Обзор книги Р. Барри и Э. Холл-МакКим «Глобальные изменения в полярных условиях»

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Peter G. Knight. Glacier: Nature and Culture. London: Reaktion Books, 2019. 223 pPeter G. Knight. Glacier: Nature and Culture. London: Reaktion Books, 2019. 223

Моделирование динамики приливного ледника Ханса (Шпицберген) на основе стохастической модели

The dynamics of the Hansbreen tidal glacier (Svalbard) is manifested at different time scales. In addition to the long-term trend, there are noticeable inter-annual fluctuations. And the last ones are precisely the subject of this work. Based on general conclusions of the theory of temporal dynamics of the massive inertial objects, the observed inter-annual changes in the length of the glacier can be explained as a result of the accumulation of anomalies of the heat fluxes and water flows. In spite the fact that the initial model of glacier dynamics is deterministically based on the physical law of conservation of ice mass (the so-called the «minimal model» was used), the model of length change is interpreted as stochastic. From this standpoint, it is the Langevin equation, which includes the effect of random temperature anomalies that can be interpreted as a white noise. From a mathematical point of view, this process is analogous to Brownian motion, i.e. the length of the Hansbreen glacier randomly fluctuates in the vicinity of its stable equilibrium position. Based on the Langevin equation, we passed to the Fokker–Planck equation, the solution of which allowed us to obtain the distribution function of the probabilities of interannual fluctuations of glacier length, which is close to the normal law. It was shown that the possible range of the variability covers the observed interval of the length fluctuations. The pdf is close to normal distribution.Для моделирования межгодовой динамики длины ледника Ханса на Шпицбергене использована «минимальная модель», интерпретируемая как стохастическое уравнение Ланжевена с переходом к уравнению Фоккера–Планка. Получена формула, выражающая дисперсию колебаний длины ледника в зависимости от его параметров. Сопоставление расчётов с данными наблюдений позволило получить хорошие результаты

Памяти Чарльза Суитинбенка

Charles Swithinbank(17.11.1926 – 27.05.2014)Памяти Чарльза Суитинбенк

Изменения высоты поверхности и баланс массы ледникового купола Академии Наук на Северной Земле

We have determined the surface-elevation change rates of the Academy of Sciences Ice Cap, Severnaya Zemlya, Russian Arctic, for two different periods: 2004–2016 and 2012/2013–2016. The former was calculated from differencing of ICESat and ArcticDEM digital elevation models, while the latter was obtained by differencing two sets of ArcticDEM digital elevation models. From these surface-elevation change rates we obtained the geodetic mass balance, which was nearly identical for both periods, at −1,72±0,67 Gt a−1, equivalent to −0,31±0,12 m w.e. a−1 over the whole ice cap area. Using an independent estimate of frontal ablation for 2016−2017 of −1,93±0,12 Gt a−1 (−0,31±0,12 m w.e. a−1), we get an estimate of the climatic mass balance not significantly different from zero, at 0,21±0,68 Gt a−1 (0,04±0,13 m w.e. a−1), which agrees with the near-zero average balance at a decadal scale observed during the last four decades. Making an observationally-based assumption on accumulation rate, we estimate the current total ablation from the ice cap, and its partitioning between frontal ablation, dominated by calving (~54%) and climatic mass balance, mostly surface ablation (~46%).На основе разновременных ЦМР установлены скорости изменения высоты поверхности ледникового купола Академии Наук на Северной Земле за два периода: 2004−2016 и 2012/2013−2016 гг. и определён геодезический баланс его массы (−1,72±0,67 Гт/год). Сделан расчёт климатического баланса массы (0,21±0,68 Гт/год) и полной абляции (−3,18 Гт/год) ледника, где на отёл приходится ≈54%, а на поверхностную абляцию – ≈46%

Исследования ледников на основе акустических измерений

The possibility of glacier ice flow studies using the method of acoustic emission (AE) in frequency range from 15 Hz to 20 kHz has been considered. A portable acoustic line system has been developed and a number of methodological issues (mounting of acoustic sensors into glacial ice, their location, reliability of acoustic coupling, etc.) have been solved. Acoustic studies of glacial ice have been performed; rock fall effect, ice cracking and ice movement on bedrock have been simulated. Correspondences of AE parameters to specific sources have been identified. The results of acoustic studies on Aldegondabreen (Spitsbergen), Central Tuyuksu and Molodezhny glaciers (northern Tien Shan) have been summarized. The dependence of the adhesive strength of ice with smooth substrate (serpentenite) on the shear rate has been considered; the effect of tor-shaped obstacle on shear force has been estimated. It is shown that the acoustic effects at cohesive ice failure on obstacles are similar to the observed natural acoustic vibrations generated in glaciers from distant sources. The results might be applied in development of the mobile ice lab and system for remote acoustic monitoring the processes in the bottom layers of glaciers.Рассмотрены возможности исследования движения льда в леднике и его анализа с помощью метода акустической эмиссии в диапазоне частот 15–20 кГц. Создана портативная измерительная акустическая линия и решён ряд методических вопросов. Выполнены акустические исследования ледникового льда, имитированы камнепад, трещинообразование в леднике и его движение по ложу. Установлены соответствия параметров акустической эмиссии определённому источнику. Обобщены результаты акустических исследований на ледниках Альдегонда (Шпицберген), Центральный Туюксу и Молодёжный (Северный Тянь-Шань). Рассмотрена зависимость адгезионной прочности соединения льда с гладкой подложкой (серпентинит) от скорости сдвига, оценено влияние препятствия в виде тора на силу сдвига. В собственных акустических спектрах исследованных ледников обнаружены акустические эффекты, характерные для разрушения льда на препятствиях. Полученные результаты можно использовать для создания мобильной ледниковой лаборатории и системы дистанционного акустического мониторинга процессов в придонных слоях ледника

Ice volume estimates from ground-penetrating radar surveys, western Nordenskiöld Land glaciers, Svalbard

As part of ongoing work within the SvalGlac project aimed to obtain a reliable estimate of the total ice volume of Svalbard glaciers and their potential contribution to sea level rise, in this contribution we present volume calculations, with detailed error estimates, for ten glaciers on western Nordenskiöld Land, central Spitsbergen, Svalbard. The volume estimates are based upon a dense net of GPR-retrieved ice thickness data collected over several field campaigns spanning the period 1999-2012, all of them except one within 2010-2012. The total area and volume of the ensemble are 113.38±0.09 km2 and 10.439±0.185 km3, respectively, while the individual areas, volumes and average ice thickness lie within 2.5-49.1 km2, 0.08-5.48 km3 and 29-108 m, respectively. The maximum recorded ice thickness, 265±15 m, corresponds to Fridtjovbreen, which has also the largest average thickness (108±1m). Available empirical formulae for Svalbard glaciers overestimate the total volume of these glaciers by 24% with respect to our calculation. On the basis of the pattern of scattering in the radargrams, we also analyse the hydrothermal structure of these glaciers. Nine out of ten are polythermal, while only one is entirely cold

Диэлектрические свойства почв и грунтов и оценка их гидротермического состояния под снежным покровом по данным радиозондирования

Snow cover significantly affects the thermal regime of the underlying soils, and its assessment and monitoring are an urgent task of remote sensing studies. To solve it, data on their dielectric properties and their dependence on physical properties are necessary. Analysis of available data showed that the relative dielectric permittivity of soils most strongly depends on their moisture content and can vary from 2 to 40. This leads to a noticeable difference in the reflection coefficient from the interface between snow cover and dry and wet soils, which can be detected by radio-echo sounding. This opens up a new way to apply radar data to assess and monitor the hydrothermal state of soils under snow cover. Compilation of data on the typical reflectance properties of different soils in areas with permafrost and seasonal snow cover might be useful. The presence of wet snow cover on the surface of wet soils makes such systematic compilation more difficult.Выполнен обзор диэлектрических свойств сухих и влажных почв и грунтов и их зависимости от минерального и органического состава, температуры и содержания воды. Показана возможность оценки гидротермического состояния этих сред под снежным покровом по данным измерений коэффициента отражения от его подошвы и полезность обобщения сведений о характерных отражающих свойствах разных почв и грунтов в районах с сезонным снежным покровом и распространением многолетней мерзлоты

Развитие подвижки в западной части ледникового купола Вавилова на Северной Земле в 1963–2017 гг.

The glaciers and ice caps in the Arctic are experiencing noticeable changes which are manifested, in particular, in the intensification of their dynamic instability. In this paper we present data on a largescale surge in the Western basin of the Vavilov ice dome on the archipelago Severnaya Zemlya, derived from satellite images and supplemented by airborne RES-2014 and available publications. Analysis of 28 space images of 1963–2017 demonstrated that the surge developed over the whole period. In the fi st decade (1963–1973), the advance was very slow – from 2–5 to 12 m/year. Since the 1980-ies, the ice movement began to accelerate from tens to a hundred of meters per a year in the 2000-ies. The sudden change happened in the year 2012 when the surge front began to move already at speeds of about 0.5 km/year. In 2015, the volume of advanced part reached almost 4 km3. Maximal speed 9.2 km/year was recorded in 2016. From 1963 to 2017, the edge of the glacier advanced by 11.7 km, and its area increased by 134.1 km2 (by 47% relative to the basin area of 1963), that caused spreading of crevasse zone up the glacier. Surface speeds reached a maximum of 25.4 m/day in 2016 and decreased to 7.6 m/day in 2017. The authors suggest that the initial activation of the southern and western edges of the ice dome could be a reaction to the climate signal, possibly occurred several centuries ago. The ice crevassing and cryo-hydrological warming of ice, enhanced by positive feedback, resulted in instability of the glacier and the displacement of the edge of the ice belt containing moraine and frozen to the bed, which transformed into a catastrophic movement. The surge was facilitated by change of bedrock conditions as the ice lobe progressed offshore from permafrost coastal zone to the area of loose marine bottom sediments with low shear strength. The surge seems to be also stimulated by anomalously warm summer of 2012.Исследованы скорости продвижения фронта и роста площади западного сектора ледникового купола Вавилова на Северной Земле с 1963 по 2017 г. Показано, как медленное продвижение фронта перешло в фазу катастрофической подвижки, которая достигла кульминации в 2016 г., когда скорости движения ледника достигали 9,2 км/год. В результате подвижки в акваторию Карского моря на расстояние 11,7 км выдвинулась ледниковая лопасть площадью 134,1 км2 и объёмом не менее 4 км3, начавшая продуцировать айсберги

Физическое моделирование контакта ледника с ложем (эксперименты)

Studies of the adhesive strength of glacial ice connection with bedrock has been studied using the analysis of the amplitude-frequency characteristics of acoustic emission (AE) in the frequency range from 15 Hz to 20,000 Hz. Identification of signal source on bed is based on physical modeling of adhesive ice fracture at the complex shear and patterns of elastic waves propagation in the ice using data on ice thickness of the ice and its acoustic properties. The experimental dependence of the ice and serpentinite substrate adhesive strength with temperature (from 0 °C to −30 °C) has been obtained at constraint axial shear. It is shown that the destruction of adhesive ice contact with substrate begins long before the maximum shear stress achieved, and AE signals in the coordinates amplitude-frequency-time have been obtained for the for static friction and sliding parts of deformation curves. Influence of shear to normal stresses ratio on the adhesive ice/substrate strength has been shown. Influence of the ratio of longitudinal and transverse shear stresses on the adhesive bond strength of ice to the substrate has been shown. The natural glacier spectra revealed periodic reduction of AE signals frequency in the middle range of frequencies. The similar effect of AE signals shifting along the frequency axis to the low frequency domain was obtained by testing of freshwater ice samples and related with expansion of the destruction scale. Practical application of the strain AE results for remote determination of the local glacial stability and for studies of glacier ice mechanics is discussed.Проведены комплексные исследования адгезионной прочности соединения льда с подложкой, предусматривающие анализ амплитудно-частотных характеристик сигналов акустической эмиссии (АЭ) в диапазоне частот от 15 до 20 тыс. Гц. Данные физического моделирования процессов адгезионного разрушения льда подтверждены результатами полевых исследований ледников Центральный Туюксу и Молодежный в Заилийском Алатау. Получена экспериментальная зависимость адгезионной прочности соединения льда с серпентинитом (подложкой) от температуры (от 0 до −25 °С) при осевом сдвиге в условиях стеснения. Показано, что адгезионный контакт лёд–подложка начинает разрушаться намного раньше достижения максимальных напряжений сдвига, причём для участков деформационных кривых (трение покоя и скольжения) получены диаграммы сигналов АЭ в координатах амплитуда–частота–время. Показано влияние соотношения продольных и поперечных сдвиговых напряжений на адгезионную прочность соединения льда с подложкой. В среднем диапазоне частот собственных акустических спектров ледников установлено периодическое уменьшение частоты заполнения сигналов АЭ. Аналогичный эффект смещения сигналов АЭ по оси частот в сторону низкочастотного диапазона получен при испытании образцов пресноводного льда и обусловлен расширением масштаба разрушения. Результаты исследований можно использовать для дистанционного изучения кинетики накопления трещин в придонных слоях ледникового льда