Spatial variability and regional trends of Antarctic ice shelf surface melt duration over 1979–2020 derived from passive microwave data

Abstract Passive microwave satellite observations are used to identify the presence of surface meltwater across Antarctica at daily intervals from July 1979 to June 2020, with a focus on ice shelves. Antarctic Peninsula ice shelves have the highest number of annual days of melt, with a maximum of 89 days. Over the entire time period, there are few significant linear trends in days of melt per year. High melt years can be split into two distinct categories, those with high melt days in Dronning Maud Land and Wilkes Land, and those with high melt days in the Antarctic Peninsula and the Bellingshausen Sea sector of West Antarctica. The first pattern coincides with significant negative correlations between melt days and spring and summer Southern Annular Mode. Both patterns also form the primary modes of spatial and annual variability in the dataset observed by Principal Component Analysis. Areas experiencing extended melt for the first time in years tend to show large decreases in subsequent winter microwave emissions due to structural changes in the firn. We use this to identify the impact of novel melt events, particularly over the austral summers of 1991/92 and 2015/16 on the Ross Ice Shelf.

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Speedup and fracturing of George VI Ice Shelf, Antarctic Peninsula

The Cryosphere ◽

10.5194/tc-7-797-2013 ◽

2013 ◽

Vol 7 (3) ◽

pp. 797-816 ◽

Cited By ~ 20

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.

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Speedup and fracturing of George VI Ice Shelf, Antarctic Peninsula

The Cryosphere Discussions ◽

10.5194/tcd-7-373-2013 ◽

2013 ◽

Vol 7 (1) ◽

pp. 373-417 ◽

Cited By ~ 3

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.

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Two decades of Antarctic coastal-change revealed by satellite imagery and deep learning

10.5194/egusphere-egu21-5344 ◽

2021 ◽

Author(s):

Celia A. Baumhoer ◽

Andreas Dietz ◽

Mariel Dirscherl ◽

Claudia Kuenzer

Keyword(s):

Deep Learning ◽

Ice Sheet ◽

Continuous Mapping ◽

Coastal Change ◽

Ice Shelf ◽

Antarctic Ice Sheet ◽

Ice Shelves ◽

Ross Ice Shelf ◽

Wilkes Land ◽

The Antarctic

Antarctica&#8217;s coastline is constantly changing by moving glacier and ice shelf fronts. The extent of glaciers and ice shelves influences the ice discharge and sea level contribution of the Antarctic Ice Sheet. Therefore, it is crucial to assess where ice shelf areas with strong buttressing forces are lost. So far, those changes have not been assessed for entire Antarctica within comparable time frames.We present a framework for circum-Antarctic coastline extraction based on a U-Net architecture. Antarctic coastal-change is calculated by using a deep learning derived coastline for the year 2018 in combination with earlier manual derived coastlines of 1997 and 2009. For the first time, this allows to compare circum-Antarctic changes in glacier and ice shelf front position for the last two decades. We found that the Antarctic Ice Sheet area decreased by -29,618&#177;1,193 km2 in extent between 1997-2008 and gained an area of 7,108&#177;1,029km2 between 2009 and 2018. Retreat dominated for the Antarctic Peninsula and West Antarctica and advance for the East Antarctic Ice Sheet over the entire investigation period. The only exception in East Antarctica was Wilkes Land experiencing simultaneous calving front retreat of several glaciers between 2009-2018. Biggest tabular iceberg calving events occurred at Ronne and Ross Ice Shelf within their natural calving cycle between 1997-2008. Future work includes the continuous mapping of Antarctica&#8217;s coastal-change on a more frequent temporal scale. &#160;

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Enhanced glacial discharge from the eastern Antarctic Peninsula since the 1700s associated with a positive Southern Annular Mode

Scientific Reports ◽

10.1038/s41598-019-50897-4 ◽

2019 ◽

Vol 9 (1) ◽

Cited By ~ 6

Author(s):

W. A. Dickens ◽

G. Kuhn ◽

M. J. Leng ◽

A. G. C. Graham ◽

J. A. Dowdeswell ◽

...

Keyword(s):

Antarctic Peninsula ◽

Isotope Composition ◽

Southern Annular Mode ◽

Ice Shelf ◽

Annular Mode ◽

Ice Shelves ◽

The North ◽

North Eastern ◽

Glacial Discharge ◽

The Antarctic

Abstract The Antarctic Peninsula Ice Sheet is currently experiencing sustained and accelerating loss of ice. Determining when these changes were initiated and identifying the main drivers is hampered by the short instrumental record (1992 to present). Here we present a 6,250 year record of glacial discharge based on the oxygen isotope composition of diatoms (δ18Odiatom) from a marine core located at the north-eastern tip of the Antarctic Peninsula. We find that glacial discharge - sourced primarily from ice shelf and iceberg melting along the eastern Antarctic Peninsula – remained largely stable between ~6,250 to 1,620 cal. yr BP, with a slight increase in variability until ~720 cal. yr. BP. An increasing trend in glacial discharge occurs after 550 cal. yr BP (A.D. 1400), reaching levels unprecedented during the past 6,250 years after 244 cal. yr BP (A.D. 1706). A marked acceleration in the rate of glacial discharge is also observed in the early part of twentieth century (after A.D. 1912). Enhanced glacial discharge, particularly after the 1700s is linked to a positive Southern Annular Mode (SAM). We argue that a positive SAM drove stronger westerly winds, atmospheric warming and surface ablation on the eastern Antarctic Peninsula whilst simultaneously entraining more warm water into the Weddell Gyre, potentially increasing melting on the undersides of ice shelves. A possible implication of our data is that ice shelves in this region have been thinning for at least ~300 years, potentially predisposing them to collapse under intensified anthropogenic warming.

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Decadal changes in south west Antarctic Peninsula Ice Shelves

10.5194/egusphere-egu21-2617 ◽

2021 ◽

Author(s):

Tom Holt ◽

Neil Glasser

Keyword(s):

Antarctic Peninsula ◽

Structural Changes ◽

Spatial And Temporal Patterns ◽

Ice Shelf ◽

Fracture Width ◽

Ice Shelves ◽

West Antarctic ◽

Flow Speeds ◽

Speed Up ◽

The Antarctic

Over the latter half of the 20th Century and beginning of the 21st Century, ice shelves around the Antarctic Peninsula have been losing mass at an accelerating rate, attributable to changes in atmospheric and oceanic conditions. Ice shelves have declined in extent and thickness, and some show signs of structural weakening. Here we investigate the glaciological changes to Bach, Stange and George VI ice shelves that fringe the Southwest Antarctic Peninsula. We used satellite imagery from 2009/10 to 2019/20 (Landsat, Sentinel and ASTER) to measure areal changes, calculate flow speeds, and quantify structural changes, focusing on open fracture width and length. We reveal a total net loss of 797.5 km2 from all three ice shelves since 2009/10, though spatial and temporal patterns of ice loss vary at individual ice fronts. Flow speeds have remained largely stable, but notable acceleration was calculated for Bach Ice Shelf, and at the northern and southern extents of George VI Ice Shelf. Open fractures have widened and lengthened over the observation periods. We conclude that Stange Ice Shelf is stable, and not under any immediate threat of enhanced recession. Continued ice-mass loss and consequential speed up of George VI South may cause further fracturing and destabilisation in the coming decades. Of more immediate concern are the glaciological changes noted for Bach Ice Shelf and George VI North; significant areas of passive ice have already, or will be soon removed, that could result in enhanced recession within the next decade.

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Major Surface Melting over the Ross Ice Shelf, Antarctica

10.5194/egusphere-egu21-6628 ◽

2021 ◽

Author(s):

Xun Zou ◽

David Bromwich ◽

Alvaro Montenegro ◽

Sheng-Hung Wang ◽

Lesheng Bai

Keyword(s):

Surface Melting ◽

Shortwave Radiation ◽

Ice Shelf ◽

Ice Shelves ◽

Low Level ◽

Ross Ice Shelf ◽

Downward Longwave Radiation ◽

Melting Period ◽

The Future ◽

The Impact

West Antarctica (WA), especially the Ross Ice Shelf (RIS), has experienced more frequent surface melting during austral summer over the past three decades. Surface melting will jeopardize the stability of ice shelves and cause potential ice loss in the future. We investigate four major melt cases over the RIS via Polar WRF simulations driven by ERA5 reanalysis data and MODIS observed albedo. Direct warm air advection, recurring foehn effect, and cloud/upper warm air introduced radiative warming are the three major regional causes of surface melting over WA. Warm marine air can warm the ice surface directly. With significant moisture transport occurring over more than 40% of the time during the melting period, the impact from net radiation can be amplified via the formation of low-level liquid water clouds. Consequently, extensive downward longwave radiation favors the melting expansion over the middle and coastal RIS. Also, for 3 of 4 melt cases, more than 50% of the melting period experiences foehn warming, which can cause a 2 &#8211; 4 &#186;C increase in surface temperature. Isentropic drawdown is usually the dominant foehn mechanism and contributes a 14 &#186;C temperature increase, especially when strong low-level blocking occurs on the upwind side. Foehn clearance and decreasing surface albedo respectively increase the downward shortwave radiation and decrease the upward shortwave radiation, significantly contributing to surface melting in areas like western Marie Byrd Land. Moreover, frequent foehn cases can enhance the turbulent mixing on the leeside and benefit sensible heat transfer when Froude number is around 1. With better understanding of the regional factors for the surface melting, the prediction of the future stability of West Antarctic Ice Shelves will be improved.

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Surface melting derived from microwave radiometers: a climatic indicator in Antarctica

Annals of Glaciology ◽

10.3189/172756407782871684 ◽

2007 ◽

Vol 46 ◽

pp. 29-34 ◽

Cited By ~ 31

Author(s):

G. Picard ◽

M. Fily ◽

H. Gallee

Keyword(s):

Microwave Remote Sensing ◽

Southern Annular Mode ◽

Temperature Pattern ◽

Mountainous Area ◽

Ice Shelf ◽

Ice Shelves ◽

Ross Ice Shelf ◽

Microwave Radiometers ◽

The Antarctic ◽

Melt Duration

AbstractThis paper aims at presenting a new dataset including the melt events derived from microwave remote sensing occurring in Antarctica from summer 1979/80 to 2005/06. The method for detecting melt events and sources of error is presented, and then trends in melt duration for every pixel are extracted from the dataset, mapped and analyzed. The analysis focuses on two particular cases, and the main results show that: (1) the trends over the period 1980–2006 in the Antarctic Peninsula match with lengthening of the melt season on the ice shelves and, surprisingly, shortening of the melt season in the mountainous area of the peninsula; and (2) the trends over the period 1996–2006 on the entire continent show a dipolar pattern, with the western regions experiencing decreasing melt duration, whereas East Antarctica and the Ross Ice Shelf experience increasing melt duration. This pattern closely mirrors the temperature pattern expected when the Southern Annular Mode is in a decreasing trend, as it is over the period 1996–2006. For further analysis and validation, the dataset has been made available at http://www-lgge.obs.ujf-grenoble.fr/~picard/melting/.

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Climatic conditions, mass balance and dynamics of Larsen B ice shelf, Antarctic Peninsula, prior to collapse

Annals of Glaciology ◽

10.3189/172756404781814573 ◽

2004 ◽

Vol 39 ◽

pp. 557-562 ◽

Cited By ~ 17

Author(s):

Pedro Skvarca ◽

Hernán De Angelis ◽

Andrés F. Zakrajsek

Keyword(s):

Mass Balance ◽

Antarctic Peninsula ◽

Satellite Image ◽

Climatic Conditions ◽

Strain Rates ◽

Ice Shelf ◽

Ice Flow ◽

Ice Shelves ◽

Additional Information ◽

Significant Acceleration

AbstractFollowing the collapse of Larsen A in 1995, about 3200 km2 of Larsen B ice shelf disintegrated in early 2002 during the warmest summer recorded on the northeastern Antarctic Peninsula. Immediately prior to disintegration the last field campaign was carried out on Larsen B. Measurements included surface net mass balance, velocity and strain rate on a longitudinal transect along Crane Glacier flowline and over a remnant section confined within Seal Nunataks that survived the collapse. In addition, an automatic weather station located nearby allowed derivation of melt days relevant to the formation and extent of surface meltwater. Repeated surveys allowed us to detect a significant acceleration in ice-flow velocity and associated increasing strain rates along the longitudinal transect. It may be possible to use this acceleration as a predictor of imminent ice-shelf collapse, applicable to ice shelves subject to similar climatic conditions. Additional information on recent ongoing changes was provided by a visible satellite image acquired in early 2003.

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

Journal of Glaciology ◽

10.3189/002214311797409811 ◽

2011 ◽

Vol 57 (204) ◽

pp. 737-754 ◽

Cited By ~ 46

Author(s):

Christopher A. Shuman ◽

Etienne Berthier ◽

Ted A. Scambos

Keyword(s):

Antarctic Peninsula ◽

Loss Rate ◽

Ice Shelf ◽

Laser Altimetry ◽

Ice Shelves ◽

Ice Volume ◽

Mass Losses ◽

Digital Elevation ◽

Modis Imagery ◽

Elevation Changes

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).

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Tabular Icebergs: Implication from Geophysical Studies of Ice Shelves

Annals of Glaciology ◽

10.3189/s0260305500016967 ◽

1980 ◽

Vol 1 ◽

pp. 55-55

Author(s):

Sion Shabtaie ◽

Charles R. Bentley

Keyword(s):

Mass Balance ◽

Sea Water ◽

Ice Thickness ◽

Ice Shelf ◽

Frictional Drag ◽

Ice Shelves ◽

Ross Ice Shelf ◽

Rift Zones ◽

Different Characteristics ◽

Ice Water

Recent geophysical and glaciological investigations of the Ross Ice Shelf have revealed many complexities in the ice shelf that can be important factors in iceberg structure. The presence of rift zones, surface and bottom crevasses, corrugations, ridges and troughs, and other features could substantially modify the hydraulics of iceberg towing and lead to disintegration of the berg in the course of transport.The relationships between the elevation above sea-level and total ice thickness for three ice shelves (Ross, Brunt, and McMurdo) are given; from them, expressions for the thickness/freeboard ratios of tabular icebergs calved from these ice shelves are obtained. The relationships obtained from the measured values of surface elevation and ice thickness are in agreement with models derived assuming hydrostatic equilibrium.Areas of brine infiltration into the Ross Ice Shelf have been mapped. Examples of radar profiles in these zones are shown. Absorption from the brine layers results in a poor or absent bottom echo. It is probable that little saline ice exists at the bottom of the Ross Ice Shelf front due to a rapid bottom melting near the ice front, and that the thickness of the saline ice at the bottom of icebergs calving from the Ross Ice Shelf is no more than a few meters, if there is any at all.We have observed many rift zones on the ice shelf by airborne radar techniques, and at one site the bottom and surface topographies of (buried) rift zones have been delineated. These rift zones play an obvious role in iceberg formation and may also affect the dynamics of iceberg transport. Bottom crevasses with different shapes, sizes, and spacings are abundant in ice shelves; probably some are filled with saline ice and others with unfrozen sea-water. Existence of these bottom crevasses could lead to a rapid disintegration of icebergs in the course of transport, as well as increasing the frictional drag at the ice-water boundary.Radar profiles of the ice-shelf barrier at four sites in flow bands of very different characteristics are shown. In some places rifting upstream from the barrier shows regular spacings, suggesting a periodic calving. Differential bottom melting near the barrier causes the icebergs to have an uneven surface and bottom (i.e. dome-shaped).Electrical resistivity soundings on the ice shelf can be applied to estimate the temperature-depth function, and from that the basal mass-balance rate. With some modifications, the technique may also be applied to estimating the basal mass-balance rates of tabular icebergs.

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