Current-controlled sedimentation in the north-western Weddell Sea

The sedimentary basins of the north-western Weddell Sea are characterized by a variety of contourite drifts. This study is aimed at their identification, spatial mapping and temporal evolution and based on the integration of a large amount of seismic data collected by different countries including the recent data of the Russian Antarctic Expedition. Most of the drifts in the region being studied are classified as separated, confined, plastered or sheeted. The chain of sediment wave fields is mapped in the western and northern Powell Basin. The earliest contourite drifts started to form in the Early Miocene or, possibly, in the Late Oligocene. The changes in the depositional pattern in the Middle Miocene and then in the Late Pliocene are thought to have resulted from successive intensification of the bottom currents. Контуритовые наносы, формируемые придонными течениями, могут использоваться для изучения циркуляции водных масс, так как по их параметрам и характеру распространения можно судить о направленности и относительной энергии придонных течений. В данной работе рассматриваются контуритовые наносы в северо-западной части моря Уэдделла, приводится схема распространения наносов и их классификация, а также реконструируется циркуляция водных масс в глубоководных бассейнах района. Исследования основаны на обобщении и интерпретации сейсмических данных отечественных и зарубежных экспедиций, большая часть которых доступна из международной библиотеки сейсмических данных по Антарктике. В результате анализа сейсмических данных в районе исследований в диапазоне глубин от 2000 до 4500 м выявлены отделенные, ограниченные, пластерные и покровные контуритовые наносы.  Зарождение донных течений в северо-западной части моря Уэдделла  началось с раскрытия бассейна Пауэлл, и развитие самых ранних  контуритовых наносов предполагается 24–23 млн лет назад. В среднем миоцене и в позднем плиоцене отмечается усиление интенсивности донных течение и более широкое развитие контуритовых наносов.

Distribution of oceanic crust in the Enderby Basin offshore East Antarctica

Seismic reflection and refraction data were collected in 2007 and 2012 to reveal the crustal fabric on a single long composite profile offshore Prydz Bay, East Antarctica. A P-wave velocity model provides insights on the crustal fabric, and a gravity-constrained density model is used to describe the crustal and mantle structure. The models show that a 230-km- wide continent–ocean transition separates stretched continental from oceanic crust along our profile. While the oceanic crust close to the continent–ocean boundary is just 3.5–5 km thick, its thickness increases northwards towards the Southern Kerguelen Plateau to 12 km. This change is accompanied by thickening of a lower crustal layer with high P-wave velocities of up to 7.5 km s–1, marking intrusive rocks emplaced beneath the mid-ocean ridge under increasing influence of the Kerguelen plume. Joint interpretations of our crustal model, seismic reflection data and magnetic data sets constrain the age and extent of oceanic crust in the research area. Oceanic crust is shown to continue to around 160 km farther south than has been interpreted in previous data, with profound implications for plate kinematic models of the region. Finally, by combining our findings with a regional magnetic data compilation and regional seismic reflection data we propose a larger extent of oceanic crust in the Enderby Basin than previously known

Depositional and erosional signatures in sedimentary successions on the continental slope and rise off Prydz Bay, East Antarctica– implications for Pliocene paleoclimate

The Prydz Bay region of Antarctica is the immediate recipient of ice and sediments transported by the Lambert Glacier, the single largest outflow from the East Antarctic Ice Sheet. The continental slope and rise provide records covering multiple glacial cycles and containing paleoclimatic information. Marine geological and geophysical data collected from the continental shelf and adjacent slope of Prydz Bay, Antarctica, including seismic reflection data, bathymetry, and core records from ODP drilling sites, reveal the history of glacial sediment transport and deposition since the early Pliocene times. Seismic facies are interpreted in terms of episodes of slope progradation, contourite, turbidite, trough-mouth fan, and mass transport deposition. Two seismic units with estimated age of early to late Pliocene and late Pliocene to recent have been analyzed in detail for the area immediately offshore the Lambert Glacier and Prydz Bay and the adjacent Mac. Robertson margin. The upper slope is dominated by episodic mass transport deposits, many of which accumulated to form a trough mouth fan since Early Pliocene times. The trough mouth fan contrasts with the adjacent steep (4-6 degrees) continental slope of the Mac. Robertson margin, where glacigenic sediments have been transported down slope as high-velocity turbidity currents via submarine channels. The distal region exhibits evidence for contrasting effects of high-energy, traction-dominated versus lower-energy, fallout-dominated suspension flows. The counter-clockwise Coriolis force modifies the erosion and deposition patterns of turbidity currents creating an asymmetric channel-levee architecture. Since the early Pliocene, turbidite sedimentation surpassed the amount of sediment reworked and transported by westward-flowing contour currents along the base of slope. On the continental rise, contourites and sediment waves were deposited in response to enhanced bottom-water formation, which is consistent with climatic cooling since late Pliocene times. This study, based on existing seismic reflection and ODP data, highlights the need for a future scientific ocean drilling proposal on the Prydz Bay continental slope and rise in order to more accurately determine the timing of the important events that have influenced the evolution of this margin

A New Grounding-line Proximal Sedimentary Record from Inner Pine Island Bay

Pine Island Glacier (PIG) is one of the fastest changing ice streams of the West Antarctic Ice Sheet. Its ice shelf underwent major calving events throughout recent years. The main factor for the considerable mass loss of PIG is sub-ice shelf melting caused by the advection of warm deep water into Pine Island Bay on the shelf of the southeastern Amundsen Sea Embayment (ASE). Unique ice conditions during expedition PS104 with RV “Polarstern” to the ASE in February-March 2017 allowed to recover a 7.59 m-gravity core in an area that had been covered by the PIG ice shelf until 2015. The sediment core PS104_008-2 was taken at a water depth of 698 m near the eastern margin of the ice shelf. The new sedimentological data from the core will provide insights into sub-ice shelf environmental conditions and the Holocene history of meltwater plume deposition and oceanic ice-shelf melting. We will present results of our new multi-proxy study, including down-core lithological changes, grain size distribution and excess 210Pb data. Occasional occurrence of calcareous benthic foraminifera shells in the lower part of the core will allow the application of radiocarbon dating. Coupled with the excess 210Pb data, the AMS 14C ages will provide constraints on sub-ice shelf sediment accumulation rates and the discharge rates of subglacial meltwater plumes

The role of lithospheric flexure in the landscape evolution of the Wilkes Subglacial Basin and Transantarctic Mountains, East Antarctica

Reconstructions of the bedrock topography of Antarctica since the Eocene–Oligocene Boundary (ca. 34 Ma) provide important constraints for modelling Antarctic ice sheet evolution. This is particularly important in regions where the bedrock lies below sea level, since in these sectors the overlying ice sheet is thought to be most susceptible to past and future change. Here we use 3D flexural modelling to reconstruct the evolution of the topography of the Wilkes Subglacial Basin (WSB) and Transantarctic Mountains (TAM) in East Antarctica. We estimate the spatial distribution of glacial erosion beneath the East Antarctic Ice Sheet, and restore this material to the topography, which is also adjusted for associated flexural isostatic responses. We independently constrain our post‐34 Ma erosion estimates using offshore sediment stratigraphy interpretations. Our reconstructions provide a better‐defined topographic boundary condition for modelling early East Antarctic Ice Sheet history. We show that the majority of glacial erosion and landscape evolution occurred prior to 14 Ma, which we interpret to reflect more dynamic and erosive early ice sheet behaviour. In addition, we use closely‐spaced 2D flexural models to test previously proposed hypotheses for a flexural origin of the TAM and WSB. The pre‐34 Ma topography shows lateral variations along the length of the TAM and WSB that cannot be explained by uniform flexure along the front of the TAM. We show that some of these variations may be explained by additional flexural uplift along the south‐western flank of the WSB and the Rennick Graben in northern Victoria Land

Pre-site Study for Deep Geological Drilling below Ekström Ice Shelf, Sub-EIS-Obs

During the last seasons and ongoing, pre-site seismic surveys have taken place in the Ekströmisen region of Dronning Maud Land, with the primary of building a stratigraphic age framework of the under-ice-shelf sediments. These sediments are overlying the Explora Wedge, a syn- or post-rift volcanic deposit. Expected ages range from Late Mesozoic to Quaternary. From new vibroseismic profiles we will select sites for short core seafloor sampling through Hot Water Drill (HWD) holes of the oldest and of the youngest sediment sequences to confine their age time span. There is further potential for drilling deeper sediment cores with the support of international partner. Deep drilling should recover the sediments overlying the Explora Escarpment, in order to discover the nature of the Explora Wedge. We expect the overlying sediment sequences to reveal the history of polar amplification and climate changes in this part of Antarctica, the build-up of the East Antarctic Ice Sheet during past warmer climates, and its Cenozoic and future variability. Having HWD holes through the shelf ice and sampling the sea floor will provide the unique opportunity for further piggy back experiments consisting of multi-disciplinary nature. Experiments and measuring setup for oceanography, sea and ice shelf physics, geophysics, geology, hydrography, biogeochemistry could be planned to characterize the ocean-ice-sediment interactions, processes and ecosystem observations

Позднеплейстоценовое оледенение и отступание ледникового покрова на шельфе Южно-Оркнейского плато, Западная Антарктика

The research aims to provide insight into reconstruction of the Late Pleistocene glaciations and ice retreat that followed the Last Glacial Maximum. The study is based on multi-channel seismic profiling and multibeam survey conducted on the shelf during the 63-rd Russian Antarctic Expedition (2018) on RV «Akademik Alexander Karpinsky». The 560-channel, 7000-m-long streamer and the Atlas Hydrosweep MD-3/30 multibeam echo-sounder were used for seismic and multibeam survey, respectively. In addition, previously collected seismic data available from the Antarctic Seismic Data Library System and bathymetry data from the «International Bathymetry Chart of the Southern Ocean» (IBCSO) Project were involved for interpretation. The multibeam survey was carried out within the Signy Trough and its flanks with depths ranging from 180 to 400 m, and covered the area of about 1500 km2. The data were collected along 43 profiles spaced at 750 m to ensure enough overlap between swaths. Variety of submarine glacial landforms formed by grounded ice was identified on shelf of the South Orkney Plateau with use of seismic and multibeam data. The most prominent of these features is the large terminal moraine at the middle shelf (previously described as the mid-shelf break) marking the greatest ice extent at the LGM. Oceanward of the large terminal moraine, the plateau-like feature (delineated by 350 and 425 m isobaths) with relatively steep outer slope is recognized from seismic data and interpreted as the distal terminal moraine formed during the pre-LGM Pleistocene glaciation. Within the Signy Trough, submarine glacial landforms mapped by multibeam survey, reflect ice retreat after the LGM; these landforms include: subglacial lineation at the western flank of the northern Signy Trough indicating fast flowing grounded ice, transverse recessional moraine ridges, lateral shear moraine on the western flank and lateral marginal moraine on the eastern flank of the Trough, two grounding zone wedges, streamlined features (drumlins) and an ice-proximal fan (presumably). The end moraine was also identified in the eastern flank of Signy Trough. It is thought to be formed due to ice (outlet glacier) re-advance during the Antarctic Cold Reversal. Numerous iceberg plough-marks were observed at least down to 370 m water depths.По данным сейсмического профилирования и детальной съёмки с помощью многолучевого эхолота на шельфе Южно-Оркнейского плато идентифицированы подводные ледниковые формы рельефа, которые маркируют распространение ледникового покрова в периоды четвертичных оледенений и этапы его отступания в позднем плейстоцене. Предполагается, что максимальное распространение ледника с его налеганием на дно произошло в один из периодов похолодания плейстоцена. Во время последнего ледникового максимума ледник достигал среднего шельфа и сформировал крупную конечную морену. После этого началось его отступание, которое происходило неравномерно. В период Антарктического холодного реверса в районе долины Сигню установлено повторное наступание ледника

Continental slope and rise geomorphology seaward of the Totten Glacier, East Antarctica (112°E-122°E)

The continental slope and rise seaward of the Totten Glacier and the Sabrina Coast, East Antarctica features continental margin depositional systems with high sediment input and consistent along-slope current activity. Understanding their genesis is a necessary step in interpreting the paleoenvironmental records they contain. Geomorphic mapping using a systematic multibeam survey shows variations in the roles of downslope and along slope sediment transport influenced by broad-scale topography and oceanography. The study area contains two areas with distinct geomorphology. Canyons in the eastern part of the area have concave thalwegs, are linked to the shelf edge and upper slope and show signs of erosion and deposition along their beds suggesting cycles of activity controlled by climate cycles. Ridges between these canyons are asymmetric with crests close to the west bank of adjacent canyons and are mostly formed by westward advection of fine sediment lofted from turbidity currents and deposition of hemipelagic sediment. They can be thought of as giant levee deposits. The ridges in the western part of the area have more gently sloping eastern flanks and rise to shallower depths than those in the east. The major canyon in the western part of the area is unusual in having a convex thalweg; it is likely fed predominantly by mass movement from the flanks of the adjacent ridges with less sediment input from the shelf edge. The western ridges formed by accretion of suspended sediment moving along the margin as a broad plume in response to local oceanography supplemented with detritus originating from the Totten Glacier. This contrasts with interpretations of similar ridges described from other parts of Antarctica which emphasise sediment input from canyons immediately up-current. The overall geomorphology of the Sabrina Coast slope is part of a continuum of mixed contourite-turbidite systems identified on glaciated margins.Australian Government 4333Australian Research Council DP170100557Italian Programma Nazionale di Richerch in Antartide (PNRA)Spanish Government CTM2014-60451-C2-1-P CTM2017-89711-C2-1-

Pre-site survey for deep drilling and new observations below Ekström Ice Shelf (Sub-EIS-Obs), Dronning Maud Land

During the last season and ongoing planning pre-site surveys are operated at the Ekströmisen, Dronning Maud Land, close to the Neumayer-Station III, with the primary target to build a stratigraphic age framework of the under-shelf-ice-sediments. These sediments are overlying the Explora Wedge, a syn- or post-rift volcanic deposit, and dipping north- to north-eastward. Expected ages could range from Late Mesozoic to Quaternary. From new vibroseismic profiles we will select sites for short core seafloor sampling of the oldest and of the youngest sediment sequences to confine their age time span. After that we could select one or several sites for potential deep drillings (several hundred-meter-deep) with the support of international partner if we could rise interest. The deep drillings should recover the sediments overlying the Explora Escarpment and should as well discover the nature of the Explora Wedge as well. We expect that the overlying sediment sequences could reveal the history of polar amplification and climate changes in this part of Antarctica, the build-up of the East Antarctic Ice Sheet during past warmer climates and its Cenozoic and future variability. The plan for seasons 2017/18 and 2018/19 are the testing of different sea floor sampling techniques through Hot Water Drill (HWD) holes. To select the drill sites for this shallow coring additional high resolution seismic will be acquired as well. Having holes through the shelf ice and sampling the sea floor will provide the unique opportunity for further piggy bag experiments consisting of multi-disciplinary nature. Experiments and measuring setup for oceanography, sea and shelf ice physics, geophysics, geology, hydrography, biogeochemistry could be planned to characterize the sea-ice and shelf ice system, underlying water column, and the sediments. Video characterization underneath the shelf ice and at the seafloor, sediment trap deployment, seafloor mapping with an AUV (Leng, DFKI, ROBEX) could lead as well to new ecosystem observations. Keywords: Deep geological drilling, EAIS build up and variability, Deglaciatio