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Day 3 - Ice and ocean interactions

Title: Change in Antarctic Bottom Water on time-scales from years to centuries: causes, consequences and implications for future observations

Presenter: Stephen Rintoul

Antarctic Climate and Ecosystems Cooperative Research Centre
Centre for Australian Weather and Climate Research
Wealth from Oceans National Research Flagship, CSIRO Marine and Atmospheric Research

Authors: S Rintoul1,2,3, E van Wijk2,3, S Sokolov1,2,3, B Pena-Molino1, E van Sebille4, R Thresher3,
M Rosenberg1

1 - Antarctic Climate and Ecosystems Cooperative Research Centre

2 - Centre for Australian Weather and Climate Research

3 - Wealth from Oceans National Research Flagship, CSIRO Marine and Atmospheric Research

4 - University of New South Wales


Antarctic Bottom Water in the Australian Antarctic Basin has warmed, freshened, become less dense, and contracted since the early 1970s. For example, the volume of the bottom water layer (neutral density greater than 28.3 kg m-3) has contracted by more than 50% over this time period. These changes are the regional expression of a signal that extends throughout much of the deep ocean. The pattern of change (decreased freshening and increased warming downstream of the sources and the lack of change in oxygen) suggest freshening of the dense source waters, rather than a reduction in the formation rate, is the primary cause of the observed contraction in AABW. A paleo-temperature proxy derived from a deep coral indicates substantial trends in AABW properties over the last 200 years, placing the more recent multi-decadal changes in perspective. The dramatic freshening of dense shelf waters following the calving of the Mertz Glacier Tongue highlights the sensitivity of bottom water properties to episodic events. Particle trajectories derived from an estimate of the Southern Ocean circulation shows that the Antarctic Circumpolar Current homogenises the bottom water produced by different source regions. Taken together, these results provide a context in which to interpret recent observations of change in the deep limb of the overturning circulation and provide some guidance on the design of future observing programs.

Title: Ice Shelf Water to the South of the Drygalski Ice Tongue

Presenter: Craig Stevens

Marine Physics, National Institute of Water and Atmospheric Research

Authors: Craig L. Stevens1, Gianetta Fusco2

1 - Marine Physics, National Institute of Water and Atmospheric Research, Greta Point, Wellington, New Zealand Geoscience Australia, GPO Box 378, Canberra ACT 2601,

2 - Dipartimento di Scienze per l’Ambiente, Universita degli Studi di Napoli “Parthenope”, Italy


We present what we believe to be the first oceanographic measurements immediately to the south of the Drygalski Ice Tongue. This floating glacier in the western Ross Sea is probably the largest of its kind at the present time. Observations included acoustic Doppler current profiler measurements, turbulence microstructure profiles, and temperature and salinity profile data. These are contextualised using extensive historical oceanographic observations to the north of the ice tongue along with satellite data. The measurements were conducted from a fast ice camp 5 km from the southern side of the ice tongue during January of 2012. The data records were of limited duration as the fast ice was breaking up and indeed the field camp region disintegrated a week after our departure. The fast ice itself exhibited signatures of platelet ice formation indicative of ice shelf water and the observations identified a deep layer of ice shelf water. The origin of this cold water and the impact of the ice tongue on coastal currents are major questions arising from this limited set of field observations.

Title: Totten Glacier, East Antarctica: How has ocean access to the ice shelf cavity shaped local elevation change patterns?

Presenter: Jamin Greenbaum

Institute for Geophysics, University of Texas at Austin

Authors: Greenbaum, J.S.1, Young, D.A.1, Roberts, J.L.2,3, Richter, T.G.1, Warner, R.C.2,3, Young, N.W.2,3, van Ommen, T.D.2,3, Siegert, M.J.4, Blankenship, D.D.1

1 - Institute for Geophysics, University of Texas at Austin

2 - Australian Antarctic Division


4 - School of Earth Sciences, Bristol University


Totten Glacier has the largest outflow of any glacier in East Antarctica and has been the focus of several geophysical studies over the last decade. In particular, the international, collaborative ICECAP Project has acquired over 10,000 line-kilometers of aerogeophysical data in the vicinity of the glacier. Several flights in 2010 and 2012 were focused on continuing the time series of surface elevation change conducted by the ICESAT mission that ended in 2009. Several other flights were flown in a regular grid pattern over the glacier and the floating ice tongue to map the subglacial context for the observed elevation change and to determine the broad scale bathymetry beneath the ice tongue using airborne gravimetry. The gravimetry experiment was expanded in 2012 with an advanced, three-axis stabilised GT-1A gravimeter with much improved production rates under challenging flight envelopes. With the new gravimeter installed, five-km spaced coast parallel survey lines were flown from the lower reaches of the cavity to about 100km seaward of the terminus to infer the location and approximate depth of potential warm water pathways from the continental shelf to the deep glacier cavity. Here we present updated elevation change measurements in the context of the new bathymetry information and show that ocean access to the cavity is complicated by high bedrock near the terminus of the glacier. Verification of warm water intrusion potential will require new oceanographic observations such as those planned for the collaborative US-Australian marine survey scheduled to sail on the NB Palmer in February 2014.

Title: Modeling inter-annual dense shelf water export in the region of the Mertz Glacier (1992-2007)

Presenter: Eva Cougnon

Institute of Marine and Antarctic Studies

Authors: Eva Cougnon1, Ben Galton-Fenzi2, Andrew Meijers3, Benoit Legrésy4

1 - IMAS, Hobart, Australia,

2 - ACE-CRC and AAD, Hobart, Australia,

3 - BAS, Cambridge, United Kingdom,

4 - LEGOS, Toulouse, France,


Ocean observations around the Australian-Antarctic basin show the importance of coastal latent heat polynyas near the Mertz Glacier Tongue (MGT) to the formation of Dense Shelf Water (DSW) and associated Antarctic Bottom Water (AABW). Here, we use a regional ocean/ice-shelf model to investigate the inter-annual variability in the export of DSW from the Adélie (west of the MGT) and the Mertz (east of the MGT) depressions from 1992 to 2007. The model simulates an annual mean export of DSW through the Adélie sill of about 0.07±0.06 Sv, in agreement with recent observations. From 1992 to 1998, the export of DSW through the Adélie (Mertz) sills peaked at 0.14 Sv (0.29 Sv) during July to November. During periods of mean to strong polynya activity (defined by the surface ocean heat loss), DSW formed in the Adélie depression can spread into the Mertz depression via the cavity under the MGT. 0.12±0.07 Sv of DSW is simulated to circulate beneath the MGT. Also, this circulation impacts the melting of the entire ice tongue, which can reach an area-averaged melt rate of 3.8±1.5 m year-1 during periods of sustained weak polynya activity, due to the increased presence of relatively warmer water interacting with the base of the ice-shelf. This melt rate is about 3 times higher than during active sustained polynya activity.

Title: Marine ice formation at the Southern McMurdo Ice Shelf

Presenter: Inka Koch

Authors: I Koch1, S Fitzsimons2, J Tison3

1 - University of Otago, Department of Geography, Dunedin, New Zealand,

2 - University of Otago, Department of Geography, Dunedin, New Zealand

3 - Laboratoire de Glaciologie, Universite Libre de Bruxelles, Brussels, Belgium 


Marine ice forms at the base of ice shelves and is thought to enhance ice shelf stability by adding layers of dense ice mass or filling bottom crevasses and rifts. Although widespread in Antarctic ice shelves, the conditions for marine ice formation remain poorly understood. This study focuses on understanding marine ice source water and formation rates at the Southern McMurdo Ice Shelf (SMIS). Basal marine ice is exposed at the degraded surface of SMIS, allowing for sampling in shallow ice cores (2-9m long) with a Kovacs corer. The extracted ice was analysed for water isotopes, major ions and ice crystal morphology. A comparison of field data with the output of a boundary layer freezing model suggests that some of the isotopically enriched marine ice at SMIS could have formed from pure sea water at very low freezing rates. However, a large range of isotopic values and a steep co-isotopic mixing slope indicate that the bulk of marine ice is of mixed glacial and sea water origin. Varying proportions of glacial water could either be sourced from deeper parts of the adjacent Ross Ice Shelf or from local surface melt percolating to the shelf bottom through tide cracks. The presence of banded and granular ice crystals in vertical thin sections together with a very low salinity of the ice suggests that the marine ice largely formed from frazil ice crystals. These ice crystals nucleate fast from supercooled water, adding thick layers of marine ice to the ice shelf base. Together with a better understanding of ocean circulation in the ice shelf cavity, results from this study will aid to predict marine ice accumulation and hence non-linear ice shelf behaviour in a changing climate.

Title: Grounding Zone Ice Thickness from Satellite: Inverse Modelling of Tidal Elastic Bending

Presenter: Oliver Marsh

Gateway Antarctica, University of Canterbury

Authors: Oliver J. Marsh1, Wolfgang Rack1, Nicholas R. Golledge2, Wendy Lawson3, Dana Floricioiu4

1 - Gateway Antarctica, University of Canterbury, Christchurch, NZ,

2 - Antarctic Research Centre, Victoria University of Wellington, Wellington, NZ, GNS Science, Avalon, Lower Hutt, NZ

3 - Department of Geography, University of Canterbury, Christchurch, NZ

4 - DLR, Oberpfaffenhofen, Wessling, Germany


Ice shelves and outlet glaciers around Antarctica are subjected to periodic forces associated with ocean tides. Vertical motion of the ice in response to these tides varies spatially across the grounding zone region where the ice shelves are supported by the land. This vertical displacement can be measured using Interferometric Synthetic Aperture Radar (InSAR) from satellite by comparing multiple interferograms with different tidal displacements. This differential method has been widely applied to mapping the location of the grounding line. Finite element modelling shows that this tidal response can be well simulated if ice thickness and internal ice properties are known. Here we discuss a new inverse modelling optimization approach, using spatial patterns of ice flexure derived from differential interferograms to calculate ice thickness in the grounding zone. Sensitivity analyses are conducted for synthetic ice profiles in 1D. The method is then applied to the Beardmore Glacier in Antarctica with results compared to new ice penetrating radar measurements of thickness from the 2010. This method improves current estimates of grounding zone ice thickness based on hydrostatic equilibrium assumptions. Thickness estimates at tracks across the grounding zone agree to within 100m with observed values. The effect of tidal flexure on ice velocity observed from TerraSAR-X speckle tracking is also discussed, with short-term velocity fluctuations compared to ground-based GPS data.

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    20 Jun 2013

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Key dates

  • 11th June 2013
    Registrations close
  • 21st June 2013
    Registrations at the AAD open for staff
  • 24th June 2013
    Registrations at the venue open
  • 24th June 2013
    Conference commences
  • 26th June 2013
    Conference concludes

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This page was last modified on 6 June 2013.