Late Pleistocene aeolian activity in Haitan Island, Southeast China: Insights from optically stimulated luminescence dating of coastal dunes on marine terraces

The 'Old Red Sand' is a type of semicemented medium-fine sandy sediment that is red(10R_4/8) or brown red(2.5YR_4/8) in colour and is found in late Quaternary deposits. The sediments have distinctive characteristics and are a critical archive for understanding climatic changes in the coastal areas of East Asia. The ages of the late Quaternary aeolian sand dunes from Haitan Island in the coastal area of South China are still in debate. In this study, three sets of marine terraces were identified in the northern region of Haitan Island. Aeolian dune sands are well preserved on the top of these terraces. Quartz Optically Stimulated Luminescence dating and the distribution of the formation ages demonstrated that the palaeo-dunes are deposits from the middle-late period of the Late Pleistocene(Q_3^(2-3)). The period may be divided into three stages, 100-90 ka, 70-60 ka, and 40-20 ka, in which the palaeo-dunes of the first two stages are more widespread and were formed separately during a low-sea level period of the Marine Isotope Stages 5 b and 4. Several depositional palaeo-flood event records were preserved during the last stage due to the increasing gradient of mountain gullies formed during the Last Glacial Maximum.

Aeolian activity in the southern Gurbantunggut Desert of China during the last 900 years

The mineral dust emitted from Central Asia has a significant influence on the global climate system.However,the history and mechanisms of aeolian activity in Central Asia remain unclear,due to the lack of well-dated records of aeolian activity and the intense wind erosion in some of the dust source areas(e.g.,deserts).Here,we present the records of aeolian activity from a sedimentary sequence in the southern Gurbantunggut Desert of China using grain size analysis and optically stimulated luminescence(OSL)dating,based on field sampling in 2019.Specifically,we used eight OSL dates to construct chronological frameworks and applied the end-member(EM)analysis for the grain size data to extract the information of aeolian activity in the southern Gurbantunggut Desert during the last 900 a.The results show that the grain size dataset can be subdivided into three EMs(EM1,EM2,and EM3).The primary modal sizes of these EMs(EM1,EM2,and EM3)are 126.00,178.00,and 283.00μm,respectively.EM1 represents a mixture of the suspension components and saltation dust,while EM2 and EM3 show saltation dust transported over a shorter distance via strengthened near-surface winds,which can be used to trace aeolian activity.Combined with the OSL chronology,our results demonstrate that during the last 900 a,more intensive and frequent aeolian activity occurred during 450-100 a BP(Before Present)(i.e.,the Little Ice Age(LIA)),which was reflected by a higher proportion of the coarse-grained components(EM2+EM3).Aeolian activity decreased during 900-450 a BP(i.e.,the Medieval Warm Period(MWP))and 100 a BP-present(i.e.,the Current Warm Period(CWP)).Intensified aeolian activity was associated with the strengthening of the Siberian High and cooling events at high northern latitudes.We propose that the Siberian High,under the influence of temperature changes at high northern latitudes,controlled the frequency and intensity of aeolian activity in Central Asia.Cooling at high northern latitudes would have significantly enhanced the Siberian High,causing its position to shift southward.Subsequently,the incursion of cold air masses from high northern latitudes resulted in stronger wind regimes and increased dust emissions from the southern Gurbantunggut Desert.It is possible that aeolian activity may be weakened in Central Asia under future global warming scenarios,but the impact of human activities on this region must also be considered.

Effects of aeolian processes on nutrient loss from surface soils and their significance for sandy desertification in Mu Us Desert, China: a wind tunnel approach

Mu Us Desert, a region with high aeolian activity, is at extremely high risk of sandy desertification. Using surface soil samples collected from Mu Us Desert of northern China, we evaluated the effects of aeolian processes on nutrient loss from surface soils by employing wind tunnel experiments. The experiments were conducted using free-stream wind velocities of 14, 16, 18 and 22 m/s. Our results showed that the fine particles （〈50 pm in diameter; 12.28% of all transported materials） carrying large nutrient Ioadings were exported outside the study area by ae- olian processes. After the erodible fine particles were transported away from the soil surfaces at low wind velocity （i.e. 14 m/s）, the following relatively high wind velocity （i.e. 22 m/s） did not have any significant effect on nutrient export, because the coefficients of variation for soil organic matter, total phosphorus, total nitrogen and available potassium were usually 〈5%. Our experimental results confirmed that aeolian processes result in a large amount of nutrient export, and consequently increase the risk of sandy desertification in arid and semi-arid ecosystems.

Near-surface wind environment in the Yarlung Zangbo River basin,southern Tibetan Plateau

Aeolian processes have been studied extensively at low elevations,but have been relatively little studied at high elevations.Aeolian sediments are widely distributed in the Yarlung Zangbo River basin,southern Tibetan Plateau,which is characterized by low pressure and low temperature.Here,we comprehensively analyzed the wind regime using data since 1980 from 11 meteorological stations in the study area,and examined the interaction between the near-surface wind and aeolian environment.The wind environment exhibited significant spatial and temporal variation,and mean wind speed has generally decreased on both annual and seasonal bases since 1980,at an average of 0.181 m/(s•10a).This decrease resulted from the reduced contribution of maximum wind speed,and depended strongly on variations of the frequency of sand-driving winds.The drift potential and related parameters also showed obvious spatial and temporal variation,with similar driving forces for the wind environment.The strength of the wind regime affected the formation and development of the aeolian geomorphological pattern,but with variation caused by local topography and sediment sources.The drift potential and resultant drift direction were two key parameters,as they quantify the dynamic conditions and depositional orientation of the aeolian sediments.Wind affected the spatial variation in sediment grain size,but the source material and complex topographic effects on the near-surface wind were the underlying causes for the grain size distribution of aeolian sands.These results will support efforts to control aeolian desertification in the basin and improve our understanding of aeolian processes in high-elevation environments.

Optically stimulated luminescence dating of sandy deposits from Gulang county at the southern margin of the Tengger Desert, China

Aeolian deposits from the deserts in northern China have been used for palaeoenvironmental research to understand aeolian sedimentology and its dynamic connection to past climate conditions. The Tengger Desert in China is sensitive to the waxing and waning of the monsoonal system. In response to past climate change, the southern margin of the Tengger Desert has evolved significantly since the last glacial period. However, previous attempts to date aeolian deposits in this region were mainly based on radiocarbon dating, which has problems when applied to aeolian deposits. Moreover, sedimentary records are limited. Accordingly, past aeolian activity in this desert remains poorly understood. In the present study, we dated sand samples from Gulang county at the southern margin of the Tengger Desert using optically stimulated luminescence (OSL) to understand the history of aeolian activity in this region. Our samples represented well-sorted aeolian sands and sandy loess. Aeolian sands are evidence of dune field buildup and sparse vegetation cover whereas sandy loess is evidence of improved stabilization of sand dunes resulting from ameliorated vegetation cover. Certain samples showed a decline in the equivalent dose (D e ) values when successive integration intervals were applied, which resulted from unstable OSL signals from non-fast components in the initial part of the decay curve. In order to obtain reliable D e estimates, we investigated component-resolved and different background subtraction approaches, and compared the resultant D e estimates. We adopted the early background subtraction method to derive D e values. Luminescence chronologies and sedimentary records indicated that sand dunes accumulation occurred before 10 ka, and sandy loess developed between 9.5 and 7.6 ka when sand dunes were stabilized as a result of increased effective moisture levels. The transition between sand dune mobilization and stabilization emphasizes the significance of an effective moisture threshold in controlling aeolian activity. Mobilization of sand dunes at ~2.3 ka might be related to an increased aridity during the Late Holocene.

Wind regime features and their impacts on the middle reaches of the Yarlung Zangbo River on the Tibetan Plateau, China

The wide valley of the Yarlung Zangbo River is one of the most intense areas in terms of aeolian activity on the Tibetan Plateau,China.In the past,the evaluation of the intensity of aeolian activity in the Quxu–Sangri section of the Yarlung Zangbo River Valley was mainly based on data from the old meteorological stations,especially in non-sandy areas.In 2020,six new meteorological stations,which are closest to the new meteorological stations,were built in the wind erosion source regions(i.e.,sandy areas)in the Quxu–Sangri section.In this study,based on mathematical statistics and empirical orthogonal function(EOF)decomposition analysis,we compared the difference of the wind regime between new meteorological stations and old meteorological stations from December 2020 to November 2021,and discussed the reasons for the discrepancy.The results showed that sandy and non-sandy areas differed significantly regarding the mean velocity(8.3(±0.3)versus 7.7(±0.3)m/s,respectively),frequency(12.9%(±6.2%)versus 2.9%(±1.9%),respectively),and dominant direction(nearly east or west versus nearly north or south,respectively)of sand-driving winds,drift potential(168.1(±77.3)versus 24.0(±17.9)VU(where VU is the vector unit),respectively),resultant drift potential(92.3(±78.5)versus 8.7(±9.2)VU,respectively),and resultant drift direction(nearly westward or eastward versus nearly southward or northward,respectively).This indicated an obvious spatial variation in the wind regime between sandy and non-sandy areas and suggested that there exist problems when using wind velocity data from non-sandy areas to evaluate the wind regime in sandy areas.The wind regime between sandy and non-sandy areas differed due to the differences in topography,heat flows,and their coupling with underlying surface,thereby affecting the local atmospheric circulation.Affected by large-scale circulations(westerly jet and Indian monsoon systems),both sandy and non-sandy areas showed similar seasonal variations in their respective wind regime.These findings provide a credible reference for re-understanding the wind regime and scientific wind-sand control in the middle reaches of the Yarlung Zangbo River Valley.

Spatiotemporal distribution of sea-island prehistoric dune sites,Holocene sea levels,and aeolian sand activities in Fujian Province,China

The lower reaches of the Minjiang River and its adjacent areas were among the most active prehistoric archaeological areas in Fujian Province.The accumulation types of Neolithic archaeological strata are roughly divided into dune sites and dune/shell mound sites.The sites can also be roughly divided into estuarine,coastal,and sea-island sites based on their geomorphic features.The cultural development of these prehistoric sites is of great significance for understanding the migration and spread of Austronesian civilization.Based on luminescence dating of typical Neolithic sites on Haitan Island,their quartz-OSL(optically stimulated luminecesence)burial ages were determined.Synthesizing previously published results,the temporospatial distribution characteristics of the sea-island sites on Haitan Island are discussed,and the relationship between Neolithic human activities and regional geomorphic processes is analyzed.The results show that:(1)the spatial and temporal distribution of the Haitan Island Neolithic sites are closely related to small-scale geomorphic features and are controlled by mesoscale geomorphic processes.The sites were mainly distributed in the foothills of two high hills along an NNE-SSW trend.With an increase in altitude,the features were distributed as“single site(I)–superimposed site–single site(II)”and appear successively.Single type sites(I)mainly appeared at low sea level,whereas single type sites(II)mainly appeared at high sea level.Superimposed sites were not subject to sea level changes.The relative elevation of the superimposed sites in the study area indicates the optimal residential area for human activities in the region.The single site with an elevation lower than the optimal residential area was mainly restricted by the lowest residential area,whereas the single site at a higher elevation than the optimal residential area was mainly affected by livelihood patterns.(2)High sea level caused by the“backwater effect”in low latitude areas in the southern hemisphere,and coastal aeolian sand activity influenced by sea level fluctuations in the middle Holocene correspond well with human activities recorded in the cultural stratigraphy of sea-island type sites.The altitude of coastal aeolian sand accumulation can be used as an indirect index to estimate the age of coastal dunes.

Holocene aeolian activities linked to Indian summer monsoon in the middle reaches of the Yarlung Zangbo River

Widespread aeolian deposits on the Tibetan Plateau(TP)have provided valuable palaeoclimatic information.However,the primary factors(e.g.,climate factors,human activity,and vegetation cover)controlling aeolian deposition remain elusive.In this paper,we use a dataset that comprises new and published ages of Holocene aeolian sand and loess in the middle reaches of the Yarlung Zangbo River to identify the primary controlling factors and palaeoclimatic implications of aeolian deposition.Several intervals of enhanced aeolian accumulation centered at 8.5-7.8,6.4-5.8,4.5-4.0,3.1-1.8,and 0.9 ka are identified,generally consistent with regional low rainfall events and weak Indian summer monsoon(ISM).This suggests that regional wetness,dominated by the ISM,may play a key role in modulating dust emissions and aeolian deposition on centennial timescales.Our results show that on centennial-to millennial-scales,ISM activity can be reconstructed by non-continuous aeolian deposits in the monsoon dominated TP.