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We present a reference, comprehensive, high-resolution, digital mosaic of ice motion in Antarctica assembled from multiple satellite interferometric synthetic-aperture radar data acquired during the International Polar Year 2007 to 2009. The data reveal widespread, patterned, enhanced flow with tributary glaciers reaching hundreds to thousands of kilometers inland over the entire continent. This view of ice sheet motion emphasizes the importance of basal-slip—dominated tributary flow over deformation-dominated ice sheet flow, redefines our understanding of ice sheet dynamics, and has far-reaching implications for the reconstruction and prediction of ice sheet evolution.

We compare the volume flux divergence of Antarctic ice shelves in 2007 and 2008 with 1979 to 2010 surface accumulation and 2003 to 2008 thinning to determine their rates of melting and mass balance. Basal melt of 1325 ± 235 gigatons per year (Gt/year) exceeds a calving flux of 1089 ± 139 Gt/year, making ice-shelf melting the largest ablation process in Antarctica. The giant cold-cavity Ross, Filchner, and Ronne ice shelves covering two-thirds of the total ice-shelf area account for only 15% of net melting. Half of the meltwater comes from 10 small, warm-cavity Southeast Pacific ice shelves occupying 8% of the area. A similar high melt/area ratio is found for six East Antarctic ice shelves, implying undocumented strong ocean thermal forcing on their deep grounding lines.

The delineation of an ice sheet grounding line, i.e., the transition boundary where ice detaches from the bed and becomes afloat in the ocean, is critical to ice sheet mass budget calculations, numerical modeling of ice sheet dynamics, ice‐ocean interactions, oceanic tides, and subglacial environments. Here, we present 15 years of comprehensive, high‐resolution mapping of grounding lines in Antarctica using differential satellite synthetic‐aperture radar interferometry (DInSAR) data from the Earth Remote Sensing Satellites 1–2 (ERS‐1/2), RADARSAT‐1 and 2, and the Advanced Land Observing System (ALOS) PALSAR for years 1994 to 2009. DInSAR directly measures the vertical motion of floating ice shelves in response to tidal oceanic forcing with millimeter precision, at a sample spacing better than 50 m, simultaneously over areas several 100 km wide; in contrast with earlier methods that detect abrupt changes in surface slope in satellite visible imagery or altimetry data. On stagnant and slow‐moving areas, we find that breaks in surface slope are reliable indicators of grounding lines; but on most fast‐moving glaciers and ice streams, our DInSAR results reveal that prior mappings have positioning errors ranging from a few km to over 100 km. A better agreement is found with ICESat's data, also based on measurements of vertical motion, but with a detection noise one order of magnitude larger than with DInSAR. Overall, the DInSAR mapping of Antarctic grounding lines completely redefines the coastline of Antarctica. Key Points Prior mapping techniques yield large uncertainties Antarctic coastline completely redefined along nearly all its outlet glaciers Underlines critical need for direct mapping of ice sheet grounding lines

The sudden propagation of a major preexisting rift (full-thickness crack) in late 2016 on the Larsen C Ice Shelf, Antarctica led to the calving of tabular iceberg A68 in July 2017, one of the largest icebergs on record, posing a threat for the stability of the remaining ice shelf. As with other ice shelves, the physical processes that led to the activation of the A68 rift and controlled its propagation have not been elucidated. Here, we model the response of the ice shelf stress balance to ice shelf thinning and thinning of the ice mélange encased in and around preexisting rifts. We find that ice shelf thinning does not reactivate the rifts, but heals them. In contrast, thinning of the mélange controls the opening rate of the rift, with an above-linear dependence on thinning. The simulations indicate that thinning of the ice mélange by 10 to 20 m is sufficient to reactivate the rifts and trigger a major calving event, thereby establishing a link between climate forcing and ice shelf retreat that has not been included in ice sheet models. Rift activation could initiate ice shelf retreat decades prior to hydrofracture caused by water ponding at the ice shelf surface.

After 8 years of decay of its ice shelf, Zachariæ Isstrøm, a major glacier of northeast Greenland that holds a 0.5-meter sea-level rise equivalent, entered a phase of accelerated retreat in fall 2012. The acceleration rate of its ice velocity tripled, melting of its residual ice shelf and thinning of its grounded portion doubled, and calving is now occurring at its grounding line. Warmer air and ocean temperatures have caused the glacier to detach from a stabilizing sill and retreat rapidly along a downward-sloping, marine-based bed. Its equal-ice-volume neighbor, Nioghalvfjerdsfjorden, is also melting rapidly but retreating slowly along an upward-sloping bed. The destabilization of this marine-based sector will increase sea-level rise from the Greenland Ice Sheet for decades to come.

The Pope, Smith, and Kohler glaciers, in the Amundsen Sea Embayment of West Antarctica, have experienced enhanced ocean-induced ice-shelf melt, glacier acceleration, ice thinning, and grounding line retreat in the past thirty years. Here we present observations of the grounding line retreat of these glaciers since 2014 using a constellation of interferometric radar satellites combined with precision surface elevation data. We find that the grounding lines develop spatially-variable, kilometre-scale, tidally-induced migration zones. After correction for tidal effects, we detect a sustained pattern of retreat coincident with high melt rates of un-grounded ice, marked by episodes of more rapid retreat. In 2017, Pope Glacier retreated 3.5 km in 3.6 months, or 11.7 km/yr. In 2016-2018, Smith West retreated at 2 km/yr and Kohler at 1.3 km/yr. While the retreat slowed down in 2018-2020, these retreat rates are faster than anticipated by numerical models on yearly time scales. We hypothesize that the rapid retreat is caused by un-represented, vigorous ice-ocean interactions acting within newly-formed cavities at the ice-ocean boundary.

The Surface Deformation and Change (SDC) mission study is investigating a synthetic aperture radar (SAR) mission that is expected to launch in the next decade, building on the foundation established by the NASA ISRO Synthetic Aperture Radar (NISAR) mission. Since 2019, the SDC study team has updated the observation needs identified by the 2017 Earth Science Decadal Survey, developing a Science and Applications Traceability Matrix (SATM) that includes an expanded set of geophysical observables (GOs). These needs were further refined by a team of discipline experts, resulting in 48 GOs. For each GO, imaging characteristics such as revisit, accuracy, resolution, polarisation, data latency, are defined in the SATM. This paper describes the benefit assessment methodology, provides an example to generate current commercial feasibility scores for each GO in the SATM, even though the SDC mission will not be launched until the next decade. This methodology generates a quantitative assessment of commercial SAR data in meeting the measurement needs of a GO defined in SDC's SATM. Our assessment suggests that current commercial SAR data are particularly useful for constraining geophysical processes that benefit from short-repeat acquisition times and high spatial resolution.

We report changes in ice velocity of a 6.5 million km2 region around South Pole encompassing the Filchner-Ronne and Ross Ice Shelves and a significant portion of the ice streams and glaciers that constitute their catchment areas. Using the first full interferometric synthetic aperture radar (InSAR) coverage of the region completed in 2009 and partial coverage acquired in 1997, we processed the data to assemble a comprehensive map of ice speed changes between those two years. On the Ross Ice Shelf, our results confirm a continued deceleration of Mercer and Whillans Ice Streams with a 12-yr velocity difference of −50 m yr−1 (−16.7%) and −100 m yr−1 (−25.3%) at their grounding lines. The deceleration spreads 450 km upstream of the grounding line and more than 500 km onto the shelf, beyond what was previously known. Ross and Filchner Ice Shelves exhibit signs of pre-calving events, representing the largest observed changes, with an increase in speed in excess of +100 m yr−1 in 12 yr. Other changes in the Ross Ice Shelf region are less significant. The observed changes in glacier speed extend on the Ross Ice Shelf along the ice streams' flow lines. Most tributaries of the Filchner-Ronne Ice Shelf show a modest deceleration or no change between 1997 and 2009. Slessor Glacier shows a small deceleration over a large sector. No change is detected on the Bailey, Rutford, and Institute Ice Streams. On the Filchner Ice Shelf itself, ice decelerated rather uniformly with a 12-yr difference in speed of −50 m yr−1, or −5% of its ice front speed, which we attribute to a 12 km advance in its ice front position. Our results show that dynamic changes are present in the region. They highlight the need for continued observation of the area with a primary focus on the Siple Coast. The dynamic changes in Central Antarctica between 1997 and 2009 are generally second-order effects in comparison to losses on glaciers in the Bellingshausen and Amundsen Seas region and on the Antarctic Peninsula. We therefore conclude that the dynamic changes shown here do not have a strong impact on the mass budget of the Antarctic continent.

Knowledge of Antarctic glacier grounding lines, which mark the transition between grounded and floating ice, is a vital parameter in determining the stability of major ice shelves and hence the ice sheet. Rapid grounding line retreat and associated mass loss has been documented at numerous Antarctic glaciers, particularly in the Amundsen Sea Embayment. However, few comprehensive grounding line mappings exist, particularly from recent years. Here, we utilize a unique record of Sentinel-1 Synthetic Aperture Radar 1 d repeat-pass imagery to generate a comprehensive retrieval of grounding line location in the Amundsen Sea Embayment in 2025 and evaluate recent changes.

Shrinking shelf and faster flowZachariae Isstroem, a large glacier in northeast Greenland, began a rapid retreat after detaching from a stabilizing sill in the late 1990s. Mouginot et al. report that between 2002 and 2014, the area covered by the glacier's ice shelf shrank by 95%; since 1999, the glacier's flow rate has nearly doubled; and its acceleration increased threefold in the fall of 2012. These dramatic changes appear to be the result of a combination of warmer air and ocean temperatures and the topography of the ocean floor at the head of the glacier. Rising sea levels should continue to destabilize the marine portion of Zachariae Isstroem for decades.Science, this issue p. 1357 After 8 years of decay of its ice shelf, Zachariae Isstroem, a major glacier of northeast Greenland that holds a 0.5-meter sea-level rise equivalent, entered a phase of accelerated retreat in fall 2012. The acceleration rate of its ice velocity tripled, melting of its residual ice shelf and thinning of its grounded portion doubled, and calving is now occurring at its grounding line. Warmer air and ocean temperatures have caused the glacier to detach from a stabilizing sill and retreat rapidly along a downward-sloping, marine-based bed. Its equal-ice-volume neighbor, Nioghalvfjerdsfjorden, is also melting rapidly but retreating slowly along an upward-sloping bed. The destabilization of this marine-based sector will increase sea-level rise from the Greenland Ice Sheet for decades to come.