Eolian Dust Accumulation Research Articles

Aeolian disruption and reworking of TARs at the Zhurong rover field site, southern Utopia Planitia, Mars

Aeolian bedforms are the signatures of wind interaction with unconsolidated, granular surface materials. Transverse aeolian ridges (TARs) are widely distributed on Mars but their formation remains enigmatic. China's Zhurong rover explored four crescent-shaped TARs, with two horns generally facing south, during the first 107 sols in southern Utopia Planitia, Mars. Rover images show that these bedforms have distinct light and dark variations on their surfaces that likely result from the combination of a bimodal distribution of particle sizes and the crust formed by the accumulation of aeolian dust. Two of these bedforms exhibit erosional forms on their west sides, where megaripples facing in a direction different from that of the crescentic bedforms they disrupt were created by more recent winds from the northeast. Differing erosional configurations of each of these bedforms in close proximity to each other are probably related to the angle between the bedform crest and the wind direction, and may further suggest that erosion of TARs starts from their two flanks. Secondary ridges of TARs widely recognized on Mars could be megaripples formed during this erosion process. At the Zhurong landing site, TARs degraded into megaripples, suggesting that they might share similar formation and evolution mechanisms there and elsewhere on Mars.

Holocene aeolian dust accumulation rates across the Chinese Loess Plateau

The Chinese Loess Plateau (CLP) is a major region of Quaternary aeolian dust deposition. However, the temporal and spatial variations of Holocene aeolian dust accumulation rate (DAR) across the CLP have not been systematically evaluated. Here, we present a synthesis of Holocene DARs across the CLP based on 36 well-dated loess sections. The results show that the DAR was relatively high during the early Holocene, lowest during the mid-Holocene, and increased substantially during the late Holocene. These trends are in good agreement with the temporal variations of the East Asian summer monsoon (EASM). We conclude that the dominant factor controlling dust storm activity across the CLP during the Holocene was EASM precipitation, rather than the East Asian winter monsoon (EAWM). However, during intervals of a strong EAWM there was a significant positive correlation between the DAR in the CLP and dust deposition in Greenland, suggesting that a strong EAWM may have elevated Asian desert dust to high altitudes, enabling it to be entrained by the westerly jet and transported for long distances. Anthropogenic influences may be superimposed on EASM-modulated dust activity. Against the same background of EASM precipitation, the DAR after 4 kyr BP was significantly higher than previously, which may be related to the intensification of human activities in the dust source areas. Notably, several intervals of high DAR during the past 2000 years were not accompanied by decreases in EASM precipitation, and instead they correspond to significant population increases in the dust source areas. • Holocene dust accumulation rates across the Chinese Loess Plateau were assessed. • EASM dominated Holocene dust storm activity across the Chinese Loess Plateau. • Anthropogenic impacts on dust activity can be traced back to at least 4 kyr BP.

OSL-dating of the Pleistocene-Holocene climatic transition in loess from China, Europe and North America, and evidence for accretionary pedogenesis

Loess deposits intercalated by paleosols are detailed terrestrial archives of Quaternary climate variability providing information on the global dust cycle and landscape dynamics. Their paleoclimatic significance is often explored by quantifying their mineral magnetic properties due to their sensitivity to local/regional hydroclimate variability. Detailed chronological assessment of such regional proxy records around the climatic transitions allow a better understanding of how regional records react to major global climatic transitions such as the Pleistocene-Holocene climatic transition. Logs of high-resolution magnetic susceptibility and its frequency dependence were used as paleoclimatic proxies to define the environmental transition from the last glacial loess to the current interglacial soil as reflected in nine loess-paleosol sequences across the northern hemisphere, from the Chinese Loess Plateau, the southeastern European loess belt and the central Great Plains, USA. The onset of increase in magnetic susceptibility above typical loess values was used to assess the onset of, and developments during, the Pleistocene-Holocene climatic transition. High-resolution luminescence dating was applied on multiple grain-sizes (4–11 μm, 63–90 μm, 90–125 μm) of quartz extracts from the same sample in order to investigate the timing of Pleistocene-Holocene climatic transition in the investigated sites. The magnetic susceptibility signal shows a smooth and gradual increase for the majority of the sites from the typical low loess values to the interglacial ones. The initiation of this increase, interpreted as recording the initiation of the Pleistocene-Holocene climatic transition at each site, was dated to 14–17.5 ka or even earlier. Our chronological results highlight the need of combining paleoclimatic proxies (magnetic susceptibility) with absolute dating when investigating the Pleistocene-Holocene climatic transition as reflected by the evolution of this proxy in order to avoid chronostratigraphic misinterpretations in loess-paleosol records caused by simple pattern correlation. The detailed luminescence chronologies evidence the continuity of eolian mineral dust accumulation regardless of glacial or interglacial global climatic regimes. Coupled with magnetic susceptibility records this indicates that dust sedimentation and pedogenesis act simultaneously and result in a non-negligible accretional component in the formation of Holocene soils in loess regions across the Northern Hemisphere. The luminescence ages allowed the modeling of accumulation rates for the Holocene soil which are similar for European, Chinese and U.S.A. loess sites investigated and vary from 2 cm ka −1 to 9 cm ka −1 . While accretional pedogenesis has often been implicitly or explicitly assumed in paleoclimatic interpretation of loess-paleosol sequences, especially in the Chinese Loess Plateau, our luminescence data add direct evidence for ongoing sedimentation as interglacial soils formed. • High-resolution magnetic susceptibility record as paleoclimate proxy. • High-resolution luminescence dating applied on multiple quartz fractions. • Initiation of magnetic susceptibility enhancement dated prior to ~11.7 ka. • Continuous dust accumulation during Pleistocene-Holocene transition and in Holocene. • Accretional Holocene soils in European, Chinese Loess Plateau and US loess sites.

Permo-Triassic aeolian red clay of southwestern England and its palaeoenvironmental implications

Late Permian and Triassic red mudstones are widely distributed and exposed in southwestern England. This homogenous, massive mudstone succession has been extensively studied for its palaeoenvironmental potential. However, its origin and palaeoenvironment remain under debate. The Triassic Mercia mudstone was early proposed to be aeolian loessic clay based on collapse nature when wetted or loaded and its similarities with aeolian clay in Quaternary Australia, but lacks experimental confirmation and is not generally accepted. In comparison with aeolian red clay in China, here we confirmed that the Triassic Mercia mudstone, together with the Upper Permian Aylesbeare mudstone, was dominated by aeolian clay. This was based on lines of evidence regarding sedimentary structure, particle grain size, geochemistry, micromorphology, and pedogenic features. The results showed that the Mercia mudstone and the Aylesbeare mudstone had sedimentary structures and grain size distributions that were similar to the aeolian red clay in the Chinese Loess Plateau. The major chemical elements correlated well with the aeolian red clay, with the exception of minor discrepancies in CaO and K2O. The similarity in the rare earth element (REE) distribution of the Mercia mudstone and the Aylesbeare mustone with aeolian red clay inferred their similar origin. Widespread pedogenic features indicated the universal development of palaeovertisols forming in alternating wet/dry climates. It was hypothesised that Permo-Triassic southwestern England was dominated by aeolian dust accumulation in a seasonal wet/dry climate, whereas perennial lakes or longstanding rivers across the study area might not exist.

Chronofunctions for new Mexico, USA soils show relationships among climate, dust input, and soil development

Rates of soil development provide critical information about the types and rates of geomorphic and landscape evolutionary processes. Soil development in arid and semiarid regions of the southwestern United States is predominantly controlled by influx of eolian dust, yet our ability to quantify the rates of morphologic development and of dust and carbonate incorporation is limited by available age control. We describe 10 pedons in the Socorro area of central New Mexico and analyze their silt, clay, and carbonate contents. These soils have well-established direct or indirect age control that we used to estimate average rates of dust and carbonate accumulation over the past ~0.5–800 ka. We also computed the profile development index (PDI) for these soils using 10 common morphologic properties and compare our resulting PDI chronofunction to those from northern and southern New Mexico. We find that the net silt-and-clay content increases in progressively older soils at rates similar to the profile-mass carbonate contents, presumably sourced primarily from eolian dust. Our chronofunction comparison indicates that soil development occurs more rapidly in higher latitude regions of New Mexico than in the drier warmer climates of the Socorro area and southern New Mexico. We interpret the N–S regional trend of soil development considering a regional climate gradient. We conclude that greater mean annual precipitation and cooler mean annual temperatures and/or slower rates of eolian dust accumulation into the soil profile at higher latitude northern sites cause the observed differences in regional soil development. This would promote greater mobility of available silt and clay, and also increase rates of soil formation, as indicated by the presence of argillans in late-Pleistocene soils of northern New Mexico.

The 3.6-Ma aridity and westerlies history over midlatitude Asia linked with global climatic cooling

Midlatitude Asia (MLA), strongly influenced by westerlies-controlled climate, is a key source of global atmospheric dust, and plays a significant role in Earth's climate system . However, it remains unclear how the westerlies, MLA aridity, and dust flux from this region evolved over time. Here, we report a unique high-resolution eolian dust record covering the past 3.6 Ma, retrieved from the thickest loess borehole sequence (671 m) recovered to date, at the southern margin of the Taklimakan desert in the MLA interior. The results show that eolian dust accumulation, which is closely related to aridity and the westerlies, indicates existence of a dry climate, desert area, and stable land surface, promoting continuous loess deposition since at least ∼3.6 Ma. This region experienced long-term stepwise drying at ∼2.7, 1.1, and 0.5 Ma, coeval with a dominant periodicity shift from 41-ka cyclicity to 100-ka cyclicity between 1.1 Ma and 0.5 Ma. These features match well with global ice volume variability both in the time and frequency domains (including the Mid-Pleistocene Transition), highlighting global cooling-forced aridity and westerlies climate changes on these timescales. Numerical modeling demonstrates that global cooling can dry MLA and intensify the westerlies, which facilitates dust emission and transport, providing an interpretive framework. Increased dust may have promoted positive feedbacks (e.g., decreasing atmospheric CO2 concentrations and modulating radiation budgets), contributing to further cooling. Unraveling the long-term evolution of MLA aridity and westerlies climate is an indispensable component of the unfolding mystery of global climate change.

Aeolian accumulation: An alternative origin of laterite on the Deccan Plateau, India

Laterite is ubiquitous in India and has been extensively studied. However, it is still controversial with respect to its origin, definition, classification, and implications in paleoclimate, tectonic history and topography evolution. Of those, the origin of laterite, either in situ weathering of protoliths or weathering of allochthonous input, is the most critical to address. The ca. 25-m-thick laterite (duricrust) capping the Deccan Plateau is conventionally hypothesized to derive from in situ weathering of the topmost basalt. However, this thick laterite lacks upward progressive weathering which is characteristic of lateritic profile. Instead, it displays: 1) homogeneity in weathering intensity through the duricrust; 2) a clear unconformable contact of laterite with red clay, which together suggests that this thick laterite is genetically unrelated to in situ weathering of the topmost basalt. Lines of evidence in mineralogy, granularity, and geochemistry proved the disconnection between this laterite and basalt, and in contrast, indicated its correlation to aeolian accumulation. In this study the laterite together with the red clay was proposed to derive from aeolian dust accumulation and weathering since 65 Ma within context of Indian plate drifting across the equator from southern to northern hemisphere.

Aeolian dust deposition and the perturbation of phosphorus transformations during long-term ecosystem development in a cool, semi-arid environment

Abstract Aeolian dust deposition is an important phosphorus (P) input to terrestrial ecosystems, but its influence on P dynamics during long-term ecosystem development remains poorly understood. In this study, we characterized P speciation using P K-edge XANES spectroscopy in surface soils (0–15 cm, A horizon) and contemporary aeolian dust collected at each site of a 3000-ky volcanic soil chronosequence in a cool, semi-arid environment. Phosphorus speciation in dust was dominated by calcium-bound P (Ca-P; 54–74%), with 11–23% iron and aluminum-bound P [(Fe + Al)-P] and 7–25% organic P (Po). In soils, Po contributed 1–23% of total P, being greater in older soils; however, the proportions of Ca-P (16–39%) and (Fe + Al)-P (48–82%) fluctuated with increasing weathering over the soil chronosequence. These soil fluctuations resulted from the accumulation and preservation of alkaline aeolian dust during pedogenesis in the semi-arid climate, which significantly increased soil Ca-P while decreasing the total amounts and relative abundances of soil (Fe + Al)-P. We suggest that the effects of an aeolian dust input on soil P transformations are functions of the relative magnitude and chemical composition of the dust input and the soil weathering intensity. For a given source of dust, when the net dust flux is greater than the weathering rate, dust accumulates and thus alters the pattern of P transformations during pedogenesis; otherwise, the dust influence on soil P transformations is negligible. By accurately identifying the chemical nature of P pools, our work highlights the advantage of P K-edge XANES spectroscopy over chemical extractions in examining soil P dynamics, and demonstrates how dust inputs can modify the Walker and Syers model of pedogenic P transformations in semi-arid environments. Overall, this work provides a foundation for understanding how dust influences P cycling during soil and ecosystem development, and indicates that dust inputs and composition, and the soil weathering rate, all must be considered for developing integrated climate-biogeochemical models with predictive power in terrestrial ecosystems.

Geochemical and detrital zircon U-Pb geochronological constraints on provenance of the Xiaomei red earth sediments (Bose Basin, Guangxi Province, southern China)

The Bose Basin in southern China is within a region influenced by the winter westerly monsoon and, thus, potentially subject to eolian dust accumulation. A red earth sequence developed on terraces of the Youjiang River (a branch of the Pearl River) records information about climate variation during the Pleistocene and its relationship to contemporaneous global climate changes. In this study, geochemical characteristics and U-Pb geochronology of detrital zircons of the red earth sequence at Xiaomei were investigated using X-ray diffraction (XRD), X-ray fluorescence (XRF), inductively coupled plasma mass spectrometry (ICP-MS), thermal ionization mass spectrometry (TIMS), and detrital zircon U-Pb dating analyses. Our results show that the red earth sediments are composed of quartz and clay minerals (kaolinite, illite, and mixed-layer illite/vermiculite) with minor hematite and goethite. Mobile elements such as CaO, MgO, Na2O, K2O, Sr and Ba are depleted and immobile elements such as TiO2, Al2O3, Fe2O3(t) and Zr are enriched in comparison with loess-paleosols of the Chinese Loess Plateau (CLP), the upper continental crust (UCC), and post-Archean Australian shale (PAAS). These data indicate that the Xiaomei red earth sediments have experienced intense chemical weathering, similar to that of the Xuancheng and Jiujiang red earth sections on the middle to lower reaches of the Yangtze River. The Xiaomei sediments have similar La/Th ratios, U/Pb vs. Th/Pb relationships, and rare earth element (REE) distributions to the CLP, UCC, and PAAS, and their low εNd(0) values are indicative of an upper crustal origin. The 147Sm/144Nd and 87Sr/86Sr ratios of the Xiaomei sediments are different from loess-paleosols of the CLP but similar to those of well-mixed river sediments. U-Pb dating of detrital zircons in the Xiaomei sediments shows that crystals from different units have slightly different age distributions. The full Xiaomei section yields a distribution similar to that of Upper Permian-Triassic clastic rocks in the Youjiang area, and the distribution of the middle to upper Xiaomei section additionally shows similarities to upper crust of the South China Craton. Our results indicate that the Xiaomei red earth sequence, which dates to the late Early to early Middle Pleistocene (~1.0–0.6Ma), accumulated predominantly from fluvially transported, locally weathered materials and, therefore, that the sediment-carrying capacity of the East Asian winter monsoon has been overestimated in previous provenance studies of red earth sediments in South China.

Provenance of loess in the central Great Plains, U.S.A. based on Nd-Sr isotopic composition, and paleoenvironmental implications

Loess of the central Great Plains, U.S.A., records intervals of Quaternary aeolian dust accumulation at rates among the highest known worldwide. This study used Nd-Sr isotopic analysis to investigate the provenance of Middle Pleistocene to Holocene loess in western and central Nebraska, U.S.A., essential information for understanding the paleoenvironmental conditions that allowed such rapid accumulation to occur at some times and not others. Nd-Sr isotopic data suggest that dust from unglaciated Great Plains landscapes has been the primary component of loess accumulated at both very high and low rates since the Middle Pleistocene. However, loess isotopic compositions all require an additional minor source with higher 87Sr/86Sr and lower εNd, most likely debris from Precambrian rocks in the Rocky Mountains, carried to the Great Plains by the Platte River system. The contribution from this secondary source—probably including glacially eroded sediment—was greater in Marine Isotope Stage (MIS) 3 and early MIS 2, but decreased somewhat just after the last glacial maximum (LGM) at the Bignell Hill section. Earlier research showed that the highest accumulation rates in that section also occurred after the LGM; thus our results likely indicate increased dust emission from unglaciated landscapes at that time. Greater plant moisture stress in a warming climate with still-low CO2 could have played a role in that increased dust production, along with lagged vegetation response; however, a strengthened westerly component of surface winds is the most straightforward explanation.

Onset of aridification by 34 Ma across the Eocene-Oligocene transition in Central Asia

Cenozoic climate has changed markedly from a warm, wet climate to the present cool, dry glacial-interglacial cycles. The largest of these cooling steps is thought to have taken place across the Eocene-Oligocene transition. Terrestrial airborne eolian loess is a direct result of land aridification; therefore, the prolonged formation of thick eolian loess deposits provides a key to aridification history in the geological past. However, the oldest eolian loess in the Asian interior has been dated to only 25–22 Ma. Here we present new sedimentological, geochemical, and magnetostratigraphic data from Cenozoic sections in southwestern Mongolia to show that the earliest eolian dust accumulation occurred by 34 Ma, ∼10 m.y. earlier than currently believed. We suggest that this oldest eolian dust accumulation provides direct evidence for enhanced aridification across the Eocene-Oligocene transition in Central Asia; this is explicable by reduced moisture transport caused by prevailing westerlies during retreat of the Neotethys Ocean. These climatic changes were related to the changing regional plate configuration as well as to global cooling and ice-sheet growth in Antarctica.

Lake Qinghai sediment geochemistry linked to hydroclimate variability since the last glacial

Geochemistry of basin sediments from semi-arid regions is valuable to understand past hydroclimatic changes. Here, we investigate the links of sedimentary geochemistry (Rb, Sr, Ca/Zr, TOC, and %CaCO3), carbonate mineralogy and ostracod shell δ18O of Lake Qinghai, a basin proximal to major dust production centers at mid-latitudes of the Northern Hemisphere, to changes in depositional conditions and hydroclimate during the past 32 ka. Surface lacustrine sediments are characterized by low-Rb, high-Sr, low-Rb/Sr, high-%CaCO3 and high-Ca/Zr values, in contrast to the chemical compositions of eolian loess (high-Rb, low-Sr, high-Rb/Sr, low-%CaCO3, and low-Ca/Zr). A direct comparison of soluble Ca and Sr in two short cores with instrumental water discharge data suggests that lacustrine precipitates in Lake Qinghai are dominated by authigenic aragonite formed under Ca2+-limited water conditions, and that the accumulation rate of aragonite dominantly depends on solute fluxes into the lake during the rainy seasons (late May to September). Our high-resolution down-core records show that sediments during the last glacial (∼32–19.8 ka) had high-Rb, low-Sr, low-%CaCO3, and low-Ca/Zr, indicating eolian dust (loess) accumulation in a desiccated basin under dry glacial conditions, further supported by grain size and pollen results. This type of sedimentation was maintained during the last deglacial (∼19.8–11.5 ka), but interrupted by episodic lacustrine precipitates with high-Sr, high-%CaCO3, high-Ca/Zr, and low-Rb. At ∼11.5 ka, sedimentary Rb/Sr, Ca/Zr, %CaCO3 and TOC show dramatic and permanent changes, implying an abrupt shift in the atmospheric circulation at the onset of the Holocene in the Lake Qinghai region. Lacustrine precipitates have persisted throughout the Holocene with a maximum during the early to mid-Holocene (∼10.5–8.0 ka). Since ∼8.0 ka, the gradual and significant decreases in aragonite and Sr accumulations in tandem with increasing dust deposit and more positive ostracod δ18O may be linked to a weakening of Asian summer monsoons during the mid-to-late Holocene. Overall, our records appear to show a high sensitivity of sediment development and geochemistry in Lake Qinghai to the regional hydroclimate changes since the last glacial.

Vegetation and environmental responses to climate forcing during the Last Glacial Maximum and deglaciation in the East Carpathians: attenuated response to maximum cooling and increased biomass burning

The Carpathian Mountains were one of the main mountain reserves of the boreal and cool temperate flora during the Last Glacial Maximum (LGM) in East-Central Europe. Previous studies demonstrated Lateglacial vegetation dynamics in this area; however, our knowledge on the LGM vegetation composition is very limited due to the scarcity of suitable sedimentary archives. Here we present a new record of vegetation, fire and lacustrine sedimentation from the youngest volcanic crater of the Carpathians (Lake St Anne, Lacul Sfânta Ana, Szent-Anna-tó) to examine environmental change in this region during the LGM and the subsequent deglaciation. Our record indicates the persistence of boreal forest steppe vegetation (with Pinus, Betula, Salix, Populus and Picea) in the foreland and low mountain zone of the East Carpathians and Juniperus shrubland at higher elevation. We demonstrate attenuated response of the regional vegetation to maximum global cooling. Between ∼22,870 and 19,150 cal yr BP we find increased regional biomass burning that is antagonistic with the global trend. Increased regional fire activity suggests extreme continentality likely with relatively warm and dry summers. We also demonstrate xerophytic steppe expansion directly after the LGM, from ∼19,150 cal yr BP, and regional increase in boreal woodland cover with Pinus and Betula from 16,300 cal yr BP. Plant macrofossils indicate local (950 m a.s.l.) establishment of Betula nana and Betula pubescens at 15,150 cal yr BP, Pinus sylvestris at 14,700 cal yr BP and Larix decidua at 12,870 cal yr BP. Pollen data furthermore support population genetic inferences regarding the regional presence of some temperate deciduous trees during the LGM (Fagus sylvatica, Corylus avellana, Fraxinus excelsior). Our sedimentological data also demonstrate intensified aeolian dust accumulation between 26,000 and 20,000 cal yr BP.

Holocene dust records from the West African Sahel and their implications for changes in climate and land surface conditions

AbstractWe reconstructed aeolian dust accumulation during the Holocene from two radiocarbon‐dated lake‐sediment sequences from the Manga Grasslands in northeastern Nigeria in order to investigate long‐term changes in the Harmattan dust system over West Africa and evaluate their possible causes. Flux values were low in the early Holocene, decreasing further to a minimum at around 6.2 kyr B.P. after which time they increased, steadily until around 2 kyr B.P. and then more sharply after this time. The long‐term variations in dust flux agree broadly with changes in the exposed area of the Lake Chad Basin to the northeast of the study sites, which vary inversely with the volume of Paleolake Megachad. More proximal sources of dust, including the fine fraction of local dune sand and floodplains of nearby rivers, have also made a contribution to the total dust load during times of enhanced dune and fluvial activity. Sharp rises in dust flux over the past century may be related to human activity. Broad patterns of change in dust flux during the Holocene agree with other reconstructions over the same period. However, we see no evidence for a stepped rise during the middle Holocene, as seen at some sites from the northeastern tropical Atlantic, suggesting that controls on the Harmattan dust system have differed from those affecting dust deposition elsewhere across northern Africa.

Evaluating Cenozoic equatorial sediment deposition anomalies for potential paleoceanographic and Pacific plate motion applications

If equatorial sediments form characteristic deposits around the equator, they may help to resolve the amount of northwards drift of the Pacific tectonic plate. Relevant to this issue, it has been shown that 230Th has been accumulating on the equatorial seabed faster than its production from radioactive decay in the overlying water column during the Holocene (Marcantonio et al. in Paleoceanography 16:260–267, 2001). Some researchers have argued that this reflects the deposition of particles with adsorbed 230Th carried by bottom currents towards the equator (“focusing”). If correct, this effect may combine with high pelagic productivity, which is also centered on the equator, to yield a characteristic signature of high accumulation rates marking the paleoequator in older deposits. Here we evaluate potential evidence that such an equatorial feature existed in the geological past. Seismic reflection data from seven meridional transects suggest that a band of equatorially enhanced accumulation of restricted latitude was variably developed, both spatially and temporally. It is absent in the interval 14.25–20.1 Ma but is well developed for the interval 8.55–14.25 Ma. We also examined eolian dust accumulation rate histories generated from scientific drilling data. A dust accumulation rate anomaly near the modern equator, which is not obviously related to the inter-tropical convergence zone, is interpreted as caused by focusing. Accumulation rates of Ba and P2O5 (proxies of export production) reveal a static equatorial signature, which suggests that the movement of the Pacific plate over the period 10–25 Ma was modest. The general transition from missing to well-developed focusing signatures around 14.25 Ma in the seismic data coincides with the mid-Miocene development of the western boundary current off New Zealand. This current supplies the Pacific with deep water from Antarctica, and could therefore imply a potential paleoceanographic or paleoclimatic origin. At 10.05–14.25 Ma, the latitudes of the seismic anomalies are up to ~2° different from the paleoequator predicted by Pacific plate-hotspot models, suggesting potentially a small change in the hotspot latitudes relative to the present day (although this inference depends on the precise form of the deposition around the equator). The Ba and P2O5 anomalies, on the other hand, are broadly compatible with plate models predicting slow northward plate movement over 10–25 Ma.

The magnitude, timing and abruptness of changes in North African dust deposition over the last 20,000 yr

Reconstructions of eolian dust accumulation in northwest African margin sediments provide important continuous records of past changes in atmospheric circulation and aridity in the region. Existing records indicate dramatic changes in North African dust emissions over the last 20ka, but the limited spatial extent of these records and the lack of high-resolution flux data do not allow us to determine whether changes in dust deposition occurred with similar timing, magnitude and abruptness throughout northwest Africa. Here we present new records from a meridional transect of cores stretching from 31°N to 19°N along the northwest African margin. By combining grain size endmember modeling with 230Th-normalized fluxes for the first time, we are able to document spatial and temporal changes in dust deposition under the North African dust plume throughout the last 20ka. Our results provide quantitative estimates of the magnitude of dust flux changes associated with Heinrich Stadial 1, the Younger Dryas, and the African Humid Period (AHP; ∼11.7–5ka), offering robust targets for model-based estimates of the climatic and biogeochemical impacts of past changes in North African dust emissions. Our data suggest that dust fluxes between 8 and 6ka were a factor of ∼5 lower than average fluxes during the last 2ka. Using a simple model to estimate the effects of bioturbation on dust input signals, we find that our data are consistent with abrupt, synchronous changes in dust fluxes in all cores at the beginning and end of the AHP. The mean ages of these transitions are 11.8±0.2ka (1σ) and 4.9±0.2ka, respectively.

Early Holocene aeolian dust accumulation in northeast China recorded in varved sediments from Lake Sihailongwan

Annually laminated sediments of Lake Sihailongwan (SHL) in northeast China preserve a high resolution record of past climatic and environmental changes. Thin sections of varved early Holocene sediments were analyzed using light optical and scanning electron microscopic methods. Sediment micro-facies and geochemical analyses reveal two different seasonal clastic layer types: spring snow melt and dust layers. Dust layers distinctly differ from snow melt layers through their finer grain size, better sorting, higher Al and lower Mg and Ca contents. In contrast to recent Lake SHL sediments, during the early Holocene silt-sized dust has been deposited after spring snow melt and after pronounced spring diatom blooms. For the time interval between 11,580 and 7060 varve years BP dust layers were quantified at annual resolution. Highest intensities and frequencies of dust accumulation are observed in the period from 11,100 to 8200 varve years BP, in good agreement with dry conditions in this time interval documented by palaeoclimatic records derived from lake sediments and loess in central Asia and northern China. Based on modern meteorological observation of dust storms in China, the dust accumulation record mirrors mainly the variation in climatic conditions governing generation of cyclone and cold air surges in the arid and semi-arid mid-latitude regions of China and Mongolia. On multidecadal and centennial time scales, solar activity might have been an additional forcing factor for dust accumulation frequency in the early Holocene. Spectral analyses reveal 205-years and 88-years periodicities in variations of dust accumulation frequency that likely reflect the de Vries (Suess) and the Gleissberg solar cycles.

Using 14C dating of stable humin fractions to assess upbuilding pedogenesis of a buried Holocene humic soil horizon, Towada volcano, Japan

The genesis of a 40-cm-thick buried Holocene humic soil horizon in a 6-m-high sequence near Towada volcano, Japan, was examined by dating stable, plant-derived humin particles by AMS-based radiocarbon ( 14C), and by analyzing stable carbon isotope ratios (δ 13C), phytolith composition, and soil chemical properties. The AMS dating yielded calibrated ages ranging from 7570–7679 to 6180−6313 cal yr BP. We obtained a strong correlation (r = 0.99, ***p < 0.001) between sample depth and the mean age. The (now buried) humic soil was formed by the incremental accumulation of tephric loess and aeolian dust at a constant rate of ~ 30 mm per century for at least 1200 years. Whilst the soil surface was slowly rising, graminaceous vegetation was supplied at a constant rate so that developmental upbuilding pedogenesis ensued. The soil was buried and isolated by the fall of the Towada-Chuseri tephra about 6200 cal yr BP. Thus the tephra-soil sequence near Towada volcano represents both developmental and retardant upbuilding pedogenesis.

Palaeoclimatic considerations of talus flatirons and aeolian deposits in Northern Fuerteventura volcanic island (Canary Islands, Spain)

Fuerteventura volcanic island has been subject to considerable aeolian activity since the Late Pleistocene. The aeolian record includes inactive aeolian deposits with interbedded entisols, whose age by OSL dating ranges between 46 and 26ky BP. The Corralejo active dune field, where sand sheets, nebkhas, coppice dunes, blowouts, barchans and transverse dunes have been described, constitutes a more recent Aeolian deposit. Here the age is about 14ky BP. On Fuerteventura Island aeolian dust has been deposited on valleys and slopes. This last type of accumulation has been affected by gully incision, producing talus flatirons. Samples taken on the apex of these palaeo-slopes indicate an OSL age of 30 and 50ky BP. A palaeoclimatic succession has been interpreted during which a prevailing arid period took place in OIS 4, with the accumulation of aeolian dust. A humid period occurred in OIS 2, during which slopes were dissected and formed talus flatirons. An arid period about 14ky BP gave rise to the Corralejo dune field, which has continued until present with slight climatic oscillations.

Effect of vegetation coverage on aeolian dust accumulation in a semiarid steppe of northern China

Wind erosion and sand storms are common phenomena in semiarid steppes of northern China and could have important impact on soil nutrient balances. Vegetation coverage is one of the key factors influencing wind erosion and aeolian dust accumulation. We conducted a field experiment to investigate the effects of vegetation coverage on airborne dust accumulation and evaluated effects of dust input on the contribution of nutrients to vegetation-mulched fields. Five vegetation coverage treatments (15%, 35%, 55%, 75% and 95%) were constructed, with 0% coverage as a control. Vegetation coverage significantly affected dust accumulation in degenerated semiarid grasslands. The amounts of dust trapped by the increasing coverages were 1.7, 1.8, 2.0, 2.1 and 2.1 times of that by the control plot, respectively. The total accumulations reached a maximum of 2.5 g m−2 day−1 at 75% coverage and remained stable with further increasing vegetation coverage. The particles in the dust trapped by treatment without vegetation coverage were significantly coarser than those by treatments with vegetation. In addition, the dust trapped by treatments with vegetation contained more organic carbon, nitrogen and phosphorus content than that by the control plot. This finding indicates that areas with higher vegetation coverage can obtain more nutrients by trapping airborne dust in semiarid steppes.