Atmospheric Dust Concentrations Research Articles

Southern Alaska as a source of atmospheric mineral dust and ice-nucleating particles.

Ice-nucleating particles (INPs) influence cloud radiative properties and climate; however, INP sources and concentrations are poorly constrained, particularly in high-latitude regions. Southern Alaska is a known source of high-latitude dust, but its contribution to atmospheric mineral dust and INP concentrations has not been quantified. We show that glacial dust collected in southern Alaska is an effective ice-nucleating material under conditions relevant for mixed-phase clouds and is more active than low-latitude dust because of a biological component that enhances its activity. We use dispersion modeling to show that this source contributes to the regional INP population and that the dust emitted is transported over a broad area of North America, reaching altitudes where it could cause cloud glaciation. Our results highlight the importance of quantifying emissions and ice-nucleating characteristics of high-latitude dusts and suggest that the ice-nucleating ability of emitted dust in these regions should be represented in models using different parametrizations to low-latitude dust.

Moats in the residual south polar cap of Mars: Ages, formation, and evolution

The residual south polar cap of Mars (RSPC) is a region comprising tabular deposits of solid CO2 averaging a few m thick resting on layered, water-ice rich deposits a few km thick. Estimates of the ages of morphologic features in the RSPC have relied on average rates of change obtained from geographically limited samples. In this work we apply image coverage of the whole RSPC at 6 m/pixel spanning up to seven Mars years to determine how well ages of RSPC forms can be modelled from recent observations, and to explore implications of the calculated chronology. Topographic troughs separating CO2 layers of different ages and thickness, termed moats, are widespread, changing, and dateable features of the RSPC. Although they all develop by the same phenomena, we divide moats into two groups based on their linear dimensions and the span of relevant spacecraft imaging: 1) moats separating large areas of CO2 ice of different age and thickness, termed sinuous boundary moats, that imaging data show are related to post-1972 CO2 deposition. 2) moats separating the walls of pits from thinner, younger, interior mounds, termed pit moats; these are not resolved in early spacecraft images. Our survey of the entire summer RSPC spanning seven Mars years yields modelled formation times for both kinds of moats that cluster largely about Mars Years (MY) 11–13. A population of smaller moats is calculated to have formed near MY 26–28. These times closely follow planet-encircling dust events in MY 9, MY 12, and MY 28 (Earth years 1971, 1977, 2007). High-resolution images show that both pit and sinuous moats are initiated by slow downward erosion of debris left by retreating scarps of CO2 ice that are flanked by brighter, accumulating CO2 ice. We find that the most probable role of the dust events in moat formation is to clear thin CO2 layers from underlying water-ice-rich materials through thermal effects of the atmospheric dust content. The age results severely limit the magnitude of variations in moat scarp retreat rates during the last 25 MY. Pit moats have limited lifetimes because scarp retreat eventually removes the interior mound that defines the inner moat wall. Pits can reach much greater ages than moats; some pits formed prior to MY -100 (Earth year 1765).

Diurnal and seasonal source‐proximal dust concentrations in complex terrain, West Greenland

AbstractDiurnal and seasonal cycles of aeolian activity are well‐constrained for low latitude dust source regions and provide valuable insights into relationships between dust emissions and environmental drivers. Such cycles have received little systematic attention in high latitude dust source areas (≥50°N and ≥40°S), and understanding them will aid the modelling of atmospheric dust over different timescales. This paper examines the timing and drivers of atmospheric dust concentration close to source at ice‐free locations c. 6 km and c. 37 km from the Greenland Ice Sheet margin. Dust concentration, and associated environmental drivers including wind speed and velocity, air temperature and humidity, was measured from April–October 2018 and April–August 2019. Measured dust concentrations were a similar order of magnitude to source‐proximal values measured globally and varied from 0 to ≥1000 μg m−3. Diurnal cycles in the environmental drivers of dust emission were similar to those observed in low latitudes, but unlike in the low latitudes, there was no clear diurnal pattern of dust concentration. Only 3 out of 17 recorded dust events showed a significant positive relationship between wind speed and dust concentration, and factors such as wind direction, humidity and sediment availability are the over‐riding controls on dust activity at the event and seasonal scales. Whereas 7 dust events are attributed to down‐valley katabatic winds, 10 events were associated with a westerly sea breeze blowing up‐valley towards the ice sheet and high atmospheric moisture content. If deposited on the ice, this dust will alter ice albedo both directly and indirectly, (e.g. through the promotion of algal blooms) affecting cryospheric melt rates. Our results demonstrate an intricate relationship between first‐order controls and dust concentration that raises challenges for modelling the uplift and subsequent dust transport from high latitude sources, especially the appropriateness of assumptions based on emissions behaviour at low latitudes.

Data-driven aeolian dust emission scheme for climate modelling evaluated with EMAC 2.55.2

Abstract. Aeolian dust has significant impacts on climate, public health, infrastructure and ecosystems. Assessing dust concentrations and the impacts is challenging because the emissions depend on many environmental factors and can vary greatly with meteorological conditions. We present a data-driven aeolian dust scheme that combines machine learning components and physical equations to predict atmospheric dust concentrations and quantify the sources. The numerical scheme was trained to reproduce dust aerosol optical depth retrievals by the Infrared Atmospheric Sounding Interferometer on board the MetOp-A satellite. The input parameters included meteorological variables from the fifth-generation atmospheric reanalysis of the European Centre for Medium-Range Weather Forecasts. The trained dust scheme can be applied as an emission submodel to be used in climate and Earth system models, which is reproducibly derived from observational data so that a priori assumptions and manual parameter tuning can be largely avoided. We compared the trained emission submodel to a state-of-the-art emission parameterisation, showing that it substantially improves the representation of aeolian dust in the global atmospheric chemistry–climate model EMAC.

Автоматизированная система управления флегматизацией взрывов пылеметановоздушной смеси в шахтной атмосфере

Introduction. The work presents a general and principal diagram of the control system, provides recommendations for the choice of a set of technical means of practical implementation of the system and justification of the application and parameters of various sensors, power supplies, controller, communications, signal converters and actuators, which use different methods and methods of processing signals of different nature, which ensures completeness and prevents distortion of signals and parameters that affect the quality of the automated system of phlegm The aim of the work is to develop and implement the technical support of an automated control system of phlegmatization explosions of dustmethane-air mixture in the mine atmosphere. Materials and methods of research. To achieve the goal of controlling phlegmatization of dust-methane-air mixture explosions in the mine atmosphere, the search and analysis of materials on this topic is carried out, an automated control system is developed and observation of its work in real conditions is made. Research results. The dependences of the upper and lower thresholds of explosiveness of dust-methane-air mixture, as well as the achievements in the study of the molecular structure of water and methane can assess the effectiveness of measures to prevent methane and dust explosions in coal mines and propose a patentable method of phlegmatization of methane explosions in coal mines. Discussion. At a choice of CTS the basic attention is given to reliability of functioning of measuring techniques, standardization of interfaces, software of controllers and processors, on the basis of which it is supposed to develop software and realization of algorithmic and mathematical maintenance of the automated control system and its debugging in industrial conditions. Conclusion. The studies have shown that the sequence of installation of nozzles along the length of the face, should not exceed 1/5-1/7 of the length of the mini-drops falling (if a weighted mini-drop falls for 6-8 seconds, at a speed of 2.5 m/s, it flies 15-20 m, and, therefore, nozzles should be set every 12-15 m). Resume. At successful approbation and positive results of the automated control system of phlegmatization of explosions of dust-methane-air mixture in a mine atmosphere it can be successfully included in the existing systems of gas protection, extending their functions and increasing the level of industrial safety of mines. Also, studies have shown that for the implementation of a phlegmatization control system of explosions of dust-methane-air mixture in a mine atmosphere to increase the accuracy it is necessary to increase humidity, which in turn leads to the need to choose the location of installation of nozzles. Suggestions. In real conditions the level of absolute moisture of 16 g/m3 is possible at a temperature not lower than 22 °C and relative humidity of not less than 90 %, therefore, the task of the automated control system of phlegmatization of dust-methane-air mixture explosions (ACS FVPS) in the mine atmosphere is to maintain the maximum absolute humidity at the existing humidity and temperature in the clearing or preparatory face, taking into account the methane and dust concentration in the mine atmosphere.

A 1.46–2.48 μm spectroscopic atlas of a T6 dwarf (1060 K) atmosphere with IGRINS: first detections of H2S and H2, and verification of H2O, CH4, and NH3 line lists

ABSTRACT We present Gemini South/IGRINS observations of the 1060 K T6 dwarf 2MASS J08173001−6155158 with unprecedented resolution ($R\equiv \lambda /\Delta \lambda =45\, 000$) and signal-to-noise ratio (S/N > 200) for a late-type T dwarf. We use this benchmark observation to test the reliability of molecular line lists used up-to-date atmospheric models. We determine which spectroscopic regions should be used to estimate the parameters of cold brown dwarfs and, by extension, exoplanets. We present a detailed spectroscopic atlas with molecular identifications across the H and K bands of the near-infrared. We find that water (H2O) line lists are overall reliable. We find the most discrepancies amongst older methane (CH4) line lists, and that the most up-to-date CH4 line lists correct many of these issues. We identify individual ammonia (NH3) lines, a hydrogen sulfide (H2S) feature at 1.5900 $\mu$m, and a molecular hydrogen (H2) feature at 2.1218 $\mu$m. These are the first unambiguous detections of H2S and H2 absorption features in an extra-solar atmosphere. With the H2 detection, we place an upper limit on the atmospheric dust concentration of this T6 dwarf: at least 500 times less than the interstellar value, implying that the atmosphere is effectively dust-free. We additionally identify several features that do not appear in the model spectra. Our assessment of the line lists is valuable for atmospheric model applications to high-dispersion, low-S/N, high-background spectra, such as an exoplanet around a star. We demonstrate a significant enhancement in the detection of the CH4 absorption signal in this T6 dwarf with the most up-to-date line lists.

Southeast Asian dust flux reconstructed using accurately dated stalagmite thorium concentrations

Mineral dust flux is an important component of the global climate system, but chronological uncertainties complicate interpretations of the timing and magnitude of paleo-dust fluxes. This study establishes a correlation between modern satellite-derived atmospheric dust concentration data and stalagmite thorium concentrations (from published records of stalagmites growing over the last 500 years), and subsequently applies this relationship to reconstruct Asian dust flux during the late Pleistocene using published records. Thorium is an element often associated with mineral dust, and because most stalagmite records are dated using uranium-thorium disequilibrium techniques, a spatiotemporally large, yet untapped, database of thorium concentrations exists. Specifically, 194 thorium records from South-East (SE) Asian stalagmites were compiled to produce a composite SE Asian dust flux record for the past 100,000 years. The new dust flux record is consistent with the perspective that dust flux is a function of westerly wind strength across Asia and regional aridity. Dansgaard-Oeschger (D-O) event expression within the median stalagmite 232Th record is variable, with several D-O events evident within stalagmite δ18O records not evident within the new dust record. This may reflect East Asian Summer Monsoon (EASM) moisture source region Sea Surface Temperature (SST) variability (affecting stalagmite δ18O) but stable westerly wind regime (resulting in invariant 232Th concentrations) or the fact that these events were too brief to trigger biome shifts. This study presents encouraging first results suggesting that stalagmite thorium concentrations partially reflect dust flux over cave sites. Although here we use a compilation of records, and the spread of data within each time slice is high, future studies at well-understood cave sites where thorium input to the cave is predominantly via dry deposition may require only single stalagmites to produce adequate absolutely dated dust reconstructions.

Satellite indicators of air quality changes over Russia due to the COVID-19 pandemic restrictions

The analysis of the dust content (pm10) and NO2 in the atmosphere over Russia for January - May 2020 in comparison with previous years was carried out. Copernicus Atmosphere Monitoring Service data archives are used as a source of information. It was found that the imposition of socio-economic restrictions due to the COVID-19 pandemic affected the content of dust and nitrogen oxide in the atmosphere unevenly for different regions of the country. The state of atmospheric dust and NO2 content has improved due to the restrictions imposed in a number of regions of the Far East (apparently, also due to restrictions on the territory of neighboring China) and, to a lesser degree, in the center of the European part of Russia. The information obtained can be used to predict the development of the social and economic situation in the coming years and to plan preventive measures to overcome the economic and social consequences of the COVID-19 pandemic, as well as to develop proposals to overcome negative consequences for the environment, including measures to optimize territorial development, nature protection and consideration of ecosystem functions.

Ocean Dust Deposition Rates Constrained in a Data‐Assimilation Model of the Marine Aluminum Cycle

AbstractAluminum (Al) is delivered to surface ocean waters by aeolian dust, making it a promising tracer to constrain dust deposition rates and the atmospheric supply of trace metal micronutrients. Over recent years, dissolved Al has been mapped along the GEOTRACES transects, providing unparalleled coverage of the world ocean. However, inferring atmospheric input rates from these observations is complicated by a suite of additional processes that influence the Al distribution, including reversible particle scavenging, biological uptake by diatoms, hydrothermal sources, sediment resuspension. Here we employ a data‐assimilation model of the oceanic Al cycle that explicitly accounts for these processes, allowing the atmospheric signal to be extracted. We conduct an ensemble of model optimizations that test different dust deposition distributions and consider spatial variations in Al solubility, thereby inferring the atmospheric Al supply that is most consistent with GEOTRACES observations. We find that 37.2 ± 11.0 Gmol/yr of soluble Al is added to the global ocean, dominated in the Atlantic Ocean, and that Al fractional solubility varies strongly as a function of atmospheric dust concentration. Our model also suggests that 6.1 ± 2.4 Gmol Al/yr is injected from hydrothermal vents, and that vertical Al redistribution through the water column is dominated by abiotic reversible scavenging rather than uptake by diatoms. Our results have important implications for the oceanic iron (Fe) budget: based on the soluble Fe:Al ratio of dust, we infer that aeolian Fe inputs lie between 3.82 and 9.25 Gmol/yr globally, and fall short of the biological Fe demand in most ocean regions.

Global Impact of ENSO on Dust Activities with Emphasis on the Key Region from the Arabian Peninsula to Central Asia

AbstractThe El Niño‐Southern Oscillation (ENSO) has been found to be closely related to dust aerosol activities in many parts of the world. However, previous studies have rarely explored the ENSO’s impacts in the global context. In this study, the responses of the interannual variability of global atmospheric dust content to the ENSO cycle (including the eastern Pacific and central Pacific types) are examined using the MERRA‐2 atmospheric aerosol reanalysis data. The ENSO‐related tropical eastern Pacific sea surface temperature (SST) anomalies in the antecedent winter (November to January) have the most significant effect on the airborne dust content in a region from the Arabian Peninsula to Central Asia during the following spring and summer (April to July), which is identified as the key region (KR) of the ENSO’s impacts. The positive (negative) tropical eastern Pacific SST anomalies in the preceding winter during the El Niño (La Niña) years correspond to significantly reduced (increased) dust column content in the following spring and summer over the KR, which was confirmed using singular value decomposition. With the above (below)‐normal winter SST anomalies in the tropical eastern Pacific, the Walker Circulation weakens (strengthens), and the divergence (convergence) over the western tropical Pacific and the convergence (divergence) over the southern tropical Indian Ocean in the lower troposphere are strengthened, which facilitate (restrain) the southward diffusion of airborne dust in the KR. Meanwhile, the increased (decreased) precipitation and soil moisture and the corresponding vegetation conditions help limit (promote) the dust emission in the KR during the El Niño (La Niña) years.

Aeolian dust dynamics in the Fergana Valley, Central Asia, since ~30 ka inferred from loess deposits

Knowledge of the interactions among atmospheric dynamics, dust emissions and climate system is essential to understand the physical mechanisms for the dust lifecycle, their role in loess formation as well as the predictions of future dust concentration. However, these issues still remain relatively poorly known in Central Asia (CA). The extensive loess deposits on the CA pediments provide a promising archive to explore atmospheric dust dynamics and climatic conditions in the past and their association with loess formation. This study investigates the granulometric and magnetic properties of a loess section (named Osh section) in the Fergana Valley, which provides a sensitive record of atmospheric dust dynamics since 30 ka based on radiometric (AMS 14C) dating. The frequency-dependent magnetic susceptibility (χfd) and the mean grain size are used to reconstruct the broad-scale effective moisture and summer atmospheric dynamics pattern in CA, respectively. The results show that the precession forcing exerts a huge influence on the wind-regime variabilities in CA, but with different physical processes under the impact of the Northern Hemisphere ice sheet (NHIS) before and after 15 ka. The origin of the sedimentation rate variations in the Osh loess is also linked to the NHIS-modulated changes of the atmospheric circulation patterns. Either the strengthened westerlies or the increased surface roughness from higher vegetation cover in loess-deposition areas have significantly accelerated the loess accumulation. As a result, these complicated influence factors of sedimentation rate change in the Osh loess section, especially during the Holocene epoch, may hamper accessibility of the authentic dust emission flux and atmospheric dust concentration in CA.

Meteorological patterns, technical validation, and chemical comparison of atmospheric dust depositions and bulk sand in the Arabian Gulf region.

This study reports seasonal variations of meteorological parameters, atmospheric dust and dust-borne heavy metals concentrations measured, over a period of two years, next to two major airports (Dubai International Airport and Abu Dhabi International Airport) in the Gulf Cooperation Council (GCC) region. On-line monitoring stations were installed at each location next to dust samplers used to frequently collect PM2.5 and PM10 on Teflon filters for metal analysis. Clear seasonal variation in meteorological parameters were identified. The particulate matter concentrations depicted from the two locations were continuously monitored. The PM2.5 concentration ranged from 50 to 100μg/m3 on normal days but reached 350-400μg/m3 per day during mild storms. The PM10 levels ranged between 100 and 250μg/m3 during normal days and spiked to 750μg/m3 during mild storms. Energy Dispersive X-Ray Analysis (EDS) revealed the presence of significant amounts of alkali and alkaline earth metals, which pose potential harm to aircraft engines. ICP analysis showed the presence of heavy and toxic metals in concentrations that may pose harm to human health. Bulk sand samples from Abu Dhabi sites showed chemical similarities to the atmospheric dust samples. The concentrations of heavy metals, PM2.5, and PM10 are at levels that require further monitoring due to their impact on human health. The two years meteorological monitoring, with the seasonal variations, provided additional regional data in the Arabian Gulf. Furthermore, the study concluded that Sand and Dust storms (SDS) occur more frequently at the northern Arabian Gulf compared to its southern region. The chemical correlation between atmospheric dust and regional desert sand suggests the localized origin of the smaller dust particles that may form by breaking apart of the ground sand grains. As a result of the ongoing urbanization in the region, it is essential to collect additional data from various locations for a longer period of time.

Dust and Radon Levels on the West Coast of Namibia – what did we learn?

Abstract The study investigated the potential for adverse health impacts from exposures to inhalable atmospheric dust and radon in the main towns along Namibia's central-western coast. An ambient air quality monitoring network was established at the end of 2016 to measure and track the inhalable dust (specifically PM10) and radon concentrations. Data collected between November 2016 and the end of December 2018 were assessed and selected PM10 samples were analysed for mineral and radionuclide content. In addition, emissions from anthropogenic sources were quantified and simulated using a regional dispersion model. Episodic dust storms associated with easterly winds are a common phenomenon during the winter months in the western part of Namibia. During such events, dust is transported over long distances westwards towards and well into the Atlantic Ocean. In view of the natural and anthropogenic nature of atmospheric dust, the study differentiated between sources of natural dust and those arising as a result of man-made processes. It was found that PM10 concentrations were, on average, higher at the coastal monitoring stations than at the stations located further inland, often exceeding the daily World Health Organisation (WHO) guideline value. Whilst high atmospheric dust concentrations were mostly associated with easterly wind conditions, sea salt was found to be a significant PM10 contributor at the coastal stations. Modelled results, which only included emissions from man-made sources, indicated that these sources contribute very little to the total PM10 concentrations measured at the coastal towns. The radiation exposure doses associated with the inhalation of atmospheric dust and radon were found to be well-below the world-wide average inhalation doses provided by the United Nations Scientific Committee on the Effects of Atomic Radiation (UNSCEAR).

Dust and radon levels on the west coast of Namibia – What did we learn?

The study investigated the potential for adverse health impacts from exposures to inhalable atmospheric dust and radon in the main towns along Namibia's central-western coast. An ambient air quality monitoring network was established at the end of 2016 to measure and track the inhalable dust (specifically PM10) and radon concentrations. Data collected between November 2016 and the end of December 2018 were assessed and selected PM10 samples were analysed for mineral and radionuclide content. In addition, emissions from anthropogenic sources were quantified and simulated using a regional dispersion model.Episodic dust storms associated with easterly winds are a common phenomenon during the winter months in the western part of Namibia. During such events, dust is transported over long distances westwards towards and well into the Atlantic Ocean. In view of the natural and anthropogenic nature of atmospheric dust, the study differentiated between sources of natural dust and those arising as a result of man-made processes.It was found that PM10 concentrations were, on average, higher at the coastal monitoring stations than at the stations located further inland, often exceeding the daily World Health Organisation (WHO) guideline value. Whilst high atmospheric dust concentrations were mostly associated with easterly wind conditions, sea salt was found to be a significant PM10 contributor at the coastal stations. Modelled results, which only included emissions from man-made sources, indicated that these sources contribute very little to the total PM10 concentrations measured at the coastal towns.The radiation exposure doses associated with the inhalation of atmospheric dust and radon were found to be well-below the world-wide average inhalation doses provided by the United Nations Scientific Committee on the Effects of Atomic Radiation (UNSCEAR).

Correlation between mars’ semidiurnal LOD amplitude variation and atmospheric dust cycle index

The Mars’ rotational rate, or equivalently its length-of-day (LOD), varies slightly due to global atmospheric changes. And the atmospheric dust cycle is considered to be one key process impacting the Mars’ atmosphere. Lewis and Barker (2005) demonstrated the close link of the semidiurnal tidal amplitude with the atmospheric dust content. In consideration of tidal effects in the Mars’ variable rotation, possible connection may exist between the Mars’ semidiurnal LOD amplitude variation and atmospheric dust cycles. In this study, the Mars’ LOD variations which are influenced by global atmosphere, and the atmospheric dust cycle index (ADCI) are computed based on eight realistic scenarios of the Martian Years (MY) 24–31 of the Martian Climate Database. The semidiurnal LOD amplitude change and the ADCI are found to be correlated at the 99% significance level, and they present similar time-varying wavelet spectral structures. In mature stages of global dust storms in MYs 25 and 28, relatively high LOD and ADCI values occurred synchronously across the time scales, ranging from a few months’ high frequency to seasonal and over one year’s lower frequency band. The close relation between the semidiurnal LOD amplitude variation and the ADCI reflects the strong coupling between the solid Mars and surficial atmosphere system, which relates primarily to the semidiurnal atmospheric tide.

Exposure Assessment of Indoor PM Levels During Extreme Dust Episodes.

Millions of people live in areas that are subject to frequent dust events; however gaps remain in our knowledge about the association between dust, air quality and corresponding particulate matter (PM) exposure levels inside buildings. This case study demonstrates how the PM2.5 and PM10 levels in an urban environment respond to strong natural dust episodes. Real-time measurements were recorded simultaneously in indoor and outdoor environments in households in the city of Beer-Sheva, Israel during several strong dust events. A typical strong event was used for a detailed analysis of PM10 and PM2.5. Outdoor daily concentrations were above 1000 µg m−3 for PM10, the maximum hourly value of which was 1320 µg m−3. The indoor PM10 peaked at about 700 µg m−3 and fluctuated in parallel with the outdoor level but with a time lag of about 15 min. Indoor air tended to remain for several hours after the dust event had subsided. Analyses of multiple events revealed that the dependence of indoor PM2.5 and PM10 on natural dust varies but is not directly linked to the level of atmospheric dust concentration. From a health perspective, the exposure risk posed by extreme indoor PM2.5 and PM10 levels generated by natural dust episodes should be considered.

Long-term (1980–2018) spatial and temporal variability of the atmospheric dust load and deposition fluxes along the North-African coast of the Mediterranean Sea

Abstract The Sahara is a major source of mineral particles for the Mediterranean Sea. The air-suspended particles alter the radiative transfer of solar and terrestrial radiation and the input of nutrients resulting from the deposition of mineral dust into the surface waters is thought to be essential for the development of marine ecosystems. In order to document the spatial and temporal variabilities of the dust atmospheric content and deposition flux close to the North-African coast where the impacts are expected to be the largest but where experimental stations are cruelly lacking, we use the MERRA-2 monthly reanalysis data of the 1980–2018 period. We have extracted the dust optical depth (AODdust), surface concentrations (Cdust), precipitations (Prcp), and deposition fluxes (Fdry, Fwet, and Ftot) of 14 areas (7 coastal and 7 offshore) regularly spaced from the Straights of Gibraltar in the west to Egypt and Cyprus in the east. The principal Component Analysis (PCA) shows that 86% of the variability of AODdust can be explained by two factors only: F1 whose influence is dominant in the Central Mediterranean and peaks in spring, and F2 whose importance decreases from Morocco to Egypt and peaks in summer. The variability of the surface concentration is more complex than that of the optical depth. AODdust and Cdust are maximal downwind of the main Algerian and Libyan dust sources, which is to say on and off the coast of the Central Mediterranean (south-Tunisia, Libya, Malta …). In spite of the climate change already underway, no long-term trend of Cdust or AODdust can yet be evidenced for any of the 14 areas between 1980 and 2018. Along the coast of the eastern basin, the low precipitations (from 6.1 to 10.5 mm month−1 on average) explain that dry deposition accounts for a significant (45–53%) proportion of the total deposition. Everywhere else, wet deposition dominates and particularly in the marine areas where it represents about 90% of the total. From 1980 to 2018, the monthly averaged Ftot did not increase significantly. It varies from 0.24 (eastern Egypt) to 0.63 g m−2 month−1 (south-Tunisia) along the North-African coast, and from 0.26 (Baleares) to 0.48 g m−2 month−1 (Malta) in the marine areas. Because of the spatial variability of the precipitations, the largest deposition fluxes do not necessarily coincide with the regions of largest atmospheric dust content.

Radiative Effect of Mineral Dust on East Asian Summer Monsoon During the Last Glacial Maximum: Role of Snow‐Albedo Feedback

AbstractMineral dust exerts great influence on modern climate. Eolian deposits reveal that atmospheric dust concentration is larger during the Last Glacial Maximum, especially over Asia. However, the larger forcing of dust on Asian climate is still not fully explored. In this study, climate model experiments are conducted to evaluate the direct radiative effect on East Asian monsoon. The results show that the radiative forcing of dust, amplified by snow albedo feedback over high‐latitude Eurasia, produces a wave‐like pattern in westerlies and weakens the monsoon southerly winds over northern China. Dust over expanded Last Glacial Maximum sources (northern Central Asia and northeastern Russia) is responsible for this perturbation of the westerlies; the absence of these dust sources at present explains why such impacts on circulations are not simulated for modern conditions. The dust‐induced anomalies in southerly wind speed and precipitation over northern China reach 29% and 41% of the glacial‐induced changes, respectively.

Saharan dust deposition initiates successional patterns among marine microbes in the Western Atlantic

AbstractDeposition of aerosolized desert dust can affect marine microbial community structure and function through pulsed addition of limiting micro‐ and macronutrients. However, few studies have captured responses to dust deposition in situ following trans‐oceanic transport. We conducted a 26‐d time series evaluating biogeochemical and microbial community response to Saharan dust deposition in surface waters in the subtropical western Atlantic (Florida Keys National Marine Sanctuary, U.S.A.). Following periods of elevated atmospheric dust concentrations, particulate and dissolved iron concentrations increased in surface waters. Autotrophic picoeukaryote abundance increased rapidly, followed by increases in the abundance of heterotrophic bacteria and Synechococcus. Concomitant to cell count changes, we observed successional shifts in bacterial community composition. The relative abundances of Prochlorococcus and Pelagibacter declined with dust arrival, while relative abundance of heterotrophic bacteria increased, beginning with Vibrionales and followed sequentially by Chrysophyceae, Rhodobacteriaceae, and Flavobacteriaceae. Finally, a peak in Synechococcus cyanobacteria was observed. These results provide new insight into microbial community succession in response to Saharan dust deposition, their association with temporal dynamics in surface water dissolved and particulate iron concentrations, and a potential role for bioprocessing of dust particles in shaping marine microbial responses to deposition events.

A 40,000-year record of aridity and dust activity at Lop Nur, Tarim Basin, northwestern China

The Taklamakan Desert is a major dust source area for northwestern China. The history of aridification and sandstorm activity of the desert is recorded in the lacustrine sediments of the Lop Nur paleolake, on the eastern margin of the desert. In this study, we used accelerator mass spectrometry 14C dating, the ln (Al/Ca) ratio, and the grain size of the non-biogenic fraction of sediment core KY01 taken from the center of Lop Nur to produce a ∼40 kyr record of local climate change. During mid–late Marine Isotope Stage (MIS) 3, increases in the ln (Al/Ca) ratio, alluvial mud content, and atmospheric dust content, and a decrease in the dust storm content indicate an overall wet climate. During MIS 2, marked decreases in the ln (Al/Ca) ratio and alluvial mud content, especially during the Last Glacial Maximum and Heinrich event 1 cold interval, indicate lowered atmospheric temperatures, as also recorded in Greenland ice cores. During MIS 2, fluvial input to the site was reduced and almost ceased, suggesting extreme aridity at Lop Nur, very strong low-altitude winds, and frequent dust storms. During early MIS 1, the contribution of dust storms to the lake sediments fell gradually and was then relatively constant, even during the Younger Dryas cold interval. This result might be ascribed to the increased supply of meltwater from snow and ice to Lop Nur, representing a response to the rise in atmospheric temperatures during the deglacial, accompanied by strong high-level winds. During 9–7 kyr BP there was an increase in the input of sediment from sandstorms, and hence an increase in low-level wind strength, possibly relating to the 8.2 kyr BP cold event. From 7.0 to ∼1.5 kyr BP there was a decrease in sandstorm input and thus a gradual weakening of the strength of low-level winds. However, after ∼1.5 kyr BP the sandstorm input increased. Overall, we conclude that dust storm activity in the region of Lop Nur since 40 kyr BP has been controlled mainly by Northern Hemisphere cold events, with atmospheric dust providing a background sedimentary component that was dominant during warm intervals. Our findings contribute to an improved understanding of the dynamics of dust transport and to the history of dust activity and the lacustrine sedimentary record in northwestern China.