symbol of climate change. Many complex mechanisms are involved in the melting of ice, and, among these processes, surface darkening due to organic material on bare ice has recently received attention from the scientific community. The presence of microbes on glaciers has been shown to decrease the albedo of ice and promote melting. Despite several studies from the Himalaya, Greenland, Andes, and Alaska, no quantitative studies have yet been conducted in the european Alps. in this paper, we made use of DnA sequencing, microscopy and field spectroscopy to describe the nature of glacier algae found at a glacier (Vadret da Morteratsch) of the European Alps and to evaluate their effect on the ice-albedo feedback. Among different algal species identified in the samples, we found a remarkable abundance of Ancylonema nordenskioeldii, a species that has never previously been quantitatively documented in the Alps and that dominates algal blooms on the Greenland ice Sheet. our results show that, at the end of the ablation season, the concentration of Ancylonema nordenskioeldii on the glacier surface is higher than that of other algal species (i.e. Mesotaenium berggrenii). Using field spectroscopy data, we identified a significant correlation between a reflectance ratio (750 nm/650 nm) and the algae concentration. This reflectance ratio could be useful for future mapping of glacier algae from remote sensing data exploiting band 6 (740 nm) and band 4 (665 nm) of the MultiSpectral Instrument (MSI) on board Sentinel-2 satellite. Here we show that the biological darkening of glaciers (i.e. the bioalbedo feedback) is also occurring in the european Alps, and thus it is a global process that must be taken into account when considering the positive feedback mechanisms related to glacier melting.
... However, in the vast majority of studies, accumulation and ablation periods are defined between fixed dates (e.g. 1 October-30 April for the accumulation period in the northern mid-latitudes) based on optimizations. As discussed in Zekollari and Huybrechts (2018), these fixed periods may not be the best to describe SMB variability through statistical correlation. Moreover, the ablation season will likely evolve in the coming century due to climate warming. ...
We present a novel approach to simulate and reconstruct annual glacier-wide surface mass balance (SMB) series based on a deep artificial neural network (ANN; i.e. deep learning). This method has been included as the SMB component of an open-source regional glacier evolution model. While most glacier models tend to incorporate more and more physical processes, here we take an alternative approach by creating a parameterized model based on data science. Annual glacier-wide SMBs can be simulated from topo-climatic predictors using either deep learning or Lasso (least absolute shrinkage and selection operator; regularized multilinear regression), whereas the glacier geometry is updated using a glacier-specific parameterization. We compare and cross-validate our nonlinear deep learning SMB model against other standard linear statistical methods on a dataset of 32 French Alpine glaciers. Deep learning is found to outperform linear methods, with improved explained variance (up to +64 % in space and +108 % in time) and accuracy (up to +47 % in space and +58 % in time), resulting in an estimated r2 of 0.77 and a root-mean-square error (RMSE) of 0.51 m w.e. Substantial nonlinear structures are captured by deep learning, with around 35 % of nonlinear behaviour in the temporal dimension. For the glacier geometry evolution, the main uncertainties come from the ice thickness data used to initialize the model. These results should encourage the use of deep learning in glacier modelling as a powerful nonlinear tool, capable of capturing the nonlinearities of the climate and glacier systems, that can serve to reconstruct or simulate SMB time series for individual glaciers in a whole region for past and future climates.
... This is also the case in the European Alps (Fischer et al., 2015;Berthier et al., 2016;Dehecq et al., 2016), where glaciers have been subject to strongly negative mass balances (e.g. Charalampidis et al., 2018;Thibert et al., 2018;Vincent et al., 2018;Zekollari & Huybrechts, 2018). By retreating, glaciers lose ice at their lower elevations which has a stabilizing feedback on their mass balance, hence reducing the imbalance between glacier geometry and the climatic conditions (hereafter referred to as 'glacier-climate imbalance'). ...
Glaciers in the European Alps rapidly lose mass to adapt to changes in climate conditions. Here, we investigate the relationship and lag between climate forcing and geometric glacier response with a regional glacier evolution model accounting for ice dynamics. The volume loss occurring as a result of the glacier‐climate imbalance increased over the early 21st century, from about 35% in 2001 to 44% in 2010. This committed loss reduced to ~40% by 2018, indicating that temperature increase was outweighing glacier retreat in the early 2000s but that the fast retreat effectively somewhat diminished glacier imbalances. We analyze the lag in glacier response for each individual glacier and find mean response times of 50 ± 28 years. Our findings indicate that the response time is primarily controlled by glacier slope and secondarily by elevation range and mass balance gradient, rather than by glacier size.
