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

Arctic sea-ice evolution as modeled by Max Planck Institute for Meteorology's Earth system model

We describe the evolution of Arctic sea ice as modeled by the Max Planck Institute for Meteorology's Earth System Model (MPI-ESM). The modeled spatial distribution and interannual variability of the sea-ice cover agree well with satellite observations and are improved relative to the model's predecessor ECHAM5/MPIOM. An evaluation of modeled sea-ice coverage based on sea-ice area gives, however, conflicting results compared to an evaluation based on sea-ice extent and is additionally hindered by uncertainties in the observational record. Simulated trends in sea-ice coverage for the satellite period range from more strongly negative than observed to positive. The observed evolution of Arctic sea ice is incompatible with modeled internal variability and probably caused by external forcing. Simulated drift patterns agree well with observations, but simulated drift speed is generally too high. Simulated sea-ice volume agrees well with volume estimates of the PIOMAS reanalysis for the past few years. However, a preceding Arctic wide decrease in sea-ice volume starts much earlier in MPI-ESM than in PIOMAS. Analyzing this behavior in MPI-ESM's ocean model MPIOM, we find that the modeled volume trend depends crucially on the specific choice of atmospheric reanalysis forcing, which casts some doubt on the reliability of estimates of volume trends. In our CMIP5 scenario simulations, we find a substantial delay in sea-ice response to increasing CO2 concentration; a seasonally ice-free Arctic can result for a CO2 concentration of around 500 ppm. Simulated winter sea-ice coverage drops rapidly to near ice-free conditions once the mean Arctic winter temperature exceeds −5°C

Electron Transfer from Cyt b559 and Tyrosine-D to the S2 and S3 states of the water oxidizing complex in Photosystem II at Cryogenic Temperatures

The Mn4CaO5 cluster of photosystem II (PSII) catalyzes the oxidation of water to molecular oxygen through the light-driven redox S-cycle. The water oxidizing complex (WOC) forms a triad with Tyrosine(Z) and P-680, which mediates electrons from water towards the acceptor side of PSII. Under certain conditions two other redox-active components, Tyrosine(D) (Y-D) and Cytochrome b (559) (Cyt b (559)) can also interact with the S-states. In the present work we investigate the electron transfer from Cyt b (559) and Y-D to the S-2 and S-3 states at 195 K. First, Y-D (aEuro cent) and Cyt b (559) were chemically reduced. The S-2 and S-3 states were then achieved by application of one or two laser flashes, respectively, on samples stabilized in the S-1 state. EPR signals of the WOC (the S-2-state multiline signal, ML-S-2), Y-D (aEuro cent) and oxidized Cyt b (559) were simultaneously detected during a prolonged dark incubation at 195 K. During 163 days of incubation a large fraction of the S-2 population decayed to S-1 in the S-2 samples by following a single exponential decay. Differently, S-3 samples showed an initial increase in the ML-S-2 intensity (due to S-3 to S-2 conversion) and a subsequent slow decay due to S-2 to S-1 conversion. In both cases, only a minor oxidation of Y-D was observed. In contrast, the signal intensity of the oxidized Cyt b (559) showed a two-fold increase in both the S-2 and S-3 samples. The electron donation from Cyt b (559) was much more efficient to the S-2 state than to the S-3 state

Measurement of Minute Liquid Volumes of Chiral Molecules Using In-Fiber Polarimetry

We report an optofluidic method that enables to efficiently measure the enantiomeric excess of chiral molecules at low concentrations. The approach is to monitor the optical activity induced by a Kagome-lattice hollow core photonic crystal fiber filled with a sub-mu L volume of chiral compounds. The technique also allows monitoring the enzymatic racemization of Rmandelic acid