The Effect of Atmospheric Forcing Resolution on Delivery of Ocean Heat to the Antarctic Floating Ice Shelves*,+

Abstract Oceanic melting at the base of the floating Antarctic ice shelves is now thought to be a more significant cause of mass loss for the Antarctic ice sheet than iceberg calving. In this study, a 10-km horizontal-resolution circum-Antarctic ocean–sea ice–ice shelf model [based on the Regional Ocean Modeling System (ROMS)] is used to study the delivery of ocean heat to the base of the ice shelves. The atmospheric forcing comes from the ERA-Interim reanalysis (~80-km resolution) and from simulations using the polar-optimized Weather Research and Forecasting Model (30-km resolution), where the upper atmosphere was relaxed to the ERA-Interim reanalysis. The modeled total basal ice shelf melt is low compared to observational estimates but increases by 14% with the higher-resolution winds and just 3% with both the higher-resolution winds and atmospheric surface temperatures. The higher-resolution winds lead to more heat being delivered to the ice shelf cavities from the adjacent ocean and an increase in the efficiency of heat transfer between the water and the ice. The higher-resolution winds also lead to changes in the heat delivered from the open ocean to the continental shelves as well as changes in the heat lost to the atmosphere over the shelves, and the sign of these changes varies regionally. Addition of the higher-resolution temperatures to the winds results in lowering, primarily during summer, the wind-driven increase in heat advected into the ice shelf cavities due to colder summer air temperatures near the coast.

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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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the Development of an Annual Iceberg Calving Dataset of the Antarctic Ice Shelves

10.5194/egusphere-egu21-9310 ◽

2021 ◽

Author(s):

Mengzhen Qi ◽

Yan Liu ◽

Xiao Cheng

Keyword(s):

Mass Balance ◽

Satellite Imagery ◽

Ice Sheet ◽

Important Variable ◽

Average Thickness ◽

Ice Shelf ◽

Ice Shelves ◽

Subsequent Research ◽

Iceberg Calving ◽

The Antarctic

<p>&#160; Iceberg calving, one of the key processes of Antarctic mass balance, has been regarded as an important variable in fine monitoring the changes of ice shelves. Based on multi-source satellite imagery, all annual calving events larger than 1 km&#178; that occurred from August 2005 to August 2019 were extracted. Also, their area, thickness, mass, and calving recurrence cycle were calculated to derive the annual iceberg calving dataset. This dataset contains the distribution of 14-year annual calving events, along with the attributes of each calving event including calving year, length, area, average thickness, mass, recurrence interval, and calving type, and it can directly reflect the magnitude characteristics and distribution of Antarctic iceberg calving in different years, which fills the gap of fine monitoring dataset of iceberg calving and provides fundamental data for subsequent research on calving mechanism and mass balance of Antarctic ice shelf-ice sheet system.</p>

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A Simplified Three-Dimensional Ice-Sheet Model Including Ice Shelves

Annals of Glaciology ◽

10.3189/s026030550000817x ◽

1990 ◽

Vol 14 ◽

pp. 17-19 ◽

Cited By ~ 2

Author(s):

W.J. Böhmer ◽

K. Herterich

Keyword(s):

Transition Zone ◽

Three Dimensional ◽

Ice Sheet ◽

Coupled System ◽

Horizontal Resolution ◽

Ice Age ◽

Ice Shelf ◽

Ice Shelves ◽

Grounding Line ◽

The Antarctic

We present a simplified numerical three-dimensional ice-sheet/ice-shelf model with a coarse horizontal resolution (100 km), designed for simulations of ice-volume changes on ice-age time scales (100 000 years and longer). The ice-sheet part uses the shallow-ice approximation to determine the flow, and includes a three-dimensional temperature calculation. The ice shelf is described in a quasi-stationary way. Ice-shelf thickness depends only on the thicknesses at the grounding line and the distances to the grounding line. The effect of the transition zone between ice sheet and ice shelf (assuming a width ≪100 km) is parameterized in terms of the ice thicknesses defined on the coarse grid. The characteristics at the base of the transition zone formally enter through a friction coefficient μ. We performed a series of sensitivity experiments with the coupled system, by integrating over 10 000 model years, starting from the present (modelled) state of the Antarctic and forcing the model by currently-observed accumulation rates. The position of the grounding line of the ice-sheet/ice-shelf model is quite sensitive to the choice of the friction parameter μ (in the range 0.025 > μ > 0.01). With μ = 0.05, the grounding line was maintained at the currently-observed position in the model.

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

Earth System Science Data ◽

10.5194/essd-13-4583-2021 ◽

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.

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A statistical fracture model for Antarctic ice shelves and glaciers

10.5194/tc-2018-5 ◽

2018 ◽

Author(s):

Veronika Emetc ◽

Paul Tregoning ◽

Mathieu Morlighem ◽

Chris Borstad ◽

Malcolm Sambridge

Keyword(s):

Large Scale ◽

Damage Mechanics ◽

Average Rate ◽

Continuum Damage Mechanics ◽

Ice Shelf ◽

Ice Shelves ◽

Flow Models ◽

Fracture Formation ◽

Iceberg Calving ◽

The Antarctic

Abstract. Antarctica and Greenland hold enough ice to raise sea level by more than 65 m if they were to melt completely. Predicting future ice sheet mass balance depends on our ability to model these ice sheets, which is limited by our current understanding of several key physical processes, such as iceberg calving. Large-scale ice flow models either ignore this process or represent it crudely. To model fracture formation, which is an important component of many calving models, Continuum Damage Mechanics as well as Linear Fracture Mechanics are commonly used. However, these methods applied across the Antarctic continent have a large number of uncertainties. Here we present an alternative, statistics-based method to model the most probable zones of nucleation of fractures. We test this approach on all main ice shelf regions in Antarctica, including the Antarctic Peninsula. We can model up to 99 % of observed fractures, with an average rate of 84 % for grounded ice and 61 % for floating ice and mean overestimation error of 26 % and 20 %, respectively, thus providing the basis for modelling calving of ice shelves. We find that Antarctic ice shelves can be classified into groups based on the factors that control fracture location. The factors that trigger fracturing as well as sustain existing fractures advected from upstream vary from one ice shelf to another.

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Climate signals from SSM/I observations of marginal ice shelves

Annals of Glaciology ◽

10.3189/s0260305500012829 ◽

1993 ◽

Vol 17 ◽

pp. 189-194

Author(s):

J.K. Ridley

Keyword(s):

Time Series ◽

Surface Layer ◽

Passive Microwave ◽

Ice Shelf ◽

Ice Shelves ◽

Brightness Temperatures ◽

Air Temperatures ◽

Climate Signals ◽

Microwave Imager ◽

The Antarctic

A time series of satellite passive microwave observations by the Special Sensor Microwave/Imager (SSM/I) instrument, of the Antarctic marginal ice shelves, reveals sharp transitions in the radiometric brightness temperatures at 19 and 37 GHz. These transitions, sometimes occurring over the period of a single day, indicate the onset of surface melting of the ice. Monitoring the day of the onset of melting and the permanent re-freezing will be a measure of rising air temperatures as a result of global warming. The response from a stable ice shelf, the Ronne, where no appreciable melting occurs, is compared with observations from the marginal ice shelves on Antarctic Peninsula. It is observed that the spectral gradient (Tb19 - Tb37) varies as a function of time on a clear annual cycle. It is shown that variations in the spectral gradient arise due both to the temperature profile within the snow and the dielectric effects of a wet surface layer.

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Melting of ice shelves and the mass balance of Antarctica

Journal of Glaciology ◽

10.1017/s0022143000002252 ◽

1992 ◽

Vol 38 (130) ◽

pp. 375-387 ◽

Cited By ~ 298

Author(s):

S.S. Jacobs ◽

H.H. Helmer ◽

C. S. M. Doake ◽

A. Jenkins ◽

R. M. Frolich

Keyword(s):

Mass Balance ◽

Ocean Circulation ◽

Field Studies ◽

Ice Shelf ◽

Negative Mass ◽

Ice Shelves ◽

Run Off ◽

Iceberg Calving ◽

Global Sea Level ◽

The Antarctic

AbstractWe calculate the present ice budget for Antarctica from measurements of accumulation minus iceberg calving, run-off and in situ melting beneath the floating ice shelves. The resulting negative mass balance of 469 Gt year−1differs substantially from other recent estimates but some components are subject to high temporal variability and budget uncertainties of 20–50%. Annual accumulation from an earlier review is adjusted to include the Antarctic Peninsula for a total of 2144 Gt year−1. An iceberg production rate of 2016 Gt year−1is obtained from the volume of large icebergs calculated from satellite images since 1978, and from the results of an international iceberg census project. Ice-shelf melting of 544 Gt year−1is derived from physical and geochemical observations of meltwater outflow, glaciological field studies and modeling of the sub-ice ocean circulation. The highest melt rates occur near ice fronts and deep within sub-ice cavities. Run-off from the ice-sheet surface and from beneath the grounded ice is taken to be 53 Gt year−1. Less than half of the negative mass balance need come from the grounded ice to account for the unattributed 0.45 mm year−1in the IPCC “best estimate” of the recent global sea-level rise.

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Finite Element Analysis of Calving From Ice Fronts

Annals of Glaciology ◽

10.1017/s0260305500002603 ◽

1982 ◽

Vol 3 ◽

pp. 103-106 ◽

Cited By ~ 35

Author(s):

James L. Fastook ◽

William F. Schmidt

Keyword(s):

Finite Element ◽

Ice Sheet ◽

Ice Shelf ◽

Element Analysis ◽

Antarctic Ice Sheet ◽

Ice Shelves ◽

Ablation Mechanism ◽

Iceberg Calving ◽

Ice Velocity ◽

The Antarctic

The Antarctic ice sheet has almost no net annual ablation on its surface, so most mass losses are by iceberg calving along its perimeter, which may be either grounded in shallow water or floating in deep water. An ice cliff forms along the perimeter in both cases. Wave action undercuts ice margins in the tide-water zone along beaches, and causes coastal calving if the rate of undercutting compares with the forward ice velocity. If the ice velocity is sufficiently greater, the ice sheet advances into deeper water and becomes a float at depths of 200 to 300 m (Robin 1979). A floating ice shelf then forms and icebergs calve along the ice front. Iceberg calving along this ice front may be due to several causes (Holdsworth 1977,Robin 1979). Since iceberg calving, either from ice shelves or in the tidewater zone of beaches between ice shelves, is the principal ablation mechanism of the Antarctic ice sheet, it is important to understand calving dynamics quantitatively. This paper presents the results of a finite-element examination of calving along floating margins of the ice sheet.

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