Exceptionally Warm and Prolonged Flow of Warm Deep Water Toward the Filchner‐Ronne Ice Shelf in 2017

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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Observed vulnerability of Filchner-Ronne Ice Shelf to wind-driven inflow of warm deep water

Nature Communications ◽

10.1038/ncomms12300 ◽

2016 ◽

Vol 7 (1) ◽

Cited By ~ 26

Author(s):

E. Darelius ◽

I. Fer ◽

K. W. Nicholls

Keyword(s):

Deep Water ◽

Ice Shelf ◽

Warm Deep Water

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Seasonal variability of ocean circulation near the Dotson Ice Shelf, Antarctica

10.21203/rs.3.rs-152149/v1 ◽

2021 ◽

Author(s):

Hee Won Yang ◽

Tae-Wan Kim ◽

Pierre Dutrieux ◽

A. K. Wahlin ◽

Adrian Jenkins ◽

...

Keyword(s):

Ocean Circulation ◽

Deep Water ◽

Warm Water ◽

Western Slope ◽

Eastern Slope ◽

Ice Shelf ◽

Significant Control ◽

West Antarctic ◽

Warm Deep Water ◽

Basal Melting

Abstract Recent rapid thinning of West Antarctic ice shelves are believed to be caused by intrusions of warm deep water that induce basal melting and seaward meltwater export. Dotson Ice Shelf has a high basal melt rate due to southward ocean heat transport in the Dotson-Getz Trough. We deployed three bottom-moored instrument arrays along the ice shelf calving front, obtaining continuous records of temperature, salinity, and current velocity throughout 2014 and 2015. Southward deep water velocities were highest along the eastern channel slope, while northward outflows of freshened ice shelf meltwater spread at intermediate depth above the western slope. Inflow warm water along the eastern slope into the sub-Dotson cavity reached a maximum of 182 MW m− 1 in Summer, 3.5 times larger than the autumn/winter values of 51 MW m− 1. The inflow correlated with the local ocean surface stress curl. At the western slope meltwater outflows were strongest during autumn and weakest in spring, following the warm influx along the eastern slope with a ~ 2–3 months delay. Ocean circulation near Dotson Ice Shelf, affected by sea ice distribution and wind, appears to be a significant control on the inflow of warm water and subsequent ice shelf melting on seasonal time-scales.

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Recent Changes in the Larsen-Weddell System

10.5194/egusphere-egu2020-603 ◽

2020 ◽

Author(s):

Ted Scambos

Keyword(s):

Deep Water ◽

Shear Zones ◽

Surface Melting ◽

Mean Flow ◽

Ice Shelf ◽

Central Pacific ◽

Ice Shelves ◽

Weddell Gyre ◽

Warm Deep Water ◽

Westerly Winds

A warming planet, and particularly the warming Pacific Ocean, has led to major changes in the Larsen-Weddell System. While somewhat less significant than those in the adjacent Amundsen-Bellingshausen Sea and its coastal ice, the changes are nonetheless dramatic indicators of a closely interconnected system, driven by increased westerly winds and their impact on surface melting and ice drift. The system very likely will see further major changes if warming continues through the 22nd Century.A warming trend in the central Pacific over the past ~80 years has induced air circulation changes over the Southern Ocean and Antarctic Peninsula. A rise in the mean speed of westerly-northwesterly winds across the northern Peninsula led to more frequent foehn events, which in turn increased surface melting on the eastern Peninsula ice shelves, and were responsible for reduced sea ice cover and more frequent shore leads on the eastern edges of the ice shelves. This likely led to greater sub-ice-shelf circulation, possibly including solar-warmed surface water (in summer) and modified Weddell Deep Water (mWDW). Around 1986, structural evidence in the form of more disrupted shear zones and increased rifting suggests that the Larsen A and B ice shelves began to thin and weaken. At this progressed, a combination of increased surface ponding and reduced backstress on the iceshelves led to a series of catastrophic break-ups due to hydrofracture, in 1995 (Larsen A shelf) and 2002 (Larsen B). &#160;More recently, thinning detected by altimetry on the northern Larsen C may have contributed to new fracturing and calving of a large iceberg there in 2016 (iceberg A-68), setting the ice shelf front significantly farther to the west than has previously been observed (since 1898).Looking forward, if the trend in increased westerly winds and Southern Annular Mode index continues, it is anticipated (modelled) that the large clockwise Weddell Gyre will increase in mean flow speed, and that warm deep water entrained from the Antarctic Circumpolar Current will more frequently mix with the mid- to deep ocean layers in the Weddell Gyre. One outcome of this is likely to be advection of warm deep water into the Ronne Ice Shelf cavity, dramatically increasing the heat available for sub-ice-shelf melting there and potentially changing ice sheet flux from the outlet glaciers significantly.

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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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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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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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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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Assessment of the structure and variability of Weddell Sea water masses in distinct ocean reanalysis products

Ocean Science ◽

10.5194/os-10-523-2014 ◽

2014 ◽

Vol 10 (3) ◽

pp. 523-546 ◽

Cited By ~ 10

Author(s):

T. S. Dotto ◽

R. Kerr ◽

M. M. Mata ◽

M. Azaneu ◽

I. Wainer ◽

...

Keyword(s):

Deep Water ◽

Sea Water ◽

Horizontal Resolution ◽

Weddell Sea ◽

Water Masses ◽

Ocean Reanalysis ◽

In Situ Data ◽

Ocean Data Assimilation ◽

Sea Bottom ◽

Warm Deep Water

Abstract. We assessed and evaluated the performance of five ocean reanalysis products in reproducing essential hydrographic properties and their associated temporal variability for the Weddell Sea, Antarctica. The products used in this assessment were ECMWF ORAS4 (European Centre for Medium-Range Weather Forecasts Ocean Reanalysis System 4), CFSR (Climate Forecast System Reanalysis), MyOcean UR025.4 (University of Reading), ECCO2 (Estimating the Circulation and Climate of the Ocean, Phase II) and SODA (Simple Ocean Data Assimilation). The present study focuses on the Weddell Sea deep layer, which is composed of the following three main water masses: Warm Deep Water (WDW), Weddell Sea Deep Water (WSDW) and Weddell Sea Bottom Water (WSBW). The MyOcean UR025.4 product provided the most accurate representation of the structure and thermohaline properties of the Weddell Sea water masses when compared with observations. All the ocean reanalysis products analyzed exhibited limited capabilities in representing the surface water masses in the Weddell Sea. The CFSR and ECCO2 products were not able to represent deep water masses with a neutral density ≥ 28.40 kg m−3, which was considered the WSBW's upper limit throughout the simulation period. The expected WDW warming was only reproduced by the SODA product, whereas the ECCO2 product was able to represent the trends in the WSDW's hydrographic properties. All the assessed ocean reanalyses were able to represent the decrease in the WSBW's density, except the SODA product in the inner Weddell Sea. Improvements in parameterization may have as much impact on the reanalyses assessed as improvements in horizontal resolution primarily because the Southern Ocean lacks in situ data, and the data that are currently available are summer-biased. The choice of the reanalysis product should be made carefully, taking into account the performance, the parameters of interest, and the type of physical processes to be evaluated.

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Oceanographic Observations from George VI Ice Shelf, Antarctic Peninsula

Annals of Glaciology ◽

10.1017/s0260305500002731 ◽

1982 ◽

Vol 3 ◽

pp. 178-183 ◽

Cited By ~ 17

Author(s):

P. Lennon ◽

J. Loynes ◽

J.G. Paren ◽

J.R. Potter

Keyword(s):

Sea Water ◽

Circulation Model ◽

Residual Flow ◽

Ice Melting ◽

Ice Shelf ◽

Linear Temperature ◽

Average Value ◽

Water Flows ◽

Warm Deep Water ◽

The World

Summer profiles of sea-water temperature, salinity and flow were obtained on George VI Ice Shelf near its northern ice front. At each depth, temperature salinity and density show little variation between sites. Their respective variation to 250 m depth confirms a linear temperature-salinity dependence. This is the first place in the world where observations confirm precisely the form of the T-S diagram predicted for fresh ice melting in sea-water. Both tidal and residual flow are small, except at the western margin of the ice front, where a strong outflow is concentrated immediately beneath the ice shelf. The observations lead to a simple circulation model for the ice-shelf regime. Warm Deep Water flows southwards into George VI Sound, replacing the colder water that spreads northwards in the surface outflow. Thermohaline exchanges beneath the ice shelf determine the salinity profile, which itself provides evidence of upwelling. Estimates can be made of the basal melt rate of the ice shelf. The rates vary from around 10 m a−1at the ice front to an average value for the ice shelf of order 1 m a−1. The average value is consistent with earlier estimates from surveys of ice-shelf strain.

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