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Heinrich events associated with millennial-scale climate oscillations during the last glacial period are prominent events of ice-sheet collapse, characterized by the dispersal of ice(berg) rafted debris and freshwater across the North Atlantic. Hudson Strait has been suggested as one of the predominant iceberg source regions. One potential mechanism triggering iceberg release invokes cryosphere-ocean interactions, where subsurface warming destabilizes the Laurentide ice sheet. Subsurface warming is facilitated by the expansion of sea ice in the Labrador Sea in combination with a slow down of the Atlantic Meridional Overturning Circulation, which prevents the release and downward mixing of heat in the water column.Here we present high-resolution reconstructions of sea ice dynamics in the outer Labrador Sea at IODP Site U1302/03 between 30 ka and 60 ka. Sea ice reconstructions are based on a suite of sympagic and pelagic biomarkers, including highly branched isoprenoids and sterols. The results suggest a transition from reduced/seasonal to extended/perennial sea ice conditions preceding the onset of iceberg rafting associated with Heinrich event 3, 4, 5, and 5a by ~0.9 ± 0.5 ka. Ongoing work on the same core and sample material will have to confirm the timing and extent of subsurface warming compared to sea ice advances.

Dimethyl sulfide (DMS) is emitted by phytoplankton species in the oceans and constitutes the largest source of naturally emitted sulfur to the atmosphere. The climate impact of secondary particles, formed through the oxidation of DMS by hydroxyl radicals, is still elusive. This study investigates the hygroscopicity and cloud condensation nuclei activity of such particles and discusses the results in relation to their chemical composition. We show that mean hygroscopicity parameters, κ, during an experiment for particles of 80 nm in diameter range from 0.46 to 0.52 or higher, as measured at both sub- and supersaturated water vapour conditions. Ageing of the particles leads to an increase in κ from, for example, 0.50 to 0.58 over the course of 3 h (Exp. 7). Aerosol mass spectrometer measurements from this study indicate that this change most probably stems from a change in chemical composition leading to slightly higher fractions of ammonium sulfate compared to methanesulfonic acid (MSA) within the particles with ageing time. Lowering the temperature to 258 K increases κ slightly, particularly for small particles. These κ values are well comparable to previously reported model values for MSA or mixtures between MSA and ammonium sulfate. Particle nucleation and growth rates suggest a clear temperature dependence, with slower rates at cold temperatures. Quantum chemical calculations show that gas-phase MSA clusters are predominantly not hydrated, even at high humidity conditions, indicating that their gas-phase chemistry should be independent of relative humidity.

The most prominent events of ice-sheet collapse in the recent geological past are so-called Heinrich events observed during millennial-scale climate oscillations of the last glacial period. They are characterized by the dispersal of ice(berg) rafted debris and freshwater across the North Atlantic, with the Hudson Strait suggested as the predominant source region. One potential mechanism triggering iceberg release invokes cryosphere-ocean interactions, where subsurface warming destabilizes the Laurentide ice sheet. In this scenario, the build-up of a subsurface heat reservoir is caused by an extensive sea ice cover in the Labrador Sea in combination with a reduced overturning circulation in the North Atlantic, preventing the release and downward mixing of heat in the water column.Here we present high-resolution reconstructions of sea ice dynamics in the outer Labrador Sea between 30 ka and 60 ka at IODP Site U1302/03, located on Orphan Knoll. Sea ice reconstructions are based on a suite of sympagic and pelagic biomarkers, including highly branched isoprenoids and sterols. These results suggest a transition from reduced/seasonal to extended/perennial sea ice conditions preceding the onset of iceberg rafting associated with Heinrich event 3, 4, 5, and 5a by a couple of hundred to a thousand years. Our preliminary results thus support the importance of sea ice in the Labrador Sea for triggering Heinrich events. Future results from the same core will have to confirm the timing and extent of subsurface warming and ocean circulation dynamics.

Dimethyl sulfide (DMS) is produced by plankton in oceans and constitutes the largest natural emission of sulfur to the atmosphere. In this work, we examine new particle formation from the primary pathway of oxidation of gas-phase DMS by OH radicals. We particularly focus on particle growth and mass yield as studied experimentally under dry conditions using the atmospheric simulation chamber AURA. Experimentally, we show that aerosol mass yields from oxidation of 50–200 ppb of DMS are low (2–7%) and that particle growth rates (8.2–24.4 nm/h) are comparable with ambient observations. An HR-ToF-AMS was calibrated using methanesulfonic acid (MSA) to account for fragments distributed across both the organic and sulfate fragmentation table. AMS-derived chemical compositions revealed that MSA was always more dominant than sulfate in the secondary aerosols formed. Modeling using the Aerosol Dynamics, gas- and particle-phase chemistry kinetic multilayer model for laboratory CHAMber studies (ADCHAM) indicates that the Master Chemical Mechanism gas-phase chemistry alone underestimates experimentally observed particle formation and that DMS multiphase and autoxidation chemistry is needed to explain observations. Based on quantum chemical calculations, we conclude that particle formation from DMS oxidation in the ambient atmosphere will most likely be driven by mixed sulfuric acid/MSA clusters clustering with both amines and ammonia.

The Petermann 2015 Expedition to Petermann Fjord and adjacent Hall Basin recovered a transect of cores from Nares Strait to under the 48 km long ice tongue of Petermann glacier, offering a unique opportunity to study ice-ocean-sea ice interactions at the interface of these realms. First results suggest that no ice tongue existed in Petermann Fjord for large parts of the Holocene, raising the question of the role of the ocean and the marine cryosphere in the collapse and re-establishment of the ice tongue. Here we use a multi-proxy approach (sea-ice related biomarkers, total organic carbon and its carbon isotopic composition, and benthic and planktonic foraminiferal abundances) to explore Holocene sea-ice dynamics at OD1507-03TC-41GC-03PC in outer Petermann Fjord. Our results are in line with a tight coupling of the marine and terrestrial cryosphere in this region and, in connection with other regional sea-ice reconstructions, give insights into the Holocene evolution of ice arches and associated landfast ice in Nares Strait. The late stages of the regional Holocene Thermal Maximum (5,500–6,900 cal yrs BP) were marked by reduced seasonal sea-ice concentrations in Nares Strait and the lack of ice arch formation. This was followed by a transitional period towards neoglacial cooling from 3,500–5,500 cal yrs BP, where a southern ice arch might have formed, but an early seasonal break-up and late formation likely caused a prolonged open water season and enhanced pelagic productivity in Nares Strait. Between 1,400 cal yrs BP and 3,500 cal yrs BP, regional records suggest the formation of a stable northern ice arch only, with a short period from 2,100–2,500 cal yrs BP where a southern ice arch might have persisted in response to atmospheric cooling spikes. A stable southern ice arch, or even double arching, is also inferred for the period after 1,400 cal yrs BP. Thus, both the inception of a small Petermann ice tongue at ~2,200 cal yrs BP and its rapid expansion at ~600 cal yrs BP are preceded by a transition towards a southern ice arch regime with landfast ice formation in Nares Strait, suggesting a stabilizing effect of landfast sea ice on Petermann Glacier.

Bio-crude from hydrothermal liquefaction (HTL) of lignocellulosic biomass is a potential alternative to conventional fossil fuels. Continuous HTL of lignocellulosic biomass requires feedstock pretreatment to obtain pumpable slurries. This work extends upon previous evaluations of pretreatment methods for obtaining stable slurries of Miscanthus х giganteus. In the current study, extensive characterization of the bio-crude and aqueous phase from HTL of thermally and chemically pretreated M. х giganteus is reported and molecular differences of these samples are evaluated. The bio-crude and aqueous phase is characterized with gas chromatography coupled to mass spectrometry using pre-derivatization with silylating reagent and methyl chloroformate, respectively. Principal component analysis shows that bio-crudes of untreated and slurry stabilized samples have higher concentrations of small organic acids and fatty acids, samples pretreated at mild alkali conditions have higher concentrations of alcohols, polyaromatics, and methylated phenolics, and samples pretreated with strong alkali conditions have higher concentrations of cyclic oxygenates and ketonized aromatics. Aqueous phases are separated based on the addition of slurry stabilizer which has higher concentrations of dicarboxylic acids and phenol. The detailed exploration of both bio-crude and aqueous phase will be of interest for other investigations of the pretreatment effects on biomass for hydrothermal liquefaction.

Hydrothermal liquefaction (HTL) is a promising technique for conversion of wet biomasses containing varying amounts of carbohydrate, protein, lipid, and lignin. In this work, mixtures of these model compounds were subjected to HTL at 335°C. As many as 67 compounds were quantitated in the aqueous phase, including small organic acids, cyclic oxygenates, fatty acids, nitrogenates, and oxygenated aromatics. The concentrations correlated with the ratio of the model compounds. Principal component analysis separated samples on the basis of their quantitative results which could be linked to their biochemical composition. Concentrations of the analytes were modeled with partial least squares regression, and high-quality predictions were made from quality control (QC) samples and to varying degrees from Dried Distillers Grains with Solubles (DDGS), Miscanthus x giganteus, and Chlorella vulgaris. Values for total organic carbon (TOC), total nitrogen (TN), and pH were also predicted from QC samples, DDGS, M. x giganteus, and C. vulgaris. Carbohydrate and lipid contents mainly influenced TOC values and could be used for minimizing loss of organics, for techno-economic analysis, and for assessing potential for anaerobic digestion and thermal gasification. Pyrazines were modeled using linear, exponential, and second-degree polynomial fits, depending on whether carbohydrate or protein was the limiting biochemical component, which could be a way of controlling nitrogen and carbon displacement to the aqueous phase. This work shows that TOC, TN, pH, and concentrations of single compounds in the aqueous phase from HTL can, in many cases, be predicted from HTL of mixtures of biomass constituents.

Finding sustainable and commercially viable sources of occlusive materials, as an alternative to petroleum, is of great interest. Inspired by the fundamental role of long chain fatty acids in maintaining skin barrier, ultralong fatty acyl derivatives with diverse structures (varied acyl chain length and different polar head; i.e. glycerol, ethylene glycol, and diethylene glycol) were synthesized. These molecules can be feasibly obtained via enzymatic esterification of fatty acids or fractionated from commercial glycerides mixture via short path distillation. The molecular packing behaviors of compounds were characterized via differential scanning calorimetry, Fourier transform infrared, and Langmuir isotherm measurements. The structure–property relationship study reveals that a glycerol molecule monoacylated with an ultralong fatty acyl is the derivative which entails the most occlusive properties of the series of ultralong chain fatty acid derivatives. Fast Fourier transform filtering (FFTF) analysis of ...

Background: Plants and in particular grasses benefit from a high uptake of silicon (Si) which improves their growth and productivity by alleviating adverse effects of biotic and abiotic stress. However, the silicon present in plant tissues may have a negative impact on the processing and degradation of lignocellulosic biomass. Solutions to reduce the silicon content either by biomass engineering or development of downstream separation methods are therefore targeted. Different cell wall components have been proposed to interact with the silica pool in plant shoots, but the understanding of the underlying processes is still limited. Results: In the present study, we have characterized silicon deposition and cell wall composition in Brachypodium distachyon wild-type and low-silicon 1 (Bdlsi1-1) mutant plants. Our analyses included different organs and plant developmental stages. In the mutant defective in silicon uptake, low silicon availability favoured deposition of this element in the amorphous form or bound to cell wall polymers rather than as silicified structures. Several alterations in non-cellulosic polysaccharides and lignin were recorded in the mutant plants, indicating differences in the types of linkages and in the three-dimensional organization of the cell wall network. Enzymatic saccharification assays showed that straw from mutant plants was marginally more degradable following a 190 °C hydrothermal pretreatment, while there were no differences without or after a 120 °C hydrothermal pretreatment. Conclusions: We conclude that silicon affects the composition of plant cell walls, mostly by altering linkages of non-cellulosic polymers and lignin. The modifications of the cell wall network and the reduced silicon concentration appear to have little or no implications on biomass recalcitrance to enzymatic saccharification.

A novel peptidase from thermophilic archaea Sulfolobus tokodaii (ST0779) is examined for its catalytic promiscuity of aldol addition, which shows comparable activity as porcine pancreatic lipase (PPL, one of the best enzymes identified for biocatalytic aldol addition) at 30 °C but much accelerated activity at elevated temperature. The molecular catalytic efficiency kcat/Km (M(-1) s(-1)) of this thermostable enzyme at 55 °C adds up to 140 times higher than that of PPL at its optimum temperature 37 °C. The fluorescence quenching analysis depicts that the binding constants of PPL are significantly higher than those of ST0779, and their numbers of binding sites show opposite temperature dependency. Thermodynamic parameters estimated by fluorescence quenching analysis unveil distinctly different substrate-binding modes between PPL and ST0779: the governing binding interaction between PPL and substrates is hydrophobic force, while the dominating substrate-binding forces for ST0779 are van der Waals and H-bonds interactions. A reasonable mechanism for ST0779-catalyzed aldol reaction is proposed based on kinetic study, spectroscopic analysis, and molecular stereostructure simulation. This work represents a successful example to identify a new enzyme for catalytic promiscuity, which demonstrates a huge potential to discover and exploit novel biocatalyst from thermophile microorganism sources.

A series of O-acylated-ω-hydroxy fatty acids (Acyl acids) of up to 34 carbons were synthesized and characterized through DSC, FTIR and Langmuir isotherm measurements to identify potential replacements to petrolatum, a highly used occlusive technology that if unrefined, it can potentially be classified as carcinogenic. Fourier transform infrared spectroscopy studies demonstrated that long acyl acids engender orthorhombic packing; packing behavior that is predominant in the lipid matrix of healthy stratum corneum, the outmost layer of the skin. In addition, Differential Scanning Calorimetry (DSC) and Langmuir isotherm studies suggested that the length of the hydrocarbon chain and the position of the ester bond influence the molecular organization of the acyl acids. For instance, 16-(tetradecanoyloxy)hexadecanoic acid (30 carbons) displayed a higher melting point (mp=68°C) than 10-(stearoyloxy)decanoic acid (28 carbons; mp=63°C) and 10-(tetradecanoyloxy)decanoic acid (24 carbons; mp=55°C) according to DSC. Moreover, Langmuir isotherm studies showed that mixtures of acyl acid with distearoylphosphatidylcholine improved packing behavior. Finally, Water Vapor Transmission Rate (WVTR) measurements showed that the compounds in fact decrease WVTR compared to untreated control (P0.001) which demonstrates the potential of these ingredients as occlusive technologies to combat skin barrier diseases.

Hydrothermal liquefaction (HTL) produces solid residue (SR) as a side-product with an organic fraction of char highly dependent on the feedstock. In this work the char from batch HTL of poplar, Spirulina, and their 1 : 1 mixture was characterized for the first time using stepwise thermal desorption and pyrolysis-gas-chromatography-mass spectrometry (py-GC-MS) along with thermochemolysis. Three distinct compound fractions were identified in the form of trapped or strongly adsorbed compounds, residual lignin, and repolymerized phenolics. The trapped or adsorbed fraction resembled the compounds in the bio-crude and aqueous phase from both poplar and Spirulina. Residual lignin was only found from poplar while repolymerized phenolics were predominantly observed from poplar through ortho and para-directed polymerization. Multiple aliphatic hydrocarbons and some alkylated pyrroles were observed from Spirulina. Co-liquefaction of biomasses led to a markedly different SR from the individual biomasses with multiple alkylated pyrroles and indoles, both volatile and non-volatile, while repolymerized phenolics diminished due to imine formation. This work demonstrates that potential bio-crude is present in the SR from both poplar and Spirulina while co-liquefaction hinders repolymerization of phenolics but also produces a vast number of volatile and non-volatile pyrroles. The work shows that additional information on the reaction pathways of HTL may be found by the characterization of the SR and provides researchers investigating biomass conversion with a method to evaluate the effects on SR formation.

Hydrothermal liquefaction is a promising technique for the production of bio-oil. The process produces an oil phase, a gas phase, a solid residue, and an aqueous phase. Gas chromatography coupled with mass spectrometry is used to analyze the complex aqueous phase. Especially small organic acids and nitrogen-containing compounds are of interest. The efficient derivatization reagent methyl chloroformate was used to make analysis of the complex aqueous phase from hydrothermal liquefaction of dried distillers grains with solubles possible. A circumscribed central composite design was used to optimize the responses of both derivatized and nonderivatized analytes, which included small organic acids, pyrazines, phenol, and cyclic ketones. Response surface methodology was used to visualize significant factors and identify optimized derivatization conditions (volumes of methyl chloroformate, NaOH solution, methanol, and pyridine). Twenty-nine analytes of small organic acids, pyrazines, phenol, and cyclic ketones were quantified. An additional three analytes were pseudoquantified with use of standards with similar mass spectra. Calibration curves with high correlation coefficients were obtained, in most cases R 2 > 0.991. Method validation was evaluated with repeatability, and spike recoveries of all 29 analytes were obtained. The 32 analytes were quantified in samples from the commissioning of a continuous flow reactor and in samples from recirculation experiments involving the aqueous phase. The results indicated when the steady-state condition of the flow reactor was obtained and the effects of recirculation. The validated method will be especially useful for investigations of the effect of small organic acids on the hydrothermal liquefaction process.