Thermodynamics of the interaction between ice shelves and the sea

Polar Record ◽  
1976 ◽  
Vol 18 (112) ◽  
pp. 37-41 ◽  
Author(s):  
C. S. M. Doake
Keyword(s):  
Ice Sheets ◽  
Ice Sheet ◽  
Snow Accumulation ◽  
Ice Shelf ◽  
Ice Shelves ◽  
Ross Ice Shelf ◽  
Surface Snow ◽  
Seaward Edge ◽  
The Antarctic

An ice shelf is a floating ice sheet, attached to land where ice is grounded along the coastline. Nourished both by surface snow accumulation and by glaciers and ice sheets flowing off the land, ice shelves can reach a considerable thickness, varying from up to 1 300 m when the ice starts to float to 200 m or less at the seaward edge (known as the ice front). Nearly all the world's ice shelves are found in Antarctica, where they cover an area of about one and a half million square kilometres. The two largest are the Ross Ice Shelf and the Filchner-Ronne ice shelf, each with an area of about half a million square kilometres. Smaller ice shelves fringe other parts of the Antarctic coastline.

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

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

<p>Antarctica’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.</p><p>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±1,193 km<sup>2</sup> in extent between 1997-2008 and gained an area of 7,108±1,029km<sup>2</sup> 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’s coastal-change on a more frequent temporal scale.  </p>

scholarly journals Mechanical analysis of pinning points in the Ross Ice Shelf, Antarctica

2018 ◽  
Vol 60 (78) ◽  
pp. 32-41 ◽  
Author(s):  
Holly Still ◽  
Adam Campbell ◽  
Christina Hulbe
Keyword(s):  
Ice Sheet ◽  
Mechanical Analysis ◽  
West Antarctica ◽  
Ice Shelf ◽  
Ice Shelves ◽  
Ross Ice Shelf ◽  
The Antarctic

ABSTRACTIce shelves regulate the rate of ice-sheet discharge along much of the Antarctic coastline. Pinning points, sites of localised grounding within floating ice, can in turn, regulate the flow and thickness of an ice shelf. While the net resistive effect of ice shelves has been quantified in a systematic way, few extant pinning points have been examined in detail. Here, complete force budgets are calculated and examined for ice rises and rumples in the Ross Ice Shelf, West Antarctica. The diverse features have different effects on ice shelf mechanics that do not depend simply on their size but may, we conclude, depend on the properties of seafloor materials.

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 Snow surface height variations on the Antarctic ice sheet in Princess Elizabeth Land, Antarctica: 1 year of data from an automatic weather station

2004 ◽  
Vol 39 ◽  
pp. 181-187 ◽  
Author(s):  
Qin Dahe ◽  
Xiao Cunde ◽  
Ian Allison ◽  
Bian Lingen ◽  
Rod Stephenson ◽  
...  
Keyword(s):  
Ice Sheet ◽  
Cloud Amount ◽  
Snow Accumulation ◽  
Strong Wind ◽  
Weather Station ◽  
Automatic Weather Station ◽  
Antarctic Ice Sheet ◽  
Total Cloud Amount ◽  
Surface Snow ◽  
The Antarctic

AbstractThe net surface snow accumulation on the Antarctic ice sheet is determined by a combination of precipitation, sublimation and wind redistribution. We present a 1 year record of hourly snow-height measurements that shows its seasonal variability. The measurements were made with an ultrasonic sensor mounted on an automatic weather station (AWS) installed at LGB69, Princess Elizabeth Land, Antarctica (70.835˚S, 77.075˚E; 1850 ma.s.l.). The average accumulation at this site is approximately 0.70 m snow a–1. Throughout the winter, between April and September, there was little change in surface snow height. The strongest accumulation occurred during the period October–March, with four episodic increases occurring during 2002. These episodic events coincided with obvious humidity ‘pulses’ and decreases of incoming solar radiation as recorded by the AWS. Observations of the total cloud amount at Davis station, 160 km north-northeast of LGB69, showed good correlation with major accumulation events recorded at LGB69. There was an obvious anticorrelation between the lowest cloud height at Davis and the daily accumulation rate at LGB69. Although there was no correlation over the total year between wind speed and accumulation at LGB69, large individual accumulation events are associated with episodes of strong wind. Strong accumulation events at LGB69 are associated with major storms in the region and inland transport of moist air masses from the coast.

scholarly journals Marine Ice Sheet Instability and Ice Shelf Buttressing Influenced Deglaciation of the Minch Ice Stream, Northwest Scotland

2018 ◽  
Author(s):  
Niall Gandy ◽  
Lauren J. Gregoire ◽  
Jeremy C. Ely ◽  
Christopher D. Clark ◽  
David M. Hodgson ◽  
...  
Keyword(s):  
Ice Sheets ◽  
Ice Sheet ◽  
Last Deglaciation ◽  
Ice Shelf ◽  
Dynamical Processes ◽  
Ice Dynamics ◽  
Surface Mass ◽  
Ice Shelves ◽  
Ice Stream ◽  
The Last Deglaciation

Abstract. Uncertainties in future sea level projections are dominated by our limited understanding of the dynamical processes that control instabilities of marine ice sheets. A valuable case to examine these processes is the last deglaciation of the British-Irish Ice Sheet. The Minch Ice Stream, which drained a large proportion of ice from the northwest sector of the British-Irish Ice Sheet during the last deglaciation, is well constrained, with abundant empirical data which could be used to inform, validate and analyse numerical ice sheet simulations. We use BISICLES, a higher-order ice sheet model, to examine the dynamical processes that controlled the retreat of the Minch Ice Stream. We simulate retreat from the shelf edge under constant "warm" surface mass balance and subshelf melt, to isolate the role of internal ice dynamics from external forcings. The model simulates a slowdown of retreat as the ice stream becomes laterally confined at a "pinning-point" between mainland Scotland and the Isle of Lewis. At this stage, the presence of ice shelves became a major control on deglaciation, providing buttressing to upstream ice. Subsequently, the presence of a reverse slope inside the Minch Strait produces an acceleration in retreat, leading to a "collapsed" state, even when the climate returns to the initial "cold" conditions. Our simulations demonstrate the importance of the Marine Ice Sheet Instability and ice shelf buttressing during the deglaciation of parts of the British-Irish Ice Sheet. Thus, geological data could be used to constrain these processes in ice sheet models used for projecting the future of our contemporary ice sheets.

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.

scholarly journals Dynamic influence of pinning points on marine ice-sheet stability: a numerical study in Dronning Maud Land, East Antarctica

2016 ◽  
Vol 10 (6) ◽  
pp. 2623-2635 ◽  
Author(s):  
Lionel Favier ◽  
Frank Pattyn ◽  
Sophie Berger ◽  
Reinhard Drews
Keyword(s):  
Data Assimilation ◽  
Sea Level ◽  
Ice Sheets ◽  
Ice Sheet ◽  
East Antarctica ◽  
Ice Shelf ◽  
Ice Dynamics ◽  
Outlet Glacier ◽  
Ice Shelves ◽  
Dronning Maud Land

Abstract. The East Antarctic ice sheet is likely more stable than its West Antarctic counterpart because its bed is largely lying above sea level. However, the ice sheet in Dronning Maud Land, East Antarctica, contains marine sectors that are in contact with the ocean through overdeepened marine basins interspersed by grounded ice promontories and ice rises, pinning and stabilising the ice shelves. In this paper, we use the ice-sheet model BISICLES to investigate the effect of sub-ice-shelf melting, using a series of scenarios compliant with current values, on the ice-dynamic stability of the outlet glaciers between the Lazarev and Roi Baudouin ice shelves over the next millennium. Overall, the sub-ice-shelf melting substantially impacts the sea-level contribution. Locally, we predict a short-term rapid grounding-line retreat of the overdeepened outlet glacier Hansenbreen, which further induces the transition of the bordering ice promontories into ice rises. Furthermore, our analysis demonstrated that the onset of the marine ice-sheet retreat and subsequent promontory transition into ice rise is controlled by small pinning points, mostly uncharted in pan-Antarctic datasets. Pinning points have a twofold impact on marine ice sheets. They decrease the ice discharge by buttressing effect, and they play a crucial role in initialising marine ice sheets through data assimilation, leading to errors in ice-shelf rheology when omitted. Our results show that unpinning increases the sea-level rise by 10 %, while omitting the same pinning point in data assimilation decreases it by 10 %, but the more striking effect is in the promontory transition time, advanced by two centuries for unpinning and delayed by almost half a millennium when the pinning point is missing in data assimilation. Pinning points exert a subtle influence on ice dynamics at the kilometre scale, which calls for a better knowledge of the Antarctic margins.

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

2020 ◽  
Vol 66 (258) ◽  
pp. 643-657 ◽  
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.

scholarly journals Pervasive ice sheet mass loss reflects competing ocean and atmosphere processes

Science ◽  
2020 ◽  
Vol 368 (6496) ◽  
pp. 1239-1242 ◽  
Author(s):  
Ben Smith ◽  
Helen A. Fricker ◽  
Alex S. Gardner ◽  
Brooke Medley ◽  
Johan Nilsson ◽  
...  
Keyword(s):  
Dynamic Response ◽  
Mass Loss ◽  
Sea Level ◽  
Ice Sheets ◽  
Ice Sheet ◽  
Snow Accumulation ◽  
Mass Change ◽  
Laser Altimetry ◽  
Ice Shelves ◽  
Ice Cloud

Quantifying changes in Earth’s ice sheets and identifying the climate drivers are central to improving sea level projections. We provide unified estimates of grounded and floating ice mass change from 2003 to 2019 using NASA’s Ice, Cloud and land Elevation Satellite (ICESat) and ICESat-2 satellite laser altimetry. Our data reveal patterns likely linked to competing climate processes: Ice loss from coastal Greenland (increased surface melt), Antarctic ice shelves (increased ocean melting), and Greenland and Antarctic outlet glaciers (dynamic response to ocean melting) was partially compensated by mass gains over ice sheet interiors (increased snow accumulation). Losses outpaced gains, with grounded-ice loss from Greenland (200 billion tonnes per year) and Antarctica (118 billion tonnes per year) contributing 14 millimeters to sea level. Mass lost from West Antarctica’s ice shelves accounted for more than 30% of that region’s total.

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