Modelling of dust generation, transport and remobilization in full-metal fusion reactors

The design, licensing and operation of magnetic confinement fusion reactors impose various limitations on the amount of metallic dust particles residing inside the plasma chamber. In this context, predictive studies of dust production and migration constitute one of the main sources of relevant data. These are mainly conducted using dust transport codes, which rely on coupled dust-plasma and dust-wall interaction models, and require external input on the dust and droplet initial conditions. Some particularities of dust modelling in reactor-relevant conditions are analyzed with an emphasis on dust generation mechanisms relevant for disruption scenarios and on dust remobilization mechanisms relevant for ramp-up scenarios. Emerging topics such as dust production by runaway electron impact and pre-plasma remobilization of magnetic dust are also discussed.

Luminescence Sensitivity of Rhine Valley Loess: Indicators of Source Variability?

Loess provides a valuable terrestrial record of past environmental conditions, including the dynamics and trajectories of air mass circulation responsible for dust transport. Here we explore variations in the luminescence sensitivity characteristics of sedimentary quartz and feldspar as possible tools for identifying changes in source down a loess-palaeosol sequence (LPS). Luminescence sensitivity is a rapidly measurable index which is the product of interplay between source lithology and the history of the quartz or feldspar clasts. Variations in sensitivity of down profile may therefore reflect changes in sediment provenance as well as other factors such as weathering through pedogenesis. We undertake an empirical investigation of the luminescence sensitivity of quartz and feldspar from different grain-size fractions from the Schwalbenberg LPS in the German Rhine valley. We compare samples from a 30 m core spanning the last full glacial cycle with samples of oxygen isotope stage (OIS) 3–2 age exposed within nearby profile. We find an overall inverse relationship between quartz and feldspar sensitivity, as well as variability in sensitivity between different quartz grain sizes. Statistical analyses yield a significant correlation between IR50 sensitivity from unprocessed sediments and clay content, and feldspar sensitivity and Si/Al ratios down the core. Since Si/Al ratios may indicate changes in provenance, the latter correlation suggests that IR50 measurements on unprocessed samples may be used to provide a reliable, rapid scan of source variability over millennial timescales.

Variations in Concentrations and Ratio of Soluble Forms of Nutrients in Atmospheric Depositions and Effects for Marine Coastal Areas of Crimea, Black Sea

Atmospheric depositions have been recently recognized as an important source of nutrients for off-shore marine systems, in line with the coastal input and physical exchange. The input of nutrients with atmospheric depositions can change their inventory and ratio in the euphotic zone, thus increase the rate of primary production and the type of predominant phytoplankton. The influence of atmospheric depositions, temporal variations of this influence and consequences of this deposition have been neglected. Monitoring of nutrients in atmospheric depositions of Crimea in 2015–2020 has allowed studying of multi-scale variations in their input to coastal areas and scaling the effects of this input. It has been found that the contribution of dry deposition in the total flux of nutrients is more significant for silicates and phosphates. Intra-annual variations in concentrations of nitrogen reveal a maximum in an urbanized area for the cold period of year, due to burning of extra fuel. On the contrary, increasing concentrations of nitrogen have been detected in a rural area in warm period. High values of concentrations of phosphorus and silica are typical for dry summer period and associated with dust transport from natural and anthropogenic sources. The N:P:Si ratio in the atmospheric depositions has been significantly shifted towards nitrogen as compared to the stoichiometric ratio. The results obtained in this work suggest that additional flux of nutrients with atmospheric depositions is minor at the annual scale, but it may change the local inventory and C:N:P ratio in the surface layer of the sea on a daily-time scale. The input of nutrients with atmospheric depositions can lead to additional (up to twofold) production of organic matter and result in additional oxygen consumption, when this surplus organic matter sinks and is oxidized, thus supporting suboxic conditions in near-shore areas.

Passive versus Active Transport of Saharan Dust Aerosols by African Easterly Waves

Theory and modeling are combined to reveal the physical and dynamical processes that control Saharan dust transport by amplifying African easterly waves (AEWs). Two cases are examined: active transport, in which the dust is radiatively coupled to the circulation; passive transport, in which the dust is radiatively decoupled from the circulation. The theory is built around a dust conservation equation for dust-coupled AEWs in zonal-mean African easterly jets. The theory predicts that, for both the passive and active cases, the dust transports will be largest where the zonal-mean dust gradients are maximized on an AEW critical surface. Whether the dust transports are largest for the radiatively passive or radiatively active case depends on the growth rate of the AEWs, which is modulated by the dust heating. The theoretical predictions are confirmed via experiments carried out with the Weather Research and Forecasting model, which is coupled to a dust conservation equation. The experiments show that the meridional dust transports dominate in the passive case, while the vertical dust transports dominate in the active case.

Antarctic and Southern Ocean dust transport pathways: Forward-trajectory modeling and rare earth element source constraints from the RICE ice core

<p>Mineral dust fertilization of Southern Ocean surface waters, and mixing with Antarctic deep-water, influences oceanic uptake of carbon dioxide and draws down global atmospheric concentrations during glacial periods. Quantifying modern variability in dust source and transport strength, especially with respect to high- and low-latitude climate phenomena (e.g. the Southern Annular Mode, El Niño Southern Oscillation), will improve understanding of this important aspect of the global carbon cycle. Using high-order geochemical provenance techniques can also reveal in greater detail what aspects of dust transport are recorded in Antarctic ice core records, allowing for better interpretation of glacial-interglacial dust records at individual sites. First, using forward trajectories and climate reanalysis data, this work explores modern variability (1979-2013) in atmospheric transport of mineral dust from Southern Hemisphere potential source areas (PSA)—primarily Australia, southern South America and southern Africa. Estimates of the relative source and transport strength of New Zealand are also discussed, and compared with other dust PSA to evaluate New Zealand’s potential contribution to Southern Ocean and Antarctic dust deposition. Extra-Antarctic dust PSA distributions are detailed for individual ice core sites, including the newly recovered Roosevelt Island Climate Evolution (RICE) ice core (79.36ºS, 161.71ºW, 550 m a.s.l.). This approach—applicable to many types of aerosol—reveals persistent, strong transport from New Zealand and Patagonia to the southern high-latitudes during all seasons. It also demonstrates that southward transport of air masses from pan-Pacific dust sources is affected by circulation variability initiated in the central tropical Pacific Ocean. High-resolution discrete sampling of the RICE core allows for unprecedented analysis of trace elements at sub-annual to annual scales. The rare earth elements (REE, lanthanide elements Lanthanum to Lutetium) can preserve the signature of their original source material and thus provide provenance constraints for dust preserved in Antarctic snow and ice. While challenging, measurements of REE concentration to the single femtogram per gram (10-15 g g-1) level have been made by combining efficient sample introduction and a jet-interface sector-field inductively coupled plasma mass spectrometer. The methodology and fidelity of these measurements are presented, in addition to results for other low-concentration elements associated with natural and anthropogenic aerosols. REE data from the RICE ice core are then used to explore possible modern sources of dust in the Ross Sea sector of Antarctica, testing hypothesized trajectory model distributions. Twentieth-century and late-Holocene (2.3 ka – present) REE data from the RICE ice core represent the first measurements of this kind from the Pacific sector of Antarctica. RICE data are compared with Holocene REE data from the Drønning Maud Land and Dome C ice cores, with consideration of REE signatures in dust samples from PSA. Data from the RICE ice core indicate fewer than 5% contributions of dust from South America, and show strong negative trends in crustal-normalized REE signatures suggesting contributions from local Antarctic dust.</p>

Antarctic and Southern Ocean dust transport pathways: Forward-trajectory modeling and rare earth element source constraints from the RICE ice core

<p>Mineral dust fertilization of Southern Ocean surface waters, and mixing with Antarctic deep-water, influences oceanic uptake of carbon dioxide and draws down global atmospheric concentrations during glacial periods. Quantifying modern variability in dust source and transport strength, especially with respect to high- and low-latitude climate phenomena (e.g. the Southern Annular Mode, El Niño Southern Oscillation), will improve understanding of this important aspect of the global carbon cycle. Using high-order geochemical provenance techniques can also reveal in greater detail what aspects of dust transport are recorded in Antarctic ice core records, allowing for better interpretation of glacial-interglacial dust records at individual sites. First, using forward trajectories and climate reanalysis data, this work explores modern variability (1979-2013) in atmospheric transport of mineral dust from Southern Hemisphere potential source areas (PSA)—primarily Australia, southern South America and southern Africa. Estimates of the relative source and transport strength of New Zealand are also discussed, and compared with other dust PSA to evaluate New Zealand’s potential contribution to Southern Ocean and Antarctic dust deposition. Extra-Antarctic dust PSA distributions are detailed for individual ice core sites, including the newly recovered Roosevelt Island Climate Evolution (RICE) ice core (79.36ºS, 161.71ºW, 550 m a.s.l.). This approach—applicable to many types of aerosol—reveals persistent, strong transport from New Zealand and Patagonia to the southern high-latitudes during all seasons. It also demonstrates that southward transport of air masses from pan-Pacific dust sources is affected by circulation variability initiated in the central tropical Pacific Ocean. High-resolution discrete sampling of the RICE core allows for unprecedented analysis of trace elements at sub-annual to annual scales. The rare earth elements (REE, lanthanide elements Lanthanum to Lutetium) can preserve the signature of their original source material and thus provide provenance constraints for dust preserved in Antarctic snow and ice. While challenging, measurements of REE concentration to the single femtogram per gram (10-15 g g-1) level have been made by combining efficient sample introduction and a jet-interface sector-field inductively coupled plasma mass spectrometer. The methodology and fidelity of these measurements are presented, in addition to results for other low-concentration elements associated with natural and anthropogenic aerosols. REE data from the RICE ice core are then used to explore possible modern sources of dust in the Ross Sea sector of Antarctica, testing hypothesized trajectory model distributions. Twentieth-century and late-Holocene (2.3 ka – present) REE data from the RICE ice core represent the first measurements of this kind from the Pacific sector of Antarctica. RICE data are compared with Holocene REE data from the Drønning Maud Land and Dome C ice cores, with consideration of REE signatures in dust samples from PSA. Data from the RICE ice core indicate fewer than 5% contributions of dust from South America, and show strong negative trends in crustal-normalized REE signatures suggesting contributions from local Antarctic dust.</p>

Optical, Geochemical and Mineralogical Characteristics of Light-Absorbing Impurities Deposited on Djankuat Glacier in the Caucasus Mountains

Supra-glacial material, including light-absorbing impurities (LAI) such as mineral dust of crustal and soil origin, black carbon, algae and cryoconite, reduce the reflectance of snow and glacier ice. The reduction depends on the amount of LAI and their physical and chemical properties, which vary spatially and temporally. Spectral reflectance data and snow and ice samples, containing LAI, were collected in the ablation zone of the Djankuat Glacier, Central Caucasus, Russia. The spectra of the samples containing mineral dust transported from deserts were characterized by negative visible near-infrared gradients and were different from the spectra of clean aged snow and exposed glacier ice and from the samples containing mineral dust produced locally. Geochemical and mineralogical analysis using X-ray diffraction and X-ray fluorescence spectrometry showed that samples containing desert dust were characterised by a high proportion of clay materials and such minerals as smectites, illite–smectites and palygorskite and by a smaller size of mineral particles. They were enriched in chromium, zinc and vanadium. The latter served as an indicator of dust transport over or origin from the oil-producing regions of the Middle East. There was a strong negative correlation between the amount of organic matter and mineral dust in the collected samples and the albedo of surfaces from which the samples were collected. The results suggested that organic matter reduced albedo more efficiently than mineral dust. The study highlighted the importance of supra-glacial material in changing the surface reflectivity of snow and glaciers in the Caucasus region.