Persistence of bubble outlets in soft, methane-generating sediments

Sediments submerged beneath many inland waterways and shallow oceans emit methane, a potent greenhouse gas, but the magnitude of the methane flux to the atmosphere remains poorly constrained. In many settings, the majority of methane is released through bubbling, and the spatiotemporal heterogeneity of this ebullition both presents challenges for measurement and impacts bubble dissolution and atmospheric emissions. Here we present laboratory-scale experiments of methane ebullition in a controlled incubation of reconstituted sediments from a eutrophic lake. Image analysis of a 0.14 m2 sediment surface area allowed identification of individual bubble outlets and resolved their location to ∼1 cm. While ebullition events were typically concentrated in bursts lasting ∼2 min, some major outlets showed persistent activity over the scale of days and even months. This persistence was surprising given the previously observed ephemerality of spatial structure at the field scale. This persistence suggests that, at the centimeter scale, conduits are reopened as a result of a drop in tensile strength due to deformation of sediments by the rising bubbles. The mechanistic insight from this work sheds light on the spatiotemporal distribution of methane venting from organic-rich sediments and has important implications for bubble survival in the water column and associated biogeochemical pathways of methane.National Science Foundation (U.S.) (1045193)United States. Department of Energy (DE-FE0013999

Xenon hydrate as an analog of methane hydrate in geologic systems out of thermodynamic equilibrium

Author Posting. © American Geophysical Union, 2019. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Geochemistry Geophysics Geosystems 20(5), (2019):2462-2472, doi:10.1029/2019GC008250.Methane hydrate occurs naturally under pressure and temperature conditions that are not straightforward to replicate experimentally. Xenon has emerged as an attractive laboratory alternative to methane for studying hydrate formation and dissociation in multiphase systems, given that it forms hydrates under milder conditions. However, building reliable analogies between the two hydrates requires systematic comparisons, which are currently lacking. We address this gap by developing a theoretical and computational model of gas hydrates under equilibrium and nonequilibrium conditions. We first compare equilibrium phase behaviors of the Xe·H2O and CH4·H2O systems by calculating their isobaric phase diagram, and then study the nonequilibrium kinetics of interfacial hydrate growth using a phase field model. Our results show that Xe·H2O is a good experimental analog to CH4·H2O, but there are key differences to consider. In particular, the aqueous solubility of xenon is altered by the presence of hydrate, similar to what is observed for methane; but xenon is consistently less soluble than methane. Xenon hydrate has a wider nonstoichiometry region, which could lead to a thicker hydrate layer at the gas‐liquid interface when grown under similar kinetic forcing conditions. For both systems, our numerical calculations reveal that hydrate nonstoichiometry coupled with hydrate formation dynamics leads to a compositional gradient across the hydrate layer, where the stoichiometric ratio increases from the gas‐facing side to the liquid‐facing side. Our analysis suggests that accurate composition measurements could be used to infer the kinetic history of hydrate formation in natural settings where gas is abundant.This work was funded in part by the U.S. Department of Energy, DOE [awards DE‐FE0013999 and DE‐SC0018357 (to R. J.) and DOE Interagency Agreement DE‐FE0023495 (to W. F. W.)]. X. F. acknowledges support by the Miller Research Fellowship at the University of California Berkeley. W. F. W. acknowledges support from the U.S. Geological Survey's Gas Hydrate Project and the Survey's Coastal, Marine Hazards and Resources Program. L. C. F. acknowledges funding from the Spanish Ministry of Economy and Competitiveness (grants RYC‐2012‐11704 and CTM2014‐54312‐P). L. C. F. and R. J. acknowledge funding from the MIT International Science and Technology Initiatives, through a Seed Fund grant. The simulation data are available on the UC Berkeley Dash repository at https://doi.org/10.6078/D1G67B.2019-11-0

Cohort-specific winter growth rates of YOY bluefish, Pomatomus saltatrix, in northeast Florida estuaries: implications for recruitment

Abstract Age and growth were determined from otoliths for 181 juvenile bluefish (Pomatomus saltatrix), collected using a variety of gear in northeast Florida during 2003 and 2005. Three distinct cohorts were identified recruiting to the near shore waters during spring, summer and autumn. Growth rates were high regardless of cohort or season. To compare pre-and post-recruitment growth rates, models were fit to individual growth trajectories using change point analysis. Post-estuarine growth rates were generally higher. Growth rates and hatching times were within the range of those obtained in other bluefish studies conducted at higher latitudes. As this is the only area where winter recruitment of bluefish has been observed, coastal Florida habitats may be essential for the bluefish stock and will need to be carefully monitored in future studies

Evolution of Microbiota in a Pharmacy Classroom Pre and Post the First Wave of the COVID-19 Pandemic

Microbiota varies over time, therefore during 2019-20 academic year, coinciding with the SARS-COV-2 pandemic, the evolution of it was evaluated in a classroom of the Faculty of Pharmacy of the University of Salamanca with mass spectrometry Matrix-assisted laser desorption ionization time-of-flight. In addition, this study was compared with others, as well as with guidelines of the European Community Commission on indoor air quality./nAfter the study, it was concluded that said classroom had very low contamination degree and that most of microbiota was saprophytic. Furthermore, it can be concluded that quantitatively fungi and quantitatively and qualitatively the bacteria did not present a health risk./nOn the other hand, the most important variables that were found were the influx of people, the frequency of cleaning and ventilation. Finally, this study shows off the lack of regulation that exists on air quality in non-industrial and non-hospital interiors.La microbiota varía con el tiempo, por ello durante el curso académico 2019-20, coincidiendo con la pandemia SARS-COV-2, se evaluó la evolución de la misma en un aula de la Facultad de Farmacia de la Universidad de Salamanca con la espectrometría de masas Matrix-assisted laser desorption ionization time-of-flight. Además, se comparó con otros estudios, así como con las directrices de la Comisión de la Comunidad Europea de calidad del aire de interiores./nTras el estudio se concluyó que dicha aula presentaba un grado de contaminación muy bajo, y que la mayoría de la microbiota era saprofítica. Asimismo, de forma general se puede concluir que de forma cuantitativa los hongos y de forma cuali-cuantitativa las bacterias no presentaban un riesgo para la salud./nPor otro lado, entre las variables más importantes encontramos la afluencia de personas, la frecuencia de limpieza y la ventilación. Finalmente, este estudio recoge la poca normativa que existe sobre la calidad del aire en interiores no industriales y no hospitalarios

Six-dimensional quasiclassical and quantum dynamics of H2 dissociation on the c(2 * 2)-Ti/Al(100) surface

The following article appeared in Journal of Chemical Physic 134.11 (2011): 114708 and may be found at http://scitation.aip.org/content/aip/journal/jcp/134/11/10.1063/1.3567397Based on a slab model of H2 dissociation on a c(2 * 2) structure with Ti atoms in the first and third layers of Al(100), a six-dimensional (6D) potential energy surface (PES) has been built. In this PES, a molecular adsorption well with a depth of 0.45 eV is present in front of a barrier of height 0.13 eV. Using this PES, H2 dissociation probabilities are calculated by the classical trajectory (CT), the quasiclassical trajectory (QCT), and the time-dependent wave-packet (TDWP) method. The QCT study shows that trajectories can be trapped by the molecular adsorption well. Higher incident energy can lead to direct H2 dissociation. Vibrational pre-excitation is the most efficient way to promote direct dissociation without trapping. We find that both rotational and vibrational excitation have efficacies close to 1.0 in the entire range of incident energies investigated, which supports the randomization in the initial conditions making the reaction rate solely dependent on the total (internal and translational) energy. The H2 dissociation probabilities from quantum dynamics are in reasonable agreement with the QCT results in the energy range 50-200 meV, except for some fluctuations. However, the TDWP results considerably exceed the QCT results in the energy range 200-850 meV. The CT reaction probabilities are too low compared with the quantum dynamical resultsThe research of J.C.C. is supported by the Marie Curie Research Training Network HYDROGE

MALDI_TOF mass spectrometry does not differentiate between brucella species, suggesting that the may represent a single species

Comunicaciones a congreso

2007-2010), the Mid-Atlantic Bight (MAB; 2009-2010) and the South Atlantic Bight (SAB; 2010-2011)

a b s t r a c t Large pelagic predators were used as biological samplers to gain information on cephalopod diversity, abundance, distribution, and their role as prey in the Northwest Atlantic Ocean. Fish predators were caught by recreational anglers in offshore waters of New Englan