Radioglaciological studies on Hurd Peninsula glaciers, Livingston Island, Antarctica

We present the results of several radio-echo sounding surveys carried out on Johnsons and Hurd Glaciers, Livingston Island, Antarctica, between the 1999/2000 and 2004/05 austral summer campaigns, which included both radar profiling and common-midpoint measurements with low (20- 25 MHz)- and high (200MHz)-frequency radars. The latter have allowed us to estimate the radio-wave velocity in ice and firn and the corresponding water contents in temperate ice, which vary between 0 and 1.6% depending on the zone. Maximum ice thickness is ~200 m, with a mean value of 93.6 ± 2.5 m. Total ice volume is 0.968 ± 0.026 km3, for an area of 10.34 ± 0.03 km2. The subglacial relief of Johnsons Glacier is quite smooth, while that of Hurd Glacier shows numerous overdeepenings and peaks. The radar records suggest that Hurd Glacier has a polythermal structure, contrary to the usual assumption that glaciers in Livingston Island are temperate. This is also supported by other dynamical and geomorphological evidence

Radio-echo sounding and ice volume estimates of western Nordenskiöld Land glaciers, Svalbard

As part of ongoing work to obtain a reliable estimate of the total ice volume of Svalbard glaciers and their potential contribution to sea-level rise, we present here 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. On the basis of the pattern of scattering in theradargrams, we also analyse the hydrothermal structure of these glaciers

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

Скорость распространения радиоволн в сухом и влажном снежном покрове

In recent years, ground-penetrating radars are widely used for measuring thickness and liquid water content in snow cover on land and glaciers. The measurement accuracy depends on radio wave velocity (RWV) adopted for calculations. The RWV depends mainly on density, water content and structure of the snow cover and ice layers in it. The density and wetness of snow, and its structure can be estimated from data on RWV, using the available experimental and theoretical relations. Satisfactory results can be obtained using the Looyenga’s (1965) equations to estimate the density and wetness of snow cover, and equations of van Beek’s (1967) showing the distinction between RWV speeds velocities in snow cover and ice layers with different prevailing orientation and sizes of air or water inclusions.RWV in dry snow with density 300 kg/m3 may vary by 32 m/µs, depending on whether the vertical or horizontal orientation of the air inclusions prevails therein. In ice with density 700 kg/m3 effect of air inclusions orientation on differences in RWV is reduced to 5 m/µs. If the inclusions are not filled with air but with water, the difference in RWV in snow is 21 m/µs, and in ice is 24 m/µs. The RWV is affected not only by orientation of the inclusions, but their elongation. Twofold elongation of ellipsoidal air and water inclusions increases the difference in RWV in snow (with a density 300 kg/m3 ) to 23 m/µs and 22 m/µs.These estimates show a noticeable influence of snow structure on RWV in snow cover. The reliability of the above RWV estimates depends significantly on a thermal state of the snow cover, and decreases during snowmelt and increases in the cold period. It strongly depends on accuracy of measurements of the RWV in snow cover and its separate layers. With sufficiently high accuracy of the measurements this makes possible to detect and identify loose layers of deep hoar and compact layers of infiltration and superimposed ice, which is important for studying the liquid water storage of snow cover and a glacier mass balance. Therefore, considerable attention should be given to accuracy of the RWV measurements in dry and wet snow cover and its individual layers. With sufficiently high accuracy of measurements of the RWV, this should allow revealing such layers and estimating their thickness and average density.Представлены результаты расчётов скорости распространения радиоволн в снежном покрове в зависимости от плотности, влажности, структуры снега и прослоек в нём льда по разным эмпирическим и теоретическим зависимостям. Различие в скорости распространения радиоволн в сухом снеге плотностью 300  кг/м3 с преобладающей вертикальной или горизонтальной ориентацией включений воздуха достигает 32  м/мкс и уменьшается до 5  м/мкс во льду плотностью 700  кг/м3. Выполненные оценки показывают заметное влияние структуры на скорость распространения радиоволн в сухом и влажном снежном покрове, что позволяет обнаруживать и идентифицировать рыхлые слои глубинной изморози и плотные слои инфильтрационного и наложенного льда

Гидротермическая структура политермического ледника на Шпицбергене по данным измерений и численного моделирования

Thickness of the upper cold ice layer in the ablation area of the polythermal glacier Grønfjordbreen (Spitsbergen) was estimated by means of numerical modeling. The results were compared with data of radio-echo sounding of the same glacier obtained in 1979 and 2012. Numerical experiments with changing water content in the lower layer of temperate ice and surface snow cover thickness made possible to compare calculated and modeled cold ice thicknesses and to estimate their changes for 33‑year period caused by regional climate change. According to data of radio-echo sounding, thickness of the cold ice layer decreased, on average, by 34 m. Numerical modeling shown similar results: the cold ice layer became thinner by 31 m and 39 m at altitudes 100–300 a.s.l. under the snow cover thickness of 1 m and 2 m. We explain this by rising of annual mean air temperature by 0,6 °С as compared to data of the nearest meteorological station Barentsburg in the same period. We believe that changes in cold ice layer thickness in polythermal glaciers can be used for estimation of changes in such regional climatic parameter as mean air temperature at different altitudes of the glacier surface in the ablation area.Для политермического ледника Восточный Грёнфьорд на Шпицбергене выполнены численное моделирование толщины верхнего слоя холодного льда в области абляции и сравнение полученных результатов с данными радиозондирования за 1979–2012 гг. Согласно данным радиозондирования, слой холодного льда за 33‑летний период стал тоньше в среднем на 34 м. Численное моделирование показало аналогичные результаты: среднее сокращение слоя холодного льда на высоте 100–300 м над ур. моря составило 31 и 39 м при толщине снежного покрова соответственно 1 и 2 м, что объясняется повышением средней положительной температуры воздуха на 0,6 °С

Влияние снежного покрова на термический режим политермического ледника в условиях Западного Шпицбергена

Influence of snow cover, climate and glacier parameters on the cold-ice layer thickness and thermal regime in the ablation area of a polythermal glacier in Western Svalbard was investigated. Numerical modeling has demonstrated that a thickness of a cold layer in a polythermal glacier depends on a relation between the ablation on the surface and the freezing rate at the layer base. If the ablation rate is lower than that of the freezing, the layer thickness grows until the ablation and freezing rates become equal. Estimations show that in a case of slightly negative air temperatures on the glacier its cold-ice layer thickness increases when the snow cover thickness grows.Для условий Западного Шпицбергена на основе математического моделирования дана оценка влияния параметров снежного покрова, климатических условий и характеристик ледника на толщину холодного слоя политермического ледника и его термический режим в области абляции. Расчёты показали, что толщина холодного слоя политермического ледника зависит от соотношения абляции и скорости промерзания на нижней границе холодного слоя ледника. Если величина абляции меньше скорости промерзания на этой границе, то толщина такого слоя будет увеличиваться пока скорость промерзания не сравняется с величиной абляции. Проведённые расчёты показали, что в условиях небольших отрицательных температур воздуха на леднике с ростом толщины снежного покрова увеличивается толщина холодной части ледника

Распределение холодного и тёплого льда в ледниках на Земле Норденшельда (Шпицберген) по данным наземного радиозондирования

Data of ground-based radio-echo sounding of 16 glaciers located on the Nordenskiold Land, Spitsbergen, carried out in springs of 1999, 2007 and 2010–2013, allowed defining five glaciers as of the cold thermal type while other eleven ones were polythermal glaciers. In the last ones (polythermal) the average thickness of the upper layer of cold ice and the bottom layer of temperate ice was equal to 11-66 m and 15-96 m, respectively. The ratio of these thicknesses varies from 0.32 to 2.28, and the volume fraction of temperate ice in the total volume of the glaciers varies from 1 to 74% and changes from 0 to 50% in the ablation zone up to 80% in the accumulation zone. Thickness of cold ice was determined by measured delay time of radar reflections from cold-temperate surface (CTS) while thickness of temperate ice was derived as a difference between the total thickness of the glacier and the thickness of its cold ice. For interpretation of radar reflections from CTS we used the noticeable distinction in character of the radar reflections from the upper and lower thicknesses of glacier: absence of internal reflections (excluding reflections from buried crevasses and glacier wells) from upper cold ice layer and a great number of reflections of hyperbolic form from the lower layer related to strong scattering of radio waves by water inclusions in the temperate ice. According to the measurements, relative power of the radar reflections from CTS is by 5,5–14,2 dB smaller than those from the bedrock, that can be considered as an indicator of smaller water content at CTS; so, the repeated measurements of their relative power can be used for estimation of temporal changes in the water content at these boundaries. In layers of the temperate ice, the series of vertical hyperbolic reflections penetrating the cold ice down to CTS and further to the bedrock were detected. Such reflections are related to buried crevasses and/or the glacier wells and can serve as sources of the water permeating during the melt periods from the glacier surface down to CTS and bedrock and, thus, influencing on the ice viscosity and fluidity as well as on velocity of the bottom sliding in the polythermal glaciers. Repeated measurements of relative power of reflections from buried crevasses and wells can also be used to study processes of freezing them through and emptying during the period before start of the surface melting. Relation between volume of temperate ice and area of 16 studied glaciers was used to estimate the probability of existence of polythermal glaciers with a temperate ice core in all 202 glaciers in the Nordenskiold Land. 72 glaciers with areas exceeding 1.79 km2 may be referred to the polythermal type. The probable total volume of temperate ice in these glaciers amounts roughly to 10 km3, and with the 95% confidence it is within the interval from 8 to 33 km3. Almost 80% of the whole temperate ice may be concentrated in only five glaciers with area more than 17 km2, that makes up 2.5% of the total number of glaciers and about 30% of their total area. Data presented in this paper demonstrate more sophisticated pattern of the cold and temperate ice distribution within the glaciers than it was earlier known that should be taken into consideration when modeling and forecasting dynamics of the polythermal glaciers and investigating internal processes of the temperate ice formation in such glaciers.По данным наземного радиозондирования 16 ледников в 1999, 2007 и 2010–2013 гг. на Земле Норденшельда установлено, что пять из них относятся к ледникам холодного типа, а 11 – к ледникам политермического типа с верхним слоем холодного льда cо средней толщиной 11–66 м и придонным слоем тёплого льда со средней толщиной 15–96 м. Около 80% всего тёплого льда сосредоточено в пяти ледниках площадью более 17 км2, которые составляют 2,5% общего числа ледников и около 30% всей их площади.

Условия на ложе и поверхности ледникового купола Вавилова (Северная Земля) во время его подвижки по данным аэрорадиозондирования

The glacier surge at Vavilov Ice Cap, Severnaya Zemlya, Russia (79°18′ N, 94°40′ E) began as early as the mid-1960s with a slow advance of its margin in the western part. Since 2012, the advance switched to the phase of catastrophic movement, which reached its climax in 2016, when the glacier velocity reached 9.2 km a‒1. An ice fan with an area of about 140 km2 advanced into the Kara Sea water area 11 km from the shore, and a strongly crevassed ice stream was formed in the ice cap itself, which continues to move now with speeds of about 2 km a‒1. The dynamic instability of Vavilov Ice Cap can be triggered by changes in basal conditions, which are still poorly known. In this study, we used airborne radio-echo sounding data acquired in September 2014 over the ice cap to characterize its surface and bedrock conditions. Based on the delay time and reflection amplitudes, the power reflection coefficient (PRC) from glacier surface and bedrock was estimated. For its calibration, we used the amplitude of reflections from the sea surface registered from different altitudes. The bedrock PRC values were converted to dielectric permittivity and compared with the glacier surface velocities in 2014 obtained from Landsat-7 images. We found a high positive correlation between the bedrock PRCs and velocities in the area with glacier speed higher than 1000 m a-1. In this area, the PRC is 20 dB higher than in the neighboring slower moving areas. Such a difference may be because the ice stream advanced on marine loose sediments with higher dielectric permittivity and conductivity and a higher reflection coefficient. The range of estimated bedrock PRCs corresponds to bed materials with relative dielectric permittivity from 5 to 10 and electrical conductivity from 10–5 to 10–2 Sm m‒1.По данным измерений времени запаздывания и амплитуд радиоотражений от ложа ледникового купола Вавилова, полученным в период быстрой подвижки его западной части, определены значения коэффициента отражения от ложа по мощности, которые коррелируют с высокими скоростями (более 1000 м/год) движения ледника в области, наступившей на участок мелководья

Изменение гидротермической структуры ледников Восточный Гренфьорд и Фритьоф на Шпицбергене

The results of ground-based RES studies (20 MHz) at the Austre Grønfjordbreen and Fridtjovbreen glaciers on Nordenskiöld Land, Svalbard, spring 2010–2012, were compared with previous airborne RES data (620 MHz) of 1979 to understand the hydrothermal structure and its changes with time for these twinned glaciers. Temperature measurements in 9 shallow ice bore holes (down to 20 m) of spring 2013, and other RES and bore-hole data (1977–2005) were also considered. Both glaciers now are polythermal ones. The ratio of cold/temperate ice volumes in Austre Grønfjordbreen is 83 and 17 per cent, and in Fridtjovbreen is 26 and 74 per cent. The water content in temperate ice estimated from radio wave velocity is ca. 2–5%. Total water content in temperate ice of Austre Grønfjordbreen is estimated as 1,8–4,5∙10−3 km3, and in Fridtjovbreen as 74–85∙10−3 km3. Over the past 33 years (1979–2012) the average thickness of the cold ice in Austre Grønfjordbreen decreased by about 34 m, and thickness of temperate ice by 9 m. In Fridtjovbreen the cold ice has thinned by 87 m, but the temperate ice became thicker by 48 m. These differences in hydrothermal structure changes of the neighboring glaciers with common climatic history are attributed to the additional effect of Fridtjovbreen surge in 1991–1997 resulted in its additional internal heating.Приведены результаты радиозондирования ледников Восточный Гренфьорд и Фритьоф на западе Земли Норденшельда (Шпицберген), полученные весной 2010–2013 гг. Установлено, что сейчас оба лед‐ ника – политермические. В леднике Восточный Гренфьорд доля холодного и тёплого льда равна соответ‐ ственно 83 и 17%, а в леднике Фритьоф – 26 и 74%. Содержание воды в тёплом льде, оцененное по ско‐ рости распространения радиоволн, составляет 2–5%. Её объём в леднике Восточный Гренфьорд равен около 1,8÷4,5∙10−3 км3, а в леднике Фритьоф – 74÷85∙10−3 км3. Сравнение с данными 1979 г. показало, что за последние 33 года средняя толщина холодного льда в леднике Восточный Гренфьорд уменьшилась при‐ мерно на 34 м, а тёплого – на 9 м. В леднике Фритьоф холодный лёд стал тоньше на 87 м, а тёплый, наобо‐ рот, стал толще на 48 м. Такие различия в изменениях гидротермической структуры соседних ледников при примерно одинаковом сокращении их общей толщины на 35–45 м могут быть связаны с тем, что изменения на леднике Восточный Гренфьорд происходили на фоне его сокращения в условиях потепления климата, а на леднике Фритьоф такие же изменения дополнительно осложнялись его подвижкой в 1991–1997 гг.