A surge of Perseibreen, Svalbard, examined using aerial photography and ASTER high resolution satellite imagery

The identification of surge activity is important in assessing the duration of the active and quiescent phases of the surge cycle of Svalbard glaciers. Satellite and aerial photographic images are used to identify and describe the form and flow of Perseibreen, a valley glacier of 59 km² on the east coast of Spitsbergen. Heavy surface crevassing and a steep ice front, indicative of surge activity, were first observed on Perseibreen in April 2002. Examination of high resolution (15 m) Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) satellite imagery confirmed this surge activity. Perseibreen retreated by almost 750 m between 1961 and 1990. Between 1990 and the summer of 2000, Perseibreen switched from retreat and its front began to advance. Rapid advance was underway during the period June 2000 to May 2001, with terminus advance at over 400 m yr⁻¹. Between May and August 2001 the rate increased to over 750 m yr⁻¹. The observed crevasse orientation indicates that ice was in longitudinal tension, suggesting the down-glacier transfer of mass. Ice surface velocities, derived from image correlation between ASTER images, were 2-2.5 m d⁻¹ between May and August 2001. The glacier was flowing at a relatively uniform speed with sharp velocity gradients located close to its lateral margins, a velocity structure typical of ice masses in the active phase of the surge cycle. The stress regime is extensional throughout and the surge appears to be initiated low on the glacier. This is similar to the active-phase dynamics of other Svalbard tidewater glaciers. Perseibreen has probably been inactive since at least 1870, a period of about 130 years to the present surge which defines a minimum length for the quiescent phase.     

The most extensive Holocene advance in the Stauning Alper, East Greenland, occurred in the Little Ice Age

We present glacial geologic and chronologic data concerning the Holocene ice extent in the Stauning Alper of East Greenland. The retreat of ice from the late-glacial position back into the mountains was accomplished by at least 11 000 cal years B.P. The only recorded advance after this time occurred during the past few centuries (the Little Ice Age). Therefore, we postulate that the Little Ice Age event represents the maximum Holocene ice extent in this part of East Greenland.     

Post‐1850 changes in Glacier Benito,North Patagonian Icefield,Chile

Glacier Benito is a temperate outlet glacier on the west side of the North Patagonian Icefield. Rates of thinning and ablation were obtained using data collected by the British Joint Services Expedition in 1972/73 and subsequent data collected in 2007 and 2011. Ice‐front recession rates were based on dendrochronological dating for the terminal moraines and aerial and satellite imagery of the ice front in 1944, 1998 and 2002. Between the first Benito survey in 1973 and 2007, the lower glacier thinned by nearly 150 m at an average rate of 4.3 m yr^?1 with the rate increasing to 6.1 m yr^?1 between 2007 and 2011, a 28.7% increase during the latter period. Increases in ice movement and ablation were negligible: ice movement for 1973 and 2007 averaged 0.45 m day^?1 and ablation averaged 0.05 m day^?1. Ice front recession along the glacier's centre line from 1886 to 2002 was approximately 1860 m. Retreat rates between 1886 and 1944 averaged 8.9 m yr^?1. Thereafter glacier asymmetry makes measurement along the glacier centre line unrepresentative of areal change until 1998 when symmetry was restored; retreat between 1944 and 1998 was 15.4 m yr^?1. From 1998 to 2002 the rate increased dramatically to 127.2 m yr^?1. Recession from the southern end of Benito's terminal moraine in the 1850s supports an early date for initial retreat of the Icefield's glaciers.     

Glacier Retreat, Mass-Balance and Thinning: Sermilik Glacier, South Greenland

This study documents thinning and retreat of the South Greenland ice margin and discusses possible reasons in the light of mass‐balance and change of dynamic conditions. Analyses of satellite images have shown that the glacier tongue of Sermilik glacier disintegrated within the past 15 years. Furthermore, the observed thinning close to the Sermilik glacier front was as much as 120 m water equivalent during this period. This figure was derived by comparing surface elevation data from a digital elevation model (1985) and laser altimeter measurements from the year 2000, showing surface elevation changes along a flow line of Sermilik glacier. Mass‐balance data from in situ measurements performed at a centre flow line of the glacier are presented. These data are compared to results from remote sensing analyses of the study area. Net ablation reconstruction over the last 41 years from positive‐degree‐day modelling, at various locations along the Sermilik glacier massbalance transect, shows an increase during the past decades. These analyses indicate that only 55% of the total thinning in this area can be explained by mass‐balance changes. The remaining 45% of the thinning is attributed to changes in the dynamic behaviour of the glacier, such as an increase of creep towards the end of the twentieth century. The significant thinning along the Qagssimiut lobe can also be explained as a combination of mass‐balance changes and changes in ice dynamic behaviour.     

Former glacial lakes of the Bunger Hills,Antarctica

The Bunger Hills in East Antarctica occupy a land area of approximately 400 km². They have been exposed by Holocene retreat of the Antarctic ice sheet and its outlet glaciers. The accompanying sea level rise flooded the marine inlets that now separate the northern islands and peninsulas from the major part of the hills. During deglaciation the continental ice sheet margin retreated south‐eastwards with several temporary halts, during which ice‐dammed lakes were formed in some valleys. These lakes were maintained long enough to permit formation of beaches of sand and gravel, and for the erosion of shore platforms and low cliffs in bedrock. Around the western end of Fish Tail Bay impressive shoreline features 20 m above sea level define a former ice‐dammed lake that was 5.5 km long. A similar 7 km long former ice‐dammed lake was formed at Lake Dolgoe. The more extensive and deeper glacial lake is revealed by well‐developed and preserved shoreline features cut at 29 m which is 16 m above present lake level. In addition, several small ice‐dammed lakes existed temporarily near Lake Shchel and in the valley to the west. Lake Fish Tail existed more than 6,900 ¹⁴C years ago and Lake Shchel probably more than 6,680 ¹⁴C years ago. It is inferred that the shore platforms and beaches were formed by lake ice and wave action over considerable periods when the lakes were impounded by steep cold ice margins. There appears to have been a balance between meltwater input and evaporative loss from the lakes in the cold dry continental climate. There is no evidence for rapid lake level fluctuations, and there was very little input of clastic sediment. This resulted in poor development of deltaic and rhythmically laminated lake floor deposits. It is suggested that such deposits are more characteristic of ice‐dammed lakes formed in association with wet‐based temperate ice than those associated with dry‐based polar ice.     

Supraglacial Debris Supply in the Cuerpo de Hombre paleoglacier (Spanish Central System): Reconstruction and Interpretation of a Rock Avalanche Event

During the deglaciation stages of the last glacial period a rock avalanche took place on the glacier that occupied the upper sector of the Cuerpo de Hombre Valley (Sierra de Béjar). The material displaced during the avalanche fell onto the ice, was transported by the glacier and later deposited as supraglacial ablation till. The cause of the avalanche was the decompression of the valley slopes after they were freed from the glacier ice (stress relaxation). Reconstruction of the ice masses has been carried out to quantify the stress relaxation that produced the collapse. The rock avalanche took place on a lithologically homogeneous slope with a dense fracture network. The avalanche left a 0.4 ha scar on the slope with a volume of displaced material of 623 ± 15 × 10³ m³. The deposit is an accumulation of large, angular, heterometric boulders (1–100 m³ in volume) with a coarse pebble‐size matrix. The avalanche can be explained as a relaxation process. This implies rock decompression once the glacier retreat left the wall ice free (debuttressing). Calculations show that the avalanche took place where the decompression stresses were highest (130–170 kPa). In the Spanish Central System paleoglaciers the largest accumulation of morainic deposits occurred after the glacial maximum and the earliest stages of the ice retreat. The process described here is used as an example to formulate a hypothesis that the largest accumulations of tills were formed in relation to enhanced slope dynamics once some glacier retreat had occurred.     

Extent and Chronology of the Ross Sea Ice Sheet and the Wilson Piedmont Glacier along the Scott Coast at and Since the Last Glacial Maximum

During the last glacial maximum, a coalescent ice mass consisting of the grounded Ross Sea ice sheet and an expanded Wilson Piedmont Glacier covered the southern Scott Coast. This coalescent ice mass was part of a larger grounded ice sheet that occupied the Ross Sea Embayment during the last glacial maximum. Deglaciation of the western Ross Sea Embayment adjacent to the southern Scott Coast was delayed until shortly before 6500 ¹⁴C yr bp , aconclusion based on ages of marine shells from McMurdo Sound, a relative sea-level curve, and algae that lived in ice-dammed lakes. Therefore, most recession of grounded ice in the Ross Sea Embayment occurred in mid to late Holocene time, after deglacial sea-level rise due to melting of Northern Hemisphere ice sheets essentially was accomplished. Rising sea level alone could not have driven grounding-line retreat back to the present-day Siple Coast.     

The Rapid Retreat of Jakobshavns Isbræ, West Greenland: Field Observations of 2005 and Structural Analysis of its Evolution

Jakobshavns Isbræ in West Greenland (terminus at ≈69° 10′ N/50° W), a major outlet glacier of the Greenland Ice Sheet and a continuously fast-moving ice stream, has long been the fastest moving and one of the most productive glaciers on Earth. It had been moving continuously at speeds of over 20 m/day with a stable front position throughout most of the latter half of the twentieth century, except for relatively small seasonal changes. In 2002, the ice stream apparently suddenly entered a phase of rapid retreat. The ice front started to break up, the floating tongue disintegrated, and the production of icebergs increased. In July 2005, we conducted an extensive aerial survey of Jakobshavns Isbræ to measure and document the present state of retreat compared to our previous field observations since 1996. We use an approach that combines structural analysis of deformation features with continuum mechanics to assess the kinematics and dynamics of glaciers, based on aerial imagery, satellite data and GPS measurements. Results from interpretation of ERS-SAR and ASTER data from 1995 to 2005 in combination with aerial imagery from 1996 to 2005 shed light on the question of changes versus stability and their causes in the Jakobshavns Isbræ dynamical system. The recently observed retreat of Jakobshavns Isbræ is attributed to climatic warming, rather than to an inherent change in the glaciodynamic system. Close to the retreating front, deformation structures are characteristic of extension and disintegration. Deformation provinces that do not border the retreating front have had the same deformation characteristics throughout the past decade (1996–2005).     

GLACIER RETREAT IN THE MARITIME ALPS AREA

In the southernmost tract of the Alps (Italian‐French Maritime Alps), extensively covered by glaciers during the Last Glacial Maximum, about 30 small glaciers were present by the end of the Little Ice Age. The aim of this paper is to document the progressive decrease towards exhaustion of these glaciers, located at the latitude of 44° N, highlighting the factors affecting their retreat. All available data sources were investigated for this work including: the annual glaciers fluctuations record, comparative analyses of historical maps and multi‐temporal oblique photographs and direct surveys in the field. The history of the Maritime Alps glaciers fluctuations was thoroughly reconstructed. Stationary conditions were observed from 1896 up to the beginning of the 1930s; since then they underwent phases of withdrawal with variable intensity. In the early 1990s, only six glaciers were still present, the extent of which were all was dramatically reduced. In the past two decades, the Maritime Alps glacier fronts experienced a global retreat of about 100 m, with a sharp acceleration after 2002. Currently ice patches along cirque walls and/or semi‐buried lenses of ice are still present; morphological evidence of permafrost creeping in the glacier forefield accounts for the incipient transition to periglacial landforms (i.e. rock glaciers). The main factors controlling glaciers retreat seem to have been their original extent at the beginning of the current regressive phase and their distance from the main chain divide. From a climatic point of view unfavourable factors for glaciers persistence have been in the last decades a remarkable and sharp temperature increase, a decrease in winter snowfall and a shift of the rainfall peak from autumn to spring.     

Glacier surge at Usherbreen, Svalbard

Usherbreen started to surge in 1978, and the front has advanced 1.5 km and covered an area of 4.5 km². During the first two years the front advanced more than 1 m/d, and the front was still advancing 0.15– 0.20m/d in 1985, seven years after the start. The mean gradient of the lower 7 km decreased from 3.3 grad. to 1.8 grad. during the surge. The volume of ice transported down the glacier from higher to lower parts during the surge was 815 x lO'm³. which is almost 20% of the total glacier volume. Old icecored ridges in front of the glacier were reactivated, and the whole ridge system was pushed forward, in the summer of 1985 at a speed of about 0.05 m/d. Parts of the ridge system were moved 200 m during this surge. New ridges were developed on the flat sandur in front of the old ridge system. This demonstrates that the glacier advanced further than in any previous surge.     

基于海冰密集度遥感数据的波弗特海海冰时空变化研究

采用美国冰雪数据中心(NSIDC)的日尺度与月尺度海冰密集度数据,将海冰密集度为15%作为阈值确定海冰外缘线位置,提取波弗特海海域的海冰外缘线,计算波弗特海的海冰密集度、海冰范围与海冰面积,然后通过海冰范围与海冰外缘线的年际变化与季节变化来分析波弗特海海冰外缘线退缩的时空变化特征与趋势。实验结果表明,1978—2015年波弗特海的海冰密集度、海冰范围与海冰面积整体变化趋势一致,减少趋势显著。37年来,海冰密集度平均每年减少约0.3%,海冰范围平均每年减少3 235 km2,海冰面积平均每年减少5 084 km2。海冰密集度在1979—1996年无明显减少趋势,1996—2015年减少趋势明显。波弗特海海冰范围一般在9月达到最小值,在11月至次年5月维持在最大值(全冰覆盖状态);海冰面积一般在9月达到最小值,在12月或者1月达到最大值。海冰范围最小值出现时间有延迟的趋势,全冰覆盖状态具有起始时间越来越晚、终止时间越来越早、持续时间越来越短的趋势,平均持续天数为212 d。     

Trends and variability of sea ice in Baffin Bay and Davis Strait, 1953–2001

The extent and duration of sea ice in Baffin Bay and Davis Strait has a major impact on the timing and strength of the marine production along West Greenland. The advance and retreat of the sea ice follows a predictable pattern, with maximum extent typically in March. We examine the area of sea ice in March in three overlapping study regions centred on Disko Bay on the west coast of Greenland. Sea ice concentration estimates derived from satellite passive microwave data are available for the years 1979-2001. We extend the record back in time by digitizing ice charts from the Danish Meteorological Institute, 1953-1981. There is reasonable agreement between the chart data and the satellite data during the three years of overlap: 1979-1981. We find a significant increasing trend in sea ice for the 49-year period (1953-2001) for the study regions that extend into Davis Strait and Baffin Bay. The cyclical nature of the wintertime ice area is also evident, with a period of about 8 to 9 years. Correlation of the winter sea ice concentration with the winter North Atlantic Oscillation (NAO) index shows moderately high values in Baffin Bay. The correlation of ice concentration with the previous winter's NAO is high in Davis Strait and suggests that next winter's ice conditions can be predicted to some extent by this winter's NAO index.     

Calving retreat and proglacial lake growth at Hooker Glacier,Southern Alps,New Zealand

Hooker Glacier in the central Southern Alps of New Zealand has undergone significant downwasting and recession (～2.14 km) during the last two centuries. High retreat rates (51 m a^?1 1986–2001, 43 m a^?1 2001–2011) have produced a large (1.22 km²) proglacial lake. We present a retreat scenario for Hooker Glacier. A retreat scenario predicts that the glacier terminus will stabilise >3 km up‐valley of the current lake outlet after 2028 when ice velocity equals calving rate.     

Deglaciation pattern in sub-aquatic — supra-aquatic transitional environment illustrated by the Klarälven valley system, Värmland, western Sweden

The downwasting of the Weichselian ice sheet in the Klarälven valley and its continuation southwards has been studied. The meltwater drainage below the highest coastline (HCL) on the plain of Lake Vänern took place subglacially causing breaking‐up and calving around tunnel mouths in the ice margin. When the ice margin reached into the extension of the Klarälven valley, the drainage pattern changed to lateral. The ice disappeared as a narrow ice tongue later than in the surrounding highland. When the tongue receded northwards it left dead‐ice bodies behind, that remained in the valley after the general retreat. Along the tongue and dead‐ice bodies glaciofluvial sediments accumulated as kame terraces, deriving from esker trains in tributary valleys. At the mouths of the tributaries, deltas were deposited. Halts in the retreat occurred at a few places marked by thresholds of till. According to the present study the HCL rises northwards, from 180 m a.s.l. at Brattforsheden to 228 m at Höljes 170 km to the north. At halts in the ice recession it dropped a few metres. A tentative dating based on the level of the HCL, the tilt of raised shorelines and the rate of shoreline regression has given the time 10900 to 10360 calibrated years BP for the retreat of the ice margin from Brattforsheden to Höljes.     

Mass balance and area changes of four High Arctic plateau ice caps, 1959–2002

Abstract Small, stagnating ice caps at high latitudes are particularly sensitive to climatic fluctuations, especially with regard to changes in ablation season temperature. We conducted mass balance measurements and GPS area surveys on four small High Arctic plateau ice caps from 1999–2002. We compared these measurements with topographic maps and aerial photography from 1959, and with previously published data. Net mass balance (b_n) of Murray Ice Cap was ?0.49 (1999), ?0.29 (2000), ?0.47 (2001), and ?0.29 (2002), all in meters of water equivalent (m w.eq.). The mass balance of nearby Simmons Ice Cap was also negative in 2000 (b_n=?0.40 m w.eq.) and in 2001 (b_n=?0.52 m w.eq.). All four ice caps experienced substantial marginal recession and area reductions of between 30 and 47% since 1959. Overall, these icecaps lost considerable mass since at least 1959, except for a period between the mid‐1960s and mid‐1970s characterized regionally by reduced summer melt, positive mass balance, and ice cap advance. The regional equilibrium line altitude (ELA) is located, on average, above the summits of the ice caps, indicating that they are remnants of past climatic conditions and out of equilibrium with present climate. The ice caps reached a Holocene maximum and were several times larger during the Little Ice Age (LIA) and their current recession reflects an adjustment to post‐LIA climatic conditions. At current downwasting rates the ice masses on the Hazen Plateau will completely disappear by, or soon after, the mid‐21st century.     

1990-2011年西昆仑峰区冰川变化的遥感监测

本文应用Landsat 5、7 TM、ETM+影像分析1990-2011年昆仑山西段昆仑峰区冰川变化特征,结果表明:1990-2011年冰川面积减少16.83 km²,退缩率仅为0.65%,冰川退缩趋势不明显。单条冰川变化有进有退,中峰冰川末端在2002-2004年以661 m/a的速率前进,初步判定为跃动冰川。1991-1998年,崇测冰川面积增加9.47 km²,冰川末端以200 m/a的速率前进,不排除有跃动冰川的可能性。尽管近年来全球气温普遍上升,大量冰川处于退缩状态,但统计已有研究结果发现近50年来青藏高原存在冰川长度、面积增加,冰川物质平衡为正的现象,表现出冰川对气候变化复杂的反馈机制。通过分析气象站点和冰芯资料,研究区周边地区气温上升、降水量缓慢增加可能是冰川微弱退缩的原因之一;增强的西风环流带来更多的降水、研究区以极大陆型大规模冰川为主,也可能是冰川退缩幅度较小的原因。     

Spatial-temporal characters of Antarctic sea ice variation

Using sea ice concentration dataset covering the period of 1968-2002 obtained from the Hadley Center of UK, this paper investigates characters of Antarctic sea ice variations .The finding demonstrates that the change of mean sea-ice extent is almost consistent with that of sea-ice area, so sea-ice extent can be chosen to go on this research. The maximum and the minimum of Antarctic sea ice appear in September and February respectively. The maximum and the maximal variation of sea ice appear in Weddell Sea and Ross Sea, while the minimum and the minimal variation of sea-ice appear in Antarctic Peninsula. In recent 35 years, as a whole, Antarctic sea ice decreased distinctly. Moreover, there are 5 subdivision characteristic regions considering their different variations. Hereinto, the sea-ice extent of Weddell Sea and Ross Sea regions extends and area increases, while the sea-ice extent of the other three regions contracts and area decreases. They are all of obvious 2-4 years and 5-7 years significant oscillation periods. It is of significance for further understanding the sea-ice-air interaction in Antarctica region and discussing the relationship between sea-ice variation and atmospheric circulation.     

QUANTIFYING UNCERTAINTY IN USING MULTIPLE DATASETS TO DETERMINE SPATIOTEMPORAL ICE MASS LOSS OVER 101 YEARS AT KÅRSAGLACIÄREN,SUB‐ARCTIC SWEDEN

Glacier mass balance and mass balance gradient are fundamentally affected by changes in glacier 3D geometry. Few studies have quantified changing mountain glacier 3D geometry, not least because of a dearth of suitable spatiotemporally distributed topographical information. Additionally, there can be significant uncertainty in georeferencing of historical data and subsequent calculations of the difference between successive surveys. This study presents multiple 3D glacier reconstructions and the associated mass balance response of Kårsaglaciären, which is a 0.89 ± 0.01 km² mountain glacier in sub‐arctic Sweden. Reconstructions spanning 101 years were enabled by historical map digitisation and contemporary elevation and thickness surveys. By considering displacements between digitised maps via the identification of common tie‐points, uncertainty in both vertical and horizontal planes were estimated. Results demonstrate a long‐term trend of negative mass balance with an increase in mean elevation, total glacier retreat (1909–2008) of 1311 ± 12 m, and for the period 1926–2010 a volume decrease of 1.0 ± 0.3 × 10^–3 km³ yr^–1. Synthesising measurements of the glaciers’ past 3D geometry and ice thickness with theoretically calculated basal stress profiles explains the present thermal regime. The glacier is identified as being disproportionately fast in its rate of mass loss and relative to area, is the fastest retreating glacier in Sweden. Our long‐term dataset of glacier 3D geometry changes will be useful for testing models of the evolution of glacier characteristics and behaviour, and ultimately for improving predictions of meltwater production with climate change.     

南极海冰的时空变化特征

依据Hadley中心提供的全球海冰密集度格点资料 ,利用诊断分析方法 ,对近 35年来南极海冰的时空变化特征进行了研究。研究表明 ,在南极地区 ,海冰平均北界和海冰总面积的变化基本一致 ,可以用海冰北界来研究南极海冰的时空变化特征。南极海冰最多和最少期分别出现在 9月和 2月 ;威德尔海和罗斯海地区海冰最多、变化最大 ,南极半岛地区海冰最少 ,变化也小 ;近 35年来环南极地区的海冰有明显的减少趋势。南极海冰变化的时空多样性十分明显 ,存在着 5个变化不同的区域 ,其中有两个区域近 35年来海冰范围扩大 ,面积增加 ,而另三个区域则海冰范围缩小 ,面积减少。不同区域的海冰都存在着较明显的 2- 3年和 5- 7年主振荡周期。南极海冰时空变化特征的研究对进一步认识南极地区海 冰 气相互作用的物理过程 ,讨论南极海冰变异与大气环流和天气气候的关系有重要意义     

The Retreat of Tien Shan Glaciers (Kyrgyzstan) Since the Little Ice Age Estimated from Aerial Photographs, Lichenometric and Historical Data

The retreat of 293 glaciers in the Tien Shan Mountains (Kyrgyz Republic) from their maximum extent during the Little Ice Age (LIA) is estimated using aerial photographs from 1980 to 1985 and maps at a scale of 1:25000, constructed during period 1956–1990. Two indices of changes are used: the linear distance from the glacier terminus to its Little Ice Age moraine and the difference in absolute elevation of the terminus and the moraine. Historical information about the front positions of glaciers in the 1880s to the 1930s was used as an indirect control of remote sensing data. The age of moraines in key regions was estimated by lichenometry. On average, Tien Shan glaciers have retreated by 989 ± 540 m since the LIA maximum. Their front elevations (dh) rose by 151 ± 105 m. These changes are similar to changes observed in the Alps and western Norway, Pamir‐Alay and Koryak plateau, but greater than in east Siberia over the same interval. Differences between four regions in Tien Shan (northern, western, inner, central) are generally small, though in the northern Tien Shan the glacier retreat and frontal rise are more prominent (1065 ± 479 m and 215 ± 140 m, respectively).