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Ridley, J, Strawbridge F, Card R, Phillips H.  1996.  Radar backscatter characteristics of a desert surface. Remote Sensing of Environment. 57:63-78.   10.1016/0034-4257(96)00018-1   AbstractWebsite

Satellite radar altimeter measurements have shown spn tial and temporal variations in the backscattered signal from desert surfaces. In order to understand these variations we have carried out extensive in situ measurements for the validation of a compilation of existing backscatter models. The model predictions are in excellent agreement with ground- and satellite-based measurements of the radar backscatter coefficient, and show that the altimeter backscatter measurements are strongly affected by variations in soil moisture following rainfall and by the presence of dew On the surface. Regional, but time-invariant, differences in backscatter are attributed to variations in surface topography.

Borsa, AA, Moholdt G, Fricker HA, Brunt KM.  2014.  A range correction for ICESat and its potential impact on ice-sheet mass balance studies. The Cryosphere. 8:345-357.: Copernicus Publications   10.5194/tc-8-345-2014   AbstractWebsite

We report on a previously undocumented range error in NASA's Ice, Cloud and land Elevation Satellite (ICESat) that degrades elevation precision and introduces a small but significant elevation trend over the ICESat mission period. This range error (the Gaussian-Centroid or "G-C" offset) varies on a shot-to-shot basis and exhibits increasing scatter when laser transmit energies fall below 20 mJ. Although the G-C offset is uncorrelated over periods ≤ 1 day, it evolves over the life of each of ICESat's three lasers in a series of ramps and jumps that give rise to spurious elevation trends of −0.92 to −1.90 cm yr−1, depending on the time period considered. Using ICESat data over the Ross and Filchner–Ronne ice shelves we show that (1) the G-C offset introduces significant biases in ice-shelf mass balance estimates, and (2) the mass balance bias can vary between regions because of different temporal samplings of ICESat. We can reproduce the effect of the G-C offset over these two ice shelves by fitting trends to sample-weighted mean G-C offsets for each campaign, suggesting that it may not be necessary to fully repeat earlier ICESat studies to determine the impact of the G-C offset on ice-sheet mass balance estimates.

Bougamont, M, Christoffersen P, Price SF, Fricker HA, Tulaczyk S, Carter SP.  2015.  Reactivation of Kamb Ice Stream tributaries triggers century-scale reorganization of Siple Coast ice flow in West Antarctica. Geophysical Research Letters. 42:8471-8480.   10.1002/2015gl065782   AbstractWebsite

Ongoing, centennial-scale flow variability within the Ross ice streams of West Antarctica suggests that the present-day positive mass balance in this region may reverse in the future. Here we use a three-dimensional ice sheet model to simulate ice flow in this region over 250years. The flow responds to changing basal properties, as a subglacial till layer interacts with water transported in an active subglacial hydrological system. We show that a persistent weak bed beneath the tributaries of the dormant Kamb Ice Stream is a source of internal ice flow instability, which reorganizes all ice streams in this region, leading to a reduced (positive) mass balance within decades and a net loss of ice within two centuries. This hitherto unaccounted for flow variability could raise sea level by 5mm this century. Better constraints on future sea level change from this region will require improved estimates of geothermal heat flux and subglacial water transport.

Jacka, TH, Abdalati W, Allison I, Carsey F, Casassa G, Fily M, Frezzotti M, Fricker HA, Genthon C, Goodwin I, Guo Z, Hamilton GS, Hindmarsh RCA, Hulbe CL, Jacka TH, Jezek KC, Scambos TA, Shuman C, Skvarca P, Takahashi S, van de Wal RSW, Vaughan DG, Wang WL, Warner RC, Wingham DJ, Young NW, Zwally HJ, Comm I.  2004.  Recommendations for the collection and synthesis of Antarctic Ice Sheet mass balance data. Global and Planetary Change. 42:1-15.   10.1016/j.gloplacha.2003.11.008   AbstractWebsite

Recent unexpected changes in the Antarctic Ice Sheet, including ice sheet thinning, ice shelf collapse and changes in ice velocities, along with the recent realization that as much as one third of ice shelf mass loss is due to bottom melt, place a new urgency on understanding the processes involved in these changes. Technological advances, including very new or forthcoming satellite-based (e.g. ICESat, CryoSat) remote sensing missions, will improve our ability to make meaningful determinations of changes in Antarctic Ice Sheet mass balance. This paper is the result of a workshop held to develop a strategy for international collaboration aimed at the collection and synthesis of Antarctic Ice Sheet mass balance data, and at understanding the processes involved so that we might predict future change. Nine sets of recommendations are made, concerning the most important and sensitive measurements, temporal ranges and study areas. A final tenth recommendation calls for increased synthesis of ice sheet data and communication between the field measurement, satellite observation and modelling communities. (C) 2004 Published by Elsevier B.V.

Fricker, HA, Allison I, Craven M, Hyland G, Ruddell A, Young N, Coleman R, King M, Krebs K, Popov S.  2002.  Redefinition of the Amery Ice Shelf, East Antarctica, grounding zone. Journal of Geophysical Research-Solid Earth. 107   10.1029/2001jb000383   AbstractWebsite

[1] New evidence is presented which shows that the Amery Ice Shelf, East Antarctica, extends similar to240 km upstream of the previously reported position. We combine a digital elevation model of the Amery Ice Shelf created from ERS-1 satellite radar altimetry with measured ice thicknesses and a simple density model in a hydrostatic (buoyancy) calculation to map the extent of the floating ice. This reveals that the ice is floating as far south as 73.2degreesS. The result is confirmed by static GPS measurements collected during three consecutive field campaigns on the Amery Ice Shelf where the vertical component of the GPS shows a clear tidal signal at 72.98degreesS. Other evidence for the grounding zone position comes from an analysis of satellite imagery, mass flux calculations, and ice radar data. The southward extension of the grounding line substantially alters the shape and dimensions of the ocean cavity beneath the ice shelf, which has implications for modeling studies of sub-ice shelf processes, such as basal melting and freezing, ocean circulation, and tides. The new grounding line position will also improve geophysical studies, where the computation of ocean tidal loading corrections is important for postglacial rebound estimates and correction of satellite altimetry measurements within the region.

Paolo, FS, Padman L, Fricker HA, Adusumilli S, Howard S, Siegfried MR.  2018.  Response of Pacific-sector Antarctic ice shelves to the El Nino/Southern Oscillation. Nature Geoscience. 11:121-+.   10.1038/s41561-017-0033-0   AbstractWebsite

Satellite observations over the past two decades have revealed increasing loss of grounded ice in West Antarctica, associated with floating ice shelves that have been thinning. Thinning reduces an ice shelf's ability to restrain grounded-ice discharge, yet our understanding of the climate processes that drive mass changes is limited. Here, we use ice-shelf height data from four satellite altimeter missions (1994-2017) to show a direct link between ice-shelf height variability in the Antarctic Pacific sector and changes in regional atmospheric circulation driven by the El Nino/Southern Oscillation. This link is strongest from the Dotson to Ross ice shelves and weaker elsewhere. During intense El Nino years, height increase by accumulation exceeds the height decrease by basal melting, but net ice-shelf mass declines as basal ice loss exceeds ice gain by lower-density snow. Our results demonstrate a substantial response of Amundsen Sea ice shelves to global and regional climate variability, with rates of change in height and mass on interannual timescales that can be comparable to the longer-term trend, and with mass changes from surface accumulation offsetting a significant fraction of the changes in basal melting. This implies that ice-shelf height and mass variability will increase as interannual atmospheric variability increases in a warming climate.

Tinto, KJ, Padman L, Siddoway CS, Springer SR, Fricker HA, Das I, Tontini FC, Porter DF, Frearson NP, Howard SL, Siegfried MR, Mosbeux C, Becker MK, Bertinato C, Boghosian A, Brady N, Burton BL, Chu W, Cordero SI, Dhakal T, Dong L, Gustafson CD, Keeshin S, Locke C, Lockett A, O'Brien G, Spergel JJ, Starke SE, Tankersley M, Wearing MG, Bell RE.  2019.  Ross Ice Shelf response to climate driven by the tectonic imprint on seafloor bathymetry. Nature Geoscience. 12:441-+.   10.1038/s41561-019-0370-2   AbstractWebsite

Ocean melting has thinned Antarctica's ice shelves at an increasing rate over the past two decades, leading to loss of grounded ice. The Ross Ice Shelf is currently close to steady state but geological records indicate that it can disintegrate rapidly, which would accelerate grounded ice loss from catchments equivalent to 11.6 m of global sea level rise. Here, we use data from the ROSETTA-Ice airborne survey and ocean simulations to identify the principal threats to Ross Ice Shelf stability. We locate the tectonic boundary between East and West Antarctica from magnetic anomalies and use gravity data to generate a new high-resolution map of sub-ice-shelf bathymetry. The tectonic imprint on the bathymetry constrains sub-ice-shelf ocean circulation, protecting the ice shelf grounding line from moderate changes in global ocean heat content. In contrast, local, seasonal production of warm upper-ocean water near the ice front drives rapid ice shelf melting east of Ross Island, where thinning would lead to faster grounded ice loss from both the East and West Antarctic ice sheets. We confirm high modelled melt rates in this region using ROSETTA-Ice radar data. Our findings highlight the significance of both the tectonic framework and local ocean-atmosphere exchange processes near the ice front in determining the future of the Antarctic Ice Sheet.