Abstract Driven by successful achievements in recovering high-resolution ice records of climate and atmospheric composition through the Late Quaternary, new ice–tephra sequences from various sites of the East Antarctic Ice Sheet (EAIS) have been studied in the last two decades spanning an age range of a few centuries to 800 kyr. The tephrostratigraphic framework for the inner EAIS, based on ash occurrence in three multi-kilometre-deep ice cores, shows that the South Sandwich Islands represent a major source for tephra, highlighting the major role in the ash dispersal played by clockwise circum-Antarctic atmospheric circulation penetrating the Antarctic continent. Tephra records from the eastern periphery of the EAIS, however, are obviously influenced by explosive activity sourced in nearby Antarctic rift provinces. These tephra inventories have provided a fundamental complement to the near-vent volcanic record, in terms of both frequency/chronology of explosive volcanism and of magma chemical evolution through time. Despite recent progress, current data are still sparse. There is a need for further tephra studies to collect data from unexplored EAIS sectors, along with extending the tephra inventory back in time. Ongoing international palaeoclimatic initiatives of ice-core drilling could represent a significant motivation for the tephra community and for Quaternary Antarctic volcanologists.

Abstract Records of fluctuations of the East Antarctic Ice Sheet (EAIS) are best preserved in proximal marine sediments. The examined section is a part of a drillcore at Site U1359 of IODP (Integrated Oceanic Drilling Program) 318 located at the eastern levee of Jussieau submarine channel off the coast of Wilkes Land. Drillcore U1359 from 200 m below seafloor (mbsf) to 600 mbsf represents samples from Mid-Miocene to Late Miocene. Heavy media separation, characterization of heavy minerals and quantification of their population were carried out using scanning electron microscopy and electron microprobe analysis. Relative abundance of various minerals at different depths revealed that amphiboles and pyroxene show antipathic relationship at some depths. Multiple sources for supply of sediments at drillhole Site U1359 have been proposed with both magmatic and metamorphic minerals and rock fragments contributing clastic sediments. Factor analysis was carried out to test this inference. Six factors were obtained out of which the first three explain 76.6% of the variance. Relating variability of the factors to the provenance allows inference of four major ice advance phases during Mid to Late Micene which are largely positively correlatable with the global climate record. Supplementary material: Table showing the linear relationship between the rows and columns of the matrix of correlation coefficients of samples is available at https://doi.org/10.6084/m9.figshare.c.3805726

Abstract Rare jökulhlaup events, also known as subglacial lake outburst flood events, have been observed at the Law Dome ice margin and provide an insight into the physical characteristics of subglacial meltwater and drainage. The subglacial topography based on data from the BEDMAP2 and ICECAP projects, together with subsurface transects of the ice margin obtained using ground-penetrating radar, reveal several lakes and lake-like depressions and the drainage pathways of two jökulhlaup events. Oxygen isotope typing of the meltwater during the most recent (2014) jökulhlaup event, combined with ice margin stratigraphy, enable the identification of ice tunnel melt pathways that exploit the 30–90° dipping basal ice layering. The presence of subglacial meltwater beneath Law Dome during the Holocene to Glacial periods is confirmed by the dendritic drainage pattern in the subglacial morphology and extensive layers of basal regelation ice and subglacial carbonate precipitate deposits found within the Løken Moraines sediments. These subglacial carbonates, including ooid layers, formed from the mixing of glacial meltwater and seawater at 72 ka BP. The combined evidence indicates that the ocean discharge of subglacial meltwater may be variable and/or is periodically blocked by basal freezing events near the ice sheet terminus.

Abstract We present a synthesis based on the interpretation of two pairs of deep seismic reflection crustal sections within the Southern Rift System (SRS) separating Australia and Antarctica. One pair of sections is from the conjugate margins between the Great Australian Bight (GAB) and Wilkes Land, in the central sector of the SRS, which broke up in the Campanian. The second pair of conjugate sections is located approximately 400 km further east, between the Otway Basin and Terre Adélie, which probably broke up in Maastrichtian time. Interpretations are based on an integrated synthesis of deep multi-channel seismic, gravity and magnetic data, together with sparse sonobuoy and dredging information, and the conjugate sections are presented with the oceanic crust removed beyond the continent–ocean boundary (COB). At first order, both conjugate pairs show a transition from thinned continental crust, through a wide and internally complex continent–ocean transition zone (COTZ), which shows features in common with magma-poor rifted margins worldwide, such as basement ridges interpreted as exhumed subcontinental mantle. In the central GAB sector, the COTZ is symmetric around the point of break-up and displays a pair of mantle ridges, one on each margin, outboard of which lies a deep-water rift basin. Break-up has occurred in the centre of this basin in this sector of the SRS. In contrast, the Terre Adélie margin is nearly 600 km wide and shows an abandoned crustal megaboudin, the Adélie Rift Block. This block is underlain by interpreted middle crust, and appears to have a mantle ridge structure inboard, as well as an outboard exhumed mantle complex from which mylonitized harzburgite has been dredged. The conjugate margin of the Beachport Sub-basin is relatively narrow ( c. 100 km wide) and does not appear to contain an exhumed mantle ridge, as observed along strike in the GAB. These observations from a single rift spreading compartment show that radically different break-up symmetries and margin architectures can result from an essentially symmetric rifting process involving multiple, paired detachment systems. This indicates the need for caution in interpreting causative mechanisms of rifting from limited conjugate sections in other rifts. We speculate that the underlying crustal composition, rheology and structural preconditioning play a significant role in partitioning strain during the transition to break-up.

Large floating glaciers are presently confined to the polar regions of Antarctica. The sedimentary facies associated with these ice masses therefore appear to be unique to the polar setting. However, there is a wide range of glacial maritime settings in Antarctica, and no single model is adequate to illustrate the variety of lithofacies to be found in these different settings. The largest floating ice masses of Antarctica are the Ross, Ronne-Filchner, and Amery Ice Shelves, which are the floating extensions of the ice sheet and occur at the confluence of large ice streams. Theoretical studies of the dynamics of large ice shelves suggest that the basal debris they transport is associated within a fairly narrow (tens of kilometers wide) transition zone where the ice is intermittently coupled to the sea floor. The zone is characterized mainly by subglacial deposits (basal tills) and glacial marine diamictons (transitional glacial marine sediments). These two sediment types are virtually identical. In the Ross Sea, surface sediments consist of diatomaceous glacial marine sediments. These sediments are relatively thin over most of the continental shelf, where they rest in sharp contact on basal tills. Transitional glacial marine sediments are rare, and basal tills grade offshore into bioclastic carbonates. These stratigraphic relations imply that the ice sheet was fully grounded on the shelf during the last glacial maximum and that seaward of this expanded ice sheet the sea floor was starved of terrigenous sediment. The retreat of the ice sheet from the continental shelf was so rapid that sub–ice shelf sediments were not deposited. Rapid retreat is expected within a foredeepened shelf setting. Fringing ice shelves represent the second most extensive bodies of floating glacial ice in Antarctica. They may contain a significant portion of ice that is accreted onto the ice shelf directly, either by surface accumulation or basal freezing of seawater. They tend to be thinner than large ice shelves, which implies conditions more suitable for basal freezing. Fringing ice shelves may contain significant englacial and supra-glacial debris that is entrained by the ice shelf from nearby tributary glaciers originating near mountains and nunataks. This implies that fringing ice shelves are more efficient at delivering sediment seaward of the grounding line than are large ice shelves. The Larsen Ice Shelf, as an example, has associated with it an extensive diamicton facies. These diamictons are overlain by predominantly terrigenous, glacial marine sediments whose grain size shows clear influence of marine currents on sedimentation. The third type of ice shelf setting studied (the George VI Ice Shelf) is one that is confined by valley walls. It is the only one of the three examples studied in which an ice shelf recessional lithofacies is clearly recognized. This lithofacies is composed of transitional glacial marine sediments that grade upward into terrigenous muds, which are inferred to be derived from subglacial meltwater outflow. The sub–ice shelf facies is overlain by diatomaceous muds and oozes, which indicates open-marine conditions. Ice tongues, while small in size, represent a significant mode of ice drainage from the Antarctic continent. The two examples studied include the shelf areas adjacent to the Drygalski Ice Tongue and the Mertz and Ninnis Ice Tongues. There is an apparent absence of a transitional glacial marine facies in these ice tongue settings. This implies more widespread dispersal of debris by currents and the icebergs that calve from the tongues. Marine facies associated with ice tongues contain a large biogenic component, which is primarily siliceous. The floating portions of tidewater glaciers represent the smallest element of floating ice masses in Antarctica, and the only ones that exist in subpolar regions of the northern Antarctic Peninsula. Recent observations have led to the discovery of tunnel valleys beneath tidewater glaciers of the northern Antarctic Peninsula. These tunnel valleys are believed to act as conduits for cooling of seawater and limited subglacial meltwater outflow to the bays and fjords. The sedimentary facies associated with floating tidewater glaciers consist of massive and laminated muds within thin sand layers. Associated facies include diamicton and siliceous mud.