Description: Past ice sheet conditions in the southern Weddell Sea remain poorly known. Previous studies have led to contradicting scenarios of maximum ice extent during the Last Glacial Maximum (LGM). Scenario A is mainly based on terrestrial data indicating limited ice sheet thickening in the hinterland and suggests a LGM grounding-line position on the inner shelf. Scenario B is based on marine geological/-physical data and concludes that the grounding line was located on the outer shelf (~650 km further offshore than in scenario A). In addition, studies suggest a complex history of ice retreat and drainage pattern since the LGM that needs further constraint. We investigated hydroacoustic data acquired during 17 expeditions. A key finding is a previously unknown stacked grounding zone wedge (GZW) located in Filchner Trough on the outer shelf showing that a palaeo-ice stream stabilized at this position at least twice. Radiocarbon dates from sediment cores indicate that (i) the GZW was formed in the early Holocene and (ii) grounded ice did not extend seaward at the LGM. Hence, the grounding line in Filchner Trough experienced dynamic changes in the Holocene and ice sheet retreat after the LGM was not linear. Ice-flow switches in the hinterland possibly explain this behaviour. Further interesting findings are made in Brunt Basin suggesting the existence of cold-based ice or impacts of large icebergs. In addition, new data will be acquired in the area with RV Polarstern in Jan-Mar 2018.

Description: Between 2010-2018 an extensive grid of seismic reflection data were collected across the grounding line and on the Ekström ice-shelf, using an on-ice vibroseis source and snowstreamer. Here they are used to investigate current ice dynamics and reconstruct the glaciological history of this region. These data show the ice-shelf thickness ranges from 170 m, near the ice-shelf front, to ~600 m near the grounding line. Relic crevasses are seen at the ice base, in the Western part of the ice shelf, which can be tracked back to a current crevasse field at the grounding line. There is also evidence of an ice-shelf basal channel, with a corresponding surface depression. Beneath the sea floor the outcrop and sub-ice extent of the volcanic Explora Wedge (generated through Jurassic rifting and seafloor spreading) is clearly imaged. The wedge is overlain by a sequence of truncated, dipping marine-sediment layers. The sediment layers were likely truncated by former ice advance and subsequent retreat; which has also left evidence in the form topographic over-deepening and glacial debris deposits at the sea floor. The debris deposits range from elongated bedforms in a topographic trough (indicating probable former ice-stream flow) to layered sediment wedges at the current ice-shelf front (indicating the likely former extent of grounded ice). The vibroseis method is fast and effective allowing for a high volume of data collection. For example, in the 2016/17 season ~280 km of multi-fold seismic reflection data were collected over a 25-day period. Future integration of these results with numerical models will provide a better understanding of past and present interactions between the ice sheet and the solid Earth in Dronning Maud Land, which will in turn improve understanding of future contributions of this region to sea-level rise.

Description: In paleoenvironmental studies, the mineralogical composition of sediments is an important indicator. In combination with other indicators, they contribute to the understanding of changes in sediment sourcing as well as in weathering and depositional processes. Fourier transforminfrared spectroscopy (FTIRS) spectra contain information on mineralogical composition because eachmineral has a unique absorption pattern in the mid-IR range. Although easily obtained, FTIR spectra are often too complex to infermineral concentrations directly. In this study, we use a calibration set of ca. 200 sediment samples conventionally measured using X-ray diffraction (XRD) in order to developmultivariate, partial least squares (PLS) regressionmodels relatingmineral contents to sediment spectra. Good correlations were obtained for the most common minerals (e.g. quartz, K-feldspar, illite, plagioclase, smectite, calcite). Correlation coefficients ranged from 0.85 to 0.92, coefficients for the validation varied from 0.64 to 0.80, the number of latent variables (PLS regression components) in the models ranged between 3 and 7 and the range of variation of the RMSEcv gradient was from 15.28 to 5.7.

Description: During field seasons 2016/17 and 2017/18, pre-site seismic surveys were undertaken in the Ekströmisen region of Dronning Maud Land, with the primary goal of building a stratigraphic age framework of sub-ice-shelf sedimentary strata. These sediments cover the Explora Wedge, a syn- or post-rift volcanic deposit. Expected ages range from Late Mesozoic to Quaternary. From new vibroseismic profiles, we selected sites for seafloor sampling with short cores through Hot Water Drill (HWD) holes of the oldest and of the youngest sedimentary sequencesto confine their age time span. There is further potential for drilling deeper sediment cores with the support of international partners. Deep drilling should recover the sediments overlying the Explora Escarpment, in order to discover the context and nature of the Explora Wedge. We expect the overlying sedimentary sequences to reveal the history of polar amplification and climate changes in this part of Antarctica, the build-up of the East AntarcticIce Sheet during past warmer climates and its Cenozoic and future variability. We successfully sampled the sea floor with different tools through HWD holes at two sites selected from the reflection seismic data close to the German Neumayer Station III, and discovered a pebbly sea floor coated with bryozoan skeletons. Present HWD holes penetrating the ice shelf to sample the sea floor will provide the unique opportunity for further piggy back experiments consisting of multi-disciplinary nature. For example, experiments and deploying measuring setup for oceanography, sea and ice shelf physics, geophysics, geology, hydrography, biogeochemistry could be potential future actions in order to characterise the ocean-ice-sediment interactions, processes and ecosystem observations. For season 2018/19 – besides additional geological sampling – it is planned to deploy a multiyear oceanographic mooring beneath the ice shelf. During future campaigns, we will try to launch an Autonomous Underwater Vehicle (AUV) either through a HWD hole, from a ship, or from the fast ice with the necessary power to operate and measure within the sub-ice shelf cavity.

Description: The detailed Holocene inundation history of the Bermuda North Lagoon may be used as model for transgressive and highstand sequences in carbonate platforms. Sedimentation and facies development were controlled largely by sea‐level rise and antecedent topography. Four late Pleistocene to Holocene sequences may be identified in North Lagoon based on a combined analysis of 200 km shallow reflection seismics and 39 cores including 29 radiometric and U/Th‐ages. The sequences were deposited during sea‐level highstands and are separated by subaerial exposure horizons that formed during sea‐level lowstands. Sequence 1 (inferred MIS 7) consists of well‐cemented carbonate sands. Sequence 2 (MIS 5) is up to 20 m thick and consists of well‐sorted, inter‐reefal sands and reef sediments with mound‐like structures. Sequence 3 (inferred MIS 3) is up to ca 6 m thick and accumulated in topographic lows of the underlying sequences some 20 m below modern sea‐level. Sequence 4 (MIS 1, Holocene) includes lagoonal sediments up to 10 m thick, and reefs that accumulated on topographic highs of the MIS 5 sequences. Holocene sediments in topographic lows include peat, peaty sediment, freshwater mud, restricted marine carbonates, and open lagoonal carbonate sediments deposited in seagrass beds, shallow water, and deeper lagoon areas. Upward fining is an expression of deepening and the development of a reef‐protected lagoon environment. Holocene sedimentation on topographic highs usually lacks freshwater and transitional facies and starts with shallow marine mollusc shell accumulations overlain by carbonate sediments that show fining upward. Packstone (68%), wackestone (22%), grainstone (9%) and mudstone (1%) textures occur in cores, with Halimeda, molluscs, coralline algae and foraminifera being the most common constituent particles; coral fragments are rare. During the Holocene, an estimated volume of 1 km3 of carbonate sediments was deposited in North Lagoon. Average sedimentation rates are estimated to be 0.32 m/kyr.

Description: The coasts of West Antarctic Peninsula are strongly influenced by glacier meltwater discharge. The spatial structure and biogeochemical composition of inshore habitats is shaped by large quantities of terrigenous particulate material deposited in the vicinity of the coast, which impacts the pelagic and benthic ecosystems. We used a multitude of geochemical and environmental variables to identify the radius extension of meltwater impact of Fourcade Glacier into the fjord system of Potter Cove, King George Island. K-means cluster algorithm, canonical correspondence analysis, variance analysis and post-hoc Tukey's multiple comparison test were applied to define and cluster coastal meltwater habitats. A minimum of 10 clusters was needed to classify the 8 km2 study area into meltwater fjord habitats (MFH), fjord habitats and marine habitats. Strontium content in surface sediments is the main geochemical indicator for lithogenic creek discharge in Potter Cove. Furthermore, bathymetry, glacier distance and geomorphic positioning are the essential habitat explaining variables. Mean and maximum MFH extent amounted to 1 km and 2 km, respectively. Extrapolation of the identified meltwater impact ranges to King George Island coastlines which are presently ice-covered bays and fjord areas indicate an overall coverage of 200–400 km2 MFH, underpinning the importance to better understand the biology and biogeochemistry in terrestrial marine transition zones.

Description: One of the major questions in palaeoclimate research is whether or not the West Antarctic Ice Sheet (WAIS) collapsed during the warmest phase of the last interglacial period (Marine Isotope Stage 5e; 130-116 ka). Several numerical models and sea-level reconstructions suggest such a collapse, but critically it has not been confirmed by WAIS proximal empirical data, yet. Answering this question by analyzing sedimentary sequences from the West Antarctic shelf requires areas that remained unaffected by 1) erosion by grounded ice, and 2) scouring by iceberg keels since MIS 5e. During RV Polarstern Expedition ANT-XXVI/3 in early 2010 we discovered such an area on the Amundsen Sea shelf for the first time. We demonstrate that the outermost section of the Cosgrove-Abbot palaeo-ice stream trough in the easternmost Amundsen Sea Embayment was not covered by grounded ice during the last glacial period, and that a part of this area was largely protected from iceberg scouring by its large water depth and a grounding zone wedge located further landward. We present combined geophysical and geological data revealing this unique location at which the state of the WIAS during the last peak interglacial may be reconstructed, and give an outlook on how this could be achieved.

Description: An extensive grid of seismic reflection data collected on Ekström Ice Shelf, East Antarctica, between 2010–2018, using an on-ice vibroseis source and snowstreamer, are used to reconstruct the glaciological and tectonic history of this region. The data clearly image the outcrop and sub-ice extent of the volcanic Explora Wedge (generated through Jurassic rifting and seafloor spreading). The wedge is overlain by a sequence of truncated, dipping marine-sediment layers. The sediment were likely truncated by former ice advance and subsequent retreat; which has also left evidence in the form topographic over-deepening and glacial debris deposits at the sea floor. The debris deposits range from elongated bedforms in a topographic trough (indicating probable former ice-stream flow) to layered sediment wedges at the current ice-shelf front (indicating the likely former extent of grounded ice). A series of sub-ice shelf geological drilling campaigns in the area will take place (2017-2019) to recover sediments from the sea floor. Combining the topography and material characteristics from vibroseis data with stratigraphic evidence from sediment cores allows a robust reconstruction in this area. Future integration of these results with numerical models will provide a better understanding of past and present interactions between the ice sheet and the solid Earth in Dronning Maud Land, which will in turn improve understanding of future contributions of this region to sea-level rise.