Emission ratio and isotopic signatures of molecular hydrogen emissions from tropical biomass burning

In this study, we identify a biomass-burning signal in molecular hydrogen (H₂) over the Amazonian tropical rainforest. To quantify this signal, we measure the mixing ratios of H₂ and several other species as well as the H₂ isotopic composition in air samples that were collected in the BARCA (Balanço Atmosférico Regional de Carbono na Amazônia) aircraft campaign during the dry season. We derive a relative H₂ emission ratio with respect to carbon monoxide (CO) of 0.31 ± 0.04 ppb ppb⁻¹ and an isotopic source signature of −280 ± 41‰ in the air masses influenced by tropical biomass burning. In order to retrieve a clear source signal that is not influenced by the soil uptake of H₂, we exclude samples from the atmospheric boundary layer. This procedure is supported by data from a global chemistry transport model. The ΔH₂ / ΔCO emission ratio is significantly lower than some earlier estimates for the tropical rainforest. In addition, our results confirm the lower values of the previously conflicting estimates of the H₂ isotopic source signature from biomass burning. These values for the emission ratio and isotopic source signatures of H₂ from tropical biomass burning can be used in future bottom-up and top-down approaches aiming to constrain the strength of the biomass-burning source for H₂. Hitherto, these two quantities relied only on combustion experiments or on statistical relations, since no direct signal had been obtained from in-situ observations

Auditory sensory memory and working memory skills : Association between frontal MMN and performance scores

Objective: Memory is the faculty responsible for encoding, storing and retrieving information, comprising several sub-systems such as sensory memory (SM) and working memory (WM). Some previous studies exclusively using clinical population revealed associations between these two memory systems. Here we aimed at investigating the relation between modality-general WM performance and auditory SM formation indexed by magnetic mismatch negativity (MMN) responses in a healthy population of young adults. Methods: Using magnetoencephalography (MEG), we recorded MMN amplitudes to changes related to six acoustic features (pitch, timbre, location, intensity, slide, and rhythm) inserted in a 4-tone sequence in 86 adult participants who were watching a silent movie. After the MEG recordings, participants were administered the WM primary subtests (Spatial Span and Letter Number Sequencing) of Wechsler Memory Scale (WMS). Results: We found significant correlations between frontal MMN amplitudes to intensity and slide deviants and WM performance. In case of intensity, the relation was revealed in all participants, while for slide only in individuals with a musical background. Conclusions: Automatic neural responses to auditory feature changes are increased in individuals with higher visual WM performance. Significance: Conscious WM abilities might be linked to pre-attentive sensory-specific neural skills of prediction and short-term storage of environmental regularities. (C) 2018 Elsevier B.V. All rights reserved.Peer reviewe

Whole-brain computation of cognitive versus acoustic errors in music : A mismatch negativity study

Previous studies have evidenced how the local prediction of physical stimulus features may affect the neural processing of incoming stimuli. Less known are the effects of cognitive priors on predictive processes, and how the brain computes local versus cognitive predictions and their errors. Here, we determined the differential brain mechanisms underlying prediction errors related to high-level, cognitive priors for melody (rhythm, contour) versus low-level, local acoustic priors (tuning, timbre). We measured with magnetoencephalography the mismatch negativity (MMN) prediction error signal in 104 adults having varying levels of musical expertise. We discovered that the brain regions involved in early predictive processes for local priors were primary and secondary auditory cortex and insula, whereas cognitive brain regions such as cingulate and orbitofrontal cortices were recruited for early melodic errors in cognitive priors. The involvement of higher-level brain regions for computing early cognitive errors was enhanced in musicians, especially in cingulate cortex, inferior frontal gyrus, and supplementary motor area. Overall, the findings expand knowledge on whole-brain mechanisms of predictive processing and the related MMN generators, previously mainly confined to the auditory cortex, to a frontal network that strictly depends on the type of priors that are to be computed by the brain.Peer reviewe

Factors controlling coccolithophore biogeography in the Southern Ocean

The biogeography of Southern Ocean phytoplankton controls the local biogeochemistry and the export of macronutrients to lower latitudes and depth. Of particular relevance is the competitive interaction between coccolithophores and diatoms, with the former being prevalent along the Great Calcite Belt (40–60°&thinsp;S), while diatoms tend to dominate the regions south of 60°&thinsp;S. To address the factors controlling coccolithophore distribution and the competition between them and diatoms, we use a regional high-resolution model (ROMS–BEC) for the Southern Ocean (24–78°&thinsp;S) that has been extended to include an explicit representation of coccolithophores. We assess the relative importance of bottom-up (temperature, nutrients, light) and top-down (grazing by zooplankton) factors in controlling Southern Ocean coccolithophore biogeography over the course of the growing season. In our simulations, coccolithophores are an important member of the Southern Ocean phytoplankton community, contributing 17&thinsp;% to annually integrated net primary productivity south of 30°&thinsp;S. Coccolithophore biomass is highest north of 50°&thinsp;S in late austral summer, when light levels are high and diatoms become limited by silicic acid. Furthermore, we find top-down factors to be a major control on the relative abundance of diatoms and coccolithophores in the Southern Ocean. Consequently, when assessing potential future changes in Southern Ocean coccolithophore abundance, both abiotic (temperature, light, and nutrients) and biotic factors (interaction with diatoms and zooplankton) need to be considered.</p

Dynamical Interaction between Atmosphere and Sea Ice in Antarctica

Abstract Sea ice that covers large parts of the polar oceans throughout most of the year responds to changes in the atmosphere or the ocean within a short period of time. The rapid decrease of the Arctic sea ice cover in the past decades has led to a fundamental discussion of the role of sea ice in the climate system. Surprisingly, in contrast to the northern hemisphere, the sea ice in the Southern Ocean has been slightly increasing over the last decades. This is owing to essentially different processes that take place around Antarctica. There, the ice is not confined to a basin as in the Arctic Ocean but can move rather freely around the Antarctic continent which results in a strong response to changes in the wind field. In this Master&apos;s thesis I examined the impact of the variations in the coastal Antarctic atmospheric boundary layer on the sea ice. By studying wind driven sea ice transport in the Southern Ocean and temporal and spatial variabilities in the period 1989 to 2006, I have revealed important characteristics of the sea ice cover and processes that determine its growth and decay. The near surface wind field over the coastal continent and ocean as well as its forcing mechanisms were described in detail by using output from a regional atmospheric climate model. This showed strong relations to key parameters that I have deduced from a satellite record of sea ice concentration and sea ice motion. The regions of the largest sea ice extent, the Ross and Weddell Seas, are also those areas where most of the sea ice transport takes place and where its variability is the largest. Interannual variations and trends of transport are associated with varying sea ice concentration just north of these areas in the Ross and Weddell Seas. Comparing the wind field and the sea ice motion, I found out that spatial patterns of persistent southerly or south-easterly winds coincide with those of ice drift. The winds in these regions result from combined effects of the large-scale pressure distribution, cold air that accumulates over the ice shelves, and large topographic barriers that alter the flow. Adjacent to the large Ross and Ronne-Filchner Ice Shelves constant outflow of cold air takes place almost year-round. Here, sea ice is constantly exported from the coastal region, and large polynyas and leads form. As the cold winds not only lead to sea ice transport but also support refreezing of the open water, these areas are associated with strong sea ice formation. I have defined an index that captures the outflow of cold continental air from the ice shelves. The long-term variations in outflow correlate well with variations of the sea ice cover and meridional sea ice transport in the Ross and western Weddell Seas. Further, the results suggest that the positive trend of sea ice cover in western Ross Sea and the negative trend in the western Weddell Sea are related to a respective seasonal increase and decrease of cold air outflow. Overall, in my thesis, I showed that the dynamical interaction between the atmospheric boundary layer and the sea ice is a regional key element in the interannual variability and the long-term changes of the sea ice cover in the Southern Ocean

Spectroscopic Properties of a Biologically Relevant [Fe2(μ-O)2] Diamond Core Motif with a Short Iron-Iron Distance

Diiron cofactors in enzymes perform diverse challenging transformations. The structures of high valent intermediates (Q in methane monooxygenase and X in ribonucleotide reductase) are debated since Fe−Fe distances of 2.5–3.4 Å were attributed to “open” or “closed” cores with bridging or terminal oxido groups. We report the crystallographic and spectroscopic characterization of a FeIII2(μ-O)2 complex (2) with tetrahedral (4C) centres and short Fe−Fe distance (2.52 Å), persisting in organic solutions. 2 shows a large Fe K-pre-edge intensity, which is caused by the pronounced asymmetry at the TD FeIII centres due to the short Fe−μ−O bonds. A ≈2.5 Å Fe−Fe distance is unlikely for six-coordinate sites in Q or X, but for a Fe2(μ-O)2 core containing four-coordinate (or by possible extension five-coordinate) iron centres there may be enough flexibility to accommodate a particularly short Fe−Fe separation with intense pre-edge transition. This finding may broaden the scope of models considered for the structure of high-valent diiron intermediates formed upon O2 activation in biology

Monolithic SiC supports with tailored hierarchical porosity for molecularly selective membranes and supported liquid-phase catalysis

Monolithic support materials with the mechanical resistance and thermal conductivity of SiC as well as tunable surface chemistry and textural properties were developed for their use in catalytic membrane reactors. After heat treatment, the extruded SiC monoliths have a monomodal distribution of macropores of a few μm in diameter depending on the particle size of the starting material. A macroporous, defect-free, smoother skin was applied onto the external wall using a solution of sub-micrometer SiC particles. These monoliths with skin could be coated successfully with molecularly selective membranes, and thus have application in membrane reactor processes. Finally, metal oxide nanoparticles were infiltrated into the macropores to modify the surface texture and chemistry, allowing the immobilization of liquid phase catalysts. The resulting multimodal distribution of pore sizes could be tuned by the choice of SiC and oxide particle sizes, number of wash-coats and calcination temperature. Mesopores created between nanoparticles had diameters of roughly 40 % of those of the nanoparticles. Small macropores, between 10−1000 nm, were also created, with bigger size and volume at higher calcination temperatures due to the metal oxide particles contraction. The developed materials were validated as support for PDMS membranes and for continuous gas-phase hydroformylation of 1-butene using Rh-diphosphite catalysts.The authors gratefully acknowledge financial support from the European Commissionwithin the Horizon2020-SPIRE project ROMEO (Grant Agreement Number 680395). Furthermore, the authors would like to thank Dr. Andreas Bösmann and M. Sc. Patrick Wolf (Universit ̈at Erlangen-Nürnberg) for the XRF measurements, as well as Markus Wist (RWTH Aachen University) for his work in the membrane fabricatio

The Southern Ocean Freshwater Input from Antarctica (SOFIA) Initiative: scientific objectives and experimental design

As the climate warms, the grounded ice sheet and floating ice shelves surrounding Antarctica are melting and releasing additional freshwater into the Southern Ocean. Nonetheless, almost all existing coupled climate models have fixed ice sheets and lack the physics required to represent the dominant sources of Antarctic melt. These missing ice dynamics represent a key uncertainty that is typically unaccounted for in current global climate change projections. Previous modelling studies that have imposed additional Antarctic meltwater have demonstrated regional impacts on Southern Ocean stratification, circulation, and sea ice, as well as remote changes in atmospheric circulation, tropical precipitation, and global temperature. However, these previous studies have used widely varying rates of freshwater forcing, have been conducted using different climate models and configurations, and have reached differing conclusions on the magnitude of meltwater–climate feedbacks. The Southern Ocean Freshwater Input from Antarctica (SOFIA) initiative brings together a team of scientists to quantify the climate system response to Antarctic meltwater input along with key aspects of the uncertainty. In this paper, we summarize the state of knowledge on meltwater discharge from the Antarctic ice sheet and ice shelves to the Southern Ocean and explain the scientific objectives of our initiative. We propose a series of coupled and ocean–sea ice model experiments, including idealized meltwater experiments, historical experiments with observationally consistent meltwater input, and future scenarios driven by meltwater inputs derived from stand-alone ice sheet models. Through coordinating a multi-model ensemble of simulations using a common experimental design, open data archiving, and facilitating scientific collaboration, SOFIA aims to move the community toward better constraining our understanding of the climate system response to Antarctic melt.</p