Stronger ocean circulation and increased melting under Pine Island Glacier ice shelf

AbstractSeveral hundred visible and thermal infrared satellite images of Antarctica’s southeast Amundsen Sea from 1986 to 2011, combined with aerial observations in 2009, show a strong inverse relation between prominent curvilinear surface depressions and the underlying basal morphology of the outer Pine Island Glacier ice shelf. Shipboard measurements near the calving front reveal positive temperature, salinity and current anomalies indicative of melt-laden, deep-water outflows near and above the larger channel termini. These buoyant plumes rise to the surface and are expressed as small polynyas in the sea ice and thermal signatures in the open water. The warm upwellings also trace the cyclonic surface circulation in Pine Island Bay. The satellite coverage suggests changing modes of ocean/ice interactions, dominated by leads along the ice shelf through 1999, fast ice and polynyas from 2000 to 2007, and larger areas of open water since 2008.

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Sub-shelf melting consequences of recent and future Pine Island Glacier ice shelf calving events

10.5194/egusphere-egu21-2972 ◽

2021 ◽

Author(s):

Alex Bradley ◽

Paul Holland ◽

Pierre Dutrieux

Keyword(s):

Continental Shelf ◽

Numerical Simulations ◽

Ocean Circulation ◽

Deep Water ◽

Ice Shelf ◽

Circumpolar Deep Water ◽

Overall Stability ◽

Glacier Ice

In recent years, the ice shelf of Pine Island Glacier has experienced several significant calving events. It is understood that the presence of the ice shelf in conjunction with a subglacial ridge provide a strong topographic barrier to warm Circumpolar Deep Water spilling onto the continental shelf, but it is not known how this barrier will respond to this recent, and possible future, calving events. In this presentation, I shall present results of numerical simulations of ocean circulation under Pine Island Glacier, which indicate a strong sensitivity to such calving events, and discuss the implications of these results for the overall stability of the glacier.

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Holocene climate change in the Bransfield Basin, Antarctic Peninsula: evidence from sediment and diatom analysis

Antarctic Science ◽

10.1017/s0954102007000788 ◽

2007 ◽

Vol 20 (1) ◽

pp. 69-87 ◽

Cited By ~ 44

Author(s):

David C. Heroy ◽

Charlotte Sjunneskog ◽

John B. Anderson

Keyword(s):

Ocean Circulation ◽

Sediment Accumulation ◽

Sedimentary Facies ◽

Ice Shelf ◽

Diatom Analysis ◽

Climate History ◽

Radiocarbon Dates ◽

Sedimentary Environments ◽

Unstable Surface ◽

Bransfield Basin

AbstractWe present the first study from the Bransfield Basin that extends through the Holocene, recording the variable climate history back to the decoupling of the ice sheet from the continental shelf ~10 650 calendar years before present (cal yr bp). Detailed sediment analysis reveals three stratigraphic units in PC-61 concomitant with three sedimentary environments, similar to sedimentary facies reported elsewhere: 1) subglacial, 2) glacial proximal/sub-ice shelf, and 3) open marine. These interpretations are based on a variety of sedimentological criteria, supported by ten AMS radiocarbon dates and detailed diatom analysis. We note two significant volcanic ash layers (tephra) at 3870 and 5500 cal yr bp from nearby Deception Island. Based on diatom assemblage analysis, we identify five separate climate regimes, highlighting a significantly shorter Mid-Holocene Climatic Optimum than reported by other studies (6800–5900 cal yr bp). This period is marked by the highest Eucampia antarctica var. antarctica and Fragilariopsis curta abundance, total diatom abundance, sediment accumulation rates, and low magnetic susceptibility. We also identify a less pronounced Neoglacial period relative to other studies, which includes an increase of Cocconeis/Rhizosolenia spp. assemblage related to unstable surface water conditions. Such observations probably reflect important regional variations in atmospheric or ocean circulation patterns.

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Thermohaline structure and circulation beneath the Langhovde Glacier ice shelf in East Antarctica

Nature Communications ◽

10.1038/s41467-021-23534-w ◽

2021 ◽

Vol 12 (1) ◽

Author(s):

Masahiro Minowa ◽

Shin Sugiyama ◽

Masato Ito ◽

Shiori Yamane ◽

Shigeru Aoki

Keyword(s):

Freezing Point ◽

East Antarctica ◽

Ice Shelf ◽

Rate Estimate ◽

Ice Shelves ◽

Plume Water ◽

Warm Deep Water ◽

Glacier Ice ◽

Basal Melting

AbstractBasal melting of ice shelves is considered to be the principal driver of recent ice mass loss in Antarctica. Nevertheless, in-situ oceanic data covering the extensive areas of a subshelf cavity are sparse. Here we show comprehensive structures of temperature, salinity and current measured in January 2018 through four boreholes drilled at a ~3-km-long ice shelf of Langhovde Glacier in East Antarctica. The measurements were performed in 302–12 m-thick ocean cavity beneath 234–412 m-thick ice shelf. The data indicate that Modified Warm Deep Water is transported into the grounding zone beneath a stratified buoyant plume. Water at the ice-ocean interface was warmer than the in-situ freezing point by 0.65–0.95°C, leading to a mean basal melt rate estimate of 1.42 m a−1. Our measurements indicate the existence of a density-driven water circulation in the cavity beneath the ice shelf of Langhovde Glacier, similar to that proposed for warm-ocean cavities of larger Antarctic ice shelves.

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Modelling the ocean circulation and the basal melting in the Prydz Bay-Amery Ice Shelf system

10.5194/egusphere-egu21-6425 ◽

2021 ◽

Author(s):

Jing Jin ◽

Antony J. Payne ◽

William Seviour ◽

Christopher Bull

Keyword(s):

Heat Transport ◽

Ocean Circulation ◽

Water Masses ◽

Prydz Bay ◽

Effect Of Temperature ◽

Oceanic Circulation ◽

Ice Shelf ◽

Thermodynamic Structure ◽

Amery Ice Shelf ◽

Basal Melting

The basal melting of the Amery Ice Shelf (AIS) in East Antarctica and its connections with the oceanic circulation are investigated by a regional ocean model. The simulated estimations of net melt rate over AIS from 1976 to 2005 vary from 1 to 2 m/yr depending primarily due to inflow of modified Circumpolar Deep Water (mCDW). Prydz Bay Eastern Costal Current (PBECC) and the eastern branch of Prydz Bay Gyre (PBG) are identified as two main mCDW intrusion pathways. The oceanic heat transport from both PBECC and PBG has significant seasonal variability, which is associated with the Antarctic Slope Current. The onshore heat transport has a long-lasting effect on basal melting. The basal melting is primarily driven by the inflowing water masses though a positive feedback mechanism. The intruding warm water masses destabilize the thermodynamic structure in the sub-ice shelf cavity therefore enhancing the overturning circulations, leading to further melting due to increasing heat transport. However, the inflowing saltier water masses due to sea-ice formation could offset the effect of temperature through stratifying the thermodynamic structure, then suppressing the overturning circulation and reducing the basal melting.

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Viscosity and elasticity: a model intercomparison of ice-shelf bending in an Antarctic grounding zone

Journal of Glaciology ◽

10.1017/jog.2017.15 ◽

2017 ◽

Vol 63 (240) ◽

pp. 573-580 ◽

Cited By ~ 7

Author(s):

CHRISTIAN T. WILD ◽

OLIVER J. MARSH ◽

WOLFGANG RACK

Keyword(s):

Young’S Modulus ◽

Ocean Circulation ◽

Young's Modulus ◽

Viscoelastic Model ◽

Ice Sheet ◽

Global Ocean ◽

Elastic Model ◽

Ice Shelf ◽

Bending Stresses ◽

Global Ocean Circulation

ABSTRACTGrounding zones are vital to ice-sheet mass balance and its coupling to the global ocean circulation. Processes here determine the mass discharge from the grounded ice sheet, to the floating ice shelves. The response of this transition zone to tidal forcing has been described by both elastic and viscoelastic models. Here we examine the validity of these models for grounding zone flexure over tidal timescales using field data from the Southern McMurdo Ice Shelf (78° 15′S, 167° 7′E). Observations of tidal movement were carried out by simultaneous tiltmeter and GPS measurements along a profile across the grounding zone. Finite-element simulations covering a 64 d period reveal that the viscoelastic model fits best the observations using a Young's modulus of 1.6 GPa and a viscosity of 1013.7 Pa s (≈ 50.1 TPa s). We conclude that the elastic model is only well-constrained for tidal displacements >35% of the spring-tidal amplitude using a Young's modulus of 1.62 ± 0.69 GPa, but that a viscoelastic model is necessary to adequately capture tidal bending at amplitudes below this threshold. In grounding zones where bending stresses are greater than at the Southern McMurdo Ice Shelf or ice viscosity is lower, the threshold would be even higher.

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Ice-shelf basal channels in a coupled ice/ocean model

Journal of Glaciology ◽

10.3189/2012jog12j003 ◽

2012 ◽

Vol 58 (212) ◽

pp. 1227-1244 ◽

Cited By ~ 56

Author(s):

Carl V. Gladish ◽

David M. Holland ◽

Paul R. Holland ◽

Stephen F. Price

Keyword(s):

Ocean Circulation ◽

Coupled System ◽

Ocean Model ◽

Subsurface Water ◽

Ice Thickness ◽

Ice Shelf ◽

First Approximation ◽

Grounding Line ◽

History Of ◽

Basal Melting

AbstractA numerical model for an interacting ice shelf and ocean is presented in which the ice- shelf base exhibits a channelized morphology similar to that observed beneath Petermann Gletscher’s (Greenland) floating ice shelf. Channels are initiated by irregularities in the ice along the grounding line and then enlarged by ocean melting. To a first approximation, spatially variable basal melting seaward of the grounding line acts as a steel-rule die or a stencil, imparting a channelized form to the ice base as it passes by. Ocean circulation in the region of high melt is inertial in the along-channel direction and geostrophically balanced in the transverse direction. Melt rates depend on the wavelength of imposed variations in ice thickness where it enters the shelf, with shorter wavelengths reducing overall melting. Petermann Gletscher’s narrow basal channels may therefore act to preserve the ice shelf against excessive melting. Overall melting in the model increases for a warming of the subsurface water. The same sensitivity holds for very slight cooling, but for cooling of a few tenths of a degree a reorganization of the spatial pattern of melting leads, surprisingly, to catastrophic thinning of the ice shelf 12 km from the grounding line. Subglacial discharge of fresh water along the grounding line increases overall melting. The eventual steady state depends on when discharge is initiated in the transient history of the ice, showing that multiple steady states of the coupled system exist in general.

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An improved bathymetry compilation for the Bellingshausen Sea, Antarctica, to inform ice-sheet and ocean models

The Cryosphere Discussions ◽

10.5194/tcd-4-2079-2010 ◽

2010 ◽

Vol 4 (4) ◽

pp. 2079-2101 ◽

Cited By ~ 3

Author(s):

A. G. C. Graham ◽

F. O. Nitsche ◽

R. D. Larter

Keyword(s):

Ocean Circulation ◽

Ice Sheet ◽

West Antarctica ◽

Ice Shelf ◽

Ice Streams ◽

Ice Shelves ◽

Sea Floor ◽

Bellingshausen Sea ◽

Warm Deep Water ◽

Basal Melting

Abstract. The southern Bellingshausen Sea (SBS) is a rapidly-changing part of West Antarctica, where oceanic and atmospheric warming has led to the recent basal melting and break-up of the Wilkins ice shelf, the dynamic thinning of fringing glaciers, and sea-ice reduction. Accurate sea-floor morphology is vital for understanding the continued effects of each process upon changes within Antarctica's ice sheets. Here we present a new bathymetric grid for the SBS compiled from shipborne echo-sounder, spot-sounding and sub-ice measurements. The 1-km grid is the most detailed compilation for the SBS to-date, revealing large cross-shelf troughs, shallow banks, and deep inner-shelf basins that continue inland of coastal ice shelves. The troughs now serve as pathways which allow warm deep water to access the ice fronts in the SBS. Our dataset highlights areas still lacking bathymetric constraint, as well as regions for further investigation, including the likely routes of palaeo-ice streams. The new compilation is a major improvement upon previous grids and will be a key dataset for incorporating into simulations of ocean circulation, ice-sheet change and history. It will also serve forecasts of ice stability and future sea-level contributions from ice loss in West Antarctica, required for the next IPCC assessment report in 2013.

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Representation of basal melting in idealised coupled ice sheet ocean models

10.5194/egusphere-egu21-10448 ◽

2021 ◽

Author(s):

Chen Zhao ◽

Rupert Gladstone ◽

Ben Galton-Fenzi ◽

David Gwyther

Keyword(s):

Ocean Circulation ◽

Critical Role ◽

Ice Sheet ◽

Ocean Model ◽

Periodic Pattern ◽

Regional Ocean Modeling System ◽

Ice Shelf ◽

Grounding Line ◽

Ocean Models ◽

Basal Melting

The ocean-driven basal melting has important implications for the stability of ice shelves in Antarctic, which largely affects the ice sheet mass balance, ocean circulation, and subsequently global sea level rise. Due to the limited observations in the ice shelf cavities, the couple ice sheet ocean models have been playing a critical role in examining the processes governing basal melting. In this study we use the Framework for Ice Sheet-Ocean Coupling (FISOC) to couple the Elmer/Ice full-stokes ice sheet model and the Regional Ocean Modeling System (ROMS) ocean model to model ice shelf/ocean interactions for an idealised three-dimensional domain. Experiments followed the coupled ice sheet&#8211;ocean experiments under the first phase of the Marine Ice Sheet&#8211;Ocean Model Intercomparison Project (MISOMIP1). A periodic pattern in the simulated mean basal melting rates is found to be highly consistent with the maximum barotropic stream function and also the grounding line retreat row by row, &#160;which is likely to be related with the gyre break down near the grounding line caused by some non-physical instability events from the ocean bottom. Sensitivity tests are carried out, showing that this periodic pattern is not sensitive to the choice of couple time intervals and horizontal eddy viscosities but sensitive to vertical resolution in the ocean model, the chosen critical water column thickness in the wet-dry scheme, and the tracer properties for the nudging dry cells at the ice-ocean interface boundary. Further simulations are necessary to better explain the mechanism involved in the couple ice-ocean system, which is very significant for its application on the realistic ice-ocean systems in polar regions.

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Constraining ice shelf basalt melting rates from isochrone data

10.5194/egusphere-egu21-3053 ◽

2021 ◽

Author(s):

Vjeran Visnjevic ◽

Reinhard Drews ◽

Clemens Schannwell ◽

Inka Koch

Keyword(s):

Ocean Circulation ◽

Radar Data ◽

Ice Shelf ◽

Ice Dynamics ◽

Ice Flow ◽

Ice Shelves ◽

Inverse Approach ◽

History Of ◽

Forward And Inverse Modeling ◽

Basal Melting

Ice shelves buttress ice flow from the continent towards the ocean, and their disintegration results in increased ice discharge.&#160; Ice-shelf evolution and integrity is influenced by surface accumulation, basal melting, and ice dynamics. We find signals of all of these processes imprinted in the ice-shelf stratigraphy that can be mapped using isochrones imaged with radar.Our aim is to develop an inverse approach to infer ice shelf basal melt rates using radar isochrones as observational constraints. Here, we investigate the influence of basalt melt rates on the shape of isochrones using combined insights from both forward and inverse modeling. We use the 3D full Stokes model Elmer/Ice in our forward simulations, aiming to reproduce isochrone patterns observed in our data. Moreover we develop an inverse approach based on the shallow shelf approximating, aiming to constrain basal melt rates using isochronal radar data and surface velocities. Insights obtained from our simulations can also guide the collection of new radar data (e.g., profile lines along vs. across-flow) in a way that ambiguities in interpreting the ice-shelf stratigraphy can be minimized. Eventually, combining these approaches will enable us to better constrain the magnitude and history of basal melting, which will give valuable input for ocean circulation and sea level rise projections.

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