scholarly journals On the settling depth of meltwater escaping from beneath Antarctic ice shelves

2021 ◽  
Author(s):  
Constantin W. Arnscheidt ◽  
John Marshall ◽  
Pierre Dutrieux ◽  
Craig D. Rye ◽  
Ali Ramadhan
Keyword(s):  
Large Scale ◽  
Ambient Conditions ◽  
Climate Trends ◽  
Ice Shelf ◽  
Buoyant Plumes ◽  
Ice Shelves ◽  
Ocean Climate ◽  
Buoyancy Forcing ◽  
Centrifugal Instability ◽  
Warming World

AbstractAntarctic glacial meltwater is thought to play an important role in determining large-scale Southern Ocean climate trends, yet recent modeling efforts have proceeded without a good understanding of how its vertical distribution in the water column is set. To rectify this, here we conduct new large-eddy simulations of the ascent of a buoyant meltwater plume after its escape from beneath an Antarctic ice shelf. We find that the meltwater’s settling depth is primarily a function of the buoyancy forcing per unit width of the source and the ambient stratification, consistent with the classical theory of turbulent buoyant plumes and in contrast to previous work that suggested an important role for centrifugal instability. Our results further highlight the significant role played by localized variability in stratification; this helps explain observed interannual variability in the vertical meltwater distribution near Pine Island Glacier. Because of the vast heterogeneity in mass loss rates and ambient conditions at different Antarctic ice shelves, a dynamic parameterization of meltwater settling depth may be crucial for accurately simulating high-latitude climate in a warming world; we discuss how this may be developed following this work, and where the remaining challenges lie.

Large-Scale Oceanographic Constraints on the Distribution of Melting and Freezing under Ice Shelves

2008 ◽  
Vol 38 (10) ◽  
pp. 2242-2255 ◽  
Author(s):  
Christopher M. Little ◽  
Anand Gnanadesikan ◽  
Robert Hallberg
Keyword(s):  
Large Scale ◽  
Oceanic Circulation ◽  
Ice Shelf ◽  
Local Circulation ◽  
Southern Boundary ◽  
Ice Shelves ◽  
Buoyancy Forcing ◽  
Freshwater Fluxes ◽  
Cyclonic Flow ◽  
Topographic Gradients

Abstract Previous studies suggest that ice shelves experience asymmetric melting and freezing. Topography may constrain oceanic circulation (and thus basal melt–freeze patterns) through its influence on the potential vorticity (PV) field. However, melting and freezing induce a local circulation that may modify locations of heat transport to the ice shelf. This paper investigates the influence of buoyancy fluxes on locations of melting and freezing under different bathymetric conditions. An idealized set of numerical simulations (the “decoupled” simulations) employs spatially and temporally fixed diapycnal fluxes. These experiments, in combination with scaling considerations, indicate that while flow in the interior is governed by large-scale topographic gradients, recirculation plumes dominate near buoyancy fluxes. Thermodynamically decoupled models are then compared to those in which ice–ocean heat and freshwater fluxes are driven by the interior flow (the “coupled” simulations). Near the southern boundary, strong cyclonic flow forced by melt-induced upwelling drives inflow and melting to the east. Recirculation is less evident in the upper water column, as shoaling of meltwater-freshened layers dissipates the dynamic influence of buoyancy forcing, yet freezing remains intensified in the west. In coupled simulations, the flow throughout the cavity is relatively insensitive to bathymetry; stratification, the slope of the ice shelf, and strong, meridionally distributed buoyancy fluxes weaken its influence.

scholarly journals A statistical fracture model for Antarctic ice shelves and glaciers

2018 ◽  
Vol 12 (10) ◽  
pp. 3187-3213 ◽  
Author(s):  
Veronika Emetc ◽  
Paul Tregoning ◽  
Mathieu Morlighem ◽  
Chris Borstad ◽  
Malcolm Sambridge
Keyword(s):  
Large Scale ◽  
Damage Mechanics ◽  
Ice Sheets ◽  
Continuum Damage Mechanics ◽  
Ice Shelf ◽  
Ice Shelves ◽  
Flow Models ◽  
Iceberg Calving ◽  
Antarctic Continent ◽  
Average Success Rate

Abstract. Antarctica and Greenland hold enough ice to raise sea level by more than 65 m if both ice sheets 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 fractured zones, an important component of many calving models, continuum damage mechanics as well as linear fracture mechanics are commonly used. However, these methods have a large number of uncertainties when applied across the entire Antarctic continent because the models were typically tuned to match processes seen on particular ice shelves. Here we present an alternative, statistics-based method to model the most probable zones of the location of fractures and demonstrate our approach on all main ice shelf regions in Antarctica, including the Antarctic Peninsula. We can predict the location of observed fractures with an average success rate of 84 % for grounded ice and 61 % for floating ice and a mean overestimation error rate of 26 % and 20 %, respectively. We found that Antarctic ice shelves can be classified into groups based on the factors that control fracture location.

scholarly journals Antarctic Supraglacial Lake Identification Using Landsat-8 Image Classification

2020 ◽  
Vol 12 (8) ◽  
pp. 1327 ◽  
Author(s):  
Anna Ruth W. Halberstadt ◽  
Colin J. Gleason ◽  
Mahsa S. Moussavi ◽  
Allen Pope ◽  
Luke D. Trusel ◽  
...  
Keyword(s):  
Large Scale ◽  
Seasonal Pattern ◽  
Ice Sheet ◽  
Training Data ◽  
Landsat 8 ◽  
Ice Shelf ◽  
Ice Shelves ◽  
Continental Scale ◽  
Lake Evolution ◽  
Supervised Classifiers

Surface meltwater generated on ice shelves fringing the Antarctic Ice Sheet can drive ice-shelf collapse, leading to ice sheet mass loss and contributing to global sea level rise. A quantitative assessment of supraglacial lake evolution is required to understand the influence of Antarctic surface meltwater on ice-sheet and ice-shelf stability. Cloud computing platforms have made the required remote sensing analysis computationally trivial, yet a careful evaluation of image processing techniques for pan-Antarctic lake mapping has yet to be performed. This work paves the way for automating lake identification at a continental scale throughout the satellite observational record via a thorough methodological analysis. We deploy a suite of different trained supervised classifiers to map and quantify supraglacial lake areas from multispectral Landsat-8 scenes, using training data generated via manual interpretation of the results from k-means clustering. Best results are obtained using training datasets that comprise spectrally diverse unsupervised clusters from multiple regions and that include rock and cloud shadow classes. We successfully apply our trained supervised classifiers across two ice shelves with different supraglacial lake characteristics above a threshold sun elevation of 20°, achieving classification accuracies of over 90% when compared to manually generated validation datasets. The application of our trained classifiers produces a seasonal pattern of lake evolution. Cloud shadowed areas hinder large-scale application of our classifiers, as in previous work. Our results show that caution is required before deploying ‘off the shelf’ algorithms for lake mapping in Antarctica, and suggest that careful scrutiny of training data and desired output classes is essential for accurate results. Our supervised classification technique provides an alternative and independent method of lake identification to inform the development of a continent-wide supraglacial lake mapping product.

scholarly journals Calving cycle of the Brunt Ice Shelf, Antarctica, driven by changes in ice shelf geometry

2019 ◽  
Vol 13 (10) ◽  
pp. 2771-2787 ◽  
Author(s):  
Jan De Rydt ◽  
Gudmundur Hilmar Gudmundsson ◽  
Thomas Nagler ◽  
Jan Wuite
Keyword(s):  
Large Scale ◽  
Ice Shelf ◽  
Ice Flow ◽  
Ice Shelves ◽  
Flow Models ◽  
Speed Up ◽  
The Antarctic ◽  
Detrimental Impact ◽  
Natural Laboratory

Abstract. Despite the potentially detrimental impact of large-scale calving events on the geometry and ice flow of the Antarctic Ice Sheet, little is known about the processes that drive rift formation prior to calving, or what controls the timing of these events. The Brunt Ice Shelf in East Antarctica presents a rare natural laboratory to study these processes, following the recent formation of two rifts, each now exceeding 50 km in length. Here we use 2 decades of in situ and remote sensing observations, together with numerical modelling, to reveal how slow changes in ice shelf geometry over time caused build-up of mechanical tension far upstream of the ice front, and culminated in rift formation and a significant speed-up of the ice shelf. These internal feedbacks, whereby ice shelves generate the very conditions that lead to their own (partial) disintegration, are currently missing from ice flow models, which severely limits their ability to accurately predict future sea level rise.

scholarly journals Ice shelf fracture parameterization in an ice sheet model

2017 ◽  
Vol 11 (6) ◽  
pp. 2543-2554 ◽  
Author(s):  
Sainan Sun ◽  
Stephen L. Cornford ◽  
John C. Moore ◽  
Rupert Gladstone ◽  
Liyun Zhao
Keyword(s):  
Enhancement Factor ◽  
Large Scale ◽  
Damage Model ◽  
Ice Sheet ◽  
Ice Shelf ◽  
Ice Flow ◽  
Ice Shelves ◽  
Order Of Magnitude ◽  
Eventual Loss ◽  
Spatially Varying

Abstract. Floating ice shelves exert a stabilizing force onto the inland ice sheet. However, this buttressing effect is diminished by the fracture process, which on large scales effectively softens the ice, accelerating its flow, increasing calving, and potentially leading to ice shelf breakup. We add a continuum damage model (CDM) to the BISICLES ice sheet model, which is intended to model the localized opening of crevasses under stress, the transport of those crevasses through the ice sheet, and the coupling between crevasse depth and the ice flow field and to carry out idealized numerical experiments examining the broad impact on large-scale ice sheet and shelf dynamics. In each case we see a complex pattern of damage evolve over time, with an eventual loss of buttressing approximately equivalent to halving the thickness of the ice shelf. We find that it is possible to achieve a similar ice flow pattern using a simple rule of thumb: introducing an enhancement factor ∼ 10 everywhere in the model domain. However, spatially varying damage (or equivalently, enhancement factor) fields set at the start of prognostic calculations to match velocity observations, as is widely done in ice sheet simulations, ought to evolve in time, or grounding line retreat can be slowed by an order of magnitude.

scholarly journals The Recent Advance of the Ross Ice Shelf Antarctica

1986 ◽  
Vol 32 (112) ◽  
pp. 464-474 ◽  
Author(s):  
S. S. Jacobs ◽  
D. R. Macayeal ◽  
J. L. Ardai
Keyword(s):  
Large Scale ◽  
Melting Rate ◽  
Spreading Rate ◽  
Ice Shelf ◽  
Ice Shelves ◽  
Ross Ice Shelf ◽  
Front Position ◽  
Iceberg Calving ◽  
Basal Melting ◽  
Available Information

AbstractThe seaward edge of the Ross Ice Shelf advanced northward at a minimum average velocity of 0.8 km a–1 between 1962 and 1985. That advance approximated velocities that have been obtained from glaciological data, indicating little recent wastage by iceberg calving. West of long. 178° E., the ice shelf has attained its most northerly position in the past 145 years, and has not experienced a major calving episode for at least 75 years. Since 1841 the ice-front position has advanced and retreated within a zone from about lat. 77° 10’S. (near long. 171° E.) to lat. 78° 40’ S. (near long. 164° W.). The central ice front is now farthest south but has the highest advance rate. Calving may occur at more frequent intervals in that sector, which also overlies the warmest ocean currents that flow into the sub-ice-shelf cavity. Available information on ice-shelf advance, thickness, spreading rate, and surface accumulation indicates a basal melting rate around 3 m a–1 near the ice front. These data and independent estimates imply that basal melting is nearly as large a factor as iceberg calving in maintaining the ice-shelf mass balance. In recent years, the Ross, Ronne, and Filchner Ice Shelves have contributed few icebergs to the Southern Ocean, while projections from a contemporaneous iceberg census are that circumpolar calving alone may exceed accumulation on the ice sheet. Large-scale ice-shelf calving may have preceded historical sightings of increased numbers of icebergs at sea.

scholarly journals Calving cycle of the Brunt Ice Shelf, Antarctica, driven by changes in ice-shelf geometry

2019 ◽  
Author(s):  
Jan De Rydt ◽  
G. Hilmar Gudmundsson ◽  
Thomas Nagler ◽  
Jan Wuite
Keyword(s):  
Large Scale ◽  
Ice Shelf ◽  
Ice Flow ◽  
Ice Shelves ◽  
Flow Models ◽  
Speed Up ◽  
The Antarctic ◽  
Detrimental Impact ◽  
Natural Laboratory

Abstract. Despite the potentially detrimental impact of large-scale calving events on the geometry and ice flow of the Antarctic Ice Sheet, little is known about the processes that drive rift formation prior to calving, or what controls the timing of these events. The Brunt Ice Shelf in East Antarctica presents a rare natural laboratory to study these processes, following the recent formation of two rifts, each now exceeding 50 km in length. Here we use a unique 50-years' time series of in-situ and remote sensing observations, together with numerical modelling, to reveal how slow changes in ice shelf geometry over time caused build-up of mechanical tension far upstream of the ice front, and culminated in rift formation and a significant speed-up of the ice shelf. These internal feedbacks, whereby ice shelves generate the very conditions that lead to their own (partial) disintegration are currently missing from ice flow models, which severely limits their ability to accurately predict future sea level rise.

scholarly journals Lateral meltwater transfer across an Antarctic ice shelf

2020 ◽  
Author(s):  
Rebecca Dell ◽  
Neil Arnold ◽  
Ian Willis ◽  
Alison Banwell ◽  
Andrew Williamson ◽  
...  
Keyword(s):  
Surface Water ◽  
Large Scale ◽  
Water Bodies ◽  
Seasonal Development ◽  
Water Volume ◽  
Landsat 8 ◽  
Ice Shelf ◽  
Ice Shelves ◽  
Melt Ponds ◽  
Track Surface

Abstract. Surface meltwater on ice shelves can be stored as slush, in melt ponds, in surface streams and rivers, and may also fill crevasses. The collapse of the Larsen B Ice Shelf in 2002 has been attributed to the sudden drainage of ~ 3000 surface lakes, and has highlighted the potential for surface water to cause ice shelf instability. Surface meltwater systems have been identified across numerous Antarctic ice shelves, however, the extent to which these systems impact ice shelf instability is poorly constrained. To better understand the role of surface meltwater systems on ice shelves, it is important to track their seasonal development, monitoring the fluctuations in surface water volume and the transfer of water across the ice shelf. Here, we use Landsat 8 and Sentinel-2 imagery to track surface meltwater across the Nivlisen Ice Shelf in the 2016–2017 melt season. Using the Fully Automated Supraglacial-Water Tracking algorithm for Ice Shelves (FASTISh), we identify and track the development of 1598 water bodies. The total volume of surface meltwater peaks on 26th January 2017 at 5.5 × 107 m3. 63 % of this total volume is held within two large linear surface meltwater systems, which are orientated along the ice shelves north-south axis and appear to migrate away from the grounding line during the melt season, facilitating large scale lateral water transfer towards the ice shelf front. This transfer is facilitated by two large surface streams, which encompass smaller water bodies and follow the surface slope of the ice shelf.

scholarly journals Lateral meltwater transfer across an Antarctic ice shelf

2020 ◽  
Vol 14 (7) ◽  
pp. 2313-2330 ◽  
Author(s):  
Rebecca Dell ◽  
Neil Arnold ◽  
Ian Willis ◽  
Alison Banwell ◽  
Andrew Williamson ◽  
...  
Keyword(s):  
Surface Water ◽  
Large Scale ◽  
Water Bodies ◽  
Seasonal Development ◽  
Water Volume ◽  
Landsat 8 ◽  
Ice Shelf ◽  
Ice Shelves ◽  
Track Surface ◽  
South Axis

Abstract. Surface meltwater on ice shelves can exist as slush, it can pond in lakes or crevasses, or it can flow in surface streams and rivers. The collapse of the Larsen B Ice Shelf in 2002 has been attributed to the sudden drainage of ∼3000 surface lakes and has highlighted the potential for surface water to cause ice-shelf instability. Surface meltwater systems have been identified across numerous Antarctic ice shelves, although the extent to which these systems impact ice-shelf instability is poorly constrained. To better understand the role of surface meltwater systems on ice shelves, it is important to track their seasonal development, monitoring the fluctuations in surface water volume and the transfer of water across ice-shelf surfaces. Here, we use Landsat 8 and Sentinel-2 imagery to track surface meltwater across the Nivlisen Ice Shelf in the 2016–2017 melt season. We develop the Fully Automated Supraglacial-Water Tracking algorithm for Ice Shelves (FASTISh) and use it to identify and track the development of 1598 water bodies, which we classify as either circular or linear. The total volume of surface meltwater peaks on 26 January 2017 at 5.5×107 m3. At this time, 63 % of the total volume is held within two linear surface meltwater systems, which are up to 27 km long, are orientated along the ice shelf's north–south axis, and follow the surface slope. Over the course of the melt season, they appear to migrate away from the grounding line, while growing in size and enveloping smaller water bodies. This suggests there is large-scale lateral water transfer through the surface meltwater system and the firn pack towards the ice-shelf front during the summer.

scholarly journals Frazil-ice growth rate and dynamics in mixed layers and sub-ice-shelf plumes

2018 ◽  
Vol 12 (1) ◽  
pp. 25-38 ◽  
Author(s):  
David W. Rees Jones ◽  
Andrew J. Wells
Keyword(s):  
Growth Rate ◽  
Crystal Growth ◽  
Large Scale ◽  
Freezing Temperature ◽  
Ice Shelf ◽  
Secondary Nucleation ◽  
Ice Dynamics ◽  
Ice Shelves ◽  
Frazil Ice ◽  
Microphysical Processes

Abstract. The growth of frazil or granular ice is an important mode of ice formation in the cryosphere. Recent advances have improved our understanding of the microphysical processes that control the rate of ice-crystal growth when water is cooled beneath its freezing temperature. These advances suggest that crystals grow much faster than previously thought. In this paper, we consider models of a population of ice crystals with different sizes to provide insight into the treatment of frazil ice in large-scale models. We consider the role of crystal growth alongside the other physical processes that determine the dynamics of frazil ice. We apply our model to a simple mixed layer (such as at the surface of the ocean) and to a buoyant plume under a floating ice shelf. We provide numerical calculations and scaling arguments to predict the occurrence of frazil-ice explosions, which we show are controlled by crystal growth, nucleation, and gravitational removal. Faster crystal growth, higher secondary nucleation, and slower gravitational removal make frazil-ice explosions more likely. We identify steady-state crystal size distributions, which are largely insensitive to crystal growth rate but are affected by the relative importance of secondary nucleation to gravitational removal. Finally, we show that the fate of plumes underneath ice shelves is dramatically affected by frazil-ice dynamics. Differences in the parameterization of crystal growth and nucleation give rise to radically different predictions of basal accretion and plume dynamics, and can even impact whether a plume reaches the end of the ice shelf or intrudes at depth.

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