scholarly journals Dynamic changes on Wilkins Ice Shelf during the 2006–2009 retreat derived from satellite observations

2016 ◽  
Author(s):  
Melanie Rankl ◽  
Johannes Jakob Fürst ◽  
Angelika Humbert ◽  
Matthias Holger Braun
Keyword(s):  
Surface Flow ◽  
Satellite Observations ◽  
Ice Shelf ◽  
Dynamic Changes ◽  
Ice Shelves ◽  
Multi Stage ◽  
Multi Temporal ◽  
Horizontal Strain ◽  
Offset Tracking ◽  
The Antarctic

Abstract. Ice shelves serve as important buttresses for upstream areas. Several large ice shelves on the Antarctic Peninsula have disintegrated or retreated, which implied dynamic consequences for upstream ice. The present study aims to assess dynamic changes on Wilkins Ice Shelf during multi-stage ice-front retreat in the last decade. A total area of 2135 ± 75 km2 was lost in the period 2008–2009. The present study uses time-series of SAR satellite observations (1994/96, 2006–2010) in order to derive variations in multi-temporal surface flow from intensity offset tracking methods. Spatial patterns of horizontal strain rate and stress components were inferred during different ice-front retreat stages. These fields are used to explain the different break-up stages and to evaluate the ice-shelf stability. For this purpose, we apply criteria which were forwarded to explain and assess past ice-shelf retreat.

scholarly journals Dynamic changes on the Wilkins Ice Shelf during the 2006–2009 retreat derived from satellite observations

2017 ◽  
Vol 11 (3) ◽  
pp. 1199-1211 ◽  
Author(s):  
Melanie Rankl ◽  
Johannes Jakob Fürst ◽  
Angelika Humbert ◽  
Matthias Holger Braun
Keyword(s):  
Time Series ◽  
Satellite Observations ◽  
Principal Strain ◽  
Strain Rates ◽  
Shelf Area ◽  
Ice Shelf ◽  
Dynamic Changes ◽  
Flow Angle ◽  
Ice Shelves ◽  
Stress Flow

Abstract. The vast ice shelves around Antarctica provide significant restraint to the outflow from adjacent tributary glaciers. This important buttressing effect became apparent in the last decades, when outlet glaciers accelerated considerably after several ice shelves were lost around the Antarctic Peninsula (AP). The present study aims to assess dynamic changes on the Wilkins Ice Shelf (WIS) during different stages of ice-front retreat and partial collapse between early 2008 and 2009. The total ice-shelf area lost in these events was 2135 ± 75 km2 ( ∼  15 % of the ice-shelf area relative to 2007). Here, we use time series of synthetic aperture radar (SAR) satellite observations (1994–1996, 2006–2010) in order to derive variations in surface-flow speed from intensity-offset tracking. Spatial patterns of horizontal strain-rate, stress and stress-flow angle distributions are determined during different ice-front retreat stages. Prior to the final break up of an ice bridge in 2008, a strong speed up is observed, which is also discernible from other derived quantities. We identify areas that are important for buttressing and areas prone to fracturing using in-flow and first principal strain rates as well as principal stress components. Further propagation of fractures can be explained as the first principal components of strain rates and stresses exceed documented threshold values. Positive second principal stresses are another scale-free indicator for ice-shelf areas, where fractures preferentially open. Second principal strain rates are found to be insensitive to ice-front retreat or fracturing. Changes in stress-flow angles highlight similar areas as the in-flow strain rates but are difficult to interpret. Our study reveals the large potential of modern SAR satellite time series to better understand dynamic and structural changes during ice-shelf retreat but also points to uncertainties introduced by the methods applied.

scholarly journals A 15-year circum-Antarctic iceberg calving dataset derived from continuous satellite observations

2021 ◽  
Vol 13 (9) ◽  
pp. 4583-4601
Author(s):  
Mengzhen Qi ◽  
Yan Liu ◽  
Jiping Liu ◽  
Xiao Cheng ◽  
Yijing Lin ◽  
...  
Keyword(s):  
Mass Loss ◽  
Ice Sheet ◽  
Satellite Observations ◽  
Ice Shelf ◽  
Time Intervals ◽  
Antarctic Ice Sheet ◽  
Ice Shelves ◽  
Iceberg Calving ◽  
Calving Rate ◽  
The Antarctic

Abstract. Iceberg calving is the main process that facilitates the dynamic mass loss of ice sheets into the ocean, which accounts for approximately half of the mass loss of the Antarctic ice sheet. Fine-scale calving variability observations can help reveal the calving mechanisms and identify the principal processes that influence how the changing climate affects global sea level through the ice shelf buttressing effect on the Antarctic ice sheet. Iceberg calving from entire ice shelves for short time intervals or from specific ice shelves for long time intervals has been monitored before, but there is still a lack of consistent, long-term, and high-precision records on independent calving events for all of the Antarctic ice shelves. In this study, a 15-year annual iceberg calving product measuring every independent calving event larger than 1 km2 over all of the Antarctic ice shelves that occurred from August 2005 to August 2020 was developed based on 16 years of continuous satellite observations. First, the expansion of the ice shelf frontal coastline was simulated according to ice velocity; following this, the calved areas, which are considered to be the differences between the simulated coastline, were manually delineated, and the actual coastline was derived from the corresponding satellite imagery, based on multisource optical and synthetic aperture radar (SAR) images. The product provides detailed information on each calving event, including the associated year of occurrence, area, size, average thickness, mass, recurrence interval, and measurement uncertainties. A total of 1975 annual calving events larger than 1 km2 were detected on the Antarctic ice shelves from August 2005 to August 2020. The average annual calved area was measured as 3549.1 km2 with an uncertainty value of 14.3 km2, and the average calving rate was measured as 770.3 Gt yr−1 with an uncertainty value of 29.5 Gt yr−1. The number of calving events, calved area, and calved mass fluctuated moderately during the first decade, followed by a dramatic increase from 2015/2016 to 2019/2020. During the dataset period, large ice shelves, such as the Ronne–Filchner and Ross ice shelves, advanced with low calving frequency, whereas small- and medium-sized ice shelves retreated and calved more frequently. Iceberg calving of ice shelves is most prevalent in West Antarctica, followed by the Antarctic Peninsula and Wilkes Land in East Antarctica. The annual iceberg calving event dataset of Antarctic ice shelves provides consistent and precise calving observations with the longest time coverage. The dataset provides multidimensional variables for each independent calving event that can be used to study detailed spatial–temporal variations in Antarctic iceberg calving. The dataset can also be used to study ice sheet mass balance, calving mechanisms, and responses of iceberg calving to climate change. The dataset, entitled “Annual iceberg calving dataset of the Antarctic ice shelves (2005–2020)”, is shared via the National Tibetan Plateau Data Center: https://doi.org/10.11888/Glacio.tpdc.271250 (Qi et al., 2021). In addition, the average annual calving rate of 18.4±6.7 Gt yr−1 for calving events smaller than 1 km2 of the Antarctic ice shelves and the calving rate of 166.7±15.2 Gt yr−1 for the marine-terminating glaciers were estimated.

scholarly journals Ice velocity changes in the Ross and Ronne sectors observed using satellite radar data from 1997 and 2009

2012 ◽  
Vol 6 (5) ◽  
pp. 1019-1030 ◽  
Author(s):  
B. Scheuchl ◽  
J. Mouginot ◽  
E. Rignot
Keyword(s):  
Order Effects ◽  
Strong Impact ◽  
Ice Shelf ◽  
Ice Streams ◽  
Dynamic Changes ◽  
Ice Shelves ◽  
Ross Ice Shelf ◽  
Catchment Areas ◽  
Ice Velocity ◽  
The Antarctic

Abstract. We report changes in ice velocity of a 6.5 million km2 region around South Pole encompassing the Filchner-Ronne and Ross Ice Shelves and a significant portion of the ice streams and glaciers that constitute their catchment areas. Using the first full interferometric synthetic aperture radar (InSAR) coverage of the region completed in 2009 and partial coverage acquired in 1997, we processed the data to assemble a comprehensive map of ice speed changes between those two years. On the Ross Ice Shelf, our results confirm a continued deceleration of Mercer and Whillans Ice Streams with a 12-yr velocity difference of −50 m yr−1 (−16.7%) and −100 m yr−1 (−25.3%) at their grounding lines. The deceleration spreads 450 km upstream of the grounding line and more than 500 km onto the shelf, beyond what was previously known. Ross and Filchner Ice Shelves exhibit signs of pre-calving events, representing the largest observed changes, with an increase in speed in excess of +100 m yr−1 in 12 yr. Other changes in the Ross Ice Shelf region are less significant. The observed changes in glacier speed extend on the Ross Ice Shelf along the ice streams' flow lines. Most tributaries of the Filchner-Ronne Ice Shelf show a modest deceleration or no change between 1997 and 2009. Slessor Glacier shows a small deceleration over a large sector. No change is detected on the Bailey, Rutford, and Institute Ice Streams. On the Filchner Ice Shelf itself, ice decelerated rather uniformly with a 12-yr difference in speed of −50 m yr−1, or −5% of its ice front speed, which we attribute to a 12 km advance in its ice front position. Our results show that dynamic changes are present in the region. They highlight the need for continued observation of the area with a primary focus on the Siple Coast. The dynamic changes in Central Antarctica between 1997 and 2009 are generally second-order effects in comparison to losses on glaciers in the Bellingshausen and Amundsen Seas region and on the Antarctic Peninsula. We therefore conclude that the dynamic changes shown here do not have a strong impact on the mass budget of the Antarctic continent.

Antarctic ice sheet response to upper-bound scenarios

2021 ◽  
Author(s):  
Sainan Sun ◽  
Frank Pattyn
Keyword(s):  
Sea Level Rise ◽  
Sea Level ◽  
Upper Bound ◽  
Ice Sheet ◽  
Climate Forcing ◽  
Ice Shelf ◽  
Antarctic Ice Sheet ◽  
Ice Shelves ◽  
Basal Sliding ◽  
The Antarctic

<p>Mass loss of the Antarctic ice sheet contributes the largest uncertainty of future sea-level rise projections. Ice-sheet model predictions are limited by uncertainties in climate forcing and poor understanding of processes such as ice viscosity. The Antarctic BUttressing Model Intercomparison Project (ABUMIP) has investigated the 'end-member' scenario, i.e., a total and sustained removal of buttressing from all Antarctic ice shelves, which can be regarded as the upper-bound physical possible, but implausible contribution of sea-level rise due to ice-shelf loss. In this study, we add successive layers of ‘realism’ to the ABUMIP scenario by considering sustained regional ice-shelf collapse and by introducing ice-shelf regrowth after collapse with the inclusion of ice-sheet and ice-shelf damage (Sun et al., 2017). Ice shelf regrowth has the ability to stabilize grounding lines, while ice shelf damage may reinforce ice loss. In combination with uncertainties from basal sliding and ice rheology, a more realistic physical upperbound to ice loss is sought. Results are compared in the light of other proposed mechanisms, such as MICI due to ice cliff collapse.</p>

scholarly journals Melting and freezing under Antarctic ice shelves from a combination of ice-sheet modelling and observations

2017 ◽  
Vol 63 (240) ◽  
pp. 731-744 ◽  
Author(s):  
JORGE BERNALES ◽  
IRINA ROGOZHINA ◽  
MAIK THOMAS
Keyword(s):  
Mass Balance ◽  
Ice Sheet ◽  
Model Parameters ◽  
Ice Shelf ◽  
Ice Shelves ◽  
Continental Scale ◽  
Model Set ◽  
Set Up ◽  
Basal Melting ◽  
The Antarctic

ABSTRACTIce-shelf basal melting is the largest contributor to the negative mass balance of the Antarctic ice sheet. However, current implementations of ice/ocean interactions in ice-sheet models disagree with the distribution of sub-shelf melt and freezing rates revealed by recent observational studies. Here we present a novel combination of a continental-scale ice flow model and a calibration technique to derive the spatial distribution of basal melting and freezing rates for the whole Antarctic ice-shelf system. The modelled ice-sheet equilibrium state is evaluated against topographic and velocity observations. Our high-resolution (10-km spacing) simulation predicts an equilibrium ice-shelf basal mass balance of −1648.7 Gt a−1 that increases to −1917.0 Gt a−1 when the observed ice-shelf thinning rates are taken into account. Our estimates reproduce the complexity of the basal mass balance of Antarctic ice shelves, providing a reference for parameterisations of sub-shelf ocean/ice interactions in continental ice-sheet models. We perform a sensitivity analysis to assess the effects of variations in the model set-up, showing that the retrieved estimates of basal melting and freezing rates are largely insensitive to changes in the internal model parameters, but respond strongly to a reduction of model resolution and the uncertainty in the input datasets.

scholarly journals Recent ice-surface-elevation changes of Fleming Glacier in response to the removal of the Wordie Ice Shelf, Antarctic Peninsula

2010 ◽  
Vol 51 (55) ◽  
pp. 97-102 ◽  
Author(s):  
J. Wendt ◽  
A. Rivera ◽  
A. Wendt ◽  
F. Bown ◽  
R. Zamora ◽  
...  
Keyword(s):  
Antarctic Peninsula ◽  
Regional Climate ◽  
Airborne Lidar ◽  
Similar Data ◽  
Ice Shelf ◽  
International Polar Year ◽  
Ice Flow ◽  
Ice Shelves ◽  
Elevation Changes ◽  
The Antarctic

AbstractRegional climate warming has caused several ice shelves on the Antarctic Peninsula to retreat and ultimately collapse during recent decades. Glaciers flowing into these retreating ice shelves have responded with accelerating ice flow and thinning. The Wordie Ice Shelf on the west coast of the Antarctic Peninsula was reported to have undergone a major areal reduction before 1989. Since then, this ice shelf has continued to retreat and now very little floating ice remains. Little information is currently available regarding the dynamic response of the glaciers feeding the Wordie Ice Shelf, but we describe a Chilean International Polar Year project, initiated in 2007, targeted at studying the glacier dynamics in this area and their relationship to local meteorological conditions. Various data were collected during field campaigns to Fleming Glacier in the austral summers of 2007/08 and 2008/09. In situ measurements of ice-flow velocity first made in 1974 were repeated and these confirm satellite-based assessments that velocity on the glacier has increased by 40–50% since 1974. Airborne lidar data collected in December 2008 can be compared with similar data collected in 2004 in collaboration with NASA and the Chilean Navy. This comparison indicates continued thinning of the glacier, with increasing rates of thinning downstream, with a mean of 4.1 ± 0.2 m a−1 at the grounding line of the glacier. These comparisons give little indication that the glacier is achieving a new equilibrium.

scholarly journals Speedup and fracturing of George VI Ice Shelf, Antarctic Peninsula

2013 ◽  
Vol 7 (3) ◽  
pp. 797-816 ◽  
Author(s):  
T. O. Holt ◽  
N. F. Glasser ◽  
D. J. Quincey ◽  
M. R. Siegfried
Keyword(s):  
Antarctic Peninsula ◽  
Structural Changes ◽  
Surface Elevation ◽  
Ice Shelf ◽  
Ice Shelves ◽  
The North ◽  
Surface Elevation Change ◽  
Elevation Changes ◽  
Negative Surface ◽  
The Antarctic

Abstract. George VI Ice Shelf (GVIIS) is located on the Antarctic Peninsula, a region where several ice shelves have undergone rapid breakup in response to atmospheric and oceanic warming. We use a combination of optical (Landsat), radar (ERS 1/2 SAR) and laser altimetry (GLAS) datasets to examine the response of GVIIS to environmental change and to offer an assessment on its future stability. The spatial and structural changes of GVIIS (ca. 1973 to ca. 2010) are mapped and surface velocities are calculated at different time periods (InSAR and optical feature tracking from 1989 to 2009) to document changes in the ice shelf's flow regime. Surface elevation changes are recorded between 2003 and 2008 using repeat track ICESat acquisitions. We note an increase in fracture extent and distribution at the south ice front, ice-shelf acceleration towards both the north and south ice fronts and spatially varied negative surface elevation change throughout, with greater variations observed towards the central and southern regions of the ice shelf. We propose that whilst GVIIS is in no imminent danger of collapse, it is vulnerable to ongoing atmospheric and oceanic warming and is more susceptible to breakup along its southern margin in ice preconditioned for further retreat.

scholarly journals Driving Forces of Circum-Antarctic Glacier and Ice Shelf Front Retreat over the Last Two Decades

2020 ◽  
Author(s):  
Celia A. Baumhoer ◽  
Andreas J. Dietz ◽  
Christof Kneisel ◽  
Heiko Paeth ◽  
Claudia Kuenzer
Keyword(s):  
Sea Ice ◽  
Surface Temperature ◽  
Sea Surface Temperature ◽  
Air Temperature ◽  
Environmental Variables ◽  
Sea Surface ◽  
Ice Shelf ◽  
Antarctic Ice Sheet ◽  
Ice Shelves ◽  
The Antarctic

Abstract. The safety band of Antarctica consisting of floating glacier tongues and ice shelves buttresses ice discharge of the Antarctic Ice Sheet. Recent disintegration events of ice shelves and glacier retreat indicate a weakening of this important safety band. Predicting calving front retreat is a real challenge due to complex ice dynamics in a data-scarce environment being unique for each ice shelf and glacier. We explore to what extent easy to access remote sensing and modelling data can help to define environmental conditions leading to calving front retreat. For the first time, we present a circum-Antarctic record of glacier and ice shelf front retreat over the last two decades in combination with environmental variables such as air temperature, sea ice days, snowmelt, sea surface temperature and wind direction. We find that the Antarctic ice sheet area shrank 29,618 ± 29 km2 in extent between 1997–2008 and gained an area of 7,108 ± 144.4 km2 between 2009 and 2018. Retreat concentrated along the Antarctic Peninsula and West Antarctica including the biggest ice shelves Ross and Ronne. Glacier and ice shelf retreat comes along with one or several changes in environmental variables. Decreasing sea ice days, intense snow melt, weakening easterlies and relative changes in sea surface temperature were identified as enabling factors for retreat. In contrast, relative increases in air temperature did not correlate with calving front retreat. To better understand drivers of glacier and ice shelf retreat it is of high importance to analyse the magnitude of basal melt through the intrusion of warm Circumpolar Deep Water (CDW) driven by strengthening westerlies and to further assess surface hydrology processes such as meltwater ponding, runoff and lake drainage.

scholarly journals Speedup and fracturing of George VI Ice Shelf, Antarctic Peninsula

2013 ◽  
Vol 7 (1) ◽  
pp. 373-417 ◽  
Author(s):  
T. O. Holt ◽  
N. F. Glasser ◽  
D. J. Quincey ◽  
M. R. Siegfried
Keyword(s):  
Antarctic Peninsula ◽  
Structural Changes ◽  
Surface Elevation ◽  
Ice Shelf ◽  
Ice Shelves ◽  
The North ◽  
Surface Elevation Change ◽  
Elevation Changes ◽  
Negative Surface ◽  
The Antarctic

Abstract. George VI Ice Shelf (GVIIS) is located on the Antarctic Peninsula, a region where several ice shelves have undergone rapid breakup in response to atmospheric and oceanic warming. We use a combination of optical (Landsat), radar (ERS 1/2 SAR) and laser altimetry (GLAS) datasets to examine the response of GVIIS to environmental change and to offer an assessment on its future stability. The spatial and structural changes of GVIIS (ca. 1973 to ca. 2010) are mapped and surface velocities are calculated at different time periods (InSAR and optical feature tracking from 1989 to 2009) to document changes in the ice shelf's flow regime. Surface elevation changes are recorded between 2003 and 2008 using repeat track ICESat acquisitions. We note an increase in fracture extent and distribution at the south ice front, ice-shelf acceleration towards both the north and south ice fronts and spatially varied negative surface elevation change throughout, with greater variations observed towards the central and southern regions of the ice shelf. We propose that whilst GVIIS is in no imminent danger of collapse, it is vulnerable to on-going atmospheric and oceanic warming and is more susceptible to breakup along its southern margin in ice preconditioned for further retreat.

scholarly journals Modelling the long-term response of the Antarctic ice sheet to global warming

1998 ◽  
Vol 27 ◽  
pp. 161-168 ◽  
Author(s):  
Roland C. Warner ◽  
W.Κ. Budd
Keyword(s):  
Global Warming ◽  
Mass Loss ◽  
Ice Sheet ◽  
Ice Shelf ◽  
Antarctic Ice Sheet ◽  
Ice Shelves ◽  
Basal Melting ◽  
The Antarctic ◽  
Term Response

The primary effects of global warming on the Antarctic ice sheet can involve increases in surface melt for limited areas at lower elevations, increases in net accumulation, and increased basal melting under floating ice. For moderate global wanning, resulting in ocean temperature increases of a few °C, the large- increase in basal melting can become the dominant factor in the long-term response of the ice sheet. The results from ice-sheet modelling show that the increased basal melt rates lead to a reduction of the ice shelves, increased strain rates and flow at the grounding lines, then thinning and floating of the marine ice sheets, with consequential further basal melting. The mass loss from basal melting is counteracted to some extent by the increased accumulation, but in the long term the area of ice cover decreases, particularly in West Antarctica, and the mass loss can dominate. The ice-sheet ice-shelf model of Budd and others (1994) with 20 km resolution has been modified and used to carry out a number of sensitivity studies of the long-term response of the ice sheet to prescribed amounts of global warming. The changes in the ice sheet are computed out to near-equilibrium, but most of the changes take place with in the first lew thousand years. For a global mean temperature increase of 3°C with an ice-shelf basal melt rate of 5 m a−1 the ice shelves disappear with in the first few hundred years, and the marine-based parts of the ice sheet thin and retreat. By 2000 years the West Antarctic region is reduced to a number of small, isolated ice caps based on the bedrock regions which are near or above sea level. This allows the warmer surface ocean water to circulate through the archipelago in summer, causing a large change to the local climate of the region.

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