CL4.27

This study investigates the underlying atmospheric dynamics associated with intense dust storms in summer 2018 over the Arabian Peninsula (AP); a major dust source at global scale. It reports, for the first time, on the formation of cyclone over the Empty Quarter Desert as important mechanism for intense dust storms over this source region. The dust direct and semi-direct radiative forcings are observed, for the first time over this source region, using high-resolution in-situ and CERES-SYN satellite observational data. The three-dimensional structure and evolution of the dust storms are inferred from state-of-the-art satellite products such as SEVIRI, AEROIASI and CALIPSO. The dynamics and thermodynamics of the boundary layer during this event are thoroughly analyzed using ERA5 reanalysis and ground based observations.

We found that a large dust storm by Shamal winds led up, through radiative forcing, to cyclone development over the Empty Quarter Desert, subsequent dust emissions, development of convective clouds and rain. The cyclogenesis over this region initiated a second intense dust storm which developed and impacted the AP for 3 consecutive days. The uplifted dust by the cyclone reached 5 km in altitude and altered the radiative budget at the surface, inducing both significant warming during night and cooling during day. The dust load uplifted by the cyclone was estimated by the mesoscale model Meso-NH to be in the order of 20 Tg, and the associated aerosol optical depth was higher than 3. The model simulates reasonably the radiative impact of the dust in the shortwave but highly underestimated its impact in the LW.

Our study stresses the importance of the dust radiative forcing in the longwave and that it should be accurately accounted for in models to properly represent the impact of dust on the Earth system especially near source areas. Missing the warming effect of dust aerosols would impact both the weather and air quality forecast, and the regional climate projections.

These results were published in November 2020 in the journal Atmospheric Research doi.org/10.1016/j.atmosres.2020.105364.

How to cite: Francis, D., Chaboureau, J.-P., Nelli, N., Cuesta, J., and Alshamsi, N.: Summertime dust storms over the Arabian Peninsula and impacts on radiation and atmospheric circulation., EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-439, https://doi.org/10.5194/egusphere-egu21-439, 2021.

Atmospheric aerosols considered as one of the main concerns in the ongoing climate change. Meteorological changes have a significant role in the inter-decadal Aerosols variation. In this talk, long term (2000-2019) aerosol optical depth (AOD) and metrological factors data from the reanalysis-based Modern Era Retrospective Analysis for Research and Applications (MERRA-2) were used provide deep insight into the relationship between meteorological factors and AOD variability over Iran during the dusty season (MJJA: May, June, July, and August). Prior to regression analyses, Iran was divided into three parts based on the climatological conditions (west part: dusty area, north part: wetter, and center: dry area). Using a multiple linear regression model, AOD variability over Iran was significantly linked to sea level pressure and soil moisture. Winter surface temperatures and relative humidity are the main contributors to MJJA AOD variability over the western and northern parts.  AOD was not affected by precipitation. Our results suggested that climatic variations strongly affect the dust cycle, with a strong dependence on wintertime conditions in the region.

How to cite: Yousefi, R., Wang, F., Ge, Q., and Shaheen, A.: Contribution of meteorological factors to AOD variability during the dusty season over Iran, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-1349, https://doi.org/10.5194/egusphere-egu21-1349, 2021.

Dust storms are frequent phenomenon in arid and semi arid regions of Iran which cover near 60 percent of the entire country in the center of Iran. Due to geographic and climatic conditions of prolonged dry conditions as well as poor land use management, dust storms occur in almost all seasons across the region. Drought is a major fator affecting the likelihood of dust storm occurrence across arid regions of Iran. We develop copula functions to investigate the effect of drought on dust storm frequency.The standardized precipitation Index (SPI) was caluclated and drought condition was defined based on SPI< -0.5. Dought severity and duration for each drought event were ca;culated and the number of dust days in each drought event ws also identified. The Archimedean copula families shoed that the probability of dust occurrence has a significant relationship to extreme drought conditions. The joint probability is then used to derive the joint return period of dust storms in relation to drought condition.

How to cite: modarres, R. and Mohit Esfahani, P.: Dust storm frequency in relation to extreme droughts in arid regions of Iran, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-1810, https://doi.org/10.5194/egusphere-egu21-1810, 2021.

Several studies have associated high dust years over South Asia to warming of the central or eastern equatorial Pacific Ocean (El Nino conditions) and the resulting weakening of the summer monsoon. Using satellite aerosol data for 2001-2018, we show that there has been a departure from this relation since the second decade of the 21st century with the North Atlantic Ocean emerging as a major driver of interannual variability of dust over South Asia. This change in relation coincides with the end of the global warming hiatus and a shift towards persistent positive phase of the winter North Atlantic Oscillation (NAO). Positive phase of the NAO induces cold phase of the spring/summer North Atlantic sea surface temperature (SST) tripole pattern. We show here that high dust activity during 2011-2018 is associated with positive SST anomaly over the mid-latitude North Atlantic and negative SST anomaly over the sub-tropical North Atlantic: the two southern arms of the SST tripole pattern. Interestingly, the relation between NAO and these two southern arms of the SST tripole has undergone changes in recent years, which has impacted the South Asian monsoon. The result is general drying over South Asia and an increase in the strength of the dust-carrying northwesterlies. Simulations with the Community Earth System Model (CESM) shows that SST tripole-like anomalies recorded during 2011-2018 over the North Atlantic can generate mid-latitude wave train that weakens the South Asian monsoon circulation, leads to surface high pressure anomalies and increase in dust emission and transport over northwest India and Pakistan. Most of the increase in the dust load can be attributed to enhanced transport at 800 hPa pressure level during May-June, which can lead to ~40-50% increase in dust concentrations at this level.

How to cite: Banerjee, P., Satheesh, S. K., and Krishna Moorthy, K.: Recent dust variability over South Asia controlled by North Atlantic SST anomalies, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-12649, https://doi.org/10.5194/egusphere-egu21-12649, 2021.

Desert dust is the most abundant aerosol by mass residing in the atmosphere. It plays a key role in the Earth’s system by influencing the radiation balance, by affecting cloud formation and cloud chemistry, and by acting as a fertilizer for the growth of phytoplankton and for soil through its deposition over the ocean and land.

Due to the nature of its emission and transport, atmospheric dust concentrations are highly variable in space and time and, therefore, require a continuous monitoring by measurements. Dust observations are best exploited by being combined with model simulations for the production of analyses and reanalyses, i.e., complete and consistent four dimensional reconstructions of the atmosphere. Existing aerosol (and dust) reanalyses for the global domain have been produced by total aerosol constraint and at relatively coarse spatial resolution, while regional reanalyses exclude some of the regions containing the major sources of desert dust in Northern Africa and the Middle East.

We present here a 10-year reanalysis data set of desert dust at a horizontal resolution of 0.1°, and which covers the domain of Northern Africa, the Middle East and Europe. The reanalysis has been produced by assimilating in the MONARCH chemical weather prediction system (Di Tomaso et al., 2017) satellite retrievals over dust source regions with specific dust observational constraint (Ginoux et al., 2012; Pu and Ginoux, 2016).

Furthermore, we describe its evaluation in terms of data assimilation diagnostics and comparison against independent observations. Statistics of analysis departures from assimilated observations prove the consistency of the data assimilation system showing that the analysis is closer to the observations than the first-guess. Temporal mean of analysis increments show that the assimilation led to an overall reduction of dust with pattern of systematic corrections that vary with the seasons, and can be linked primarily to misrepresentation of source strength.

Independent evaluation of the analysis with AERONET observations indicates that the reanalysis data set is highly accurate, and provides therefore a reliable historical record of atmospheric desert dust concentrations in a recent decade.

References

Di Tomaso, E., Schutgens, N. A. J., Jorba, O., and Pérez García-Pando, C. (2017): Assimilation of MODIS Dark Target and Deep Blue observations in the dust aerosol component of NMMB-MONARCH version 1.0, Geosci. Model Dev., 10, 1107-1129.

Ginoux, P., Prospero, J. M., Gill, T. E., Hsu, N. C. and Zhao, M. (2012): Global-Scale Attribution of Anthropogenic and Natural Dust Sources and Their Emission Rates Based on Modis Deep Blue Aerosol Products. Rev Geophys 50.

Pu, B., and Ginoux, P. (2016). The impact of the Pacific Decadal Oscillation on springtime dust activity in Syria. Atmospheric Chemistry and Physics, 16(21), 13431-13448.

Acknowledgements

The authors acknowledge the DustClim project which is part of ERA4CS, an ERA-NET initiated by JPI Climate, and funded by FORMAS (SE), DLR (DE), BMWFW (AT), IFD (DK), MINECO (ES), ANR (FR) with co-funding by the European Union (435690462); PRACE (eDUST/eFRAGMENT1/eFRAGMENT2), RES (AECT-2020-3-0013/AECT-2019-3-0001/AECT-2020-1-0007) for awarding access to MareNostrum at BSC and for technical support.

How to cite: Di Tomaso, E., Escribano, J., Ginoux, P., Basart, S., Macchia, F., Barnaba, F., Castrillo, M., Formenti, P., Jorba, O., Mona, L., Montané, G., Mytilinaios, M., Obiso, V., Schutgens, N., Votsis, A., Werner, E., and PérezGarcía-Pando, C.: A 10-year regional reanalysis of desert dust aerosol at high spatial resolution, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-11644, https://doi.org/10.5194/egusphere-egu21-11644, 2021.

The magnitude of the climate forcing associated with mineral dust aerosols remains uncertain, due in part to a lack of direct observations on dust source areas. While modeling and satellite studies provide spatially extensive constraints, these studies must be supported by surface-validating, in situ dust monitoring. Our study focuses on Patagonia, the main source of dust to the southern oceans (>45ºS), a region of low biological productivity potentially susceptible to increased micronutrient fertilization through dust deposition and associated atmosphere‐to‐ocean CO₂ flux. This mechanism is hypothesized to have contributed significantly to the last interglacial‐to‐glacial climatic transition. However, the dust‐phytoplankton biomass connection remains contentious for the present‐day climate system.

We analysed multi-year time series of surface dust-related visibility reduction (DRVR) and dust mass sampling at four downwind coastal monitoring sites, along with key meteorological time series at these same sites. We find that local DRVR across Patagonia is partly controlled by long-term water deficit (i.e., months), while same-day conditions play a smaller role, reflective of water retention properties of fine-grained dust-emitting soils in low-moisture conditions. This conclusion is supported independently by reanalysis data showing that large-scale dust outbreaks are usually associated with anomalously high long-term water deficit. By combining visibility data with surface dust sampling we were able to derive emission rates associated with regional patches of dust-emitting surfaces and test the skill of dust emission schemes to simulate dust activity close to the sources. Our results suggest that the inclusion of long-term hydrologic soil balance may improve the performance of dust emission schemes in climate models.

We also analyzed the impact of southernmost Patagonian dust emissions on southwestern Atlantic Ocean continental shelf and proximal open ocean satellite chlorophyll‐a concentration. We used the DRVR and mass flux time series of the southernmost site to model dust emission, transport, and deposition to the ocean. We then performed a dust event‐based analysis of chlorophyll‐a time series, using a novel approach by which time series are corrected for post‐depositional particle advection due to ocean currents. Finally, we performed total iron determinations, release experiments and iron solid speciation analysis in dust samples. Iron is a key micronutrient limiting phytoplankton biomass in high‐nutrient, low‐chlorophyll oceans such as offshore of the 200‐m isobath off Patagonia. We find no compelling evidence for an influence of dust as an enhancer of phytoplankton biomass either on shelf or proximal open ocean waters of the southwestern Atlantic Ocean. For open ocean waters this is consistent with a lack of source‐inherited bioavailable iron in dust samples. Future case studies addressing similar questions should concentrate on dust sources with identified high contents of bioavailable iron, particularly in the Southern Hemisphere where atmospheric processing of iron-bearing particles is weak.

How to cite: Cosentino, N., Gaiero, D., Ruiz-Etcheverry, L., Lambert, F., Bia, G., Simonella, L., Coppo, R., Torre, G., Saraceno, M., and Tur, V.: Present-day Patagonian dust emissions: Mass flux constraints, meteorological triggers and the effect on phytoplankton biomass, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-156, https://doi.org/10.5194/egusphere-egu21-156, 2021.

In this study, the Weather Research and Forecasting model coupled with chemistry (WRF-Chem) is employed to simulate a dust process in Northwest China during May 2018. The model's ability to simulate the dust process in Northwest China is firstly evaluated using various satellite-retrieved and observational data. The four-dimensional assimilation method is also used to optimize meteorological data and effectively improve the simulation of the dust process.

Fig. 1. Differences of wind field (unit: m/s) between the simulations (a-d: unassimilated; e-h: assimilated) and the observations at 03:00 UTC on 20–23 May.

The comparisons between the simulations based on five dust emission schemes within WRF-Chem and the observations show that, the Shao01 scheme overall has good performance in simulating the emission flux, the spatial pattern of source region, as well as the spatiotemporal variation of dust mass concentration, during this dust process. In comparison to Shao01, the GOCART AFWA and Shao04 schemes can also produce quite similar spatial pattern of dust source region, but tend to overestimate or underestimate dust emission and mass concentration. The Shao11 scheme fails to simulate the dust process since the importance of the fully disturbed particle size distribution is omitted. It is also noted that the GOCART scheme can well reproduce dust emission processes under weak wind erosion but underestimate dust emission flux under strong wind erosion. In addition, the GOCART scheme has produced some spurious emissions and thus blurred the distribution of dust source region.

Fig. 2. The averaged dust emission flux (unit: μg/m²/s) from the GOCART (a), GOCART AFWA (b), Shao01 (c), Shao04 (d) and Shao11 (e) schemes during 17–23 May.

Fig. 3. Variations of daily (a) and hourly (b) surface PM₁₀ concentrations, friction velocity (c) and 10 m wind speed (d) at the Turpan station during 17–23 May.

Northwest China is covered by mountains, basins, deserts and other landforms, thus the complex terrain is one of the key factors to influence the dust process over the region. Our study shows that after being emitted, the airborne dust transported toward the east and west. The dust to the east was diffused rapidly, but the portion toward the west was blocked and accumulated at the edges of the mountains and thus produced dust weather characterized by high dust concentration and long lifetime. The dust accumulated at the edges of the mountains could reach an altitude of more than 6 km due to wind and thermal effect, and finally arrive at Tibetan Plateau and eastern China.

Fig. 4. The simulated (with Shao01 scheme) dust (unit: μg /m³) transport path (a-c) during 20–23 May and vertical profiles of 38.5°N (d) and 85°E (g) at 05:00 UTC on 21 May, 36°N (e) and 95° E (h) at 06:00 UTC on 22 May and 36°N (f) and 98°E (i) at 05:00 UTC on 23 May.

How to cite: Zhao, J., Ma, X., Wu, S., and Sha, T.: Dust emission and transport in Northwest China: WRF-Chem simulation and comparisons with multi-sensor observations, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-4677, https://doi.org/10.5194/egusphere-egu21-4677, 2021.

Mineral dust plays a significant role in climate change and air quality, but large uncertainties remain in terms of dust emission prediction. In this study, we improved the treatments of dust emission process in a Global 3-D Chemical Transport model (GEOS-Chem) v12.6.0, by incorporating the geographical variation of aerodynamic roughness length (Z₀), smooth roughness length (Z_0s), soil texture, introducing Owen effect and Lu and Shao (1999) formulation of sandblasting efficiency α. To investigate the impact of the modifications incorporated in the model, several sensitivity simulations were performed for a severe dust storm during March 27, 2015 to April 2, 2015 over northern China. Results show that simulated threshold friction velocity is very sensitive to the updated Z₀ and Z_0s field, with the relative difference ranging from 10% to 60% compared to the original model with uniform value. An inclusion of Owen effect leads to an increase in surface friction velocity, which mainly occurs in the arid and semi-arid regions of northwest China. The substitution of fixed value of α assumed in original scheme with one varying with friction velocity and soil texture based on observations reduces α by 50% on average, especially over regions with sand texture. Comparisons of sensitivity simulations and measurements show that the revised scheme with the implement of updates provides more realistic threshold friction velocities and PM₁₀ mass concentrations. The performance of the improved model has been evaluated against surface PM₁₀ observations as well as MODIS aerosol optical depth (AOD) values, showing that the spatial and temporal variation of mineral dust are better captured by the revised scheme. Due to the inclusion of the improvement, average PM₁₀ concentrations at observational sites are more comparable to the observations, and the average mean bias (MB) and normalized mean bias (NMB) values are reduced from -196.29μg m^-3 and -52.79% to -47.72μg m^-3 and -22.46% respectively. Our study suggests that the erodibility factor, sandblasting efficiency and soil-related properties which are simply assumed in the empirical scheme may lack physical mechanism and spatial-temporal representative. Further study and measurements should be conducted to obtain more realistic and detailed map of these parameters in order to improve dust representation in the model. 

How to cite: Tian, R., Ma, X., and Zhao, J.: A revised mineral dust emission scheme in GEOS-Chem: improvements in dust simulations over China, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-9167, https://doi.org/10.5194/egusphere-egu21-9167, 2021.

Mineral dust is an important component of the climate system, affecting radiation, cloud formation, biogeochemical cycles, as well as having negative effects on solar energy budget and human health. All these processes are affected from the size of the particles which is significantly underestimated by the Earth System Models. Here, we present results from a first attempt to modify the size distribution parameterizations in the GOCART-AFWA dust scheme of WRF - Chem, by including the large dust particles with diameters greater than 20 µm to describe the mineral dust cycle. The parameterization is based on Saharan dust observational datasets from FENNEC and SAMUM campaigns. We investigate the impact of the extended size distribution on the overall transported dust load and also the impact of particle settling considerations in deposition rates. The model results are compared with airborne dust measurements from AER-D campaign. In order to achieve the best agreement with the observations, an artificial force that counteracts gravity approximately by 80% for the large particles is needed, indicating the presence of one or more under-represented physical processes in the model.

Acknowledgment: This research was supported by D-TECT (Grant Agreement 725698) funded by the European Research Council (ERC) under the European Union's Horizon 2020 research and innovation programme. 

How to cite: Drakaki, E., Tsekeri, A., Amiridis, V., Solomos, S., Gkikas, A., Proestakis, E., Spyrou, C., Mallios, S., Marinou, E., Ryder, C. L., and Katsafados, P.: A modeling insight into the transport of large dust particles, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-7374, https://doi.org/10.5194/egusphere-egu21-7374, 2021.

The aeolian dust deposits in the Chinese Loess Plateau (CLP) contain valuable information about past environmental changes in Asia. Unlocking this information requires knowledge on the Asian dust sources and dust transport mechanisms, and how the different source regions contribute to the total dust loading and deposition over the CLP.  By studying the dust transport and deposition under present day conditions using the Lagrangian Particle Dispersion model,  FLEXPART,  and the FLEXDUST dust emission model, we aim to better understand the dust signal in the Chinese loess records to constrain their interpretation as paleoclimate proxies.  

Here we present results from a 20 year simulation of transport and deposition of aeolian dust over the CLP from 1999 until 2019, during the dust event season March until May. Both FLEXPART and FLEXDUST are driven by ERA5 ECMWF meteorological reanalysis data. FLEXPART is set up in a receptor oriented configuration, where many computational particles are released from the receptor points at each timestep. The computational particles are followed for 5 days backward in time probing for possible source regions. The end product is emission sensitivity, i.e. how sensitive the receptor is to emissions in possible source regions. The emission sensitivity establishes a linear relation between the source and receptor. Therefore, multiplying the emission sensitivity with the dust emission flux estimated by FLEXDUST produces a map of the source contribution for each receptor point. To investigate the difference in source regions between the fine and coarse dust, we include two particle sizes, 2 μm and 20 μm, in our simulation. The output from the model is compared against Asian polar vortex (APV) and Asian winter monsoon indices to identify how changes in the large scale atmospheric circulation affect the interannual variation of dust transport and deposition, and to determine whether the amount of deposited dust over the CLP is primarily governed by changes in the emission strength or by changes in the atmospheric circulation.  

How to cite: Haugvaldstad, O., Tang, H., Kaakinen, A., and Stordal, F.: Aeolian dust sources, transport and deposition over the Chinese Loess Plateau during 1999-2019: A study using the FLEXDUST and FLEXPART models, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-3870, https://doi.org/10.5194/egusphere-egu21-3870, 2021.

Saltations, secondary knock-out of particles, and their rolling over the surface in the abrasion process are the main source of micron- and submicron-sized particles near the surface [1]. Zones with different aerosol generation rates and wiping dynamics emerge around growing aeolian structures [3,4]. On the leeward slope, larger particles remain in the embedding zone and abrasion is less active. On the windward slope, fractions of smaller size accumulate in the zone of cascade capture of layers by wind [2], and abrasion is predominant.

The occurrence of aeolian forms varies in time depending on their height. Three areas are considered: 1-3 m, 1-3 cm, <1 cm. The effect of changes in wind direction at intervals of a few hours changes the length of zones near aeolian structures. Thus, the cascade trapping zone expands and the accumulation zone narrows. Aeolian microstructures on the surface of the windward slope decrease the length of the cascade capture zone, leaving structures with a height > 1 cm almost unchanged.

We consider a sample of data from summer field measurements obtained in the evening with close values of air temperature (30-32°C) and wind speeds (6.1-6.5 m/s). Observations were made on a perennial patch of unfixed sands about 1.5 km long and 200-300 m wide at 5 km to the west of Naryn Khuduk settlement (Kalmykia, 2010-2020). The lines of dune ridges for this area extend approximately in the latitudinal direction.

Based on the empirical functions of aerosol size and mass distribution, the classification related to the wind direction in relation to the line of windward and leeward slopes connection was obtained. When the wind direction changes from frontal to tangential along the slopes, mass concentrations of coarse aerosol fraction increase. This can be related to the processes of chipping for newly involved large particles from the layers of the leeward slope setting zone. The phenomenon is also illustrated by the observed emergence on the surface of a ripple with a ridge spacing of 10-30 cm during the next day of a micro-ridge with a period of 1-2 cm. For the windward slope line change model [5], it was obtained that the fraction of detached particles decreases with the growth of new structures. The presence of aeolian ripples [6] and larger particles generally reduces the fraction of particles moving in the wind flow.  There is weakening of wiping intensity at collision and reduction of concentration of submicron particles as a result, as compared to the case of absence of developed microrelief. The type of aerosol distribution function is influenced by the size of the embedding and cascade trapping zones and the composition of the layer of particles involved in collisions and displacements near the surface.

The study was supported by the Russian Science Foundation project 20-17-00214.

1.Houser C.A., Nickling W.G. Sedimentology. 48(2). 255,. (2001)

2.Chepil W.S. Soil Science  60(4) 305.(1945)

3.Anderson R. Sedimentology 34, 943 (1987).

4.Hoyle R., Woods A. Phys. Rev. E 56, 6861 (1997).

5.Malinovskaya E.A. Izvestiya. Atmospheric and Oceanic Physics 55(2) 218 (2019)

6. Malinovskaya E. et al. EGU2019-3693-1 (2019)

How to cite: Malinovskaya, E., Chkhetiani, O., and Maksimenkov, L.: On the relationship of aeolian relief, microrelief and wind direction with the concentration of dust aerosol in the near-surface layer, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-14013, https://doi.org/10.5194/egusphere-egu21-14013, 2021.

Dust aerosols consist on a variety of minerals with different physic and chemical properties. As such, they interact with short and long wave radiation, potentially form clouds, act as nutrients modulating biogeochemical cycles, or influence atmospheric chemistry, differently. Most current state-of-the-art Earth System Models (ESMs) neglect the complexity in dust composition, mainly due to computational constraints, but also to the existing uncertainties in the size resolved composition of parent soils, the resulting distribution of minerals in airborne dust, and the scarcity of observations to constrain them.

Within this work, we assess the variability of global dust composition due to uncertainties in the characterization of the parent soil mineralogy. To that end, we consider two available global soil mineralogy atlases, developed by Claquin et al. (1999) –C1999- and Journet et al. (2014) –J2014-, which represent respectively 8 and 12 relevant minerals for climate (namely: illite, smectite/montmorillonite, kaolinite, calcite, gypsum, hematite, quartz, and feldspars in C1999, and those plus chlorite, vermiculite, goethite, and mica in J2014). Thanks to a recently developed feature of the MONARCH atmospheric-chemistry model, we are able to explicitly resolve the minerals’ atmospheric cycle. Therefore, we define two global experiments to assess changes on airborne dust composition attributed to the soil mineralogy assumptions and provide a measure of their variability. We also perform a preliminary evaluation of the global mineralogy results against available observations of mineral fractions in surface dust concentration.

Our results will inform the climate modelling community about the potential variability in dust composition, an aspect that will gain relevance as ESMs continue growing in complexity and new processes to better characterize aerosols’ forcing or biogeochemical cycles are added. Further observational constraints, such as those that will derive from the EMIT NASA mission on soil composition or the FRAGMENT experimental campaigns on airborne dust characterization, will be key in the near future to improve our understanding of the impact of dust mineralogy on fundamental climate features.

How to cite: Gonçalves Ageitos, M., Dawson, M., Obiso, V., Klose, M., Miller, R., Jorba, O., and Pérez García-Pando, C.: Variability in modelled airborne dust mineralogy derived from global soil composition uncertainties, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-10848, https://doi.org/10.5194/egusphere-egu21-10848, 2021.

In the semi-arid Sahel region, wet deposition can represent more than half of the total annual deposition and are associated to different rainfall types, from stratiform precipitation to convective systems. Surface parameters such as temperature, wind speed, wind direction as well as rainfall rate can be used to distinguish these situations. We investigate the behaviour of dust wet deposition at the event-scale based on a multiannual (2007 to 2016) monitoring of wet deposition fluxes, PM10 concentration, precipitation and meteorological parameters in two Sahelian stations Banizoumbou (Niger, 13.54°N, 2.66 E) and Cinzana (Mali, 13.28°N, 5.93°W) of the INDAAF network. Rainfall events have been classified into three types: (i) stratiform, convective associated with (ii) weak precipitation or (iii) intense precipitation. This classification is based on selected criteria regarding evolutions of surface temperature, of wind speed and direction before and after the rainfall onset as well as on the event rainfall rate. Based on an interpretation of hundreds of single events, almost 25% of wet deposition events are associated with non-convective situation, more than 40% with atmospheric convective situation and weak precipitation, and more than 35% events with atmospheric convective situation combined with intense precipitation. This exhaustive work over a long-time period of measurements illustrates the predominance of convective situations regarding wet deposition in the two Sahelian stations. Washout ratios (WR) have been computed from PM10 concentrations, precipitation and deposition fluxes for each kind of events when data were concomitant. The dependency of WR to precipitation amount is shown to differ depending on the rain types. For instance, the decreasing dependency of WR with the precipitation amount of non-convective events has been quantified and could be explained by a dilution effect of the deposition. On the contrary, no clear dependency of WR with the precipitation has been observed for atmospheric convective conditions associated with intense rainfall rate.

How to cite: Audoux, T., Laurent, B., Marticorena, B., Bergametti, G., Rajot, J. L., Féron, A., and Gaimoz, C.: Multiannual study of convective and stratiform situations associated to wet deposition of desert dust in the Sahelian band, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-4359, https://doi.org/10.5194/egusphere-egu21-4359, 2021.

Aeolian Saharan mineral dust particles can be transported over long distances. Great amounts of Saharan mineral dust particles are transported westwards over the Atlantic Ocean towards the Caribbean islands especially during the boreal summer months. During the transport they can either have a direct environmental effect by absorbing, emitting and scattering radiation or an indirect effect by changing cloud micro-physical properties and by modifying cloud lifetime or formation.

Our recent studies indicate that elevated transported Saharan dust layers, so-called Saharan Air Layers (SALs), come along with enhanced concentrations of water vapor compared to the surrounding atmosphere. Radiative transfer simulations reveal that not the dust particles inside the SALs but the enhanced concentrations of water vapor play the dominant role for atmospheric heating in dust-laden subtropical regions. In this way water vapor has the potential to impact both atmospheric stability and turbulent properties not only inside the SALs but also at lower atmospheric levels.  To study the effects of water vapor on atmospheric turbulence and stability in SAL-regions, we performed wavelet analyses as well as calculations of power spectra on the basis of airborne lidar backscatter and water vapor measurements by the DLR lidar system WALES during the NARVAL-II research campaign. For an in-depth investigation of SAL-properties, several research flights during NARVAL-II were designed to lead over dust-laden regions upstream the Caribbean island of Barbados. Our analysis shows that water vapor heating does not only have an effect on the stability and turbulence of SALs by maintaining their confining inversions and promoting vertical mixing in their interior, but also hinders the development of shallow marine convection below.

In our presentation we will give an overview of the performed measurements and radiative transfer simulations as well as of the conducted stability and turbulence analyses by means of calculated power spectra and wavelet analyses.

How to cite: Gutleben, M., Groß, S., and Wirth, M.: Impacts of long-range-transported Saharan dust layers on atmospheric stability and turbulence in the trades, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-7063, https://doi.org/10.5194/egusphere-egu21-7063, 2021.

Mineral dust plays an important role in the ocean’s carbon cycle through the input of nutrients and metals which potentially fertilise phytoplankton, and by ballasting organic matter from the surface ocean to the sea floor. However, time series and records of open-ocean dust deposition fluxes are sparse. Here, we present a multi-year time series of Saharan dust collected by dust-collecting buoys that are monitoring dust in the equatorial North Atlantic Ocean as well as by moored sediment traps at the buoys' positions at ~21°N/21°W and ~11°N/23°W. We present dust-flux data as well as particle-size distribution data, and make a comparison of the dust collected from the atmosphere at the ocean surface with the dust settling through the ocean and intercepted by the submarine sediment traps. See: www.nioz.nl/dust

How to cite: Stuut, J.-B., Guerreiro, C., Brummer, G.-J., and van der Does, M.: Present-day Saharan dust observed over the Atlantic Ocean, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-7449, https://doi.org/10.5194/egusphere-egu21-7449, 2021.

For the in-orbit calibration and validation of the Aeolus products, ESA organized the Aeolus Tropical campaign, which will take place on June-July 2021 at Cape Verde region. During the campaign, Aeolus underfights will be performed with several aircrafts (by DLR, NASA, LATMOS, and the University of Nova Gorica (UNG)) and advanced ground-based instrumentation will be deployed in Mindelo island within ASKOS (https://askos.space.noa.gr/) experiment. ASKOS observations will provide an unprecedented dataset for the aerosol and wind conditions in the region, in order to provide reference values for the Cal/Val of the mission. Apart from the main aerosol Cal/Val objective of ASKOS, the foreseen synergistic activities will provide a wealth of information to address scientific questions posed by the participating groups on dust characterization, transportation and it’s impact of radiation and cloud formation.

Here, we report on the status of the ASKOS preparations for the evaluation of the aerosol and cloud product, focusing on the instrumentation requirements and availability, as well as the engagement of the scientific community so far. ASKOS will deploy advanced ground-based and airborne remote sensing and in-situ instrumentation, including the full ACTRIS aerosol and cloud remote sensing/in-situ facilities and airborne in-situ sensors to be operated on drones and/or aircrafts. The main ground-based remote sensing instrumentation in Cape Verde will consist of sophisticated lidar systems, including the EVE lidar, a circular polarization system that is tailored to mimic the Aeolus measurement from ground, the multi-wavelength Polly-XT and the WALL-E prototype for detecting particle orientation. The instrumentation will also include sun-photometers such as AERONET-CIMEL, but also polarimeters to advance microphysical retrievals for non-spherical particles such as dust. Cloud remote sensors including a cloud radar and a microwave radiometer will operate in parallel along with meteorological radiosondes. In-situ sensors at surface and onboard UAVs and light aircrafts will be available. ASKOS will be fully supported by several operational modeling simulations for meteorological and atmospheric composition forecasting. ASKOS will remain open to contributions from other communities and research groups and more synergies will be pursued in the future.

How to cite: Marinou, E., Amiridis, V., Mavropoulou, I., Baars, H., Kazadzis, S., Rosoldi, M., Ene, D., Barreto, A., Casadio, S., Zenk, C., Sciare, J., Mocnik, G., Kandler, K., Stuut, J.-B., Rodrigez, S., Knipertz, P., Rutz, T., Komppula, M., Daskalopoulou, V., and Hloupis, G. and the ASKOS team: The ASKOS experiment for the validation of Aeolus L2A aerosol product, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-13781, https://doi.org/10.5194/egusphere-egu21-13781, 2021.

The new polarization lidar nicknamed “WALL-E” is designed to monitor dust orientation. Dust orientation has not been extensively investigated for the Earth’s atmosphere, where dust is considered to be randomly-oriented. For monitoring dust orientation, the new polarization lidar emits linearly- and elliptically-polarized light at 1064 nm and detects the linear and circular polarization of the backscattered light. This is done with two lasers emitting in an interleaved fashion, and two telescopes collecting the backscattered light from both lasers. The measurements are performed at variable viewing angles and provide direct flags of dust orientation, along with more detailed information on particle microphysics. The first measurements for dust in Athens are presented.

Acknowledgements. The work is supported by the European Research Council under the European Community’s Horizon 2020 research and
innovation framework program/ERC grant agreement 725698 (D-TECT). We acknowledge PRACE for awarding us access to MareNostrum
at Barcelona Supercomputing Center (BSC), Spain. The work was supported by computational time granted from the Greek Research &
Technology Network (GRNET) in the National HPC facility - ARIS - under project ID pa170906-ADDAPAS, pr005038-REMOD and pr009019-EXEED.

How to cite: Tsekeri, A., Freudenthaler, V., Amiridis, V., Doxastakis, G., Louridas, A., Georgoussis, G., Metallinos, S., Gasteiger, J., Siomos, N., Paschou, P., Georgiou, T., Tsaknakis, G., Evangelatos, C., and Binietoglou, I.: Polarization lidar for detecting dust orientation: first measurements, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-13039, https://doi.org/10.5194/egusphere-egu21-13039, 2021.

The physical and chemical properties of dust, i.e. its particle size distribution (PSD), mineralogical composition, shape and mixing state determine its climate effects. However, the lack of experimental data and understanding of the emitted dust and its relationship with the parent sediment and atmospheric forcing limit the extension of climate and dust models to account for potentially important regional variations in dust properties. In this context, the FRontiers in dust minerAloGical coMposition and its Effects upoN climate (FRAGMENT) project is dedicated to understand, constrain and calculate the global mineralogical composition of dust along with its effects upon climate. In September 2019, we conducted an intensive dust field campaign as a part of FRAGMENT near M’hamid El Ghizlane in Morocco, at the edge of the Sahara Desert. During the measurement period, dust events occurred frequently (about every 1-2 days) with varying intensity.

In this contribution, we provide a comprehensive overview and analysis of the sediment and airborne samples collected, and of the time-resolved measurements of dust concentration, PSD, optical properties and atmospheric forcing. We use mineralogical analyses of wet-sieved (totally disturbed) and dry-sieved (minimally disturbed) sediment samples at high particle-size resolution to better understand the fragmentation of sediment aggregates during wind erosion. We analyse the temporal variability of the number and volume PSDs along with the associated size-resolved dust emission fluxes using data from three optical particle counters deployed at different heights. We discuss the size-resolved particle composition, morphology, and mixing-state of the suspended dust determined by single particle analysis with electron microscopy coupled with energy dispersive X-ray detection from samples collected on sticky carbon substrates with cascade impactors, flat-plate samplers, and free-wing impactors. Finally, scattering coefficients at 450, 525 and 635 nm and seven different angles (from 0º to 90º) obtained with a polar nephelometer and absorption coefficients at 370, 470, 520, 590, 660, 880 and 950 nm obtained with an aethalometer are used to analyse the variability of extensive and intensive optical parameters, such as scattering and absorption Ångström exponents (SAE and AAE), backscatter fraction (BF) and multi-wavelength single scattering albedo (SSA) for both PM2.5 and PM10 dust fractions in combination with PSD and meteorological measurements.

How to cite: Pérez García-Pando, C., González-Florez, C., González-Romero, A., Panta, A., Yus-Díez, J., Alastuey, A., Kandler, K., Klose, M., Querol, X., Reche, C., Pandolfi, M., Dupont, S., Etyemezian, V., Nikolich, G., Escribano, J., Clark, R., Elhmann, B., Greenberger, R., Tajeddine, K., and Ivančič, M.: Towards understanding the size distribution, composition and optical properties of freshly emitted dust and its relationship with the parent sediment, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-13606, https://doi.org/10.5194/egusphere-egu21-13606, 2021.

Salt particles from saline lakes and playas play important roles in many processes related to atmospheric chemistry and climate system, especially active in aerosol and cloud formations due to their high hygroscopicity and efficient ice nucleation ability. However, physiochemical natures of these salts are relatively poorly understood due to their chemical complexity. Deepened understandings on playa-origin aerosol particles are desired and are expected to improve current climate models. Only a few studies have investigated the climate impacts of the salts from saline lakes and playas, from the perspectives of hygroscopicity, cloud condensation nuclei activity and ice nucleation ability.^1-3

In this study, the investigated salts are collected from the Qaidam Basin, which is one of the largest regions of saline lakes and playas on Earth. Four saline lake areas (Chaka, Keke, Qarhan and Mang’ai) are selected as the sampling sites, and four forms of samples are compared, including lake brines, crystalized brines, lakebed salts and crust salts. The cations (Na⁺, K⁺, Mg²⁺ and Ca²⁺) and anions (Cl⁻, SO₄²⁻, and NO₃⁻) are simultaneously measured by the ion chromatography. A vapor sorption analyzer is used to measure the hygroscopic properties. To thoroughly understand the hygroscopic behaviors, the AIOMFAC model is used to predict the deliquescence RH (DRH) based on the chemical matrix of each sample.

From the ionic composition perspective, the crystalized brines and the brines show similar ionic textures, indicating that the crystalized brines well reflect the complex mineral composition of brines. In contrast, the natural solid salts, including lakebed salts and crust salts, show distinct mineral compositions from the brines, i.e., mainly NaCl, regardless of chemical composition of nearby lakes, suggesting that halite is the prevailing salt on the massive landscape exposed to the atmosphere. The hygroscopicity experimental results are well described by the AIOMFAC model, based on the ionic composition. The results show that the water uptake by crystalized salts is initialized by MgCl₂ at RH 30-40%. For natural salts, the hygroscopic behavior is similar to NaCl except for the QH lakebed salt, which is co-influenced by both NaCl and KCl. The findings presented in this study improve our understandings of the physical and chemical properties of surface salts spread across the Qaidam Basin, and the implications to climate systems on Planet Earth and Mars are discussed.

Reference

¹ K. A. Koehler et al., Journal of Geophysical Research: Atmospheres 112 (2007)

² K. A. Pratt et al., J. Geophys. Res.-Atmos. 115, D15301 (2010) 17.

³ M. Tang et al., Journal of Geophysical Research: Atmospheres 124 (2019) 10844.

How to cite: Li, J., Liu, W., Zhang, X., Wang, S., and Kong, X.: Chemical and Hygroscopic Characterization of Surface Salts in Qaidam Basin: Implications for Climates, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-1208, https://doi.org/10.5194/egusphere-egu21-1208, 2021.

Despite its importance, hygroscopicity of mineral dust aerosol remains highly uncertain. In this work, we investigated water adsorption and hygroscopicity of different mineral dust samples at 25 ∘C, via measurement of sample mass at different relative humidity (RH, up to 90 %) using a vapor sorption analyzer. Mineral dust samples examined (21 in total) included seven authentic mineral dust samples from different regions in the world and 14 major minerals contained in mineral dust aerosol. At 90 % RH, the mass ratios of adsorbed water to the dry mineral ranged from 0.0011 to 0.3080, largely depending on the BET surface areas of mineral dust samples. The fractional surface coverages of adsorbed water were determined to vary between 1.26 and 8.63 at 90 % RH, and it was found that the Frenkel–Halsey–Hill (FHH) adsorption isotherm could describe surface coverages of adsorbed water as a function of RH well, with AFHH and BFHH parameters in the range of 0.15–4.39 and 1.10–1.91, respectively. The comprehensive and robust data obtained would largely improve our knowledge of hygroscopicity of mineral dust aerosol.

How to cite: Tang, M., Chen, L., Peng, C., and Gu, W.: On mineral dust hygroscopicity, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-576, https://doi.org/10.5194/egusphere-egu21-576, 2021.

Salt aerosol from saline lakes and playas has been recognized to affect climate in the global scale, but the understandings of the chemical and physical natures of these salts are still limited due to their complex chemical composition. The Qaidam Basin, one of the largest and driest deserts on Earth, is composed of many saline lakes and is regarded as a good terrestrial analogue for Mars due to similar environment conditions and elementary composition(Xiao et al., 2017). The study on the chemical characteristics of salts from Qaidam Basin is helpful to explore their influences on climate and reveal the physical and chemical factors affecting the paleoclimate of both Planet Earth and Mars.

In this study, four types of salt samples (brines, crystalized brines, lakebed salts and crust salts) collected at and near four saline lakes (Chaka, Keke, Qarhan and Mang’ai) in the Qaidam Basin are studied for their physicochemical characteristics. The common cations (Na⁺, K⁺, Mg²⁺ and Ca²⁺) and anions (Cl⁻, SO₄²⁻, and NO₃⁻) are determined by ion chromatography (IC), and the elemental compositions are measured by energy dispersive X-ray fluorescence (EDXRF) spectrometry. The chemical composition results are analyzed by positive matrix factorization (PMF)(Paatero and Tapper, 1994). The pH of sample brines and solutions are measured, and the governing factors are discussed.

The common elements detected by XRF and IC have excellent consistency. Notably, the crystalized brines exhibit similar ionic compositions with brines, suggesting that the crystalized brines well reflect the complex mineral composition of brines and evaporative crystallization can be used for brine preservation. However, the natural solid salts (lakebed salts and crust salts) present obvious composition differences. Mg₂⁺ and SO₄^2- are primarily found in brines, while the natural solid salts are dominated by NaCl and KCl. The pH of the brines and salt solutions are found to correlate to Mg²⁺ concentrations and potentially affected by ambient CO₂ uptake. The electrical conductivities of sample solutions are not linearly scaled by the dilution factors, indicating that balanced reactions and buffer systems exist in the salt textures. Three interpretable factors are identified by the PMF analysis, and the differences of sample types and sampling sites are clearly reflected by the three factors. The lakebed salts (except for the QH lakebed salt) presented excellently correlation with the crust salts, and the crystalized salts are greatly correlated with the brines. This study improves the understandings of the physiochemical features of saline lake and playa salts in Qaidam Basin, and the roles that surface salts potentially play in the climate systems of both Planet Earth and Mars are discussed.

Reference

Paatero, P., and Tapper, U., Environmetrics, 5, 111-126, 1994.

Xiao, L., Wang, J., Dang, Y., et al., Earth-Sci Rev, 164, 84-101, 2017.

How to cite: Liu, W., Li, J., Santos, L., Boman, J., Zhang, X., Wang, S., and Kong, X.: Chemical Characterization of Saline Lake and Playa Salts in Qaidam Basin: Implications for Climates of Planet Earth and Mars, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-1233, https://doi.org/10.5194/egusphere-egu21-1233, 2021.

Abstract

The DONAIRE network (Pey et al. 2020) monitors the phenomenology of geochemical, magnetic and mineralogical variations of bulk atmospheric deposition in the Iberian Peninsula- Balearic Island. In this work we focus on recent North African dust deposition with a double objective: 1) to characterize the main geochemical fingerprints with respect to other sources of pollution; 2) to perform a source apportionment study to identify different desert-dust source areas. We used one year of data (June 2016-July 2017) from 15 monitoring sites (regional and remote, urban, industrial, or agricultural). We focus here on the impact caused by the main 4 North African dust deposition events globally affected this network.

Our results evidence that dust deposition patterns are controlled by: i) the meteorological scenario behind dust transport, ii) the occurrence/absence of wet deposition, and iii) the local-to-regional nearby topography. In general, the largest dust-deposition events occur nearby mountain barriers during low-pressure systems approaching Iberia and NW Africa.

Moderate to intense dust deposition events are well characterized by their chemical composition. The Fe/Ti, Na/Al, K/Al or (Ca+Mg)/Fe ratios reveal a number of patterns across the network. For example, Fe/Ti ratio varies from around 10-13 during warm-season events to 22-35 during cold season episodes, potentially indicating different North-African dust sources.

The best source apportionment solution extracts 10 factor/sources, from which three are mineral in composition. Two of them are interpreted as different North African dust mixture-of-sources, whereas the third mineral factor corresponds to regional dust particles. The overall contribution of such desert-dust sources may explain up to 90% of total episodic deposition during the most intense events.

These results indicate that chemical fingerprinting could be used to infer the recent North African dust deposition history. Studies on lake and peatland sequences following a similar approach are in progress and preliminary data show they be used to trace Saharan dust during the Holocene and reconstruct its relationship with climate phases.

Reference

Pey J., Larrasoaña J.C., Pérez N., Cerro J.C., Castillo S. et al. (2020). Phenomenology and geographical gradients of atmospheric deposition in southwestern Europe: results from a multi-site monitoring network. Sci. Tot. Environ., 140745. https://doi.org/10.1016/j.scitotenv.2020.140745.

Acknowledgements

POSAHPI (PID2019-108101RB-I00) and DONAIRE (CGL2015-68993-R) projects funded by Spanish Agencia Estatal de Investigación and FEDER Funds.

How to cite: Pey, J., Larrasoaña, J. C., Reyes, J., Pérez, N., Cerro, J. C., Castillo, S., Mata, M. P., Orellana-Macías, J. M., Causapé, J., Valero-Garcés, B. L., Oliva-Urcia, B., Santos-González, J., and González-Gutiérrez, R. B.: Geochemical fingerprints and North-African dust sources: results from a multisite network of aerosol deposition in the south-western Europe, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-10896, https://doi.org/10.5194/egusphere-egu21-10896, 2021.

Airborne desert dust is one of the most abundant aerosols and an important factor in climate
change. After deposition in the sea, mineral dust acts as the nutrient. In this study, the climatology
of desert dust deposition in the Adriatic Sea was investigated with special reference to the possible
source and mineralogical characteristics of transported dust from North Africa. The effect is
particularly examined in unique, isolated marine system, Rogoznica Lake (RL; 43° 32 ’N, 15° 58’
E) through its biological response.
For that purpose, the MERRA-2 reanalysis data for dust deposition in the period 1989-
2019 were used. Annual dust deposition cycle in the Adriatic Sea has maximum in spring and fall
with stronger deposition in central and south. Wet deposition accounts for 63-92% of total
deposition and 75% of data contains less than 1.5% of the mass. Intensity classes are defined for
the remaining 25% and each refers to about 30% of the mass. On average, over 73 days per year
is of weak, 14.6 of moderate, and 3.65 of extreme intensity, which varies spatially. In order to
detect the specific synoptic patterns for the dust transport in relation to the dust sources activity
and deposition in the Adriatic Sea, the EOF analysis on 850 hPa was utilized. Positive or negative
mode phases correspond to deposition anomalies in the Adriatic Sea and can be related to particular
dust sources in North Africa.
Given the seasonal strong physicochemical stratification, relatively small volume, and only
source of freshwater and nutrients through precipitation during stratification, the Rogoznica Lake
proved ideal for monitoring desert dust deposition events, by monitoring nutrient concentration in
the surface layer (0–2 m). For the 2000-2012 period no correlation with MERRA-2 deposition
time series were found, but biological activity as a direct consequence of nutrient increase was
observed during deposition events. Since the Adriatic Sea was proved to be phosphate (P) and iron
(Fe) limited, the mineralogical database was used to estimate the amount of deposited P and Fe
during intense deposition events.

How to cite: Mifka, B., Ciglenečki, I., and Telišman Prtenjak, M.: Climatology of dust deposition in the Adriatic Sea and biological response of Rogoznica Lake (central Adriatic), EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-5793, https://doi.org/10.5194/egusphere-egu21-5793, 2021.

Loess is an important archive of environmental change covering approximately 10% of the Earth’s terrestrial surface. Numerous studies have analyzed loess deposits and in particular loess-paleosol sequences. To analyze these sequences, it is important to know the spatial distribution of aeolian sediments, their location relative to potential source areas, and the geomorphology of the sink area. We investigated these aspects by compiling a new map of aeolian sediments in Europe using highly resolved geodata from 27 countries (Lehmkuhl et al., in press). To determine the most relevant factors for the European loess distribution, we further mapped potential source areas and divided the map into different facies domains. We analyzed the geomorphological and paleoenvironmental effects on the deposition and preservation of Late Pleistocene loess. Finally, the geodata-based results were compared with results obtained from high-resolved regional numerical climate-dust experiments for the Last Glacial Maximum (LGM) in Europe, which were performed with the LGM-adapted Weather Research and Forecasting model coupled with Chemistry (WRF-Chem-LGM; Schaffernicht et al., 2020).  Complementing the mapping-based findings with the WRF-Chem-LGM experiments results in an improved understanding of the Late Pleistocene loess landscape in Europe.

References:

Lehmkuhl, F., Nett, J.J., Pötter, S., Schulte, P., Sprafke, T., Jary, Z., Antoine, P., Wacha, L., Wolf, D., Zerboni, A., Hošek, J., Marković, S.B., Obreht, I., Sümegi, P., Veres, D., Zeeden, C., Boemke, B., Schaubert, V., Viehweger, J., Hambach, U. (in press). Loess landscapes of Europe – Mapping, geomorphology, and zonal differentiation. Earth-Science Reviews. Doi: https://doi.org/10.1016/j.earscirev.2020.103496

Schaffernicht, E.J., Ludwig, P., Shao, Y., 2020. Linkage between dust cycle and loess of the last Glacial Maximum in Europe. Atmospheric Chemistry and Physics 20, 4969–4986. Doi:10.5194/acp-20-4969-2020.

How to cite: Nett, J. J. (., Lehmkuhl, F., Schaffernicht, E. J., Pötter, S., Schulte, P., Ludwig, P., Sprafke, T., and Hambach, U.: Comparing a new paleomap of European loess landscapes to an atmospheric dust circulation model, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-4345, https://doi.org/10.5194/egusphere-egu21-4345, 2021.

Different climate and environmental conditions dominated in the Carpathian Basin and the adjacent northern Italy/Adriatic region during the Last Glacial Maximum (LGM), as compared to today. For instance, high dust accumulation rates recorded in loess deposits point to an active dust cycle during the LGM. We investigated the climate conditions and regional dust cycle based on high-resolution (grid spacing of ~8.5 km) regional climate simulations for LGM conditions. The model output is in good agreement with proxy data, reproducing cold and dry conditions for the LGM. Highest dust emissions are simulated to the east of the Alpine ice sheet and in the Kvarner Bay region. While simulated dust deposition plumes in the northern Carpathian Basin indicate prevailing northerly (NW, N and NE) winds during dust events, strong Bora winds flowing down the slopes of the Dinaric Alps appear to play a major role in the local to regional dust cycle in the northern Adriatic region. From a seasonal perspective, the simulated dust cycle is most active during late winter and spring. A detailed analysis of climate and environmental conditions at key areas reveals that high wind speeds and low precipitation rates during late winter and spring correlate well with high dust emissions. In contrast, lower wind speeds, increasing precipitation, and the greening of vegetation prevent high dust emissions during summer and autumn. The occurrence of cyclonic circulation patterns in the Adriatic shelf region reveals that individual cyclones played an important role in transporting dust particles from the alluvial Po plain towards the eastern Adriatic loess deposition sites.

How to cite: Ludwig, P., Gavrilov, M. B., Markovic, S. B., Ujvari, G., and Lehmkuhl, F.: Simulated regional dust cycle in the Carpathian Basin and the Adriatic Sea region during the Last Glacial Maximum, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-5227, https://doi.org/10.5194/egusphere-egu21-5227, 2021.

Loess deposits are globally important dust archives but are often limited by imprecise chronological control. In particular, loess records adjacent to former ice sheets seldom have detailed, independent age models yet have the potential to elucidate the causes of past high latitude (>50° N in Northern Hemisphere) coarse dust emission close to former ice sheets, a relatively poorly known aspect of past dust dynamics. Loess deposits in southern Britain were formed in close proximity to western parts of the last glacial Eurasian ice sheets. However, currently their age and accumulation rate remain poorly known, limiting interpretation of the controls on last glacial coarse dust emission and deposition in the region.

Here we apply high sampling resolution quartz optically stimulated luminescence (OSL) to constrain the timing of dust accumulation and loess formation at the Pegwell Bay site in east Kent, SE England. The OSL ages and Bayesian (Bacon) age modelling results are the most detailed to date for western European loess, and show that loess began to accumulate around c. 25 ka, coinciding with Heinrich event 2 and the coupling of Fennoscandian and British-Irish ice sheets. There were two phases of greatly enhanced dust accumulation at the site, at 25-23.5 ka and 20-19 ka, separated by a lower accumulation rate period. Loess accumulation appears to have stopped or been dramatically reduced after 19-18 ka. We propose that the dynamics of the British-Irish and Fennoscandian Ice Sheets, associated glacial lake drainage, and linked reorganisations of atmospheric circulation, act to control loess accumulation at the site. In particular, we argue that both periods of enhanced dust accumulation were caused by advance-retreat phases of the North Sea ice lobe, and associated drainage of Dogger Lake. These events would have led to abrupt input of sediment-rich ice dammed lake and melt water from northern and eastern England and the North Sea into the exposed southern North Sea basin. This would have dramatically increased sediment availability for transport and deposition as loess in SE England. Easterly and north-easterly winds that could have transported this dust to SE England would have been enhanced by presence of an ice sheet anticyclone, enlarged during Fennoscandian and British-Irish ice sheet coalescence, as well as katabatic winds and easterly flow occurring on the northern side of Atlantic cyclones forced south of southern Britain by the extended western British-Irish ice sheet. As such, last glacial dust dynamics and loess accumulation in Britain is highly influenced by the interaction of the British-Irish and Fennoscandian ice sheets, Atlantic storm tracks, and the topography and drainage of the exposed North Sea basin.

How to cite: Stevens, T., Sechi, D., Bradák, B., Orbe, R., Baykal, Y., Cossu, G., Tziavaras, C., Andreucci, S., and Pascucci, V.: Abrupt last glacial loess-dust deposition over Southeast England coupled with dynamics of the British-Irish Ice Sheet, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-5957, https://doi.org/10.5194/egusphere-egu21-5957, 2021.

High-resolution colour analyses of key loess-soil sequences (LPSs) in the Ukrainian part of Dnieper River basin - one of the major European rivers and the largest river in the borderland between Central and Eastern Europe. The subject of the study were LPSs from the Last Glaciation with a thickness of up to 10 meters. The aim of our studies is to reconstruct the Upper Pleistocene paleogeographic transformations recorded in the Dnieper LPSs.

In our study area the causative geomorphological agent was dust was blown away by wind from the exposed surfaces rich in loose fine-grained material (e.g. from a wide valley of a big river) and deposited on the land surface as silt covers of different thickness and spatial extent; in warm (interphase, interstadial) periods of the Weichselian it was fixed by vegetation and was the parent rock for the successively developing soils of different pedogenesis types. In the Last Glaciation the zone of long (~1000 km) and generally sub-meridional valley of the Dnieper River was located in the peri- and extraglacial zone and characterized by strong spatial climate gradient depending on the distance from the ice sheet extent. In our times this river flows across several vegetation-landscape zones (forest→forest-steppe→steppe).

The spectrophotometer made it possible to carry out colour analyses of individual units distinguished within LPSs, taking into account a number of parameters such as: CIELAB color space variables L* (luminance, i.e. lightness [0-100]), a* (>0: red, < 0: green), and b* (>0: yellow, < 0: blue), derived parameters like the Redness Index (RI) and the RGB variables (min., max, average). The analysed LPSs showed relatively high variability of the above mentioned parameters reflecting activity of sedimentation processes (=primary loess) as well as pedogenic changes (soil horizons of different stratigraphic rank) and slope transformations (reworked material). The results of these analyses (presented mainly as curve lines and heatmaps) specify characteristics of environmental conditions of individual litho- and pedostratigraphic units. The advantage of the analysed parameters is their high sensitivity reflecting variability of environmental parameters having global, but also regional or even just local significance.

Research carried out as part of the grant of National Science Centre, Poland as the project no. 2018/31/B/ST10/01507 entitled “Global, regional and local factors determining the palaeoclimatic and palaeoenvironmental record in the Ukrainian loess-soil sequences along the Dnieper River Valley - from the proximal areas to the distal periglacial zone”.

How to cite: Mroczek, P., Łanczont, M., Komar, M., Hołub, B., Gozhik, P., and Nawrocki, J.: High-resolution color variations of Weichselian loess-palaeosol sequences in the Dnieper River basin (Ukraine), EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-15181, https://doi.org/10.5194/egusphere-egu21-15181, 2021.

The is a mounting evidence that global emissions of dust were significantly higher during glacial than interglacial periods of the Pleistocene, and probably the Pliocene epochs. this pattern is observed in records from the low and mid latitudes, albeit with a varying degree of amplitude. During these time periods spanning 4 million years, the Earth climate underwent major transitions, such as the initiation of the Northern Hemisphere Glaciations and the Mid Pleistocene Transition. In parallel, dust transport and deposition on the oceans might have underwent stepwise increases, mainly during glacials. However, it is not clear yet if such changes are representative of global or regional climate response. Thus, dust records in marine sediments reflect changes in the different processes that drive the emission, transport, and deposition of dust on the oceans. In here, we report a compilation of marine dust records spanning the Pliocene-Pleistocene from all the major ocean basins. The synthesis of dust records on a global scale allows the identification of common patterns of variability and drivers. We analyse the data to infer changes in the global atmospheric circulation on orbital time scale, and to assess its meridional and zonal response during major climate transitions since the Pliocene.

How to cite: Teruel, O., Rosell-Melè, A., and Penalva-Arias, N.: Global patterns of oceanic dust deposition during Pliocene-Pleistocene transitions, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-10616, https://doi.org/10.5194/egusphere-egu21-10616, 2021.