ALBERT

Description: Tephra provides regional chronostratigraphical marker horizons that can link different climate archives with highly needed accuracy and precision. The results presented in this work exemplify, however, that the intermittent storage of tephra in ice sheets and during its subsequent iceberg transport, especially during glacial stages, constitutes a potential source of serious error for the application of tephrochronology to Nordic Seas and North Atlantic sediment archives. The peak shard concentration of the rhyolitic component of the North Atlantic Ash Zone II (NAAZ-II) tephra complex, often used to correlate marine and ice core records in Marine Isotope Stage (MIS) 3, is shown to lag the eruption event by ca. 100–400 years in some North Atlantic and Norwegian Sea cores. While still allowing for a correlation of archives on millennial timescales, this time delay in deposition is a major obstacle when addressing the lead–lag relationship on short timescales (years to centuries). A precise and accurate determination of lead–lag relationships between archives recording different parts of the climate system is crucial in order to test hypotheses about the processes leading to abrupt climate change and to evaluate results from climate models. Copyright # 2011 John Wiley & Sons, Ltd.

Description: Axial volcanic ridges (AVRs) are found on most slow-spreading mid-ocean ridges and are thought to be the main locus of volcanism there. In this study we present high-resolution mapping of a typical, well-defined AVR on the Mid-Atlantic Ridge at 45°N. The AVR is characterized by “hummocky terrain,” composed typically of hummocks with pillowed or elongate pillowed flanks with pillowed or lobate lava flow summits, often with small haystacks sitting on their highest points. The AVR is surrounded by several areas of “flat seafloor,” composed of lobate and sheet lava flows. The spatial and morphological differences between these areas indicate different eruption processes operating on and off the AVR. Volcanic fissures are found all around and on the AVR, although those with the greatest horizontal displacement are found on the ridge crest and flat seafloor. Clusters of fissures may represent volcanic vents. Extremely detailed comparisons of sediment coverage and examination of contact relations around the AVR suggest that many of the areas of flat seafloor are of a similar age or younger than the hummocky terrain of the AVR. Additionally, all the lavas surveyed have similar degrees of sediment cover, suggesting that the AVR was either built or resurfaced in the same 50 ka time frame as the flat seafloor.

Description: Direct estimations of turbulent fluxes and atmospheric stability were performed from a sonic anemometer at 50 m height on a meteorological mast at the Horns Rev wind farm in the North Sea. The stability and flux estimations from the sonic measurements are compared with bulk results from a cup anemometer at 15 m height and potential temperature differences between the water and the air above. Surface flux estimations from the advanced weather research and forecast (WRF) model are also validated against the sonic and bulk data. The correlation between the sonic and bulk estimates of friction velocity is high and the highest among all velocity comparisons. From the sonic–bulk–WRF inter-comparison, it is found that the atmospheric stability measures at the sonic height tend to be closer to the neutral value than the WRF and bulk estimates, which are performed within an air layer closer to the surface, not only from a systematic bulk and WRF under-prediction of the friction velocity when compared with the sonic value but also because of the lower magnitude of the sonic heat flux compared with that from the WRF simulations. Although they are not measured but parameterized or estimated, the bulk–WRF comparisons of friction velocity and 10 m wind speed show good agreement. It is also shown that on a long-term basis, the WRF and bulk estimates of stability are nearly equal and that a correction towards a slightly stable atmospheric condition has to be applied to the long-term wind profile at Horns Rev and at other locations over the North Sea, the correction being larger for points close to the coast.

Description: Metagenomic techniques are used to analyse bacterial communities allowing both culturable and unculturable species to be represented. However, the screening of oral metagenomic samples can be hindered by high animal host DNA content. This study evaluated methods for the reduction of human DNA concentrations within oral metagenomic samples. Plaque samples were collected from 27 patients presenting with periodontal disease and treated to remove human DNA using either selective lysis of eukaryotic cells at several buffer concentrations or differential centrifugation after treatment with trypsin and/or detergents. Human and bacterial DNA levels were determined by quantitative polymerase chain reaction (qPCR). The human DNA content of plaque extracts was significantly reduced by all treatments compared with an untreated control (P 〈 0.05). However, differential centrifugation simultaneously reduced the bacterial DNA content unless samples were pretreated with a detergent. Observations of Gram stained samples that were processed using differential centrifugation without detergent suggest that many bacteria remain adhered to human cells. An approach that uses differential centrifugation in parallel with selective lysis is recommended to fully represent the oral microbiota in metagenomic samples, including those tightly adhered to human cells and more delicate bacteria such as Mycoplasma.

Description: Marine myxobacteria (Enhygromyxa, Plesiocystis, Pseudoenhygromyxa, Haliangium) are phylogenetically distant from their terrestrial counterparts. Salimabromide is the first natural product from the Plesiocystis/Enhygromyxa clade of obligatory marine myxobacteria. Salimabromide has a new tetracyclic carbon skeleton, comprising a brominated benzene ring, a furano lactone residue, and a cyclohexane ring, bridged by a seven-membered cyclic moiety. The absolute configuration was deduced from experimental and calculated CD data. Salimabromide revealed antibiotic activity towards Arthrobacter cristallopoietes.

Description: Methane is a potent greenhouse gas and large-scale rapid release of methane from hydrate may have contributed to past abrupt climate change inferred from the geological record. The discovery in 2008 of over 250 plumes of methane gas escaping from the seabed of the West Svalbard continental margin at ~400 m water depth (mwd) suggests that hydrate is dissociating in the present-day Arctic. Here we model the dynamic response of hydrate-bearing sediments over a period of 2300 years and investigate ocean warming as a possible cause for present-day and likely future dissociation of hydrate, within 350–800 mwd, west of Svalbard. Future temperatures are given by two climate models, HadGEM2 and CCSM4, and scenarios, Representative Concentration Pathways (RCPs) 8.5 and 2.6. Our results suggest that over the next three centuries 5.3–29 Gg yr−1 of methane may be released to the Arctic Ocean on the West Svalbard margin.

Description: This article compares the quality of Raman images obtained using metallurgical and oil immersion objectives to map complex structures in two and three dimensions. While the performance of these objectives for depth profiling planar structures has been discussed at length in the literature, the same comparison has not yet been made for 3D mapping of complex objects, where additional complications are introduced by non-planar geometries. Studying samples with increasing complexity shows that the oil immersion objective is strongly preferred because it yields brighter images with better contrast, and eliminates some new and confusing artefacts that do not arise with simple planar objects.

Description: Although it has been more than 30 years since the discovery of deep-sea hydrothermal vents, comprehending the interconnections between hydrothermal venting and microbial life remains a challenge. Here we investigate abiotic-biotic linkages in low-temperature hydrothermal biotopes at Desperate and Lilliput on the southern Mid-Atlantic Ridge. Both sites are basalt-hosted and fluids exhibit the expected chemical signatures. However, contrasting crustal permeabilities have been proposed, supporting pervasive mixing at Desperate but restricting circulation at Lilliput. In Desperate fluids, sulfide and O2 were readily available but H2 hardly detectable. Under incubation conditions (oxic unamended, sulfide-spiked, oxic and anoxic H2 -spiked at 18°C), only sulfide oxidation by Thiomicrospira fuelled biomass synthesis. Microbial phylogenies from Desperate incubation experiments resembled those of the natural samples suggesting that the incubation conditions mimicked the environment. In Lilliput fluids, O2 was limited, whereas sulfide and H2 were enriched. Autotrophy appeared to be stimulated by residual sulfide and by amended H2 . Yet, based on bacterial phylogenies only conditions in anoxic H2 -spiked Lilliput incubations appeared similar to parts of the Lilliput habitat. In anoxic H2 -spiked Lilliput enrichments Campylobacteraceae likely supported biomass production through H2 oxidation. We argue that the diverging circulation patterns arising from different subseafloor permeabilities act as major driving forces shaping these biotope structures.