Aeolian Salt Research Articles

Cavernous Weathering in Aeolian Sandstones: An Example from the Yongningshan Hill of the Loess Plateau, Northwest China

AbstractCavernous weathering is commonly found on sandstone slopes in different environments. Either a single dominant process or polygenetic agents require to be invoked in order to interpret the development. The Yongningshan hill of the central Loess Plateau is representative of cliff dwellings in Northwest China, which is characterized by well‐developed cavernous weathering features and provides a good opportunity for the better understanding of sandstone weathering in the Loess Plateau. Multiple methods, including field survey, in‐situ rock strength measurement, along with experiments on samples for microscopic observation, element composition and salt chemistry, were employed to investigate the controlling factors of cavernous weathering. The results show that cavern development is different on the four slopes with the western slope hosting massive honeycombs, tafoni and hardened surfaces. The porous and permeable aeolian sandstones are fundamental, because they provide space and pathways for the transportation of water and salt, honeycombs dominantly aligning within the lamination of cross‐beds. The environmental factors such as the seasonal wetting and drying cycle, aeolian salt, moisture and water vapor are key factors for the development of cavernous weathering forms. The northern and northwestern wind‐blown dust storms have brought abundant salts, the lengthier dry periods of the wetting and drying cycle being beneficial for salt accumulation within caverns, favoring salt weathering.

Aeolian Carbon Salts in the Taklamakan and Badanjilin Deserts in Northwestern China and Their Potential Role in Global Carbon Cycle

Previous studies have suggested that a significant loop in the carbon cycle may be hidden in the global desert areas (both low latitude and middle latitude). Due to the complexity of salt formation involved in atmosphere-landscape relation, there are few study involved into the pool of secondary carbonates in world desert soils, particularly in arid areas in northern China. Large sandy deserts in the middle latitudes of northwestern China were investigated in this study. The physical and geochemical examinations are carried out into soluble carbon salts in modern and ancient dune sediments from the inland deserts in northwestern China, with the aim to explore the composition of carbon salts in aeolian sediments and their possible environmental implications for global carbon cycle. The results show that the aeolian salt has high alkalinities, which are mainly determined by evaporitic alkaline earth carbonates. The carbonates are secondary salt in origin and are possibly introduced from the atmosphere into the pedosphere by a carbon-fixation process. Owing to the high capability to neutralize atmospheric carbonic acid, large desert area, and the strong potential of carbonate preservation in soil under arid climate, the middle-latitude Chinese deserts can be potentially qualified as a significant contributor to the global carbon cycle. But the low-latitude deserts in tropic areas may be not able to provide such a contribution.

Hydrological indications of aeolian salts in mid-latitude deserts of northwestern China

Large sandy deserts in middle latitude of northwestern China were studied on salt variations in modern and ancient aeolian sediments, aiming to explore their hydrological indications at the present and past. Globally, sulphate is rich in arid to semi-arid deserts, including the aeolian loess sediments in China and soils in low-latitude deserts, but is less common in the aeolian sediments from the mid-latitude deserts in this study. The compositional differences between aeolian salts and local natural waters is evident, indicating the chemistry of aeolian salts and the associated parent brines may be significantly different than that predicted for hydrologically closed systems. The formation of aeolian salts in the studied deserts is strongly controlled by earth surface processes in a large scale but not in a local scale. Vertical changes in facies and salinities are abrupt in the studied palaeo-aeolian sediment samples, which were interbedded by lacustrine/fluvial sediments with OSL and 14C ages ranging between 40 and 2 ka BP, reflecting rapid high-amplitude changes in hydrological settings during late Pleistocene to later Holocene in these ancient playa systems. A great difference in salt composition between aeolian and lacustrine sediments suggests that the inorganic salt is a latent geoproxy in revealing local hydrological variations and climate change in the desert areas. But the environmental indications could be amphibolous for the sedimentary sequences with dual/multiple depositional end-members; under this situation an increase in sequence salinity does not always represent an enhanced environmental aridity. Ancient playas are arid or humid at the same time based on several sporadic records is not a valid approach to correlation of salt deposits in adjacent saline playa basin in the studied areas. Effects of earth surface processes including erosion, deposition and other processes on sediment properties will bias the hydrological implications of sediment salinity.

Atmospheric significance of aeolian salts in the sandy deserts of northwestern China

Abstract. Large sandy deserts in the middle latitudes of northwestern China were investigated for soluble salt variations in modern and ancient aeolian sediments, aiming to explore the environmental significance of “aeolian salts”. Results revealed that aeolian salt variations have a clear relationship with the changing meridional and zonal gradients of the desert locations and the aeolian differentiation effect, but are weakly linked to local geological conditions. Atmospheric depositions of water-soluble chemical species are an important process/source contributing to aeolian salt. Sequential variations of soluble salts in sedimentary profiles interbedded with aeolian and non-aeolian deposits and their palaeoenvironmental implications in the hinterland areas of these deserts were further evaluated, based on the constraints of OSL dating and radiocarbon dating data. The results indicate that inorganic salts may be a latent geoproxy in revealing regional palaeoclimatic changes in desert areas for sediments deposited under a single depositional environment, but the interpretation should be more cautious for sediments deposited under diverse depositional conditions. This study presents evidence of the atmospheric origin of aeolian salt in sandy deserts, with limited climatic significance in palaeoenvironmental reconstruction.

Impacts of soil crusts on soil physicochemical characteristics in different rainfall zones of the arid and semi-arid desert regions of northern China

Soil crusts commonly form in arid and semi-arid desert regions once shifting sand dunes stabilize. The crusts affect soil properties such as texture and fertility. However, the role of crusts depends on the species composition, their physiological activity, and their stage of evolution, and varies with precipitation and season. In this study, the soil properties of physical and biological crusts in different rainfall zones of the arid and semi-arid desert regions of northern China were analyzed. More developed crusts had finer soil texture. The impact on chemical properties was greater in areas with higher precipitation. Contents of soil organic carbon (SOC), total nutrients, available N, and exchangeable ions did not vary among crust types in a hyperarid region. SOC, total N and P, and available N increased with crust development at 150–400 mm rainfall. Soil crusts increased available P during the initial stage of development. Crust development increased available K at 300–400 mm precipitation, but not at ≤250 mm precipitation. CaCO3 changes were related to windblown dust and soil moisture in the crust. Electrical conductivity and total salinity varied in response to variation of soil nutrients and aeolian salt accumulation. The pH did not vary greatly between crust types and sites. Crust development was accompanied by soil alkalization. Ca2+ was more abundant than other cations. Crust development did not influence Cl−, but increased HCO3 − and Na+. During crust development, SO4 2− and K+ contents decreased, and Mg2+ increased, in regions with ≤250 mm precipitation. The opposite changes occurred at 300–400 mm precipitation.

Salts in the clay playas of China’s arid regions: gone with the wind

In China’s arid regions, aeolian salts are transported along with dust aerosols, but their contents and the emission rates are poorly understood. Using samples with undisturbed surfaces and artificially disrupted surfaces (to simulate human disturbances such as reclamation, planting, trampling by animals, and other activities), the transport rates for windblown material and the salt contents of clay playa surfaces were investigated in a wind tunnel. The results showed that under wind velocities ranging from 8 to 22 m/s, wind erosion rates ranged between 0.009 and 0.066 g/m2/s for the undisturbed surfaces and between 0.011 and 0.048 g/m2/s for the artificially disrupted playa surfaces. Although the amount of wind-transported material that was captured was too small to allow an analysis of individual salt contents using the available equipment, electrical conductivity measurements and correlation analysis revealed mean total salt contents of 9.59 g/kg in the transported materials collected above the sealed playa surfaces versus 3.38 g/kg in materials from the same surfaces that were artificially cracked after testing the sealed surfaces. Given the large areas containing clay playas in China’s arid regions, these results will improve our understanding of aeolian salt transport in arid China and will facilitate interpretation of the sources of aeolian salts.

Aeolian salts in Gobi deserts of the western region of Inner Mongolia: Gone with the dust aerosols

Gobi deserts of the western region of Inner Mongolia are potential dust source area and a dominant source of soluble salts that are transported into eastern Asia and the western Pacific. Currently, the salt species, their emission magnitudes, and their spatial trends in this source area are poorly understood. In the present study, we used intact surface samples and wind tunnel experiments, combined with salt and particle size data, to estimate the spatial trends of ionic species and the contents of terrestrial-derived soluble salts in this region. The salt contents in the surface materials range between 0.28 and 14.78‰ (by mass). However, the salt contents in materials transported by the wind ranged between 1.55 and 16.95‰. In this region, the soluble salts in the PM50 and PM10 fractions ranging between 0.008 and 0.913‰ and between 0.004 and 0.583‰, respectively, with SO42− and Ca2+ contents far higher than those observed in previous studies in East Asia and the western Pacific. Areas with the highest salt emissions were located in the western Ala Shan Plateau and in southwestern Mongolia, and the contents decreased moving towards the southeastern Ala Shan Plateau. In addition, wind tunnel experiments showed that under wind velocities ranging from 8 to 22m/s, the soluble salts ranged between 0.64 and 8.49%, with a mean of 3.45%. Given the significance of western Inner Mongolia for global dust emissions, the emissions of terrestrial-derived soluble salts from these areas should be carefully evaluated in future dust aerosol studies.

Dryland salinity and vector-borne disease emergence in southwestern Australia

Broad-scale clearing of native vegetation for agriculture in southwestern Australia has resulted in severe ecosystem degradation, which has been compounded by the subsequent development of large areas of dryland salinity; decreased transevaporation allows the water table to rise, dissolving ancient aeolian salt deposits and creating saline surface pools. The mosquito-borne disease Ross River virus has been noted as a potential adverse human health outcome in salinity-affected regions because the principal vector, Aedes camptorhynchus, is salt tolerant and thrives preferentially in such systems. To understand the geology and ecology underlying the relationship between land clearing and disease emergence, we examine the relationship between dryland salinity processes that determine the dissolved solids profile of saline pools in affected areas, the mosquito vectors and interactions with the human population within the disease cycle. Aedes camptorhynchus is able to survive in a wide range of salinities in pools created by dryland salinity processes. The link with disease emergence is achieved where population distribution and activity overlaps with the convergence of environmental and ecological conditions that enhance disease transmission.

Gamma-ray remote sensing of aeolian salt sources in the Murray–Darling Basin, Australia

This paper presents a new technique for mapping regional salt sources that has major implications for salinity management in southeastern Australia. This was achieved by analyzing a regional mosaic of airborne gamma-ray emission derivatives and verified by existing airborne electromagnetic and drilling data. A significant correlation was found between aeolian (windblown) materials, upland salts and gamma-ray signatures. This is consistent with the conceptual model that much of the salt in the upland areas of the Murray–Darling Basin is sourced from deposited aeolian materials that have been derived from deflationary events in salt-bearing landscapes in the western arid part of the basin. From gamma-ray emissions, and based on an observed relationship with borehole salinity, concentrated aeolian salt source deposits contained about 0.7% potassium and 10 ppm thorium. Using this signature on normalized data, an Euclidean distance algorithm provided mapping and information relating to salt-mobility pathways over a wide region. The resulting gamma-ray salt source model (GSM) facilitates focussed management of salinity infiltration zones in catchments across the basin.

Halogen geochemistry of the McMurdo dry valleys lakes, Antarctica: Clues to the origin of solutes and lake evolution

We have determined the halogen and boron concentrations in the ice-covered lakes of Taylor Valley, Antarctica, to better establish the sources of salts and evolutionary histories of these unusual water bodies. In addition, we report on a series of 129I measurements that were compared with previous 36Cl data that also help constrain the source of solutes and histories of the lakes. The new data, when put into context of previous work on these systems over the past forty years, allow us to make the following conclusions. The primary source of solutes to Lake Hoare, the youngest of the lakes, is the dissolution of marine aerosols and aeolian salts and the chemical weathering of dust on the glaciers. The geochemistry of Lake Fryxell, the brackish water lake, is primarily dominated by the diffusion from a halite-saturated brine at the sediment-water interface and the recent infilling of the lake by glacier meltwater. These waters have chemical weathering and marine aerosols components. Lake Bonney has two distinct lobes whose hypersaline hypolimnia have different chemistries. Both of the lobes are remnants of ancient marine waters that have been modified by the input of weathering products. This lake has also been modified by periods of cryogenic concentration when solutes have been lost via mineral precipitation. Thus the geochemistry of Lake Bonney owes its unusual geochemistry, in part, to variations in the climate in the Taylor Valley over at least the past 300kyr. The 129I data from the Taylor Valley are similar to those from fracture fluids in crystalline rocks from the Northern Hemisphere.

Polyphasic origin of salinity in the Senegal delta and middle valley

Saline areas are a major obstacle to the development of sustainable irrigated agriculture in the Senegal valley. They have been attributed to the incorporation of marine salts in the sediments during the last marine transgression. However, this does not explain their geomorphological situation and geochemical features. They are distributed as strips about 100–200 m wide and several kilometers long, which are composed of two parallel substrips, one located in the depressions of former creek beds, and the other on higher ground on the southern bank. In these two substrips, the chemical composition of salinity and its distribution in the soil suggest that it arises from more than one source. Comparison of saline areas of the middle valley with present-day salt accumulation in the delta suggests a four-stage salinization process, which involves evaporation from a shallow water table, aeolian salt accumulation as clay dunes, deep transformation of shell beds into gypseous layers under temporary acid conditions induced by oxidation of pyrite under the mangrove vegetation, and secondary salinization by runoff. The four-stage model agrees with a regional salinity chemical database and the geomorphology of the saline areas. In the Senegal valley, the lower middle valley and the delta can therefore be regarded as a chronosequence, the recent salinity features occurring in the delta and the more developed ones upriver at the limit of the marine transgression.