Dune Mobility Research Articles

Short-Term Foredune Dynamics in Response to Invasive Vegetation Control Actions

Efforts to control the spread of invasive alien species (IAS) in coastal dunes are essential to protect biodiversity and maintain the integrity of the ecosystem. However, the timing and extent of these control measures often do not consider their potential impact on dune morphodynamics. This study investigated how IAS control measures can affect sand dune mobility. Research involved monitoring short-term morphological and vegetation changes using close-range remote sensing along with historical wind data. Findings revealed that changes in vegetation cover significantly impacted dune system evolution, notably increasing sand mobility when IAS vegetation was removed. Considering the seasonal wind regime, dominated by offshore winds in the summer, removing vegetation during this period can promote seaward sediment transport, potentially resulting in sediment loss to the beach. These findings highlight the importance of understanding sediment mobility patterns when planning vegetation control actions within dune restoration strategies.

Exploring the complexities of sand dune transformation: the role of anthropogenic degradation and climatic conditions

Introduction: The sandy soils in the arid Southern Balkhash region have experienced anthropogenic degradation, leading to the formation of bare mobile sand dunes. This transformation has created significant challenges for the growth of cattle feed, particularly in areas with high economic activity. As a consequence, the socio-economic situation of the local population has been significantly worsened, and even the development of tourism has not helped. The objective of this study was to investigate the relationship between the seasonal mobility of sand dune landforms and their hydrothermal regimes, as well as the climatic conditions of the region.Methods: To achieve the study objective, we conducted field investigations and collected data on the mobility of sand dunes, hydrothermal conditions, and climatic factors in the region. Measurements were taken during the summer months when dominant North-East, North-North-East winds prevailed, with an average frequency of 20.4–26.7 days per month and wind speeds ranging from 3.0 to 3.7 m/s, occasionally reaching up to 11.90–13.3 m/s. We also analyzed humidity, air temperature, and atmospheric precipitation levels.Results: Our findings revealed that during the summer months, a fresh-sided layer of sand actively supplied the windward part of the sand dune to the leeward one. This process occurred under very low humidity, high air temperature, and slight atmospheric precipitation conditions. Consequently, the moisture content of the surface root layer (0–20 cm) of the sand dune accumulation zone decreased to 0.2% in the middle and at the end of summer.Discussion: The observed relationship between the seasonal mobility of sand dunes and their hydrothermal regimes, along with the climatic conditions, provides valuable insights for the development of effective technologies to rehabilitate anthropogenically degraded desert sandy soils that have transformed into mobile sands. This knowledge can serve as a theoretical basis for addressing the challenges faced by cattle breeding in the region and improving the socio-economic situation of the local population.

Do topographic changes tell us about variability in aeolian sediment transport and dune mobility? Analysis of monthly to decadal surface changes in a partially vegetated and biocrust covered dunefield

Vegetation and biological soil crust (biocrust) cover can have a stabilizing effect on dunes by fixing sediment in-place and increasing surface roughness, thus limiting dune mobility, sediment transport, and erosion. These biological effects influence rates of aeolian activity and thus surficial changes, though variability in wind and sediment supply may obscure these topographic effects. In this study, we compare monthly measures of sediment transport and decadal estimates of dune mobility to repeat topographic changes measured as a net volume change in sediment storage (difference in volume between all positive and negative topographic changes) and total volume change (absolute summed volume of all positive and negative changes) for areas of bare, vegetated, and biocrusted sand within a dunefield with limited sediment supply and unimodal winds. We found that monthly net volume changes normalized by area were similar between bare sand and sand with at least 20 % vegetation cover. However, total volume change was significantly greater for bare sand and correlated with monthly sediment flux estimates (R2 = 0.46), though the relationship was significantly improved by including monthly changes in surface roughness (R2 = 0.8). Longer-term decadal trends in topographic change showed larger total volume changes with the greatest decreases in vegetation canopy cover. Additionally, decadal total volume changes strongly correlated with estimates of dune mobility (R2 = 0.99). We also found that increased total volume changes did not necessarily signal increased net volume changes for all land cover types. Specifically, increases in total volume change for bare sand resulted in near equal or lower net volume changes, as both positive (deposition) and negative (erosion) change increased with sediment transport. Conversely, less mobile land covers, such as biocrust covered sand, increased in erosion without significant increases in total volume change, demonstrating that more stable surfaces might exhibit a larger topographic change imbalance than mobile sediment surfaces under the same conditions. This study highlights the importance of considering multiple measures of topographic change for interpreting sediment mobility, transport, and availability. Additionally, we hypothesize a novel framework for remote sensing-based empirical studies aimed at interpreting aeolian landscape evolution resulting from climate change effects on weather as well as biological controls such as vegetation and biocrusts.

Decadal changes in vegetation cover within coastal dunes at the regional scale in Victoria, SE Australia

Vegetation is a critical boundary condition for the stability of coastal dunes. Globally, vegetation cover is increasing on the coast with many dunes being stabilised in the past decades. This pattern is driven by site-specific (e.g., coastal management) and global (e.g., climatic changes) factors. This study examines changes in dune vegetation during the past six decades at the regional scale along the southeast coast of Australia to understand the relative importance of the climate and human interventions in vegetation cover change. A total area of >31,000 ha, comprising 53% of the open coast of Victoria was studied. Since the 1960's, a general trend of dune stabilisation and coastal greening has occurred with total vegetation cover increasing from 61% to 84% coverage until 2020. At the regional scale, the increase in vegetation cover has been primarily driven by both climatic-related drivers, such as rising temperature, elevating CO2 concentrations and declining windiness, and state-wide coastal management interventions (e.g., marram grass planting, fencing, fire control, grazing removal). The only areas where there was a decline in total area of vegetation was where substantial coastal recession had occurred. The decrease in vegetation is a result of a loss of land area rather than a loss of plant biomass over the dunefields. Therefore, it is considered that the overall decadal changes in both climate and coastal management are forcing the dunes toward a more stabilised state at the regional scale. At the same time, compelling local drivers (e.g., storms and local sediment deficiency) can be the most crucial factor to regulate vegetation change and shift dune mobility at the site-specific scale.

Managing Coastal Sand Drift in the Anthropocene: A Case Study of the Manawatū-Whanganui Dune Field, New Zealand, 1800s-2020s

Abstract In the Anthropocene, dunes act as a natural defence from sea-level rise and storm surges while providing 'ecosystem' services. This article uses scientific and historical data to examine the Manawatū-Whanganui dune field in New Zealand from the nineteenth to the twenty-first century. Dunes that were destabilised due to European settlements and their activities were drifting inland causing social, economic and political problems. Attempts to prevent dune mobility occurred at the time in many parts of the world. Thus, knowledge was shared between countries through experts and migrants. The consequences of the implemented solutions and new environmental conditions mean that dunes are still a major issue in the region. A comparative analysis of historical and present-day dune management practices provides a better understanding of long-term dune drift. In conclusion, interdisciplinary analyses of long-term relations between dunes and society must be taken into account for their holistic management.

A new aeolian activity proxy based on analysis of the grain size characteristics of surface soils across the Tengger Desert, northwest China, and its application to a Quaternary aeolian succession

The arid regions of northwestern China are dominated by extensive areas of mobile sand dunes. These features cause environmental problems and exert global climatic impacts; however, due to the lack of systematically-applied indicators of aeolian activity, direct evidence of past changes in aeolian activity is unreliable, especially for aeolian sand source regions. In this paper, we analyze the end-member (EM) distributions of various types of surface soil across the Tengger Desert in northwestern China, and devise a sensitive proxy for aeolian activity using a spatio-temporal substitution approach. This proxy is then used to evaluate a Quaternary aeolian succession and to understand the response of aeolian activity to regional climate change. Our results suggest that gradual increases in the coarse-grained EM components 3–5 reflect enhanced dune mobility and reduced vegetation coverage, which are a direct function of the intensity of regional aeolian activity. In the aeolian section, coarse- and medium-grained sand layers resemble modern semi-mobile and mobile dunes, whereas fine-grained sand layers are analogous to vegetated fixed/semi-fixed or semi-mobile dunes. Combining this record with independent multi-proxy evidence from the same section leads us to conclude that strong aeolian activity coincided with a dry climate, sparse vegetation cover, and strong surface winds during the Last Glacial Maximum, and that these conditions gradually attenuated at the beginning of the Last Deglacial. These inferences are in accord with independent paleoclimate records from this region, confirming that the intensity of aeolian activity in the southeastern Tengger Desert is closely associated with large-scale climate change. Our findings show that our EM proxy can be used to infer the intensity of aeolian activity and to reliably reconstruct the evolution of deserts in northwestern China.

Optically stimulated luminescence dating and paleoclimatic implications of the Holocene dune sands in the Hunshandake Sandy Land, Northeast China

Aeolian sediments are important geological archives of paleoclimate changes. Due to the fragile ecosystem of desert, sand dune mobility is particularly sensitive to climate change, and is thus important for revealing the stabilization and mobilization processes of dunes during the geological past. In northeastern China, several sandy lands are located in the East Asian monsoonal region, and desert evolution has been used to infer the waxing and waning of monsoonal climate. However, the relationship between dynamic aeolian landscapes and forcing mechanisms is still under debate due to the complex nature of the aeolian dune systems. In this study, we analyse two aeolian sand dune sections in the Hunshandake Sandy Land, northeast China, located at the northern edge of the East Asian summer monsoon, explore regional paleoclimatic changes during the Holocene. We carried out high-resolution optically stimulated luminescence (OSL) dating to develop a well-constrained chronology for the dune sands, as well as analyses of multiple climatic proxies including magnetic susceptibility, particle size, and color parameters, to obtain knowledge about dune mobility and climatic changes. Our results indicate that the early Holocene was characterized by the accumulation of aeolian dune sands, implying an arid climate, driven by an enhanced East Asian winter monsoon. Paleosols were generally developed in the mid-Holocene (∼8 and 4 ka) when the sand dunes were stabilized by vegetation under a relatively warm and humid climate driven by an enhanced East Asian summer monsoon. In the late Holocene, from ∼4 ka to the present, climate returned to an arid and semi-arid phase, marked by aeolian dune sands with some weakly-developed paleosols. Through comparison of the aeolian record with the other East Asian monsoonal records and the sea-surface temperature of the North Pacific, we suggest that the evolution of the East Asian monsoon, which was paced by both the melting and expansion from the Northern Hemisphere ice sheet as well as the changes of solar radiation, played an important role in driving climate change in the Hunshandake Sandy Land during the Holocene.

Spatiotemporal Dynamics of Vegetation Index in an Oasis-Desert Transition Zone and Relationship with Environmental Factors

The oasis-desert transition zone (TZ) is an ecological buffer zone between a mobile desert and an oasis, which are important in reducing the forward mobility of sand dunes and wind and sand hazards in an oasis. In this study, the Dunhuang Oasis and its TZ in the Hexi Corridor (China) were examined. Based on the annual normalized vegetation index (NDVI) at each buffer distance of the TZ from 1987 to 2015, combing the watershed hydrology, oasis crop cultivation structure and industrial economic status, partial least squares regression models and a correlation analysis were used to examine the spatial and temporal changes in the vegetation gradient of the oasis TZ and the factors influencing those changes. (1) Spatially, the NDVI values in the TZ generally decreased gradually before stabilizing with a buffer distance (average decrease of 0.01–0.03 per 300 m). (2) Temporally, the mean values of the NDVI in the TZ show an overall wavelike variation across years. The annual average maximum NDVI value was 0.11 in 1987, whereas the annual average minimum value was 0.07 in 2014. (3) During the 1987–2015, runoff, tourist populations and water consumption for orchards were significantly and positively correlated with the NDVI; the year-end arable land area and the total industrial output value were significantly and negatively correlated with the NDVI; the rural per capita net income and water consumption for grain planting were not significantly and positively correlated with the NDVI; water consumption for the sum of vegetable and melon planting, water consumption for cotton planting, urbanization and rural populations were not significantly and negatively correlated with the NDVI. (4) The farm TZ NDVI is more strongly influenced by human activities than the undisturbed natural TZ.

How desertification in northern China will change under a rapidly warming climate in the near future (2021–2050)

Arid, semi-arid, and semi-humid regions (drylands) with fragile ecological balance have undergone dramatic climate change in past decades, and how the desertification will change under a continuous warming background still remain uncertain. In this study, the bias-corrected Community Earth System Model outputs from Coupled Model Intercomparison Project phase 5 were dynamically downscaled using the Weather Research and Forecasting (WRF) model, based on which the evolution trend of desertification over northern China (NC) in the past (1972–2000) and the near future period (2021–2050) under the RCP8.5 scenario were analyzed using the dune mobility index, and the impacts of climate change on the intensification or reversal of desertification over NC in the near future were explored. The results show that WRF downscaling can reproduce the desertification changes over NC in the past. The regions with a high risk of desertification are mainly located on the border of the desert and gobi. Under a rapidly warming climate in the near future, desertification will likely reverse in most regions of NC, especially for regions north of 40°N over NC. Potential evapotranspiration changes will exacerbate desertification, while precipitation changes will promote rehabilitation, and wind speed changes show obvious local impacts on desertification. The results in this study imply that, with rising temperatures in the future, the extent of desertification will not always continue, desertification will likely reverse at the front and margin of deserts and gobi, and responses of desertification to climate change have significant spatial differences.

The largest Quaternary inland eolian system in Brazil: Eolian landforms and activation/stabilization phases of the Xique-Xique dune field

Eolian systems are sensitive to vegetation and climate changes, but also to the sediment supplied by neighbor depositional systems. This sensitivity is manifested in the alternation between periods of sand dune mobility and stability. In the Xique-Xique eolian system, the largest Quaternary interior dune field in Brazil (∼8000 km2), the neighboring depositional system responsible for the sand supply is the São Francisco River. We interpreted periods of dune activity and stabilization by mapping eolian landforms of this system, describing depositional facies under them and dating by optically stimulated luminescence (OSL-SAR). The stabilized parabolic landforms characterized and mapped (all formed by SE to E winds) were simple megadunes (25.5 ± 4.4 to 5.8 ± 2.0 ka), compound dunes (15.8 ± 1.2 to 5.2 ± 1.4 ka) and perched dunes (14.0 ± 1.0 and 1.2 ± 0.1 ka). We also recognized eolian plains (14.0 ± 2.1 to 6.5 ± 0.7 ka) and active parabolic dunes. Eolian deposits of undifferentiated landforms have also been described and dated (253.8 ± 19.0 to 8.2 ± 1.3 ka). The ages obtained allowed identification of two main phases of dune activity (∼60 to 18 ka and ∼16 to 5 ka) separated by a short period of stabilization marked by a paleosol (∼18 ka). The main periods of eolian activity are associated with phases of fluvial aggradation and high sediment supply, whereas dune stabilization since 5 ka is correlated with low sediment supply during the Late Holocene fluvial incision phase. The periods of eolian activity and stabilization respond not only to climate changes in the area occupied by the eolian system but mainly to local fluvial sediment supply by the river, which in turn can respond to more regional climatic controls. The Xique-Xique eolian system results from the coupling of abundant sediment supply from the fluvial system, high eastern wind speeds, and a significant wind deceleration caused by mountains on the western border of the dune field.

Insights into the age and genesis of the clay dunes in the Suhongtu Basin, Alashan Plateau, China

Clay dunes are characterized by high content of silt and clay and they are both a unique aeolian landform and an important paleoenvironmental archive attesting to changing climatic and hydrological conditions. Although clay dunes have been identified on several continents, they have attracted relatively little research attention. Numerous clay dunes are developed in the Suhongtu (SHT) Basin, Alashan Plateau, China. However, their genesis, age, and process of evolution are unknown. In this study we measured the grain size of various clay dune samples using dynamic image analysis (DIA) and laser diffraction analysis (LDA). Comparison of the results obtained by the two methods revealed significant differences between them: the grain size of clay dune samples obtained by DIA have a unimodal distribution (with a mode at ~200–400 μm), and the grain-size composition is dominated by medium sand; while the results obtained using LDA show a bimodal distribution (with modes at ~4 and 200–400 μm), and the grain-size composition consists mainly of clay and silt. This indicates that the clay dunes in the SHT Basin are formed by wind transport and accumulation in the form of the mixing of sand-sized aggregates of clay-silt with quartz sand grains. The morphology, mobility, and sedimentary structures of the clay dunes in the SHT Basin differ substantially from those of the well-studied clay dunes in Australia and North America, which can be mainly attributed to the relatively low clay content, abundant sand source and extremely arid conditions. During field investigations we studied seven stratigraphic sections, comprising multiple aeolian clay dune and lacustrine units, with age control provided by optically stimulated luminescence (OSL) and AMS 14C dating. Lacustrine sediments in the basal parts of sections yielded OSL age between 7.84 ± 0.71 ka and 6.33 ± 0.84 ka, suggesting that the SHT Basin was occupied by a lake during 7.8–6.3 ka when the precipitation was relatively high and the climate was humid. The oldest clay dune deposit, with an AMS 14C age of 1.27 cal kyr B.P, probably represents the onset of the modern clay dune landscape in the SHT Basin. Most of the clay dune deposits yielded OSL ages between 0.50 ± 0.04 ka and 0.18 ± 0.05 ka, indicating aeolian reactivation in the past ~500 years.

Biocrust‐induced extracellular polymeric substances are responsible for dune stabilization in the Negev

AbstractThere is no consensus over the factors responsible for dune stabilization in arid regions, with some scholars maintaining that dust (i.e., silt and clay) plays a major role in dune stabilization. Aiming to explore the principal driving factor responsible for dune stabilization in the Negev, we compared various biocrusts having different biomass and compressive strength, and performed surface degradation and illuviation experiments with dust in the presence or absence of biocrusts in order to assess the crust role in impeding wind erosion and dust illuviation. We show that dust cannot be regarded as the primary driving factor for crust strength and subsequently for dune stabilization in the Negev, as suggested in some publications. This function is however fulfilled by extracellular polymeric substances (EPS, mostly polysaccharides), which are excreted by the biocrust (mainly cyanobacteria), and serve as a cementing agent for the establishing crust and therefore for the dust. Exhibiting high water absorption and strong adhering properties, EPS is responsible for granting strength to the crust, impeding wind erosion and dust illuviation, thus providing the necessary cementing agent, which facilitates dune stabilization in the Negev. Global warming which may result in frequent droughts and high input of dust may not contribute to dune stabilization as suggested by some scholars, but rather will negatively affect dune stabilization, as it may result in EPS degradation and subsequently in dune mobilization.

Changes in the vegetation cover of transgressive dune fields: A case study in Cape Woolamai, Victoria

AbstractChanges in vegetation cover and dune mobility of Woolamai dune fields on the southeast coast of Australia were quantified based on a time series of aerial imagery (1939 to 2020). Results showed that the dune fields have shifted from nearly all bare sand (with <5% vegetation cover) to a new quasi‐equilibrium state, being almost fully stabilized by vegetation (>80%) from 1939 to 2020. Three temporal stages of vegetation change were identified, namely: (I) early expansion over 1939–1975; (II) rapid growth from 1976 to 2010; and (III) recent ‘quasi‐equilibrium’ state in 2010–2020. In stage I, complex impacts of climate and human activities co‐existed with uncertainty of the dominant factor. In this early stage, vegetation growth was constrained to the low and sheltered areas, indicating the influence of topography. Rapid vegetation growth took place in 1976–2010 (stage II), during which a re‐vegetation programme combined with favourable climate conditions promoted vegetation growth. In the last decade (stage III), vegetation might have reached a new quasi‐equilibrium when the vegetation almost reached a maximum. The slight loss of vegetation could be attributed to weed control and an unfavourable climate for growth (drier and windier) in Woolamai dune fields.This study showed that variations in vegetation cover and dune mobility through time are not simply linked to a single factor but depend on the occurrence of multiple factors (e.g. topography, climate and human activities) that promote stability, or alternatively, mobility of the dune system. This research contributes to expanding our understanding of the complexity of the bio‐geomorphologic dynamics in dune fields. It also provides detailed observational evidence for the historical trajectory of vegetation expansion from the bare dune fields to a fully stabilized state, which can be used to verify and refine models for other similar dune sites.

Aeolian mobility in the Middle São Francisco Dune Field, Northeast Brazil, as a response to Caatinga's droughts and land-use changes

In the last decade, the semiarid northeast of Brazil (Caatinga biome) has experienced one of the most prolonged and most severe droughts ever recorded in regional history. The study of the landscape changes contributes to understanding the environmental, social, and economic consequences of extreme climate events in the region. Here, we investigate the marginal area of the Middle São Francisco dune field, where in recent years, aeolian landforms development and their migration have been observed. To map the migration line of the aeolian front, we used 2002–2019 high-resolution images, from which we estimate the migration rates and evaluate the monthly migration rates for several interannual intervals, particularly during the drought peaks. In the area of greatest migration, the dunes advanced 210 m in 18 years. In the first decade, under climatic conditions closer to the historical average, dunes migrated ~15 m/y, while in the second decade, they migrated 80 m at a rate of 9.4 m/y. Examining the ranges of intra-annual migrations, we estimate that the highest mobility rate was almost five times greater than the rate at the end of the decade. In addition, we calculated a dune mobility index and the dune's morphological patterns. We conclude that the morphodynamic processes of dune formation and migration were triggered mainly by vegetation removal from river banks. The more severe climatic conditions during the last drought (2012–2017) enabled the dunes to migrate relatively quickly. The last few years (2017–2019) were marked by a considerable reduction in aeolian mobility and stabilization of expansion margins, inducing the formation of barchan-parabolic dunes.

Monitoring Sand Drift Potential and Sand Dune Mobility over the Last Three Decades (Khartouran Erg, Sabzevar, NE Iran)

Aeolian sediments cover about 6% of the earth’s surface, of which 97% occur in arid regions, and these sediments cover about 20% of the world’s lands. Sand drifts can harm sensitive ecosystems; therefore, this research has aimed to study wind regimes and the monitoring of sand drift potential and dune mobility in the Khartouran Erg (NE Iran). The study investigated 30 years of wind speed and direction to better understand sand dune mobility processes using the Fryberger and Tsoar methods. The results of the wind regime study showed that the eastern (33.4%) and northeastern (14.3%) directions were more frequent, but the study of winds greater than the threshold (6 m/s) in winter, spring, and autumn indicated the dominance of eastern and northern wind directions. Findings of calm winds showed that winters (40.4%) had the highest frequency, and summers (15%) had the lowest frequency; the annual frequency was 30%. The average wind speed in summers was the highest (4.38 m/s), and, in the winters, it was the lowest (2.28 m/s); the annual average wind speed was 3.3 m/s. The annual drift potential (DP = 173 VU) showed that it was categorized as low class, and the winds carried sand to the southwest. The monitoring of drift potential showed that there was a sharp increase between 2003 and 2008, which could have been attributed to a change in wind speeds in the region. Unite directional index, the index of directional variability, has been alternating from 0.3 to 0.6 for 30 years. Furthermore, monitoring of sand mobility recorded a value from 0.1 to 0.4, and the lowest and highest values were registered from 0.08 to 0.9, with an average of 0.27. Finally, it can be concluded that sand dunes have been fixed for a long time, and the intensity of the mobility index is affected by climate changes.

Controls of pedogenesis in a fluvial-eolian succession of Cenomanian age in northern Patagonia

Although interactions between eolian and fluvial systems are well documented in both modern and ancient environments, there are few studies of such deposits that also address the paleosols that developed within them. The Cenomanian Candeleros and Huincul formations of the Neuquén Basin, Northern Patagonia, Argentina, provides an excellent opportunity to do so. These formations preserve mixed fluvial-eolian and fluvial systems, respectively, with associated pedogenesis. We identify five lithofacies associations (fluvial channel deposits [FA1], deposits of unconfined fluvial flows [FA2], floodplain deposits [FA3], eolian-dune deposits [FA4], and wet interdune deposits [FA5]), and five pedotypes (calcic Protosols [P1], Vertisols [P2], vertic and gleyed Protosols [P3a and P3b, respectively], vertic Calcisols [P4], and argillic Protosols [P5]). The lower Candeleros Formation is characterized by eolian dune deposits with calcic Protosols and wet interdune deposits with Vertisols and vertic and gleyed Protosols. The middle part of the formation is dominated by deposits of unconfined fluvial flows with vertic Protosols and, in the upper part of the unit, there are channel deposits with vertic Calcisols. The Huincul Formation is characterized by fluvial deposits with argillic Protosols.Changes in paleosol development have been recorded throughout the two formations. Small-scale changes, recognized in the lower Candeleros Formation, comprise a chrono-toposequence, in which calcic Protosols, Vertisols, vertic and gleyed Protosols are genetically associated with FA4 and FA5. Calcic Protosols developed on the dunes and gleyed Protosols in the inner part of the interdunes subjected to temporal waterlogging. When the dunes were vegetated and pedogenesis promoted dune fixation, the rate of dune mobility was slow and the ancient soils developed into Vertisols. In turn, the absence of vegetation was linked to a relatively high rate of dune migration, the time of soil development was limited, and, as a result, vertic Protosols were preserved. The analysis of soil-forming factors as large-scale controlling factors showed that throughout the succession, variations on the type of paleosol and the sedimentary environment over time were controlled by changes in ancient climate. Mid-Cretaceous global climate reconstructions suggest that the paleosols developed in northern Patagonia were located near the limit between the Southern Mid-latitude Warm Humid Belt and the Southern Hot Arid Belt. Seasonally arid and semi-arid conditions prevailed in this area, although there was a temporal trend towards a temperate subhumid climate.

Lateglacial and Holocene climate change in the NE Tibetan Plateau: Reconciling divergent proxies of Asian summer monsoon variability

The nature of Holocene Asian summer monsoon (ASM) evolution documented by diverse natural archives remains controversial, with a contentious issue being whether or not a strong Asian summer monsoon prevailed during the early Holocene. Here we present sequences of multiple proxies measured in sediment cores from Genggahai Lake in the NE Tibetan Plateau (NETP). The results suggest that a higher lake level and relatively lower terrestrial vegetation cover occurred synchronously during the early Holocene (11.3–8.6kyrcalBP), compared with the period from 8.6 to 6.9 kyrcalBP. This finding clearly reflects the existence of different hydroclimatic conditions between the lake and its catchment due to diverse driving mechanisms. The early Holocene high stand of the lake, as demonstrated by the stratigraphic variability of the remains of aquatic biota, may have responded to the strengthened ASM and increased monsoonal precipitation; the relatively low vegetation cover in the marginal region of the Asian monsoon during the early Holocene, and the coeval widespread active sand dune mobility in both the NE Tibetan Plateau and NE China, most likely resulted from a low level of effective moisture due to high evaporation, and hence they cannot be interpreted as evidence of a weak ASM. Our results potentially reconcile the current divergent interpretations of various proxy climate records from the region. Our findings suggest that the ASM evolution was characterized by a consistent pattern across the monsoonal regions, as indicated by the oxygen isotope record of Chinese speleothems.

Geomorphological and ecological change in a coastal foreland dune system, Sandscale haws, Cumbria, UK: the management challenges posed by climate change

Many coastal sand dune systems in the UK and other parts of the world have experienced a decline in bare sand extent and dune mobility over the past 70 years, accompanied by increased coverage of coarse grass, scrub and woodland vegetation. This has raised concerns amongst nature conservationists about the survival of dune specialist species. Opinions are divided, however, regarding what management interventions should be made to counteract these trends. This paper reviews the factors which have contributed to progressive dune system stabilization at Sandscale Haws, located on the Irish Sea coast in Northwest England, considers the implications for the site of UKCP18 future climate change projections, and discusses the options and plans for future adaptive management. Analaysis of aerial photographs indicated a large reduction in bare sand area between 1946 and 1988 (from >34% to 9% of the dune system), since when there has been a further decline to 1.7%. Consideration of the evidence suggests that a trend towards a warmer, slightly wetter and less windy climate has been the main driver of stabilization, although atmospheric nitrogen deposition, increasing atmospheric CO2 concentrations, reduced grazing intensity, reduced human disturbance from the mid-1980s onwards and a tendency for shoreline progradation on the west-facing coast have played contributing roles. Some species characteristic of open habitats can still be found in good numbers in parts of the dune system, but without increased management it is likely they will decline further and some may become locally extinct. Since the site is of national and international importance for a number of nationally scarce plant and animal species it is considered that there is both a legal and an ethical duty to attempt to maintain suitable habitat for their survival. As a National Nature Reserve Sandscale Haws provides a suitable ‘natural laboratory’ within which to research the effectiveness of different intervention methods. A number of small-scale dune rejuvenation methods have been trialled since 2015, and options for larger scale interventions, including turf stripping and possible dune notching, are currently being evaluated as part of the nation-wide Dynamic Dunescapes project.

Classification of Atlantic Coastal Sand Dune Vegetation Using In Situ, UAV, and Airborne Hyperspectral Data

Mapping coastal dune vegetation is critical to understand dune mobility and resilience in the context of climate change, sea level rise, and increased anthropogenic pressure. However, the identification of plant species from remotely sensed data is tedious and limited to broad vegetation communities, while such environments are dominated by fragmented and small-scale landscape patterns. In June 2019, a comprehensive multi-scale survey including unmanned aerial vehicle (UAV), hyperspectral ground, and airborne data was conducted along approximately 20 km of a coastal dune system in southwest France. The objective was to generate an accurate mapping of the main sediment and plant species ground cover types in order to characterize the spatial distribution of coastal dune stability patterns. Field and UAV data were used to assess the quality of airborne data and generate a robust end-member spectral library. Next, a two-step classification approach, based on the normalized difference vegetation index and Random Forest classifier, was developed. Results show high performances with an overall accuracy of 100% and 92.5% for sand and vegetation ground cover types, respectively. Finally, a coastal dune stability index was computed across the entire study site. Different stability patterns were clearly identified along the coast, highlighting for the first time the high potential of this methodology to support coastal dune management.

The effect of wind speed averaging time on the calculation of sand drift potential: New scaling laws

Drift potential (DP) is a key factor used to quantify aeolian sand transport, and it is often used for predicting wind erosion and dune mobility under climate change scenarios. It is proportional to the mean of the cube of the wind speed at a 10-m height when that wind speed is above 6.2 m/s (12 knots), a speed threshold above which sand can be transported by the wind. DP depends on the temporal resolution and the averaging time of the wind velocity measurements. Usually, either a 10-min or 1-h mean wind speed is used to calculate the DP, although different studies have used different averaging periods for calculating the mean wind speed and, consequently, the DP. Here, we perform a comprehensive analysis of an extensive, long-term wind speed database from different locations around the world and from reanalysis data sources, and show that DP decreases with the averaging time of the wind speed. The decrease of DP versus the averaging time interval can be approximated by a stretched exponential function. In addition, the relative decrease of DP, as a function of the maximum DP, is smaller for high wind speed sites. This result is a consequence of the fact that high DP sites are characterized by longer clusters of successive wind speed events above the threshold velocity; they are thus less affected by the time averaging process. Interestingly, the clusters' lengths decay exponentially with wind speed and faster for low DP sites. Our new results have important implications for calculating the effective DP and for better estimating the biases that result from using wind data with different averaging times, which is a common problem in aeolian research. We also found an approximate linear relation between DP and the wind power that is close to the analytic approximation for the relation between the two. This new finding has many important applications since it will allow one to calculate DP from wind power data and vice versa. In addition, it implies that the same scaling laws found for DP also exist for the wind power.