Measurements of snow accumulation are critical for reliable prediction of future ice mass loss and hence projections of sea level change. However, there are currently very few published in situ measurements of snow accumulation in the Pine Island–Thwaites glacier catchment of the Amundsen Sea Embayment, and none from low elevation sites west of 100.77° longitude. Here measurements of snow accumulation over an 11 month period in 2016 are reported for six sites in the Pine Island–Thwaites glacier catchment. The average accumulation rates of 0.10±0.01 to 1.26±0.22 m w.e. yr-1 are comparable with those derived from airborne radar for the period 1985–2009, suggesting very high rates of snowfall, particularly in the vicinity of the grounding line.

We use satellite radar interferometry to investigate changes in the location of the Petermann Glacier grounding line between 1992 and 2011. The grounding line location was identified in 17 quadruple-difference interferograms produced from European Remote Sensing (ERS)-1/2 data – the most extensive time series assembled at any ice stream to date. There is close agreement (20.6 cm) between vertical displacement of the floating ice shelf and relative tide amplitudes simulated by the Arctic Ocean Dynamics-based Tide Model 5 (AODTM-5) Arctic tide model. Over the 19 a period, the groundling line position varied by 470 m, on average, with a maximum range of 7.0 km observed on the north-east margin of the ice stream. Although the mean range (2.8 km) and variability (320 m) of the grounding line position is considerably lower if the unusually variable north-east sector is not considered, our observations demonstrate that large, isolated movements cannot be precluded, thus sparse temporal records should be analysed with care. The grounding line migration observed on Petermann Glacier is not significantly correlated with time (R2 = 0.22) despite reported ice shelf thinning and episodes of large iceberg calving, which suggests that unlike other ice streams, on the south-west margin of the Greenland ice sheet, Petermann Glacier is dynamically stable.

An extensive set of shore-parallel fractures are observed at the grounding line of Kamb Ice Stream (KIS) in West Antarctica. Seismicity measured in the grounding zone is, as elsewhere around Antarctica, tidally forced and moreover strand cracks propagate nearly exclusively on the falling tide. Measured surface deflection and a model of fracture propagation are used to conclude that bending on the falling tide favors propagation while bending on the rising tide suppresses propagation. Without the perturbation due to tidal bending, strand cracks would be rare and appear farther downstream than observed. We speculate that the very large number of cracks observed at KIS is due to the stagnant-to-floating transition at that grounding line, which allows cyclic bending of the same ice and relatively large stretching rates.

Present-day mass loss from the West Antarctic ice sheet is centred on the Amundsen Sea Embayment (ASE), primarily through ice streams, including Pine Island, Thwaites and Smith glaciers. To understand the differences in response of these ice streams, we ran a perturbed parameter ensemble, using a vertically-integrated ice flow model with adaptive mesh refinement. We generated 71 sets of three physical parameters (basal traction coefficient, ice viscosity stiffening factor and sub-shelf melt rate), which we used to simulate the ASE for 50 years. We also explored the effects of different bed geometries and basal sliding laws. The mean rate of sea-level rise across the ensemble of simulations is comparable with current observed rates for the ASE. We found evidence that grounding line dynamics are sensitive to features in the bed geometry: simulations using BedMap2 geometry resulted in a higher rate of sea-level rise than simulations using a rougher geometry, created using mass conservation. Modelled grounding-line retreat of all the three ice streams was sensitive to viscosity and basal traction, while the melt rate was more important in Pine Island and Smith glaciers, which flow through more confined ice shelves than Thwaites, which has a relatively unconfined shelf.

A mass balance calculation was made for the floating part of Byrd Glacier, using 1978–79 ice elevation and velocity data, over the 45 km of Byrd Glacier from its grounding line to where it leaves its fjord and merges with the Ross Ice Shelf. Smoothed basal melting rates were relatively uniform over this distance and averaged 12 ± 2 m yr−1.

The Weddell Sea region arguably represents the largest unknown in quantifying the Antarctic contribution to the global water balance following the Last Glacial Maximum (LGM). This paper reviews the available onshore and offshore geological evidence constraining the volume of formerly expanded ice in the Weddell Sea embayment, focusing on the West Antarctic Ice Sheet (WAIS) and provides a preliminary reconstruction of the WAIS during the LGM. Dating control is generally poor and so our WAIS reconstruction is based on the assumption that the evidence of most recent ice sheet expansion dates to the LGM. Our reconstruction is intended to provide initial constraints with which glaciological models can be compared and shows grounded ice extent, flow directions, and ice surface elevations. Both marine and terrestrial geological evidence imply a substantial expansion of ice in the Weddell Sea embayment. Marine evidence shows that ice sheets were grounded in Crary Trough in the southern Weddell Sea and on the Antarctic Peninsula continental shelf during the LGM. Inland, the ice thickened by between 400 m (Ellsworth and Palmer Land) and 1900 m (Ellsworth Mountains). Ice core evidence suggests that the interior of the ice sheet remained the same or even thinned relative to present. The main unknowns now concern the exact location of the grounding line on some sectors of the shelf and the timing of ice sheet grounding and retreat. The limited radiocarbon data that exist on the eastern shelf indicates that the East Antarctic Ice Sheet retreated from the shelf prior to the LGM.

Semi-continuous, linear accumulations of poorly-sorted debris are present on the surface of the remnant Larsen-A Ice Shelf, Antarctic Peninsula. These accumulations form a complex of debris bands extending parallel to the front of the ice shelf for several kilometres. Landsat imagery shows that the debris bands originated as lateral moraines along the Nordenskjöld Coast. Almost 80% of clasts sampled from these debris accumulations have shape/roundness characteristics consistent with glacier transport in the zone of basal traction. Angular and very angular clasts account for 15% and 22% of clasts in the pebble- and cobble/boulder-sized fractions, respectively, and originated by rockfall from valley/nunatak sides, with subsequent passive glacier transportation. Lithological analysis indicates that the debris is derived locally from the Nordenskjöld Coast, Cape Fairweather region and interior of the Antarctic Peninsula. Episodic melt-out and resedimentation of this debris from the front of the ice shelf would deliver pulses of coarse-grained sediment to the sea floor. Therefore, coarse-grained debris can also be released along the calving margin of small polar ice shelves fringing mountainous terrain, and could potentially be confused with sediment deposited at the grounding line of Antarctic ice-shelves. Sedimentological criteria to differentiate between these environments are proposed in this paper.