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

Mapping Intimacies ◽

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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The role of Pine Island Glacier ice shelf basal channels in deep-water upwelling, polynyas and ocean circulation in Pine Island Bay, Antarctica

Annals of Glaciology ◽

10.3189/2012aog60a062 ◽

2012 ◽

Vol 53 (60) ◽

pp. 123-128 ◽

Cited By ~ 39

Author(s):

Kenneth D. Mankoff ◽

Stanley S. Jacobs ◽

Slawek M. Tulaczyk ◽

Sharon E. Stammerjohn

Keyword(s):

Ocean Circulation ◽

Deep Water ◽

Open Water ◽

Positive Temperature ◽

Ice Shelf ◽

Amundsen Sea ◽

Buoyant Plumes ◽

Surface Circulation ◽

Glacier Ice ◽

Fast Ice

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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Water Mass Characteristics and Distribution Adjacent to Larsen C Ice Shelf, Antarctica

10.5194/egusphere-egu2020-112 ◽

2020 ◽

Author(s):

Katherine Hutchinson ◽

Julie Deshayes ◽

Jean-Baptiste Sallee ◽

Julian Dowdeswell ◽

Casimir de Lavergne ◽

...

Keyword(s):

Continental Shelf ◽

Ocean Circulation ◽

Deep Water ◽

Water Mass ◽

Heat Content ◽

Weddell Sea ◽

Global Ocean ◽

Spatial And Temporal Variability ◽

Ice Shelf ◽

Shed Light

The physical oceanographic environment, water mass mixing and transformation in the area adjacent to Larsen C Ice Shelf (LCIS) are investigated using hydrographic data collected during the Weddell Sea Expedition 2019. The results shed light on the ocean conditions adjacent to a thinning LCIS, on a continental shelf that is a source region for the globally important water mass, Weddell Sea Deep Water (WSDW). Modified Weddell Deep Water (MWDW), a comparatively warmer water mass of circumpolar origin, is identified on the continental shelf and is observed to mix with local shelf waters, such as Ice Shelf Water (ISW), which is a precursor of WSDW. Oxygen measurements enable the use of a linear mixing model to quantify contributions from source waters revealing high levels of mixing in the area, with much spatial and temporal variability. Heat content anomalies indicate an introduction of heat, presumed to be associated with MWDW, into the area via Jason Trough. Furthermore, candidate parent sources for ISW are identified in the region, indicating the potential for the circulation of continental shelf waters into the ice shelf cavity. This highlights the possibility that offshore climate signals are conveyed under LCIS. ISW is observed within Jason Trough, likely exiting the sub-ice shelf cavity en route to the Slope Current. This onshore-offshore flux of water masses links the region of the Weddell Sea adjacent to northern LCIS to global ocean circulation and Bottom Water characteristics via its contribution to ISW and hence WSDW properties.&#160;What remains to be clarified is whether MWDW found in Jason Trough has a direct impact on basal melting and thus thinning of LCIS. More observations are required to investigate this, in particular direct observations of ocean circulation in Jason Trough and underneath LCIS. Modelling experiments could also shed light on this, and so preliminary results based on NEMO global simulations explicitly representing the circulation in under-ice shelf seas, will be presented.&#160;

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Sensitivity of Circumpolar Deep Water Transport and Ice Shelf Basal Melt along the West Antarctic Peninsula to Changes in the Winds

Journal of Climate ◽

10.1175/jcli-d-11-00307.1 ◽

2012 ◽

Vol 25 (14) ◽

pp. 4799-4816 ◽

Cited By ~ 82

Author(s):

Michael S. Dinniman ◽

John M. Klinck ◽

Eileen E. Hofmann

Keyword(s):

Continental Shelf ◽

Antarctic Peninsula ◽

Deep Water ◽

Constant Factor ◽

Ice Shelf ◽

The West ◽

Ice Shelves ◽

Circumpolar Deep Water ◽

West Antarctic ◽

West Antarctic Peninsula

Abstract Circumpolar Deep Water (CDW) can be found near the continental shelf break around most of Antarctica. Advection of this relatively warm water (up to 2°C) across the continental shelf to the base of floating ice shelves is thought to be a critical source of heat for basal melting in some locations. A high-resolution (4 km) regional ocean–sea ice–ice shelf model of the west Antarctic Peninsula (WAP) coastal ocean was used to examine the effects of changes in the winds on across-shelf CDW transport and ice shelf basal melt. Increases and decreases in the strength of the wind fields were simulated by scaling the present-day winds by a constant factor. Additional simulations considered effects of increased Antarctic Circumpolar Current (ACC) transport. Increased wind strength and ACC transport increased the amount of CDW transported onto the WAP continental shelf but did not necessarily increase CDW flux underneath the nearby ice shelves. The basal melt underneath some of the deeper ice shelves actually decreased with increased wind strength. Increased mixing over the WAP shelf due to stronger winds removed more heat from the deeper shelf waters than the additional heat gained from increased CDW volume transport. The simulation results suggest that the effect on the WAP ice shelves of the projected strengthening of the polar westerlies is not a simple matter of increased winds causing increased (or decreased) basal melt. A simple budget calculation indicated that iron associated with increased vertical mixing of CDW could significantly affect biological productivity of this region.

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Warm Circumpolar Deep Water at the Western Getz Ice Shelf Front, Antarctica

Geophysical Research Letters ◽

10.1029/2018gl081354 ◽

2019 ◽

Vol 46 (2) ◽

pp. 870-878 ◽

Cited By ~ 7

Author(s):

K. M. Assmann ◽

E. Darelius ◽

A. K. Wåhlin ◽

T. W. Kim ◽

S. H. Lee

Keyword(s):

Deep Water ◽

Ice Shelf ◽

Circumpolar Deep Water

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Circulation of modified Circumpolar Deep Water and basal melt beneath the Amery Ice Shelf, East Antarctica

Journal of Geophysical Research Oceans ◽

10.1002/2015jc010697 ◽

2015 ◽

Vol 120 (4) ◽

pp. 3098-3112 ◽

Cited By ~ 23

Author(s):

Laura Herraiz-Borreguero ◽

Richard Coleman ◽

Ian Allison ◽

Stephen R. Rintoul ◽

Mike Craven ◽

...

Keyword(s):

Deep Water ◽

East Antarctica ◽

Ice Shelf ◽

Circumpolar Deep Water ◽

Amery Ice Shelf

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Glacial Meltwater Identification in the Amundsen Sea

Journal of Physical Oceanography ◽

10.1175/jpo-d-16-0221.1 ◽

2017 ◽

Vol 47 (4) ◽

pp. 933-954 ◽

Cited By ~ 11

Author(s):

Louise C. Biddle ◽

Karen J. Heywood ◽

Jan Kaiser ◽

Adrian Jenkins

Keyword(s):

Dissolved Oxygen ◽

Deep Water ◽

Ocean Model ◽

Water Type ◽

Ice Shelf ◽

Amundsen Sea ◽

Glacial Meltwater ◽

Circumpolar Deep Water ◽

Water Characteristics ◽

Multiparameter Analysis

AbstractPine Island Ice Shelf, in the Amundsen Sea, is losing mass because of warm ocean waters melting the ice from below. Tracing meltwater pathways from ice shelves is important for identifying the regions most affected by the increased input of this water type. Here, optimum multiparameter analysis is used to deduce glacial meltwater fractions from water mass characteristics (temperature, salinity, and dissolved oxygen concentrations), collected during a ship-based campaign in the eastern Amundsen Sea in February–March 2014. Using a one-dimensional ocean model, processes such as variability in the characteristics of the source water masses on shelf and biological productivity/respiration are shown to affect the calculated apparent meltwater fractions. These processes can result in a false meltwater signature, creating misleading apparent glacial meltwater pathways. An alternative glacial meltwater calculation is suggested, using a pseudo–Circumpolar Deep Water endpoint and using an artificial increase in uncertainty of the dissolved oxygen measurements. The pseudo–Circumpolar Deep Water characteristics are affected by the under ice shelf bathymetry. The glacial meltwater fractions reveal a pathway for 2014 meltwater leading to the west of Pine Island Ice Shelf, along the coastline.

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Inversion of IceBridge gravity data for continental shelf bathymetry beneath the Larsen Ice Shelf, Antarctica

Journal of Glaciology ◽

10.3189/2012jog11j033 ◽

2012 ◽

Vol 58 (209) ◽

pp. 540-552 ◽

Cited By ~ 27

Author(s):

James R. Cochran ◽

Robin E. Bell

Keyword(s):

Continental Shelf ◽

Ocean Circulation ◽

Gravity Data ◽

Radar Data ◽

Ice Shelf ◽

Ice Shelves ◽

Free Air ◽

Free Air Gravity ◽

Larsen Ice Shelf ◽

Possible Cause

AbstractA possible cause for accelerated thinning and break-up of floating marine ice shelves is warming of the water in the cavity below the ice shelf. Accurate bathymetry beneath large ice shelves is crucial for developing models of the ocean circulation in the sub-ice cavities. A grid of free-air gravity data over the floating Larsen C ice shelf collected during the IceBridge 2009 Antarctic campaign was utilized to develop the first bathymetry model of the underlying continental shelf. Independent control on the continental shelf geologic structures from marine surveys was used to constrain the inversion. Depths on the continental shelf beneath the ice shelf estimated from the inversion generally range from about 350 to 650 m, but vary from <300 to >1000 m. Localized overdeepenings, 20-30 km long and 900-1000 m deep, are located in inlets just seaward of the grounding line. Submarine valleys extending seaward from the overdeepenings coalesce into two broad troughs that extend to the seaward limit of the ice shelf and appear to extend to the edge of the continental shelf. The troughs are generally at a depth of 550-700 m although the southernmost mapped trough deepens to over 1000 m near the edge of the ice shelf just south of 68° S. The combination of the newly determined bathymetry with published ice-draft determinations based on laser altimetry and radar data defines the geometry of the water-filled cavity. These newly imaged troughs provide a conduit for water to traverse the continental shelf and interact with the overlying Larsen C ice shelf and the grounding lines of the outlet glaciers.

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Warm water flow and mixing beneath Thwaites Glacier ice shelf, West Antarctica

10.5194/egusphere-egu2020-19934 ◽

2020 ◽

Author(s):

Anna Wåhlin ◽

Bastien Queste ◽

Alastair Graham ◽

Kelly Hogan ◽

Lars Boehme ◽

...

Keyword(s):

Water Flow ◽

Deep Water ◽

Autonomous Underwater Vehicle ◽

Warm Water ◽

Ice Shelf ◽

Mixing Processes ◽

Spatial Gradients ◽

West Antarctic ◽

Warm Deep Water ◽

Glacier Ice

The fate of the West Antarctic Ice Sheet is the largest remaining uncertainty in predicting sea-level rise through the next century, and its most vulnerable and rapidly changing outlet is Thwaites Glacier . Because the seabed slope under the glacier is retrograde (downhill inland), ice discharge from Thwaites Glacier is potentially unstable to melting of the underside of its floating ice shelf and grounding line retreat, both of which are enhanced by warm ocean water circulating underneath the ice shelf. Recent observations show surprising spatial variations in melt rates, indicating significant knowledge gaps in our understanding of the processes at the base of the ice shelf. Here we present the first direct observations of ocean temperature, salinity, and oxygen underneath Thwaites ice shelf collected by an autonomous underwater vehicle, a Kongsberg Hugin AUV. These observations show that while the western part of Thwaites has outflow of meltwater-enriched circumpolar deep water found in the main trough leading to Thwaites, the deep water (> 1000 m) underneath the central part of the ice shelf is in connection with Pine Island Bay - a previously unknown westward branch of warm deep water flow. Mid-depth water (700 - 1000 m) enters the cavity from both sides of a buttressing point and large spatial gradients of salinity and temperature indicate that this is a region of active mixing processes. The observations challenge conceptual models of ice-ocean interactions at glacier grounding zones and identify a main buttressing point as a vulnerable region of change currently under attack by warm water inflow from all sides: a scenario that may lead to ungrounding and retreat more quickly than previously expected.

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