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

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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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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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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The calving and drift of iceberg B-9 in the Ross Sea, Antarctica

Antarctic Science ◽

10.1017/s0954102090000335 ◽

1990 ◽

Vol 2 (3) ◽

pp. 243-257 ◽

Cited By ~ 40

Author(s):

Harry (J.R.) Keys ◽

S.S. Jacobs ◽

Don Barnett

Keyword(s):

Ocean Circulation ◽

Ross Sea ◽

Maximum Velocity ◽

Open Water ◽

Ice Thickness ◽

Ice Shelf ◽

East Central ◽

North West ◽

Ross Ice Shelf ◽

Subsurface Current

Major rifts is the Ross Ice Shelf controlled the October 1987 calving of the 154 × 35 km “B-9” iceberg, one of the longest on record. The 2000 km, 22 month drift of this iceberg and the quite different tracks of smaller bergs that calved with it have extended our understanding of the ocean circulation in the Ross Sea. B-9 initially moved north-west for seven months until deflected southward by a subsurface current which caused it to collide with the ice shelf in August 1988. It then completed a 100 km-radius gyre on the east-central shelf before resuming its north-westerly drift. Based upon weekly locations, derived from NOAA-10 and DMSP satellite and more frequent ARGOS data buoy positions, B-9 moved at an average speed of 2.4 km day−1 over the continental shelf. It was not grounded there at any time, but cast a large shadow of open water or reduced ice thickness during the austral winters. B-9 was captured by the continental slope current in May 1989, and attained a maximum velocity of 13 km day−1 before breaking into three pieces north of Cape Adare in early August 1989.

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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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Ice shelf basal melt rates from a high-resolution digital elevation model (DEM) record for Pine Island Glacier, Antarctica

The Cryosphere ◽

10.5194/tc-13-2633-2019 ◽

2019 ◽

Vol 13 (10) ◽

pp. 2633-2656 ◽

Cited By ~ 5

Author(s):

David E. Shean ◽

Ian R. Joughin ◽

Pierre Dutrieux ◽

Benjamin E. Smith ◽

Etienne Berthier

Keyword(s):

High Resolution ◽

Ocean Circulation ◽

Heat Content ◽

Elevation Change ◽

Ice Shelf ◽

Amundsen Sea ◽

The North ◽

Digital Elevation ◽

Grounding Line ◽

Basal Melting

Abstract. Ocean-induced basal melting is responsible for much of the Amundsen Sea Embayment ice loss in recent decades, but the total magnitude and spatiotemporal evolution of this melt is poorly constrained. To address this problem, we generated a record of high-resolution digital elevation models (DEMs) for Pine Island Glacier (PIG) using commercial sub-meter satellite stereo imagery and integrated additional 2002–2015 DEM and altimetry data. We implemented a Lagrangian elevation change (Dh∕Dt) framework to estimate ice shelf basal melt rates at 32–256 m resolution. We describe this methodology and consider basal melt rates and elevation change over the PIG ice shelf and lower catchment from 2008 to 2015. We document the evolution of Eulerian elevation change (dh∕dt) and upstream propagation of thinning signals following the end of rapid grounding line retreat around 2010. Mean full-shelf basal melt rates for the 2008–2015 period were ∼82–93 Gt yr−1, with ∼200–250 m yr−1 basal melt rates within large channels near the grounding line, ∼10–30 m yr−1 over the main shelf, and ∼0–10 m yr−1 over the North shelf and South shelf, with the notable exception of a small area with rates of ∼50–100 m yr−1 near the grounding line of a fast-flowing tributary on the South shelf. The observed basal melt rates show excellent agreement with, and provide context for, in situ basal melt-rate observations. We also document the relative melt rates for kilometer-scale basal channels and keels at different locations on the ice shelf and consider implications for ocean circulation and heat content. These methods and results offer new indirect observations of ice–ocean interaction and constraints on the processes driving sub-shelf melting beneath vulnerable ice shelves in West Antarctica.

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

Nature Geoscience ◽

10.1038/ngeo1188 ◽

2011 ◽

Vol 4 (8) ◽

pp. 519-523 ◽

Cited By ~ 380

Author(s):

Stanley S. Jacobs ◽

Adrian Jenkins ◽

Claudia F. Giulivi ◽

Pierre Dutrieux

Keyword(s):

Ocean Circulation ◽

Ice Shelf ◽

Glacier Ice

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Experimental design for three interrelated Marine Ice-Sheet and Ocean Model Intercomparison Projects

Geoscientific Model Development Discussions ◽

10.5194/gmdd-8-9859-2015 ◽

2015 ◽

Vol 8 (11) ◽

pp. 9859-9924 ◽

Cited By ~ 5

Author(s):

X. S. Asay-Davis ◽

S. L. Cornford ◽

G. Durand ◽

B. K. Galton-Fenzi ◽

R. M. Gladstone ◽

...

Keyword(s):

Ocean Circulation ◽

Ice Sheet ◽

Ocean Model ◽

Model Verification ◽

Second Phase ◽

Model Intercomparison ◽

Ice Shelf ◽

Amundsen Sea ◽

Ice Dynamics ◽

Future Projections

Abstract. Coupled ice sheet-ocean models capable of simulating moving grounding lines are just becoming available. Such models have a broad range of potential applications in studying the dynamics of marine ice sheets and tidewater glaciers, from process studies to future projections of ice mass loss and sea level rise. The Marine Ice Sheet-Ocean Model Intercomparison Project (MISOMIP) is a community effort aimed at designing and coordinating a series of model intercomparison projects (MIPs) for model evaluation in idealized setups, model verification based on observations, and future projections for key regions in the West Antarctic Ice Sheet (WAIS). Here we describe computational experiments constituting three interrelated MIPs for marine ice sheet models and regional ocean circulation models incorporating ice shelf cavities. These consist of ice sheet experiments under the Marine Ice Sheet MIP third phase (MISMIP+), ocean experiments under the ice shelf-ocean MIP second phase (ISOMIP+) and coupled ice sheet-ocean experiments under the MISOMIP first phase (MISOMIP1). All three MIPs use a shared domain with idealized bedrock topography and forcing, allowing the coupled simulations (MISOMIP1) to be compared directly to the individual component simulations (MISMIP+ and ISOMIP+). The experiments, which have qualitative similarities to Pine Island Glacier Ice Shelf and the adjacent region of the Amundsen Sea, are designed to explore the effects of changes in ocean conditions, specifically the temperature at depth, on basal melting and ice dynamics. In future work, differences between model results will form the basis for evaluation of the participating models.

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Inflow of Warm Circumpolar Deep Water in the Central Amundsen Shelf*

Journal of Physical Oceanography ◽

10.1175/2010jpo4431.1 ◽

2010 ◽

Vol 40 (6) ◽

pp. 1427-1434 ◽

Cited By ~ 84

Author(s):

A. K. Wåhlin ◽

X. Yuan ◽

G. Björk ◽

C. Nohr

Keyword(s):

Deep Water ◽

Water Mass ◽

Acoustic Doppler Current Profiler ◽

Intermediate Water ◽

Amundsen Sea ◽

Ice Shelves ◽

Circumpolar Deep Water ◽

Ice Melt ◽

West Antarctic ◽

Glacier Ice

Abstract The thinning and acceleration of the West Antarctic Ice Sheet has been attributed to basal melting induced by intrusions of relatively warm salty water across the continental shelf. A hydrographic section including lowered acoustic Doppler current profiler measurements showing such an inflow in the channel leading to the Getz and Dotson Ice Shelves is presented here. The flow rate was 0.3–0.4 Sv (1 Sv ≡ 106 m3 s−1), and the subsurface heat loss was estimated to be 1.2–1.6 TW. Assuming that the inflow persists throughout the year, it corresponds to an ice melt of 110–130 km3 yr−1, which exceeds recent estimates of the net ice glacier ice volume loss in the Amundsen Sea. The results also show a 100–150-m-thick intermediate water mass consisting of Circumpolar Deep Water that has been modified (cooled and freshened) by subsurface melting of ice shelves and/or icebergs. This water mass has not previously been reported in the region, possibly because of the paucity of historical data.

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Experimental design for three interrelated marine ice sheet and ocean model intercomparison projects: MISMIP v. 3 (MISMIP +), ISOMIP v. 2 (ISOMIP +) and MISOMIP v. 1 (MISOMIP1)

Geoscientific Model Development ◽

10.5194/gmd-9-2471-2016 ◽

2016 ◽

Vol 9 (7) ◽

pp. 2471-2497 ◽

Cited By ~ 52

Author(s):

Xylar S. Asay-Davis ◽

Stephen L. Cornford ◽

Gaël Durand ◽

Benjamin K. Galton-Fenzi ◽

Rupert M. Gladstone ◽

...

Keyword(s):

Ocean Circulation ◽

Ice Sheet ◽

Ocean Model ◽

Model Verification ◽

Second Phase ◽

Model Intercomparison ◽

Ice Shelf ◽

Amundsen Sea ◽

Ice Dynamics ◽

Future Projections

Abstract. Coupled ice sheet–ocean models capable of simulating moving grounding lines are just becoming available. Such models have a broad range of potential applications in studying the dynamics of marine ice sheets and tidewater glaciers, from process studies to future projections of ice mass loss and sea level rise. The Marine Ice Sheet–Ocean Model Intercomparison Project (MISOMIP) is a community effort aimed at designing and coordinating a series of model intercomparison projects (MIPs) for model evaluation in idealized setups, model verification based on observations, and future projections for key regions of the West Antarctic Ice Sheet (WAIS). Here we describe computational experiments constituting three interrelated MIPs for marine ice sheet models and regional ocean circulation models incorporating ice shelf cavities. These consist of ice sheet experiments under the Marine Ice Sheet MIP third phase (MISMIP+), ocean experiments under the Ice Shelf-Ocean MIP second phase (ISOMIP+) and coupled ice sheet–ocean experiments under the MISOMIP first phase (MISOMIP1). All three MIPs use a shared domain with idealized bedrock topography and forcing, allowing the coupled simulations (MISOMIP1) to be compared directly to the individual component simulations (MISMIP+ and ISOMIP+). The experiments, which have qualitative similarities to Pine Island Glacier Ice Shelf and the adjacent region of the Amundsen Sea, are designed to explore the effects of changes in ocean conditions, specifically the temperature at depth, on basal melting and ice dynamics. In future work, differences between model results will form the basis for the evaluation of the participating models.

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