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Supplementary material 3-2

Knowledge of sub-ice shelf sedimentary sequences, ice-ocean interactions, and biological activities is still relatively sparse, largely due to the challenges involved in accessing ice shelf cavities. The Sub-EIS-Obs project, funded by the Alfred-Wegener-Institute (AWI) and the Federal Institute for Geosciences and Natural Resources (BGR) in Germany, is a multidisciplinary study, which aims to recover and characterize sediment sequences beneath the Ekström Ice Shelf (EIS) in East Antarctica. The project addresses several research objectives, such as the crustal evolution during the breakup of Gondwana, the build-up and variability of the East Antarctic Ice Sheet (EAIS) throughout the Cenozoic, reconstruction of grounding-line dynamics, sedimentary and erosional processes beneath the ice stream and shelf, and multidisciplinary observations of climate induced changes in ice-ocean interactions. A pre-site seismic survey campaign was carried out on the Ekström Ice Shelf in 2016/2017 and 2017/2018, resulting in 615 km of multi-fold seismic data. Based on these data, four different units were defined, which, according to preliminary interpretation, document geologic history of the breakup of Gondwana in the Jurassic (Explora-Wedge volcanic deposits) and ongoing marine and glacio-marine sedimentation during the Meso- and Cenozoic. On top of all strata a glacio-marine surface cover deposited during the Last Glacial Maximum and Holocene sedimentation is indicated in the seismic profiles. In order to sample all units separately, coring locations were selected accordingly. A hot water drilling system was used to drill holes through the shelf ice (ice thicknessesrange between∼210 and 330 m), enabling the deployment of a gravity corer, a Wippermann Grabber, a vibro-and a hammer coring system manufactured by Jilin University (Changchun, China), and a UWITEC percussioncorer (BAS corer). Moreover, a camera installed in a pressure housing enabled recording of high-resolution videofootage of the seafloor and associated benthic ecosystems as well as the base of the ice shelf. In addition, a Conductivity-Temperature-Depth probe was attached to all coring devices in order to record the oceanographic properties of the water column. Here, we present first results from the Sub-EIS-Obs sediment sampling campaigns 2017/2018 and 2018/2019. We present an overview of the long-term project aims, sampling strategy, perfor-mance of the hot water drilling operation, and recovered geological samples, and the video footages of the seafloor.

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.

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.

On the island of Lesvos in the north-eastern Aegean Sea, thrust sheets of mantle peridotite override a tectonic melange containing metasediments, metabasalts and a few metagabbros. Previous workers have collectively called the above rock types the “Lesvos ophiolite” and suggested it represents Neotethyan (Jurassic) oceanic crust of N-MORB and IAT affinities. However, the complete absence of a sheeted dyke complex and of a layered cumulate sequence, in turn overlain by isotropic gabbros does not support the ophiolite description. The basalts of the melange define two distinct groups on the basis of Nb/Y values: the Vatera (low Nb/Y) and the Melange (high Nb/Y) groups. The Vatera basalts show multi-element profiles and REE patterns lying well within the field of N-MORB with the exception of Y and HREE abundances that are lower than those of N-MORB and match those of E-MORB. They originated by similar to 10% melting of depleted MORB mantle that carried a small amount (similar to 3%) of an enriched (OIB-like) components corroborated by moderate initial epsilon Nd values (+4.6-+6.2). The Melange basalts, in contrast, have multi-element profiles and REE patterns typical of within-plate compositions, transitional between E-MORB and OIB. They originated by