Abstract The Hale impact crater is a large complex crater ( c. 150 × c. 125 km) in the southern hemisphere of Mars. Recurring slope lineae have been observed on its central-peak slopes, as have relatively youthful gully-like landforms; the latter are observed adjacent to or in the midst of the former, as well as on all of the rim-material slopes. Three of the gullied slopes on the northern-rim materials exhibit landscape features that, on Earth, are synonymous with wet periglaciation, i.e. landscape modification by the freeze–thaw cycling of water. These features include: (1) gelifluction-like lobes; (2) patches of surface polygonization, possibly underlain by ice wedges and formed by thermal-contraction cracking; and (3) shallow, rimless and polygonized basins morphologically akin to terrestrial alases. Here, we use the spatial association of the gully-like landforms together with the putatively wet periglacial assemblages or complexes to deduce and ascribe, albeit indirectly, a wet origin to the former.

Abstract Near the South Pole, a large subglacial lake exists beneath the East Antarctic Ice Sheet less than 10 km from where the bed temperature is inferred to be −9°C. A thermodynamic model was used to investigate the apparent contradiction of basal water existing in the vicinity of a cold bed. Model results indicate that South Pole Lake is freezing and that neither present-day geothermal flux nor ice flow is capable of producing the necessary heat to sustain basal water at this location. We hypothesize that the lake comprises relict water formed during a different configuration of ice dynamics when significant frictional heating from ice sliding was available. Additional modelling of assumed basal sliding shows frictional heating was capable of producing the necessary heat to fill South Pole Lake. Independent evidence of englacial structures measured by airborne radar revel ice-sheet flow was more dynamic in the past. Ice sliding is estimated to have ceased between 16.8 and 10.7 ka based on an ice chronology from a nearby borehole. These findings reveal major post-Last Glacial Maximum ice-dynamic change within the interior of East Antarctica, demonstrating that the present interior ice flow is different than that under full glacial conditions.

Abstract Although the flow of the East Antarctic Ice Sheet is well constrained from surface measurements and altimetry, our knowledge of the dynamic processes within the ice sheet remains limited. Recent high-resolution radar data from the Gamburtsev Subglacial Mountains in central East Antarctica reveal a series of anomalous englacial reflectors in the lower half of the ice column that cannot be explained by conventional ice flow. Expanding on previous analyses, we describe the geometrical and morphological features of 12 of these anomalous reflectors. Our description reveals a previously unacknowledged diversity in size, geometry and internal structure of these reflectors. We are able to identify four distinct morphological features: (1) fingers; (2) inclusions; (3) sheets; and (4) folds. The ‘fingers’ and ‘inclusions’ probably form by shear instabilities at the boundary between the reflectors and the surrounding meteoric ice. The ‘sheets’ highlight that basal ice can be uplifted off of the bed and above surrounding meteoric ice, and the ‘folds’ may have formed in local regions of converging flow associated with subglacial topography. The study provides key insights into the rheology, stress and deformational regimes deep within the central East Antarctic Ice Sheet.

Abstract Drilling fluid (DF) is one of the main sources of chemical and biological contamination of deep ice cores and lake water samples in the exploration of Subgalcial Antarctic Lake Environments (SALE). In this study, we investigated the contamination of an ice core that represented the first samples of refrozen lake water obtained 1 year after the unsealing of Lake Vostok in 2012. We show that these samples contain inclusions of the DF with a concentration of at least 16.7 mg l −1 (0.0019% or 19 ppmv). This makes it extremely difficult to obtain reliable data on the real chemical composition of the lake water. The focus of our study is the organic components of the DF, which built up in the secondary ice while the water was freezing in the borehole. Of all the possible organic compounds of the DF, only phenol congeners (up to 32.4 mg l −1 ) and dichlorofluoroethane HCFC-141b (14.4 mg l −1 ), a DF densifier, were found in the central channel, which is the last part of the core to freeze in the borehole. We conclude that the phenol compounds emerge due to physical processes, namely fractionation, during freezing, rather than any chemical reaction between the DF and the lake water. Supplementary material: The detailed chemical data are available at https://doi.org/10.6084/m9.figshare.c.3783641