scholarly journals Pan–ice-sheet glacier terminus change in East Antarctica reveals sensitivity of Wilkes Land to sea-ice changes

2016 ◽  
Vol 2 (5) ◽  
pp. e1501350 ◽  
Author(s):  
Bertie W. J. Miles ◽  
Chris R. Stokes ◽  
Stewart S. R. Jamieson
Keyword(s):  
Sea Ice ◽  
Drainage Basin ◽  
Ice Sheet ◽  
East Antarctica ◽  
Position Change ◽  
Outlet Glacier ◽  
Ocean Stratification ◽  
Glacier Terminus ◽  
Warm Deep Water ◽  
Wilkes Land

The dynamics of ocean-terminating outlet glaciers are an important component of ice-sheet mass balance. Using satellite imagery for the past 40 years, we compile an approximately decadal record of outlet-glacier terminus position change around the entire East Antarctic Ice Sheet (EAIS) marine margin. We find that most outlet glaciers retreated during the period 1974–1990, before switching to advance in every drainage basin during the two most recent periods, 1990–2000 and 2000–2012. The only exception to this trend was in Wilkes Land, where the majority of glaciers (74%) retreated between 2000 and 2012. We hypothesize that this anomalous retreat is linked to a reduction in sea ice and associated impacts on ocean stratification, which increases the incursion of warm deep water toward glacier termini. Because Wilkes Land overlies a large marine basin, it raises the possibility of a future sea level contribution from this sector of East Antarctica.

scholarly journals Simultaneous disintegration of outlet glaciers in Porpoise Bay (Wilkes Land), East Antarctica, and the long-term speed-up of Holmes Glacier

2016 ◽  
Author(s):  
B. W. J. Miles ◽  
C. R. Stokes ◽  
S. S. R. Jamieson
Keyword(s):  
Sea Ice ◽  
East Antarctica ◽  
High Temporal Resolution ◽  
Ice Flow ◽  
Outlet Glacier ◽  
Ice Shelves ◽  
Glacier Terminus ◽  
Wilkes Land ◽  
Speed Up

Abstract. The floating ice shelves and glacier tongues which fringe the Antarctic continent are important because they help buttress ice flow from the ice sheet interior. Dynamic feedbacks associated with glacier calving have the potential to reduce buttressing and subsequently increase ice flow into the ocean. However, there are few high temporal resolution studies on glacier calving, especially in East Antarctica. Here we use remote sensing to investigate monthly glacier terminus change across six marine-terminating outlet glaciers in Porpoise Bay (−76° S, 128° E), Wilkes Land (East Antarctica), between November 2002 and March 2012. This reveals a large simultaneous calving event in January 2007, resulting in a total of ~ 2900 km2 of ice being removed from glacier tongues. Our observations suggest that sea-ice must be removed from glacier termini for any form of calving to take place, and we link this major calving event to a rapid break-up of the multi-year sea-ice which usually occupies Porpoise Bay. Using sea-ice concentrations as a proxy for glacier calving, and by analysing available satellite imagery stretching back to 1963, we reconstruct the long-term calving activity of the largest glacier in Porpoise Bay: Holmes (West) Glacier. This reveals that its present-day velocity (~ 1450 m a−1) is approximately 50 % faster than between 1963 and 1973 (~ 900 m a−1). We also observed the start of a large calving event in Porpoise Bay in March 2016 that is consistent with our reconstructions of the periodicity of major calving events. These results highlight the importance of sea-ice in modulating outlet glacier calving and velocity in East Antarctica.

scholarly journals Sub-decadal variations in outlet glacier terminus positions in Victoria Land, Oates Land and George V Land, East Antarctica (1972–2013)

2017 ◽  
Vol 29 (5) ◽  
pp. 468-483 ◽  
Author(s):  
A.M. Lovell ◽  
C.R. Stokes ◽  
S.S.R. Jamieson
Keyword(s):  
Antarctic Peninsula ◽  
East Antarctica ◽  
West Antarctica ◽  
Position Change ◽  
Outlet Glacier ◽  
Glacier Terminus ◽  
Victoria Land ◽  
Decadal Scale ◽  
Decadal Variations ◽  
The Antarctic

AbstractRecent work has highlighted the sensitivity of marine-terminating glaciers to decadal-scale changes in the ocean–climate system in parts of East Antarctica. However, compared to Greenland, West Antarctica and the Antarctic Peninsula, little is known about recent glacier change and potential cause(s), with several regions yet to be studied in detail. In this paper, we map the terminus positions of 135 glaciers along the coastline of Victoria Land, Oates Land and George V Land from 1972–2013 at a higher temporal resolution (sub-decadal intervals) than in previous research. These three regions span a range of climatic and oceanic conditions and contain a variety of glacier types. Overall, from 1972–2013, 36% of glaciers advanced, 25% retreated and the remainder showed no discernible change. On sub-decadal timescales, there were no clear trends in glacier terminus position change. However, marine-terminating glaciers experienced larger terminus position changes compared with terrestrial glaciers, and those with an unconstrained floating tongue exhibited the largest variations. We conclude that, unlike in Greenland, West Antarctica and the Antarctic Peninsula, there is no clear glacier retreat in the study area and that most of the variations are more closely linked to glacier size and terminus type.

scholarly journals Oligocene–Miocene paleoceanography off the Wilkes Land Margin (East Antarctica) based on organic-walled dinoflagellate cysts

2017 ◽  
Author(s):  
Peter K. Bijl ◽  
Alexander J. P. Houben ◽  
Julian D. Hartman ◽  
Jörg Pross ◽  
Ariadna Salabarnada ◽  
...  
Keyword(s):  
Sea Ice ◽  
Ice Sheet ◽  
Critical Factor ◽  
East Antarctica ◽  
Atmospheric Co2 ◽  
Time Intervals ◽  
Integrated Ocean Drilling Program ◽  
Co2 Concentrations ◽  
Wilkes Land ◽  
Atmospheric Co2 Concentrations

Abstract. Next to atmospheric CO2 concentrations, oceanographic conditions are a critical factor determining the stability of Antarctic marine-terminating ice sheets. The Oligocene and Miocene epochs (~ 34–5 Ma) were time intervals with atmospheric CO2 concentrations between those of present-day and those expected for the near future. As such, these time intervals may bear information to resolve the uncertainties that still exist in the projection of future ice-sheet volume decline. We present organic-walled dinoflagellate cyst (dinocyst) assemblages from chronostratigraphically well-constrained Oligocene to mid-Miocene sediments from Integrated Ocean Drilling Program Expedition (IODP) Site U1356. Situated offshore the Wilkes Land continental margin, East Antarctica, the sediment core has archived past dynamics of an ice sheet that is today mostly grounded below sea level. We interpret dinocyst assemblages in terms of paleoceanographic change on different time scales, i.e., on glacial-interglacial and long-term variability. Sea-ice indicators occur only for the first 1.5 Ma following the full Antarctic continental glaciation during the early Oligocene, and after the Middle Miocene Climatic Optimum. During the remainder of the Oligocene and Miocene dinocysts suggest a weaker-than-modern sea-ice season. The assemblages generally bear strong similarity to present-day open-ocean, high-nutrient settings north of the sea ice edge, with episodic dominance of temperate species similar to the present-day subtropical front. Oligotrophic and temperate surface waters prevailed over the site notably during interglacial time intervals, suggesting that the position of the (subpolar) oceanic frontal systems have varied in concordance with Oligocene-Miocene glacial-interglacial climate variability.

scholarly journals Simultaneous disintegration of outlet glaciers in Porpoise Bay (Wilkes Land), East Antarctica, driven by sea ice break-up

2017 ◽  
Vol 11 (1) ◽  
pp. 427-442 ◽  
Author(s):  
Bertie W. J. Miles ◽  
Chris R. Stokes ◽  
Stewart S. R. Jamieson
Keyword(s):  
Sea Ice ◽  
East Antarctica ◽  
High Temporal Resolution ◽  
Ice Flow ◽  
Envisat Asar ◽  
Glacier Terminus ◽  
Wilkes Land ◽  
Break Up ◽  
Atmospheric Circulation Anomalies ◽  
Landfast Sea Ice

Abstract. The floating ice shelves and glacier tongues which fringe the Antarctic continent are important because they help buttress ice flow from the ice sheet interior. Dynamic feedbacks associated with glacier calving have the potential to reduce buttressing and subsequently increase ice flow into the ocean. However, there are few high temporal resolution studies on glacier calving, especially in East Antarctica. Here we use ENVISAT ASAR wide swath mode imagery to investigate monthly glacier terminus change across six marine-terminating outlet glaciers in Porpoise Bay (76° S, 128° E), Wilkes Land (East Antarctica), between November 2002 and March 2012. This reveals a large near-simultaneous calving event in January 2007, resulting in a total of  ∼  2900 km2 of ice being removed from glacier tongues. We also observe the start of a similar large near-simultaneous calving event in March 2016. Our observations suggest that both of these large calving events are driven by the break-up of the multi-year sea ice which usually occupies Porpoise Bay. However, these break-up events appear to have been driven by contrasting mechanisms. We link the 2007 sea ice break-up to atmospheric circulation anomalies in December 2005 weakening the multi-year sea ice through a combination of surface melt and a change in wind direction prior to its eventual break-up in January 2007. In contrast, the 2016 break-up event is linked to the terminus of Holmes (West) Glacier pushing the multi-year sea ice further into the open ocean, making the sea ice more vulnerable to break-up. In the context of predicted future warming and the sensitivity of sea ice to changes in climate, our results highlight the importance of interactions between landfast sea ice and glacier tongue stability in East Antarctica.

scholarly journals Late Oligocene obliquity-paced contourite sedimentation in the Wilkes Land margin of East Antarctica: implications for paleoceanographic and ice sheet configurations

2017 ◽  
Author(s):  
Ariadna Salabarnada ◽  
Carlota Escutia ◽  
Ursula Röhl ◽  
C. Hans Nelson ◽  
Robert McKay ◽  
...  
Keyword(s):  
Southern Ocean ◽  
Sea Ice ◽  
Ross Sea ◽  
Global Climate ◽  
Ice Sheet ◽  
East Antarctica ◽  
Late Oligocene ◽  
Early Oligocene ◽  
Geochemical Parameters ◽  
Wilkes Land

Abstract. The late Oligocene experienced atmospheric concentrations of CO2 between 400 and 750 ppm, which are within the IPCC projections for this century, assuming unabated CO2 emissions. However, Antarctic ice sheet and Southern Ocean paleoceanographic configurations during the late Oligocene are not well resolved, but are important to understand the influence of high-latitude Southern Hemisphere feedbacks on global climate under such CO2 scenarios. Here, we present late Oligocene (26–25 Ma) ice sheet and paleoceanographic reconstructions recorded in sediments recovered by IODP Site U1356, offshore of the Wilkes Land margin in East Antarctica. Our study, based on a combination of sediment facies analysis, physical properties, and geochemical parameters, shows that glacial and interglacial sediments are continuously reworked by bottom-currents, with maximum velocities occurring during the interglacial periods. Glacial sediments record poorly ventilated, low-oxygenation bottom water conditions, interpreted to represent a northward shift of westerly winds and surface oceanic fronts. During interglacial times, more oxygenated and ventilated conditions prevailed, which suggests enhanced mixing of the water masses with enhanced current velocities. Micritic limestone intervals within some of the interglacial facies represent warmer paleoclimatic conditions when less corrosive warmer northern component water (e.g. North Atlantic sourced deep water) had a greater influence on the site. The lack of iceberg rafted debris (IRD) throughout the studied interval contrasts with early Oligocene and post-Oligocene sections from Site U1356 and with late Oligocene strata from the Ross Sea (CRP and DSDP 270), which contain IRD and evidence for coastal sea ice and glaciers. These observations, supported by elevated paleotemperatures and the absence of sea-ice, suggest that between 26 and 25 Ma reduced glaciers or ice caps occupied the terrestrial lowlands of the Wilkes Land margin. Unlike today, the continental shelf was not over-deepened, and thus marine-based ice sheet expansion was likely limited to coastal regions. Combined, these data suggest that ice sheets in the Wilkes Subglacial Basin were largely land-based, and therefore retreated as a consequence of surface melt during late Oligocene, rather than direct ocean forcing and marine ice sheet instability processes as it did in younger past warm intervals. Spectral analysis on late Oligocene sediments from the eastern Wilkes Land margin show that the glacial-interglacial cyclicity and resulting displacements of the Southern Ocean frontal systems between 26–25 Ma were forced by obliquity.

scholarly journals Dynamic influence of pinning points on marine ice-sheet stability: a numerical study in Dronning Maud Land, East Antarctica

2016 ◽  
Vol 10 (6) ◽  
pp. 2623-2635 ◽  
Author(s):  
Lionel Favier ◽  
Frank Pattyn ◽  
Sophie Berger ◽  
Reinhard Drews
Keyword(s):  
Data Assimilation ◽  
Sea Level ◽  
Ice Sheets ◽  
Ice Sheet ◽  
East Antarctica ◽  
Ice Shelf ◽  
Ice Dynamics ◽  
Outlet Glacier ◽  
Ice Shelves ◽  
Dronning Maud Land

Abstract. The East Antarctic ice sheet is likely more stable than its West Antarctic counterpart because its bed is largely lying above sea level. However, the ice sheet in Dronning Maud Land, East Antarctica, contains marine sectors that are in contact with the ocean through overdeepened marine basins interspersed by grounded ice promontories and ice rises, pinning and stabilising the ice shelves. In this paper, we use the ice-sheet model BISICLES to investigate the effect of sub-ice-shelf melting, using a series of scenarios compliant with current values, on the ice-dynamic stability of the outlet glaciers between the Lazarev and Roi Baudouin ice shelves over the next millennium. Overall, the sub-ice-shelf melting substantially impacts the sea-level contribution. Locally, we predict a short-term rapid grounding-line retreat of the overdeepened outlet glacier Hansenbreen, which further induces the transition of the bordering ice promontories into ice rises. Furthermore, our analysis demonstrated that the onset of the marine ice-sheet retreat and subsequent promontory transition into ice rise is controlled by small pinning points, mostly uncharted in pan-Antarctic datasets. Pinning points have a twofold impact on marine ice sheets. They decrease the ice discharge by buttressing effect, and they play a crucial role in initialising marine ice sheets through data assimilation, leading to errors in ice-shelf rheology when omitted. Our results show that unpinning increases the sea-level rise by 10 %, while omitting the same pinning point in data assimilation decreases it by 10 %, but the more striking effect is in the promontory transition time, advanced by two centuries for unpinning and delayed by almost half a millennium when the pinning point is missing in data assimilation. Pinning points exert a subtle influence on ice dynamics at the kilometre scale, which calls for a better knowledge of the Antarctic margins.

scholarly journals Numerical modelling of a fast-flowing outlet glacier: experiments with different basal conditions

1996 ◽  
Vol 23 ◽  
pp. 237-246 ◽  
Author(s):  
Frank Pattyn
Keyword(s):  
Deformation Process ◽  
Drainage Basin ◽  
Ice Sheet ◽  
Outlet Glacier ◽  
Transient Behaviour ◽  
Cyclic Behaviour ◽  
System A ◽  
Basal Ice ◽  
Equal Importance ◽  
Fully Coupled

Recent observations in Shirase Drainage Basin. Enderby Land, Antarctica, show that the ice sheet is thinning at the considerable rate of 0.5–1.0 m a −1. Surface velocities in the stream area reach more than 2000 ma−1, making Shirase Glacier one of the fastest-flowing glaciers in East Antarctica. A numerical investigation of the present stress field in Shirase Glacier shows the existence of a large transition zone 200 km in length where both shearing and stretching are of equal importance, followed by a stream zone of approximately 50 km, where stretching is the major deformation process.In order to improve insight into the present transient behaviour of the ice-sheet system, a two-dimensional time-dependent flowline model has been developed, taking into account the ice-stream mechanics. Both bedrock adjustment and ice temperature are taken into account and the temperature field is fully coupled to the ice-sheet velocity field.Experiments were carried out with different basal motion conditions in order to understand their influence on the dynamic behaviour of the ice sheet and the stream area in particular. Results revealed that when basal motion becomes the dominant deformation process, (partial) disintegration of the ice sheet is counteracted by colder basal-ice temperatures due to higher advection rates. This gives rise to a cyclic behaviour in ice-sheets response and large changes in local imbalance values.

scholarly journals Oligocene TEX<sub>86</sub>-derived seawater temperatures from offshore Wilkes Land (East Antarctica)

2017 ◽  
Author(s):  
Julian D. Hartman ◽  
Francesca Sangiorgi ◽  
Ariadna Salabarnada ◽  
Francien Peterse ◽  
Alexander J. P. Houben ◽  
...  
Keyword(s):  
Sea Ice ◽  
Bottom Water ◽  
Ice Sheet ◽  
Temperature Variability ◽  
Sea Surface ◽  
Ice Volume ◽  
Sst Variability ◽  
Wilkes Land ◽  
The Antarctic

Abstract. Today, the temperature of the surface waters near the Antarctic coast is a determining factor in the formation of Antarctic Bottom Water (AABW) through sea-ice production, sea-ice extent, and the extent of the ice shelf. For the Oligocene, deep-sea benthic foraminiferal oxygen isotope (δ18O) reconstructions suggest that the volume of the Antarctic continental ice sheet(s) varied substantially both on million-year and on orbital timescales after its inception in the early Oligocene, and even reached larger than modern-day volumes. Replication of such dynamicity through physical modeling remains problematic, suggesting the existence of complex feedbacks between the cryosphere, the ocean and the atmosphere. To assess the relation between cryosphere, ocean and atmosphere, knowledge of sea surface conditions close to the Antarctic margin is essential. We present a TEX86-based surface water paleotemperature record measured on Oligocene sediments from Integrated Ocean Drilling Program (IODP) Site U1356, offshore Wilkes Land, Antarctica. This record allows us to reconstruct the magnitude of seawater temperature variability and trends on both million-year and on glacial-interglacial timescales. TEX86 index values suggest surface temperatures between 10 and 21 °C during the Oligocene, which is on the upper end of the few available reconstructions. Sea surface temperature (SST) maxima occur around 30.5 and 25 Ma, irrespective of the calibration equation chosen. Based on glacial-interglacial lithological alternations we have established that SST variability between glacial intervals and their successive interglacials ranged between 1.8–3.2 °C. As benthic foraminiferal δ18O data incorporate both an ice-volume and a temperature component, our reconstructed Oligocene temperature variability could have implications for current Oligocene ice-volume estimates. If the long-term ad orbital SST variability is representative of that of the nearby region of deep-water formation, we can assess the impact of this temperature record on the volume and dynamics of the Antarctic ice sheet(s) by comparing it with the δ18O trends and variability. From this comparison, we argue that a significant portion of the variability and trends contained in long-term δ18O records can be explained by variability in Southern high-latitude temperature. If indeed a large part of the δ18O variability is due to large glacial-interglacial bottom-water temperature shifts, the Oligocene Antarctic ice volume was less sensitive to climate change than previously assumed.

Investigating the climate variability in the Totten area using NEMO-LIM regional model.

2020 ◽  
Author(s):  
Guillian Van Achter ◽  
Charles Pelletier ◽  
Thierry Fichefet
Keyword(s):  
Sea Ice ◽  
Ocean Circulation ◽  
Ice Sheet ◽  
Regional Model ◽  
East Antarctica ◽  
Shelf Area ◽  
Ice Shelf ◽  
Ice Shelves ◽  
Landfast Ice ◽  
The Impact

&lt;p&gt;The Totten ice shelf drains over 570 000 km&amp;#178; of East Antarctica. Most of the ice sheet that drains through the Totten ice-shelf is from Aurora Subglacial Basin and is marine based making the region potentially vulnerable to rapid ice sheet colapse.&lt;br&gt;Understanding how the changes in ocean circulation and properties are causing increased basal melt of Antarctic ice shelves is crucial for predicting future sea level rise.&lt;br&gt;In the context of the The PARAMOUR project (decadal predictability and variability of polar climate: the role of atmosphere-ocean-cryosphere multiscale interaction), we use a high resolution NEMO-LIM 3.6 regional model to investigate the variability and the predictability of the coupled climate system over the Totten area in East Antarctica.&lt;br&gt;In this poster, we will present our on-going work about the impact of landfast ice over the variability of the system. Landfast ice is sea ice that is fastened to the coastline, to the sea floor along shoals or to grouded icebergs. Current sea ice models are unable to represent very crudely the formation, maintenance and decay of coastal landfast ice. We applyed several parameterization for modeling landfast ice over the Totten ice shelf area.&lt;/p&gt;

scholarly journals Mass balance of the Sør Rondane glacial system, East Antarctica

2015 ◽  
Vol 56 (70) ◽  
pp. 63-69 ◽  
Author(s):  
Denis Callens ◽  
Nicolas Thonnard ◽  
Jan T.M. Lenaerts ◽  
Jan M. Van Wessem ◽  
Willem Jan Van de Berg ◽  
...  
Keyword(s):  
Mass Balance ◽  
Drainage Basin ◽  
Ice Sheets ◽  
Ice Sheet ◽  
Antarctic Ice Sheet ◽  
Outlet Glacier ◽  
Surface Mass ◽  
Mass Budget ◽  
Grounding Line ◽  
The Antarctic

AbstractMass changes of polar ice sheets have an important societal impact, because they affect global sea level. Estimating the current mass budget of ice sheets is equivalent to determining the balance between surface mass gain through precipitation and outflow across the grounding line. For the Antarctic ice sheet, grounding line outflow is governed by oceanic processes and outlet glacier dynamics. In this study, we compute the mass budget of major outlet glaciers in the eastern Dronning Maud Land sector of the Antarctic ice sheet using the input/output method. Input is given by recent surface accumulation estimates (SMB) of the whole drainage basin. The outflow at the grounding line is determined from the radar data of a recent airborne survey and satellite-based velocities using a flow model of combined plug flow and simple shear. This approach is an improvement on previous studies, as the ice thickness is measured, rather than being estimated from hydrostatic equilibrium. In line with the general thickening of the ice sheet over this sector, we estimate the regional mass balance in this area at 3.15 ± 8.23 Gt a−1 according to the most recent SMB model results.

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