Showing papers on "Accumulation zone published in 2013"
TL;DR: In this article, the authors provide a comprehensive overview of the studies of glaciers in the tropical Andes conducted in recent decades leading to the current status of the glaciers in terms of climate change.
Abstract: . The aim of this paper is to provide the community with a comprehensive overview of the studies of glaciers in the tropical Andes conducted in recent decades leading to the current status of the glaciers in the context of climate change. In terms of changes in surface area and length, we show that the glacier retreat in the tropical Andes over the last three decades is unprecedented since the maximum extension of the Little Ice Age (LIA, mid-17th–early 18th century). In terms of changes in mass balance, although there have been some sporadic gains on several glaciers, we show that the trend has been quite negative over the past 50 yr, with a mean mass balance deficit for glaciers in the tropical Andes that is slightly more negative than the one computed on a global scale. A break point in the trend appeared in the late 1970s with mean annual mass balance per year decreasing from −0.2 m w.e. in the period 1964–1975 to −0.76 m w.e. in the period 1976–2010. In addition, even if glaciers are currently retreating everywhere in the tropical Andes, it should be noted that this is much more pronounced on small glaciers at low altitudes that do not have a permanent accumulation zone, and which could disappear in the coming years/decades. Monthly mass balance measurements performed in Bolivia, Ecuador and Colombia show that variability of the surface temperature of the Pacific Ocean is the main factor governing variability of the mass balance at the decadal timescale. Precipitation did not display a significant trend in the tropical Andes in the 20th century, and consequently cannot explain the glacier recession. On the other hand, temperature increased at a significant rate of 0.10 °C decade−1 in the last 70 yr. The higher frequency of El Nino events and changes in its spatial and temporal occurrence since the late 1970s together with a warming troposphere over the tropical Andes may thus explain much of the recent dramatic shrinkage of glaciers in this part of the world.
499 citations
TL;DR: In this article, the authors present three-dimensional, high-resolution simulations of ice melting at the calving face of Store Glacier, a tidewater glacier in West Greenland, using the Massachusetts Institute of Technology general circulation model.
Abstract: We present three-dimensional, high-resolution simulations of ice melting at the calving face of Store Glacier, a tidewater glacier in West Greenland, using the Massachusetts Institute of Technology general circulation model. We compare the simulated ice melt with an estimate derived from oceanographic data. The simulations show turbulent upwelling and spreading of the freshwater-laden plume along the ice face and the vigorous melting of ice at rates of meters per day. The simulated August 2010 melt rate of 2.0±0.3 m/d is within uncertainties of the melt rate of 3.0±1.0 m/d calculated from oceanographic data. Melting is greatest at depth, above the subglacial channels, causing glacier undercutting. Melt rates increase proportionally to thermal forcing raised to the power of 1.2-1.6 and to subglacial water flux raised to the power of 0.5-0.9. Therefore, in a warmer climate, Store Glacier melting by ocean may increase from both increased ocean temperature and subglacial discharge. Key Points Simulated melt agrees with estimates from a hydrographic survey of the glacier. With more runoff, glaciers will melt faster at constant ocean temperature. ©2013. American Geophysical Union. All Rights Reserved.
166 citations
TL;DR: In this article, the results of a detailed mapping campaign and ground-based measurements of ablation rate, terminus retreat and ice loss are reported for the period 2003-10.
Abstract: Recent studies of Himalayan glacier recession indicate that there is wide variability in terminus retreat rate and mass balance in the different sectors of the mountain range, primarily linked to the topography and climate of the region. Variable retreat rates of glacier termini and inadequate supporting field data (e.g. mass balance, ice thickness, velocity, etc.) in the Himalayan glaciers make it difficult to develop a coherent picture of climate change impacts. In this study, the results of a detailed mapping campaign and ground-based measurements of ablation rate, terminus retreat and ice loss are reported for the period 2003―10. In addition, background information from an old glacier map (Survey of India, 1962) was compiled and terminus recession measurements were carried out from 1990 field photographs of Chorabari Glacier, central Himalaya. Our ablation stake network results suggest that the influence of debris cover is significant for Chorabari Glacier mass balance and terminus retreat. The terminus survey finds that the glacier is retreating, but at a lower rate than many other non-debris-covered glaciers in the region. The recession and ablation data (particularly in the upper ablation area at higher altitudes) suggest that the ice volume loss of the glaciers is of greater magnitude than the slow terminus retreat and, if the process continues, the lowermost part of the glacier may reduce to a quasi-stationary position while significant ice loss continues.
145 citations
TL;DR: In this paper, the authors used satellite observations to show that, between 1992 and 2011, the Pine Island Glacier hinge line retreated at a rate of 0.95 ± 0.09 km yr−1 despite a progressive steepening and shoaling of the glacier surface and bedrock slopes, respectively.
Abstract: We use satellite observations to show that, between 1992 and 2011, the Pine Island Glacier hinge line retreated at a rate of 0.95 ± 0.09 km yr−1 despite a progressive steepening and shoaling of the glacier surface and bedrock slopes, respectively, which ought to impede retreat. The retreat has remained constant because the glacier terminus has thinned at an accelerating rate of 0.53 ± 0.15 m yr−2, with comparable changes upstream. This acceleration is consistent with an intensification of ocean-driven melting in the cavity beneath the floating section of the glacier. The pattern of hinge-line retreat meanders and is concentrated in isolated regions until ice becomes locally buoyant. Because the glacier-ocean system does not appear to have reached a position of relative stability, the lower limit of sea level projections may be too conservative.
92 citations
TL;DR: It is proposed that the observed increased thinning of Totten Glacier is due to enhanced basal melting caused by a decrease in cold polynya water reaching its cavity, and this hypothesis is supported with passive microwave data ofpolynya extent variability.
Abstract: Analysis of ICESat-1 data (2003–2008) shows significant surface lowering of Totten Glacier, the glacier discharging the largest volume of ice in East Antarctica, and less change on nearby Moscow University Glacier. After accounting for firn compaction anomalies, the thinning appears to coincide with fast-flowing ice indicating a dynamical origin. Here, to elucidate these observations, we apply high-resolution ice–ocean modelling. Totten Ice Shelf is simulated to have higher, more variable basal melting rates. We link this variability to the volume of cold water, originating in polynyas upon sea ice formation, reaching the sub-ice-shelf cavity. Hence, we propose that the observed increased thinning of Totten Glacier is due to enhanced basal melting caused by a decrease in cold polynya water reaching its cavity. We support this hypothesis with passive microwave data of polynya extent variability. Considering the widespread changes in sea ice conditions, this mechanism could be contributing extensively to ice-shelf instability.
88 citations
TL;DR: In this paper, an integrated approach for characterizing the current behavior of a small, avalanche-fed glacier at low altitude in the Italian Alps, combining geomorphological, geophysical and high-resolution geodetic surveying with a terrestrial laser scanner is presented.
Abstract: Smaller glaciers (<0.5 km2) react quickly to environmental changes and typically show a large scatter in their individual response. Accounting for these ice bodies is essential for assessing regional glacier change, given their high number and contribution to the total loss of glacier area in mountain regions. However, studying small glaciers using traditional techniques may be difficult or not feasible, and assessing their current activity and dynamics may be problematic. In this paper, we present an integrated approach for characterizing the current behaviour of a small, avalanche-fed glacier at low altitude in the Italian Alps, combining geomorphological, geophysical and high-resolution geodetic surveying with a terrestrial laser scanner. The glacier is still active and shows a detectable mass transfer from the accumulation area to the lower ablation area, which is covered by a thick debris mantle. The glacier owes its existence to the local topo-climatic conditions, ensured by high rock walls which enhance accumulation by delivering avalanche snow and reduce ablation by providing topographic shading and regulating the debris budget of the glacier catchment. In the last several years the glacier has displayed peculiar behaviour compared with most glaciers of the European Alps, being close to equilibrium conditions in spite of warm ablation seasons. Proportionally small relative changes have also occurred since the Little Ice Age maximum. Compared with the majority of other Alpine glaciers, we infer for this glacier a lower sensitivity to air temperature and a higher sensitivity to precipitation, associated with important feedback from increasing debris cover during unfavourable periods.
54 citations
TL;DR: In this article, the authors present 2.5 yr of meteorological data collected from the glacier surface from October 2009 to February 2012, and calculate surface energy fluxes for the meteorological station site using a physical mass and energy-balance model driven by measured meteorology data and additional input parameters that were determined by Monte Carlo optimization.
Abstract: . The Lewis Glacier on Mt Kenya is one of the best-studied tropical glaciers, but full understanding of the interaction of the glacier mass balance and its climatic drivers has been hampered by a lack of long-term meteorological data. Here we present 2.5 yr of meteorological data collected from the glacier surface from October 2009 to February 2012. The location of measurements is in the upper portion of Lewis Glacier, but this location experiences negative annual mass balance, and the conditions are comparable to those experienced in the lower ablation zones of South American glaciers in the inner tropics. In the context of other glaciated mountains of equatorial East Africa, the summit zone of Mt Kenya shows strong diurnal cycles of convective cloud development as opposed to the Rwenzoris, where cloud cover persists throughout the diurnal cycle, and Kilimanjaro, where clear skies prevail. Surface energy fluxes were calculated for the meteorological station site using a physical mass- and energy-balance model driven by measured meteorological data and additional input parameters that were determined by Monte Carlo optimization. Sublimation rate was lower than those reported on other tropical glaciers, and melt rate was high throughout the year, with the glacier surface reaching the melting point on an almost daily basis. Surface mass balance is influenced by both solid precipitation and air temperature, with radiation providing the greatest net source of energy to the surface. Cloud cover typically reduces the net radiation balance compared to clear-sky conditions, and thus the frequent formation of convective clouds over the summit of Mt Kenya and the associated higher rate of snow accumulation are important in limiting the rate of mass loss from the glacier surface. The analyses shown here form the basis for future glacier-wide mass and energy balance modeling to determine the climate proxy offered by the glaciers of Mt Kenya.
51 citations
01 Jul 2013
46 citations
TL;DR: In this article, the authors used multi-sensor C-band synthetic aperture radar (SAR) images of the Dongkemadi and its neighbouring glaciers in the central area of the Qinghai-Tibetan Plateau to study the changing snow/firn line across different days, seasons, and years.
38 citations
TL;DR: The longest continuous glacier annual mass balance data set in North America is the Lemon Creek Glacier and Taku Glacier observed by the Juneau Icefield Research Program (JIRP).
Abstract: . The annual surface mass balance records of the Lemon Creek Glacier and Taku Glacier observed by the Juneau Icefield Research Program are the longest continuous glacier annual mass balance data sets in North America. Annual surface mass balance (Ba) measured on Taku Glacier averaged +0.40 m a−1 from 1946–1985, and −0.08 m a−1 from 1986–2011. The recent annual mass balance decline has resulted in the cessation of the long-term thickening of the glacier. Mean Ba on Lemon Creek Glacier has declined from −0.30 m a−1 for the 1953–1985 period to −0.60 m a−1 during the 1986–2011 period. The cumulative change in annual surface mass balance is −26.6 m water equivalent, a 29 m of ice thinning over the 55 yr. Snow-pit measurements spanning the accumulation zone, and probing transects above the transient snow line (TSL) on Taku Glacier, indicate a consistent surface mass balance gradient from year to year. Observations of the rate of TSL rise on Lemon Creek Glacier and Taku Glacier indicate a comparatively consistent migration rate of 3.8 to 4.1 m d−1. The relationship between TSL on Lemon Creek Glacier and Taku Glacier to other Juneau Icefield glaciers (Norris, Mendenhall, Herbert, and Eagle) is strong, with correlations exceeding 0.82 in all cases. doi:10.5065/D6NZ85N3
36 citations
TL;DR: The relationship between glacier area change and elevation zone indicates that glacier change is not only dominated by climate change but also affected by glacier dynamics, which are related to local topography.
Abstract: Glaciers' runoff in the Qilian Mountains serves as a critical water resource in the northern sections of the Gansu province, the northeastern sections of the Qinghai province, and the northeastern fringe of the Tibetan Plateau. Changes in the glacial area and volume around the highest peak of the Qilian Mountains, i.e., Tuanjiefeng Peak, were estimated using multi-temporal remote-sensing images and digital elevation models, and all possible sources of uncertainty were considered in detail. The total glacier area decreased by 16.1±6.34 km2 (9.9±3.9%) during 1966 to 2010. The average annual glacier shrinkage was −0.15% a−1 from 1966 to 1995, −0.61% a−1 from 1995 to 2000, −0.20% a−1 from 2000 to 2006, and −0.45% a−1 from 2006 to 2010. A comparison of glacier surface elevations using digital elevation models derived from topographic maps in 1966 and from the Shuttle Radar Topography Mission in 1999 suggests that 65% of the grid cells has decreased, thereby indicating that the glacier thickness has declined. The average change in glacier thickness was −7.3±1.5 m (−0.21±0.04 m·a−1) from 1966 to 1999. Glaciers with northeastern aspects thinned by 8.3±1.4 m from 1966 to 1999, i.e., almost twice as much as those with southwestern aspects (4.3±1.3 m). The ice volume decreased by 11.72±2.38×108 m3 from 1966 to 1999, which was about 17.4% more than the value calculated from the statistical relationship between glacier area and volume. The relationship between glacier area change and elevation zone indicates that glacier change is not only dominated by climate change but also affected by glacier dynamics, which are related to local topography. The varied response of a single glacier to climate change indicates that the glacier area change scheme used in some models must be improved.
TL;DR: In this article, the authors present the most recent assessment of the Gangotri glacier dynamics, combining the use of interferometric techniques on synthetic aperture radar data and sub-pixel offset tracking on Advanced Spaceborne Thermal Emission and Reflection Radiometer ASTER satellite imagery.
Abstract: Glacier mass variations have a direct impact on some of the key components of the global water cycle, including sea level rise and freshwater availability. Apart from being one of the largest Himalayan glaciers, Gangotri is one of the sources of water for the Ganges river, which has a considerable influence on the socioeconomic structure of a largely over-populated catchment area accounting for ∼26% of India’s landmass. In this study, we present the most recent assessment of the Gangotri glacier dynamics, combining the use of interferometric techniques on synthetic aperture radar data and sub-pixel offset tracking on Advanced Spaceborne Thermal Emission and Reflection Radiometer ASTER satellite imagery. Results show that on average, the Gangotri glacier snout has receded at a rate of 21.3 ± 3 m year−1 over a period of 6 years 2004–2010. While glacier surface velocity near the snout is estimated to be between 24.8 ± 2.3 and 28.9 ± 2.3 m year−1, interior portions of the glacier recorded velocities in the range of 13.9 ± 2.3 to 70.2 ± 2.3 m year−1. Further, the average glacier surface velocity in the northern lower portions 28.1 ± 2.3 m year−1 is observed to be significantly lower than in the southern higher portions 48.1 ± 2.3 m year−1 of the Gangotri glacier. These values are calculated with an uncertainty of less than 5 m year−1. Results also highlight a consistent retreat and non-uniform dynamics of the Gangotri glacier.
TL;DR: In this paper, the average of rangewide estimates of the equilibrium line altitude (ELA), the boundary between the upper snow and ice accumulation zone and the lower ablation zone, of many late Pleistocene glaciers parallels, and is only 200-300 m above, the altitude of the lower limit of the lakes.
Abstract: The 600-km-long Sierra Nevada underwent extensive Pleistocene glaciation except for its southernmost 100 km. Presently, ∼1700 small glaciers and ice masses near the crest of the range occur above 3250 m in elevation; these covered an area of ∼50 km 2 in 1972. Fourteen of the largest glaciers decreased by about one half in area during the period from 1900 to 2004. Rock glaciers, generally glacial ice covered by 1–10 m of rockfall debris, occur in about the same span of the range as ice and permanent snowfields. They are, on average, lower by 200–300 m, apparently because of the insulating layer of rocky rubble that protects their internal ice from the sun’s heat and from wind. The principal Pleistocene glacial stages are the Sherwin (ca. 820 ka), Tahoe (170–130 and ca. 70 ka), Tioga (14–28 ka), and Recess Peak (13 ka). Some 7040 glacial lakes, produced primarily by quarrying from bedrock, were mostly exposed after recession of the Tioga glacial stage. The lakes largely mark the area of primary snow accumulation. Below the lower limit of the lakes, ice flowed downward into river-cut canyons, forming major trunk glaciers within the zone of ablation. The range is in general a westward-tilted block upfaulted on its east side. Therefore, the main late Pleistocene trunk glaciers (Tahoe/Tioga) west of the crest extend 25–60 km, whereas those east of the crest extend only 5–20 km. Because of higher precipitation northward, glacial features such as the toes of existing glaciers and rock glaciers, as well as the late season present-day snowline, all decrease in elevation northward. Likewise, the elevation of the lower limit of glacial lakes, an indication of the zone of snow accumulation during the late Pleistocene, decreases about the same degree. This similarity suggests that the overall climate patterns of the late Pleistocene, though cooler, were similar to those of today. The east slope glaciers show a similar northward depression, but they are ∼500–1000 m higher. The upper part of the glacial system was erosive over a broad highland area as the evenly distributed ice in the accumulation zone moved to lower elevation. The abundant lake basins record this erosive action. The lower part of the glacier system was largely confined to major preexisting river canyons in which melting dominated. The average of rangewide estimates of the equilibrium line altitude (ELA)—the boundary between the upper snow and ice accumulation zone and the lower ablation zone—of many late Pleistocene glaciers parallels, and is only 200–300 m above, the altitude of the lower limit of the lakes. Hence, the lake zone provides a means of estimating the ELA.
TL;DR: In this paper, the authors carried out GPS and ground-penetrating radar (GPR) measurements at Yala Glacier, a benchmark glacier in Nepal, to investigate recent glacier changes in the Himalayan region.
Abstract: To investigate recent glacier changes in the Himalayan region, we carried out GPS and ground-penetrating radar (GPR) measurements at Yala Glacier, a benchmark glacier in Nepal. Glacier surface elevation and ice thickness were surveyed along a 1.5 km profile from the glacier top to the terminus. Ice flow velocity was measured at five locations by surveying stakes for either 1 year or 4 day periods. Obtained surface elevation and ice velocity were compared with those measured in 1982 and 1996. The mean ice thickness along the radar profile was 36 m in 2009 and the ice has been thinning at rates of -0.69 � 0.25 and -0.75 � 0.24 m a -1 during the periods 1982-96 and 1996-2009, respectively. The thinning rate increases down-glacier, reaching a magnitude up to -1.8 m a -1 near the terminus from 1996 to 2009. The ice velocity has reduced by >70% from 1982 to 2009 in the lower half of the glacier. By assuming a constant driving stress over the glacier, the total ice volume in 2009 was estimated as 0.061 km 3 . Our results indicate that Yala Glacier has lost � 40% of its ice volume over the last 27 years and that the rate of the mass loss has accelerated over the last decade.
TL;DR: In this article, the authors explored whether persistent ice crystal precipitation from supercooled layer clouds can be explained by time-dependent, stochastic ice nucleation using an approximate, analytical model and a large-eddy simulation (LES) cloud model.
Abstract: [1] The question of whether persistent ice crystal precipitation from supercooled layer clouds can be explained by time-dependent, stochastic ice nucleation is explored using an approximate, analytical model and a large-eddy simulation (LES) cloud model. The updraft velocity in the cloud defines an accumulation zone, where small ice particles cannot fall out until they are large enough, which will increase the residence time of ice particles in the cloud. Ice particles reach a quasi-steady state between growth by vapor deposition and fall speed at cloud base. The analytical model predicts that ice water content (wi) has a 2.5 power-law relationship with ice number concentration (ni). wi and ni from a LES cloud model with stochastic ice nucleation confirm the 2.5 power-law relationship, and initial indications of the scaling law are observed in data from the Indirect and Semi-Direct Aerosol Campaign. The prefactor of the power law is proportional to the ice nucleation rate and therefore provides a quantitative link to observations of ice microphysical properties.
TL;DR: In this paper, the authors apply a two-dimensional higher-order thermomechanical flowband model to simulate present-day ice temperature and velocity along the main flowline of East Rongbuk Glacier, Qomolangma (Mount Everest), Himalaya.
Abstract: Knowledge of present-day ice temperature and velocity is important in order to determine how fast a glacier will respond to present and future climate change. We apply a two-dimensional higher-order thermomechanical flowband model to simulate present-day ice temperature and velocity along the main flowline of East Rongbuk Glacier, Qomolangma (Mount Everest), Himalaya. We use recent (2005-11) observational data to validate the numerical model. Modelled and observed ice surface velocities exhibit good agreement. Modelled ice temperatures agree well with observed values in two shallow boreholes that are similar to 18 m deep. The model suggests that the ablation zone of East Rongbuk Glacier, km 4 to km 10 from the glacier head, is underlain by temperate ice.
TL;DR: In this paper, a two-dimensional mechanically-coupled model of heat flow is applied to synthetic glacier geometries in order to explore the environmental controls on flowband thermal structure.
Abstract: . Water entrapped in glacier accumulation zones represents a significant latent heat contribution to the development of thermal structure. It also provides a direct link between glacier environments and thermal regimes. We apply a two-dimensional mechanically-coupled model of heat flow to synthetic glacier geometries in order to explore the environmental controls on flowband thermal structure. We use this model to test the sensitivity of thermal structure to physical and environmental variables and to explore glacier thermal response to environmental changes. In different conditions consistent with a warming climate, mean glacier temperature and the volume of temperate ice may either increase or decrease, depending on the competing effects of elevated meltwater production, reduced accumulation zone extent and thinning firn. For two model reference states that exhibit commonly-observed thermal structures, the fraction of temperate ice is shown to decline with warming air temperatures. Mass balance and aquifer sensitivities play an important role in determining how the englacial thermal regimes of alpine glaciers will adjust in the future.
TL;DR: In this paper, surface exposure dating and radiocarbon ages of stumps beneath the Tiedemann Glacier were used to demonstrate that the glacier reached its maximum Holocene extent at about 2.7 ka.
01 Dec 2013
TL;DR: In this article, the authors explored whether persistent ice crystal precipitation from supercooled layer clouds can be explained by time-dependent, stochastic ice nucleation using an approximate, analytical model and a large-eddy simulation (LES) cloud model.
Abstract: [1] The question of whether persistent ice crystal precipitation from supercooled layer clouds can be explained by time-dependent, stochastic ice nucleation is explored using an approximate, analytical model and a large-eddy simulation (LES) cloud model. The updraft velocity in the cloud defines an accumulation zone, where small ice particles cannot fall out until they are large enough, which will increase the residence time of ice particles in the cloud. Ice particles reach a quasi-steady state between growth by vapor deposition and fall speed at cloud base. The analytical model predicts that ice water content (wi) has a 2.5 power-law relationship with ice number concentration (ni). wi and ni from a LES cloud model with stochastic ice nucleation confirm the 2.5 power-law relationship, and initial indications of the scaling law are observed in data from the Indirect and Semi-Direct Aerosol Campaign. The prefactor of the power law is proportional to the ice nucleation rate and therefore provides a quantitative link to observations of ice microphysical properties.
TL;DR: Based on field observations of mass balance and glacier temperature at Baishui Glacier No.1, its accumulation, ablation, net balance and near-surface ice temperature structure were analyzed and studied in this article.
Abstract: The accumulation and ablation of a glacier directly reflect its mass income and wastage, and ice temperature indicates glacier’s climatic and dynamic conditions. Glaciological studies at Baishui Glacier No.1 in Mt. Yulong are important for estimating recent changes of the cryosphere in Hengduan Mountains. Increased glacier ablation and higher ice temperatures can cause the incidents of icefall. Therefore, it is important to conduct the study of glacier mass balance and ice temperature, but there are few studies in relation to glacier’s mass balance and active-layer temperature in China’s monsoonal temperate glacier region. Based on the field observations of mass balance and glacier temperature at Baishui Glacier No.1, its accumulation, ablation, net balance and near-surface ice temperature structure were analyzed and studied in this paper. Results showed that the accumulation period was ranged from October to the following mid-May, and the ablation period occurred from mid-May to October, suggesting that the ablation period of temperate glacier began about 15 days earlier than that of continental glaciers, while the accumulation period began about 15 days later. The glacier ablation rate was 6.47 cm d−1 at an elevation of 4600 m between June 23 and August 30, and it was 7.4 cm d−1 at 4800 m between June 26 and July 11 in 1982, moreover, they respectively increased to 9.2 cm d−1 and 10.8 cm d−1 in the corresponding period and altitude in 2009, indicating that glacier ablation has greatly intensified in the past years. The temperature of the main glacier body was close to melting point in summer, and it dropped from the glacier surface and reached a minimum value at a depth of 4–6 m in the ablation zone. The temperature then rose to around melting point with the depth increment. In winter, the ice temperature rose gradually with the increasing depth, and close to melting point at the depth of 10 m. Compared with the data from 1982, the glacier temperature has risen in the ablation zone in recent decades.
TL;DR: In this paper, a network of 11 ablation stakes was installed on the lower glacier of the Franz Josef Glacier to measure the extent of ablation on the surface in the ablation zone.
Abstract: Melt rates on glaciers are strongly influenced by the presence of supraglacial debris, which can either enhance or reduce ablation relative to bare ice. Most recently, Franz Josef Glacier has entered into a phase of strong retreat and downwasting, with the increasing emergence of debris on the surface in the ablation zone. Previously at Franz Josef Glacier, melt has only been measured on bare ice. During February 2012, a network of 11 ablation stakes was drilled into locations of varying supraglacial debris thickness on the lower glacier. Mean ablation rates over 9 days varied over the range 1.2–10.1 cm d−1, and were closely related to debris thickness. Concomitant observations of air temperature allowed the application of a degree-day approach to the calculation of melt rates, with air temperature providing a strong indicator of melt. Degree-day factors (d f) varied over the range 1.1–8.1 mm d−1 °C−1 (mean of 4.4 mm d−1 °C−1), comparable with rates reported in other studies. Mapping of the curre...
TL;DR: Brady Glacier has a mean equilibrium line altitude (ELA) of 745m and accumulation area ratio (AAR) of 040 as discussed by the authors The zero balance ELA is 600m and equilibrium AAR 065.
Abstract: Brady Glacier is a large Alaskan tidewater glacier that is beginning a period of substantial retreat Examination of 27 Landsat and MODIS images from the period 2003 to 2011 indicates that Brady Glacier has a mean equilibrium line altitude (ELA) of 745 m and accumulation area ratio (AAR) of 040 The zero balance ELA is 600 m and equilibrium AAR 065 The negative mass balance associated with the increased ELA has triggered thinning of 20–100 m over most of the glacier below the ELA from 1948 to 2010 The thinning has caused substantial retreat of seven calving distributary termini of the glacier Thinning and retreat have led to an increase in the width of and water depth at the calving fronts In contrast, the main terminus has undergone only minor retreat since 1948 In 2010, several small proglacial lakes were evident at the terminus By 2000, a permanent outlet river issuing from Trick Lake had developed along the western glacier margin Initial lake development at the terminus combined with continued mass losses will lead to expansion of the lakes at the main terminus and retreat by calving The glacier bed is likely below sea level along the main axis of Brady Glacier to the glacier divide Retreat of the main terminus in the lake will likely lead to a rapid calving retreat similar to Bear, Excelsior, Norris, Portage and Yakutat glaciers Copyright © 2013 John Wiley & Sons, Ltd
TL;DR: In this article, a mathematical formulation of the dissipation is developed and applied to a simple glacier geometry, and the amount of melt energy available follows directly from the lowering of the center of gravity of the glacier.
Abstract: . In this note, the total dissipative melting in temperate glaciers is studied. The analysis is based on the notion that the dissipation is determined by the loss of potential energy due to the downward motion of mass (ice, snow, meltwater and rain). A mathematical formulation of the dissipation is developed and applied to a simple glacier geometry. In the next step, meltwater production resulting from enhanced ice motion during a glacier surge is calculated. The amount of melt energy available follows directly from the lowering of the centre of gravity of the glacier. To illustrate the concept, schematic calculations are presented for a number of glaciers with different geometric characteristics. Typical dissipative melt rates, expressed as water-layer depth averaged over the glacier, range from a few centimetres per year for smaller glaciers to half a metre per year for Franz Josef Glacier, one of the most active glaciers in the world (in terms of mass turnover). The total generation of meltwater during a surge is typically half a metre. For Variegated Glacier a value of 70 cm is found, for Kongsvegen 20 cm. These values refer to water layer depth averaged over the entire glacier. The melt \textit{rate} depends on the duration of the surge. It is generally an order of magnitude greater than water production by `normal' dissipation. On the other hand, the additional basal melt rate during a surge is comparable in magnitude with the water input from meltwater and precipitation. This suggests that enhanced melting during a surge does not grossly change the total water budget of a glacier. Basal water generated by enhanced sliding is an important ingredient in many theories of glacier surges. It provides a positive feedback mechanism that actually makes the surge happen. The results found here suggest that this can only work if water generated by enhanced sliding accumulates in a part of the glacier base where surface meltwater and rain have no or very limited access. This finding seems compatible with the fact that, on many glaciers, surges are initiated in the lower accumulation zone.
TL;DR: Omnsbreen is a small (<0.5 km2) and degrading glacier situated at the regional lower limit of present-day permafrost distribution and glaciation.
Abstract: Omnsbreen is a small (<0.5 km2) and degrading glacier situated at the regional lower limit of present-day permafrost distribution and glaciation. At present, the existence of Omnsbreen is mainly de...
TL;DR: In this paper, the authors used the PTAA (precipitation-temperature-area-altitude) model to estimate the net, ablation and accumulation daily balances, as well as runoff of Bering Glacier, Alaska.
Abstract: . The historical net, ablation and accumulation daily balances, as well as runoff of Bering Glacier, Alaska are determined for the 1951–2011 period with the PTAA (precipitation-temperature-area-altitude) model, using daily precipitation and temperature observations collected at the Cordova and Yakutat weather stations, together with the area-altitude distribution of the glacier. The model mean annual balance for this 61 yr period is −0.6 m w.e., the accumulation balance is +1.4 and the ablation balance is −2.0 m w.e. Average annual runoff is 2.5 m w.e. Periodic surges of this glacier transport large volumes of ice to lower elevations where the ablation rate is higher, producing more negative balances and increasing runoff. Runoff from Bering Glacier (derived from simulated ablation and precipitation as rain) is highly correlated with four of the glacier surges that have occurred since 1951. Ice volume loss for the 1972–2003 period measured with the PTAA model is 2.7 km3 w.e. a−1 and closely agrees with losses for the same period measured with the geodetic method. It is proposed that the timing and magnitude of daily snow accumulation and runoff, both of which are controlled by the glacier's area-altitude distribution and are calculated with the PTAA model, can be used to determine the probability that a glacier will surge.
TL;DR: In this paper, the authors analyzed tree-ring growth anomalies on the glacier and at a control site at the tree line over the 20-year period 1987-2006, and found that trees growing on the glaciers presented the highest percentages of abrupt growth changes (AGC>+70% with respect to the four previous years.
Abstract: Debris-covered glaciers may host several biological forms that colonize the debris cover, especially if the glacier tongue reaches sufficiently low altitudes (down to about 1700 m a.s.l. at Miage Glacier, Western Italian Alps) thus allowing also tree growth. Supraglacial trees colonizing the debris-covered tongue are strongly influenced in growth and distribution by substrate characteristics and instability. The tree age distribution at Miage Glacier presents a positive gradient towards the glacier terminus, which was found to be related to the decreasing glacier surface velocity. By analysing tree-ring growth anomalies on the glacier and at a control site at the tree line over the 20-year period 1987–2006, it was found that trees growing on the glacier presented the highest percentages of abrupt growth changes (AGCs)>+70% with respect to the four previous years. Considering tree displacement on the glacier surface over the same 20-year period and the recorded AGCs, it was found that the central-lower portion of the southern lobe towards the margins was the most unstable. The temporal analysis of AGC>+40% confirmed a period of higher glacier surface instability, reaching a maximum in the years 1988 (on lobe S) and 1989 (on lobe N), probably related to the passage of a kinematic wave in the glacier tongue. Our analysis suggests that supraglacial trees hold useful information on the glacier tongue dynamics and that both AGC>+70% and AGC>+40% may be used as a proxy for substrate instability in spatio-temporal reconstructions in the Alpine environment.
TL;DR: In this paper, the authors applied seven ALOS/PALSAR images and the offset-tracking method to derive the displacement field of the largest mountain glacier in Asia, i.e., the South Inylchek Glacier.
Abstract: Glaciers are characterized by their flowabilityMeasurement of their velocity can provide important information for the study of glacier mass balance and glacier involved hazardsThis paper applies seven ALOS/PALSAR images and the offset-tracking method to derive the displacement field of the largest mountain glacier in Asia,ie,the South Inylchek GlacierThe temporal continuity of SAR images and the debris coverage of South Inylchek Glacier make the offset-tracking method successfully acquire continuous surface displacementsSeveral natural events such as snowfall in the firn basins,ablation of superimposed ice and development of crevasses in steep sections still have some influence on the resultsHowever,the derived surface displacement maps of different periods are highly consistent with each otherThe detail analysis reveals the following rules of the South Inylchek Glacier′s motion: the velocity reduces from glacier axis to both sides,and increases from its origin to snowline and then reduces towards the end;the velocity is positively and nonlinearly correlated with the slope,especially when the slope increases sharply from 1° to 16°,the surge velocity will give rise to crevasses on the glacier;under the influence of glacial lake level changes,the velocity of tributary at the tail can surge to 96 cm/d;the summer velocity is 5~10 cm/d higher than winter oneSeen from all results,the normal velocity of the glacier trunk is between 20 and 50 cm/d,but can reach 65 cm/d in special placeThe statistics of sampling points in the tongue indicates that mean velocity of different periods lies between 279 and 333 cm/dCompared to the record in 2004,velocity derived in this research reduces about 5 cm/d
Journal Article•
TL;DR: In this article, an analysis of the geological framework,depositional filling feature and hydrocarbon accumulation condition, the geological factorts favorable to the deep basin gas accumulation and its exploration potential were discussed.
Abstract: Deep basin gas is a special type of gas accumulation with an upside-down relation between water and gas,and gentle structure,tight reservoirs rock and sustainable gas supply are the main conditions to form this type of gas accumulation.In Xihu sag,based on an analysis of the geological framework,depositional filling feature and hydrocarbon accumulation condition,the geological factorts favorable to the deep gas accumulation and its exploration potential were discussed.The overall sedimentation pattern of Pinghu formation in the sag is characterized by the complex depositional system of marine-terrestrial facies over a wide and gentle topography and the multiple interbedded assemblages of source,reservoir and seal,which formed in a wide,shallow and low-energy environment during an oscillatory marine regression.The fine-grained sandstones developed in widespread tidal deltas and shallow-water deltas have become the tight sandstones by severe compaction and cemention,which may serve as the effective reservoirs of deep basin gas.The source rocks of coal measures are wide in distribution,large in thickness and great in gas generation potential,and have maintained hydrocarbon expulsion up to now,providing a sufficient gas source for the deep basin gas accumulation.These source rocks of coal measures are closely intercalated with the tight sandstones in a layer-cake mode,which is favorable to forming the deep basin gas accumulation.There are three zones vertically in the gas accumulation in Xihu sag,i.e.the saturation zone of deep basin gas,the gas-water transition zone and the conventional hydrocarbon accumulation zone,indicating the features of the deep basin gas accumulation.
TL;DR: In this article, the authors present a method for determining trends in ELA change at McCall Glacier, Alaska, USA, over the last 50 years, based on mapping of the cold-temperate transition surface (CTS), marking the limit between cold and temperate ice of a polythermal glacier.
Abstract: Knowledge of glacier equilibrium-line altitude (ELA) changes and trends in time is essential for future predictions of glacier volumes. We present a novel method for determining trends in ELA change at McCall Glacier, Alaska, USA, over the last 50 years, based on mapping of the cold–temperate transition surface (CTS), marking the limit between cold and temperate ice of a polythermal glacier. Latent heat release from percolating meltwater and precipitation keeps the ice column temperate in the accumulation area. A change from accumulation to ablation zone reduces this heat release, leading locally to glacier ice cooling. By mapping the CTS along the whole glacier length using radio-echo sounding and employing a thermodynamic model, the timing of the cooling was determined, from which past ELAs were constructed. These are in accord with mass-balance measurements carried out on McCall Glacier since the 1950s. We show that with a warming climate, McCall Glacier tends to cool in a counter-intuitive way.
TL;DR: In this paper, an ice core recovered from Guoqu glacier on Mt. Geladaindong and analyzed using a Single Particle Soot Photometer provides the first long-term (1843-1982) record of BC concentrations from the Central Tibetan Plateau.
Abstract: . Black carbon (BC) deposited on snow and glacier surfaces can reduce albedo and lead to accelerated melt. An ice core recovered from Guoqu glacier on Mt. Geladaindong and analyzed using a Single Particle Soot Photometer provides the first long-term (1843–1982) record of BC concentrations from the Central Tibetan Plateau. The highest concentrations are observed from 1975–1982, which corresponds to a 2.0-fold and 2.4-fold increase in average and median values, respectively, relative to 1843–1940. BC concentrations post-1940 are also elevated relative to the earlier portion of the record. Causes for the higher BC concentrations include increased regional BC emissions and subsequent deposition, and melt induced enrichment of BC, with the melt potentially accelerated due to the presence of BC at the glacier surface. A qualitative comparison of the BC and Fe (used as a dust proxy) records suggests that if changes in the concentrations of absorbing impurities at the glacier surface have influenced recent glacial melt, the melt may be due to the presence of BC rather than dust. Guoqu glacier has received no net ice accumulation since the 1980s, and is a potential example of a glacier where an increase in the equilibrium line altitude is exposing buried high impurity layers. That BC concentrations in the uppermost layers of the Geladaindong ice core are not substantially higher relative to deeper in the ice core suggests that some of the BC that must have been deposited on Guoqu glacier via wet or dry deposition between 1983 and 2005 has been removed from the surface of the glacier, potentially via supraglacial or englacial meltwater.