Conference Agenda

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Session Overview
4AM1: Cryosphere & geodesy
Thursday, 23/Mar/2017:
11:15am - 12:30pm

Session Chair: Roland Pail
Session Chair: C K Shum

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11:15am - 11:30am

Large Precipitation Event Influences Sub-Glacier Hydrology and Ice Flow of Recovery Ice Stream, East Antarctica

Indrani Das1, Nicole Schlegel2, Ted Scambos3, Bea Csatho4, Greg Babonis4

1Columbia University, United States of America; 2Jet Propulsion Laboratory, NASA, California, USA; 3University of Colorado in Boulder, Boulder, USA; 4University at Buffalo, Buffalo, New York, USA

We observe a period of anomalous net positive accumulation of several gigatons over Recovery Ice Stream in 2006 using both GRACE and climate model data. The accumulation anomaly, manifest by higher-than-average precipitation, reversed the sign of Recovery Ice Stream mass balance over a period of a few months as observed by GRACE within the course of a year. ICESat and IceBridge laser altimetry data confirmed a thickening signal corresponding to the precipitation event. The timing of the precipitation event was correlated with movement of water in subglacial lakes over the Recovery Ice Stream. We propose that the large precipitation event caused a significant change in the ice overburden pressure at the base of the ice sheet, prompting subglacial water movement. This anomalous precipitation event may not be an isolated incident; climate models and reanalysis data suggest events of similar magnitude may occur a few times in a decade. We will present preliminary results using satellite and airborne laser altimetry and modeling.

11:30am - 11:45am

Estimate of Regional Glacial Isostatic Adjustment in Antarctica Considering a Lateral Varying Earth Structure (ESA-STSE Project REGINA)

Ingo Sasgen1, Alba Martín-Español2, Alexander Horvath3, Volker Klemann4, Elizabeth J. Petrie5, Bert Wouters6, Martin Horwath7, Roland Pail3, Jonathan L. Bamber2, Peter J. Clarke8, Hannes Konrad9, Mark R. Drinkwater10

1Alfred Wegener Institute, Germany; 2School of Geographical Sciences, University of Bristol, University Road, Clifton, Bristol BS8 1SS, United Kingdom.; 3Institut für Astronomische und Physikalische Geodäsie, Technische Universität München, Arcisstraße 21, 80333 München, Germany.; 4Department of Geodesy, GFZ German Research Centre for Geosciences, Telegrafenberg, 14473 Potsdam, Germany.; 5School of Geographical and Earth Sciences, University of Glasgow, Glasgow, G12 8QQ, United Kingdom.; 6Institute for Marine and Atmospheric Research, Utrecht University, Princetonplein 5, 3584 CC, Utrecht, The Netherlands.; 7Institut für Planetare Geodäsie, Technische Universität Dresden, Helmholtzstr. 10, 01069 Dresden, Germany.; 8School of Civil Engineering and Geosciences, Newcastle University, Newcastle, NE1 7RU, United Kingdom.; 9School of Earth and Environment, University of Leeds, Leeds, LS2 9JT, United Kingdom.; 10Mission Science Division, European Space Agency, European Space Research and Technology Centre, Keplerlaan 1, Noordwijk 2201 AZ, The Netherlands.

The mass balance of the Antarctic ice sheet from satellite gravimetry, and to a lesser extent altimetry, observations remains uncertain due to the poorly known correction for the glacial isostatic adjustment of the solid Earth (GIA). Although much progress has been made in consistently modelling ice-sheet evolution, related bedrock deformation and sea-level change, predictions of GIA remain ambiguous due to the lack of observational constraints in Antarctica. Here, we present an improved GIA estimate based on the joint inversion of GRACE, Envisat/ICESat and GPS measurements, making use of the different sensitivities of the satellite observations to surface-mass and solid Earth processes. We base our joint inversion on viscoelastic response functions to a disc load forcing, allowing us to account for lateral variations in the lithosphere thickness and mantle viscosity in Antarctica. Our estimate is able to reproduce extreme GPS-measured uplift rates (up to 3 cm yr-1) in the Amundsen Sea Embayment, indicating that large parts of the uplift are caused by GIA induced by recent load changes in the presence of a low-viscosity upper mantle. We compare our GIA inversion estimate with the prediction obtained with a coupled model of the ice sheet and solid Earth, as well as with published estimates. We evaluate its impact on the determination of ice-mass balance in Antarctica from gravimetry and altimetry. The results presented here are the final results of the Support To Science Element Project REGINA and its Supplementary Study of the European Space Agency,

11:45am - 12:00pm

Arctic Gravity Field from Cryosat-2

Ole Baltazar Andersen, Per Knudsen, Adili Abulaitijiang, Simon Holmes

DTU spac, Denmark

Cryosat-2 data offers a unique possibility to derive the Arctic gravity due to its near geodetic orbit of 369 days repeat. Its the only satellite besides the old ERS-1 flown 20 years ago which provide satellit altimetry of geodetic quality in the Arctic Ocean.

We will present and evaluate our new DTU15 global marine gravity field as well as our pre-releasable DTU17 arctic gravity field in the Arctic Ocean.

Both are based on retracked altimetry from Cryosat-2 and ERS-1 in the Arictic Ocean. In the Arctic Ocean we are testing an new combined empirical/physical retracking system that uses physical retracking of the LRM data using a reduced parameter system in combination with empirical retracking of the SAR and SAR-In data in particularly high latitude regions.

An advantage of the Cryosat-2 is its ability of provide new accurate sea surface height information for gravity field determination in the northernmost part of the Arctic Ocean upto 88N where no altimeters have measured before.

Also the first evaluation of the use of Cryosat-2 SAR data in a few relative narrow fjords of Greenland will be presented.

12:00pm - 12:15pm

High-Resolution Mass Changes of the Greenland and Antarctica Ice Sheets from Combined CryoSat and GRACE Inversion

Rene Forsberg, Sebastian Simonsen

DTU Space, Denmark

The combination of space-based remote sensing data, especially gravity field changes from GRACE and elevation changes from CryoSat, may yield time series of Greenland and Antarctica mass balance with both high temporal and spatial resolution, highlighting the varying individual mass loss behaviour of major glaciers systems, while still keeping a “correct” overall ice sheet wide mass loss, within the uncertainty of the glacial-isostatic effects. Although the GIA-related errors continue to be large in Antarctica, the temporal changes in mass balance are well determined, and show significant acceleration both over the Antarctic Peninsula and the Pine Island/Thwaites glacier systems. For Greenland the large yearly melt event of 2012 followed by extraordinary cool summers have meant that the Greenland ice sheet mass loss have been slightly decreasing during the CryoSat period 2010-16, with large variations between individual glaciers and ice streams.

In the presentation we outline change results from CryoSat and GRACE 2010-2016, for both Greenland and Antarctica, and outline the basis of a high resolution point mass estimation method, and the associated use firn compaction and density models. We also include estimates of the northern Canadian ice cap changes to reduce GRACE leakage errors for Greenland. We estimate an overall mass balance of Greenland around -265 GT/yr and for Antarctica -145 GT/yr, representing nearly a doubling of Antarctica mass loss since 2002, while Greenland show only relatively small overall accelerations, with large regional melt region variations, clearly pointed out by CryoSat.

12:15pm - 12:30pm

High Mountain Asia Glacier Mass Balance Estimates Using Satellite Geodetic Observations

Jian Sun

Ohio State University, United States of America

The 2013 Intergovernmental Panel for Climate Assessment (IPCC) Fifth Assessment Report (AR5) concluded that the observed and explained geophysical causes of global geocentric sea-level rise, 1993–2010, is much closer towards closure. However, the discrepancy reveals that up to approximately 30% of the observed sea-level rise remains unexplained, despite contemporary reports on reconciled mass balance estimates ofice-sheet and mountain glaciers during the early 21st century. This discrepancy is primarily attributable to the wide range of estimates of respective contributions of Greenland and Antarctic ice-sheets and mountain glaciers to sea-level rise. In particular, the High Mountain Asian glacier systems remains a focus of public and scientific debate, as the uncertainty of its mass balance estimates and its future projection have a significant implication of water resource problems affecting 1.5 billion people in the region. It is also not clear, in the case of the High Mountain Asia glacier system that glacier ablation would instantaneously contribute to sea-level rise, as melt water is largely dammed up resulting from anthropogenic activities in the region. The use of satellite altimetry for glacier elevation change has been problematic primarily because of steep terrains causing grossly inaccurate gradient corrections hindering the ability to generate ice elevation time series. Here we use available DEMs developed using the Indian Cartosat-1 (2.5 m resolution) and the KH-9 Hexagon, and ALOS PALSAR and Envisat ASAR InSAR measurements over glaciers, such as the Siachen Glacier system in the East Karakoram for gradient corrections to generate altimetry-based glacier elevation time series. In particular, we use ICESat and multi-mission radar altimeter data including TOPEX, ERS-1/-2, Envisat, SARAL/Altika, CryoSat-2, as well as GRACE gravimetry data, and improved mountain glacier masks developed using optical/IR and SAR data, to provide an update of the glacier mass balance estimate in the High Mountain Asia region.

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