Tributary Glaciers Research Articles

Modeling the instantaneous response of glaciers after the collapse of the Larsen B Ice Shelf

AbstractFollowing the disintegration of the Larsen B Ice Shelf, Antarctic Peninsula, in 2002, regular surveillance of its ∼20 tributary glaciers has revealed a response which is varied and complex in both space and time. The major outlets have accelerated and thinned, smaller glaciers have shown little or no change, and glaciers flowing into the remnant Scar Inlet Ice Shelf have responded with delay. In this study we present the first areawide numerical analysis of glacier dynamics before and immediately after the collapse of the ice shelf, combining new data sets and a state‐of‐the‐art numerical ice flow model. We simulate the loss of buttressing at the grounding line and find a good qualitative agreement between modeled changes in glacier flow and observations. Through this study, we seek to improve confidence in our numerical models and their ability to capture the complex mechanical coupling between floating ice shelves and grounded ice.

Velocities of the Amery Ice Shelf's primary tributary glaciers, 2004–12

AbstractMonitoring the rate of ice flow into ice shelves is vital to understanding how, where and when mass changes occur in Antarctica. Previous observations of ice surface velocity indicate that the Amery Ice Shelf and tributary glaciers have been relatively stable over the period 1968 to 1999. This study measured the displacement of features on the ice surface over a sequence of Landsat 7 images separated by approximately one year and spanning 2004 to 2012 using the surface feature tracking software IMCORR. The focus is on the region surrounding the southern grounding zone of the Amery Ice Shelf and its primary tributary glaciers: the Fisher, Lambert and Mellor glaciers. No significant changes in surface velocity were observed over this period. Accordingly, the velocity fields from each image pair between 2004 and 2012 were used to synthesize an average velocity dataset of the Amery Ice Shelf region and to compare it to previously published velocity datasets and in situ global positioning system velocity observations. No significant change in ice surface velocities was found between 2004 and 2012 in the Amery Ice Shelf region, which suggests that it continues to remain stable.

Charles Swithinbank

Charles Swithinbank

Oceanic and atmospheric forcing of Larsen C Ice-Shelf thinning

Abstract. The catastrophic collapses of Larsen A and B ice shelves on the eastern Antarctic Peninsula have caused their tributary glaciers to accelerate, contributing to sea-level rise and freshening the Antarctic Bottom Water formed nearby. The surface of Larsen C Ice Shelf (LCIS), the largest ice shelf on the peninsula, is lowering. This could be caused by unbalanced ocean melting (ice loss) or enhanced firn melting and compaction (englacial air loss). Using a novel method to analyse eight radar surveys, this study derives separate estimates of ice and air thickness changes during a 15-year period. The uncertainties are considerable, but the primary estimate is that the surveyed lowering (0.066 ± 0.017 m yr−1) is caused by both ice loss (0.28 ± 0.18 m yr−1) and firn-air loss (0.037 ± 0.026 m yr−1). The ice loss is much larger than the air loss, but both contribute approximately equally to the lowering because the ice is floating. The ice loss could be explained by high basal melting and/or ice divergence, and the air loss by low surface accumulation or high surface melting and/or compaction. The primary estimate therefore requires that at least two forcings caused the surveyed lowering. Mechanisms are discussed by which LCIS stability could be compromised in the future. The most rapid pathways to collapse are offered by the ungrounding of LCIS from Bawden Ice Rise or ice-front retreat past a "compressive arch" in strain rates. Recent evidence suggests that either mechanism could pose an imminent risk.

Evolution of surface velocities and ice discharge of Larsen B outlet glaciers from 1995 to 2013

Abstract. We use repeat-pass SAR data to produce detailed maps of surface motion covering the glaciers draining into the former Larsen B Ice Shelf, Antarctic Peninsula, for different epochs between 1995 and 2013. We combine the velocity maps with estimates of ice thickness to analyze fluctuations of ice discharge. The collapse of the central and northern sections of the ice shelf in 2002 led to a near-immediate acceleration of tributary glaciers as well as of the remnant ice shelf in Scar Inlet. Velocities of most of the glaciers discharging directly into the ocean remain to date well above the velocities of the pre-collapse period. The response of individual glaciers differs and velocities show significant temporal fluctuations, implying major variations in ice discharge as well. Due to reduced velocity and ice thickness the ice discharge of Crane Glacier decreased from 5.02 Gt a−1 in 2007 to 1.72 Gt a−1 in 2013, whereas Hektoria and Green glaciers continue to show large temporal fluctuations in response to successive stages of frontal retreat. The velocity on Scar Inlet ice shelf increased 2–3-fold since 1995, with the largest increase in the first years after the break-up of the main section of Larsen B. Flask and Leppard glaciers, the largest tributaries to Scar Inlet ice shelf, accelerated. In 2013 their discharge was 38% and 46% higher than in 1995.

The evolving instability of the remnant Larsen B Ice Shelf and its tributary glaciers

Following the 2002 disintegration of the northern and central parts of the Larsen B Ice Shelf, the tributary glaciers of the southern surviving part initially appeared relatively unchanged and hence assumed to be buttressed sufficiently by the remnant ice shelf. Here, we modify this perception with observations from IceBridge altimetry and InSAR-inferred ice flow speeds. Our analyses show that the surfaces of Leppard and Flask glaciers directly upstream from their grounding lines lowered by 15 to 20 m in the period 2002–2011. The thinning appears to be dynamic as the flow of both glaciers and the remnant ice shelf accelerated in the same period. Flask Glacier started accelerating even before the 2002 disintegration, increasing its flow speed by ∼55% between 1997 and 2012. Starbuck Glacier meanwhile did not change much. We hypothesize that the different evolutions of the three glaciers are related to their dissimilar bed topographies and degrees of grounding. We apply numerical modeling and data assimilation that show these changes to be accompanied by a reduction in the buttressing afforded by the remnant ice shelf, a weakening of the shear zones between its flow units and an increase in its fracture. The fast flowing northwestern part of the remnant ice shelf exhibits increasing fragmentation, while the stagnant southeastern part seems to be prone to the formation of large rifts, some of which we show have delimited successive calving events. A large rift only 12 km downstream from the grounding line is currently traversing the stagnant part of the ice shelf, defining the likely front of the next large calving event. We propose that the flow acceleration, ice front retreat and enhanced fracture of the remnant Larsen B Ice Shelf presage its approaching demise.

Peculiar Characteristics of Fragmentation of Glaciers: A Case Study of Western Himalaya, India

The areal extent of many Himalayan glaciers is decreasing where number of glaciers is increasing. This increasing number is subject to the fragmentation of limbs of main trunk glacier. However, disintegration of limbs is not observed in all the glacier system. This paper emphases the scenario of the fragmentation occurred in glaciers. Two glaciers from the two different basins have been taken into the consideration for this study. The peculiar characteristic of these glaciers is that, the tributary glaciers are showing less retreat in compare to main trunk glaciers. Due to this reason the rate of shift in snout is higher in main trunk glaciers than tributary glaciers. However, in recent data the tributary glaciers have experienced little higher loss in glacial ice than main glacier. But the shift of snout in main trunk glacier is no doubt surprising since past. Therefore, various parameters have been examined to identify the cause of such a behavior of glaciers. The common factors observed in both the glaciers are accumulation area ratio which is higher, snow line altitude which is lower in tributary glaciers for the period of 2005-2013. Another factor is the orientation as tributary glaciers are towards NE direction. In addition, slope of Dharlang glacier (main limb) is 4? where it is 18? in tributary glacier.

Assessment of historical changes (1959-2012) and the causes of recent break-ups of the Petersen ice shelf, Nunavut, Canada

AbstractAerial photography and satellite imagery of the Petersen ice shelf, Nunavut, Canada, from 1959 to 2012 show that it was stable until June 2005, after which a series of major calving events in the summers of 2005, 2008, 2011 and 2012 resulted in the loss of ∼61% of the June 2005 ice-shelf area. This recent series of calving events was initiated by the loss of extensive regions of ˃50-year-old multi-year landfast sea ice from the front of the ice shelf in summer 2005. Each subsequent calving event has been preceded by open-water conditions and resulting loss of pack-ice pressure across the front of the ice shelf, and most occurred during record warm summers. Ground-penetrating radar (GPR) ice thickness measurements and RADARSAT-2 derived observations of surface motion indicate that tributary glaciers provided total ice input of 1.19-5.65 Mta–1 to the ice shelf from 2011 to 2012, far below the mean surface loss rate of 28.45 Mta–1. With recent losses due to calving and little evidence for current basal freeze-on, this suggests that the Petersen ice shelf will no longer exist by the 2040s, or sooner if further major calving events occur.

Small-scale modeling of ice flow perturbations induced by sudden ice shelf breakup

The sudden breakup of ice shelves is expected to result in significant acceleration of inland glaciers, a process related to the removal of the buttressing effect exerted by the ice shelf on the tributary glaciers. In this paper, this process is analyzed by means of scaled analogue experiments reproducing the flow of a valley glacier draining an ice sheet grounded above sea level into an ice shelf, and analyzing the dynamic perturbations resulting from ice shelf disintegration and removal of buttressing effect. Models show a significant increase in glacier velocity close to its outlet following ice shelf breakup, a transient effect that does not significantly propagate upstream towards the ice sheet and rapidly decays with time. Basal lubrication and variations in ice thickness do not significantly influence the process that thus leaves the ice sheet almost unaffected by flow perturbations.

Ice Volume Estimates from Ground-Penetrating Radar Surveys, Wedel Jarlsberg Land Glaciers, Svalbard

We present ground-penetrating radar (GPR)—based volume calculations, with associated error estimates, for eight glaciers on Wedel Jarlsberg Land, southwestern Spitsbergen, Svalbard, and compare them with those obtained from volume-area scaling relationships. The volume estimates are based upon GPR ice-thickness data collected during the period 2004–2013. The total area and volume of the ensemble are 502.91 ± 18.60 km2 and 91.91 ± 3.12 km3, respectively. The individual areas, volumes, and average ice thickness lie within 0.37–140.99 km2, 0.01–31.98 km3, and 28–227 m, respectively, with a maximum recorded ice thickness of 619 ± 13 m on Austre Torellbreen. To estimate the ice volume of unsurveyed tributary glaciers, we combine polynomial cross-sections with a function providing the best fit to the measured ice thickness along the center line of a collection of 22 surveyed tributaries. For the time-to-depth conversion of GPR data, we test the use of a glacierwide constant radio-wave velocity chosen on the basis of local or regional common midpoint measurements, versus the use of distinct velocities for the firn, cold ice, and temperate ice layers, concluding that the corresponding volume calculations agree with each other within their error bounds.

The glacial (MIS 3-2) outlet glacier of the Marsyandi Nadi-icestream-network with its Ngadi Khola tributary glacier (Manaslu- and Lamjung Himalaya): The reconstructed lowering of the Marsyandi Nadi ice stream tongue down in to the southern Himalaya Foreland

For the reconstruction of past climate variations, investigations on the history of glaciers are necessary. In the Himalaya, investigations like these have a rather short tradition in comparison with other mountains on earth. At the same time, this area on the southern margin of Tibet is of special interest because of the question as to the monsoon-influence that is connected with the climate-development. Anyhow, the climate of High Asia is of global importance. Here for the further and regionally intensifying answer to this question, a glacial glacier reconstruction is submitted from the Central-Himalaya, more exactly from the Manaslu-massif. Going on down-valley from the glacial-historical investigations of 1977 in the upper Marsyandi Khola (Nadi) and the partly already published results of field campaigns in the middle Marsyandi Khola and the Damodar- and Manaslu Himal in the years 1995, 2000, 2004 and 2007, new geomorphological and geological field- and laboratory data are introduced here from the Ngadi (Nadi) Khola and the lower Marsyandi Nadi from the inflow of the Ngadi (Nadi) Khola down to the southern mountain foreland. There has existed a connected ice-stream-network drained down to the south by a 2,100–2,200 m thick and 120 km long Marsyandi Nadi main valley glacier. At a height of the valley bottom of c. 1,000 m a.s.l. the Ngadi Khola glacier joined the still c. 1,300 m thick Marsyandi parent glacier from the Himalchuli-massif (Nadi (Ngadi) Chuli) — the south spur of the Manaslu Himal. From here the united glacier tongue flowed down about a further 44 km to the south up to c. 400 m a.s.l. (27°57′38″N/84°24′56″E) into the Himalaya fore-chains and thus reached one of or the lowest past ice margin position of the Himalayas. The glacial (LGP (Last glacial period), LGM (Last glacial maximum) Wurm, Stage 0, MIS 3-2) climatic snowline (ELA = equilibrium line altitude) has run at 3,900 to 4,000 m a.s.l. and thus c. 1,500 altitude meters below the current ELA (Stage XII) at 5,400–5,500 m a.s.l. The reconstructed, maximum lowering of the climatic snowline (ΔELA = depression of the equilibrium line altitude) about 1,500 m corresponds at a gradient of 0.6°C per 100 altitude meters to a High Glacial decrease in temperature of 9°C (0.6 × 15 = 9). At that time the Tibetan inland ice has caused a stable cold high, so that no summer monsoon can have existed there. Accordingly, during the LGP the precipitation was reduced, so that the cooling must have come to more than only 9°C.

Firn air depletion as a precursor of Antarctic ice-shelf collapse

AbstractSince the 1970s, the sudden, rapid collapse of 20% of ice shelves on the Antarctic Peninsula has led to large-scale thinning and acceleration of its tributary glaciers. The leading hypothesis for the collapse of most of these ice shelves is the process of hydrofracturing, whereby a water-filled crevasse is opened by the hydrostatic pressure acting at the crevasse tip. This process has been linked to observed atmospheric warming through the increased supply of meltwater. Importantly, the low-density firn layer near the ice-shelf surface, providing a porous medium in which meltwater can percolate and refreeze, has to be filled in with refrozen meltwater first, before hydrofracturing can occur at all. Here we build upon this notion of firn air depletion as a precursor of ice-shelf collapse, by using a firn model to show that pore space was depleted in the firn layer on former ice shelves, which enabled their collapse due to hydrofracturing. Two climate scenario runs with the same model indicate that during the 21st century most Antarctic Peninsula ice shelves, and some minor ice shelves elsewhere, are more likely to become susceptible to collapse following firn air depletion. If warming continues into the 22nd century, similar depletion will become widespread on ice shelves around East Antarctica. Our model further suggests that a projected increase in snowfall will protect the Ross and Filchner–Ronne Ice Shelves from hydrofracturing in the coming two centuries.

One million cubic kilometers of fossil ice in Valles Marineris: Relicts of a 3.5 Gy old glacial landsystem along the Martian equator

Self-consistent landform assemblages suggest that Valles Marineris, the giant valley system that stretches along the Martian equator, was entirely glaciated during Late Noachian to Early Hesperian times and still contains huge volumes of fossil ice. Some of these glacial landform assemblages are illustrated here, with representative examples selected in three regions: Ius Chasma, Central Candor Chasma and the junction between Coprates Chasma and Capri Chasma. A morphological boundary separating an upper spur-and-gully morphology from a smooth basal escarpment has been spectacularly preserved along valley walls throughout Valles Marineris. The boundary winds around topographic obstacles and displays long-wavelength variations in elevation. It is associated with lateral benches, hanging valleys and truncated spurs. Comparisons with terrestrial analogs indicate that it is most reasonably interpreted as a glacial trimline. Chasma floors are covered by various kinds of terrains, including hummocky terrains, platy terrains, lateral banks, layered benches and a draping mantle. Landforms in these terrains and their spatial relationship with the interpreted trimline suggest that they correspond to various disintegration stages of an ancient glacial fill, currently protected by a superficial cover of ablation till. Altogether, these landforms and terrains compose a full glacial landsystem with wet-based glaciers that were able to flow and slide over their beds. It was most probably fed by ice accumulating at low elevations directly from the atmosphere onto valley floors and walls, with only minor contributions from tributary glaciers flowing down from higher elevations. Similar fossil glacial landsystems dating back from the early Martian history are to be expected in many other low-latitude troughs such as chasmata, chaos, valleys, impact craters and other basins.

Variable glacier response to atmospheric warming, northern Antarctic Peninsula, 1988–2009

Abstract. The northern Antarctic Peninsula has recently exhibited ice-shelf disintegration, glacier recession and acceleration. However, the dynamic response of land-terminating, ice-shelf tributary and tidewater glaciers has not yet been quantified or assessed for variability, and there are sparse data for glacier classification, morphology, area, length or altitude. This paper firstly classifies the area, length, altitude, slope, aspect, geomorphology, type and hypsometry of 194 glaciers on Trinity Peninsula, Vega Island and James Ross Island in 2009 AD. Secondly, this paper documents glacier change 1988–2009. In 2009, the glacierised area was 8140±262 km2. From 1988–2001, 90% of glaciers receded, and from 2001–2009, 79% receded. This equates to an area change of −4.4% for Trinity Peninsula eastern coast glaciers, −0.6% for western coast glaciers, and −35.0% for ice-shelf tributary glaciers from 1988–2001. Tidewater glaciers on the drier, cooler eastern Trinity Peninsula experienced fastest shrinkage from 1988–2001, with limited frontal change after 2001. Glaciers on the western Trinity Peninsula shrank less than those on the east. Land-terminating glaciers on James Ross Island shrank fastest in the period 1988–2001. This east-west difference is largely a result of orographic temperature and precipitation gradients across the Antarctic Peninsula, with warming temperatures affecting the precipitation-starved glaciers on the eastern coast more than on the western coast. Reduced shrinkage on the western Peninsula may be a result of higher snowfall, perhaps in conjunction with the fact that these glaciers are mostly grounded. Rates of area loss on the eastern side of Trinity Peninsula are slowing, which we attribute to the floating ice tongues receding into the fjords and reaching a new dynamic equilibrium. The rapid shrinkage of tidewater glaciers on James Ross Island is likely to continue because of their low elevations and flat profiles. In contrast, the higher and steeper tidewater glaciers on the eastern Antarctic Peninsula will attain more stable frontal positions after low-lying ablation areas are removed, reaching equilibrium more quickly.

Mass loss of Larsen B tributary glaciers (Antarctic Peninsula) unabated since 2002

Ice mass loss continues at a high rate among the large glacier tributaries of the Larsen B Ice Shelf following its disintegration in 2002. We evaluate recent mass loss by mapping elevation changes between 2006 and 2010/11 using differencing of digital elevation models (DEMs). The measurement accuracy of these elevation changes is confirmed by a ‘null test’, subtracting DEMs acquired within a few weeks. The overall 2006–2010/11 mass loss rate (9.0 ± 2.1 Gt a−1) is similar to the 2001/02–2006 rate (8.8 ± 1.6 Gt a−1), derived using DEM differencing and laser altimetry. This unchanged overall loss masks a varying pattern of thinning and ice loss for individual glacier basins. On Crane Glacier, the thinning pulse, initially greatest near the calving front, is now broadening and migrating upstream. The largest losses are now observed for the Hektoria/Green glacier basin, having increased by 33% since 2006. Our method has enabled us to resolve large residual uncertainties in the Larsen B sector and confirm its state of ongoing rapid mass loss.

Antarctic ice-sheet loss driven by basal melting of ice shelves

Accurate prediction of global sea-level rise requires that we understand the cause of recent, widespread and intensifying glacier acceleration along Antarctic ice-sheet coastal margins. Atmospheric and oceanic forcing have the potential to reduce the thickness and extent of floating ice shelves, potentially limiting their ability to buttress the flow of grounded tributary glaciers. Indeed, recent ice-shelf collapse led to retreat and acceleration of several glaciers on the Antarctic Peninsula. But the extent and magnitude of ice-shelf thickness change, the underlying causes of such change, and its link to glacier flow rate are so poorly understood that its future impact on the ice sheets cannot yet be predicted. Here we use satellite laser altimetry and modelling of the surface firn layer to reveal the circum-Antarctic pattern of ice-shelf thinning through increased basal melt. We deduce that this increased melt is the primary control of Antarctic ice-sheet loss, through a reduction in buttressing of the adjacent ice sheet leading to accelerated glacier flow. The highest thinning rates occur where warm water at depth can access thick ice shelves via submarine troughs crossing the continental shelf. Wind forcing could explain the dominant patterns of both basal melting and the surface melting and collapse of Antarctic ice shelves, through ocean upwelling in the Amundsen and Bellingshausen seas, and atmospheric warming on the Antarctic Peninsula. This implies that climate forcing through changing winds influences Antarctic ice-sheet mass balance, and hence global sea level, on annual to decadal timescales.

Longitudinal surface structures (flowstripes) on Antarctic glaciers

Abstract. Longitudinal surface structures ("flowstripes") are common on many glaciers but their origin and significance are poorly understood. In this paper we present observations of the development of these longitudinal structures from four different Antarctic glacier systems; the Lambert Glacier/Amery Ice Shelf area, the Taylor and Ferrar Glaciers in the Ross Sea sector, Crane and Jorum Glaciers (ice-shelf tributary glaciers) on the Antarctic Peninsula, and the onset zone of a tributary to the Recovery Glacier Ice Stream in the Filchner Ice Shelf area. Mapping from optical satellite images demonstrates that longitudinal surface structures develop in two main situations: (1) as relatively wide flow stripes within glacier flow units and (2) as relatively narrow flow stripes where there is convergent flow around nunataks or at glacier confluence zones. Our observations indicate that the confluence features are narrower, sharper, and more clearly defined features. They are characterised by linear troughs or depressions on the ice surface and are much more common than the former type. Longitudinal surface structures within glacier flow units have previously been explained as the surface expression of localised bed perturbations but a universal explanation for those forming at glacier confluences is lacking. Here we propose that these features are formed at zones of ice acceleration and extensional flow at glacier confluences. We provide a schematic model for the development of longitudinal surface structures based on extensional flow that can explain their ridge and trough morphology as well as their down-ice persistence.

Trends in 20th century and recent glacier fluctuations in the Karakoram Mountains

The article provides an overview on the trends of 20th century and recent glacier fluctuations since the end of the 19th century in the Karakoram Mountains. Recent glacier variations in the subtropical mountain range of the Karakoram Mountains were surveyed on the base of field observations carried out in the period of 1992–2006 on 57 glaciers. Historical documents, such as photographs and travel reports, as well as air and satellite images have been included in the compilation. The occurrence of ice-dammed lakes, which have mainly been formed by advances of tributary glaciers into the trunk valleys, has been used as further indicators for glacier fluctuations. Even though a considerable part of the Karakoram glaciers have shown signs of glacier retreat, most of the longer glaciers (> 45 km), such as the Baltoro and Batura glaciers, have been rather stationary in the last century. Even some of the clean glaciers, such as the Yazghil and Barpu glaciers, did not retreat significantly. Singular glacier advances and surges occurred over the entire study period, whereas the average distance of the surges has apparently become smaller over time. The glacier behaviour of the avalanche-fed glacier is highly dynamic. Geomorphological indicators, as localised glacier thickening resulting in overtopping and breakthroughs of lateral moraines, the new moraine formation and the shape of the glacier tongue has to be handled carefully for drawing conclusions on the entire mass balance of a glacier. In the whole, the dynamics of the Karakoram glaciers proves to be different from the neighbouring mountain ranges, such as the Himalayas and Tienshan, which are characterized by a dominant glacier retreat. The reasons lie in the different topographical and climatic settings. Topography is apart from the complex climatic situation one of the major controlling factors governing the individual glacier fluctuations in the Karakoram Mountains.

Application of a minimal glacier model to Hansbreen, Svalbard

Abstract. Hansbreen is a well studied tidewater glacier in the southwestern part of Svalbard, currently about 16 km long. Since the end of the 19th century it has been retreating over a distance of 2.7 km. In this paper the global dynamics of Hansbreen are studied with a minimal glacier model, in which the ice mechanics are strongly parameterised and a simple law for iceberg calving is used. The model is calibrated by reconstructing a climate history in such a way that observed and simulated glacier length match. In addition, the calving law is tuned to reproduce the observed mean calving flux for the period 2000–2008. Equilibrium states are studied for a wide range of values of the equilibrium line altitude. The dynamics of the glacier are strongly nonlinear. The height-mass balance feedback and the water depth-calving flux feedback give rise to cusp catastrophes in the system. For the present climatic conditions Hansbreen cannot survive. Depending on the imposed climate change scenario, in AD 2100 Hansbreen is predicted to have a length between 10 and 12 km. The corresponding decrease in ice volume (relative to the volume in AD 2000) is 45 to 65%. Finally the late-Holocene history of Hansbreen is considered. We quote evidence from dated peat samples that Hansbreen did not exist during the Holocene Climatic Optimum. We speculate that at the end of the mid-Holocene Climatic Optimum Hansbreen could advance because the glacier bed was at least 50 m higher than today, and because the tributary glaciers on the western side may have supplied a significant amount of mass to the main stream. The excavation of the overdeepening and the formation of the shoal at the glacier terminus probably took place during the Little Ice Age.

2001–2009 elevation and mass losses in the Larsen A and B embayments, Antarctic Peninsula

AbstractWe investigate the elevation and mass-balance response of tributary glaciers following the loss of the Larsen A and B ice shelves, Antarctic Peninsula (in 1995 and 2002 respectively). Our study uses MODIS imagery to track ice extent, and ASTER and SPOT5 digital elevation models (DEMs) plus ATM and ICESat laser altimetry to track elevation changes, spanning the period 2001–09. The measured Larsen B tributary glaciers (Hektoria, Green, Evans, Punchbowl, Jorum and Crane) lost up to 160 m in elevation during 2001–06, and thinning continued into 2009. Elevation changes were small for the more southerly Flask and Leppard Glaciers, which are still constrained by a Larsen B ice shelf remnant. In the northern embayment, continued thinning of >3 m a−1 on Drygalski Glacier, 14 years after the Larsen A ice shelf disintegrated, suggests that mass losses for the exposed Larsen B tributaries will continue for years into the future. Grounded ice volume losses exceed 13 km3 for Crane Glacier and 30 km3 for the Hektoria–Green–Evans glaciers. The combined mean loss rate for 2001–06 is at least 11.2 Gt a−1. Our values differ significantly from published mass-budget-based estimates for these embayments, but are a reasonable fraction of GRACE-derived rates for the region (∼40 Gt a−1).