scholarly journals Numerical experiments on isotopic diffusion in polar snow and firn using a multi-layer energy balance model

2017 ◽  
Author(s):  
Alexandra Touzeau ◽  
Amaëlle Landais ◽  
Samuel Morin ◽  
Laurent Arnaud ◽  
Ghislain Picard
Keyword(s):  
Isotopic Composition ◽  
Solid Phase ◽  
Ice Cores ◽  
Balance Model ◽  
Snow Layer ◽  
Vapor Diffusion ◽  
Kinetic Fractionation ◽  
Polar Snow ◽  
Seasonal Signal ◽  
The Impact

Abstract. To evaluate the impact of vapor diffusion onto isotopic composition variations in the snow pits and then in ice cores, we introduced water isotopes in the detailed snowpack model Crocus. The isotopes routine is run with a 1 s resolution. At each step and for each snow layer, 1) the initial isotopic composition of vapor is taken at equilibrium with solid phase, 2) kinetic fractionation is applied during transport, and 3) condensation is realized. We study the different effects of temperature gradient, compaction, wind compaction and precipitation on the final vertical isotopic profiles. We also run complete simulations of vapor and isotopic diffusion at GRIP, Greenland and at Dome C, Antarctica over periods of 1 or 10 years. The vapor diffusion tends to smooth the original seasonal signal, with an attenuation of 9.5 % of the original signal over 10 years at GRIP. This is smaller than the observed attenuation in ice cores, indicating that the model underestimates attenuation due to diffusion or that other processes, such as ventilation, also contribute to the observed attenuation. At Dome C, the attenuation is stronger (14 %), probably because of the lower accumulation and stronger δ18O gradients. Because vapor diffusion is not the only process responsible of the signal attenuation, it would be useful to implement in the model ventilation of the snowpack and exchanges with the atmosphere to evaluate their contribution.

scholarly journals Numerical experiments on vapor diffusion in polar snow and firn and its impact on isotopes using the multi-layer energy balance model Crocus in SURFEX v8.0

2018 ◽  
Vol 11 (6) ◽  
pp. 2393-2418 ◽  
Author(s):  
Alexandra Touzeau ◽  
Amaëlle Landais ◽  
Samuel Morin ◽  
Laurent Arnaud ◽  
Ghislain Picard
Keyword(s):  
Isotopic Composition ◽  
Solid Phase ◽  
Ice Cores ◽  
Balance Model ◽  
Snow Layer ◽  
Vapor Diffusion ◽  
Kinetic Fractionation ◽  
Polar Snow ◽  
Seasonal Signal ◽  
The Impact

Abstract. To evaluate the impact of vapor diffusion on isotopic composition variations in snow pits and then in ice cores, we introduced water isotopes in the detailed snowpack model Crocus. At each step and for each snow layer, (1) the initial isotopic composition of vapor is taken at equilibrium with the solid phase, (2) a kinetic fractionation is applied during transport, and (3) vapor is condensed or snow is sublimated to compensate for deviation to vapor pressure at saturation. We study the different effects of temperature gradient, compaction, wind compaction, and precipitation on the final vertical isotopic profiles. We also run complete simulations of vapor diffusion along isotopic gradients and of vapor diffusion driven by temperature gradients at GRIP, Greenland and at Dome C, Antarctica over periods of 1 or 10 years. The vapor diffusion tends to smooth the original seasonal signal, with an attenuation of 7 to 12 % of the original signal over 10 years at GRIP. This is smaller than the observed attenuation in ice cores, indicating that the model attenuation due to diffusion is underestimated or that other processes, such as ventilation, influence attenuation. At Dome C, the attenuation is stronger (18 %), probably because of the lower accumulation and stronger δ18O gradients.

Validation of atmospheric reanalyses over the Weddell Sea, Antarctica, using observations from drifting buoys

2021 ◽  
Author(s):  
John King ◽  
Gareth Marshall ◽  
Steve Colwell ◽  
Clare Allen-Sader ◽  
Tony Phillips
Keyword(s):  
Sea Ice ◽  
Austral Summer ◽  
Longwave Radiation ◽  
Weddell Sea ◽  
Balance Model ◽  
Atmospheric Conditions ◽  
Snow Layer ◽  
Near Surface ◽  
The Impact ◽  
Drifting Buoys

<p> </p><p>Global atmospheric reanalyses are frequently used to drive ocean-ice models but few data are available to assess the quality of these products in the Antarctic sea ice zone. We utilise measurements from three drifting buoys that were deployed on sea ice in the southern Weddell Sea in the austral summer of 2016 to validate the representation of near-surface atmospheric conditions in the ERA-Interim and ERA5 reanalyses produced by the European Centre for Medium Range Weather Forecasts (ECMWF). The buoys carried sensors to measure atmospheric pressure, air temperature and humidity, wind speed and direction, and downwelling shortwave and longwave radiation. One buoy remained in coastal fast ice for most of 2016 while the other two drifted northward through the austral winter and exited the pack ice during the following austral summer. Comparison of buoy measurements with reanalysis data indicates that both reanalyses represent the surface pressure field in this region accurately. Reanalysis temperatures are, however, biased warm by around 2 °C in both products, with the largest biases seen at the lowest temperatures. We suggest that this bias is a result of the simplified representation of sea ice in the reanalyses, in particular the lack of an insulating snow layer on top of the ice. We use a simple surface energy balance model to investigate the impact of the reanalysis biases on sea ice thermodynamics.</p>

Water vapor isotopic signature along the EAIIST traverse (East Antarctica Plateau)

2021 ◽  
Author(s):  
Mathieu Casado ◽  
Christophe Leroy-Dos Santos ◽  
Elise Fourré ◽  
Vincent Favier ◽  
Cécile Agosta ◽  
...  
Keyword(s):  
Water Vapor ◽  
Isotopic Composition ◽  
Ice Cores ◽  
East Antarctica ◽  
Polar Regions ◽  
Surface Mass ◽  
Antarctic Plateau ◽  
Starting Point ◽  
Weather Stations ◽  
The Impact

<p>Stable water isotopes are effective hydrological tracers due to fractionation processes throughout the water cycle, and thus, the stable isotopes from ice cores can serve as valuable proxies for past changes in the climate and local environment of polar regions. Proper interpretation of these isotopes requires to understand the influence of each potential fractionating process, such as initial evaporation over the ocean and precipitation events, but also the effects of post-depositional exchange between snow and moisture in the atmosphere. Thanks to new developments in infrared spectroscopy, it is now possible to continuously monitor the isotopic composition of atmospheric water vapor in coordination with discrete snow sampling. This allows us to readily document the isotopic and mass exchanges between snow and vapor as well as the stability of the atmospheric boundary layer, as has recently been shown on the East Antarctic Plateau at Kohnen (Ritter et al., TC, 2016) and Dome C (Casado et al., ACP, 2016) stations where substantial diurnal isotopic variations have been recorded.</p><p>In this study, we present the first vapor monitoring of an East Antarctic transect that covered more than 3600 km over a period of 3 months from November 2019 to February 2020 as part of the EAIIST mission. The isotopic record therefore describes the evolution from typical coastal values to highly depleted values deep inside the continent on the high-altitude plateau. In parallel, we also monitored the vapor isotopic composition at two stations: the coastal starting point of Dumont D’Urville (DDU) and the plateau halfway point of Dome C. Two automatic weather stations (at Paleo and Megadunes sites) were also installed in a previously unexplored region of the East Antarctic plateau that was covered by this transect. This suite of cross-calibrated vapor isotope observations and weather stations, coupled with Modele Atmospherique Régional (MAR) climate modeling, offers a unique opportunity to compare the spatial and temporal gradients of humidity, temperature, and water vapor isotopic composition in East Antarctica during the summer season, and to estimate how the water vapour isotope measurements at Dome C and DDU are representative of the conditions in East Antarctica. The quantitative agreement between the EAIIST record and those recorded at DDU and Dome C stations at the times the raid was nearby, gives confidence in the quality of the results acquired on this traverse. Although further comparisons with the surface snow isotopic composition are required to quantify the impact of the snow-atmosphere exchanges on the local surface mass balance, these initial results of vapor isotopic composition show the potential of using water stables isotopes to evaluate hydrological processes in East Antarctica and better reconstruct past climate changes through ice cores.</p>

Seasonal variations in the properties and structural composition of sea ice and snow cover in the Bellingshausen and Amundsen Seas, Antarctica

1997 ◽  
Vol 43 (143) ◽  
pp. 138-151 ◽  
Author(s):  
M. O. Jeffries ◽  
K. Morris ◽  
W.F. Weeks ◽  
A. P. Worby
Keyword(s):  
Sea Ice ◽  
Isotopic Composition ◽  
Snow Cover ◽  
Sea Water ◽  
Ice Cores ◽  
Ice Cover ◽  
Snow Accumulation ◽  
Ice Formation ◽  
Frazil Ice ◽  
Core Sets

AbstractSixty-three ice cores were collected in the Bellingshausen and Amundsen Seas in August and September 1993 during a cruise of the R.V. Nathaniel B. Palmer. The structure and stable-isotopic composition (18O/16O) of the cores were investigated in order to understand the growth conditions and to identify the key growth processes, particularly the contribution of snow to sea-ice formation. The structure and isotopic composition of a set of 12 cores that was collected for the same purpose in the Bellingshausen Sea in March 1992 are reassessed. Frazil ice and congelation ice contribute 44% and 26%, respectively, to the composition of both the winter and summer ice-core sets, evidence that the relatively calm conditions that favour congelation-ice formation are neither as common nor as prolonged as the more turbulent conditions that favour frazil-ice growth and pancake-ice formation. Both frazil- and congelation-ice layers have an av erage thickness of 0.12 m in winter, evidence that congelation ice and pancake ice thicken primarily by dynamic processes. The thermodynamic development of the ice cover relies heavily on the formation of snow ice at the surface of floes after sea water has flooded the snow cover. Snow-ice layers have a mean thickness of 0.20 and 0.28 m in the winter and summer cores, respectively, and the contribution of snow ice to the winter (24%) and summer (16%) core sets exceeds most quantities that have been reported previously in other Antarctic pack-ice zones. The thickness and quantity of snow ice may be due to a combination of high snow-accumulation rates and snow loads, environmental conditions that favour a warm ice cover in which brine convection between the bottom and top of the ice introduces sea water to the snow/ice interface, and bottom melting losses being compensated by snow-ice formation. Layers of superimposed ice at the top of each of the summer cores make up 4.6% of the ice that was examined and they increase by a factor of 3 the quantity of snow entrained in the ice. The accumulation of superimposed ice is evidence that melting in the snow cover on Antarctic sea-ice floes ran reach an advanced stage and contribute a significant amount of snow to the total ice mass.

Development of Strategies for Glycopeptide Synthesis: An Overview on the Glycosidic Linkage

2020 ◽  
Vol 24 (21) ◽  
pp. 2475-2497
Author(s):  
Andrea Verónica Rodríguez-Mayor ◽  
German Jesid Peralta-Camacho ◽  
Karen Johanna Cárdenas-Martínez ◽  
Javier Eduardo García-Castañeda
Keyword(s):  
Chemical Synthesis ◽  
Solid Phase ◽  
Building Blocks ◽  
Heterogeneous Environments ◽  
Phase Synthesis ◽  
Low Concentrations ◽  
Biological Sources ◽  
Synthetic Routes ◽  
The Impact ◽  
Potential Use

Glycoproteins and glycopeptides are an interesting focus of research, because of their potential use as therapeutic agents, since they are related to carbohydrate-carbohydrate, carbohydrate-protein, and carbohydrate-lipid interactions, which are commonly involved in biological processes. It has been established that natural glycoconjugates could be an important source of templates for the design and development of molecules with therapeutic applications. However, isolating large quantities of glycoconjugates from biological sources with the required purity is extremely complex, because these molecules are found in heterogeneous environments and in very low concentrations. As an alternative to solving this problem, the chemical synthesis of glycoconjugates has been developed. In this context, several methods for the synthesis of glycopeptides in solution and/or solid-phase have been reported. In most of these methods, glycosylated amino acid derivatives are used as building blocks for both solution and solid-phase synthesis. The synthetic viability of glycoconjugates is a critical parameter for allowing their use as drugs to mitigate the impact of microbial resistance and/or cancer. However, the chemical synthesis of glycoconjugates is a challenge, because these molecules possess multiple reaction sites and have a very specific stereochemistry. Therefore, it is necessary to design and implement synthetic routes, which may involve various protection schemes but can be stereoselective, environmentally friendly, and high-yielding. This review focuses on glycopeptide synthesis by recapitulating the progress made over the last 15 years.

Introduction to geomicrobiology

2018 ◽  
Author(s):  
David L. Kirchman
Keyword(s):  
Fossil Fuels ◽  
Solid Phase ◽  
Direct Reduction ◽  
Iron Oxidation ◽  
Mineral Dissolution ◽  
Precipitation Process ◽  
Soluble Ions ◽  
Chemolithoautotrophic Bacteria ◽  
The Impact

Geomicrobiology, the marriage of geology and microbiology, is about the impact of microbes on Earth materials in terrestrial systems and sediments. Many geomicrobiological processes occur over long timescales. Even the slow growth and low activity of microbes, however, have big effects when added up over millennia. After reviewing the basics of bacteria–surface interactions, the chapter moves on to discussing biomineralization, which is the microbially mediated formation of solid minerals from soluble ions. The role of microbes can vary from merely providing passive surfaces for mineral formation, to active control of the entire precipitation process. The formation of carbonate-containing minerals by coccolithophorids and other marine organisms is especially important because of the role of these minerals in the carbon cycle. Iron minerals can be formed by chemolithoautotrophic bacteria, which gain a small amount of energy from iron oxidation. Similarly, manganese-rich minerals are formed during manganese oxidation, although how this reaction benefits microbes is unclear. These minerals and others give geologists and geomicrobiologists clues about early life on Earth. In addition to forming minerals, microbes help to dissolve them, a process called weathering. Microbes contribute to weathering and mineral dissolution through several mechanisms: production of protons (acidity) or hydroxides that dissolve minerals; production of ligands that chelate metals in minerals thereby breaking up the solid phase; and direct reduction of mineral-bound metals to more soluble forms. The chapter ends with some comments about the role of microbes in degrading oil and other fossil fuels.

A solid-phase extraction method that eliminates matrix effects of complex pulp mill effluents for the analysis of lipophilic wood extractives

2020 ◽  
Vol 35 (4) ◽  
pp. 577-588
Author(s):  
Sebastian España Orozco ◽  
Philipp Zeitlinger ◽  
Karin Fackler ◽  
Robert H. Bischof ◽  
Antje Potthast
Keyword(s):  
Solid Phase Extraction ◽  
Matrix Effects ◽  
Solid Phase ◽  
Internal Standard ◽  
Pulp Mill ◽  
Phase Extraction ◽  
Wood Extractives ◽  
Wood Extractive ◽  
Pulp Mill Effluents ◽  
The Impact

AbstractThe extraction of lipophilic wood extractives from pulp and paper process waters proves to be a challenging task, due to harsh and alternating process and sample conditions. This study has determined the potential use of polymeric sorbents for solid-phase extraction (SPE) and compared to classical silica-based reversed-phase packed columns, with polymeric hydrophilic-lipophilic balanced (HLB) cartridges being the sorbent with the most potential. Recovery functions were obtained with an internal standard mixture representative for the main lipophilic wood extractive groups, which are fatty acids and alcohols, sterols, sterol esters and triglycerides. The impact of pH, sample volume and sample matrix, expressed as TOC and cations, on the retention behavior of lipophilic extractives during SPE of industrial samples were determined with polymeric HLB sorbent. High variations in the composition of pulp mill matrices led to different optimal extraction conditions. Thus, a new SPE protocol was developed, which bypasses matrix interferences and omits the loss of analytes due to sample preparation. The method is applicable to different pulp mill effluents with large discrepancies in pH and sample matrices, resulting in recoveries >90 % with RSD <5 % for all lipophilic wood extractives.

scholarly journals Solid-Phase Extraction Embedded Dialysis (SPEED), an Innovative Procedure for the Investigation of Microbial Specialized Metabolites

Marine Drugs ◽  
2021 ◽  
Vol 19 (7) ◽  
pp. 371
Author(s):  
Phuong-Y Mai ◽  
Géraldine Le Goff ◽  
Erwan Poupon ◽  
Philippe Lopes ◽  
Xavier Moppert ◽  
...  
Keyword(s):  
Solid Phase Extraction ◽  
Solid Phase ◽  
Chemical Space ◽  
Molecular Profile ◽  
Phase Extraction ◽  
Specialized Metabolites ◽  
Streptomyces Albidoflavus ◽  
Cultivation Process ◽  
The Impact

Solid-phase extraction embedded dialysis (SPEED technology) is an innovative procedure developed to physically separate in-situ, during the cultivation, the mycelium of filament forming microorganisms, such as actinomycetes and fungi, and the XAD-16 resin used to trap the secreted specialized metabolites. SPEED consists of an external nylon cloth and an internal dialysis tube containing the XAD resin. The dialysis barrier selects the molecular weight of the trapped compounds, and prevents the aggregation of biomass or macromolecules on the XAD beads. The external nylon promotes the formation of a microbial biofilm, making SPEED a biofilm supported cultivation process. SPEED technology was applied to the marine Streptomyces albidoflavus 19-S21, isolated from a core of a submerged Kopara sampled at 20 m from the border of a saltwater pond. The chemical space of this strain was investigated effectively using a dereplication strategy based on molecular networking and in-depth chemical analysis. The results highlight the impact of culture support on the molecular profile of Streptomyces albidoflavus 19-S21 secondary metabolites.

scholarly journals A Study of the Impact of Graphite on the Kinetics of SPS in Nano- and Submicron WC-10%Co Powder Compositions

Ceramics ◽  
2021 ◽  
Vol 4 (2) ◽  
pp. 331-363
Author(s):  
Eugeniy Lantcev ◽  
Aleksey Nokhrin ◽  
Nataliya Malekhonova ◽  
Maksim Boldin ◽  
Vladimir Chuvil'deev ◽  
...  
Keyword(s):  
Activation Energy ◽  
Solid Phase ◽  
Continuous Heating ◽  
Diffusion Creep ◽  
Hard Alloys ◽  
Fine Grained ◽  
Plasma Sintering ◽  
Spark Plasma ◽  
The Impact ◽  
Kinetics Of

This study investigates the impact of carbon on the kinetics of the spark plasma sintering (SPS) of nano- and submicron powders WC-10wt.%Co. Carbon, in the form of graphite, was introduced into powders by mixing. The activation energy of solid-phase sintering was determined for the conditions of isothermal and continuous heating. It has been demonstrated that increasing the carbon content leads to a decrease in the fraction of η-phase particles and a shift of the shrinkage curve towards lower heating temperatures. It has been established that increasing the graphite content in nano- and submicron powders has no significant effect on the SPS activation energy for “mid-range” heating temperatures, QS(I). The value of QS(I) is close to the activation energy of grain-boundary diffusion in cobalt. It has been demonstrated that increasing the content of graphite leads to a significant decrease in the SPS activation energy, QS(II), for “higher-range” heating temperatures due to lower concentration of tungsten atoms in cobalt-based γ-phase. It has been established that the sintering kinetics of fine-grained WC-Co hard alloys is limited by the intensity of diffusion creep of cobalt (Coble creep).

scholarly journals Effect of snow microstructure variability on Ku-band radar snow water equivalent retrievals

2019 ◽  
Vol 13 (11) ◽  
pp. 3045-3059 ◽  
Author(s):  
Nick Rutter ◽  
Melody J. Sandells ◽  
Chris Derksen ◽  
Joshua King ◽  
Peter Toose ◽  
...  
Keyword(s):  
Spatial Variability ◽  
Layer Thickness ◽  
Snow Water Equivalent ◽  
Estimation Accuracy ◽  
Snow Layer ◽  
Data Set ◽  
Snow Water ◽  
Retrieval Errors ◽  
Snow Microstructure ◽  
The Impact

Abstract. Spatial variability in snowpack properties negatively impacts our capacity to make direct measurements of snow water equivalent (SWE) using satellites. A comprehensive data set of snow microstructure (94 profiles at 36 sites) and snow layer thickness (9000 vertical profiles across nine trenches) collected over two winters at Trail Valley Creek, NWT, Canada, was applied in synthetic radiative transfer experiments. This allowed for robust assessment of the impact of estimation accuracy of unknown snow microstructural characteristics on the viability of SWE retrievals. Depth hoar layer thickness varied over the shortest horizontal distances, controlled by subnivean vegetation and topography, while variability in total snowpack thickness approximated that of wind slab layers. Mean horizontal correlation lengths of layer thickness were less than a metre for all layers. Depth hoar was consistently ∼30 % of total depth, and with increasing total depth the proportion of wind slab increased at the expense of the decreasing surface snow layer. Distinct differences were evident between distributions of layer properties; a single median value represented density and specific surface area (SSA) of each layer well. Spatial variability in microstructure of depth hoar layers dominated SWE retrieval errors. A depth hoar SSA estimate of around 7 % under the median value was needed to accurately retrieve SWE. In shallow snowpacks <0.6 m, depth hoar SSA estimates of ±5 %–10 % around the optimal retrieval SSA allowed SWE retrievals within a tolerance of ±30 mm. Where snowpacks were deeper than ∼30 cm, accurate values of representative SSA for depth hoar became critical as retrieval errors were exceeded if the median depth hoar SSA was applied.

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