Crustal structure of northern Spitzbergen along the deep seismic transect between the Molloy Deep and Nordaustlandet

A deep seismic sounding experiment was performed during the expedition ARKTIS XV/2of the RV Polarstern and the Polish ship Eltanin in 1999 in the continent-ocean transitionzone of northwestern Svalbard, along the 430-km-long profile AWI-99200. The profile runsfrom the Molloy Deep in the vicinity of an active spreading axis in the northern Atlantic toNordaustlandet. Seismic energy (airgun andTNTshots)was recorded by seismic land (onshore)stations, OBSs and hydrophone systems, with airgun shots recorded up to 200 km onshore and50 km offshore. The data recorded along the entire profile provide an excellent database fora detailed seismic modelling of the crustal P-wave velocity field along the profile track. Aminimal depth of about 6 km to the Moho discontinuity was found east of the Molloy Deep.Here, the upper mantle exhibits a P-wave velocity of about 7.9 km s−1, and the crustal thicknessdoes not exceed 4 km. The continent-ocean transition zone to the east is characterized by acomplex seismic velocity structure. The Moho interface reaches a maximum depth of 28 kmbeneath the continental part of the profile, with a P-wave velocity in the upper mantle of8.15 km s−1. The continental crust consists of three layers with P-wave velocities of about5.5, 5.9-6.0 and 6.2-6.6 km s−1, respectively. In addition, we have found two reflectors in themantle lithosphere at depths of 14-42 and 40-50 km dipping NE. The evolution of the regionappears to be within a shear-rift tectonic setting. The continent-ocean transition zone is mostlydominated by extension, so the last stage of the development of this margin can be classifiedas rifting. The uplifted Moho boundary close to the Molloy Deep can be interpreted as thesouthwestern end of the Molloy Ridge

The distribution of ciliates on Ecology Glacier (King George Island, Antarctica): relationships between species assemblages and environmental parameters

Ciliates are important consumers of pico- and nano-sized producers, are nutrient regenerators, and are an important food source for metazoans. To date, ecological research on ciliates has focused on marine ecosystems rather than on glacier habitats. This paper presents the first major study on ciliates from the Ecology Glacier (South Shetland Islands, Antarctica). The objective of the study was to investigate the structure and spatial distribution of ciliate communities and to identify the environmental factors determining the structure of the assemblages. Microbial communities were collected from three habitats: surface snow, cryoconite holes, and glacier streams. Sampling was carried out every 3–4 days from January 17 to February 24, 2012. A total of 18 ciliate taxa were identified. The species richness, abundance, and biomass of protozoa differed significantly between the stations studied with the lowest numbers in streams on the glacier surface and the highest numbers in cryoconite holes. The RDA performed to specify the direct relationships between the abundance of ciliate taxa and environmental variables showed obvious differences between studied habitats. The analysis showed that all variables together explained 62.4 % of total variance. However, variables thatsignificantly explained the variance in ciliate communities in cryoconite holes, snow, and surface streams were temperature, conductivity, and total nitrogen. Further research is required to explain the impact of biotic factors influencing the presence of ciliates, including the abundance of bacteria, microalgae, and small Metazoa

Continent–ocean-transition across a trans-tensional margin segment: off Bear Island, Barents Sea

A 410 km long Ocean Bottom Seismometer profile spanning from the Bear Island, Barents Sea to oceanic crust formed along the Mohns Ridge has been modelled by use of ray-tracing with regard to observed P-waves. The northeastern part of the model represents typical continental crust, thinned from ca. 30 km thickness beneath the Bear Island to ca. 13 km within the Continent–Ocean-Transition. Between the Hornsund FZ and the Knølegga Fault, a 3–4 km thick sedimentary basin, dominantly of Permian/Carboniferous age, is modelled beneath the ca. 1.5 km thick layer of volcanics (Vestbakken Volcanic Province). The P-wave velocity in the 3–4 km thick lowermost continental crust is significantly higher than normal (ca. 7.5 km s–1). We interpret this layer as a mixture of mafic intrusions and continental crystalline blocks, dominantly related to the Paleocene-Early Eocene rifting event. The crystalline portion of the crust within the south-western part of the COT consists of a ca. 30 km wide and ca. 6 km thick high-velocity (7.3 km s–1) body. We interpret the body as a ridge of serpentinized peridotites. The magmatic portion of the ocean crust accreted along the Knipovich Ridge from continental break-up at ca. 35 Ma until ca. 20 Ma is 3–5 km thicker than normal. We interpret the increased magmatism as a passive response to the bending of this southernmost part of the Knipovich Ridge. The thickness of the magmatic portion of the crust formed along the Mohns Ridge at ca. 20 Ma decreases to ca. 3 km, which is normal for ultra slow spreading ridges

Culturable bacteria community development in postglacial soils of Ecology Glacier, King George Island, Antarctica

Glacier forelands are excellent sites in which to study microbial succession because conditions change rapidly in the emerging soil. Development of the bacterial community was studied along two transects on lateral moraines of Ecology Glacier, King George Island, by culture-dependent and culture-independent approaches (denaturating gradient gel electrophoresis, DGGE). Environmental conditions such as cryoturbation and soil composition affected both abundance and phylogenetic diversity of bacterial communities. Microbiocenosis structure along transect 1(severe cryoturbation) differed markedly from that along transect 2 (minor cryoturbation). Soil physical and chemical factors changed along the chronosequence (time since exposure) and influenced the taxonomic diversity of cultivated bacteria (CB), particularly along transect 2. Arthrobacter spp. played a pioneer role, and were present in all soil samples, but were most abundant along transect 1. Cultivated bacteria isolated from transect 2 were taxonomically more diverse than those cultivated from transect 1; those from transect 1 tended to express a broader range of enzyme and assimilation activities. Our data suggest that cryoturbation is a major factor in controlling bacterial community development in postglacial soils, shed light on microbial succession in glacier forelands, and add a new parameter to models that describe succession phenomena