ALBERT

Description: Marine phytoplankton blooms are annual spring events that sustain active and diverse bloom-associated bacterial populations. Blooms vary considerably in terms of eukaryotic species composition and environmental conditions, but a limited number of heterotrophic bacterial lineages — primarily members of the Flavobacteriia, Alphaproteobacteria and Gammaproteobacteria — dominate these communities. In this Review, we discuss the central role that these bacteria have in transforming phytoplankton-derived organic matter and thus in biogeochemical nutrient cycling. On the basis of selected field and laboratory-based studies of flavobacteria and roseobacters, distinct metabolic strategies are emerging for these archetypal phytoplankton-associated taxa, which provide insights into the underlying mechanisms that dictate their behaviours during blooms.

Description: Owing to the turbulent nature of the ocean, mesoscale eddies are omnipresent. The impact of these transitory and approximately circular sea surface temperature fronts on the overlying atmosphere is not well known. Stationary fronts such as the Gulf Stream have been reported to lead to pronounced atmospheric changes1, 2. However, the impact of transient ocean eddies on the atmosphere has not been determined systematically, except on winds and to some extent clouds3, 4, 5, 6. Here, we examine the atmospheric conditions associated with over 600,000 individual eddies in the Southern Ocean, using satellite data. We show that ocean eddies locally affect near-surface wind, cloud properties and rainfall. The observed pattern of atmospheric change is consistent with a mechanism in which sea surface temperature anomalies associated with the oceanic eddies modify turbulence in the atmospheric boundary layer. In the case of cyclonic eddies, this modification triggers a slackening of near-surface winds, a decline in cloud fraction and water content, and a reduction in rainfall. We conclude that transient mesoscale ocean structures can significantly affect much larger atmospheric low-pressure systems that swiftly pass by at the latitudes investigated.

Description: An influence of solar irradiance variations on Earth’s surface climate has been repeatedly suggested, based on correlations between solar variability and meteorological variables1. Specifically, weaker westerly winds have been observed in winters with a less active sun, for example at the minimum phase of the 11-year sunspot cycle2, 3, 4. With some possible exceptions5, 6, it has proved difficult for climate models to consistently reproduce this signal7, 8. Spectral Irradiance Monitor satellite measurements indicate that variations in solar ultraviolet irradiance may be larger than previously thought9. Here we drive an ocean–atmosphere climate model with ultraviolet irradiance variations based on these observations. We find that the model responds to the solar minimum with patterns in surface pressure and temperature that resemble the negative phase of the North Atlantic or Arctic Oscillation, of similar magnitude to observations. In our model, the anomalies descend through the depth of the extratropical winter atmosphere. If the updated measurements of solar ultraviolet irradiance are correct, low solar activity, as observed during recent years, drives cold winters in northern Europe and the United States, and mild winters over southern Europe and Canada, with little direct change in globally averaged temperature. Given the quasiregularity of the 11-year solar cycle, our findings may help improve decadal climate predictions for highly populated extratropical regions

Description: The volcanic arc of the Hellenic subduction zone with its four volcanic centers is of major relevance when evaluating the seismovolcanic hazard for the Aegean region. We present results from a 22-station temporary seismic network (CYCNET) in the central Hellenic Volcanic Arc (HVA). CYCNET recordings allow to analyze the level and spatio-temporal evolution of microseismic activity in this region for the first time. A total of 2175 events recorded between September 2002 and July 2004 are analyzed using statistical methods, cluster analysis and relative relocation techniques. We identify distinct regions with significantly varying spatiotemporal behavior of microseismicity. A large portion of the seismic activity within the upper crust is associated with the presence of islands representing horst structures that were generated during the major Oligocene extensional phase. In contrast, the central part of the Cyclades metamorphic core complex remains aseismic considering our magnitude threshold of 1.8 except one spot where events occur swarm-like and with highly similar waveforms. The highest activity in the study area was identified along the SW–NE striking Santorini–Amorgos zone. Within this zone the submarine Columbo volcano exhibits strong temporal variations of seismic activity on a high background level. This activity is interpreted to be directly linked to the magma reservoir and therein the migration of magma and fluids towards the surface. NE of Columbo where no volcanic activity has yet been reported we observe a similar seismicity pattern with small-scaled activity spots that might represent local pathways of upward migrating fluids or even developing volcanic activity within this zone of crustal weakness. In contrast, the Santorini and Milos volcanic complexes do not show significant temporal variations and low to moderate background activity, respectively. Relating our results to the distribution of historical earthquakes and the GPS-derived horizontal velocity field we conclude that the Santorini–Amorgos zone is presently in the state of right-lateral transtension reflecting a major structural boundary of the volcanic arc subdividing it into a seismically and volcanically quiet western and an active eastern part.

Description: The granule floatation is a serious issue of the anammox (anaerobic ammonium oxidation) process when high loading rates are applied that results in instability or even system collapse. The present study reports the granule floatation in an anammox reactor when high loading rates were applied. The comparison of enlarged photos taken for the settling and floating granules showed that the two kinds of granules both contained macroscopic gas pockets accounting for 11 +/- 14% of total volume. The settling granules had gas tunnels that could release the gas bubbles, while the floating granules did not. The presence of gas bubbles enclosed in the gas pockets led to the small density of 979.2 +/- 15.8 mg L(-1) and flotation of anammox granules. Consequently, the flotation caused washout of anammox granules and the deterioration of anammox process (volumetric removal rate decreased from 4.00 to 2.46 kg N m(-3) d(-1)). The collection of floating granules, breaking them into small pieces and then returning to the anammox reactor proved an effective control strategy. The volumetric removal rate was finally up to 16.5 kg N m(-3) d(-1) after the control strategy was put into use.

Description: The anaerobic oxidation of methane (AOM), by converting methane to bicarbonate which is then precipitated as extensive carbonate crusts, is an important methane sink in the Earth’s ocean systems. Here we employ a multidisciplinary approach to investigate the role of microorganisms in carbonate precipitation using biomarker analysis, scanning electron microscopy (SEM) and X-ray diffraction. We examined two microbial mats from the Black Sea and found that one comprised carbonate in both aragonite and Mg calcite forms and most likely ANME-1 archaea, whereas the other contained only Mg calcite and most likely ANME-2 archaea. We conclude, as have others, that the different microbial communities could impart different influences on carbonate mineralogy and morphology. Although further research is needed, this is a contribution to our understanding of those relationships, which could prove critical in the interpretation of ancient sedimentary deposits.

Description: The spatial variability in the mix of species making up Cold-water coral reef communities is not well known. In this study abundances of a selection of megafauna (Lophelia pertusa, Madrepora oculata, Paragorgia arborea, Primnoa resedaeformis, Mycale lingua, Geodia baretti, Acesta excavata and fish) were quantified throughout 9 manned submersible video transects from 3 reef complexes (Røst Reef, Sotbakken Reef and Traena Reef) on the Norwegian margin. Substrate type (coral structure, rubble, exposed hardground or soft sediment) was also recorded. Variations in the densities of these fauna (with respect to both reef complex and substrate type) were investigated, with spatial covariance between species assessed. For the majority of fauna investigated, densities varied by both reef and substrate. Spatial covariance indicated that some species may be utilising similar habitat niches, but that minor environmental differences may favour colonisation by one or other at a particular reef. Fish densities were generally higher in regions with biogenic substrate (coral structure and coral rubble substrates) than in areas of soft or hardground substrate. Further, fish were more abundant at the northerly Sotbakken Reef at time of study than elsewhere. Community structure varied by reef, and therefore management plans aimed at maintaining the biodiversity of reef ecosystems on the Norwegian margin should take this lack of homogeneity into account.

Description: The Cap de Creus continental shelf and Cap de Creus canyon are located in the southern most sector of the Gulf of Lions, in the northwestern Mediterranean. The Cap de Creus continental shelf contains sandy and muddy sediments and an abrupt morpho­ logy, with rocky outcrops, relict bioherms, erosive features, and planar bedforms. The Cap de Creus canyon breaches the shelf at a depth of 110 m and denotes a marked dif­ ference in the morphology between the northern and the southern flank, reflecting a different depositional regime. The most common substrates correspond to coarse and medium sands (28%) and silty sediments (40%). The most common megabenthic assemblages of the shelf correspond to the communities of "offshore detritic" (31.95%) and "coastal terrigenous muds" (36.99%), mostly dominated by sea pens, alcyonaceans, and ceriantharians. The northern flank of the Cap de Creus canyon is predominantly depositional, whereas the southern flank is erosional. Rocky outcrops provide the sub­ stratum for cold­water coral (CWC) communities' development, in which the white coral Madrepora oculata is the most abundant species.

Description: There is growing concern about the transfer of methane originating from water bodies to the atmosphere. Methane from sediments can reach the atmosphere directly via bubbles or indirectly via vertical turbulent transport. This work quantifies methane gas bubble dissolution using a combination of bubble modeling and acoustic observations of rising bubbles to determine what fraction of the methane transported by bubbles will reach the atmosphere. The bubble model predicts the evolving bubble size, gas composition, and rise distance and is suitable for almost all aquatic environments. The model was validated using methane and argon bubble dissolution measurements obtained from the literature for deep, oxic, saline water with excellent results. Methane bubbles from within the hydrate stability zone (typically below 500 m water depth in the ocean) are believed to form an outer hydrate rim. To explain the subsequent slow dissolution, a model calibration was performed using bubble dissolution data from the literature measured within the hydrate stability zone. The calibrated model explains the impressively tall flares (〉1300 m) observed in the hydrate stability zone of the Black Sea. This study suggests that only a small amount of methane reaches the surface at active seep sites in the Black Sea, and this only from very shallow water areas (〈100 m). Clearly, the Black Sea and the ocean are rather effective barriers against the transfer of bubble methane to the atmosphere, although substantial amounts of methane may reach the surface in shallow lakes and reservoirs.

Description: The anaerobic oxidation of methane (AOM) with sulphate, an area currently generating great interest in microbiology, is accomplished by consortia of methanotrophic archaea (ANME) and sulphate-reducing bacteria1, 2. The enzyme activating methane in methanotrophic archaea has tentatively been identified as a homologue of methyl-coenzyme M reductase (MCR) that catalyses the methane-forming step in methanogenic archaea3, 4. Here we report an X-ray structure of the 280 kDa heterohexameric ANME-1 MCR complex. It was crystallized uniquely from a protein ensemble purified from consortia of microorganisms collected with a submersible from a Black Sea mat catalysing AOM with sulphate4. Crystals grown from the heterogeneous sample diffract to 2.1 Å resolution and consist of a single ANME-1 MCR population, demonstrating the strong selective power of crystallization. The structure revealed ANME-1 MCR in complex with coenzyme M and coenzyme B, indicating the same substrates for MCR from methanotrophic and methanogenic archaea. Differences between the highly similar structures of ANME-1 MCR and methanogenic MCR include a F430 modification, a cysteine-rich patch and an altered post-translational amino acid modification pattern, which may tune the enzymes for their functions in different biological contexts.