Lavrentyev, Ivan I

Saks T., Rinterknecht V., Lavrentiev I., Béra G., Mattea E., Hoelzle M.

The Koksu River valley is located in the Pamir‐Alay mountain range and contains 25 glaciers larger than 1 km2 and numerous smaller glaciers. The largest glacier in the catchment is Abramov Glacier with a current surface area of 22.55 km2 (in 2022), which was extensively monitored between 1965 and 1999, and resumed in 2011. The long and detailed mass balance time series provide, among other information, benchmark climate variables for the Pamir‐Alay range. We report 10 new cosmogenic 10Be exposure dates of glacial moraines directly deposited by Abramov Glacier to extend the glacial history of the valley. Six boulders indicate that the Local Last Glacial Maximum occurred at 17.1±1.0 ka. Four boulders suggest a Little Ice Age (LIA) glacial advance around AD 1750. Secular glacier mass balance reconstructions suggest a progressively negative mass balance since the LIA advance. The decrease in mass balance accelerated in the last quarter of the 20th century. Results from repeated ground penetrating radar (GPR) measurements suggest that Abramov Glacier lost about 403 million m3 of ice volume between 1986 and 2018. Based on the reconstruction of the glacier surface, the corresponding equilibrium line altitude, which is closely correlated with the mass balance, increased by about 70 to 80 m during this period. Our results also suggest that Abramov Glacier has become increasingly out of equilibrium with the climate over the last two decades. This is supported by repeated GPR measurements of the tongue area, which indicate a dramatic decrease in glacier area and ice volume over the period 1986–2018.

Mikhalenko V., Kutuzov S., Toropov P., Legrand M., Sokratov S., Chernyakov G., Lavrentiev I., Preunkert S., Kozachek A., Vorobiev M., Khairedinova A., Lipenkov V.

Abstract. In this study, we present a seasonally resolved accumulation record spanning from 1750 to 2009 Common Era (CE), based on a 181.8 m ice core obtained from the Elbrus Western Plateau in the Caucasus. We implemented various methods to account for uncertainties associated with glacier flow, layer thinning, and dating. Additionally, we applied a novel approach to calculate a seasonal calendar for meteorological data, enabling comparison with ice core records. The reconstructed accumulation data were compared with available meteorological data, gridded precipitation records, and paleo-reanalysis data. Reconstructed accumulation is representative for a large region south of the Eastern European plain and Black Sea region with summer precipitation being the primary driver of precipitation variability. We identified a statistically significant relationship between changes in regional precipitation and fluctuations in the North Atlantic Oscillation (NAO) index, which is, however, not stable over the entire period covered by the ice core.

Lavrentiev I.I., Nosenko G.A., Glazovsky A.F., Shein A.N., Ivanov M.N., Leopold Y.K.

Small glaciers of the Polar Urals are at the limits of their existence. Their state and changes serve as an important natural indicator of modern climatic changes. In 2019 and 2021, we performed ground-based radar studies of one of these glaciers, the IGAN Glacier, to measure ice thickness and snow cover. We used Picor-Led (1600 MHz), and VIRL-7 (20 MHz) GPRs. According to these data, the glacier has an average thickness of 49 m, maximum 113 m. The glacier has a polythermal structure: a cold ice layer with an average thickness of 12 m (maximum 43 m), overlaps the temperate ice with an average thickness of 37 m (maximum 114 m in the upper part of the glacier). The volume of ice contained in the glacier (in its studied part) is 14.3 × 106 m3, of which 10.89 × 106 m3 is temperate ice and 3.44 × 106 m3 is cold ice. For comparison: according to the radar data of 1968, the total ice thickness then reached 150 m in the central part, and the thickness of the upper layer of cold ice was 40–50 m. Radar snow measurement survey allowed us to plot the distribution of seasonal snow thickness over the glacier surface in 2019 and 2021, where a general spatial pattern of snow thickness increase from 2 m on the glacier terminus to 8 m and more towards the back wall of the cirque which is due to the significant influence of avalanche nourishment and wind transport. Over the last decade, the glacier has lost about 3.2 × 106 m3 of ice, and if the rate of loss continues, it may disappear in 40–50 years. However, this process may have a non-linear character, as it involves not only climatic factors, but also local terrain features, on the one hand contributing to a high accumulation of snow, on the other hand – to the formation of a glacial lake during glacier retreat, which may intensify ablation.

Lavrentiev I.I., Smirnov A.M., Toropov P.A., Elagina N.E., Kiseleva T.D., Drozdov E.D., Degtyarev A.I.

Received August 29, 2023; revised 4, September 2023; accepted October 2, 2023In June 2023, mass-balance and meteorological observations on Elbrus were expanded: monitoring of the Mikelchiran glacier on the northern slope of the volcano was added to the permanent observations on the southern slope (Garabashi glacier). Such synchronized observations on the opposite macro-slopes of Elbrus have not been carried out before.

Chizhova J.N., Mikhalenko V.N., Kutuzov S.S., Lavrentiev I.I., Lipenkov V.Y., Kozachek A.V.

Received July 28, 2023; revised September 2, 2023; accepted October 2, 2023A study of the isotope signature of glacial ice in the Western Elbrus Plateau (the Caucasus) was made on the basis of five ice cores obtained in different years with high resolution. It was shown that the isotopic characteristics of ice are associated with the processes of accumulation and wind scouring of snow. Three ice cores were obtained in 2013 (C–1, C–2 and C–3), one in 2017 (C–4) and one more in 2018 (C–5). Core sampling was performed with a resolution of 5 cm. Isotopic analysis was done at the CERL laboratory (AARI) using a Picarro L2130-i isotope analyzer, the accuracy was 0.06‰ for δ18О and 0.30‰ for δ2Н. The values of δ18О and δ2Н of the ice of the Western Plateau generally vary from –5 to –30‰ and from –18.7 to –225.8‰, respectively, with well-defined seasonality. Comparison of the isotope record for all cores showed that the differences in accumulation for individual seasons reach 0.3 m w. eq., differences in accumulation for individual seasons averaged over 5 years is approximately 0.2 m w.eq. The absolute differences in the average seasonal values of δ18O associated with wind scouring and spatial redistribution of snow (deposition noise), averaged over 5 years, reached 1.38‰. The irregularity of precipitation amount within the season and errors in core dating are an additional contribution to non-climate variance (noise of definition). The absolute difference in the average seasonal values of δ18О associated with this type of noise averaged over 5 years is 1.7‰. Thus, the total uncertainty for two different types of noise can be estimated at 2.2‰, which is about 20% of the annual seasonal amplitude of δ18O values of the glacier ice in the Western Plateau (the average difference between the δ18O values of warm and cold seasons is ~10–11‰). One of the problems of linking the isotope record to the annual temperature record at the weather station was solved by using ammonium concentrations for dating the C-1 ice core and calculating the “ideal” annual variation of δ18O values by a cosine function of the annual amplitude. Using ammonium ion (\({\text{NH}}_{4}^{ + }\)) concentration each annual layer in C-1 ice core was divided into two parts associated to snow deposition in winter and in summer. It also showed δ18O values associated to change of seasons. The calculation of the cosine function showed the simplified δ18O values for each month of a particular year, due to which the δ18O values of the season boundaries in the ice core were linked to calendar months. This assimilation allowed us to compare the obtained average seasonal values of δ18О from the core with instrumental observations at the Klukhorskiy Pass meteorological station. The δ18O values of winter seasons have a weak relationship with surface temperatures, not only due to wind erosion, but also due to the high interannual variability of snow accumulation. At the same time, the average δ18O values of the warm seasons are significantly positive correlated with surface temperature (r = 0.7, p = 0.1), so ice core δ18O records can be used as a temperature proxy of the warm period.

Mikhalenko V., Kutuzov S., Toropov P., Legrand M., Sokratov S., Chernyakov G., Lavrentiev I., Preunkert S., Kozachek A., Vorobiev M., Khairedinova A., Lipenkov V.

Abstract. In this study, we present a seasonal-resolution accumulation record spanning the period from 1750 to 2009 Common Era (CE), based on a 181.8-m ice core obtained from the Elbrus Western Plateau in the Caucasus. We implemented various methods to account for uncertainties associated with glacier flow, layer thinning, and dating. Additionally, we developed a novel approach to calculate a seasonal calendar for meteorological data, enabling comparison with ice core records. The reconstructed accumulation data were compared with available meteorological data, gridded precipitation records, and paleo reanalysis data. Reconstructed accumulation is representative for a large region south of Eastern European plain and Black sea region. Summer precipitation was found to be the primary driver of precipitation variability. We identified a statistically significant but unstable in time relationship between changes in precipitation in the region and fluctuations of the North Atlantic Oscillation (NAO) index.

Mikhalenko V., Kutuzov S., Toropov P., Legrand M., Sokratov S., Chernyakov G., Lavrentiev I., Preunkert S., Kozachek A., Vorobiev M., Khairedinova A., Lipenkov V.

Lavrentiev I.I., Nosenko G.A., Glazovsky A.F., Shein A.N., Ivanov M.N., Leopold Y.K.

Small glaciers of the Polar Urals are at the limits of their existence. Their state and changes serve as an important natural indicator of modern climatic changes. In 2019 and 2021, we performed ground-based radar studies of one of these glaciers, the IGAN Glacier, to measure ice thickness and snow cover. We used Picor-Led (1600 MHz), and VIRL–7 (20 MHz) GPRs. According to these data, the glacier has an average thickness of 49 m, maximum 114 m. The glacier has a polythermal structure: a cold ice layer with an average thickness of 12 m (maximum 43 m), overlaps the temperate ice with an average thickness of 37 m (maximum 114 m in the upper part of the glacier). The volume of ice contained in the glacier (in its studied part) is 14.3 × 106 m3, of which 10.89 × 106 m3 is temperate ice and 3.44 × 106 m3 is cold ice. For comparison: according to the radar data of 1968, the total ice thickness then reached 150 m in the central part, and the thickness of the upper layer of cold ice was 40–50 m. Radar snow gauge survey allowed to build schemes of seasonal snow thickness distribution over the glacier surface in 2019 and 2021, where there is a general spatial pattern of snow thickness growth from 2 m on the glacier terminus to 8 m or more to the rear wall of the corrie, which is due to the significant influence of avalanche feeding and wind transport. The glacier has lost about 3.2 × 106 m3 of ice per last decade, if the rate of loss continues, it may disappear in 40–50 years. However, this process may have a non-linear nature, as it involves not only climatic factors, but also local terrain features, on the one hand contributing to a high accumulation of snow, on the other – the formation of a glacial lake during glacier retreat, which may increase ablation.

Lavrentiev I.I., Kutuzov S.S., Mikhalenko V.N., Sudakova M.S., Kozachek A.V.

Khromova T.E., Nosenko G.A., Glazovsky A.F., Muraviev A.Y., Nikitin S.A., Lavrentiev I.I.

Macheret Y.Y., Glazovsky A.F., Vasilenko E.V., Lavrentiev I.I., Matskovsky V.V.

Kochtitzky W., Copland L., Van Wychen W., Hugonnet R., Hock R., Dowdeswell J.A., Benham T., Strozzi T., Glazovsky A., Lavrentiev I., Rounce D.R., Millan R., Cook A., Dalton A., Jiskoot H., et. al.

In the Northern Hemisphere, ~1500 glaciers, accounting for 28% of glacierized area outside the Greenland Ice Sheet, terminate in the ocean. Glacier mass loss at their ice-ocean interface, known as frontal ablation, has not yet been comprehensively quantified. Here, we estimate decadal frontal ablation from measurements of ice discharge and terminus position change from 2000 to 2020. We bias-correct and cross-validate estimates and uncertainties using independent sources. Frontal ablation of marine-terminating glaciers contributed an average of 44.47 ± 6.23 Gt a−1 of ice to the ocean from 2000 to 2010, and 51.98 ± 4.62 Gt a−1 from 2010 to 2020. Ice discharge from 2000 to 2020 was equivalent to 2.10 ± 0.22 mm of sea-level rise and comprised approximately 79% of frontal ablation, with the remainder from terminus retreat. Near-coastal areas most impacted include Austfonna, Svalbard, and central Severnaya Zemlya, the Russian Arctic, and a few Alaskan fjords. As glaciers terminate into the ocean, mass is lost through frontal ablation where the ice meets the ocean. Here the authors estimate decadal frontal ablation from 2000 to 2020 of 1496 glaciers in the Northern Hemisphere, and find that frontal ablation makes up 79% of ice discharge to the ocean.

Borisik A., Novikov A., Lavrentiev I., Glazovsky A.

<p>Glaciers on Svalbard have been shrinking in recent decades in response to current climate change. Most of them have decreased in size, area and surface elevation with stable negative or even accelerated changes in mass balance. Many of them are of the polythermal type, and as they shrink, their thermal regime might also change significantly depending on climate and local parameters, such as distribution of ice facies, firn thickness, and other factors affecting hydrology and glacier movement. In this study, we used data from repeated GPR surveys in 2010/12 and 2020/21 to identify likely changes in the thermal regime of the two polythermal glaciers Fridtjovbreen and Erdmanbreen in the western part of the Nordenskiöldland. These changes we have identified by comparison of changes in the depth of the internal reflection horizon (IRH) which corresponds to the cold-temperate transition surface (CTS) in polythermal glaciers.</p><p>Comparison of radio-echo sounding (RES) data obtained along the same transverse and longitudinal transects shows that in the last decade the most prominent CTS changes have occurred in the upper western basin of the Fridtjovbreen, where the mean total ice thickness decreased with rate −0.76 m a<sup>-1</sup> (from 151 to 144 m in 9 years), meanwhile the thickness of the temperate ice core decreased with rate −2.52 m a<sup>-1</sup> (from 115 to 92 m). As a result, with a general reduction in the thickness of the glacier, its upper cold layer increased from 36 to 52 m. These changes we attribute to the reduction of the firn area in this basin, which resulted in less thermal insulation and water retention and internal refreezing, and, therefore, in the fast cold front penetration into the glacier body with rates more than 3 times higher than the glacier thinning.</p>

ХРОМОВА Т.Е., НОСЕНКО Г.А., ГЛАЗОВСКИЙ А.Ф., МУРАВЬЕВ А.Я., НИКИТИН С.А., ЛАВРЕНТЬЕВ И.И.

The new Inventory of the Russian glaciers has been created at the Institute of Geography of the Russian Academy of Sciences mainly on the basis of the Sentinel 2 satellite images for 2016–2019 with the aim of assessing the current state of glacier systems and as a basis for monitoring and re-inventorying. Delineation of glacier outlines was manually made to reduce uncertainties, especially for small glaciers. The database structure is compatible with the global and national glacier archives and includes the main glacial parameters. Additionally a classification of possible catastrophic phenomena of glacial genesis was developed: dynamically unstable glaciers, glacier lakes, icebergs, etc. The data base is available online (www.glacrus.ru). At present, there are 22 glacial systems in Russia with a total area of 54,518 km2. The largest glacial systems by area are located in the Arctic archipelagos: Novaya Zemlya, Severnaya Zemlya, and Franz Josef Land. The glacial systems of the Caucasus, Kamchatka, and Altai are the largest by area in the continental part of Russia. The main group consists of 13 small glacial systems, the area of which does not exceed 100 km2. They are located in different glaciological zones: from the De Long Islands in the Arctic to the Eastern Sayan in southern Siberia. Since the compilation of the USSR glacier Inventory (1965–1982), the area of glaciers has decreased by 5,594 km2, or 9.3%. The area of polar glaciers has decreased in smaller degree than that of glaciers in mountainous regions. The results of our research confirm the trend of reducing the area of glaciers throughout the Russian territory. The magnitude and rate of changes depend on local climatic and orographic features. The exception is the glaciers of the volcanic regions of Kamchatka, the area of which has increased or remained unchanged.

МАЧЕРЕТ Ю.Я., ГЛАЗОВСКИЙ А.Ф., ВАСИЛЕНКО Е.В., ЛАВРЕНТЬЕВ И.И., МАЦКОВСКИЙ В.В.

The distribution of cold and temperate ice and water in polythermal glaciers significantly affects their dynamics, thermal and hydrological regime. Radar techniques are an effective remote method of their studies that allows one to determine a glacier thickness by the delay time and to estimate the water content in temperate ice and at bedrock by the intensity of reflections from the interface between cold and temperate ice and the glacier bed. In case study of Austre Gronfjordbreen in Spitsbergen and Central Tuyksu glacier in Tien Shan we consider the features of their hydrothermal structure in spring and summer periods using the data of ground-based radio-­echo sounding at frequency of 20 MHz. To estimate the relative water content, we used data from measurements of relative power reflections from the cold-temperate ice interface, at the bedrock, and from the temperate ice body. In these glaciers (Austre Gronfjordbreen and Central Tuyksu), the average thickness of cold and temperate ice is, respectively, 61 ± 6 and 27 ± 2 m, and 39 ± 4 and 20 ± 2 m, the volume of cold ice is 0.466 ± 0.005 km 3 and 0.044 ± 0.002 km 3 , and volume of temperate ice is 0.104 ± 0.001 and 0.034 ± 0.001 km 3 . Warm ice contains 2080 × 10 3 and 680 × 10 3 m 3 of water, respectively, with an average content of 2%. Measurements along the longitudinal profiles of these glaciers showed that in some parts on Austre Gronfjordbreen in the spring period the average intensity of reflections from the cold­temperate ice interface and the bedrock is −0.02 – −26.3 and −6.0 – −11.8 dB, respectively, and at the whole profile this is −13.36 dB. At Central Tuyuksu glacier the spring values are −14.5 – −32.4 and −29.6 dB, respectively. We attribute such differences of glaciers to the different water content in the temperate ice below and above these boundaries, to the specific distribution of the ice facies zones and glacial nourishment, to the different intensity of surface melting in the spring and summer periods, and to the different crevassing and velocity of glaciers.

Švinka L., Karušs J., Lamsters K.

Auer A.G., van der Bilt W.G., Schomacker A., Bakke J., Støren E.W., Buckby J.M., Cederstrøm J.M., van der Plas S.

Abstract Accelerated Arctic warming and wetting has global impacts, as the region’s glaciers and ice caps respond to variations in temperature and precipitation, impacting global sea-level change. But as the observations needed to calibrate models are scarce, predictions cannot confirm if increases in snowfall can help offset melt. Here, we analyze two 14,000-year-long glacier-fed lake sediment records from the Svalbard archipelago to examine the response of a resilient ice cap (Åsgardfonna) to warmer-than-present Holocene Thermal Maximum conditions. End-Member Modelling allowed us to unmix the diluted grain size signal of rock flour – a widely used proxy for past glacier change, and surface runoff – an indicator of hydrological intensification. Our findings reveal that Åsgardfonna survived and may have advanced despite warmer conditions, possibly due to enhanced snowfall driven by sea-ice loss. This suggests that future increases in precipitation could moderate glacier retreat in similar settings.

Steidl V., Bamber J.L., Zhu X.X.

Abstract. The ice thickness of the world's glaciers is mostly unmeasured, and physics-based models to reconstruct ice thickness cannot always deliver accurate estimates. In this study, we use deep learning paired with physical knowledge to generate ice thickness estimates for all glaciers of Spitsbergen, Barentsøya, and Edgeøya in Svalbard. We incorporate mass conservation and other physically derived conditions into a neural network to predict plausible ice thicknesses even for glaciers without any in situ ice thickness measurements. With a glacier-wise cross-validation scheme, we evaluate the performance of the physics-informed neural network. The results of these proof-of-concept experiments let us identify several challenges and opportunities that affect the model's performance in a real-world setting.

Diaconu C., Heidler K., Bamber J.L., Zekollari H.

Wang K., Wu Y., Qiu X., Zhu J., Zheng D., Shangguan S., Pan J., Liu Y., Jiang L., Li X.

Cai Y., He Y., Lang S., Cui X., Zhang X., Yao Z.

Hartl L., Schmitt C., Stuefer M., Jenckes J., Page B., Crawford C., Schmidt G., Yang R., Hock R.

Wu R., Liu G., Bao X., Lv J., Shama A., Zhang B., Mao W., Chen J., Yang Z., Zhang R.

Hu S., Zhou T., Wu B.

High-Mountain Asia (HMA) is an important source of freshwater since it holds the largest reservoir of frozen water outside the polar regions. HMA feeds ten great rivers, ultimately supporting more than 2 billion people. However, the threat of accelerated glacier melt, which is a consequence of unprecedented global warming since the early 1950s, threatens water resources in the surrounding countries. Accurate predictions of the near-term temperature change and synergistic mass loss of glaciers are essential but challenging to implement because of the impacts of internal climate variability. Here, based on large ensembles of state-of-the-art decadal climate prediction experiments, we provide evidence that the internally generated surface air temperature variations in HMA can be predicted multiple years in advance, and the model initialization has robust added value to the decadal prediction skill. Real-time decadal forecasts suggest that the HMA will experience accelerated warming in 2025-2032, where the surface warming will increase by 0.98 °C (0.67 to 1.33 °C; 5 % to 95 % range) relative to the reference period 1991-2020, which is equivalent to 1.75 times the observed warming during 2016-2023. The decadal predictability originates from extratropical Pacific decadal variability modes, which modulate the convective heating in the tropical Pacific and influence HMA via the eastward-propagating atmospheric Kelvin waves. Accelerated warming in the coming decade will likely increase the shrinkage of the glacier volume over the HMA by 1.4 %. This change poses unprecedented challenges, including potential water scarcity, ecosystem disruption, and increased risk of natural disasters, to HMA and surrounding regions.

Legrand M., Vorobyev M., Bokuchava D., Kutuzov S., Plach A., Stohl A., Khairedinova A., Mikhalenko V., Vinogradova M., Eckhardt S., Preunkert S.

Abstract. Atmospheric ammonia (NH3) is a key transboundary air pollutant that contributes to the impacts of nitrogen and acidity on terrestrial ecosystems. Ammonia also contributes to the atmospheric aerosol that affects air quality. Emission inventories indicate that NH3 was predominantly emitted by agriculture over the 19th and 20th centuries but, up to now, these estimates have not been compared to long-term observations. To document past atmospheric NH3 pollution in south-eastern Europe, ammonium (NH4+) was analysed along an ice core extracted from Mount Elbrus in the Caucasus, Russia. The NH4+ ice-core record indicates a 3.5-fold increase in concentrations between 1750 and 1990 CE. Remaining moderate prior to 1950 CE, the increase then accelerated to reach a maximum in 1989 CE. Comparison between ice-core trends and estimated past emissions using state-of-the-art atmospheric transport modelling of submicron-scale aerosols (FLEXPART (FLEXible PARTicle dispersion) model) indicates good agreement with the course of estimated NH3 emissions from south-eastern Europe since ∼ 1750 CE, with the main contributions from south European Russia, Türkiye, Georgia, and Ukraine. Examination of ice deposited prior to 1850 CE, when agricultural activities remained limited, suggests an NH4+ ice concentration related to natural soil emissions representing ∼ 20 % of the 1980–2009 CE NH4+ level, a level mainly related to current agricultural emissions that almost completely outweigh biogenic emissions from natural soil. These findings on historical NH3 emission trends represent a significant contribution to the understanding of ammonia emissions in Europe over the last 250 years.

Zheng C., Zhang Z., Kong X., Granger D., Zhao Z., Zhang Z.

Tibetan Plateau and its surrounding mountains (TPSM) have experienced prominent glacier retreat since the Global Last Glacial Maximum, while the detailed deglaciation process remains unclear. To investigate the spatiotemporal pattern of the glacier retreat history, we compiled 196 moraines dating from 26.5 to 10 ka based on 994 boulder 10Be exposure age from seven regions on the TPSM and calculated the separated component Gaussians of moraine ages. The result shows that synchronous glacier retreat across the entire TPSM began around 22 ka in response to onset of rising local summer insolation. Moraine abandonment centered at five stages, i.e., 22–20, 19–18 ka, 17–16, 14.5–12.9, and 11.6–10 ka. Synchronous retreat occurred at 22–20 ka and 14.5–12.9 ka in all seven regions, while at 19–18 ka, it occurred in all regions except Tianshan. Pamir and NE Tibet showed no retreat at 17–16 ka, likely due to the sustained influence of the Westerlies. The stage at 11.6–10 ka was absent in Central Tibet due to lack of chronology from the perched moraines therein. This work offers new insights into the evolution of the cryosphere and adjustments in atmospheric circulation on the TPSM.

Sobisevich A., Kuzmin Y., Likhodeev D., Kotov A., Desherevsky A., Myasnikov A., Gravirov V., Presnov D., Kanonidi K., Puzich I., Dudarov Z., Dolov S., Suvorova I., Sentsov A., Balashov G.

A full-scale geophysical observatory in the North Caucasus, which was established to study volcanic activity in the Elbrus area, has been functioning for more than 10 years. Results of experimental studies performed at the observatory, located in the deep tunnel, are presented. Special attention is paid to the stability of metrologically significant parameters of precise information-measuring systems, taking into account different nature noises. Technical characteristics of installed geophysical instruments are given, and the principles of their operation are described. Examples of instrumental observations are also presented; for example, tidal deformations reflecting structural features of the geological environment in the area of the Elbrus volcanic edifice and associated with the presence of magmatic structures were investigated. It was shown that diurnal and semidiurnal harmonics observed in the microvariations of temperature can be caused, among other things, by the influence of tidal effects on the convective component of heat–mass transfer.

Liang W., Duan W., Chen Y., Fang G., Zou S., Li Z., Qiu Z., Lyu H.

Abstract The Kumalak River, a typical alpine glacierized catchment in the Tianshan region, experiences complex flooding driven by glacier meltwater, snowmelt, and rainfall. However, the mechanisms driving these processes under climate change remain unclear. To address this, a SWAT-Glacier hydrological model and a degree–day factor model were used for snowmelt, glacier meltwater, and rainfall calculations. Two Long Short-Term Memory (LSTM) models (LSTM-SG and LSTM-DDF) were developed using these inputs, and additive decomposition and integrated gradient methods were applied to interpret flood mechanisms. Glacier meltwater was found to dominate annual maximum flood (AMF) events, while snowmelt drove annual spring maximum flood (AMFSp) events. For AMF events (1960–2018), contributions were 10.01–12.21% from snowmelt, 60.49–60.92% from glacier meltwater, and 26.86–29.50% from rainfall. For AMFSp events (1961–2018), contributions were 48.49–56.08% from snowmelt, 16.12–22.08% from glacier meltwater, and 27.79–29.42% from rainfall. These findings provide critical insights for enhancing flood prediction and optimizing water resource management.

Zhu Q.H., Li H.L., Ke C.Q.

AbstractIn order to monitor the dynamic changes of an unnamed glacier (called G1 Glacier) located in the Karakoram in detail, glacier surface velocities were extracted from 165 Sentinel‐1 SAR images with 12‐day and 24‐day time intervals from 2014 to 2020, glacier elevation changes were obtained from four ASTER stereo images, and glacier terminus evolutions were derived from four Landsat 8 images. Based on the high‐density glacier surface velocity results, four consecutive glacier sub‐surge events of the G1 Glacier ranging from 6 months to 1 yr between 2015 and 2019 were confirmed for the first time, accompanied by sporadic pulse events before and after the four sub‐surges. The velocity changes and impact range of the four glacier sub‐surges showed a trend of first increasing, then stabilizing and finally decreasing. At the same time, the accelerating area gradually moved downstream of the glacier. The changes in glacier elevation and the evolutions in the glacier terminus also proved the occurrence of glacier acceleration events. Sentinel‐1 SAR images with shorter time intervals could be used to identify multiple sub‐surge events and pulse events within a complete surge. Combining four sub‐surges and multiple pulse events, a complete chain of glacier large‐scale acceleration events from pulse to surge and then to pulse could be summarized, which might mean that the effective identification of pulse events provides the possibility for the early warning of glacier surge events.

Van Wychen W., Jiskoot H., Shannon K., Gorwill C.

Fuentes-Franco R., Docquier D., Koenigk T., Zimmermann K., Giorgi F.

AbstractWe use an ensemble of models participating in the Coupled Model Intercomparison Project phase 6 (CMIP6) to analyse the number of days with extreme winter precipitation over Northern Europe and its relationship to the North Atlantic Oscillation (NAO), for the historical period 1950–2014 and two future 21st-century scenarios. Here we find that over Northern Europe, the models project twice more extreme precipitation days by the end of the 21st century under the high-emission scenario compared to the historical period. We also find a weakening of the NAO variability in the second half of the 21st century in the high greenhouse gas emission scenario compared to the historical period, as well as an increasing correlation between extreme winter precipitation events and the NAO index in both future scenarios. Models with a projected decrease in the NAO variability across the 21st century show a positive trend in the number of days with extreme winter precipitation over Northern Europe. These results highlight the role played by NAO in modulating extreme winter precipitation events.

Kronenberg M., van Pelt W., Machguth H., Fiddes J., Hoelzle M., Pertziger F.

Abstract. Several studies identified heterogeneous glacier mass changes in western High Mountain Asia over the last decades. Causes for these mass change patterns are still not fully understood. Modelling the physical interactions between glacier surface and atmosphere over several decades can provide insight into relevant processes. Such model applications, however, have data needs which are usually not met in these data-scarce regions. Exceptionally detailed glaciological and meteorological data exist for the Abramov Glacier in the Pamir Alay range. In this study, we use weather station measurements in combination with downscaled reanalysis data to force a coupled surface energy balance–multilayer subsurface model for Abramov Glacier for 52 years. Available in situ data are used for model calibration and validation. We find an overall negative mass balance of −0.27 mw.e.a-1 for 1968/1969–2019/2020 and a loss of firn pore space causing a reduction of internal accumulation. Despite increasing air temperatures, we do not find an acceleration of glacier-wide mass loss over time. Such an acceleration is compensated for by increasing precipitation rates (+0.0022 mw.e.a-1, significant at a 90 % confidence level). Our results indicate a significant correlation between annual mass balance and precipitation (R2 = 0.72).

Lavrentiev I.I., Kutuzov S.S., Mikhalenko V.N., Sudakova M.S., Kozachek A.V.

Nagavciuc V., Ionita M., Kern Z., McCarroll D., Popa I.

Numerical simulations indicate that extreme climate events (e.g., droughts, floods, heat waves) will increase in a warming world, putting enormous pressure on society and political decision-makers. To provide a long-term perspective on the variability of these extreme events, here we use a ~700 years tree-ring oxygen isotope chronology from Eastern Europe, in combination with paleo-reanalysis data, to show that the summer drying over Eastern Europe observed over the last ~150 years is to the best of our knowledge unprecedented over the last 700 years. This drying is driven by a change in the pressure patterns over Europe, characterized by a shift from zonal to a wavier flow around 1850CE, leading to extreme summer droughts and aridification. To our knowledge, this is the first and longest reconstruction of drought variability, based on stable oxygen isotopes in the tree-ring cellulose, for Eastern Europe, helping to fill a gap in the spatial coverage of paleoclimate reconstructions. More extreme summer droughts and aridification in eastern Europe since 1850, relative to the past 700 years, probably resulted from a shift in atmospheric circulation patterns over the continent, suggest tree-ring cellulose oxygen isotope records.

Markle B.R., Steig E.J.

Abstract. Oxygen and hydrogen isotope ratios in polar precipitation are widely used as proxies for local temperature. In combination, oxygen and hydrogen isotope ratios also provide information on sea surface temperature at the oceanic moisture source locations where polar precipitation originates. Temperature reconstructions obtained from ice-core records generally rely on linear approximations of the relationships among local temperature, source temperature, and water-isotope values. However, there are important nonlinearities that significantly affect such reconstructions, particularly for source region temperatures. Here, we describe a relatively simple water-isotope distillation model and a novel temperature reconstruction method that accounts for these nonlinearities. Further, we examine in detail many of the parameters, assumptions, and uncertainties that underlie water-isotope distillation models and their influence on these temperature reconstructions. We provide new reconstructions of absolute surface temperature, condensation temperature, and source region evaporation temperature for all long Antarctic ice-core records for which the necessary data are available. These reconstructions differ from previous estimates due to both our new model and reconstruction technique, the influence of which is investigated directly. We also provide thorough uncertainty estimates for all temperature histories. Our reconstructions constrain the pattern and magnitude of polar amplification in the past and reveal asymmetries in the temperature histories of East and West Antarctica.

Azisov E., Hoelzle M., Vorogushyn S., Saks T., Usubaliev R., Esenaman uulu M., Barandun M.

Mass balance measurements for Golubin glacier in Northern Tien Shan, Kyrgyzstan, have been discontinuous over the last century, with significant data gaps. We provide a unique over 100-year-long mass balance series on daily resolution. We applied a temperature index model calibrated with glaciological measurements and validated with secular mass balances derived from independent length change observations. A comparison with other recent geodetic studies reveals good agreement. Golubin lost −0.16 ± 0.45 m w.e. a−1 from 1900/1901 to 2020/2021. From the long-term mass balance time series, we identify a shift to a more negative/less positive regime with time, with a steepening of the ablation and accumulation gradients, especially for the past two decades. We observe a parallel shift of the mass balance gradient accompanied by a rotation of the ablation gradient due to increased ablation at the glacier tongue and accumulation above the equilibrium line altitude. This tendency is believed to intensify in the future, affecting glaciers’ mass balance sensitivity to changes in atmospheric conditions and year-to-year variability and resulting in irregular melt water release feeding the rivers that provide water to Bishkek. These kinds of datasets are sparse for Tien Shan and, yet, indispensable to enhancing our understanding of glacier changes in High Mountain Asia.

Zhang W., Hou S., Wu S., Pang H., Sneed S.B., Korotkikh E.V., Mayewski P.A., Jenk T.M., Schwikowski M.

Abstract. Net accumulation records derived from alpine ice cores provide the most direct measurement of past precipitation. However, quantitative reconstruction of accumulation for past millennia remains challenging due to the difficulty in identifying annual layers in the deeper sections of ice cores. In this study, we propose a quantitative method to reconstruct annual accumulation from alpine ice cores for past millennia, using as an example an ice core drilled at the Chongce ice cap in the northwestern Tibetan Plateau (TP). First, we used laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) technology to develop ultra-high-resolution trace element records in three sections of the ice core and identified annual layers in each section based on seasonality of these elements. Second, based on nine 14C ages determined for this ice core, we applied a two-parameter flow model to established the thinning parameter of this ice core. Finally, we converted the thickness of annual layers in the three sample sections to past accumulation rates based on the thinning parameter derived from the ice flow model. Our results show that the mean annual accumulation rates for the three sample sections are 109 mm yr−1 (2511–2541 years BP), 74 mm yr−1 (1682–1697 years BP), and 68 mm yr−1 (781–789 years BP), respectively. For comparison, the Holocene mean precipitation is 103 mm yr−1. This method has the potential to reconstruct continuous high-resolution precipitation records covering millennia or even longer time periods.

Tielidze L.G., Nosenko G.A., Khromova T.E., Paul F.

Abstract. An updated glacier inventory is important for understanding glacier behaviour given the accelerating glacier retreat observed around the world. Here, we present data from a new glacier inventory for two points in time (2000, 2020) covering the entire Greater Caucasus (Georgia, Russia, and Azerbaijan). Satellite imagery (Landsat, Sentinel, SPOT) was used to conduct a remote-sensing survey of glacier change. The 30 m resolution Advanced Spaceborne Thermal Emission and Reflection Radiometer Global Digital Elevation Model (ASTER GDEM; 17 November 2011) was used to determine aspect, slope, and elevations, for all glaciers. Glacier margins were mapped manually and reveal that in 2000 the mountain range contained 2186 glaciers with a total glacier area of 1381.5 ± 58.2 km2. By 2020, the area had decreased to 1060.9 ± 33.6 km2 a reduction of 23.2 ± 3.8 % (320.6 ± 45.9 km2) or −1.16 % yr−1 over the last 20 years in the Greater Caucasus. Of the 2223 glaciers, 14 have an area > 10 km2, resulting in the 221.9 km2 or 20.9 % of total glacier area in 2020. The Bezengi Glacier with an area of 39.4 ± 0.9 km2 was the largest glacier mapped in the 2020 database. Glaciers between 1.0 and 5.0 km2 accounted for 478.1 km2 or 34.6 % in total area in 2000, while they accounted for 354.0 km2 or 33.4 % in total area in 2020. The rates of area shrinkage and mean elevation vary between the northern and southern and between the western, central, and eastern Greater Caucasus. Area shrinkage is significantly stronger in the eastern Greater Caucasus (−1.82 % yr−1), where most glaciers are very small. The observed increased summer temperatures and decreased winter precipitation along with increased Saharan dust deposition might be responsible for the predominantly negative mass balances of Djankuat and Garabashi glaciers with long-term measurements. Both glacier inventories are available from the Global Land Ice Measurements from Space (GLIMS) database and can be used for future studies.

Millan R., Mouginot J., Rabatel A., Morlighem M.

The effect of climate change on water resources and sea-level rise is largely determined by the size of the ice reservoirs around the world and the ice thickness distribution, which remains uncertain. Here, we present a comprehensive high-resolution mapping of ice motion for 98% of the world’s total glacier area during the period 2017–2018. We use this mapping of glacier flow to generate an estimate of global ice volume that reconciles ice thickness distribution with glacier dynamics and surface topography. The results suggest that the world’s glaciers have a potential contribution to sea-level rise of 257 ± 85 mm, which is 20% less than previously estimated. At low latitudes, our findings highlight notable changes in freshwater resources, with 37% more ice in the Himalayas and 27% less ice in the tropical Andes of South America, affecting water availability for local populations. This mapping of glacier flow and thickness redefines our understanding of global ice-volume distribution and has implications for the prediction of glacier evolution around the world, since accurate representations of glacier geometry and dynamics are of prime importance to glacier modelling. Potential sea-level rise from the world’s glaciers is 20% less than previously thought, according to an estimate based on high-resolution maps of glacier ice velocity and thickness.

Kochtitzky W., Copland L.

We mapped the terminus position for every marine-terminating glacier in the Northern Hemisphere for 2000, 2010, and 2020, including the Greenland Ice Sheet, to provide the first complete measure of their variability. In total, these 1,704 glaciers lost an average of 389.7 ± 1.6 km2 a−1 (total 7,527 ± 31 km2) from 2000 to 2020 with 123 glaciers becoming no longer marine-terminating over this period. Overall, 85.3% of glaciers retreated, 2.5% advanced, and the remaining 12.3% did not change outside of uncertainty limits. Outlet glaciers of the Greenland Ice Sheet are responsible for 61.9% of total area loss, although their rate of retreat was 34% less in 2010–2020 than 2000–2010. Glaciers with the largest area loss terminate in ice shelves or ice tongues, are surge-type, have an unstable basal geometry, or have an unusually wide calving margin.

Friedl P., Seehaus T., Braun M.

Abstract. Consistent and continuous data on glacier surface velocity are important inputs to time series analyses, numerical ice dynamic modeling and glacier mass flux computations. Since 2014, repeat-pass synthetic aperture radar (SAR) data have been acquired by the Sentinel-1 satellite constellation as part of the Copernicus program of the EU (European Union) and ESA (European Space Agency). It enables global, near-real-time-like and fully automatic processing of glacier surface velocity fields at up to 6 d temporal resolution, independent of weather conditions, season and daylight. We present a new global data set of glacier surface velocities that comprises continuously updated scene-pair velocity fields, as well as monthly and annually averaged velocity mosaics at 200 m spatial resolution. The velocity information is derived from archived and new Sentinel-1 SAR acquisitions by applying a well-established intensity offset tracking technique. The data set covers 12 major glacierized regions outside the polar ice sheets and is generated in an HPC (high-performance computing) environment at the University of Erlangen-Nuremberg. The velocity products are freely accessible via an interactive web portal that provides capabilities for download and simple online analyses: http://retreat.geographie.uni-erlangen.de (last access: 6 October 2021). In this paper, we give information on the data processing and how to access the data. For the example region of Svalbard, we demonstrate the potential of our products for velocity time series analyses at very high temporal resolution and assess the quality of our velocity products by comparing them to those generated from very high-resolution TerraSAR-X SAR and Landsat-8 optical (ITS_LIVE, GoLIVE) data. The subset of Sentinel-1 velocities for Svalbard analyzed in this paper is accessible via the GFZ Potsdam Data Services under the DOI https://doi.org/10.5880/fidgeo.2021.016 (Friedl et al., 2021). We find that Landsat-8 and Sentinel-1 annual velocity mosaics are in an overall good agreement, but speckle tracking on Sentinel-1 6 d repeat acquisitions derives more reliable velocity measurements over featureless and slow-moving areas than the optical data. Additionally, uncertainties of 12 d repeat Sentinel-1 mid-glacier scene-pair velocities have less than half (< 0.08 m d−1) of the uncertainties derived for 16 d repeat Landsat-8 data (0.17–0.18 m d−1).

Tepes P., Gourmelen N., Nienow P., Tsamados M., Shepherd A., Weissgerber F.

Arctic glaciers and ice caps (GIC) are losing mass rapidly, and this process is expected to continue during the 21st century owing to polar amplification of climate warming. Here, we use seven years of CryoSat-2 swath interferometric altimetry to track changes in the volume of Arctic GIC. From these data, we produce a pan-Arctic assessment of GIC mass imbalance, and we partition their losses into signals associated with atmospheric processes and glacier dynamics. Between 2010 and 2017, Arctic GIC lost 609 ± 7 Gt of ice, contributing 0.240 ± 0.007 mm per year to global sea level rise. While surface ablation is responsible for 87% of losses across the Arctic, dynamic imbalance is increasing in the Barents and Kara Sea region where it now accounts for 43% of total ice loss. Arctic GIC's dynamic imbalance is associated with a northward shift of Atlantic climate, and this effect should be considered in global sea level projections. • CryoSat-2 interferometric altimetry tracking pan-arctic changes in land ice volume. • High-resolution swath processing to estimate surface ablation and ice discharge. • Arctic glaciers and ice caps display a sustained rate of loss since the early 2000s. • Ice dynamics account for 43% of total mass loss in the Barents and Kara Sea region. • Dynamic imbalance is driven by polar amplification of warming and sea ice decline.

Valler V., Franke J., Brugnara Y., Brönnimann S.

Hugonnet R., McNabb R., Berthier E., Menounos B., Nuth C., Girod L., Farinotti D., Huss M., Dussaillant I., Brun F., Kääb A.

Glaciers distinct from the Greenland and Antarctic ice sheets are shrinking rapidly, altering regional hydrology1, raising global sea level2 and elevating natural hazards3. Yet, owing to the scarcity of constrained mass loss observations, glacier evolution during the satellite era is known only partially, as a geographic and temporal patchwork4,5. Here we reveal the accelerated, albeit contrasting, patterns of glacier mass loss during the early twenty-first century. Using largely untapped satellite archives, we chart surface elevation changes at a high spatiotemporal resolution over all of Earth’s glaciers. We extensively validate our estimates against independent, high-precision measurements and present a globally complete and consistent estimate of glacier mass change. We show that during 2000–2019, glaciers lost a mass of 267 ± 16 gigatonnes per year, equivalent to 21 ± 3 per cent of the observed sea-level rise6. We identify a mass loss acceleration of 48 ± 16 gigatonnes per year per decade, explaining 6 to 19 per cent of the observed acceleration of sea-level rise. Particularly, thinning rates of glaciers outside ice sheet peripheries doubled over the past two decades. Glaciers currently lose more mass, and at similar or larger acceleration rates, than the Greenland or Antarctic ice sheets taken separately7–9. By uncovering the patterns of mass change in many regions, we find contrasting glacier fluctuations that agree with the decadal variability in precipitation and temperature. These include a North Atlantic anomaly of decelerated mass loss, a strongly accelerated loss from northwestern American glaciers, and the apparent end of the Karakoram anomaly of mass gain10. We anticipate our highly resolved estimates to advance the understanding of drivers that govern the distribution of glacier change, and to extend our capabilities of predicting these changes at all scales. Predictions robustly benchmarked against observations are critically needed to design adaptive policies for the local- and regional-scale management of water resources and cryospheric risks, as well as for the global-scale mitigation of sea-level rise. Analysis of satellite stereo imagery uncovers two decades of mass change for all of Earth’s glaciers, revealing accelerated glacier shrinkage and regionally contrasting changes consistent with decadal climate variability.