Getting around Antarctica: new high-resolution mappings of the grounded and freely-floating boundaries of the Antarctic ice sheet created for the International Polar Year

Two ice-dynamic transitions of the Antarctic ice sheet – the boundary of grounded ice features and the freelyfloating boundary – are mapped at 15-m resolution by participants
of the International Polar Year project ASAID using customized software combining Landsat-7 imagery and ICESat/GLAS laser altimetry. The grounded ice boundary is
53 610 km long; 74% abuts to floating ice shelves or outlet glaciers, 19% is adjacent to open or sea-ice covered ocean, and 7% of the boundary ice terminates on land. The freelyfloating boundary, called here the hydrostatic line, is the most landward position on ice shelves that expresses the full amplitude of oscillating ocean tides. It extends 27 521 km and is discontinuous. Positional (one-sigma) accuracies of the
grounded ice boundary vary an order of magnitude ranging from ±52m for the land and open-ocean terminating segments to ±502m for the outlet glaciers. The hydrostatic line is less well positioned with errors over 2 km. Elevations along each line are selected from 6 candidate digital elevation models based on their agreement with ICESat elevation
values and surface shape inferred from the Landsat imagery. Elevations along the hydrostatic line are converted to ice thicknesses by applying a firn-correction factor and a flotation criterion. BEDMAP-compiled data and other airborne data are compared to the ASAID elevations and ice
thicknesses to arrive at quantitative (one-sigma) uncertainties of surface elevations of ±3.6, ±9.6, ±11.4, ±30 and ±100m for five ASAID-assigned confidence levels. Over one-half of the surface elevations along the grounded ice boundary and over one-third of the hydrostatic line elevations are ranked in the highest two confidence categories.
A comparison between ASAID-calculated ice shelf thicknesses and BEDMAP-compiled data indicate a thin-ice bias of 41.2±71.3m for the ASAID ice thicknesses. The relationship
between the seaward offset of the hydrostatic line from the grounded ice boundary only weakly matches a prediction based on beam theory. The mapped products
along with the customized software to generate them and a variety of intermediate products are available from the National
Snow and Ice Data Center.

Alley, R. B., Blankenship, D. D., Rooney, S. T., and Bentley, C. R.:
Sedimentation beneath ice shelves – the view from ice stream B,
Mar. Geol., 85, 101–120, 1989.
Anandakrishnan, S., Voigt, D. E., Alley, R. R., and King, M.
A.: Ice stream D flow speed is strongly modulated by the tide
beneath the Ross Ice Shelf, Geophys. Res. Lett., 30(7), 1361,
doi:10.1029/2002GL016329, 2003.
Bamber, J. L., Gomez-Dans, J. L., and Griggs, J. A.: A new 1 km
digital elevation model of the Antarctic derived from combined
satellite radar and laser data – Part 1: Data and methods, The
Cryosphere, 3, 101–111, doi:10.5194/tc-3-101-2009, 2009. Bindschadler, R. A. and Vornberger, P. L.: Detailed elevation map
of ice stream C using satellite imagery and airborne radar, Ann.
Glaciol., 20, 327–335, 1994.
Bindschadler, R. A., Vornberger, P. L., King, M., and Padman, L.:
Tidally-Driven Stick-Slip Motion in the Mouth of Whillans Ice
Stream, Antarctica, Ann. Glaciol., 36, 263–272, 2003.
Bindschadler, R., Vornberger, P., Fleming, A., Fox, A., Mullins, J.,
Binnie, D., Paulsen, S. J., Granneman, B., and Gorodetzky, D.:
The Landsat Image Mosaic of Antarctica, Remote Sens. Environ.,
112(12), 4214–4226, doi:10.1016/j.rse.2008.07.006, 2008.
Bindschadler, R. A., Wichlacz, A., and Choi, H.: An Illustrated
Guide to Using ASAID Software, NASA Technical Memorandum,
TM-2011-215879, 21 pp., 2011.
Bohlander, J. and Scambos, T.: Antarctic coastlines and grounding
line derived from MODIS Mosaic of Antarctica (MOA), Boulder,
Colorado USA: National Snow and Ice Data Center, Digital
media, 2007.
Brunt, K. M., Fricker, H. A., Padman, L., and O’Neel, S.: ICESat-
Derived Grounding Zone for Antarctic Ice Shelves, Boulder,
Colorado USA: National Snow and Ice Data Center, Digital media,
2010a.
Brunt, K. M., Fricker, H. A., Padman, L., Scambos, T. A., and
O’Neel, S.: Mapping the grounding zone of the Ross Ice Shelf,
Antarctica, Using ICESat laser altimetry, Ann. Glaciol., 51(55),
71–79, 2010b.
Corr, H. F. J., Doake, C. S. M., Jenkins, A., and Vaughan, D. G.: Investigations
of an “ice plain” in the mouth of Pine Island Glacier,
Antarctica, J. Glaciol., 47(156), 51–57, 2001.
Ferrigno, J. G., Mullins, J. L., Stapleton, J. A., Chavez, P. S., Velasco,
M. G.,Williams, R. S., Delinski, G. F., and Lear, D.: Satellite
Image Map of Antarctica, U.S. Geological Survey, Miscellaneous
Investigations Map Series, Map 1-2560, 1996.
Fricker, H. A. and Padman, L.: Ice shelf grounding zone structure
from ICESat laser altimetry, Geophys. Res. Lett., 33, L15502,
doi:10.1029/2006GL026907, 2006.
Fricker, H. A., Coleman, R., Padman, L., Scambos, T. A.,
Bohlander, J., and Brunt, K. M.: Mapping the grounding
zone of the Amery Ice Shelf, East Antarctica using In-
SAR, MODIS and ICESat, Antarct. Sci., 21(5), 515–532,
doi:10.1017/S095410200999023X, 2009.
Joughin, I., Smith, B. E., and Holland, D. M.: Sensitivity of
21st Century Sea Level to Ocean-Induced Thinning of Pine
Island Glacier, Antarctica, Geophys. Res. Lett., 37, L20502,
doi:10.1029/2010GL044819, 2010.
Korona J., Berthier, E., Bernard, M., Remy, F., and Thouvenot, E.:
SPIRIT. SPOT 5 stereoscopic survey of Polar Ice: Reference Images
and Topographies during the fourth International Polar Year
(2007–2009), ISPRS J. Photogramm., 64, 204–212, 2009.
Lee, D. S., Storey, J. C., Choate, M. J., and Hayes, R. W.:
Four Years of Landsat-7 On-Orbit Geometric Calibration and
Performance, IEEE T. Geosci. Remote, 42(12), 2786–2795,
doi:10.1109/TGRS.2004.836769, 2004.
Liu, H., Jezek, K., Li, B., and Zhao, Z.: Radarsat Antarctic Mapping
Project digital elevation model version 2, Boulder, CO: National
Snow and Ice Data Center, Digital media, 2001.
Lythe, M. B., Vaughan, D. G., and BEDMAP Consortium,
BEDMAP: A new ice thickness and subglacial topographic
model of Antarctica, J. Geophys. Res., 106(B6), 11335–11351,
2001. Payne, A. J., Vieli, A., Shepherd, A. P., Wingham, D. J., and Rignot,
E.: Recent dramatic thinning of largest West Antarctic ice
stream triggered by oceans, Geophys. Res. Lett., 31(23), L23401,
doi:10.1029/2004GL021284, 2004.
Payne, A. J., Holland, P. R., Shepherd, A. P., Rutt, I. C., Jenkins, A.,
and Joughin, I.: Numerical modeling of ocean-ice interactions
under Pine Island Bay’s ice shelf, J. Geophys. Res., 112, C10019,
doi:10.1029/2006JC003733, 2007.
Pritchard, H. D., Arthern, R. J., Vaughan, D. G., and Edwards,
L. A.: Extensive dynamic thinning on the margins of the
Greenland and Antarctic ice sheets, Nature, 461, 971–975,
doi:10.1038/nature08471, 2009.
Rignot, E.: Tidal motion, ice velocity and melt rate of Petermann
Gletscher, Greenland, measured from radar interferometry, J.
Glaciol., 42(142), 476–485, 1996.
Rignot, E., Bamber, J. L., van den Broeke, M. R., Davis,
C., Yonghong, L., van deBerg, W. J., and van Meijgaard,
E.: Recent Antarctic ice mass loss from radar interferometry
and regional climate modeling, Nat. Geosci., 1, 106–110,
doi:10.1038/ngeo102, 2008.
Rignot, E., Mouginot, J., and Scheuchl, B.: Antarctic grounding
line mapping from differential satellite radar interferometry,
Geophys. Res. Lett., 38, L10504, doi:10.1029/2011GL047109,
2011.
Schoof, C.: Ice sheet grounding line dynamics: Steady states,
stability, and hysteresis, J. Geophys. Res., 112, F03S28,
doi:10.1029/2006JF000664, 2007.
Shepherd, A., Wingham, D. J., and Mansley, J. A. D.: Inland thinning
of the Amundsen Sea sector, Geophys. Res. Lett., 29(10),
1364, doi:10.1029/2001GL014183, 2002. Thomas, R., Rignot, E., Casassa, G., Kanagaratnam, P., Acuna, C.,
Akins, T., Brecher, H., Frederick, E., Gogineni, P., Krabill, W.,
Manizade, S., Ramamoorthy, H., Rivera, A., Russell, R., Sonntag,
J., Swift, R., Yungel, J., and Zwally, J.: Accelerated sealevel
rise from West Antarctica, Science, 306(5694), 255–258,
2004.
Thomas, R. H., Stephenson, S. N., Bindschadler, R. A., Shabtaie,
S., and Bentley, C. R.: Thinning and grounding line retreat on
the Ross Ice Shelf, Ann. Glaciol., 11, 165–172, 1988.
van den Broeke, M. R., van de Berg, W. J., and van Meijgaard, E.:
Firn depth correction along the Antarctic grounding line, Antarct.
Sci., 20(5), 1–5, doi:10.1017/S095410200800148X, 2008.
Vaughan, D. G.: Tidal Flexure at Ice Sheet Margins, J. Geophys.
Res., 100(B4), 6213–6224, 1995.
Wiens, D. A., Anandakrishnan, S.,Winberry, J. P., and King,M. A.:
Simultaneous teleseismic and geodetic observations of the stickslip
motion of an Antarctic ice stream, Nature, 453, 770–774,
doi:10.1038/nature06990, 2008.
Wildey, R. L.: Generalized photoclinometry for Mariner 9, Icarus,
25, 613–626, 1975.
Yamanokuchi, T., Doi, K., and Shibuya, K.: Validation of grounding
line of the East Antarctic Ice Sheet derived by ERS-1/2 interferometric
SAR data, Polar Geoscience, 18, 1–14, 2005.
Zwally, H. J., Schutz, R., Bentley, C., Bufton, J., Herring, T., Minster,
J., Spinhirne, J., and Thomas, R.: GLAS/ICESat L2 Antarctic
and Greenland Ice Sheet Altimetry Data V001, Boulder, CO:
National Snow and Ice Data Center, Digital media, 2003.