X-ray Fluorescence Core Scanning Research Articles

Tracing rate and extent of human-induced hypoxia during the last 200 years in the mesotrophic lake, Tiefer See (NE Germany)

Abstract. The global spread of lake hypoxia, [O2] < 2 mg L−1, during the last 2 centuries has had a severe impact on ecological systems and sedimentation processes. While the occurrence of hypoxia was observed in many lakes, a detailed quantification of hypoxia spread at centennial timescales remained largely unquantified. We track the evolution of hypoxia and its controls during the past 200 years in a lake, Tiefer See (TSK; NE Germany), using 17 gravity cores recovered from between 10 and 62 m water depth in combination with lake monitoring data. Lake hypoxia was associated with the onset of varve preservation in the TSK and has been dated by varve counting to 1918 ± 1 at 62 m water depth and reached a lake floor depth of 16 m in 1997 ± 1. This indicates that oxygen concentration fell below the threshold for varve preservation at the lake floor (> 16 m). Sediment cores at 10–12 m depth do not contain varves indicating good oxygenation of the upper-water column. Monitoring data show that the threshold for hypoxia, and the intensity and duration of hypoxia which are sufficient for varve preservation, is a period of 5 months of [O2] < 5 mg L−1 and 2 months of [O2] < 2 mg L−1. Detailed total organic carbon (TOC), δ13Corg, and X-ray fluorescence (XRF) core scanning analyses of the short cores indicate that the decline in dissolved oxygen (DO) started several decades prior to the varve preservation. This proves a change in the depositional conditions in the lake, following a transition phase of several decades during which varves were not preserved. Furthermore, varve preservation does occur at seasonal stratification and does not necessarily require permanent stratification.

Interpretation and implications of high-resolution hydroclimatic records of the past 7,000 years based on Gaho paleolake sediments in South Korea

In this study, we investigated the past hydroclimate and its controlling factors over East Asia by reconstructing hydroclimate variability during the middle-to-late Holocene using rainfall-driven sedimentary features in the Gaho paleolake, Hapcheon County on the southern Korean Peninsula. Based on radiocarbon dates, median grain sizes, and elemental ratios of strontium (Sr), titanium (Ti), and zirconium (Zr) measured by high-resolution X-ray fluorescence core scanning, we tested potential indicators of past heavy rainfall. During the past 7000 years, temporal changes in median grain size and elemental ratios (Sr/Ti and Zr/Ti) were found to be similar to those in the Asian monsoonal precipitation index and sea surface temperature (SST) in the western North Pacific region, suggesting that periods with increased elemental ratios may have been influenced by intensified regional rainfall events and higher SSTs. During the past 2000 years, time series of Sr/Ti and Zr/Ti ratios in the paleolake sediments appeared to covary with a megadrought period (AD 1593–1698; 357-252 cal BP), flooding events in the 1500s, and the collapse of ancient nations in Korea and other parts of East Asia. This similarity between sedimentary records and historical events suggests considerable potential for the dating of elemental ratios in lake sediments as high-resolution analogs of past hydrological events to support historical records.

X-ray Fluorescence Core Scanning for High-Resolution Geochemical Characterisation of Soils

X-ray fluorescence (XRF) core scanners are commonly used for fine-scale geochemical analysis in sediment studies, but data are semi-quantitative and require calibration to convert geochemical element counts to concentrations. Application of XRF core scanning in soil science remains largely untapped. This study employed an ITRAX core scanner to scan grassland soil cores and developed a novel calibration method based on a chemometric approach to characterise soil geochemistry. As soil samples are collected based on depth sampling, this study investigated whether higher resolution element concentrations could be inferred from lower resolution reference samples and if regression models from multiple cores could apply to a new core at the same resolution. Reference concentrations were obtained for all cores at 10 cm intervals, with validation conducted at 1 cm for a single core. Two calibration curve types were proposed: one based on the single core’s 10 cm data to validate references at 1 cm intervals; and another using all cores, with each core serving as a test item after exclusion from the training set. Various preprocessing measures and feature selection techniques were tested. Results showed successful calibration for elements Ca, P, Zn, Sr, and S, with high R2 values of 0.94, 0.93, 0.93, 0.92 and 0.91, respectively. The study presents a novel method for calibrating XRF core scanning element counts, demonstrating its potential for high-resolution soil analysis.

Evidence of Middle Holocene landslide-generated tsunamis recorded in lake sediments from Saqqaq, West Greenland

Abstract. The Vaigat strait (Sullorsuaq) in West Greenland is well known for its susceptibility to landslides and historical landslide-generated tsunamis. Recent mapping of the seabed in the Vaigat strait has revealed several prehistoric giga-scale (volumes of 109 m3) tsunamigenic landslides. However, the timing of these giga-scale tsunamis is largely unconstrained, but they are assumed to have occurred after the last deglaciation. Here, we report on lake sediment core records from four coastal lakes located between 19 and 91 m above sea level (a.s.l.) on the Saqqaq foreland at the eastern end of the Vaigat strait. We use a multiproxy approach including X-ray fluorescence (XRF) and magnetic susceptibility core scanning along with a screening for marine diatoms to identify at least two tsunami deposits in two of the four sediment cores. Radiocarbon dating of aquatic macrofossils and bulk samples suggest that the tsunami events occurred at ca. 7.6 and 7.3 ka cal BP. Using a previously published relative sea level curve from Vaskebugt, Arveprinsen Ejland (Alluttoq), located 40 km southeast of Saqqaq, we infer wave runup heights of ca. 41–66 and 45–70 m, respectively, for the two tsunami events. These runup heights from prehistoric tsunamis are 1 to 2 orders of magnitude higher than the historic landslide-tsunami runup heights at Saqqaq which only reached an elevation of ca. 3 m in November 2000. While we found deposits from two tsunami events in the lake sediments, landforms from at least nine giga-scale landslides are present on the seafloor of Vaigat. We infer that these deposits probably represent the two most recent tsunamis identified in the Vaigat strait and that the older tsunamis must have happened between the last deglaciation and the oldest sediment in the lakes, i.e., between ca. 10.0 and 8.5 ka cal BP.

First assessment of changes in dust sources in the black forest during the Holocene: case study at Wildseemoor

A 600 cm peat sequence was extracted from the ombrotrophic peat bog Wildseemoor in the northern Black Forest, covering the last ca. 10,000 years thus allowing for identification of potential changes in dust input during the Holocene. Such information is critical to the understanding of past environmental change at the local to supra-regional scale and helps with interpreting, in particular, fire history and its links to both climate change and anthropogenic impacts. Dust composition change was investigated using X-ray fluorescence core scanning (XRF-CS) to establish bulk chemical composition of lithogenic input to the peatland, using element signatures, and in particular the ratios of Ca/Ti and Ti/Zr. Two main different sources of dust could be differentiated, a local and a distal (long-distance) dust source, which show variations through time. Distal dust input is elevated during the early Holocene (ca. 8,800 - 8,300 cal BP), as well as around 5,000 cal BP, 3,000 cal BP, 2,300 cal BP and the last ca. 200 years. Distal dust might originate from remobilized loess deposits in the Upper Rhine Graben or, periodically, more distant sources such as the Sahara or the Massif Central. Local dust input roughly correlates to peaks in charcoal influx after ca. 3,850 cal BP, potentially recording phases of increased anthropogenic influence in the surroundings of Wildseemoor. Additional research in nearby bogs (from the Black Forest and the Vosges), as well as more precise geochemical fingerprinting of the different dust sources, is needed to explore the regional extent and significance of Holocene environmental changes recorded at Wildseemoor.

A machine-learning workflow to integrate high-resolution core-based facies into basin-scale stratigraphic models for the Wolfcamp and Third Bone Spring Sand, Delaware Basin

The characterization of subsurface reservoirs that are dominated by mudrock facies is hindered by the inherent heterogeneity and high degree of spatial variability typical of mudrock depositional systems. Subsurface reservoir properties that include porosity and permeability, fluid saturations, stratigraphic thicknesses of reservoir units, and source rock potential are ultimately controlled by the spatial distribution of sedimentary rock facies, which supports efforts to improve subsurface characterization workflows. Although core-based data provide direct measurements of rock attributes that are used to inform static reservoir models, capturing high-resolution core-based rock facies and downscaling these observations to tie to lower-resolution wireline logs remains a challenge. The effort to integrate core-based facies to reservoir-scale models is especially difficult when trying to capture thin-bedded heterogeneity that is common to mudrock systems. Herein, a workflow is developed and applied to visualize and integrate multivariate and spatially complex core-based data sets with wireline logs. Formation-specific core-based chemofacies training data sets are developed by integrating core descriptions with chemofacies clusters developed from high-resolution X-ray fluorescence core scanning. Core-based rock attribute data (e.g., XRD mineralogy, total porosity, and total organic matter content) are used to describe the chemofacies, providing a means to upscale low-resolution rock attribute measurements to high-resolution core-based chemofacies. Supervised core-based chemofacies training data sets are then used with neural network multiclass classification machine-learning tools to train triple combo wireline logs (gamma ray, deep resistivity, bulk density, and neutron porosity) to predict rock facies from wireline logs, providing a new approach to apply core-based facies classifications to wireline log studies. A basin-scale case study that applies this workflow is described for the Third Bone Spring Sand and units of the Wolfcamp Formation in the Delaware Basin of West Texas, United States.

Exploring a Mallorca cave flooding during the Little Ice Age using nondestructive techniques on a stalagmite: micro-CT and XRF core scanning

AbstractThis study focuses on characterizing a discontinuity within the Seán stalagmite (4.75–7.75 cm) by means of two nondestructive techniques: (1) high-resolution micro-computed tomography (micro-CT) and (2) X-ray fluorescence (XRF) core scanning (XRFCS). Micro-CT was used to study the stalagmite density, and XRFCS was applied to obtain the qualitative elemental composition and colour measurements. The new data obtained from nondestructive techniques have been combined with previously published geochemical data and fabric determinations from the same stalagmite found in Sa Balma des Quartó cave in Mallorca. The two methodologies applied in the present study have improved the characterization of the distinctive horizon. The micro-CT images identified the layer as a minor event due the high air content. The distinctive horizon is characterized by a high Ti-content, indicating the arrival of terrigenous particles. Based on those observations, together with the fact that the micrite layer appears filling the gaps between the older columnar fabric, we argue that the micrite layer may represent a major flooding event inside the cave after the year 1616 ± 23 CE and before the year 1623 ± 28 CE, which can be related to an extreme rainfall event. This hypothesis is further supported by the observed cave flooding during the autumn of 2018.

Natural and human-induced ecosystem change in SE Europe since AD 1700 derived from a partially varved sediment record from Lake Vouliagmeni (Greece)

To reconstruct naturally and anthropogenically induced environmental change in SE Europe since the Little Ice Age, we have examined five partially varved sediment cores from coastal Lake Vouliagmeni, Greece. Our reconstructions are based on a multi-proxy approach including microfacies analysis, X-ray fluorescence core scanning, radionuclide dating (210Pb, 137Cs, and 241Am), and palynological analysis (pollen, spores, and dinoflagellate cysts). A 131 -cm-long composite record that encompasses the past c. 300 years reveals 181 varves of endogenic and mixed clastic-biogenic types. The formation of these varves was controlled by seasonal variability in clastic input and primary productivity. The non-varved intervals consist of homogenous lake sediments and turbidite deposits. Based on a chronology developed through radionuclide dating, varve counting and exclusion of turbidites from the sequence, we have compared our proxy data with meteorological data and historical records of earthquakes and human activities. Our results suggest that the surroundings of Lake Vouliagmeni experienced relatively wet conditions during the late solar Maunder Minimum (1645–1715 AD) and relatively dry conditions during the Dalton Minimum (1790–1830 AD), which highlights the hydroclimatic heterogeneity in SE Europe during the Little Ice Age. The evaluation of historical documentation suggests that the majority of the turbidites is related to lake-slope instabilities following earthquake shocks. Human impact on Lake Vouliagmeni includes (i) a change in aquatic biota following the artificial connection of the lake to the sea at c. 1880 AD, and (ii) expansion of agricultural areas and reduction of natural forests around the lake due to population growth over the past 300 years.

Sediment flux and early diagenesis inferred from high-resolution XRF-CS data and iron and arsenic sulfides during the last 30 kyr in Lake Urmia, Iran: Implications for studies of hypersaline lakes

We analyzed by high resolution X-ray fluorescence core scanning (XRF-CS) the elemental composition of a 12.5 m long composite sediment core extracted from the hypersaline Lake Urmia (NW Iran). The main objective of the study was to reconstruct on a high temporal scale, the changes in sediment origin/inflow and water levels of Lake Urmia over the last 30,000 years. Combined with previously obtained results on 14C accelerated mass spectrometry (AMS) chronology, grain size and distribution of major minerals, albeit with a much lower temporal resolution than the XRF-CS data, this multi-proxy approach allowed recognition of specific hydrological changes and associated sedimentary processes in the Lake Urmia basin, including physical and chemical weathering, depositional fluxes and carbonate crystallization processes in lake water, and early diagenesis in anoxic bottom sediments. The high natural logarithm ratios (ln-ratios) of K/Ti, Ca/Ti and Sr/Ca, and low ln-ratios of Rb/Sr reveal increasing chemical weathering in the catchment area in conjunction with increasing authigenic carbonate precipitation in the lake. These findings reflect wet conditions, high lake levels and less saline water during the following intervals (i) 29.8–20.2, (ii) 15.2–13.3, (iii) 11.8–5.6 and (iv) 4.1–2.3 cal kBP. In contrast, the increasing ln-ratios of Rb/Sr associated with decreasing ln-ratios of K/Ti, Ca/Ti and Sr/Ca indicates enhanced erosion in the catchment area linked to drier conditions, lower lake levels and more saline conditions predominating at around 30–29.8 cal kBP, 20.2–15.2, 13.3–11.8, and 5.6–4.1 cal kBP. Based on the As-XRF-CS pattern and magnetic parameters we identified iron and naturally-occurring arsenic sulfides rarely reported from saline lakes, acting as specific indicators of anoxic conditions in the lake bottom environment. Moreover, XRF-CS data revealed short-lived periods with increasing chemical weathering in the catchment area at (i) 28.6–28.3, (ii) 27.3–27.1, (iii) 4.1–3.6 and (iv) 3.4–3.3 cal kBP, as well as increasing erosion at (i) 27.0–26.8, (ii) 26.3–26.0, (iii) 25.6–25.3 and (iv) 24.6–24.4 cal kBP. Overall, this study confirms the previously reported findings concerning the sediments of Lake Urmia as well as completing these, both by providing more details on the environment for the periods already identified and by highlighting events of short duration. In particular, the results reported here permit better definition of the processes of chemical weathering versus erosion in the catchment area, and of the oxygenation levels of the lake bottom. The close correlation of these long- and short-term changes with the North Atlantic climate system clearly indicates that the Lake Urmia area has been affected mainly by this system during the last 30 cal kBP.Over and above their value with regard to Lake Urmia, these new data fill an important gap in eastern Mediterranean/western Asia paleoclimate records as a whole, providing unique and continuous 30 cal kBP information on the possible driving mechanisms of the observed changes. These can be compared to existing data on paleoenvironmental and climatic changes on regional and global scales and can also be used in global circulation models.

Evidence of recent sea-level rise and the formation of a classic Maya canal system inferred from Boca Paila cave sediments, Sian Ka'an biosphere, Mexico

Cave sediments along the eastern coast of the Yucatán Peninsula contain important records of paleoenvironmental change that have not been fully explored. Reconstructing environmental changes in Boca Paila lagoon reveals details about sea level, flooding of the Sian Ka'an Biosphere, and the timeline of occupation at Muyil, an important Classic Maya maritime trading site. Three sediment cores (BP1, BP2, and BP3) were collected from a cave system beneath Boca Paila lagoon in the Sian Ka'an Biosphere. Radiocarbon dating, geochemical (X-Ray Fluorescence Core Scanning, δ13C, C/N), and microfossil (foraminifera, diatoms, pollen) analyses were performed. The combined results show three distinct phases of coastal evolution. Phase 1 (1157 BCE or earlier), an upland area with mangrove associate Conocarpus erectus, grasses, and ferns, is characterized by: organic-rich detrital peat; a relative absence of foraminifera and diatoms; organic geochemistry results within terrestrial ranges (δ13C values of −28‰ to −26‰); and low Sr/Ca, Si/Ti, and Ti/K ratios. These indicate dry conditions at the karst surface. Phase 2 (1157 BCE – 312 CE), a shallow wetland, is represented by: an increase in weathering products (Ti/K) and diatom productivity (Si/Ti); more positive δ13C values (−27‰ to −22‰) and decreasing C/N ratios; and increased marine foraminifera (e.g., Ammodiscus sp.). These indicate more open water conditions. Phase 3 (>312 CE), a wetland/lagoon environment, is characterized by: carbonate-rich marl; a greater diversity of foraminifera (Ammonia spp., Elphidium spp., Rosalina spp., and Bolivina spp.), diatoms (Cyclotella meneghiniana, Craticula spp., Amphora spp., Hyalosynedra laevigata, and Grammatophora spp.) and pollen (from mangroves, ferns, grasses, palms, and pine); increased Si/Ti and Sr/Ca values; and mixed marine and terrestrial organic geochemistry values (δ13C values of −22‰ to −20‰). These indicate increased input of marine organic sediment during sea-level rise. Sea-level and climate records support the interpretation of a dry upper karst environment prior to ∼1157 BCE, with sea-level rise forming shallow (<50 cm) wetlands by ∼312 CE. Previous archaeological analysis estimates that the first settlers arrived at Muyil ∼350 BCE, but that population expansion and construction of most structures occurred during the Postclassic (925–1550 CE). Sea-level rise would have been an important factor in the expansion of coastal settlements and trade routes; continued sea-level rise after ∼312 CE allowed for the formation of deeper lagoons and channels connecting the coast to Muyil and other inland sites which would likely not have been navigable prior to the Early Classic period (250–600 CE) as they would be too shallow. This study highlights the impacts of environment on society, as well as the importance of karst cave systems for obtaining paleoenvironmental records.

Lunar nodal tidal cycle influences on the input of coarse sediments during the last glaciation in the deep South China Sea

Cross-slope transport of coarse sediments is thought to be dominated by gravity-flow or hyperpycnal-flow processes triggered by hydrodynamic events. However, whether long-term non-event hydrological processes can affect longitudinal transport is still unclear. Here, high-resolution (1 mm) X-ray fluorescence core scanning combined with coarse-fraction observation has been conducted on a laminated sequence (dated as last glacial 14.3–20.8 cal ka BP) of Core MD05-2892 in the South China Sea. The laminae show interbedded millimeter-scale dark and light layers. Dark layers are distinguished by coarse-grained (sand-containing clayey silt) sediments rich in Ca, Zr, and Si, whereas light layers are characterized by fine-grained (silty clay) deposits rich in K, Ti, and Fe. Accordingly, Zr/K and Si/K ratios are used to indicate lamina occurrences, and the ratios are well correlated to grayness. Spectral analyses of the ratios and grayness all present a persistent ∼18.6-yr cycle, which is interpreted as the lunar nodal tidal cycle. This signal in laminae could be related to remobilization of coarse sediments via mean high-water-line variations driven by the lunar nodal tide during the last glacial sea-level lowstand. Coarse sediments were more likely transported from the shelf break via suspended-load-dominated hyperpycnal flow to the slope to form dark layers during periods of strengthened tidal activity, while fine sediments were dispersed via hemipelagic transport to form light layers during periods of weakened tidal activity. Our study highlights for the first time that the lunar nodal tide could periodically trigger the transport of coarse sediments from the shelf to the deep sea.

Foraminiferal sandy contourite of the Limpopo Corridor (Mozambique margin): Facies characterization and paleoceanographic record

Contourites encompass a wide variety of sedimentary facies. Some of them show common facies with others deep-water deposits, such as turbidites and hemipelagites. Sedimentological characterization at macro- and microscales is valuable to discriminate those close facies but the distinction is not always clear. Contourites are increasingly used in paleoceanographic and paleoclimatic reconstructions. Improving their characterization is therefore essential to their interpretations.This study aims at characterizing a foraminiferal sandy contourite facies from a sediment core collected on top of a contourite drift under the influence of the Antarctic Intermediate Water/North Atlantic Deep-Water interface located in the Limpopo Corridor (Mozambique margin, Indian Ocean) at 2000 m depth. This work is based on a detailed analysis of the sedimentary record using physical properties (gamma density and magnetic susceptibility) as well as laser grain size and X-Ray Fluorescence core scanning data.Our results show that: (1) the foraminiferal sand is vertically continuous and homogenous over 633 kyr with an average sedimentation rate of 0.26 cm.kyr−1; (2) this contourite facies results from sedimentation with low terrigenous inputs under stable hydrodynamic conditions over time, with relatively strong bottom currents for this water depth (∼16 cm.s−1); (3) during glacial stages, sedimentation rates are lower and bottom current speed is higher than during interglacial stages. We also propose the concept of “Contourite Graphical Chart” which summaries the theoretical distribution of contourite endmembers from cross-plot of “sorting versus grain-size median D50” and their related sedimentary processes.This study highlights the relevance of condensed foraminiferal sandy contourites as long time-scale paleoceanographic archives and provides new insights for studies related to paleoclimatology and paleoecology.

Impact of the Yellow River capture on the paleoenvironmental changes of Hongze Lake, China

The Yellow River (YR) capture of the Huai River had a profound effect on the landscape evolution, ecology, and social development in China, disrupting the evolution of some vital shallow floodplain lakes. Because of the absence of lacustrine sediment provenance analysis, previous studies were inadequate in distinguishing the influence of YR capture on paleoenvironmental changes in these lakes, especially on landscape evolution, redox conditions, lake level changes, and organic productivity. The current study aims to use X-ray fluorescence-core scanning (XRF-CS) and multivariate statistics on a 9.8 m sediment core from Hongze Lake (HZL), China, to analyze the impact of the YR capture on the lake's paleoenvironmental changes and the sediment provenance simultaneously. High-resolution images, magnetic susceptibility, and XRF-based multi-element data were obtained using a GEOTEK Multi-Sensor Core Logger. The calcium (Ca) content indicates the presence of YR sediment in HZL, given the high Ca content in YR sediment and the identification of mainly exogenous sources of Ca in HZL. The high values of Ca indicate that 48.7% of the sediment in the center of HZL is related to the YR's incursion. Periods of higher Ca content coincide with periods of higher oxygenation levels of the lake (as indicated by the ratio of manganese to titanium) and lower organic content in the lake sediment (as indicated by the ratio of incoherent to coherent scatter). These analyses reveal that the YR's capture of HZL significantly increased the lake's oxygen level. Furthermore, the decrease in the organic content of sediment tends to be the result of the accelerated deposition caused by the YR. The decrease in Ca content coincides with an increase in lake levels (as indicated by magnetic susceptibility). Thus, it can be inferred that the embankment on the eastern side of HZL, built to increase lake storage, has reduced the incursion frequency of the YR.

Influence of lake-basin morphology on climate-sediment transfer functions: Early Eocene Wilkins Peak Member, Green River Formation, Wyoming

Lacustrine strata are often among the highest-resolution terrestrial paleoclimate archives available. The manner in which climate signals are registered into lacustrine deposits varies, however, as a function of complex sedimentologic and diagenetic processes. The retrieval of reliable records of climatic forcing therefore requires a means of evaluating the potential influence of changing sedimentary transfer functions. Here, we use high-resolution X-ray fluorescence core scanning of the Wilkins Peak Member of the Green River Formation to characterize the long-term evolution of transfer functions in an ancient lacustrine record. Our analysis identifies a shift in the frequency distribution of Milankovitch-band variance between the lower and middle Wilkins Peak Member across a range of temporally calibrated elemental intensity records. Spectral analysis of the lower Wilkins Peak Member shows strong short eccentricity, obliquity, precession, and sub-Milankovitch−scale variability, while the middle Wilkins Peak Member shows strong eccentricity variability and reduced power at higher frequencies. This transition coincides with a dramatic decline in the number and volume of evaporite beds. We attribute this shift to a change in the Wilkins Peak Member depositional transfer function caused by evolving basin morphology, which directly influenced the preservation of bedded evaporite as the paleolake developed from a deeper, meromictic lake to a shallower, holomictic lake. The loss of bedded evaporite, combined with secondary evaporite growth, results in reduced obliquity- and precession-band power and enhanced eccentricity-band power in the stratigraphic record. These results underscore the need for careful integration of basin and depositional system history with cyclostratigraphic interpretation of the dominant astronomical signals preserved in the stratigraphic archive.

Disentangling the impact of anthropogenic and natural processes on the environment in a subtropical subalpine lake catchment in northeastern Taiwan over the past 150 years

Human activities impose significant changes on sedimentation processes and vegetation cover within lake catchments. However, the needed time for an anthropogenically disturbed natural state to be reversed back to its natural state by environmental protection programs is still ambiguous. Here we employ a multi-proxy approach to delineate major environmental disturbances such as logging and forest fires on the catchment in Cueifong Lake, a subtropical subalpine lake in northeastern Taiwan. X-ray Fluorescence (XRF) core scanning, bulk total organic carbon (TOC), bulk total nitrogen (TN), stable carbon isotope (δ13Corg) analysis, and macro-charcoal counting were utilized to reconstruct changes in the catchment environment based on a sediment core from Cueifong Lake. The results show that the element content changed distinctly around 1975 CE, which coincided with the onset of profound deforestation in the lake vicinity recorded in historical documents and aerial photos. After the cessation of the logging event, the detrital input increased, accompanied by decreasing C/N ratios and increasing δ13Corg values. This suggests that increased terrestrial nutrient input promoted algae growth. After the deforestation phase, our results imply a gradual recovery of elemental composition in the catchment environment. By extrapolating the XRF element records, we suggest that it might take >50 years for the sedimentary regime to reach its pre-logging baseline. In contrast to the depositional system, the C/N and δ13Corg shifted significantly - potentially irreversibly - towards an algae-dominant environment instead of recovering to the pre-logging condition. This could be due to both 1) the changes in the different vegetation species used for reforestation and/or 2) anthropogenically introduced fishes in the 1980s. This study proposes the first assessment of the needed recovery time for subtropical Asian subalpine forests after large-scale logging activity and thus provides an apparent reference for policy decisions on natural resource development and environmental protection.

Quantifying calcium carbonate and organic carbon content in marine sediments from XRF-scanning spectra with a machine learning approach

Geochemical variations of sedimentary records contain vital information for understanding paleoenvironment and paleoclimate. However, to obtain quantitative data in the laboratory is laborious, which ultimately restricts the temporal and spatial resolution. Quantification based on fast-acquisition and high-resolution provides a potential solution but is restricted to qualitative X-ray fluorescence (XRF) core scanning data. Here, we apply machine learning (ML) to advance the quantification progress and target calcium carbonate (CaCO3) and total organic carbon (TOC) for quantification to test the potential of such an XRF-ML approach. Raw XRF spectra are used as input data instead of software-based extraction of elemental intensities to avoid bias and increase information. Our dataset comprises Pacific and Southern Ocean marine sediment cores from high- to mid-latitudes to extend the applicability of quantification models from a site-specific to a multi-regional scale. ML-built models are carefully evaluated with a training set, a test set and a case study. The acquired ML-models provide better results with R2 of 0.96 for CaCO3 and 0.78 for TOC than conventional methods. In our case study, the ML-performance for TOC is comparably lower but still provides potential for future optimization. Altogether, this study allows to conveniently generate high-resolution bulk chemistry records without losing accuracy.

An automatic sediment-facies classification approach using machine learning and feature engineering

The delineation of sediment facies provides essential background information for a broad range of investigations in geosciences but is often constrained in quality or quantity. Here we leverage improvements in machine learning and X-ray fluorescence core scanning to develop an improved approach to automatic sediment-facies classification. This approach was developed and tested on a regional-scale high-resolution elemental dataset from sediment cores covering various sediment facies typical for the southern North Sea tidal flat, Germany. We use a machine-learning-built classification model involving simple but powerful feature engineering to simulate the observational behavior of sedimentologists and find that approach has 78% accuracy, followed by error analysis. The model classifies the majority of sediment facies and also, importantly, highlights critical sections for further investigation. Research resources can thus be allocated more efficiently. We suggest that our approach could provide a generalizable blueprint that can be applied and adapted for the research question and data type at hand.

Accurately calibrated X-ray fluorescence core scanning (XRF-CS) record of Ti ∕ Al reveals Early Pleistocene aridity and humidity variability over North Africa and its close relationship to low-latitude insolation

Abstract. In eastern Mediterranean sediments, the titanium-to-aluminum ratio (Ti/Al) captures relative variability in eolian to river-derived material and predominantly integrates climate signals over the Saharan and Sahel regions. Long Ti/Al time series can, therefore, provide valuable records of North African humidity and aridity changes. X-ray fluorescence core scanning (XRF-CS) can generate near-continuous Ti/Al records with relatively modest effort and in an acceptable amount of time, provided that accurate Ti/Al values are acquired. Calibration of raw XRF-CS data to those of established analytical methods is an important pathway for obtaining the required accuracy. We assess how to obtain reliable XRF-CS Ti/Al calibration by using different calibration reference sample sets for a long sediment record from ODP Site 967 (eastern Mediterranean Sea). The accuracy of reference concentrations and the number of reference samples are important for reliable calibration. Our continuous Ti/Al record allows detailed time series analysis over the past 3 Myr. Near-direct control of low-latitude insolation on the timing and amplitude of North African aridity and humidity is observed from 3 to ∼ 1.2 Ma. In our Ti/Al record, most arid North African intervals (i.e., with the longest period and highest amplitude) occur after the mid-Pleistocene transition (MPT; ∼ 1.2–0.7 Ma), when ice ages intensified. We also observe a subdued relationship between low-latitude insolation and North African climate after the MPT. These findings support the growing consensus that African climate became more sensitive to remote high-latitude climate when a threshold ice volume was reached during the MPT.

Late Holocene hydroclimatic changes inferred from a karst peat archive in the western Guizhou Plateau, SW China

The paleoenvironmental implications of Ca-related indices of peat from karst regions are poorly understood. In this study, we analyze a 450-cm peat core drilled from a sub-alpine karst mountain in the western Guizhou Plateau, SW China. This core is analyzed for carbonate contents and loss on ignition (LOI). High-resolution X-ray fluorescence (XRF) core scanning was also performed to see the variation of chemical compositions. Based on these measurements and 12 accelerator mass spectrometry (AMS)14C dates, we reconstructed the history of hydroclimatic shifts in SW China and explored the significance of Ca-related indices. The reconstructed hydroclimatic conditions were consistent with the stalagmite, lacustrine sediment, and peat records from the regions controlled by the Indian monsoon. Abrupt decreases in precipitation and temperature were clearly shown during the 4.2 ka and Little Ice Age (LIA) cold events. High carbonate contents in the Yejiping peat during the Medieval Warm Period (MWP) were linked to a warm and humid climate. Additionally, wavelet analysis shows that variations in Ca content have 500, 125, 103, 80, 58, 43, 20, and 12-a quasi-periods, which correspond to the Gleissberg, Pacific Decadal Oscillation (PDO), and Schwabe cycles. Our results highlight the importance of Ca-related indices in peat deposits from karst depressions and provide a detailed description of the MWP and the LIA.

Application of a back propagation neural network model based on genetic algorithm to in situ analysis of marine sediment cores by X-ray fluorescence core scanner

The use of core scanners to perform X-ray fluorescence (XRF) spectroscopic analysis can only obtain the intensities of the target elements, which is not conducive for application in marine geology research. In this paper, using a core scanner, in situ measurements were performed on 15 components: Al2O3, SiO2, K2O, CaO, TiO2, MnO, Fe2O3, V, Cr, Zn, Rb, Sr, Y, Zr, and Ba. We explored the feasibility of reducing the effect of interstitial water by normalizing the original intensity using the intensity of Ca and the ratio of coherent to incoherent and attempted to introduce a genetic algorithm-back propagation neural network model and use its nonlinear fitting capability to correct the matrix effect. The prediction precision of this method was 0.6–15.4%. The proposed method is suitable for the rapid analysis of major and minor components in marine sediment core samples, while taking full advantage of the high-resolution of the XRF core scanner.