Cross-Slope Observations in the Bellingshausen Sea, Southern Ocean

2020 ◽  
Author(s):  
Ria Oelerich ◽  
Karen J. Heywood ◽  
Gillian M. Damerell ◽  
Andrew F. Thompson
Keyword(s):  
Current System ◽  
Amundsen Sea ◽  
Ice Shelves ◽  
West Antarctic ◽  
Bellingshausen Sea ◽  
Average Current ◽  
Adcp Data ◽  
Basal Melting ◽  
Antarctic Slope Current ◽  
The Antarctic

<p>The Bellingshausen Sea, located between the West Antarctic Peninsula and the Amundsen Sea, is poorly observed, compared with its neighbours. The Antarctic Slope Front (ASF), that rings the continental slope of Antarctica, supports a westward current (the Antarctic Slope Current). The structure and variability of this current affect exchange processes close to Antarctica such as the transport of warm Circumpolar Deep Water onto the Antarctic continental shelf. This water mass is responsible for the transport of heat across the shelf and therefore the basal melting of ice shelves. Due to the lack of observations, it is still unclear if the ASF even exists in the Bellingshausen Sea or if there are other processes moderating the transport of warm water onto the shelf.</p><p>We present ship-based and glider-based CTD data collected in 2007 and 2019, which in total provide 7 cross-slope sections in the Bellingshausen Sea. Geostrophic velocities are referenced to lowered ADCP data, shipboard ADCP data and the Dive Average Current. Cumulative transports show remarkable differences between the years 2007 and 2019. The sections of 2007 provide cumulative transports of up to 3.5 Sv eastward. In contrast, the sections in 2019 have cumulative transports up to 2 Sv westward. The sections from 2007 and 2019 are in very similar locations, indicating a temporal change rather than a spatial change.</p><p>We compare the cross-slope sections from the observations with sections from the NEMO 1/12 ° model output. A time series of cumulative transports from the model, covering the years from 2000 to 2010, allows us to identify seasonality and interannual variability in this current system.</p>

scholarly journals The Antarctic Coastal Current in the Bellingshausen Sea

2021 ◽  
Vol 15 (9) ◽  
pp. 4179-4199
Author(s):  
Ryan Schubert ◽  
Andrew F. Thompson ◽  
Kevin Speer ◽  
Lena Schulze Chretien ◽  
Yana Bebieva
Keyword(s):  
Coastal Current ◽  
Boundary Current ◽  
The West ◽  
Amundsen Sea ◽  
West Antarctic Ice Sheet ◽  
Ice Shelves ◽  
West Antarctic ◽  
Bellingshausen Sea ◽  
Basal Melting ◽  
The Antarctic

Abstract. The ice shelves of the West Antarctic Ice Sheet experience basal melting induced by underlying warm, salty Circumpolar Deep Water. Basal meltwater, along with runoff from ice sheets, supplies fresh buoyant water to a circulation feature near the coast, the Antarctic Coastal Current (AACC). The formation, structure, and coherence of the AACC has been well documented along the West Antarctic Peninsula (WAP). Observations from instrumented seals collected in the Bellingshausen Sea offer extensive hydrographic coverage throughout the year, providing evidence of the continuation of the westward flowing AACC from the WAP towards the Amundsen Sea. The observations reported here demonstrate that the coastal boundary current enters the eastern Bellingshausen Sea from the WAP and flows westward along the face of multiple ice shelves, including the westernmost Abbot Ice Shelf. The presence of the AACC in the western Bellingshausen Sea has implications for the export of water properties into the eastern Amundsen Sea, which we suggest may occur through multiple pathways, either along the coast or along the continental shelf break. The temperature, salinity, and density structure of the current indicates an increase in baroclinic transport as the AACC flows from the east to the west, and as it entrains meltwater from the ice shelves in the Bellingshausen Sea. The AACC acts as a mechanism to transport meltwater out of the Bellingshausen Sea and into the Amundsen and Ross seas, with the potential to impact, respectively, basal melt rates and bottom water formation in these regions.

scholarly journals The Antarctic Coastal Current in the Bellingshausen Sea

2021 ◽  
Author(s):  
Ryan Schubert ◽  
Andrew F. Thompson ◽  
Kevin Speer ◽  
Lena Schulze Chretien ◽  
Yana Bebieva
Keyword(s):  
Coastal Current ◽  
Boundary Current ◽  
The West ◽  
Amundsen Sea ◽  
Ice Shelves ◽  
West Antarctic ◽  
Run Off ◽  
Bellingshausen Sea ◽  
Basal Melting ◽  
The Antarctic

Abstract. The ice shelves of the West Antarctic Ice Sheet experience basal melting induced by underlying warm, salty Circumpolar Deep Water. Basal meltwater, along with run-off from ice sheets, supplies fresh buoyant water to a circulation feature near the coast, the Antarctic Coastal Current (AACC). The formation, structure and coherence of the AACC has been well documented along the West Antarctic Peninsula (WAP). Observations from instrumented seals collected in the Bellingshausen Sea offer extensive hydrographic coverage throughout the year, providing evidence of the continuation of the westward flowing AACC from the WAP towards the Amundsen Sea. The observations reported here demonstrate that the coastal boundary current enters the eastern Bellingshausen Sea from the WAP, flows westward along the face of multiple ice shelves, including the westernmost Abbot Ice Shelf. The presence of the AACC in the western Bellingshausen has implications for the export of water properties into the eastern Amundsen Sea, which we suggest may occur through multiple pathways either along the coast or along the continental shelf break. The temperature, salinity and density structure of the current indicates an increase in baroclinic transport as the AACC flows from the east to the west and as it entrains meltwater from the ice shelves in the Bellingshausen Sea. The AACC acts as a mechanism to transport meltwater out of the Bellingshausen Sea and into the Amundsen and Ross Seas, with the potential to impact basal melt rates and bottom water formation.

scholarly journals Melting and freezing under Antarctic ice shelves from a combination of ice-sheet modelling and observations

2017 ◽  
Vol 63 (240) ◽  
pp. 731-744 ◽  
Author(s):  
JORGE BERNALES ◽  
IRINA ROGOZHINA ◽  
MAIK THOMAS
Keyword(s):  
Mass Balance ◽  
Ice Sheet ◽  
Model Parameters ◽  
Ice Shelf ◽  
Ice Shelves ◽  
Continental Scale ◽  
Model Set ◽  
Set Up ◽  
Basal Melting ◽  
The Antarctic

ABSTRACTIce-shelf basal melting is the largest contributor to the negative mass balance of the Antarctic ice sheet. However, current implementations of ice/ocean interactions in ice-sheet models disagree with the distribution of sub-shelf melt and freezing rates revealed by recent observational studies. Here we present a novel combination of a continental-scale ice flow model and a calibration technique to derive the spatial distribution of basal melting and freezing rates for the whole Antarctic ice-shelf system. The modelled ice-sheet equilibrium state is evaluated against topographic and velocity observations. Our high-resolution (10-km spacing) simulation predicts an equilibrium ice-shelf basal mass balance of −1648.7 Gt a−1 that increases to −1917.0 Gt a−1 when the observed ice-shelf thinning rates are taken into account. Our estimates reproduce the complexity of the basal mass balance of Antarctic ice shelves, providing a reference for parameterisations of sub-shelf ocean/ice interactions in continental ice-sheet models. We perform a sensitivity analysis to assess the effects of variations in the model set-up, showing that the retrieved estimates of basal melting and freezing rates are largely insensitive to changes in the internal model parameters, but respond strongly to a reduction of model resolution and the uncertainty in the input 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.

Some future projections from coupling the U.K. Earth System Model to the Antarctic ice sheets

2021 ◽  
Author(s):  
Anthony Siahaan
Keyword(s):  
Radiative Forcing ◽  
Climate Model ◽  
Ice Sheet ◽  
Mass Gain ◽  
Ice Shelves ◽  
Positive Effects ◽  
Basal Melting ◽  
The Antarctic ◽  
The Impact ◽  
Increasing Precipitation

<p>A UKESM climate model which is coupled annually to the BISICLES ice sheet model to enable a two way interactions in Antarctica has been developed <br>and run through a small ensemble of four SSP1-1.9 & SSP5-8.5 scenario members. Under the extreme anthropogenic forcing, all the initial condition <br>ensemble members develop strong melting under the cold & large Ross and Filchner-Ronne ice-shelves, where it starts after the first half of simulation <br>period for the former and in the last decade of the run for the latter. Despite that, during the 85 years timescale of these scenario runs, the stronger radiative forcing has positive effects on the ice-sheet mass gain through increasing precipitation on grounded ice regions which offsets the impact of basal melting in ice discharge across the grounding lines.</p>

scholarly journals initMIP-Antarctica: an ice sheet model initialization experiment of ISMIP6

2019 ◽  
Vol 13 (5) ◽  
pp. 1441-1471 ◽  
Author(s):  
Hélène Seroussi ◽  
Sophie Nowicki ◽  
Erika Simon ◽  
Ayako Abe-Ouchi ◽  
Torsten Albrecht ◽  
...  
Keyword(s):  
Initial Conditions ◽  
Ice Sheet ◽  
Model Intercomparison ◽  
Surface Mass ◽  
Ice Shelves ◽  
External Forcings ◽  
Intercomparison Project ◽  
Model Initialization ◽  
Basal Melting ◽  
The Antarctic

Abstract. Ice sheet numerical modeling is an important tool to estimate the dynamic contribution of the Antarctic ice sheet to sea level rise over the coming centuries. The influence of initial conditions on ice sheet model simulations, however, is still unclear. To better understand this influence, an initial state intercomparison exercise (initMIP) has been developed to compare, evaluate, and improve initialization procedures and estimate their impact on century-scale simulations. initMIP is the first set of experiments of the Ice Sheet Model Intercomparison Project for CMIP6 (ISMIP6), which is the primary Coupled Model Intercomparison Project Phase 6 (CMIP6) activity focusing on the Greenland and Antarctic ice sheets. Following initMIP-Greenland, initMIP-Antarctica has been designed to explore uncertainties associated with model initialization and spin-up and to evaluate the impact of changes in external forcings. Starting from the state of the Antarctic ice sheet at the end of the initialization procedure, three forward experiments are each run for 100 years: a control run, a run with a surface mass balance anomaly, and a run with a basal melting anomaly beneath floating ice. This study presents the results of initMIP-Antarctica from 25 simulations performed by 16 international modeling groups. The submitted results use different initial conditions and initialization methods, as well as ice flow model parameters and reference external forcings. We find a good agreement among model responses to the surface mass balance anomaly but large variations in responses to the basal melting anomaly. These variations can be attributed to differences in the extent of ice shelves and their upstream tributaries, the numerical treatment of grounding line, and the initial ocean conditions applied, suggesting that ongoing efforts to better represent ice shelves in continental-scale models should continue.

scholarly journals Modelling the long-term response of the Antarctic ice sheet to global warming

1998 ◽  
Vol 27 ◽  
pp. 161-168 ◽  
Author(s):  
Roland C. Warner ◽  
W.Κ. Budd
Keyword(s):  
Global Warming ◽  
Mass Loss ◽  
Ice Sheet ◽  
Ice Shelf ◽  
Antarctic Ice Sheet ◽  
Ice Shelves ◽  
Basal Melting ◽  
The Antarctic ◽  
Term Response

The primary effects of global warming on the Antarctic ice sheet can involve increases in surface melt for limited areas at lower elevations, increases in net accumulation, and increased basal melting under floating ice. For moderate global wanning, resulting in ocean temperature increases of a few °C, the large- increase in basal melting can become the dominant factor in the long-term response of the ice sheet. The results from ice-sheet modelling show that the increased basal melt rates lead to a reduction of the ice shelves, increased strain rates and flow at the grounding lines, then thinning and floating of the marine ice sheets, with consequential further basal melting. The mass loss from basal melting is counteracted to some extent by the increased accumulation, but in the long term the area of ice cover decreases, particularly in West Antarctica, and the mass loss can dominate. The ice-sheet ice-shelf model of Budd and others (1994) with 20 km resolution has been modified and used to carry out a number of sensitivity studies of the long-term response of the ice sheet to prescribed amounts of global warming. The changes in the ice sheet are computed out to near-equilibrium, but most of the changes take place with in the first lew thousand years. For a global mean temperature increase of 3°C with an ice-shelf basal melt rate of 5 m a−1 the ice shelves disappear with in the first few hundred years, and the marine-based parts of the ice sheet thin and retreat. By 2000 years the West Antarctic region is reduced to a number of small, isolated ice caps based on the bedrock regions which are near or above sea level. This allows the warmer surface ocean water to circulate through the archipelago in summer, causing a large change to the local climate of the region.

scholarly journals Viscous and elastic buoyancy stresses as drivers of ice-shelf calving

2020 ◽  
Vol 66 (258) ◽  
pp. 643-657 ◽  
Author(s):  
Cyrille Mosbeux ◽  
Till J. W. Wagner ◽  
Maya K. Becker ◽  
Helen A. Fricker
Keyword(s):  
Ice Sheet ◽  
Elastic Model ◽  
Ice Shelf ◽  
Ice Shelves ◽  
Bending Stresses ◽  
Iceberg Calving ◽  
Basal Melting ◽  
The Antarctic ◽  
The Impact ◽  
Maximum Stresses

AbstractThe Antarctic Ice Sheet loses mass via its ice shelves predominantly through two processes: basal melting and iceberg calving. Iceberg calving is episodic and infrequent, and not well parameterized in ice-sheet models. Here, we investigate the impact of hydrostatic forces on calving. We develop two-dimensional elastic and viscous numerical frameworks to model the ‘footloose’ calving mechanism. This mechanism is triggered by submerged ice protrusions at the ice front, which induce unbalanced buoyancy forces that can lead to fracturing. We compare the results to identify the different roles that viscous and elastic deformations play in setting the rate and magnitude of calving events. Our results show that, although the bending stresses in both frameworks share some characteristics, their differences have important implications for modeling the calving process. In particular, the elastic model predicts that maximum stresses arise farther from the ice front than in the viscous model, leading to larger calving events. We also find that the elastic model would likely lead to more frequent events than the viscous one. Our work provides a theoretical framework for the development of a better understanding of the physical processes that govern glacier and ice-shelf calving cycles.

scholarly journals Impact of transient increases in atmospheric CO2 on the accumulation and mass balance of the Antarctic ice sheet

1997 ◽  
Vol 25 ◽  
pp. 137-144 ◽  
Author(s):  
Siobhan P. O’Farrell ◽  
John L. McGregor ◽  
Leon D. Rotstayn ◽  
William F. Budd ◽  
Christopher Zweck ◽  
...  
Keyword(s):  
Sea Level Rise ◽  
Sea Level ◽  
Ice Sheet ◽  
Coupled Model ◽  
Negative Contribution ◽  
Antarctic Ice Sheet ◽  
Ice Shelves ◽  
Basal Melting ◽  
Main Effects ◽  
The Antarctic

The response of the Antarctic ice sheet to climate change over the next 500 years is calculated using the output of a transient-coupled ocean-atmosphere simulation assuming the atmospheric CO2value increases up to three times present levels. The main effects on the ice sheet on this time-scale include increasing rates of accumulation, minimal surface melting, and basal melting of ice shelves. A semi-Lagrangian transport scheme for moisture was used to improve the model’s ability to represent realistic rates of accumulation under present-day conditions, and thereby increase confidence in the anomalies calculated under a warmer climate. The response of the Antarctic ice sheet to the warming is increased accumulation inland, offset by loss from basal melting from the floating ice, and increased ice flow near the grounding line. The preliminary results of this study show that the change to the ice-sheet balance for the transient-coupled model forcing amounted to a minimal sea-level contribution in the next century, but a net positive sea-level rise of 0.21 m by 500 years. This new result supercedes earlier results that showed the Antarctic ice sheet made a net negative contribution to sea-level rise over the next century. However, the amplitude of the sea-level rise is still dominated In the much larger contributions expected from thermal expansion of the ocean of 0.25 m for 100 years and 1.00 m for 500 years.

scholarly journals Variability of the Antarctic Slope Current System in the Northwestern Weddell Sea

2017 ◽  
Vol 47 (12) ◽  
pp. 2977-2997 ◽  
Author(s):  
Marina Azaneu ◽  
Karen J. Heywood ◽  
Bastien Y. Queste ◽  
Andrew F. Thompson
Keyword(s):  
Current System ◽  
Water Layer ◽  
Bottom Layer ◽  
Weddell Sea ◽  
The South ◽  
Orkney Islands ◽  
Dense Water ◽  
South Orkney Islands ◽  
Antarctic Slope Current ◽  
The Antarctic

AbstractThe dense water outflow from the Antarctic continental shelf is closely associated with the strength and position of the Antarctic Slope Front. This study explores the short-term and spatial variability of the Antarctic Slope Front system and the mechanisms that regulate cross-slope exchange using highly temporally and spatially resolved measurements from three ocean gliders deployed in 2012. The 22 sections along the eastern Antarctic Peninsula and west of the South Orkney Islands are grouped regionally and composited by isobaths. There is consistency in the front position around the Powell Basin, varying mostly between the 500- and 800-m isobaths. In most of the study area the flow is bottom intensified. The along-slope transport of the Antarctic Slope Current (upper 1000 m) varies between 0.2 and 5.9 Sv (1 Sv ≡ 106 m3 s−1) and does not exhibit a regional pattern. The magnitude of the velocity field shows substantial variability, up to twice its mean value. Higher eddy kinetic energy (0.003 m2 s−2) is observed in sections with dense water, possibly because of baroclinic instabilities in the bottom layer. Distributions of potential vorticity show an increase toward the shelf along isopycnals and also in the dense water layer. Glider sections located west of the South Orkney Islands indicate a northward direction of the flow associated with the Weddell Front, which differs from previous estimates of the mean circulation. This study provides some of the first observational confirmation of the high-frequency variability associated with an active eddy field that has been suggested by recent numerical simulations in this region.

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