Beschreibung: We carried out a combined vibro-explosive seismic survey on Halvfarryggen, a local ice dome south of Neumayer III. The Vibroseis survey was grid shaped to provide spatial information about the glaciological and geological substructure. The center survey line was also surveyed with explosive reflection and refraction seismic set-ups. The ice bed contact we interpret as a frozen till layer overlaying bedrock. Velocity analysis from refractions seen in far offset data, we obtain a pressure-wave velocity 〉5000 m/s. We therefore interpret the bedrock as igneous.

Beschreibung: The Weddell Sea sector is one of the main formation sites for Antarctic Bottom Water and an outlet for about one fifth of Antarctica’s continental ice volume. Over the last few decades, studies on glacialegeological records in this sector have provided conflicting reconstructions of changes in ice-sheet extent and ice-sheet thickness since the Last Glacial Maximum (LGM at ca 23e19 calibrated kiloyears before present, cal ka BP). Terrestrial geomorphological records and exposure ages obtained from rocks in the hinterland of the Weddell Sea, ice-sheet thickness constraints from ice cores and some radiocarbon dates on offshore sediments were interpreted to indicate no significant ice thickening and locally restricted grounding-line advance at the LGM. Other marine geological and geophysical studies concluded that subglacial bedforms mapped on theWeddell Sea continental shelf, subglacial deposits and sediments over-compacted by overriding ice recovered in cores, and the few available radiocarbon ages from marine sediments are consistent with major ice-sheet advance at the LGM. Reflecting the geological interpretations, different icesheet models have reconstructed conflicting LGM ice-sheet configurations for the Weddell Sea sector. Consequently, the estimated contributions of ice-sheet build-up in the Weddell Sea sector to the LGM sealevel low-stand of w130 m vary considerably. In this paper, we summarise and review the geological records of past ice-sheet margins and past icesheet elevations in the Weddell Sea sector. We compile marine and terrestrial chronological data constraining former ice-sheet size, thereby highlighting different levels of certainty, and present two alternative scenarios of the LGM ice-sheet configuration, including time-slice reconstructions for post- LGM grounding-line retreat. Moreover, we discuss consistencies and possible reasons for inconsistencies between the various reconstructions and propose objectives for future research. The aim of our study is to provide two alternative interpretations of glacialegeological datasets on Antarctic Ice- Sheet History for the Weddell Sea sector, which can be utilised to test and improve numerical icesheet models

Beschreibung: This poster presents results and performance of an operational vibroseis system used in Antarctica on the Ekströmisen and its catchment area. The about 500 km long overland traverse covered very different surface regimes in the elevation range from sea level up to 1000 m in the austral season 2013/14. The presentation is the successful culmination of a six-year effort to develop an operational vibroseis system for Antarctica and Greenland. Over three weeks the campaign acquired: • 407 km of seismic profiles in total, thereof • 110 km in 6-fold resolution with 125 m shot spacing • 25 km in 3-fold resolution with 250 m shot spacing. The remaining distance was covered in single-fold with 750 m shot spacing. The traverse used a well-established 60 channel 1.5 km streamer and a new setup with a vibroseis Buggy “EnviroVibe” with Mattracks on a polyethylen sled. The sled had a hole in the center to lower the vibrator pad directly onto the snow surface. With this setup data production varied between 20 km/day for 6-fold and 40 km/day for single fold for a decent 9h day of measurements. The combination of Mattracks with the PE-sled was especially advantageous on hard and rough surfaces because of the flexibility of each and the relatively lose mounting by cargo straps and wooden blocks. Production speeds were limited by the snow streamer, which had an increasing damage rate of geophone groups for velocities above 6 km/h. The source system itself could easily accommodate transfer velocities of 15 km/h. In combination with the streamer winch mounted in front of the source on a separate freight sled the channel spacing could be reduced to fractions of the 25 m spacing interval by combining several sweeps at the same location, thus increasing spatial resolution. The vibrator source was operated with a 10-250 Hz sweep over 10 s with 80% of the peak force of 66 kN. On soft surfaces a setup-sweep was utilized. Preliminary data analysis shows that sea floor geomorphology, subglacial sedimentary layering and englacial layering can be clearly imaged in the respective resolution of the source’s bandwidth. Interestingly, the ration of p-wave to s-wave energy varied considerably depending on the surface characteristics. In comparison to airborne and ground-based radar surveys, the system was able to image very steep sidewalls of subglacial trenches because of the large offset aperture where radar systems did not provide any reflections. Such system will help to considerably improve the future characterisation of sublglacial and englacial environments.

Beschreibung: We carried out a combined vibro-explosive seismic survey on Halvfarryggen, a local ice dome south of the German research station Neumayer III. The Vibroseis survey was grid shaped to provide spatial information about the glaciological and geological substructure. The center survey line was also surveyed with explosive reflection and refraction seismic set-ups. The ice bed contact we interpret as a frozen till layer overlaying bedrock. From velocity analysis of refractions seen in far offset data, we obtain a pressure-wave velocity 〉5000 m/s. We therefore interpret the bedrock as igneous, which supplements previous magnetic and gravimetric data sets.

Beschreibung: The breakup of Gondwana is manifested by coeval early Jurassic Karoo magmatism in South Africa and East Antarctica. In South Africa, the large volumes of volcanic rocks of the adjoining Lebombo and Mwenetzi-Save monoclines represent a volcanic rift margin, and in East Antarctica, a corresponding feature, the Explora Wedge is buried below sediments and floating ice shelves on the continental margin of Dronning Maud Land. We use the seismic vibrator source to explore the sub-ice geology in Antarctica, and the new seismic reflection and available regional aeromagnetic data enable us to outline a dogleg landward extent of the Explora Wedge in Dronning Maud Land. The congruent inboard wedge geometries on the two continents define a high quality constraint, which facilitate for the first time, a geologically consistent and tight reconstruction of Africa relative to East Antarctica within Gondwana. The uncertainties in correlations of major geological features (mobile belts) from one continent to the other may now be of the order of ten’s of kilometers rather than hundreds of kilometers.

Beschreibung: We present implementations of vibroseis system configurations with a snowstreamer for over-ice long-distance seismic traverses (〉100 km). The configurations have been evaluated in Antarctica on ice sheet and ice shelf areas in the period 2010–2014. We discuss results of two different vibroseis sources: Failing Y-1100 on skis with a peak force of 120 kN in the frequency range 10–110 Hz; IVI EnviroVibe with a nominal peak force of 66 kN in the nominal frequency range 10–300 Hz. All measurements used a well-established 60 channel 1.5 km snowstreamer for the recording. Employed forces during sweeps were limited to less than 80% of the peak force. Maximum sweep frequencies, with a typical duration of 10 s, were 100 and 250 Hz for the Failing and EnviroVibe, respectively. Three different concepts for source movement were employed: the Failing vibrator was mounted with wheels on skis and pulled by a Pistenbully snow tractor. The EnviroVibe was operated self-propelled on Mattracks on the Antarctic plateau. This lead to difficulties in soft snow. For later implementations the EnviroVibe with tracks was put on a polyethylene (PE) sled. The sled had a hole in the center to lower the vibrator baseplate directly onto the snow surface. With the latter setup, data production varied between 20 km/day for 6-fold and 40 km/day for single fold for 9 h/day of measurements. The combination of tracks with the PE-sled was especially advantageous on hard and rough surfaces because of the flexibility of each component and the relatively lose mounting. The systems presented here are suitable to obtain data of subglacial and sub-seabed sediment layers and englacial layering in comparable quality as obtained from marine geophysics and land-based explosive surveys. The large offset aperture of the streamer overcomes limitations of radar systems for imaging of steep along-track subglacial topography. With joint international scientific and logistic efforts, large-scale mapping of Antarctica's and Greenland's subglacial geology, ice-shelf cavity geometries and sea-bed strata, as well as englacial structures can be achieved.

Beschreibung: The first Vibroseis reflection survey at Antarctica was successfully carried out by the Alfred Wegener Institute in 2010. Based on the results of the vibrator in combination with a snow streamer, a grid survey was carried out at Halvfarryggen Dronning Maud Land, East Antarctica, in 2011. Halvfarryggen is a 900m thick local ice dome close to the grounding line constraining the east side of the Eksrömisen ice shelf. Here we present the first results of the Vibroseis reflection survey where we focus on the stratigraphy of the ice column and the underlying strata of the dome. From the main grid line seismic reflection data were also collected using explosives. Resolution and penetration of the Vibroseis and explosive data sets are compared and discussed as well as the logistics of each method.

Beschreibung: We carried out a combined Vibroseis-Explosive survey in combination with a snowstreamer at Halvfarryggen, a local ice dome at a triple point in the vicinity of the German Antarctic research station NeumayerIII. The Vibroseis survey was grid shaped to give spatial information about the glaciological and geological substructure. The center survey line was also surveyed with explosives and compared with the Vibroseis data. Internal ice reflections, clearly visible with explosives are not well visible in the Vibroseis data except for the strongest and deepest internal reflection. We interpret this deepest internal ice reflector as ice crystals orientated in to a single maximum. The ice bed contact we interpret as a frozen till layer overlaying bedrock. From velocity analysis derived from refractions seen in far offset data, we interpret the bedrock as igneous.