The impact of recent and future calving events on the Larsen C ice shelf

Abstract. The Antarctic Peninsula has seen rapid and widespread changes in the extent of its ice shelves in recent decades, including the collapse of the Larsen A and B ice shelves in 1995 and 2002, respectively. In 2017 the Larsen C ice shelf (LCIS) lost around 10 % of its area by calving one of the largest icebergs ever recorded (A68). This has raised questions about the structural integrity of the shelf and the impact of any changes in its extent on the flow of its tributary glaciers. In this work, we used an ice flow model to study the instantaneous impact of changes in the thickness and extent of the LCIS on ice dynamics, and in particular on changes in the grounding line flux (GLF). We initialised the model to a pre-A68 calving state, and first replicated the calving of the A68 iceberg. We found that there was a limited impact on upstream flow – with speeds increasing by less than 10 % across almost all of the shelf – and a 0.5 % increase in GLF. This result is supported by observations of ice velocity made before and after the calving event. We then perturbed the ice-shelf geometry through idealised calving and thinning experiments of increasing magnitude. We found that significant changes to the geometry of the ice shelf, through both calving and thinning, resulted in limited changes in GLF. For example, to produce a doubling of GLF from calving, the new calving front needed to be moved to 5 km from the grounding line, removing almost the entire ice shelf. For thinning, over 200 m of the ice-shelf thickness had to be removed across the whole shelf to produce a doubling of GLF. Calculating the increase in GLF (607 %) after removing the entire ice shelf allowed us to quantify the total amount of buttressing provided by the LCIS. From this, we identified that the region of the ice shelf in the first 5 km downstream of the grounding line provided over 80 % of the buttressing capacity of the shelf. This is due to the large resistive stresses generated in the narrow, local embayments downstream of the largest tributary glaciers.

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Uncertainties in Mass Balance Estimation of the Antarctic Ice Sheet Using Input-output Method

10.5194/egusphere-egu21-5589 ◽

2021 ◽

Author(s):

Yijing Lin ◽

Yan Liu

Keyword(s):

Mass Balance ◽

Ice Sheet ◽

Data Uncertainty ◽

Ice Thickness ◽

Input Output ◽

Ice Dynamics ◽

Grounding Line ◽

Ice Velocity ◽

The Antarctic ◽

The Impact

Input-Output method (IOM) is a common method for estimating ice sheet mass balance, which shows ice dynamics in mass loss to analyze the response of ice sheet to climate change. However, compared with the altimetry method and the gravity method, the mass balance estimation using IOM has relatively large uncertainty. Assessing the impact of the uncertainties of each component in IOM on the mass balance estimation is conducive to effectively lowering uncertainty in the Antarctic mass budget estimate but of which there has been little quantitative analysis. We assess the uncertainty in the mass balance due to methodological differences in IOM, compare the differences of surface mass balance (SMB, input) in diverse versions and at different spatial scales, and evaluate the uncertainty in ice discharge (FG, output) due to data uncertainty in ice thickness, ice velocity and grounding line. Results showed that the SMBs at different scales are more divergent than that in different versions, resulting in a variation of 216.7 Gt yr-1 in Antarctica, of which the Antarctic peninsula accounts for 55.1%, followed by East Antarctica. The largest variation in FG due to uncertainty in the location of the grounding line is observed, where a 1 km retreat and a 1 km advance of the Antarctic grounding line would respectively result in FG reductions of 82.8 Gt yr-1 and 272.7 Gt yr-1, which are significant in all regions, with the FG corresponding to a 1 km retreat of grounding line in the islands being closer to the multi-year average SMB of the islands. The difference in Antarctic FG due to different ice thickness products is 124.4 Gt yr-1, consistent with the trend in the thickness of ice shelves, and that due to different ice velocity products is only 18.7 Gt yr-1. Within the same margin of error, systematic errors in ice thickness and ice velocity result in an order of magnitude higher difference of FG than random errors.

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Efficient Location and Extraction of the Iceberg Calved Areas of the Antarctic Ice Shelves

Remote Sensing ◽

10.3390/rs12162658 ◽

2020 ◽

Vol 12 (16) ◽

pp. 2658

Author(s):

Mengzhen Qi ◽

Yan Liu ◽

Yijing Lin ◽

Fengming Hui ◽

Teng Li ◽

...

Keyword(s):

Extraction Process ◽

Ice Shelf ◽

Extraction Area ◽

Ice Shelves ◽

Textural Characteristics ◽

Iceberg Calving ◽

Ice Velocity ◽

The Antarctic ◽

Omission Errors

Continuous, rapid, and precise monitoring of calving events contributes to an in-depth understanding of calving mechanisms, which have the potential to cause significant mass loss from the Antarctic ice sheet. The difficulties in the precise monitoring of iceberg calving lie with the coexistence of ice shelf advances and calving. The manual location of iceberg calving is time-consuming and painstaking, while achieving precise extraction has mostly relied on the surface textural characteristics of the ice shelves and the quality of the images. Here, we propose a new and efficient method of separating the expansion and calving processes of ice shelves. We visualized the extension process by simulating a new coastline, based on the ice velocity, and detected the calved area using the simulated coastline and single-temporal post-calving images. We extensively tested the validity of this method by extracting four annual calving datasets (from August 2015 to August 2019) from the Sentinel-1 synthetic aperture radar mosaic of the Antarctic coastline. A total of 2032 annual Antarctic calving events were detected, with areas ranging from 0.05 km2 to 6141.0 km2, occurring on almost every Antarctic ice shelf. The extraction accuracy of the calved area depends on the positioning accuracy of the simulated coastline and the spatial resolution of the images. The positioning error of the simulated coastline is less than one pixel, and the determined minimum valid extraction area is 0.05 km2, when based on 75 m resolution images. Our method effectively avoids repetition and omission errors during the calved area extraction process. Furthermore, its efficiency is not affected by the surface textural characteristics of the calving fronts and the various changes in the frontal edge velocity, which makes it fully applicable to the rapid and accurate extraction of different calving types.

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Viscous and elastic buoyancy stresses as drivers of ice-shelf calving

Journal of Glaciology ◽

10.1017/jog.2020.35 ◽

2020 ◽

Vol 66 (258) ◽

pp. 643-657 ◽

Cited By ~ 1

Author(s):

Cyrille Mosbeux ◽

Till J. W. Wagner ◽

Maya K. Becker ◽

Helen A. Fricker

Keyword(s):

Ice Sheet ◽

Elastic Model ◽

Ice Shelf ◽

Ice Shelves ◽

Bending Stresses ◽

Iceberg Calving ◽

Basal Melting ◽

The Antarctic ◽

The Impact ◽

Maximum Stresses

AbstractThe Antarctic Ice Sheet loses mass via its ice shelves predominantly through two processes: basal melting and iceberg calving. Iceberg calving is episodic and infrequent, and not well parameterized in ice-sheet models. Here, we investigate the impact of hydrostatic forces on calving. We develop two-dimensional elastic and viscous numerical frameworks to model the ‘footloose’ calving mechanism. This mechanism is triggered by submerged ice protrusions at the ice front, which induce unbalanced buoyancy forces that can lead to fracturing. We compare the results to identify the different roles that viscous and elastic deformations play in setting the rate and magnitude of calving events. Our results show that, although the bending stresses in both frameworks share some characteristics, their differences have important implications for modeling the calving process. In particular, the elastic model predicts that maximum stresses arise farther from the ice front than in the viscous model, leading to larger calving events. We also find that the elastic model would likely lead to more frequent events than the viscous one. Our work provides a theoretical framework for the development of a better understanding of the physical processes that govern glacier and ice-shelf calving cycles.

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Changes in ice-shelf buttressing following the collapse of Larsen A Ice Shelf, Antarctica, and the resulting impact on tributaries

Journal of Glaciology ◽

10.1017/jog.2016.77 ◽

2016 ◽

Vol 62 (235) ◽

pp. 905-911 ◽

Cited By ~ 4

Author(s):

SAM ROYSTON ◽

G. HILMAR GUDMUNDSSON

Keyword(s):

Antarctic Peninsula ◽

Surface Velocity ◽

Ice Shelf ◽

Mass Redistribution ◽

Grounding Line ◽

Modelling Studies ◽

Speed Up ◽

Stringent Test ◽

The Antarctic ◽

The Impact

ABSTRACTThe dominant mass-loss process on the Antarctic Peninsula has been ice-shelf collapse, including the Larsen A Ice Shelf in early 1995. Following this collapse, there was rapid speed up and thinning of its tributary glaciers. We model the impact of this ice-shelf collapse on upstream tributaries, and compare with observations using new datasets of surface velocity and ice thickness. Using a two-horizontal-dimension shallow shelf approximation model, we are able to replicate the observed large increase in surface velocity that occurred within Drygalski Glacier, Antarctic Peninsula. The model results show an instantaneous twofold increase in flux across the grounding line, caused solely from the reduction in backstress through ice shelf removal. This demonstrates the importance of ice-shelf buttressing for flow upstream of the grounding line and highlights the need to explicitly include lateral stresses when modelling real-world settings. We hypothesise that further increases in velocity and flux observed since the ice-shelf collapse result from transient mass redistribution effects. Reproducing these effects poses the next, more stringent test of glacier and ice-sheet modelling studies.

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Characteristics of ice rises and ice rumples in Dronning Maud Land and Enderby Land, Antarctica

Journal of Glaciology ◽

10.1017/jog.2020.77 ◽

2020 ◽

Vol 66 (260) ◽

pp. 1064-1078

Author(s):

Vikram Goel ◽

Kenichi Matsuoka ◽

Cesar Deschamps Berger ◽

Ian Lee ◽

Jørgen Dall ◽

...

Keyword(s):

Mass Balance ◽

Ice Cores ◽

Ice Thickness ◽

Ice Shelf ◽

Ice Dynamics ◽

Surface Mass ◽

Ice Shelves ◽

The Past ◽

Dronning Maud Land ◽

The Antarctic

AbstractIce rises and rumples, locally grounded features adjacent to ice shelves, are relatively small yet play significant roles in Antarctic ice dynamics. Their roles generally depend upon their location within the ice shelf and the stage of the ice-sheet retreat or advance. Large, long-stable ice rises can be excellent sites for deep ice coring and paleoclimate study of the Antarctic coast and the Southern Ocean, while small ice rises tend to respond more promptly and can be used to reveal recent changes in regional mass balance. The coasts of Dronning Maud Land (DML) and Enderby Land in East Antarctica are abundant with these features. Here we review existing knowledge, presenting an up-to-date status of research in these regions with focus on ice rises and rumples. We use regional datasets (satellite imagery, surface mass balance and ice thickness) to analyze the extent and surface morphology of ice shelves and characteristic timescales of ice rises. We find that large parts of DML have been changing over the past several millennia. Based on our findings, we highlight ice rises suitable for drilling ice cores for paleoclimate studies as well as ice rises suitable for deciphering ice dynamics and evolution in the region.

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Modelling present-day basal melt rates for Antarctic ice shelves using a parametrization of buoyant meltwater plumes

The Cryosphere ◽

10.5194/tc-12-49-2018 ◽

2018 ◽

Vol 12 (1) ◽

pp. 49-70 ◽

Cited By ~ 28

Author(s):

Werner M. J. Lazeroms ◽

Adrian Jenkins ◽

G. Hilmar Gudmundsson ◽

Roderik S. W. van de Wal

Keyword(s):

Temperature Field ◽

Ice Sheet ◽

Detailed Knowledge ◽

Ocean Temperature ◽

Ice Shelf ◽

Antarctic Ice Sheet ◽

Ice Shelves ◽

Grounding Line ◽

The Antarctic ◽

Line Depth

Abstract. Basal melting below ice shelves is a major factor in mass loss from the Antarctic Ice Sheet, which can contribute significantly to possible future sea-level rise. Therefore, it is important to have an adequate description of the basal melt rates for use in ice-dynamical models. Most current ice models use rather simple parametrizations based on the local balance of heat between ice and ocean. In this work, however, we use a recently derived parametrization of the melt rates based on a buoyant meltwater plume travelling upward beneath an ice shelf. This plume parametrization combines a non-linear ocean temperature sensitivity with an inherent geometry dependence, which is mainly described by the grounding-line depth and the local slope of the ice-shelf base. For the first time, this type of parametrization is evaluated on a two-dimensional grid covering the entire Antarctic continent. In order to apply the essentially one-dimensional parametrization to realistic ice-shelf geometries, we present an algorithm that determines effective values for the grounding-line depth and basal slope in any point beneath an ice shelf. Furthermore, since detailed knowledge of temperatures and circulation patterns in the ice-shelf cavities is sparse or absent, we construct an effective ocean temperature field from observational data with the purpose of matching (area-averaged) melt rates from the model with observed present-day melt rates. Our results qualitatively replicate large-scale observed features in basal melt rates around Antarctica, not only in terms of average values, but also in terms of the spatial pattern, with high melt rates typically occurring near the grounding line. The plume parametrization and the effective temperature field presented here are therefore promising tools for future simulations of the Antarctic Ice Sheet requiring a more realistic oceanic forcing.

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Geometry and ice dynamics of the Darwin–Hatherton glacial system, Transantarctic Mountains

Journal of Glaciology ◽

10.1017/jog.2017.60 ◽

2017 ◽

Vol 63 (242) ◽

pp. 959-972

Author(s):

METTE K. GILLESPIE ◽

WENDY LAWSON ◽

WOLFGANG RACK ◽

BRIAN ANDERSON ◽

DONALD D. BLANKENSHIP ◽

...

Keyword(s):

Ice Sheet ◽

Ice Thickness ◽

Ice Shelf ◽

Ice Dynamics ◽

Ross Ice Shelf ◽

Basal Ice ◽

Grounding Line ◽

Ice Flows ◽

Ice Velocity ◽

The Mean

ABSTRACTThe Darwin–Hatherton Glacial system (DHGS) connects the East Antarctic Ice Sheet (EAIS) with the Ross Ice Shelf and is a key area for understanding past variations in ice thickness of surrounding ice masses. Here we present the first detailed measurements of ice thickness and grounding zone characteristics of the DHGS as well as new measurements of ice velocity. The results illustrate the changes that occur in glacier geometry and ice flux as ice flows from the polar plateau and into the Ross Ice Shelf. The ice discharge and the mean basal ice shelf melt for the first 8.5 km downstream of the grounding line amount to 0.24 ± 0.05 km3 a−1 and 0.3 ± 0.1 m a−1, respectively. As the ice begins to float, ice thickness decreases rapidly and basal terraces develop. Constructed maps of glacier geometry suggest that ice drainage from the EAIS into the Darwin Glacier occurs primarily through a deep subglacial canyon. By contrast, ice thins to <200 m at the head of the much slower flowing Hatherton Glacier. The glaciological field study establishes an improved basis for the interpretation of glacial drift sheets at the link between the EAIS and the Ross Ice Sheet.

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Changes in ice dynamics and mass balance of the Antarctic ice sheet

Philosophical Transactions of The Royal Society A Mathematical Physical and Engineering Sciences ◽

10.1098/rsta.2006.1793 ◽

2006 ◽

Vol 364 (1844) ◽

pp. 1637-1655 ◽

Cited By ~ 77

Author(s):

Eric Rignot

Keyword(s):

Mass Balance ◽

Sea Level ◽

Ice Sheet ◽

East Antarctica ◽

West Antarctica ◽

Ice Shelf ◽

Ice Dynamics ◽

Antarctic Ice Sheet ◽

Ice Shelves ◽

The Antarctic

The concept that the Antarctic ice sheet changes with eternal slowness has been challenged by recent observations from satellites. Pronounced regional warming in the Antarctic Peninsula triggered ice shelf collapse, which led to a 10-fold increase in glacier flow and rapid ice sheet retreat. This chain of events illustrated the vulnerability of ice shelves to climate warming and their buffering role on the mass balance of Antarctica. In West Antarctica, the Pine Island Bay sector is draining far more ice into the ocean than is stored upstream from snow accumulation. This sector could raise sea level by 1 m and trigger widespread retreat of ice in West Antarctica. Pine Island Glacier accelerated 38% since 1975, and most of the speed up took place over the last decade. Its neighbour Thwaites Glacier is widening up and may double its width when its weakened eastern ice shelf breaks up. Widespread acceleration in this sector may be caused by glacier ungrounding from ice shelf melting by an ocean that has recently warmed by 0.3 °C. In contrast, glaciers buffered from oceanic change by large ice shelves have only small contributions to sea level. In East Antarctica, many glaciers are close to a state of mass balance, but sectors grounded well below sea level, such as Cook Ice Shelf, Ninnis/Mertz, Frost and Totten glaciers, are thinning and losing mass. Hence, East Antarctica is not immune to changes.

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Uncertainties in mass balance estimation of the Antarctic Ice Sheet using the input and output method

10.5194/tc-2021-325 ◽

2021 ◽

Author(s):

Yijing Lin ◽

Yan Liu ◽

Zhitong Yu ◽

Xiao Cheng ◽

Qiang Shen ◽

...

Keyword(s):

Mass Balance ◽

Scale Effect ◽

Ice Sheet ◽

Ice Thickness ◽

Clear Understanding ◽

Antarctic Ice Sheet ◽

Grounding Line ◽

Ice Velocity ◽

The Antarctic ◽

The Impact

Abstract. The input-output method (IOM) is one of the most popular methods of estimating the ice sheet mass balance (MB), with a significant advantage in presenting the dynamics response of ice to climate change. Assessing the uncertainties of the MB estimation using the IOM is crucial to gaining a clear understanding of the Antarctic ice-sheet mass budget. Here, we introduce a framework for assessing the uncertainties in the MB estimation due to the methodological differences in the IOM, the impact of the parameterization and scale effect on the modeled surface mass balance (SMB, input), and the impact of the uncertainties of ice thickness, ice velocity, and grounding line data on ice discharge (D, output). For the assessment of the D’s uncertainty, we present D at a fine scale. Compared with the goal of determining the Antarctic MB within an uncertainty of 15 Gt yr−1, we found that the different strategies employed in the methods cause considerable uncertainties in the annual MB estimation. The uncertainty of the RACMO2.3 SMB caused by its parameterization can reach 20.4 Gt yr−1, while that due to the scale effect is up to 216.7 Gt yr−1. The observation precisions of the MEaSUREs InSAR-based velocity (1–17 m yr−1), the airborne radio-echo sounder thickness (±100 m), and the MEaSUREs InSAR-based grounding line (±100 m) contribute uncertainties of 17.1 Gt yr−1, 10.5 ± 2.7 Gt yr−1 and 8.0~27.8 Gt yr−1 to the D, respectively. However, the D’s uncertainty due to the remarkable ice thickness data gap, which is represented by the thickness difference between the BEDMAP2 and the BedMachine reaches 101.7 Gt yr−1, which indicates its dominant cause of the future D’s uncertainty. In addition, the interannual variability of D caused by the annual changes in the ice velocity and ice thickness are considerable compared with the target uncertainty of 15 Gt yr−1, which cannot be ignored in annual MB estimations.

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Mass balance of East Antarctic glaciers and ice shelves from satellite data

Annals of Glaciology ◽

10.3189/172756402781817419 ◽

2002 ◽

Vol 34 ◽

pp. 217-227 ◽

Cited By ~ 76

Author(s):

Eric Rignot

Keyword(s):

Mass Balance ◽

Snow Accumulation ◽

Glacier Mass Balance ◽

Ice Shelf ◽

Ice Shelves ◽

Mass Fluxes ◽

Grounding Line ◽

Ice Velocity ◽

Flux Gate ◽

Mass Discharge

AbstractThe velocity and mass discharge of nine major East Antarctic glaciers not draining into the Ross or Filchner–Ronne Ice Shelves is investigated using interferometric synthetic aperture radar (InSAR) data from the European Remote-sensing Satellite 1and 2 (ERS-1/2) andRADARSAT-1. The glaciers are: David,Ninnis, Mertz, Totten, Scott, Denman, Lambert, Shirase and Stancomb-Wills. InSAR is used to locate their grounding line with precision. Ice velocity is measured with either InSAR or a speckle-tracking technique. Ice thickness is deduced from prior-determined ice-shelf elevation assuming hydrostatic equilibrium. Mass fluxes are calculated both at the grounding line and at a flux gate located downstream. The grounding-line flux is compared to a mass input calculated from snow accumulation to deduce the glacier mass balance. The calculation is repeated at the flux gate downstream of the grounding line to estimate the average bottom melt rate of the ice shelf under steady-state conditions. The main results are: (1) Grounding lines are found several tens of km upstream of prior-identified positions, not because of a recent ice-sheet retreat but because of the inadequacy of prior-determined grounding-line positions. (2) No gross imbalance between outflow and inflow is detected on the nine glaciers being investigated, with an uncertainty of 10–20%. Prior-determined, largely positive mass imbalances were due to an incorrect localization of the grounding line. (3) High rates of bottom melting (24±7 mice a–1) are inferred near grounding zones, where ice reaches the deepest draft. A few glaciers exhibit lower bottom melt rates (4±7 mice a–1). Bottom melting, however, appears to be a major source of mass loss on Antarctic ice shelves.

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