scholarly journals Seasonal control of Petermann Gletscher ice-shelf melt by the ocean's response to sea-ice cover in Nares Strait

2017 ◽  
Vol 63 (238) ◽  
pp. 324-330 ◽  
Author(s):  
E. L. SHROYER ◽  
L. PADMAN ◽  
R. M. SAMELSON ◽  
A. MÜNCHOW ◽  
L. A. STEARNS
Keyword(s):  
Sea Ice ◽  
Mass Loss ◽  
Ocean Circulation ◽  
Greenland Ice Sheet ◽  
Ice Shelf ◽  
Near Surface ◽  
Eastern Side ◽  
Nares Strait ◽  
Landfast Sea Ice ◽  
Basal Melting

AbstractPetermann Gletscher drains ~4% of the Greenland ice sheet (GrIS) area, with ~80% of its mass loss occurring by basal melting of its ice shelf. We use a high-resolution coupled ocean and sea-ice model with a thermodynamic glacial ice shelf to diagnose ocean-controlled seasonality in basal melting of the Petermann ice shelf. Basal melt rates increase by ~20% in summer due to a seasonal shift in ocean circulation within Nares Strait that is associated with the transition from landfast sea ice to mobile sea ice. Under landfast ice, cold near-surface waters are maintained on the eastern side of the strait and within Petermann Fjord, reducing basal melt and insulating the ice shelf. Under mobile sea ice, warm waters are upwelled on the eastern side of the strait and, mediated by local instabilities and eddies, enter Petermann Fjord, enhancing basal melt down to depths of 200 m. The transition between these states occurs rapidly, and seasonal changes within Nares Strait are conveyed into the fjord within the same season. These results suggest that long-term changes in the length of the landfast sea-ice season will substantially alter the structure of Petermann ice shelf and its contribution to GrIS mass loss.

scholarly journals Interannual changes of the floating ice shelf of Petermann Gletscher, North Greenland, from 2000 to 2012

2014 ◽  
Vol 60 (221) ◽  
pp. 489-499 ◽  
Author(s):  
Andreas Münchow ◽  
Laurie Padman ◽  
Helen A. Fricker
Keyword(s):  
Mass Loss ◽  
Three Dimensional ◽  
Greenland Ice Sheet ◽  
Altimeter Data ◽  
Ice Shelf ◽  
Laser Altimetry ◽  
Laser Altimeter ◽  
Airborne Laser ◽  
Tracking Surface ◽  
Basal Melting

AbstractPetermann Gletscher, northwest Greenland, drains 4% of the Greenland ice sheet into Nares Strait. Its floating ice shelf retreated from 81 to 48 km in length during two large calving events in 2010 and 2012. We document changes in the three-dimensional ice-shelf structure from 2000 to 2012, using repeated tracks of airborne laser altimetry and ice radio-echo sounding, ICESat laser altimetry and MODIS visible imagery. The recent ice-shelf velocity, measured by tracking surface features between flights in 2010 and 2011, is ~1.25 km a−1, ~15–30% faster than estimates made before 2010. The steady- state along-flow ice divergence represents 6.3 Gta−1 mass loss through basal melting (~5Gta−1) and surface melting and sublimation (~1.0Gta−1). Airborne laser altimeter data reveal thinning, both along a thin central channel and on the thicker ambient ice shelf. From 2007 to 2010 the ice shelf thinned by ~5 m a−1, which represents a non-steady mass loss of ~4.1 Gta−1. We suggest that thinning in the basal channels structurally weakened the ice shelf and may have played a role in the recent calving events.

scholarly journals Circulation beneath the Filchner Ice Shelf, Antarctica, and its sensitivity to changes in the oceanic environment: a case-study

1998 ◽  
Vol 27 ◽  
pp. 99-104 ◽  
Author(s):  
K. Grosfeld ◽  
R. Gerdes
Keyword(s):  
Sea Ice ◽  
Mass Loss ◽  
Ocean Circulation ◽  
Large Scale ◽  
Ocean Model ◽  
Current Situation ◽  
Weddell Sea ◽  
Ice Formation ◽  
Shelf Area ◽  
Ice Shelf

We investigate the sensitivity of the ocean circulation in the Filchner Trough to changes in the large-scale oceanic environment and its impact on the mass balance of the Filchner Ice Shelf, Antarctica. Three experiments with a three-dimensional ocean model describe (i) the current situation, (ii) a scenario with increased ocean temperatures, and (iii) a scenario with reduced sea-ice formation rates on the adjacent continental shelf. in the final discussion brief results of a combined scenario with increased ocean temperatures and reduced sea-ice formation are presented. The changes from the current situation affect the circulation in the Filchner Trough, and melting and freezing processes beneath the ice shelf. The latter affect the amount and properties of Ice Shelf Water (ISW), a component of Antarctic Bottom Water. Net basal melt rates provide an overall measure for the changes: while the control run yields 0.35 m a−1 net melting averaged over the Filchner Ice Shelf area, the warming scenario results in a more than twofold increase in ice-shelf mass loss. Reduced production of High Salinity ShelfWater due to smaller sea-ice formation rates in the second scenario leads, on the other hand, to a decrease in basal mass loss, because the deep cavity is less well ventilated than in the control run. ISW is cooled and the ice shelf is stabilized under this scenario, which is arguably the more likely development in the southern Weddell Sea.

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

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

<p>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.</p>

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

2012 ◽  
Vol 58 (212) ◽  
pp. 1227-1244 ◽  
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.

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

2010 ◽  
Vol 4 (4) ◽  
pp. 2079-2101 ◽  
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.

Representation of basal melting in idealised coupled ice sheet ocean models

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

<p>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–ocean experiments under the first phase of the Marine Ice Sheet–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,  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.</p>

Constraining ice shelf basalt melting rates from isochrone data

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

<p>Ice shelves buttress ice flow from the continent towards the ocean, and their disintegration results in increased ice discharge.  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.</p><p>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.</p>

Holocene sea-ice dynamics in Petermann Fjord 

2021 ◽  
Author(s):  
Henrieka Detlef ◽  
Brendan Reilly ◽  
Anne Jennings ◽  
Mads Mørk jensen ◽  
Matt O'Regan ◽  
...  
Keyword(s):  
Sea Ice ◽  
Carbon Isotopic Composition ◽  
Greenland Ice Sheet ◽  
Ekman Transport ◽  
Tight Coupling ◽  
Ice Dynamics ◽  
The Holocene ◽  
Nares Strait ◽  
Sea Ice Dynamics ◽  
Landfast Ice

<p>Today Nares Strait is covered by sea ice for 11 months per year. The seasonal sea-ice regime and formation of landfast ice depend on the development of ice arches. Historically a northern and southern ice arch have been observed in Robeson Channel and Smith Sound, respectively, with only the southern arch leading to a complete freeze up of the strait. In recent decades, the northern arch has become more prominent, indicating a regime shift in Nares Strait sea-ice dynamics with important consequences for the export of ice from the Lincoln Sea, the regional oceanography, and the ecosystem related to the annual opening of the North Water Polynya lee of the southern ice arch. Modelling studies suggest a link between mobile sea ice and enhanced Ekman transport of modified Atlantic Water to Greenland fjord systems bordering Nares Strait. Further, a reduction in the fjords’ fast ice season, in response to Nares Strait sea-ice dynamics, might decrease its buttressing effect on the marine-terminating outlet glaciers in northern Greenland. One such glacier is Petermann Glacier, draining 4% of the Greenland Ice Sheet and terminating in a 48 km long ice tongue in Petermann Fjord.</p><p>The Petermann 2015 Expedition to Petermann Fjord and adjacent Hall Basin recovered a transect of cores from Nares Strait to under the 48 km long ice tongue of Petermann glacier. First results suggest that no ice tongue existed in Petermann Fjord for large parts of the Holocene, raising the question of the role of the ocean and the marine cryosphere in the collapse and re-establishment of the ice tongue. We present a multi-proxy study (sea-ice related biomarkers, total organic carbon and its carbon isotopic composition, and benthic and planktonic foraminiferal abundances) exploring the Holocene sea-ice dynamics at site OD1507-03TC-41GC-03PC in outer Petermann Fjord. Our results are in line with a tight coupling of the marine and terrestrial cryosphere in this region and, in connection with other regional sea-ice reconstructions, give insights into the Holocene evolution of ice arches and associated landfast ice in Nares Strait.</p>

High-resolution ocean/sea ice/ice shelf simulation of the 79° North Glacier and Zachariae Isstrøm

2021 ◽  
Author(s):  
Claudia Wekerle ◽  
Ralph Timmermann ◽  
Qiang Wang ◽  
Rebecca McPherson
Keyword(s):  
Sea Ice ◽  
Continental Shelf ◽  
Model Performance ◽  
Greenland Ice Sheet ◽  
Atlantic Water ◽  
Ocean Model ◽  
The Arctic ◽  
Ice Shelf ◽  
Time Period ◽  
Mesh Resolution

<p>The 79° North Glacier (79NG) is the largest of the marine terminating glaciers fed by the  Northeast Greenland Ice Stream (NEGIS), which drains around 15% of the Greenland ice sheet. The 79NG is one of the few Greenland glaciers with a floating ice tongue, and is strongly influenced by warm Atlantic Water originating from Fram Strait and carried towards it through a trough system on the Northeast Greenland continental shelf.</p><p>Considering the decrease in thickness of the 79NG and also of the neighboring Zachariae Isstrøm (ZI), we aim to understand the processes that potentially lead to the decay of these glaciers. As a first step we present here an ocean-sea ice simulation which explicitly resolves the cavities of the 79NG and ZI glaciers, applying the Finite-Element Sea ice-Ocean Model (FESOM). We take advantage of the multi-resolution capability of FESOM and locally increase mesh resolution in the vicinity of the 79NG to 700 m. The Northeast Greenland continental shelf is resolved with 3 km, and the Arctic Ocean and Nordic Seas with 4.5 km. The simulation is conducted for the time period 1980 to 2018, using JRA-55 atmospheric reanalysis. Solid and liquid runoff from Greenland is taken from the Bamber et al. 2018 dataset. The flow of warm Atlantic water into the glacier and outflow of meltwater is compared to observational data from measurement campaigns. We further use current and hydrographic data from moorings deployed in Norske Trough to assess the model performance in carrying warm water towards the glacier. This simulation spanning several decades allows us to investigate recent changes in basal melt rates induced by oceanic processes, in particular warm Atlantic Water transport towards the glacier.</p>

Evaluating Met Office uncoupled and coupled forecasts during the Iceland Greenland Seas Project field campaign in 2018

2021 ◽  
Author(s):  
Chris Barrell ◽  
Ian Renfrew ◽  
Steven Abel ◽  
Andrew Elvidge ◽  
John King
Keyword(s):  
Sea Ice ◽  
Ocean Circulation ◽  
Rapid Change ◽  
Coupled Model ◽  
Vital Role ◽  
Meridional Overturning Circulation ◽  
Global Ocean ◽  
Near Surface ◽  
Field Campaign ◽  
Important Region

<div> <p>During a cold-air outbreak (CAO) a cold polar airmass flows from the frozen land or ice surface, over the marginal ice zone (MIZ), then out over the comparatively warm open ocean. This constitutes a dramatic change in surface temperature, roughness and moisture availability, typically causing rapid change in the atmospheric boundary layer. Consequently, CAOs are associated with a range of severe mesoscale weather phenomena and accurate forecasting is crucial. Over the Nordic Seas CAOs also play a vital role in global ocean circulation, causing densification and sinking of ocean waters that form the headwaters of the Atlantic meridional overturning circulation. </p> </div><div> <p>To tackle the lack of observations during wintertime CAOs and improve scientific understanding in this important region, the Iceland Greenland Seas Project (IGP) undertook an extensive field campaign during February and March 2018. Aiming to characterise the atmospheric forcing and the ocean response, particularly in and around the MIZ, the IGP made coordinated ocean-atmosphere measurements, involving a research vessel, a research aircraft, a meteorological buoy, moorings, sea gliders and floats.  </p> </div><div> <p>The work presented here employs these novel observational data to evaluate output from the UK Met Office global operational forecasting system and from a pre-operational coupled ocean-ice-atmosphere system. The Met Office aim to transition to a coupled operational forecast in the coming years, thus verification of model versions in development is essential. Results show that this coupled model’s sea ice is generally more accurate than a persistent field. However, it can also suffer from cold-biased sea surface temperatures around the MIZ, which influences the modelled near-surface meteorology. Both these effects demonstrate the crucial importance of accurate sea ice simulation in coupled model forecasting in the high latitudes. Hence, an ice edge metric is then used to quantify the accuracy of the coupled model MIZ edge at two ocean grid resolutions. </p> </div>

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