Sediment Availability Research Articles

Environmental control of the present-day sediment export along the extratropical Andes

Understanding how the environmental factors that determine erosion operate is essential to know the past and future evolution of the Earth and adequately manage natural resources. In this work, the main controlling factors of the current sediment export in the western side of the extratropical Andes (20°-55°S) are investigated using multidecadal series of specific suspended sediment yields from 42 rivers, as well as land cover, climatic, cryospheric, topographic, seismological and geological data. Through an automatic selection of Generalized Additive Models based on predictability and complexity, it was found that the combined effects of extreme runoff, glacier cover and channel steepness explain ~90 % of the spatial variability of sediment export. The runoff effect varies from positive for hyper-arid and semi-arid settings to slightly negative for moderate and wet settings, probably because of an associated increase in vegetation coupled with a recurrence and magnitude of floods that becomes greater than the time it takes for the basins to generate sediment. Cryosphere and channel steepness influences were also observed on the average suspended sediment concentration, which is less associated with water availability and more associated with erodibility and sediment availability.

El Niño–Southern Oscillation (ENSO)-driven hypersedimentation in the Poechos Reservoir, northern Peru

Abstract. Although extreme El Niño events (EENEs) have always impacted hydrological anomalies and sediment transport in South America, their intensification by global warming and their association with changes in human activities and land cover after humid periods may lead to the acceleration of sediment transfers in river systems and dam reservoirs. This situation may threaten soil and water resources in arid and semiarid regions highly dependent on water originating from large dams. In this study, we investigated the sediment sequence accumulated in the Poechos Reservoir (northern Peru) and provided a retrospective reconstruction of the interactions of El Niño–Southern Oscillation (ENSO), agricultural practices and vegetation cover changes with sediment dynamics (1978–2019). To this end, a sediment core was dated and characterized by physical and chemical analyses (e.g., scanner tomography, X-ray fluorescence, particle size analysis) to estimate the evolution of sedimentation rates and changes in sediment sources during the last 5 decades. Sediment tracing results indicated the occurrence of changes in sediment sources associated with positive and negative phases of the Eastern Pacific index with a greater contribution of the lowland dry-forest area in comparison to that of the Andean area to sediment during the El Niño events (mean contribution of 76 %; up to 90 % during the coastal El Niño events (CENEs) of 2016–2017). This source contribution was mostly controlled by the stationary rainfall occurring during the EENEs in the lowland dry-forest area characterized by a low vegetation cover. Overall, after an extreme phase of ENSO, like after the EENE 1982–1983, the normal discharges and persistent sediment supplies from the middle- and upper-catchment parts led to river aggradation and the storage of substantial amounts of sediment in alluvial plains. In the absence of a significant EENE between 1983 and 1997, the large volume of sediment stored in the alluvial plains was exported by the EENE 1997–1998 resulting in an increase in sedimentation rate of 140 % after 1997 with a significant aggradation of the deltaic zone of the reservoir. In addition to the impact of extreme climate events on sediment dynamics, the development of agriculture along the riverine system after an extreme phase of ENSO increased the availability of sediments in the main channel of the rivers, easily transported by the next EENE. This study suggests that intensification of human activities associated with a higher frequency of extreme rainfall events amplified the quantity of sediment transported by the river system, which will significantly decrease the lifespan of the reservoir, which is essential to meeting the freshwater demands of the farmers and the populations living in this arid and semiarid region.

Holocene aeolian activity triggered by climate change and endorheic-exorheic drainage transition in the Headwater Region of the Yellow River, Tibetan Plateau

The Headwater Region of the Yellow River (HRYR) is located in the northeastern Tibetan Plateau at an altitude higher than 4000 m above sea level. Modern aeolian sandy land is widely distributed in the HRYR, and the reactivation of paleo aeolian sediments under the disturbance of climate change and human activities has become a hot issue since the past decades. However, the chronology of paleo aeolian sediments in this region remains poorly understood. In this study, 22 samples of aeolian sediments were collected from six sections and dated using optical stimulated luminescence (OSL). Combining the OSL data with 15 previously published OSL ages from three sections in the HRYR, the following results were obtained. The oldest aeolian sand sediments in the HRYR are dated at 7.12 ± 0.39 ka. The remaining aeolian sediments were deposited in the late Holocene, ranging between 3.29 ± 0.42 ka and 0.18 ± 0.01 ka. In the late Holocene, phases of intensifying aeolian activities were recorded by clusters of OSL ages at 2.12–1.81 ka, 1.30–1.26 ka, and the Little Ice Age. In our dataset (37 OSL ages), 27 ages correspond to the past millennium and the aeolian activity phases mainly occurred in the Little Ice Age. The relatively scarce aeolian sand deposits in the early Holocene is likely due to the existence of Maduo Paleolake, which maintained a high water stand, inhibiting the availability of sediments for wind erosion. The absence of mid-Holocene aeolian sediments in this region is attributed to the optimum climate during this period although the HRYR had opened around 7.0 ka BP. Coupled with the drier and cooler climate, the exposure of lacustrine sediments during the endorheic-exorheic drainage transition (EEDT) of the HRYR ultimately triggered enhanced aeolian activities in the late Holocene.

UNDERSTANDING THE BENEFITS AND LIMITATIONS OF COASTAL NBS

As Coastal NBS are implemented more widely it is important to be clear in our definition of NBS and understand the benefits and limitations of the various approaches. Coastal NBS involve using natural features to offer, or improve, coastal protection while producing additional economic, environmental and social benefits. There are, however, a broad range of solutions spanning the creation of large expanses of habitats, hybrids of habitats and harder engineered structures and ecological enhancements of existing infrastructure. Costs and performance therefore vary widely and not all NBS are low cost or self-maintaining. In many instances the capacity for sedimentary habitats to self-maintain will depend on sediment availability and this emphasizes the need to consider whole life costs when comparing NBS with more traditional harder defences. The incorporation of habitat components can however bring multiple benefits for both nature and people. Implemented correctly, Coastal NBS therefore have the potential to be ‘no regret’ solutions in many locations.

Mesoscale Shoreline Evolution on a Carbonate Sand Island: Anegada, British Virgin Islands

Anegada, the easternmost island of the Virgin Islands group (Caribbean Sea), is a low Pleistocene carbonate platform surrounded by Horseshoe Reef, the world’s third-largest fringing reef. The western part of the island consists of an extensive beachridge plain (>40 ridges). The sandy carbonate shoreline exists in three morphodynamic domains that exhibit distinctive behaviour over the 59-year study period (1953 to 2012). The northern shore is dominated by westerly longshore drift under fair-weather conditions and cross-shore sediment transport during high-energy events. Storm wave run-up and high nearshore sediment availability contribute to the construction of shore-parallel beachridges. The western end of the island is affected by refracted waves that drive strong erosion and sediment transport. This is reflected in a succession of alternating rapid shoreline recession and progradation phases over the study period. The south–central shoreline is exposed to low wave energy and is stable and colonised by mangroves. The fringing reef plays a dominant role in mesoscale shoreline morphodynamics, both as a sediment source and in wave energy dissipation. Quasi-stable points and embayments suggest a strong influence of the reef framework in controlling the shoreline’s morphology and position. Sediment transfer from the reef to the shoreline appears to take place via shore-oblique, linear sediment transport pathways that develop across the lagoon in response to the modification of incoming waves. Cannibalisation of the shoreline sediment over the past 50 years is leading to straightening of the shoreline planform. This is counter to the long-term (Holocene) development of beachridges and suggests a change from a strongly positive to negative sediment budget.

Distinctive sedimentary processes on two contrasting tidal flats of the Yellow River Delta

Coastal tidal flats provide valuable ecosystems, but are highly sensitive to tidal dynamics, sea-level rise, and human activities. Tidal inundation depth and frequency are known to affect tidal flat morphodynamics. However, the causes, processes and extent remain uncertain, particularly given the associated changes in sediment availability. In this study, we monitored the hydrodynamics, sediment transport, and morphological changes on two tidal flats in the northern and southern parts of the Yellow River Delta, with contrasting tidal regimes. The data showed that longer inundation periods under diurnal tides gained additional sediment and deposition than under semi-diurnal tides, because of the associated increase in water depth and sediment availability. The wave impact increased at the site with a semi-diurnal tidal regime owing to the lower water depth, where a larger bed shear stress led to tidal flat erosion. These results indicated that the combination of tidal regime and the occurrence of powerful waves played a joint role in controlling bed erosion, sediment availability, and short-term tidal flat evolution. This has implications for coping with delta erosion by enhancing local sediment availability in diurnal tidal regions and restoring vegetation to attenuate waves in semi-diurnal regions of the Yellow River Delta.

High spatiotemporal resolution analysis on suspended sediment and microplastic transport of a lowland river

The suspended sediment (SS) and microplastic (MP) transport in rivers is quite a complex process, influenced by several spatially and temporally changing factors (e.g., hydrology, sediment availability, human impact). Researchers usually investigate these factors individually and based on limited repetition in space and time. Therefore, this study aims to compare the driving factors of SS and MP transport by applying dense temporal (72 measurements) and spatial monitoring (at 26 sites). This study was performed on the medium-sized Tisza River, Central Europe. The suspended sediment concentration (SSC) was measured by water sampling and estimated based on Sentinel-2 images, while MP concentration was measured by pumping of water (1 m3). The SSC of the Tisza varied between 12.6 and 322.5 g/m3, whereas the MP concentration ranged 0–129 item/m3. Most of the transported particles were fibers (81–98 %), thus, it was assumed that MPs originated from wastewater. The results reflect that the hydrological conditions basically influence the SS and MP concentrations, as a strong positive correlation was found (ρSSC–MP = 0.6) between them during a year; however, the correlation during floods (minor floods: ρ = 0.63; medium floods: ρ = 0.41) was higher than at low stages (ρ = 0.1). It was assumed that run-off and mobilization of channel materials both contribute to increased SS and MP transport during floods. In contrary, the importance of mobilization of channel materials and wastewater input increase during low stages. The repeated measurements revealed that slope and velocity conditions, proximity of sources, tributaries, and dams influence the longitudinal changes in SS and MP concentrations. However, the effects of tributaries and dams are ambiguous (especially for MP) and require further research. The longitudinal measurements were conducted at low stages; hence, moderate negative correlations (ρ2021 = −0.35; ρ2022 = −0.41) were found between the SS and MP concentrations. Therefore, additional monitoring during (overbank) floods and denser spatial sampling are required to precisely reveal the spatiotemporal changes of SS and MP concentrations in rivers.

Dune interactions record changes in boundary conditions

Abstract Windblown dunes are common features in our solar system, forming on planetary surfaces that span wide ranges in gravity and both atmospheric and sediment properties. The patterns formed by their crests, which are readily visible from orbital images, can record information about recent changes in boundary conditions, such as shifts in wind regime or varying sediment availability. Here, we demonstrate that the density of dune interactions (where neighboring crestlines are close to each other) within a dune field is an indicator of such changes. Using orbiter-based images of 46 dune fields on Earth and Mars, we compiled a database of pattern parameters including dune spacing, crestline orientation, and interaction density. Combined with sediment fluxes derived from ERA5-Land data and a martian global circulation model, we also compiled dune turnover time scales (the time it takes for a dune to migrate one dune length) for each investigated dune field. First, we show that dune fields undergoing changes in boundary conditions display higher than expected dimensionless interaction indices. Second, dune fields with longer turnover times display a wider range in interaction indices on both Earth and Mars because they are more likely to be observed while still adjusting to recent changes in boundary conditions. Thus, a dune field’s interaction index offers a novel tool to detect and possibly quantify recent environmental change on planetary surfaces.

Statistical self-similarity of detrital zircon U-Pb ages reveals sedimentary provenance: A case study from the Chinese Loess Plateau

A major concern of the geoscience community is often where sediments originally come from — this is a material's provenance. Tracing provenance allows us to determine how a material moved from its source to its sink, and thereby to evaluate the tectonic and paleoclimatic history. Detrital zircon UPb geochronology has long been used for this purpose. However, current approaches to measuring (dis)similarity in zircon age distributions may lead to erroneous geologic interpretations. Here we propose an Age-Number fractal model to characterize zircon age densities and perform intersample comparisons using multidimensional scaling. The advantage of the new method is that compared to such traditional methods as Kolmogorov-Smirnov test, it accentuates holistic rather than partial differences between two age distributions and is less-affected by data biases related to grain-size sorting and uneven sample sizes. We then use this model to unravel the debatable provenance of the Chinese Loess Plateau (CLP) by comparing the zircon ages of Quaternary loess on the CLP with that of loose sediments from potential source regions. The model divides the CLP into four distinct provenance zones, receiving materials primarily from the northeastern Tibetan Plateau, upper Yellow River, and/or Mu Us Desert. Our observations corroborate that the aeolian (East Asian monsoon and Westerlies) and fluvial (Yellow River) processes play a joint role in the dust deposition. A new pattern of spatial heterogeneity in the loess provenance is established and can be interpreted as a combined effect of atmospheric circulation patterns, availability of riverine sediments, and such factors as aridification, implying a more dynamically-evolved CLP than previous thought. Our results will aid future development and interpretation of the dust-based paleoclimatic proxies.

Diurnal and seasonal source‐proximal dust concentrations in complex terrain, West Greenland

AbstractDiurnal and seasonal cycles of aeolian activity are well‐constrained for low latitude dust source regions and provide valuable insights into relationships between dust emissions and environmental drivers. Such cycles have received little systematic attention in high latitude dust source areas (≥50°N and ≥40°S), and understanding them will aid the modelling of atmospheric dust over different timescales. This paper examines the timing and drivers of atmospheric dust concentration close to source at ice‐free locations c. 6 km and c. 37 km from the Greenland Ice Sheet margin. Dust concentration, and associated environmental drivers including wind speed and velocity, air temperature and humidity, was measured from April–October 2018 and April–August 2019. Measured dust concentrations were a similar order of magnitude to source‐proximal values measured globally and varied from 0 to ≥1000 μg m−3. Diurnal cycles in the environmental drivers of dust emission were similar to those observed in low latitudes, but unlike in the low latitudes, there was no clear diurnal pattern of dust concentration. Only 3 out of 17 recorded dust events showed a significant positive relationship between wind speed and dust concentration, and factors such as wind direction, humidity and sediment availability are the over‐riding controls on dust activity at the event and seasonal scales. Whereas 7 dust events are attributed to down‐valley katabatic winds, 10 events were associated with a westerly sea breeze blowing up‐valley towards the ice sheet and high atmospheric moisture content. If deposited on the ice, this dust will alter ice albedo both directly and indirectly, (e.g. through the promotion of algal blooms) affecting cryospheric melt rates. Our results demonstrate an intricate relationship between first‐order controls and dust concentration that raises challenges for modelling the uplift and subsequent dust transport from high latitude sources, especially the appropriateness of assumptions based on emissions behaviour at low latitudes.

Winds of opportunity: The effects of wind on intertidal flat accretion

Intertidal ecosystems are threatened by sea level rise and anthropogenic pressures. Understanding the processes controlling the morphodynamic developments of tidal flats is crucial for sustainable management of these systems. Analysis of three extensive fieldwork campaigns carried out on two adjacent mudflats fringing the Dutch Western Wadden Sea (from 2016 to 2018) provides important new insights into the conditions controlling a permanent increase of tidal flat elevation (‘accretion’), in which the wind and consolidation processes play a pivotal role. Sediment temporarily settles (‘deposition’) on the flats during a period of high suspended sediment availability and water level setup (often following a storm). A tidal flat accretes when a new layer of sediment over-consolidates: a state in which the bed strength is much larger than it would attain during inundated conditions, due to high stresses experienced during prolonged drying. This happens when a phase of sediment deposition is followed by a sufficiently long period with a low ambient water table (phreatic level) and aerial exposure. The chronological order of sediment deposition and over-consolidation provides a window of opportunity for tidal flat accretion. Such a window of opportunity depends on the hydrodynamic forcing (tides, waves, wind), on the consolidation state of the bed, and on sediment availability. Wind plays a crucial role in creating the conditions for tidal flat accretion because the wind direction influences the duration of a low water table and aerial exposure and therefore (over-)consolidation rates, which we refer to as the ‘winds of opportunity’. An abundance of sediment may even limit tidal flat accretion, because large deposition rates substantially increase consolidation timescales.

The Application of CNN-Based Image Segmentation for Tracking Coastal Erosion and Post-Storm Recovery

Coastal erosion due to extreme events can cause significant damage to coastal communities and deplete beaches. Post-storm beach recovery is a crucial natural process that rebuilds coastal morphology and reintroduces eroded sediment to the subaerial beach. However, monitoring the beach recovery, which occurs at various spatiotemporal scales, presents a significant challenge. This is due to, firstly, the complex interplay between factors such as storm-induced erosion, sediment availability, local topography, and wave and wind-driven sand transport; secondly, the complex morphology of coastal areas, where water, sand, debris and vegetation co-exists dynamically; and, finally, the challenging weather conditions affecting the long-term small-scale data acquisition needed to monitor the recovery process. This complexity hinders our understanding and effective management of coastal vulnerability and resilience. In this study, we apply Convolutional Neural Networks (CNN)-based semantic segmentation to high-resolution complex beach imagery. This model efficiently distinguishes between various features indicative of coastal processes, including sand texture, water content, debris, and vegetation with a mean precision of 95.1% and mean Intersection of Union (IOU) of 86.7%. Furthermore, we propose a new method to quantify false positives and negatives that allows a reliable estimation of the model’s uncertainty in the absence of a ground truth to validate the model predictions. This method is particularly effective in scenarios where the boundaries between classes are not clearly defined. We also discuss how to identify blurry beach images in advance of semantic segmentation prediction, as our model is less effective at predicting this type of image. By examining how different beach regions evolve over time through time series analysis, we discovered that rare events of wind-driven (aeolian) sand transport seem to play a crucial role in promoting the vertical growth of beaches and thus driving the beach recovery process.

Alluvial development during climate fluctuations depicted with spectral decomposition of the Middle Triassic to Lower Jurassic post‐rift succession in the Horda Platform (Norway) and the impact on reservoir properties

AbstractFor the first time, this study presents interpretations of alluvial fans in spectral decomposition RGB Blends, analysed in seismic time slices from the Middle Triassic to Lower Jurassic stratigraphical interval of the Horda Platform (northern North Sea). The time slices record a shifting alluvial fan front, fluvial variability, uplift and erosion and reveals depositional elements that may set the common conception of the geological development of this area during the Early–Middle Mesozoic up for discussion. Results show that the Upper Triassic Lunde Formation in the eastern margin of the Horda Platform was characterized by the deposition of coalesced alluvial fans. A variable extent of the fan front through the Upper Triassic is linked to interplaying allogenic factors: uplifted source areas in the aftermath of Early–Middle Triassic rifting determined sediment availability; climate transitioning from arid to semi‐humid, with increasingly fluctuating precipitation, controlled sedimentation, and run‐off; provenance dictated bulk sedimentology and affected prevailing alluvial processes. An overall retreat of the fan system through the Late Triassic coincided with a significant change in landscape characteristics at the transition into the overlying Statfjord Group. Uplift and initial tilting of the Horda Platform caused landscape degradation and the formation of plateaus and incised valleys, contemporaneous with increased humidity and marine transgression, forming estuaries. The shift in depositional style has implications for reservoir properties, creating complexity and heterogeneity in terms of facies distribution and connectivity, which may benefit potential CO2 storage. Upper Triassic alluvial fan development in the Horda Platform (northern North Sea) depicted through spectral decomposition of seismic time slices Enhanced level of seismic stratigraphic interpretation with RGB blending Impact of allogenic factors on alluvial depositional development Implications of alluvial variability on reservoir properties

Aeolian sedimentation in the Vychegda river valley, north-eastern Europe, during MIS 2–1

Aeolian sediments and landforms of the former continental ice sheets' periphery can be used as invaluable sources of information on palaeoenvironmental changes. In the Northeastern Europe, there is very limited knowledge on the structure and age of the aeolian deposits and landforms. This study presents the first data on distribution and chronology of aeolian sediments and landforms in the Vychegda River basin (northeast of the East European Plain). Using grain-size analysis, radiocarbon and OSL dating, we were able to determine the age of the sediments found in the region and study their lithological composition. We discovered aeolian sediments comprising the upper parts of the most river terraces throughout the valley; they come in forms of dunes, dune fields, and sandy or loess-like covers. Previously it was argued that the terraces’ upper parts were comprised by glaciolacustrine deposits, but lithological composition of these sediments showed their aeolian origin. It was found that most of the aeolian sediments have formed in the Late Glacial, between 17 and 10.5 ka. We consider that increased fluvial activity and melting of permafrost were the main causes of the aeolian processes activization and that sediment availability was the most important controlling factor during that time.

Geological sketch map and implications for ice flow of Thwaites Glacier, West Antarctica, from integrated aerogeophysical observations.

The geology beneath Thwaites Glacier, the Antarctic glacial catchment most vulnerable to climate change, is unknown. Thwaites Glacier lies within the West Antarctic Rift System, but details of the subglacial geology relevant to glacial flow, including sediment availability, underlying lithology, and heat flux, are lacking. We present the first sketch map of the subglacial geology of Thwaites Glacier, interpreted from maps of airborne gravity, magnetic and radar data, supported by 2D models and 3D inversion of subsurface properties, and the regional geological context. A zone of Cretaceous mafic magmatism extending ~200 km inland from the coast is interpreted, while sedimentary basins are restricted to a region 150 to 200 km inboard of the coast, underlying just 20% of the catchment. Several granitic subglacial highlands are identified, forming long-lived topographic highs. Our geological interpretation places constraints on the basal properties of Thwaites Glacier, laying the foundation for both improved predictions of ice sheet change and studies of West Antarctic tectonics.

Long‐Term Monitoring of Coupled Vegetation and Elevation Changes in Response to Sea Level Rise in a Microtidal Salt Marsh

AbstractTight interplays between physical and biotic processes in tidal salt marshes lead to self‐organization of halophytic vegetation into recurrent zonation patterns developed across elevation gradients. Despite its importance for marsh ecomorphodynamics, however, the response of vegetation zonation to changing environmental forcings remains difficult to predict, mostly because of lacking long‐term field observations of vegetation evolution in the face of changing rates of sea level rise and marsh vertical accretion. Here we present novel data of coupled marsh elevation‐vegetation distribution collected in the microtidal Venice Lagoon (Italy) over nearly two decades. Our results suggest that: (a) despite increasing absolute marsh elevations (i.e., above a fixed datum), vertical accretion rates across most of the studied marsh were not high enough to compensate for relative sea‐level rise (RSLR), thus leading to a progressive marsh drowning; (b) accretion rates ranging 1.7–4.3 mm/year are overall lower than the measured RSLR rate (4.4 mm/year) and strongly site‐specific. Accretion rates vary largely at sites within distances of a few tens of meters, being controlled by local elevation and sediment availability from eroding marsh edges; (c) vegetation responds species‐specifically to changes in environmental forcings by modifying species‐preferential elevation ranges. For the first time, we observe the consistency of a sequential vegetation‐species zonation with increasing marsh elevations over 20 years. We suggest this is the signature of vegetation resilience to changes in external forcings. Our results highlight a strong coupling between geomorphological and ecological dynamics and call for spatially distributed marsh monitoring and spatially explicit biomorphodynamic models of marsh evolution.

Barrier breach recovery in a lacustrine environment: Role of sediment supply and shoreline development

Barrier breaching in response to high water levels and storm activity is common in the Laurentian Great Lakes of North America. Lacustrine breach recovery depends on the availability and transport of sediment from both alongshore and offshore sources and interannual variations in water levels. The recovery of two barrier breaches along the east coast of Point Pelee foreland, located on the north shore of Lake Erie, was monitored during a period of record high-water levels between 2016 and 2022. Despite both breaches developing during the same period, the southern breach (East Beach, EB) started to recover and close despite increasing water levels, while the northern breach (Hillman Marsh, HM) did not recover even as water levels fell below pre-breach levels. The opposing responses and hysteresis curves of the breaches are associated with differences in the availability of sediment from adjacent shorelines due to varying degrees of human impacts at each site. The increased sediment supply from more natural and diffusive shorelines adjacent to EB allowed for breach recovery, whereas a limited sediment supply from the highly fortified shoreline at HM prohibited breach recovery. If barrier recovery or reformation further landward is not possible, sensitive marsh habitat critical to migratory birds will be exposed to increasing wave energy, particularly as the extent and duration of lake ice decreases with climate change.

Meta-analysis of a large bedload transport rate dataset

The estimation of bedload transport, a type of coarse fluvial sediment motion, is challenging because of higher-order, complex, and time-variable environmental processes. Still, models for calculating bedload transport mostly rely on semi-empirical formulae derived from time-averaged laboratory flume or field measurements and involve cross-section averaging of hydro-environmental parameters. Additionally, many models assume infinite, constant availability of sediment, which is unrealistic in natural environments. While most published models yield excellent results on the dataset they were trained on, they may be significantly inaccurate when applied to other cases. Also, more recent formulae relying on considerable amounts of data still lead to high calculation uncertainty. While the importance of short-term dynamics, for example, driven by turbulence, for bedload transport is well known, this study investigates the relevance of time-variable processes at monthly to seasonal scales. Our analysis of a large dataset and remote sensing data shows evidence for seasonal variability in measurements of bedload transport rates and challenges the validity of Gaussian statistics for interpolating bedload transport models. Measured bedload transport rates were smaller when snowmelt was taking place and when no glacier was present in the catchment, and were best represented by extreme value distributions. By controlling for biases from measurement devices, geomorphic patterns, and the presence of an upstream dam, we show that steady, constant at-a-station hydraulics only explain a limited share of the variance in the measurements. Ultimately, a model for estimating bedload transport rates should consider the temporal variability of processes across all scales, from turbulence to climate.

High-resolution OSL dating of loess in Adventdalen, Svalbard: Late Holocene dust activity and permafrost development

There is considerable uncertainty over the nature and causes of Holocene dust activity in the Arctic, and its links to climatic changes. Loess deposits act as near-source archives of dust deposition and provide a means to address these uncertainties. Here we develop a fully independent age model for a loess core taken in Adventdalen, Svalbard, based on 136 quartz luminescence ages taken at 2 cm intervals. This represents the most detailed luminescence dating analysis undertaken to date on a sedimentary archive. Extensive laboratory tests and stratigraphic consistency indicate that the quartz luminescence ages are reliable. Together with grain size and cryostratigraphic analyses, as well as stratigraphic investigation of an adjacent loess exposure, the exceptional detail of the chronology combined with Bayesian age modelling uniquely allows changes in loess accumulation rates, particle size and permafrost development to be reconstructed over the last 3000 yrs on 101–103 yr timescales. The results show that loess deposition was mostly continuous over this interval, albeit with a short period of reworking or non-aeolian sedimentation during the Little Ice Age. Permafrost development in the loess is dominantly syngenetic, with ice contents increasing with depth. There is considerable variability in loess mass accumulation rate over the late Holocene, with peaks occurring during the last 250 yrs, as well as at 750–900, 1050–1200, 1400–1600, 1900–2450 and possibly 2700–3000 a. These peaks generally coincide with increased coarse silt deposition, potentially suggesting a link with greater wind activity. However, the peaks also seem to coincide with possible warm phases on Svalbard, which would rather imply that temperature-driven sediment availability in glaciofluvial source areas is the main control on dustiness in Adventdalen. In any case, the rates of loess deposition in the Adventdalen core are exceptionally high globally (up to 0.35 cm yr−1/2900 g m−2 yr−1 sedimentation and mass accumulation rates, respectively), and if representative of wider patterns across Svalbard, may suggest that the archipelago is a more important high latitude dust source than previously realised.

On the Geomorphic, Meteorological, and Hydroclimatic Drivers of the Unusual 2018 Early Summer Salt Dust Storms in Central Asia

AbstractA series of synoptically forced dust events, including an extreme salt storm from the Aralkum desert, stuck large parts of Central Asia during early summer 2018, causing flight cancellation, widespread haze, and salt deposition on croplands. This manuscript explores the geomorphic, meteorological, and hydroclimatic drivers of the unusual dust activity based on the three prerequisite factors of dust outbreak: sediment supply, sediment availability, and dust‐uplifting winds. Dry lake beds and lower river floodplains are identified as the source area of frequent dust episodes likely due to the abundant supply of fine‐grain sediments. Whereas, minimal dust activity was detected at the region's major sandy deserts. The salt dust storms were triggered by cold intrusion and strong postfrontal winds at the southeast flank of a rapidly developing anticyclone over western Russia which was enhanced by the Scandinavian blocking upstream. The 2018 early summer dust events in Central Asia were identified as part of spatially compounding weather hazards linked to a slow‐moving synoptic wave pattern across the Northern Hemisphere midlatitudes. Finally, the aeolian sediment availability at the dust source areas was enhanced by below‐average soil moisture and vegetation during summer 2018 linked to reduced precipitation in the preceding winter. The 2017/18 winter precipitation deficit was driven by a double‐dip, Central Pacific La Niña episode associated with large‐scale precipitation‐suppressing subsidence and enhanced moisture flux divergence over Central Asia.