ALBERT

Description: Nitrogen fixation — the reduction of dinitrogen (N2) gas to biologically available nitrogen (N) — is an important source of N for terrestrial and aquatic ecosystems. In terrestrial environments, N2-fixing symbioses involve multicellular plants, but in the marine environment these symbioses occur with unicellular planktonic algae. An unusual symbiosis between an uncultivated unicellular cyanobacterium (UCYN-A) and a haptophyte picoplankton alga was recently discovered in oligotrophic oceans. UCYN-A has a highly reduced genome, and exchanges fixed N for fixed carbon with its host. This symbiosis bears some resemblance to symbioses found in freshwater ecosystems. UCYN-A shares many core genes with the 'spheroid bodies' of Epithemia turgida and the endosymbionts of the amoeba Paulinella chromatophora. UCYN-A is widely distributed, and has diversified into a number of sublineages that could be ecotypes. Many questions remain regarding the physical and genetic mechanisms of the association, but UCYN-A is an intriguing model for contemplating the evolution of N2-fixing organelles.

Description: Gorgonians are a key group of organisms in benthic marine communities with a wide bathymetric and geographical distribution. Although their presence on continental shelves and slopes has been known for more than 100 years, knowledge concerning the ecology of deep gorgonian species is still in a very preliminary stage. To overcome this situation, gorgonian assemblages located at 40–360 m depth were studied over a large geographical area on the continental shelf and upper slope of the Menorca Channel (Western Mediterranean Sea). A quantitative analysis of video transects recorded by a manned submersible and a remotely operated vehicle, were used to examine the diversity, distribution and demography of gorgonian species. Results showed high gorgonian diversity within this depth range (a total of nine species were observed) compared to Mediterranean coastal areas. Gorgonian assemblages on the continental shelf and upper slope were mostly monospecific (respectively 73% and 76% of occupied sampling units contained one single species), whereas shelf edge assemblages were highly multispecific (92% of occupied sampling units contained several species). This contrasts with the monospecificity of Mediterranean coastal gorgonian assemblages. Gorgonian populations on the continental shelf were mostly dominated by small colonies (88% of measured colonies) with few intermediate and large colonies (12% of measured colonies). In deeper areas small colonies were still dominant (60% of measured colonies), but intermediate and large colonies were much more abundant (40% of measured colonies). This suggests high recruitment rates on the continental shelf, but perturbations (trammel nets, long lines and strong storms) may limit the presence of intermediate and large colonies. Conversely, on the shelf edge and upper slope a more stable environment may allow colonies to reach larger dimensions. The identification and ecological characterization of these deep assemblages further extends the current knowledge about Mediterranean gorgonians, and is fundamental in improving the management and conservation of deep benthic ecosystems.

Description: This study reconstructs the history of multiple industrial and urban mercury (Hg) emissions recorded in the sediment archive of Lake Luitel (France) from AD similar to 1860 to AD 2011. For this purpose, we provide a well constrained short-lived radionuclides continuous age-depth relationship of the sediment sequence (mean accumulation rate of 5.18 +/- 0.28 mm.yr(-1)) with Hg accumulation rates (Hg AR), Hg isotopic composition and extensive historical data. Hg AR were stable around 45 mu g.m(-2).y(-1) from 1860 to WWI and rose to reach their maximum at the end of WWII (250 mu g m(-2) y(-1)) followed by a gradual decreased to reach about 90 mu g m(-2) y(-1) in the current period. Normalization to a terrigenous Hg proxy highlighted the dominance of atmospheric Hg inputs to the lake. The combination of Hg AR with isotopic signatures through the use of binary mixing (Delta Hg-199 vs 1/Hg AR) models and isotopic plots (and comparison to literature data) allowed us to identify the main industrial and urban historical inputs. The major outcome of this study is that the Hg mass independent fractionation (MIF) signature did not enable the identification of particular anthropogenic sources but reflected an integrated pool of industrial and urban emissions which tend to shift to less negative MIF values (mean: -0.15 +/- 0.04%) during their period of maximum emissions. Temporal MIF and Hg AR variations depict the rising Hg emissions from the industrial revolution (1860-1910) to the modern industrial and urban development period (1950-1980). Mass dependent fractionation (MDF) signatures enabled the identification of major contributors in relation to their relative intensities lying between two endmember pools: (i) the combustion activities (smelters, cement factories and urban heating) with more negative delta Hg-202 values, and (ii) the chemical and electrometallurgical activities (electrochemistry, chlor-alkali) with higher delta Hg-202 values. Unconformities of MIF and MDF signatures were observed during WWI, WWII and interwar period, and were attributed to drastic and rapid changes in regional industrial activities. Finally, recent laws regarding Hg emissions (1998-2011) prove their efficiency as Hg AR decreased with a return to more negative MIF and MDF signatures such as during the industrial revolution period. Our study highlights that the combination of Hg isotopic data with Hg AR in sediment archives is a useful tool for reconstructing the history of anthropogenic Hg emissions, and has the potential to identifiy their relative contributions.

Description: Polysialic acid (PSA) serves as a hydrophilic polymer and affords conjugated biologically active molecules a longer circulation time in vivo. Furthermore, PSA could potentially target tumor tissues and help achieve better curative effects. In this study, PSA was conjugated with octadecyl dimethyl betaine (BS18) to yield a PSA-BS18 conjugate. The PSA-BS18 modified liposomal epirubicin (EPI-SL), had a particle size of 133.63 ± 0.92 nm, a zeta potential of −26.23 ± 1.50 mV and an encapsulation efficiency (%EE) of 96.23 ± 1.16%. In vitro release studies showed that PSA-BS18 could delay EPI release from the modified liposomes. The MTT assay suggested that EPI-SL led to stronger cytotoxic activity than that exhibited by common and PEGylated liposomes. The pharmacokinetic study showed that EPI-SL prolonged the residence time of the EPI in the blood compared with that observed from common liposomes. Bio-distribution results obtained from tumor-bearing mice clearly demonstrated that PSA-BS18 increased the accumulation of modified liposomes in tumors compared with that of common liposomes. In the antitumor efficacy study, EPI-SL showed the best antitumor and life-prolonging effects among all of the tested formulations. These findings strongly indicate EPI-SL might have great potential as an effective approach for anticancer therapy.

Description: Massive microbial mats covering up to 4-meter-high carbonate buildups prosper at methane seeps in anoxic waters of the northwestern Black Sea shelf. Strong 13C depletions indicate an incorporation of methane carbon into carbonates, bulk biomass, and specific lipids. The mats mainly consist of densely aggregated archaea (phylogenetic ANME-1 cluster) and sulfate-reducing bacteria (Desulfosarcina/Desulfococcusgroup). If incubated in vitro, these mats perform anaerobic oxidation of methane coupled to sulfate reduction. Obviously, anaerobic microbial consortia can generate both carbonate precipitation and substantial biomass accumulation, which has implications for our understanding of carbon cycling during earlier periods of Earth's history.

Description: Two modes of decrease in load bearing capacity of granular materials are discussed in view of experimental results. Both relate to the fact that frictional materials exhibit nonassociated plastic flow and they undergo considerable volume changes, either contraction or dilation. One mode consists of the instability that may occur in certain regions of stress space and potentially result in liquefaction of the granular material. It is the fact that loading of contracting soil (resulting in large plastic strains) can occur under decreasing stresses that may lead to unstable behavior under undrained conditions. As long as the soil remains drained, it will remain stable in the region of potential instability. The other mode is initiated by localization of plastic strains and subsequent development of shear bands, which in granular materials is followed by a decrease in load bearing capacity. These two modes are mutually exclusive and they occur for different loading and material conditions as discussed here on the basis of experimental observations.

Description: The interior of the Australian continent shows evidence for late Quaternary to Recent fault-controlled mantle 3He and CO2 degassing. A series of interconnected NW-striking sinistral faults, the Norwest fault zone (NFZ), in south-central Australia are associated with travertine mounds, the latter show a regular spacing of 50–70 km. U-series ages on 26 samples range from to (2σ errors) and suggest a clustering every ∼3–4 ka since ∼26 ka. Geochemical data demonstrate a remarkable mantle-to-groundwater connection. Isotopic data indicate that the groundwater is circulating to depths 〉3 km and interacting with Neoproterozoic/Cambrian basement and mantle volatiles. 3He/4He isotope ratios show that the He comes in part from the mantle. This demonstrates that the NFZ cuts through the entire crust and provides pathways for mantle degassing. Scaling relationships suggest that the series of sinistral faults that make up the NFZ are interconnected at depths and have a significant strike length of 60–70 km or more. The NFZ occurs where a major compositional boundary and a significant heat flow anomaly occurs, and a major step in lithospheric thickness has been mapped. We discuss a tectonic model in which recent stress field, heat flow and lithospheric structure in central Australia reactivated a set of steeply dipping Neoproterozoic faults, which may now be growing into a crustal/lithospheric-scale structure.

Description: Highlights • Synthesis of timescales of magmatic processes at spreading centres. • Compilation of drilled MORB glass compositions, chemical stratigraphy of the oceanic crust. • No chemical difference between MORB sampled from active ridges or by drilling. • Chemical variations on timescales 〈 1 ka reflect changes in melt recharge relative to fractionation. • Changes in the composition of melt entering crust occur over timescales of 10 to 100 ka. Abstract Oceanic crust is continuously created at mid-ocean ridges by decompression melting of the upper mantle as it upwells due to plate separation. Decades of research on active spreading ridges have led to a growing understanding of the complex magmatic, tectonic and hydrothermal processes linked to the formation of new oceanic igneous crust. However, less is known about the timescales of magmatic processes at mid-ocean ridges, including melting in and melt extraction from the mantle, fractional crystallisation, crustal assimilation and/or magma mixing. In this paper, we review the timescales of magmatic processes by integrating radiometric dating, chemical and petrological observations of mid-ocean ridge basalts (MORBs) and geophysical models. These different lines of evidence suggest that melt extraction and migration, and crystallisation and mixing processes occur over timescales of 1 to 10,000 a. High-resolution geochemical stratigraphic profiles of the oceanic crust using drill-core samples further show that at fast-spreading ridges, adjacent flow units may differ in age by only a few 100 a. We use existing chemical data and new major- and trace-element analyses of fresh MORB glasses from drill-cores in ancient Atlantic and Pacific crust, together with model stratigraphic ages to investigate how lava chemistry changes over 10 to 100 ka periods, the timescale of crustal accretion at spreading ridges which is recorded in the basalt stratigraphy in drilled sections through the oceanic crust. We show that drilled MORBs have compositions that are similar to those of young MORB glasses dredged from active spreading ridges (lavas that will eventually be preserved in the lowermost part of the extrusive section covered by younger flows), showing that the dredged samples are indeed representative of the bulk oceanic crust. Model stratigraphic ages calculated for individual flows in boreholes, together with the geochemical stratigraphy of the drilled sections, show that at fast-spreading ridges, magma compositions vary over 〈 100 to 1000 a, likely due to variations in the relative rates of crystallisation and melt recharge. However, on longer timescales of 10 to 100 ka, variations in the composition of the primitive melt feeding the ridge lead to chemical variations in the erupted lavas, likely as a function of thermal and/or chemical heterogeneity of the mantle source. The further understanding of these temporal variations in magma composition, especially at shorter timescales of less than a few centuries, is a promising area for future research.

Description: Highlights • A serpentinised peridotite basement is strongly supported by S-waves analysis • Depth dependent serpentinisation resembles to that observed at magma-poor margins. • Mantle exhumation was preceded by MOR-type magmatism and later intraplate volcanism. Summary The Tyrrhenian basin opened in the Neogene following the E–SE retreat of the Appenines–Calabrian subduction system and the subsequent back-arc extension of an orogenic crust. The resultant crustal structure includes a complex distribution of continental, back-arc magmatism, and mantle-exhumation domains. A clear example of this complex structure is found in the central and deepest part of the basin (i.e. Magnaghi–Vavilov sub-basin) where geophysical data supported that the bulk of the basement is composed of partially serpentinised peridotite representing exhumed mantle rocks, and intruded by basalts forming low ridges and volcanic edifices. However, those data sets cannot univocally demonstrate the widespread presence of serpentinised mantle rocks, let alone the percentage of serpentinisation. Here, we use S-wave arrivals and available geological information to further constrain the presence of mantle serpentinisation. Travel times of converted S-waves were used to derive the overall Vp/Vs and Poisson's ratio (σ), as well as S-wave velocity of the basement in the Magnaghi-Vavilov Basins. This analysis reveals Vp/Vs ≈ 1.9 (σ ≈ 0.3) that strongly supports a serpentinised peridotite forming the basement under the basins, rather than oceanic-type gabbro/diabase. P-wave velocity models is later used to quantify the amount of serpentinisation from fully serpentinised (up to 100%) at the top of the basement to 〈 10% at 5–7 km deep, with a depth distribution similar to continent–ocean Transition zones at magma-poor rifted margins. Seismic reflection profiles show normal faulting at either flank of the Magnaghi–Vavilov Basin that is potentially responsible for the onset of serpentinisation and later mantle exhumation. These results, together with basement sampling information in the area, suggests that the late stage of mantle exhumation was accompanied or soon followed by the emplacement of MOR-type basalts forming low ridges that preceded intraplate volcanism responsible for the formation of large volcanoes in the area.

Description: Dilution experiments were performed to estimate phytoplankton growth and microzooplankton grazing rates at two sites: freshwater (Nida) and brackish water (Smiltyne) in the Curonian Lagoon (SE Baltic Sea). Using the size-fractionation approach and dilution experiments, we found that the microzooplankton community was able to remove up to 78% of nanophytoplankton (2–20 μm) standing stock and 130% of the total daily primary production in the brackish waters of the lagoon, and up to 83% of standing stock and 76% of the primary production of picophytoplankton (0.2–2 μm) in the freshwater part. The observed differences were attributed to the changes in ciliate community size and trophic structure, with larger nano-filterers (30–60 μm) dominating the brackish water assemblages and pico-nano filterers (〈20 μm and 20–30 μm) prevailing in the freshwater part of the lagoon.