ORCID Profile
0000-0003-3615-9171
Current Organisation
University of Oxford
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Publisher: Copernicus GmbH
Date: 15-05-2023
DOI: 10.5194/EGUSPHERE-EGU23-15791
Abstract: The recent catastrophic flooding across the world& #8217 s driest inhabited continent & #8211 Australia & #8211 has highlighted an urgent need to understand the climatic (atmospheric) and hydrological (land surface) mechanisms comprising hydroclimate. Records of past hydrologic change may help in this endeavor by informing us about different hydroclimate states and their manifestation on the land surface. By virtue of its antiquity, aridity and relative paucity of available sediment, however, the Australian continent preserves few records of long-term hydroclimate. As a result, we know little about long-term water availability and the drivers of surface hydrology and climate circulation, particularly for the dry inland regions where water resources and sensitive land surfaces need to be carefully managed.& One of the few areas in dryland Australia which preserves semi-continuous deposition of hydrologic change is the Willandra Lakes system. The Willandra Lakes are located on the semi-arid desert margin of southeastern Australia, yet its headwaters lie in the temperate eastern highlands. Long-term lake filling and drying is consequently driven by rainfall in the headwaters and hydrologic connectivity both across the catchment and between the lakes. These environmental changes & #8211 both long and short in duration & #8211 are recorded in the sediments of the downwind transverse dunes (lunettes). In this study we investigate long-term hydrologic connectivity across the catchment and between the lakes. Our approach uses a novel integration of both classical lake-level reconstruction based on lunette sedimentology, stratigraphy and luminescence geochronology, with hydrologic modelling of key event time slices over the last 60 ky, fed into a palaeoclimate model. We characterize the land-surface response to various hydroclimate states, so improving our understanding of dryland atmosphere-hydrosphere interactions.&
Publisher: Copernicus GmbH
Date: 04-03-2021
DOI: 10.5194/EGUSPHERE-EGU21-6067
Abstract: & & Many dryland regions of the world are at high risk of desertification from combined human land use and anthropogenic climate change. One symptom of desertification is the reactivation of previously stable dunefields. Since morphologies of stable dunes are thought to reflect wind regimes at the time of their formation, the degree to which dune orientation reflects modern winds may be one way to assess changes in wind regimes and the progression of desertification in a region.& & & & Here we investigate the relationship between wind dynamics and desert dune orientation in one region at risk of desertification, southeast Kazakhstan in Central Asia, on the basis of open-source software and open-access datasets. Using Google Earth Engine, we map dunes or interdune spaces within six palaeo-dunefields in the Ili-Balkhash area, by performing a multi-layer object-based image analysis (OBIA) on satellite remote sensing data (Sentinel-2 optical imagery and SRTM digital elevation models). A semi-automated GIS approach is used to undertake data cleansing and the quantification of dominant palaeo-dunefield orientations. The resulting orientation trends are concurrent with the region& #8217 s topography: The dunefields within the Ili valley show a narrow, mostly E-W oriented trend concurrent with the course of the valley while the orientation ranges become broader towards the open pre-Balkhash area.& & & & We then predict modern dune orientations by applying the maximum gross bedform-normal transport rule on reanalysed wind data for 2008-2018. This approach by Rubin and Hunter (1987) allows the deduction of sand transport and resulting bedform trends from wind direction frequencies. The predicted modern orientation trends for the dunefields in the Ili-Balkhash area yield only partial consensus with observed palaeo-bedform trends. We therefore propose that modern wind regimes are not exclusively responsible for existing dune morphologies in the region, and that dune orientation may be inherited from earlier wind regimes.& &
Publisher: MDPI AG
Date: 21-12-2021
DOI: 10.3390/QUAT5010001
Abstract: Loess provides a valuable terrestrial record of past environmental conditions, including the dynamics and trajectories of air mass circulation responsible for dust transport. Here we explore variations in the luminescence sensitivity characteristics of sedimentary quartz and feldspar as possible tools for identifying changes in source down a loess-palaeosol sequence (LPS). Luminescence sensitivity is a rapidly measurable index which is the product of interplay between source lithology and the history of the quartz or feldspar clasts. Variations in sensitivity of down profile may therefore reflect changes in sediment provenance as well as other factors such as weathering through pedogenesis. We undertake an empirical investigation of the luminescence sensitivity of quartz and feldspar from different grain-size fractions from the Schwalbenberg LPS in the German Rhine valley. We compare s les from a 30 m core spanning the last full glacial cycle with s les of oxygen isotope stage (OIS) 3–2 age exposed within nearby profile. We find an overall inverse relationship between quartz and feldspar sensitivity, as well as variability in sensitivity between different quartz grain sizes. Statistical analyses yield a significant correlation between IR50 sensitivity from unprocessed sediments and clay content, and feldspar sensitivity and Si/Al ratios down the core. Since Si/Al ratios may indicate changes in provenance, the latter correlation suggests that IR50 measurements on unprocessed s les may be used to provide a reliable, rapid scan of source variability over millennial timescales.
Publisher: Copernicus GmbH
Date: 03-03-2021
DOI: 10.5194/EGUSPHERE-EGU21-1721
Abstract: & & Loess & #8211 a homogeneous, predominantly silt-sized aeolian sediment & #8211 has long been recognised as a valuable terrestrial record of past environmental conditions. Loess deposits drape some 10% of the Earth& #8217 s land surface, accumulating almost continuously in some regions. Most aeolian dust is thought not to travel far, often deriving from fine-grained material transported by rivers from glaciated regions. The provenance of loess sediment is inferred from the trajectories of atmospheric circulation systems and how these may have changed in intensity and influence over a region through time. The most frequently used techniques for correlating aeolian dust deposits with likely source areas, including bulk geochemistry, age distributions of detrital zircons, and Sr-Nd isotope ratios in clays, remain limited in the information they may provide about loess provenance. Since loess is dominated by silicate minerals & #8211 namely, quartz and feldspars & #8211 it is advantageous to explore their potential as indicators of source changes within loess-paleosol sequences (LPS). Increasingly, researchers have been exploring variations in the luminescence characteristics of sedimentary quartz and feldspar as possible provenance tools. Of a range of approaches so far applied, luminescence sensitivity is the quickest to measure and provides a means to rapidly assess potential changes in sediment source down LPS.& & & & Luminescence sensitivity & #8211 the signal intensity per absorbed radiation dose & #8211 arises from the efficiency of charge traffic between traps and luminescence centres within a crystalline framework. In a sedimentary context, sensitivity is the product of interplay between source lithology and the history of the mineral in question. Consequently, shifts in sediment provenance may be observed through variations in luminescence sensitivity down LPS. Despite the presence of thick loess deposits across Europe, however, this approach has yet to be tested on this continent.& & & & Here we undertake an empirical investigation of the luminescence sensitivity characteristics of quartz and feldspar from different grain-size fractions at the Schwalbenberg LPS in the German Rhine valley. The Schwalbenberg LPS has recently been shown to respond to variability in Atlantic-driven climate oscillations in fine detail it follows, therefore, that changes in source will likely be recorded in its sediments. We test the potential of luminescence sensitivity as an indicator of changes in sediment source through time, comparing s les from a 30 m core (REM3) spanning the last full glacial cycle, with s les of oxygen isotope stage (OIS) 3-2 age exposed within a c. 6 m profile on the southern margins of the deposit. The temporal overlap of the two localities during OIS3 enables comparison of luminescence characteristics with respect to possible provenance during that timeframe we find an inverse relationship between quartz and feldspar sensitivity, as well as variability in sensitivity between different quartz grain sizes. There is some indication that feldspar sensitivity increases during periods of soil formation down the core. These observations may suggest source variability over millennial timescales.& &
Location: United Kingdom of Great Britain and Northern Ireland
No related grants have been discovered for Maike Nowatzki.