Deposition Events Research Articles

Uneven response of microbial communities to intense dust deposition across the coastal transition zone off Mauritania

The eastern North Atlantic region receives large Saharan dust deposition inputs, providing nutrients and trace metals to the surface waters. We assessed the effects of intense dust deposition on phytoplankton and bacteria cell abundances, metabolic activity, and community structure, along a surface productivity gradient in the Mauritanian-Senegalese upwelling system. Dust concentrations above 4 mg L-1 were added to triplicate microcosms in four bioassay experiments, each lasting three days, increasing nitrate, phosphate and, to a lesser extent, silicate seawater concentrations. Even though dust deposition enhanced both heterotrophic and photosynthetic activity, bacterial production responded faster and stronger than primary production, especially as oligotrophic conditions increased. Bacterial production rates in oligotrophic waters almost tripled one day after the enrichment. However, such favorable response could not be observed on the total organic carbon production until a lag phase of 2 days and whilst under moderate eutrophic conditions. Dust enrichment benefited the presence of certain planktonic groups over others according to their nutrient requirements. Indicator species analysis revealed that our dust-treated microcosms were consistently characterized by Raphid-pennate diatoms, as well as by Hyphomonas genus of Alphaproteobacteria and several species of Alteromonas Gammaproteobacteria. Yet, changes in microbial community structure and composition were primarily shaped by the starting conditions of each experiment. These findings indicate that increasing dust deposition events and the weakening of the Mauritanian-Senegalese upwelling system under climate change may result in a more heterotrophic system, particularly in oligotrophic waters, reducing its potential to function as an atmospheric carbon sink.

Quantifying sediment and particulate phosphorus accumulation in restored floodplain wetlands using beryllium‐7 as a tracer

AbstractFloodplain wetlands in agricultural river basins provide critical ecosystem services such as nutrient retention, flood mitigation, carbon sequestration and ecological habitats and are a key component of a nature‐based solution approach to restoration. In the context of the global challenge to reducing impact increasingly intensive food production on downstream ecosystems, restoration of wetlands in river floodplains offers a practical means for downstream retention and mitigation of P flux from upstream agricultural land. Data on short term, flood event related, accretion rates are, however, difficult to acquire via conventional monitoring yet such information is essential for restoration planning and scenario testing. Here, we evaluate a promising approach that applies naturally‐occurring short‐lived fallout radionuclide (FRN) 7Be as a tracer to quantify sediment and, by association, particulate phosphorus retention rates in restored floodplain wetlands. Following a series of major inundation events, a restored floodplain unit was sampled to determine 7Be inventories of the floodplain relative to an undisturbed reference site. This was undertaken in conjunction with direct measurement of sedimentation as an independent check of FRN results. Accretion rates up to 27 kg m−2 were recorded using 7Be for recent deposition events compared to a longer term annual average rate of ca. 6 kg m−2 derived from 137Cs measurements. While accretion rates varied spatially and temporally, there was excellent coherence between FRN‐based measurements and direct measurements once rigorous correction for particle size effects on tracer properties had been undertaken. The study demonstrates the important contribution that FRN technology can make to support wetland management and restoration initiatives and the essential need for a systems thinking approach across the soil‐sediment continuum. Such decision support tools will become increasingly important in the 21st century with growing anthropogenic pressure on aquatic ecosystems related to upstream food production, and implementation of more nature‐based solutions such as restored wetlands to counteract these pressures.

Evolution of sediment grain-size profiles on a sheltered, continental shelf in response to punctuated flood deposition

The evolution and preservation of flood deposits on continental shelves offshore river mouths is influenced by the dynamic relationship between punctuated discharge events and post-deposition processes. These short-term dynamic changes at the seafloor that ultimately shape the sedimentary record are difficult to monitor and not well understood. The aim of this study was to examine how punctuated deposition of flood sediments from a coastal river on the continental shelf, biological mixing and winnowing interplay in shaping grain size profiles and their transient evolution, and the preservation of flood layers in the sedimentary record. For this end an observations-based model was devised for the northern shelf of the sheltered, hyper-arid Gulf of Aqaba-Eilat, where infrequent floods from ephemeral rivers occur ∼ yr−1 and there is low physical perturbation by currents and waves in between, conditions that facilitate the examination of grain size profiles' evolution in time. The model shows that in between floods mixing and winnowing shape grain size profiles in the seafloor, causing the sediment to coarsen from the top down and shape a subsurface peak of the fine flood-sediments. Over longer time periods, without additional floods, mixing and winnowing gradually erase the peak of fines, coarsening the entire mixed layer thus nulling the flood layers' chances of preservation. This important role of winnowing near the sediment surface is missing in previous studies. Concurrently, our modelling suggests that long-term positive sedimentation, usually estimated on the years' time-scale, is comprised of a series of short-term, steep sediment deposition events brought by the punctuated floods (lasting hours to days) and followed by a gradual (months to years' time-scale) winnowing of finer sediments (erosion). These high-resolution dynamics that were captured by the model and included short-term flood depositions and their reoccurrence, could not be deduced from the long-term sedimentary records.

Multi-scale, multi-style soft-sediment deformation structures preserved in Cenozoic fluvial deposits, southeastern Brazil: Evidence of impact shaking?

Soft-sediment deformation (SSD) structures preserved in sedimentary successions can record significant seismic events which occurred during or right after deposition. The integrated analysis of sedimentary facies, depositional architecture, and SSD data can determine the relative temporal relationship between deposition and deformational events, and reveal the origin and mechanisms involved in the deformation and the resulting structures. The São Paulo Formation in southeastern Brazil preserves Cenozoic alluvial deposits which characterize most of the geology of the homonymous metropolis area. This succession preserves fluvial channel and floodplain deposits, with associated debris-flow dominated alluvial fan deposits, and preserves abundant SSD structures in a wide range of dimensions and morphologies. These deformation structures include small- and large-scale folds, multi-scale vents of varied geometries, ball-and-pillow structures, and clastic dykes. Here we provide an integrated analysis of sedimentary facies, depositional architecture data, and SSD data from the São Paulo Formation, in order to discuss the deformation mechanisms and plausible triggering mechanisms responsible for the development of such structures. Our interpretation is that SSD structures in the São Paulo Formation were likely triggered by a Cenozoic meteor impact recorded by a crater near the study area.

Multiple particle identification by sequential frequency-shift measurement of a micro-plate

• A resonant cantilevered micro-plate is proved to be a promising candidate that can sequentially detect multiple particles. • The identification of multiple particles is regarded as an optimization problem via genetic algorithm to replace the widely-used least squares method. • Better identification accuracy is illustrated by exquisitely updating the modal shape changes of a micro-plate after each particle adsorption. • An experimental strategy based on focused ion beam and scanning probe microscopy verifies the applicability of the theoretic framework in designing and evaluating micro/nano sensors. The detection of multiple particles has been mainly studied by examining the flexural vibration properties of a one-dimensional Euler-Bernoulli beam under the assumption that the vibration mode shapes are unchanged. In fact, with the torsional vibration of the detector, valuable pieces of information can be derived, while the detection process is facilitated. Besides, the mode shapes of the detector can be easily changed by measuring multiple adsorbates or heavy analytes, which can fundamentally affect the detecting accuracy. To the best of our knowledge, these two issues have not yet been systematically considered in the literature. Along these lines, in this work, a theoretical framework is introduced to detect both the masses and positions of multiple particles absorbed on a two-dimensional micro-plate, where the history of the mass deposition events is sequentially measured from the recorded frequency shifts. The detection of multiple particles was realized by using an optimization process via the genetic algorithm, which circumvents the initial value and the local optimum problems that the widely-used least-squares method could be confronted with. In addition, an improved detection accuracy was ensured by exquisitely updating the modal shape changes of a micro-plate after the adsorption of each particle. To validate the proposed method, the frequency shifts were obtained by running modal analysis, where 20 μ concentrated masses were added sequentially on the top surface of the micro-plate modelling. As was expected, all particles could be effectively identified with enhanced accuracy. Furthermore, experimental validation was performed on Si-based micro-plates cantilevered, which were fabricated by focused ion beam milling and sequentially loaded by carrying out Pt depositions from the measured frequency shifts of the micro-plate structure before and after each sequential Pt deposition, the loaded masses and their positions in both the length and width directions were extracted. The results obtained from the model are in good agreement with the estimation based on scanning electron microscopy. The proposed method is anticipated to be further applied to multiple particle detection applications in many fields including biology, medicine and chemistry.

Updated trends for atmospheric mercury in the Arctic: 1995-2018.

The Arctic region forms a unique environment with specific physical, chemical, and biological processes affecting mercury (Hg) cycles and limited anthropogenic Hg sources. However, historic global emissions and long range atmospheric transport has led to elevated Hg in Arctic wildlife and waterways. Continuous atmospheric Hg measurements, spanning 20 years, and increased monitoring sites has allowed a more comprehensive understanding of how Arctic atmospheric mercury is changing over time. Time-series trend analysis of TGM (Total Gaseous Mercury) in air was performed from 10 circumpolar air monitoring stations, comprising of high-Arctic, and sub-Arctic sites. GOM (gaseous oxidised mercury) and PHg (particulate bound mercury) measurements were also available at 2 high-Arctic sites. Seasonal mean TGM for sub-Arctic sites were lowest during fall ranging from 1.1 ng m-3 Hyytiälä to 1.3 ng m-3, Little Fox Lake. Mean TGM concentrations at high-Arctic sites showed the greatest variability, with highest daily means in spring ranging between 4.2 ng m-3 at Amderma and 2.4 ng m-3 at Zeppelin, largely driven by local chemistry. Annual TGM trend analysis was negative for 8 of the 10 sites. High-Arctic seasonal TGM trends saw smallest decline during summer. Fall trends ranged from -0.8% to -2.6% yr-1. Across the sub-Arctic sites spring showed the largest significant decreases, ranging between -7.7% to -0.36% yr-1, while fall generally had no significant trends. High-Arctic speciation of GOM and PHg at Alert and Zeppelin showed that the timing and composition of atmospheric mercury deposition events are shifting. Alert GOM trends are increasing throughout the year, while PHg trends decreased or not significant. Zeppelin saw the opposite, moving towards increasing PHg and decreasing GOM. Atmospheric mercury trends over the last 20 years indicate that Hg concentrations are decreasing across the Arctic, though not uniformly. This is potentially driven by environmental change, such as plant productivity and sea ice dynamics.

Terrestrial and marine organic matter evidence from a Cretaceous deep-sea chert of Japan: Implications for enhanced hydrological cycle during the Aptian OAE 1a

The early Aptian Oceanic Anoxic Event (OAE 1a; ca. 120 Ma) was accompanied by a massive eruption of the Ontong Java Plateau, doubling atmospheric pCO₂, and increasing sea surface temperature by 4–8 °C. In this study, we attempted a palynological analysis of the Hauterivian to Cenomanian deep–sea chert from the Goshikinohama site, and successfully obtained a variety of microremains, mainly represented by amorphous organic matter, aggregations of organic and inorganic particles, and cuticle fragments. One Hauterivian and many Aptian samples unexpectedly yielded terrestrial plant material, such as resins and wood fragments with tracheids, which represent the first record of terrestrial plant microremains from deep-sea pelagic chert. The occurrence of wood fragments within the negative and positive δ13C excursions during the OAE 1a can be correlated with an interval of increased atmospheric CO₂ level. We can also suggest that the occurrence of resins, mainly within the mudstone-rich chert intervals of the early Aptian negative δ13C peak and the middle-upper Aptian interval, are possibly related with periods with sea-level drops. Similar massive resin deposition events have been linked with intensified hydrological cycling during other abrupt climatic disruptions, such as the Carnian Pluvial Event, the Triassic−Jurassic boundary, and the Paleocene−Eocene Thermal Maximum. Therefore, an increase of terrestrial plant burial in deep–sea chert is likely linked with a massive plant discharge related with enhanced hydrological cycles, such as intensified storms and/or some sea–level change during the OAE 1a.

Producing Processes of the Trace Fossil Asteriacites lumbricalis Revisited: Different Ophiuroid Behaviors Produce Different Trace Forms

The star-shaped trace fossil Asteriacites lumbricalis is produced by ophiuroids and has two different forms. One form has four distinct arms with transverse fine and parallel striations and one indistinct arm without striations, and the producing process has been studied already. In this study, we clarified the producing process of another form with five distinct radiating arms and fine striations by aquarium observations of extant ophiuroids. The form was produced when ophiuroids were covered with a thin sand layer (11–39% of the arm length in thickness). After covered by thin sand, ophiuroids raised their five arms with one to five tips protruded vertically above the sand cover, raised and slanted the disc in the sand, and then obliquely emerged onto the sand cover. Finally, they returned to horizontal postures creeping on the sand. The trace left on the substratum was very similar in shape to the trace fossil from Hettangian (Lower Jurassic) in Blumenrod, Germany. The producing process of the repetitive multiple traces of A. lumbricalis was revealed by aquarium observations. When an ophiuroid was alternately covered with a thin sand layer and then with a thin abrasive layer as mud substratum, the ophiuroid left a vertically stacked series of traces which gradually shifted the horizontal position. This unique form of A. lumbricalis was produced by escaping of ophiuroids from successive deposition events.

A double-strand-break model for the relative biological effectiveness of electrons based on ionization clustering.

The effectiveness of ionizing radiation regarding DNA damage induction depends on its spatial energy deposition pattern. For electrons an increased effectiveness is observed at low kinetic energies due to the enhanced density of energy deposition events at electron track ends. A model is presented, which enables the calculation of the double-strand-break (DSB) yield and the relative biological effectiveness (RBE) for DSB induction of electrons. The model applies the mean free path between two ionizations and the assumption that two ionizations within a certain threshold distance are necessary to potentially lead to a DSB. Next to an expression for the electron RBE according to its common definition, a local RBE is determined, which describes the electrons' local effectiveness at a defined point on their track. This local RBE allows a better understanding of microscopic processes resulting from radiation and can be used, for instance, to describe the mean effectiveness of the mixed electron radiation field as a function of the radial distance to the center of an ion track. The presented model reflects the experimentally observed increased effectiveness of low-energetic electrons. It will be used in a future work to improve RBE predictions for ions performed with the local effect model.

Cambrian/Ordovician boundary as a milestone in the sedimentation history of the southern Siberian craton: Evidence from U-Pb dating of detrital zircons

The paper presents petrographic, geochemical, and new U-Pb zircon (LA-ICP-MS) geochronological data on the Upper Lena Fm. sediments which make part of the Cambrian sedimentary cover of the Siberian craton. The composition of lithic fragments in these clastic sediments, including mafic and felsic volcanics and granitoids, along with the correlation of major element ratios and the values of trace-element ratios point to predominant igneous (mainly felsic) rocks in the provenance. The U-Pb ages of detrital zircons from the sampled Upper Lena Fm. sandstones are mostly Early Paleozoic (∼500 Ma), with very few Archean-Paleoproterozoic determinations and quite many Neoproterozoic zircons. Ediacaran and Earliest Cambrian clastic sediments bearing Early Precambrian and Neoproterozoic detrital zircons, as well as Neoproterozoic and Early Paleozoic complexes of the Central Asian Orogenic Belt, could provide material for the Upper Lena clastic deposition. The geochronological evidence shows that the Upper Lena Fm. sandstones were deposited over vast territories of the southern Siberian craton in the Late Cambrian, in a single sedimentary basin, and originated from the same provenance. The Upper Lena deposition event in the Late Cambrian, immediately before the Ordovician period, makes a key milestone in the geological history of Siberia: the end of a large-scale Early Cambrian transgression and the beginning of gradual uplift of the southern craton margin, at least till the Carboniferous, which was associated with the formation of the Central Asian Orogenic Belt, a major tectonic unit of Asia.

Development of modified microdosimetric kinetic model for relative biological effectiveness in proton therapy.

To predict the biological effects of ionising radiation, the quantity of biological dose is introduced instead of the physical absorbed dose. In proton therapy, a constant relative biological effectiveness (RBE) of 1.1 is usually applied clinically as recommended by the International Commission of Radiation Units and Measurements. This study presents a new model, based on the modified microdosimetric kinetic model (MMKM), for calculating variable RBE values based on experimental data on the induction of DNA double-strand breaks (DSBs) within cells. The MMKM was proposed based on experimental data for the yield of DSBs in mammalian cells, which allows modification of the yield of primary lesions in the MKM. In this approach, a unique function named f(LET), which describes the relation between RBE and linear energy transfer (LET), was considered for charged particles. In the presented model (DMMKM), the MMKM approach was developed further by considering different f(LET)s for different relevant ions involved in energy deposition events in proton therapy. Although experimental data represent the dependence of the yield of primary lesions on the ion species, the DSB yield (assumed as the main primary lesion) is assumed independent of the ion species in the MMKM. In the DMMKM, by considering the yield of primary lesions as a function of the ion species, the α and β values are in better agreement with the experimental data as compared to those of the MKM and MMKM approaches. The biological dose in the DMMKM is predicted to be lower than that in the MMKM. Further, in the proposed model, the variation of the β parameter is higher than the constant value assumed in the MKM, at the distal end of the spread-out Bragg peak (SOBP). Moreover, the level of cell death estimated by the MMKM at the SOBP region is higher than that obtained based on the DMMKM. It is concluded that considering modified f(LET)s in the model developed here is more consistent with experimental results than when MMKM and MKM approaches are considered. The DMMKM examines the biological effects with full detail and will, therefore, be effective in improving proton therapy.

Monitoring of Anthropogenic Sediment Plumes in the Clarion-Clipperton Zone, NE Equatorial Pacific Ocean

The abyssal seafloor in the Clarion-Clipperton Zone (CCZ) in the NE Pacific hosts the largest abundance of polymetallic nodules in the deep sea and is being targeted as an area for potential deep-sea mining. During nodule mining, seafloor sediment will be brought into suspension by mining equipment, resulting in the formation of sediment plumes, which will affect benthic and pelagic life not naturally adapted to any major sediment transport and deposition events. To improve our understanding of sediment plume dispersion and to support the development of plume dispersion models in this specific deep-sea area, we conducted a small-scale, 12-hour disturbance experiment in the German exploration contract area in the CCZ using a chain dredge. Sediment plume dispersion and deposition was monitored using an array of optical and acoustic turbidity sensors and current meters placed on platforms on the seafloor, and by visual inspection of the seafloor before and after dredge deployment. We found that seafloor imagery could be used to qualitatively visualise the redeposited sediment up to a distance of 100 m from the source, and that sensors recording optical and acoustic backscatter are sensitive and adequate tools to monitor the horizontal and vertical dispersion of the generated sediment plume. Optical backscatter signals could be converted into absolute mass concentration of suspended sediment to provide quantitative data on sediment dispersion. Vertical profiles of acoustic backscatter recorded by current profilers provided qualitative insight into the vertical extent of the sediment plume. Our monitoring setup proved to be very useful for the monitoring of this small-scale experiment and can be seen as an exemplary strategy for monitoring studies of future, upscaled mining trials. We recommend that such larger trials include the use of AUVs for repeated seafloor imaging and water column plume mapping (optical and acoustical), as well as the use of in-situ particle size sensors and/or particle cameras to better constrain the effect of suspended particle aggregation on optical and acoustic backscatter signals.

Thermal Neutron Measurement Capability of a Single Crystal CVD Diamond Detector near the Reactor Core Region of UTR-KINKI

Thermal neutron flux evaluation using a single crystal diamond detector (SDD) was carried out in the core region of the UTR-KINKI reactor where a mixed radiation field by thermal and fast neutrons and gamma-ray exists. The pulse shape discrimination method to extract pulses with a rectangular shape as well as a wide pulse-width was established to exclude pulses induced by gamma-rays. The SDD, using a 6LiF thermal neutron converter, is able to detect pulse events caused not only by fast neutrons but also by thermal neutrons through energy depositions into the diamond by energetic alpha and triton particles induced by thermal neutrons. Additionally, the SDD without the thermal neutron converter was used for the measurement of the energy deposition events only by fast neutrons. A comparison of the pulse counts of the SDD with or without the thermal neutron convertor deduced the energy deposition spectra by thermal neutrons. The thermal neutron flux in the core region of the UTR-KINKI reactor was evaluated to be 7.6×106 n cm−2 s−1 W−1 up to a reactor power of 1 W.

Kinetic Monte Carlo modeling of oxide thin film growth.

In spite of the increasing interest in and application of ultrathin film oxides in commercial devices, the understanding of the mechanisms that control the growth of these films at the atomic scale remains limited and scarce. This limited understanding prevents the rational design of novel solutions based on precise control of the structure and properties of ultrathin films. Such a limited understanding stems in no minor part from the fact that most of the available modeling methods are unable to access and robustly sample the nanosecond to second timescales required to simulate both atomic deposition and surface reorganization at ultrathin films. To contribute to this knowledge gap, here we have combined molecular dynamics and adaptive kinetic Monte Carlo simulations to study the deposition and growth of oxide materials over an extended timescale of up to ∼0.5ms. In our pilot studies, we have examined the growth of binary oxide thin films on oxide substrates. We have investigated three scenarios: (i) the lattice parameter of both the substrate and thin film are identical, (ii) the lattice parameter of the thin film is smaller than the substrate, and (iii) the lattice parameter is greater than the substrate. Our calculations allow for the diffusion of ions between deposition events and the identification of growth mechanisms in oxide thin films. We make a detailed comparison with previous calculations. Our results are in good agreement with the available experimental results and demonstrate important limitations in former calculations, which fail to sample phase space correctly at the temperatures of interest (typically 300-1000K) with self-evident limitations for the representative modeling of thin films growth. We believe that the present pilot study and proposed combined methodology open up for extended computational support in the understanding and design of ultrathin film growth conditions tailored to specific applications.

Phytoplanktonic response to simulated volcanic and desert dust deposition events in the South Indian and Southern Oceans

AbstractContrasting concentrations of macronutrients and micronutrients induce different nutrient limitations of the oceanic productivity and shape the composition of the phytoplankton communities of the South Indian Ocean and Indian sector of the Southern Ocean. o assess the phytoplankton response to nutrient release by desert dust and volcanic ash aerosols in these distinct biogeochemical regions, we conducted microcosm incubation experiments. A dry or wet deposition of either dust from Patagonia or ash from the Icelandic volcano Eyjafjallajökull or dissolved nutrients (Si, Fe, N and/or P) were added to trace metal clean incubations of surface seawater collected from five stations. These deposition experiments enabled the measurement of the biological response along with solubility calculations of nutrients. Both types of aerosols alleviated the iron deficiency occurring in the Southern Ocean during austral summer and resulted in a 24–110% enhancement of the primary production, depending on the station. The release of dissolved silicon may also have contributed to this response, although to a lesser extent, whereas neither the dust nor the ash relieved the nitrogen limitation in the low‐nutrient and low‐chlorophyll area. Diatom growth was responsible for 40% to 100% of the algal biomass increase within the responding stations, depending on the region and aerosol type. The high particle concentrations that are characteristic of ash deposition following volcanic eruptions may be of equal or higher importance to phytoplankton compared to desert dust, despite ashes' lower nutrient solubility to the ocean.

Presence of the Herbaceous Marsh Species Schoenoplectus americanus Enhances Surface Elevation Gain in Transitional Coastal Wetland Communities Exposed to Elevated CO2 and Sediment Deposition Events.

Coastal wetlands are dynamic ecosystems that exist along a landscape continuum that can range from freshwater forested wetlands to tidal marsh to mudflat communities. Climate-driven stressors, such as sea-level rise, can cause shifts among these communities, resulting in changes to ecological functions and services. While a growing body of research has characterized the landscape-scale impacts of individual climate-driven stressors, little is known about how multiple stressors and their potential interactions will affect ecological functioning of these ecosystems. How will coastal wetlands respond to discrete climate disturbances, such as hurricane sediment deposition events, under future conditions of elevated atmospheric CO2? Will these responses vary among the different wetland communities? We conducted experimental greenhouse manipulations to simulate sediment deposition from a land-falling hurricane under future elevated atmospheric CO2 concentrations (720 ppm CO2). We measured responses of net primary production, decomposition, and elevation change in mesocosms representing four communities along a coastal wetland landscape gradient: freshwater forested wetland, forest/marsh mix, marsh, and mudflat. When Schoenoplectus americanus was present, above- and belowground biomass production was highest, decomposition rates were lowest, and wetland elevation gain was greatest, regardless of CO2 and sediment deposition treatments. Sediment addition initially increased elevation capital in all communities, but post-deposition rates of elevation gain were lower than in mesocosms without added sediment. Together these results indicate that encroachment of oligohaline marshes into freshwater forested wetlands can enhance belowground biomass accumulation and resilience to sea-level rise, and these plant-mediated ecosystem services will be augmented by periodic sediment pulses from storms and restoration efforts.

Modeling an Extreme Dust Deposition Event to the French Alpine Seasonal Snowpack in April 2018: Meteorological Context and Predictions of Dust Deposition

AbstractMineral dust is an important aerosol in the atmosphere and is known to reduce snow albedo upon deposition. Model predictions of dust deposition events in snow covered mountain regions are challenging due to the complexity of aerosol‐cloud interactions and the specifics of mountain meteorological systems. We use a case study of dust deposition between 30 March and 5 April 2018 to the French alpine snowpack to study the processes that control dust deposition to the seasonal snowpack. To understand processes controlling dust transport and deposition to snow, we use a combination of in situ observations at Col du Lautaret in the French Alps, satellite remote sensing, the Copernicus Atmosphere Monitoring Service (CAMS) reanalysis global atmospheric composition, and the regional model WRF‐Chem. Specifically, we investigate the role of increased model spatial resolution within WRF‐Chem in capturing mountain meteorology, precipitation, and predicted dust deposition. Regional model results are also compared to the reanalysis global CAMS products including aerosols in the atmosphere and predicted dust deposition fluxes. We conclude that predicted mountain meteorology (e.g., precipitation) is better with increased model resolution (3 × 3 km resolution WRF‐Chem domain). This improved meteorology has significant impacts on predicted dry and wet dust deposition to the alpine snowpack. Dry deposition is important in the western part of the French Alps at low altitudes, while wet deposition dominates over the complex higher altitude mountain terrain.

Post-UHP tectonic evolution of the East Kunlun orogenic belt, northern tibetan plateau: insight from the regional-scale crustal anatexis

ABSTRACT Extensive crustal anatexis is common during the decompressional exhumation of deeply subducted continental crust and the delamination of a collision‐thickened orogenic lithosphere, indicating that determining the timing of partial melting can provide insights into the possible tectonic evolution during orogenic processes. An integrated study of petrology, zirconology and whole-rock geochemical compositions from migmatites and pegmatites in the Nageng, Langmuri and Wulonggou area of the East Kunlun orogenic belt, is presented in this study. The protoliths of these migmatites include Tonian sedimentary rocks and ca. 440 Ma arc-related dioritic rock. Together with previous studies, an extensive crustal anatexis event recorded by anatectic zircons occurred after ca. 410 Ma. In addition, hafnium isotope analyses indicate that the anatectic zircons may or may not inherit their Hf isotope compositions from protolith zircons during partial melting, depending on whether or not the garnet Hf contributes to the Hf budget of anatectic melt. Thus, the most reasonable method to trace the source of granite is to compare the Hf isotope composition of anatectic zircon in migmatite and magmatic zircon in contemporaneous granite. By such method, anatectic melt produced by migmatites in this study could account for both penecontemporaneous A- and I-type granites with high magmatic zircon εHf(t) values and S-type granites with low magmatic zircon εHf(t) values. As the extensive crustal anatexis is later than both metamorphic peak and amphibole-facies retrogression of high-pressure and ultrahigh-pressure (HP-UHP) metamorphic rocks, it is reasonable that post-collision orogenic collapse of the collision‐thickened orogenic lithosphere as a result of delamination and asthenospheric upwelling occurred after ca. 410 Ma, which is also supported by contemporaneous granulite-facies metamorphism, molasse deposition, and magmatic events including Xiarihamu mafic-ultramafic intrusions, A-type granites, and mafic dykes formed in the continental rifting setting.

Climatology of Dust Deposition in the Adriatic Sea; a Possible Impact on Marine Production

AbstractAtmospheric mineral dust deposition plays an important role in providing nutrients to marine ecosystems. In this study, the climatology of dust deposition in the Adriatic Sea area was determined for the first time based on Modern‐Era Retrospective Analysis for Research and Applications, version 2 reanalysis from 1989 to 2019. The annual cycle of deposition exhibits two maxima: a stronger maxima in March–April and a weaker maxima in November. Wet deposition is a dominant process with a relative contribution to overall deposition from 67.35% to 88.53%. Deposition hot spots are along the Montenegrin coast and Otrant. The average contribution of dust deposition events (DDEs) is 16.5% (60.2 dy yr−1), with the strongest deposition during 1999–2009 and a positive trend in deposited mass during the study period. The effect of dust deposition on primary production is observed by a high level of oxygen saturation up to 250% (usually it is lower, up to 150%) in the stratified middle water layer (5–8 m) of the central Adriatic marine system (Rogoznica Lake) during an intense wet deposition episode. Such extreme values of oxygen saturation can be taken as an indication of biological activity related to an increase in phytoplankton abundance and activity, diatoms in particular.

Deposition rates and residence time of litter varies among beaches in the Lofoten archipelago, Norway

A considerable portion of marine litter pollutes the world's coastlines. Its accumulation on beaches represents the product of deposition and retention, processes which are not well understood. A mark-recapture study was performed with a two-week sampling interval at three sites in Lofoten, Norway. Deposition and retention vary over relatively small spatial scales (approx. 13 km radius). No correlation was found among sites in the timing of high and low deposition events, suggesting these are governed by local factors. Contrastingly, the correlation in the timing of high and low retention events was generally stronger among sites, suggesting these may be affected by regional factors. The results underline the importance of customising cleanup frequency for different beaches as spatiotemporal variation in the relative importance of deposition and retention dictate the optimal frequency for maximal removal of litter from circulation in the local marine environment, which cannot be discerned from accumulation (i.e., standing stock) alone.