Description: The history of glaciations on Southern Hemisphere sub-polar islands is unclear. Debate surrounds the extent and timing of the last glacial advance and termination on sub-Antarctic South Georgia in particular. Using sea-floor geophysical data and marine sediment cores, we resolve the record of past glaciation offshore of South Georgia giving insight into glacier response to climate variability through the transition from the Last Glacial Maximum to Holocene. We show a widespread, coherent sea-bed imprint of shelf-wide ice-sheet advance and retreat in the form of glacially-carved cross-shelf troughs, suites of end and recessional moraines, as well as populations of streamlined bedforms. Glacial troughs began to infill with sediments after c. 18 ka B.P. consistent with interpretations of an extensive last glacial advance and early onset of a progressive, and potentially rapid, deglaciation to coastal limits. A fjord-mouth moraine formed during renewed glacier resurgence between c. 15,170 and 13,340 yrs ago. From the geometry of moraines in adjacent fjords, we infer that many of South Georgia’s glaciers advanced during this period of cooler, wetter climate, known as the Antarctic Cold Reversal, extending the geographic footprint of the cryospheric response to an Antarctic climate pattern into the Atlantic sector of the Southern Ocean. We conclude that the last glaciation of South Georgia was extensive, and the sensitivity of its glaciers to climate variability during the last termination more significant than implied by previous studies. Keywords: Sub-Antarctic; ice-cap reconstruction; multibeam bathymetry; sediment cores

Description: Numerous articles have recently reported on gas seepage offshore Svalbard, because of gas emission that may be due to gas hydrate dissociation, possibly triggered by anthropogenic ocean warming. Here we report on findings for a much broader extent of seepage in water depths at and shallower than the gas hydrate stability zone. More than a thousand gas seepage sites imaged as acoustic flares generate a hundreds of kilometer-long plume. Most flares were detected in the vicinity of the Hornsund Fracture Zone. We postulate that the gas ascends from depth along the fracture zone; its discharge is focused on bathymetric highs and is constrained by glaciomarine and Holocene sediments in the troughs. A fraction of this dissolved methane (~1.8%) was oxidized whereas a minor but measureable fraction (0.05%) was transferred into the atmosphere in August 2015. The large scale seepage reported here is not linked to anthropogenic warming.

Description: The history of glaciations on Southern Hemisphere sub-polar islands is unclear. Debate surrounds the extent and timing of the last glacial advance and termination on sub-Antarctic South Georgia in particular. Here, using sea-floor geophysical data and marine sediment cores, we resolve the record of glaciation offshore of South Georgia through the transition from the Last Glacial Maximum to Holocene. We show a sea-bed landform imprint of a shelf-wide last glacial advance and progressive deglaciation. Renewed glacier resurgence in the fjords between c. 15,170 and 13,340 yr ago coincided with a period of cooler, wetter climate known as the Antarctic Cold Reversal, revealing a cryospheric response to an Antarctic climate pattern extending into the Atlantic sector of the Southern Ocean. We conclude that the last glaciation of South Georgia was extensive, and the sensitivity of its glaciers to climate variability during the last termination more significant than implied by previous studies.

Description: The Walvis Ridge-Rio Grande Rise System is the only seamount chain in the Atlantic that is known being continuously active since the Cretaceous (130 Ma) and one of very few worldwide, that links an active hotspot (Tristan-Gough) with a continental flood basalt province (the Paraná-Etendeka province in South America and Africa). Previous work has documented age-progressive volcanism along at least parts of the Walvis Ridge and several initiatives acquired new geophysical and petrological data from seamounts of the Walvis Ridge and its southerly neighbours over the last decade. The youngest stretch of the Walvis Ridge, the islands of Tristan da Cunha, was the focus of the ISOLDE project within the DFG priority program SPP1375 „South Atlantic Margin Processes and Links with onshore Evolution (SAMPLE)”. Temporary seismological and magneto-telluric measurements were carried out to characterize the upper mantle in the search for evidence of a mantle plume. Two expeditions with R/V MARIA S. MERIAN headed towards this remote area to install and dismantle ocean-bottom stations in 2012 and 2013, respectively. Hydroacoustic data were collected along the tracks and around the islands, allowing a first detailed bathymetric insight to the area, underpinned by backscatter and sediment echo sounder observations. One unexpected outcome was the discovery of a new submarine volcano, Isolde Seamount, at the eastern flanks of Nightingale Island. Isolde lies very close to the assumed site of a submarine eruption in 2004, known only from floating pumice and seismicity. Further submarine volcanic centres could be mapped around the islands. Of interest are two volcanic fields, each about 20 x 40 km across, to the NW of Inaccessible Island, where small monogenetic volcanic cones and young lava flows were mapped. Young volcanic activity seems to extend up to 250 km westwards from the Tristan group to about 14.8 W, where we mapped a small volcanic cone on top of old abyssal hills only 130 km east of the Mid-Atlantic Ridge. Further westward, normal seafloor fabric, with clearly defined abyssal hills, dominates the seafloor. Scattered volcanic activity is visible along and in close vicinity to the Tristan da Cunha Fracture Zone. The intraplate volcanic fields as well as the scattered probably monogenetic submarine volcanoes could indicate that the Tristan mantle plume (or at least part of it) currently sits to the west/southwest of Tristan da Cunha.

Description: Among the worldwide expeditions conducted with German research vessels (RVs), an enormous amount of hydro-acoustic data, especially bathymetry, is acquired. Since 1995, the BSH (German Federal Maritime and Hydrographic Agency) is collecting bathymetric datasets, mainly from the RVs METEOR, M.S.MERIAN & SONNE. The institute built up a static website (http://www.bsh.de/de/Meeresdaten/Seevermessung_und_Wracksuche/Bathymetrie/index.jsp) that allows reviewing all the track lines of the research vessels where data is available. Although mandatory, some of the datasets never reached BSH. Upon request, the accessible data will be available for download via FTP from the BSH web-portal. For a more contemporary and sustainable approach in accessing bathymetric metadata and data of all German research vessels, we created a bathymetry showcase within the MaNIDA project (2011/2-2014; http://www.manida.org/) and the resulting “Data Portal German Marine Research” (http://manida.awi.de/). A PostGIS database based on the ISO 19139-2:2012 standard was set up and a solitaire frontend-GUI developed, which allows ingestion of cruise metadata and the automatic acquisition of hydro-acoustic metadata on the entity level (per recorded raw data survey-line). In parallel, the dataset will be archived in PANGAEA (https://www.pangaea.de/) and metadata then completed with the link to the stored dataset. The Bathy-Meta-Database and its services run as a surplus-portal of PANGAEA. This development lead to our participation of the EMODnet Bathymetry Project (http://portal.emodnet-bathymetry.eu/) where metadata is shown for every grid-cell of the compilation of bathymetric datasets while an adapted, world-wide GEBCO dataset (http://www.gebco.net/) fills the gaps across the European seas. The most recent development deals with retrieving metadata from processed bathymetry, based on further software development and the utilization of the open-source suite MB-System (http://www.mbari.org/products/research-software/mb-system/), which concatenates the long-term storage of raw & processed bathymetry in PANGAEA.