scholarly journals Modeling Ocean–Cryosphere Interactions off Adélie and George V Land, East Antarctica

2017 ◽  
Vol 30 (1) ◽  
pp. 163-188 ◽  
Author(s):  
Kazuya Kusahara ◽  
Hiroyasu Hasumi ◽  
Alexander D. Fraser ◽  
Shigeru Aoki ◽  
Keishi Shimada ◽  
...  
Keyword(s):  
Sea Ice ◽  
Interannual Variability ◽  
Ocean Circulation ◽  
Pressure System ◽  
Amundsen Sea ◽  
Ice Shelves ◽  
Coastal Polynya ◽  
Dominant Feature ◽  
Ice Production ◽  
Basal Melting

Ocean–cryosphere interactions along the Adélie and George V Land (AGVL) coast are investigated using a coupled ocean–sea ice–ice shelf model. The dominant feature of the Mertz Glacier Tongue (MGT), located at approximately 145°E, was a highly productive winter coastal polynya system, until its calving in February 2010 dramatically changed the regional “icescape.” This study examines the annual mean, seasonal, and interannual variabilities of sea ice production; basal melting of the MGT; ice shelves, large icebergs, and fast ice; Dense Shelf Water (DSW) export; and bottom water properties on the continental slope and rise, and assesses the impacts of the calving event. The interannual variability of the winter coastal polynya regime is dominated by the regional offshore winds and air temperature, which are linked to activity of the Amundsen Sea low pressure system. This is the main driver of the interannual variability of DSW exported from the AGVL region. The calving event led to a decrease in sea ice production that resulted in a decrease in the density of DSW export. Subsequently, there is extensive freshening downstream over the continental shelf and slope regions. In addition, it is found that the calving event causes a significant decrease in the mean melt rate of the MGT, resulting from a decrease in ocean heat flux into the cavity due to ocean circulation changes.

scholarly journals Ocean circulation and sea-ice thinning induced by melting ice shelves in the Amundsen Sea

2017 ◽  
Vol 122 (3) ◽  
pp. 2550-2573 ◽  
Author(s):  
Nicolas C. Jourdain ◽  
Pierre Mathiot ◽  
Nacho Merino ◽  
Gaël Durand ◽  
Julien Le Sommer ◽  
...  
Keyword(s):  
Sea Ice ◽  
Ocean Circulation ◽  
Amundsen Sea ◽  
Ice Shelves

Interannual variability in primary productivity driven by sea-ice phenology in the Amundsen Sea polynyas, not ice shelves melting.

2021 ◽  
Author(s):  
Guillaume Liniger ◽  
Sebastien Moreau ◽  
Delphine Lannuzel ◽  
Fernando Paolo ◽  
Peter Strutton
Keyword(s):  
Sea Ice ◽  
Interannual Variability ◽  
Primary Productivity ◽  
Net Primary Productivity ◽  
Light Availability ◽  
Southern Annular Mode ◽  
Sea Ice Concentration ◽  
Amundsen Sea ◽  
Ice Shelves ◽  
Ice Coverage

<p>Ice shelves have been melting, thinning and retreating along the coast of West Antarctica for the past four decades, most notably in the Amundsen Sea sector. This area hosts two highly productive coastal polynyas, the Pine Island polynya and the Amundsen Sea polynya, whose opening triggers two of the largest phytoplankton blooms in the Southern Ocean. Previous work in the area suggests that ice shelf melting and thinning increases the iron content of coastal seawater, which could potentially boost ocean primary productivity locally. In this work, we use historical (1992-2017) remote sensing observations of net primary productivity, sea-ice concentration and rate of ice shelves melting to investigate the strength of this connection for these two large polynyas. We used the Abbot, Cosgrove, Pine Island, Thwaites, Dotson and Getz ice shelves for our analyses. Our initial results suggest no significant trends in net primary productivity though time but a large interannual variability for both polynyas. The basal melt rate and ice thinning seem to not be the main drivers of this interannual variability in these polynyas, but sea-ice coverage variability does seem to play a strong role, potentially allowing increased light availability and stratification. Further investigations of circumpolar deep water inputs and climate modes related to ice shelves melting such as El Niño or the southern annular mode are needed to clarify our findings. Our preliminary study points the complexity of ice-ocean systems, where several co-occurring processes influence coastal primary productivity, with consequences for carbon cycling and the climate system.</p>

scholarly journals The Impact of Overturning and Horizontal Circulation in Pine Island Trough on Ice Shelf Melt in the Eastern Amundsen Sea

2019 ◽  
Vol 49 (1) ◽  
pp. 63-83 ◽  
Author(s):  
Benjamin G. M. Webber ◽  
Karen J. Heywood ◽  
David P. Stevens ◽  
Karen M. Assmann
Keyword(s):  
Continental Shelf ◽  
Ocean Circulation ◽  
Circulation Model ◽  
Shelf Break ◽  
Ekman Pumping ◽  
Overturning Circulation ◽  
Amundsen Sea ◽  
Ice Shelves ◽  
Basal Melting ◽  
The Impact

AbstractThe ice shelves around the Amundsen Sea are rapidly melting as a result of the circulation of relatively warm ocean water into their cavities. However, little is known about the processes that determine the variability of this circulation. Here we use an ocean circulation model to diagnose the relative importance of horizontal and vertical (overturning) circulation within Pine Island Trough, leading to Pine Island and Thwaites ice shelves. We show that melt rates and southward Circumpolar Deep Water (CDW) transports covary over large parts of the continental shelf at interannual to decadal time scales. The dominant external forcing mechanism for this variability is Ekman pumping and suction on the continental shelf and at the shelf break, in agreement with previous studies. At the continental shelf break, the southward transport of CDW and heat is predominantly barotropic. Farther south within Pine Island Trough, northward and southward barotropic heat transports largely cancel, and the majority of the net southward temperature transport is facilitated by baroclinic and overturning circulations. The overturning circulation is related to water mass transformation and buoyancy gain on the shelf that is primarily facilitated by freshwater input from basal melting.

scholarly journals Brief communication: PICOP, a new ocean melt parameterization under ice shelves combining PICO and a plume model

2019 ◽  
Vol 13 (3) ◽  
pp. 1043-1049 ◽  
Author(s):  
Tyler Pelle ◽  
Mathieu Morlighem ◽  
Johannes H. Bondzio
Keyword(s):  
Ocean Circulation ◽  
Numerical Models ◽  
Three Dimensional ◽  
Ice Sheet ◽  
Ice Shelf ◽  
Ice Streams ◽  
Amundsen Sea ◽  
Ice Shelves ◽  
Grounding Line ◽  
Basal Melting

Abstract. Basal melting at the bottom of Antarctic ice shelves is a major control on glacier dynamics, as it modulates the amount of buttressing that floating ice shelves exert onto the ice streams feeding them. Three-dimensional ocean circulation numerical models provide reliable estimates of basal melt rates but remain too computationally expensive for century-scale projections. Ice sheet modelers therefore routinely rely on simplified parameterizations based on either ice shelf depth or more sophisticated box models. However, existing parameterizations do not accurately resolve the complex spatial patterns of sub-shelf melt rates that have been observed over Antarctica's ice shelves, especially in the vicinity of the grounding line, where basal melting is one of the primary drivers of grounding line migration. In this study, we couple the Potsdam Ice-shelf Cavity mOdel (PICO, Reese et al., 2018) to a buoyant plume melt rate parameterization (Lazeroms et al., 2018) to create PICOP, a novel basal melt rate parameterization that is easy to implement in transient ice sheet numerical models and produces a melt rate field that is in excellent agreement with the spatial distribution and magnitude of observations for several ocean basins. We test PICOP on the Amundsen Sea sector of West Antarctica, Totten, and Moscow University ice shelves in East Antarctica and the Filchner-Ronne Ice Shelf and compare the results to PICO. We find that PICOP is able to reproduce inferred high melt rates beneath Pine Island, Thwaites, and Totten glaciers (on the order of 100 m yr−1) and removes the “banding” pattern observed in melt rates produced by PICO over the Filchner-Ronne Ice Shelf. PICOP resolves many of the issues contemporary basal melt rate parameterizations face and is therefore a valuable tool for those looking to make future projections of Antarctic glaciers.

scholarly journals Simulating or prescribing the influence of tides on the Amundsen Sea ice shelves

2019 ◽  
Vol 133 ◽  
pp. 44-55 ◽  
Author(s):  
Nicolas C. Jourdain ◽  
Jean-Marc Molines ◽  
Julien Le Sommer ◽  
Pierre Mathiot ◽  
Jérôme Chanut ◽  
...  
Keyword(s):  
Sea Ice ◽  
Amundsen Sea ◽  
Ice Shelves

scholarly journals Evolution of the Amundsen Sea Polynya, Antarctica, 2016–2021

2021 ◽  
Author(s):  
Grant J. Macdonald ◽  
Stephen F. Ackley ◽  
Alberto M. Mestas-Nuñez
Keyword(s):  
Sea Ice ◽  
Reanalysis Data ◽  
Sea Ice Concentration ◽  
Amundsen Sea ◽  
Annual Variations ◽  
Ice Concentration ◽  
Ice Conditions ◽  
Sar Imagery ◽  
Key Sites ◽  
Ice Production

Abstract. Polynyas are key sites of ice production during the winter and are important sites of biological activity and carbon sequestration during the summer. The Amundsen Sea Polynya (ASP) is the fourth largest Antarctic polynya, has recorded the highest primary productivity and lies in an embayment of key oceanographic significance. However, knowledge of its dynamics, and of sub-annual variations in its area and ice production, is limited. In this study we primarily utilize Sentinel-1 SAR imagery, sea ice concentration products and climate reanalysis data, along with bathymetric data, to analyze the ASP over the period November 2016–March 2021. Specifically, we analyze (i) qualitative changes in the ASP's characteristics and dynamics, and quantitative changes in (ii) summer polynya area, (iii) winter polynya area and ice production. From our analysis of SAR imagery we find that ice produced by the ASP becomes stuck in the vicinity of the polynya and sometimes flows back into the polynya, contributing to its closure and limiting further ice production. The polynya forms westward off a persistent chain of grounded icebergs that are located at the site of a bathymetric high. Grounded icebergs also influence the outflow of ice and facilitate the formation of a 'secondary polynya' at times. Additionally, unlike some polynyas, ice produced by the polynya flows westward after formation, along the coast and into the neighboring sea sector. During the summer and early winter, broader regional sea ice conditions can play an important role in the polynya. The polynya opens in all summers, but record-low sea ice conditions in 2016/17 cause it to become part of the open ocean. During the winter, an average of 78 % of ice production occurs in April–May and September–October, but large polynya events often associated with high winds can cause ice production throughout the winter. While passive microwave data or daily sea ice concentration products remain key for analyzing variations in polynya area and ice production, we find that the ability to directly observe and qualitatively analyze the polynya at a high temporal and spatial resolution with Sentinel-1 imagery provides important insights about the behavior of the polynya that are not possible with those datasets.

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.

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>

scholarly journals Formation, Flow, and Disintegration Of Ice Shelves

1979 ◽  
Vol 24 (90) ◽  
pp. 259-271 ◽  
Author(s):  
G. De Q. Robin
Keyword(s):  
Sea Ice ◽  
Thick Layer ◽  
Big Bang ◽  
Bottom Surface ◽  
Minor Importance ◽  
Ice Shelf ◽  
Creep Failure ◽  
Ice Shelves ◽  
Basal Melting ◽  
Inland Ice

AbstractIce shelves may develop either by continued thickening of sea ice that is held fast to the shore, or by the seaward extension of inland ice. For both processes, as well as for an understanding of ablation and of accumulation at the bottom surface of ice shelves, we need to understand melting and freezing processes in relation to salinity, temperature, and pressure. Consideration of these factors shows that basal melting beneath the thicker parts of ice shelves is much greater than is generally appreciated. This could be sufficient to bring the estimated mass balance of Antarctica into approximate equilibrium. It appears that most Antarctic ice shelves are dependent on the supply of inland ice for their continued existence. However the thick layer of sea ice beneath the Amery Ice Shelf is readily explained in terms of sub-ice water circulation.Transport of heat and mass by water motion beneath ice shelves has the potential to change ice thicknesses by similar amounts to that caused by internal deformation of the ice shelf. Bottom freezing due to thermal conduction throughout the ice shelf is of minor importance.While attention is drawn to the basic equations for flow of ice shelves, it is pointed out that they have yet to be applied satisfactorily to the problem of iceberg calving. This appears from field observations to be due primarily to creep failure of spreading ice shelves, possibly aided by impact from floating icebergs. Recent observations show the effectiveness and likely quantitative importance of this “big bang” theory of iceberg formation in Antarctica.A brief discussion of the effects of climatic change on the disintegration of ice shelves is presented.

scholarly journals Amundsen Sea ice production and transport

2005 ◽  
Vol 110 (C12) ◽  
Author(s):  
Karen M. Assmann ◽  
Hartmut H. Hellmer ◽  
Stanley S. Jacobs
Keyword(s):  
Sea Ice ◽  
Amundsen Sea ◽  
Ice Production
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