Changes In Sediment Composition Research Articles

NEOICHNOLOGY OF TROPICAL AND ARID SCORPIONS: ENVIRONMENTAL IMPACTS ON BURROW CONSTRUCTION AND FORM

ABSTRACT Scorpions are intermediate predators in numerous terrestrial environments, and many are temporarily to permanently fossorial. As a result, they play key roles in terrestrial food webs, in soil development, and as ecosystem engineers. However, scorpions have a poorly described ichnofossil record likely due to an inadequate understanding of their trace morphology. Critical to correcting this is assessing the variability of burrows constructed by phylogenetically, geographically, and environmentally distinct scorpions. Five extant scorpions, Heterometrus spinifer, Pandinus imperator, Pandipalpus viatoris, Hadrurus arizonensis, and Paravaejovis spinigerus were studied through neoichnological experiments under varying substrate conditions. Burrow casts produced were described and compared across species and different substrate conditions. Tropical scorpions excavated sediment and carried it away from the burrow to produce open, straight-to-sinuous, subvertical tunnels to branching tunnel systems with single to multiple entrances and often chambers. Arid scorpions excavated with rapid leg movements to throw sediment behind the body to produce single to linked networks of U-shaped burrows as well as subvertical tunnels to tunnel networks with single to multiple entrances and rarely chambers. Changes in sediment composition and moisture tended to reduce burrow production but did not significantly alter burrow morphology. All scorpion burrows, regardless of species, bore a moderate-to-high similarity despite differences in excavation styles and architecture suggesting that scorpions produce burrows of consistent form regardless of phylogenetic or environmental distance. The result of these studies provides key ichnotaxobases of scorpion burrows which can be used to identify them in the fossil record and improve interpretations of ancient terrestrial ecosystems.

LUSI sediment characteristics and its distribution pathway in the porong river

The Porong River has been utilized to remove mud from the Sidoarjo mud volcano through the spillway since September 2006. The existence of Sidoarjo Mud (LUSI) in the river adds to the source of sediment, resulting in high-capacity sediment transport and increased sediment concentration, affecting the ecosystem and river capacity. To determine sediment deposition around the LUSI outfall area, this study analyzed nine sections to obtain bed material data. Each section has three observation points to collect material samples to produce comprehensive data. The cross-section stretches from the LUSI outfall area downstream, with a cross-sectional distance of 1 km, so the total length is 9.5 km. The study found clear changes in sediment composition across the analyzed area, with sand dominating the sediment profile in the upper reaches of the LUSI outfall. Sand dominance is due to local scour on the bridge pillars and groundsills on the river bed. In addition, these muds show characteristic depositional pathways, concentrated mainly along the river banks. This study highlights the importance of understanding sediment dynamics, influenced by variations in sediment sources, in disaster management and mitigation.

Changed sediment composition prevents recovery of macrobenthic community four years after a shoreface nourishment at the Holland coast

Sand nourishment is a widespread management strategy to protect sandy coasts against erosion. Nourishments can impact the benthic fauna directly by burial and indirectly by changing environmental conditions such as bottom shear stress and/or sediment composition (grain size distribution). The macrobenthic community in soft-bottom environments is often strongly correlated with sediment composition, however, because of the strong correlation with other environmental conditions, it is difficult to determine the direct effects of sediment composition on the macrobenthic community from field observations. Nourishments can temporarily break this correlation allowing to study the relation between sediment composition and macrobenthic community more or less independent from other environmental factors. In 2017, a shoreface nourishment was constructed at the Holland coast near Callantsoog at a water depth of about 10 m. Because the influence of waves is limited at this depth, the nourishment is not very mobile. Sediment composition and macrobenthos was monitored at the nourished site and two reference locations before (2015 and 2016), and in 2021, four years after nourishment. In 2021, the sediment composition at the nourished site was much coarser (median grain size 330 ± 59 μm) than in the years before nourishment (195 ± 34 μm), while the sediment composition at the reference locations remained comparable over the years. The average number of taxa per sample at the nourishment decreased from 14.1 before nourishment to 3.0 taxa in 2021. Also the average total density at the nourishment location decreased from 12731 ind.m−2 before nourishment to 320 ind.m−2 in 2021. While before nourishment, the composition of the macrobenthic community at the nourished site was comparable to the southern reference location, in 2021 the macrobenthic community was more comparable to the community at the coarser sediments of the northern reference. Clearly, four years after the nourishment, the macrobenthic community has not recovered due to the presence of coarser sediments at the nourished site. Logistic regressions show that most of the dominant species have a negative correlation with median grain size, but some species are more sensitive to changes in sediment composition than others. The sensitivity of the macrobenthos to sediment composition illustrates the importance of using sediments of similar grain size as in the placement area, especially for nourishments in the deeper parts of the shoreface.

Temporal Variability of Fluvial Sand Composition: An Annual Time Series From Four Rivers in SW Germany

AbstractThe sampling of fluvial sediment is subject to many sources of uncertainty, for example, time and location, and the number of samples collected. It is nevertheless commonly assumed that a sample taken at one time and location provides a somewhat averaged compositional signal. Any spatial or temporal variability of this signal is often neglected. This study investigates how the composition of bed load sand changes over an observation period of 1 year in four river basins with differing bedrock geology in southwestern Germany. Up to 12 bulk sediment samples were taken at the same locations using the same approach and analyzed for their granulometry and geochemistry. The results indicate that (a) different grain sizes yield different compositions due to source rock composition and hydraulic sorting effects, (b) bulk sediment composition changes temporally due to changing grain‐size distribution, and (c) compared to the bulk sample, the composition of narrow grain sizes is temporally more stable but nevertheless has an average variability of 15%. Because heavy mineral‐bound elements such as Zr have the highest variability, we relate a major component of compositional variability to temporally varying heavy mineral concentrations in response to hydrodynamic processes. Mixing modeling demonstrates that the fluvial sand faithfully reflects its catchment geology and that the sediment sources do not change substantially during the observation period, even during a flooding event. We conclude (a) that the causes for compositional variability may be disentangled using chemical and granulometric time series data and (b) that narrow grain sizes yield representative source rock contributions.

Influence of sediment composition on morphology and internal structure of mixed siliciclastic–bioclastic coastal barriers: Contribution of flume experiments

ABSTRACTCoastal barriers are dynamic systems, the morphology and architecture of which are controlled by local hydrodynamics, sea‐level fluctuations at different timescales, geological heritage and sediment composition. Coastal barriers may be composed of siliciclastic sediments, bioclastic sediments, or a mixture of both. Mixed siliciclastic–bioclastic sediments (as common as ‘pure’ sediments) are still little represented in the literature. Changes in sediment composition could affect sedimentary processes which are involved in the construction and stability of coastal barriers due to a different hydrodynamic behaviour between bioclastic and siliciclastic particles. In this study, wave‐flume experiments were used to investigate the role of sediment compositional mixing on the morphology and architecture of coastal barriers. Three different siliciclastic/bioclastic mixtures were exposed to regular wave forcing, together with mean water level fluctuations to create regressive and transgressive depositional units. Compositional mixtures responded similarly in first‐order to mean water‐level fluctuations, with the formation of a bar at low water level. Its subsequent on‐shore migration and reworking as berm deposits during rising water level stages, and with the formation of washover deposits during high water level stages. In detail, the increasing content of bioclastic sediment increased the beachface slope and reduced the length of washover deposits. The faster aggradation of washover sheets with bioclastic‐rich mixtures accelerated the barrier recovery after a submersion and breaching event. A strong segregation between the siliciclastic and the bioclastic grains was observed in the different depositional units, which is attributed both to the coarse size (grain‐size control) and to the flat‐shape (compositional control) of the bioclastic particles.

Novel luminescence diagnosis of storm deposition across intertidal environments

Salt marshes provide valuable nature-based, low-cost defences protecting against coastal flooding and erosion. Storm sedimentation can improve the resilience of salt marshes to accelerating rates of sea-level rise, which poses a threat to salt marsh survival worldwide. It is therefore important to be able to accurately detect the frequency of storm activity in longer-term sediment records to quantify how storms contribute to salt marsh resilience. Luminescence is able to infer how long mineral grains were exposed to sunlight prior to burial (e.g., the presence or absence of sediment processing). This study used sediment cores collected from the Ribble Estuary, North West England, to show that luminescence properties of sand-sized K-feldspar grains can diagnose the differential modes of deposition across intertidal settings (i.e., sandflat, mudflat and salt marsh) in longer-term sediment records by detecting the variability in sediment bleaching potential between settings (i.e., sediment exposure to sunlight), thus establishing a framework for the interpretation of luminescence properties of intertidal sediments. It then used modern sediment samples collected before and after a storm event to show how such properties can diagnose changes in sediment processing (i.e., bleaching potential) of mudflat sediments caused by storm activity, despite no changes in sediment composition being recorded by geochemical and particle size distribution analyses. This new luminescence approach can be applied to longer-term sediment records to reveal (and date) changes in the environment of deposition and/or depositional dynamics where there is no obvious stratigraphic evidence of such.

Fingerprinting sources of beach sands by grain-size, using mid-infrared spectroscopy (MIRS) and portable XRF. Implications for coastal recovery along a tsunami-struck delta coastline

Determining modern sediment provenance along sandy beaches helps understanding coastline dynamics and can therefore assist coastal management. Provenance analysis relies usually on mineralogical, elemental, and isotopic fingerprinting of sediment sources. Mid-Infrared Spectroscopy (MIRS) offers a rapid and non-destructive alternative. It relies on the identification of molecular-bonds in organic and inorganic materials. Thus far, MIRS has been used to fingerprint fine-grained sediments in mountainous and agricultural catchments. Here we use MIRS to analyze a range of sediment grain sizes (<0.25 mm; 0.25–0.5 mm; 0.5–2 mm) in modern fluvial and coastal sands, located in the delta of the Aceh River in Sumatra. Variations in molecular bond associations are compared to variations in major element concentration, quantified by portable X-ray fluorescence (pXRF) on a subset of samples. Covariations between MIRS and pXRF data are used to predict major element concentrations in all samples. Discriminant Analysis (DA) is used to classify sand-feeding streams into groups possessing distinctive MIRS fingerprints. DA proximity relationships are then used to predict the contribution of each source group to trunk stream sand and beach sands. The best discrimination is obtained among sands belonging to the medium grain-size fraction. Simple forward modeling of the expected contributions of the different sources is used to shade light on the DA-predicted association patterns. It helps discussing the biases introduced by sediment compositional changes from the headwaters to the coast, especially hydrodynamic sorting. We find that sand composition along the delta shoreline is primarily controlled by the asymmetric dispersal of sediment from the Aceh River mouth, owing to directional longshore drift. Local variations are generated by particle-size effects and by the propensity of the coast to erode or thicken over the past century. The coastal stretches the most severely damaged by the 2004 Indian Ocean Tsunami exhibit the greatest variations in apparent provenance between sub-fractions.

Sources and degradation of organic matter and its relation to trophic status in the core sediments of a tropical mangrove ecosystem along the Southwest coast of India

Present study has been designed to reveal the organic matter sources (algal vs. terrestrial), trophic status, the role of diagenesis and the applicability of biogeochemical indicators in a highly urbanized tropical mangrove forest. This has been achieved through a multiproxy approach by investigating the downcore distribution of bulk elemental properties (Total organic carbon (TOC%), total nitrogen (TN%)), biochemical composition, phytopigments and total hydrolysable amino acids (THAA). Both cores have a strong increase in algal biomass in the upper more fine grained part while core C2 has higher land plant fraction in its lower part compared to C1. The THAA profile decreased downcore ranging from 6.07 to 602.93 μmol g−1, contributing 7–53% THAA-N and 6–23% THAA-C to the sediments. Amino acids namely, serine (Ser) and tyrosine (Tyr) suggesting the contribution of fresh plankton organic matter likely by bacterial activity, while valine (Val), phenylalanine (Phe), isoleucine (Iso) and leucine (Lue) indicated more land plant derived organic matter. The surface dominance of proteins (PRT) and phaeophytin (Phaeo) pigment supporting the change from a more land plant derived organic matter to a more aquatic/marine driven productivity in the upper core sediments. Biochemical ratio (PRT/CHO >1), biopolymeric carbon (BPC), algal contribution to BPC (AL%-BPC) and degradation index (DI) indicated eutrophication related with the increase in algal organic matter. Based on mol%, amino acids viz., glycine (Gly) and alanine (Ala) were significantly enriched in downcore diagenetically reworked sediments indicating the growth of bacterial colonies and the selective preservation of bacterial biomass. Organic matter transformation from labile form into refractory character and vice versa through bacterial reworking, plays a major role in the development from oligotrophy to hypertrophy in the Cochin lagoon. The increasing urbanization have caused anthropogenic induced change in sediment composition, and recent eutrophication changed a more land plant dominated aquatic system to enhanced algal productivity.

The Late Miocene‐Early Pliocene Biogenic Bloom in the Eastern Equatorial Pacific: New Insights From Integrated Ocean Drilling Program Site U1335

AbstractThe late Miocene‐early Pliocene “biogenic bloom” (BB) manifests as greatly enhanced biogenic sedimentation in sites along the Equator that has been linked to cooler sea surface temperature (SST) in the eastern equatorial Pacific (EEP). However, the full extent and geometry of the BB in the EEP is less known. To improve on this, we have generated new carbonate content (CaCO3%) and bulk carbonate stable isotope (δ13C and δ18O) records spanning the last 7 Ma at IODP Site U1335, located ca. 5° north of the Equator and to the west of the EEP. Site U1335 δ13C and δ18O records display high‐frequency variations coupled to changes in sediment composition and physical properties comparable to patterns seen at on‐Equator sites further east. During the late Miocene and the early Pliocene bulk δ18O is higher at Site U1335 compared to two off‐Equator sites further east, suggesting cooler SSTs generated by stronger equatorial upwelling reaching northwest of the modern core‐equatorial upwelling belt. Enhanced upwelling at Site U1335 is supported by relatively higher sedimentation rates prior to 4.6 Ma, symptomatic of higher biological production during the BB. These observations suggest that during the BB the equatorial upwelling circulation was more focused and less parallel to the Equator compared to present day.

Community-level spatiotemporal synchrony: new metric and application to White Sea meiobenthic harpacticoids

Synchrony is a multifaceted biological phenomenon exhibited at various levels of organization. Here, we introduce the concept of structural synchrony, defined as the coherence of structural variations in multispecies assemblages occurring at a certain spatiotemporal scale, and propose a direct measure of this type of synchrony. This approach was first tested on numeric simulations imitating various types of model community dynamics and then applied to a large data set on White Sea intertidal harpacticoids, covering a wide range of spatial (decimeters to 140 m) and temporal (days to 25 yr) scales. Scale-specific analysis revealed distinct patterns and allowed us to draw inferences about processes that drive community dynamics. Short-term (up to 1 mo) changes occurred independently or even anti-synchronically, possibly due to trophic-driven migrations. On a seasonal scale, a high degree of within-habitat synchrony occurred at time intervals of 2-3 mo or longer but dropped with increasing spatial distance; this pattern is most likely caused by seasonal reproductive dynamics of populations. At the interannual scale, external exposure, i.e. long-term changes in sediment composition, appeared to be the strongest synchronizing force for the harpacticoid community, while this factor was locally active and became most apparent at the within-habitat scale. We evaluate the advantages and limitations of our framework, highlighting its broad domain of application and anticipating potential extensions. We encourage ecologists to integrate structural synchrony analysis into their toolbox to quantitatively evaluate spatiotemporal community dynamics and to link these dynamics with underlying processes.

Widespread lithogenic control of marine authigenic neodymium isotope records? Implications for paleoceanographic reconstructions

Our understanding of past ocean-climate dynamics is informed by multiple paleocirculation proxies including δ13C, 231Pa/230Th, and radiogenic neodymium isotopes (εNd). Of these, the εNd signature of marine authigenic phases is of particular importance as it is considered a robust circulation proxy applicable across timescales, permitting circulation reconstructions during periods of rapid, climatically-induced biological or chemical change (e.g. productivity, pH). However, growing evidence of non-conservative behavior and a widespread sedimentary source (benthic flux via pore water) of Nd to the global ocean suggests that authigenic εNd records do not strictly record a water mass signature, highlighting the need to reconsider interpretations of the authigenic record. To examine the impact of a sedimentary influence on the authigenic record, here we compile paired authigenic and detrital neodymium records from every major ocean basin and from 80 Ma to present. We then focus on just the North Atlantic Ocean basin to examine if this relationship holds up regionally and how authigenic εNd changes relate to sediment composition changes from two scientific ocean drill cores spanning the past 25 ka. We present a new conceptual framework to guide our discussion that examines the coupling or decoupling of authigenic and detrital εNd in terms of the relative importance of each of the three major potential controls as defined in the existing literature (bottom water, pore water, sediments) on the authigenic record. Our compilation reveals a strong linear relationship between detrital εNd and authigenic εNd (correlation coefficient = 0.86, n = 871), demonstrating a widespread influence of lithogenically sourced neodymium on authigenic εNd. We find the same is true within the North Atlantic, with the authigenic records at both locations strongly influenced by the sediments and likely not recording bottom water neodymium values. Emerging evidence for a lithogenic or benthic flux influence on the budgets of a wide range of trace elements suggests that our interpretative framework will be broadly useful for understanding the behavior of trace elements and their isotopes at the sediment-water interface.

Near-field changes in the seabed and associated macrobenthic communities due to marine aggregate extraction on tidal sandbanks: A spatially explicit bio-physical approach considering geological context and extraction regimes

Based on data from Multibeam Echosounders (MBES) and Van Veen grab samples, near-field effects of marine aggregate extraction by trailing suction hopper dredgers in the Belgian part of the North Sea were assessed on a decadal scale. The combined approach allowed to investigate and compare seabed and macrobenthic community characteristics for three extraction areas with similar ecological settings, but with a different geological context and each subjected to a different extraction regime. MBES measurements detected slight alterations of the seabed for areas exposed to a continuous, low extraction regime (monthly average volume = 17 to 83 × 103 m3). However, no significant changes in sediment composition nor the macrobenthic community could be attributed to this low extraction regime. High and continuous extraction in the most intensely extracted area (monthly average volume = 164 × 10³ m³) increased surface heterogeneity and created a local depression, hereby exposing clay and gravel from the underlying geological layer. In this area, the highest environmental impact was observed, as the physical changes in the seabed triggered a shift towards a more heterogeneous, transitional macrobenthic community including opportunistic species and species typically associated with muddy sands. Together with the species already present, this resulted in a local increase in macrobenthos density, species richness and biomass. A high but periodic extraction without screening activity on the most offshore located extraction area (monthly average volume = 230 × 10³ m³, averaged for those months where extraction took place) led to a redistribution of the medium to fine sand fraction and a winnowing of coarse sediment and shell fragments. The decreased median grain size induced a shift in the macrobenthic community from a typical medium to coarse sand Hesionura elongata community towards medium to fine sand representatives of the Nephtys cirrosa community, although the overall macrobenthic density and biomass in this extraction area remained stable. Based on these results, we conclude that extraction regime and local geological context are important factors driving the near-field environmental impact of marine aggregate extraction on tidal sandbanks.

Quaternary environmental changes in tropical Lake Towuti, Indonesia, inferred from end‐member modelling of X‐ray fluorescence core‐scanning data

ABSTRACTContinental and marine sediments are composed of a mixture from different sources and are influenced by a variety of environmental factors and transport processes prior to deposition. For analysis and interpretation, these sources and processes are often challenging to disentangle. We show that end‐member modelling of X‐ray fluorescence (XRF) core‐scanning data helps to overcome these challenges by unmixing different environmental signals from high‐resolution sediment geochemical records. We apply this approach to a 100 m long lacustrine succession from Lake Towuti, Indonesia, to separate the regional climate and tectonic history from local ecological and diagenetic processes. The resulting six end‐members (EMs) are interpreted to represent changes in ecological (EM1), climatic (EMs 2–4), tectonic (EM 5) and geomorphic (EM6) processes determining changes in sediment composition. Because end‐member analysis allows for the tracking of transient and overlapping processes, climatic changes can be followed throughout the 100 m‐long succession, suggesting alternating wet and dry periods in Central Sulawesi over long (several 100 000 years) time scales. We show that end‐member analysis on elemental data sets offers a detailed and objective means to disentangle depositional processes in sedimentary successions resulting from varying tectonic and environmental factors involved in sediment formation and deposition.

The Segmented Zambezi Sedimentary System from Source to Sink: 1. Sand Petrology and Heavy Minerals

The Zambezi River rises at the center of southern Africa, flows across the low-relief Kalahari Plateau, meets Karoo basalt, plunges into Victoria Falls, follows along Karoo rifts, and pierces through Precambrian basement to eventually deliver its load onto the Mozambican passive margin. Reflecting its polyphase evolution, the river is subdivided into segments with different geological and geomorphological character, a subdivision finally fixed by man’s construction of large reservoirs and faithfully testified by sharp changes in sediment composition. Pure quartzose sand recycled from Kalahari desert dunes in the uppermost tract is next progressively enriched in basaltic rock fragments and clinopyroxene. Sediment load is renewed first downstream of Lake Kariba and next downstream of Lake Cahora Bassa, documenting a stepwise decrease in quartz and durable heavy minerals. Composition becomes quartzo-feldspathic in the lower tract, where most sediment is supplied by high-grade basements rejuvenated by the southward propagation of the East African rift. Feldspar abundance in Lower Zambezi sand has no equivalent among big rivers on Earth and far exceeds that in sediments of the northern delta, shelf, and slope, revealing that provenance signals from the upper reaches have ceased to be transmitted across the routing system after closure of the big dams. This high-resolution petrologic study of Zambezi sand allows us to critically reconsider several dogmas, such as the supposed increase of mineralogical “maturity” during long-distance fluvial transport, and forges a key to unlock the rich information stored in sedimentary archives, with the ultimate goal to accurately reconstruct the evolution of this mighty river flowing across changing African landscapes since the late Mesozoic.

Spatio-temporal differences of sediment accumulation rate in the Lake Gościąż (Central Poland) as a response of meteorological conditions and lake basin morphometry

Weather conditions and lake basin morphometry are of key importance in the study of sediment accumulation rate in lakes. This study aims to determine how these factors affect spatial and seasonal variations in sedimentation rate in the epilimnion and hypolimnion of Lake Gościąż. To determine sedimentation rates, six sedimentation traps were set up at different locations and depths in the lake. Weather data were obtained from a meteorological station near the lake. Furthermore, temperature in the lake water column was measured continuously, and during field work oxygenation and transparency were also measured. Seasonal changes in sediment composition were analyzed on smear slides under microscope. The study showed that sedimentation rate increased as bottom steepness increased, and that there was more sediment in the hypolimnion than the epilimnion, especially in spring and autumn. There was a clear seasonal variation in early-spring and autumn peaks in sedimentation. The obtained results were significantly dependent on bottom relief, wind and air temperature through these factors’ influence on water temperature. The results show that the sediment accumulation rate in Lake Gościąż depends on the hydrodynamic conditions, which are determined by wind speed, wind direction, water temperature, and the shape and steepness of the lake basin. The relief features of the lake bottom and its orientation relative to the prevailing wind are significant factors in the spatial differentiation in sediment accumulation rate and composition of sedimenting material. It has been shown that the lake’s shallow-water zone (littoral and sublittoral) is an important source of the material accumulated in the profundal zone. The patterns and mechanisms of the course of contemporary sedimentation in Lake Gościąż, as determined based on the conducted investigations, can be applied in the study of other lakes and in assessing the representativeness of sampling sites for laminated bottom sediments to be used in palaeo-environmental studies.

Temporal change in the molluscan assemblages (bivalves and gastropods) of Frobisher Bay, Nunavut, Canada, over 50 years

Long-term studies provide an effective way to assess the ecological impacts of decades-long environmental change in Arctic coastal benthic environments, but are rarely undertaken in the Canadian Arctic. In light of this, historical datasets can be compared with modern samples to examine temporal differences in benthic community structure. Frobisher Bay, Nunavut, provides a unique opportunity to use a historical census to examine the impacts that long-term environmental changes have had on the marine benthos. Between 1967 and 1976, and in 2016, infaunal samples were collected in inner Frobisher Bay and were compared to determine how the molluscan assemblages have changed between the two time periods. Molluscan assemblages in two regions of inner Frobisher Bay (Iqaluit and Cairn Island) were examined to minimize sampling discrepancies between the two time periods. A long-term increase in mean annual air temperature and a decline in the length of the ice cover season were observed. Both regions exhibited some change in sediment composition and quality as well as in molluscan assemblage between the two time periods, and species diversity indices also indicated some change between these time periods. Both the 1967–1976 and 2016 molluscan datasets provide a baseline for future long-term studies in a changing Arctic.

Evaluation of pollutants characteristics and effect of dissolved and particulate contaminants in tributaries of an urban watershed

The importance of tributary management is increasing owing to the increase and diversity of pollutant sources in watersheds. In this study, the characteristics of dissolved and particulate contaminants in tributaries of the Anyang watershed, South Korea, were investigated using various analytical indicators (e.g., organic matter, nutrients, and spectroscopic analysis), heat maps, and multivariate analysis techniques, including cluster analysis and principal component analysis (PCA), to evaluate water quality characteristics of the tributaries and major pollutant sources. The influence of particulate matter from each tributary was also evaluated by investigating changes in sediment composition and re-suspended sediment oxygen demand (RSOD) at the mainstream of Anyang. The heat map patterns of the evaluated tributaries reflect sufficiently the characteristics of the pollutant sources, which enables the differentiation of the pollutant source according to the tributary locations and seasons. PCA results showed that water quality and spectral indicators reflected the different characteristics of the tributary; thus, it enabled a more diverse evaluation of tributary depending on pollutant source and season. The tributary watershed showed a high suspended solids (SS) discharge load depending on the watershed area (r = 0.94, p < 0.05), and the sediment near the tributary with higher SS discharge load revealed a higher content of fine sand (0.002–0.2 mm, r = 0.84, p < 0.05). The finer the particles derived from tributaries are, the higher the increase in RSOD is due to resuspension, most of which are caused by microbial activity (> 80%). Our results demonstrate that comprehensive and visual evaluation—including spectral indicators and heat maps analysis—of the tributary characteristics of pollutant sources is an efficient approach of broadening the knowledge of the distribution and effects of particulate matter from tributaries.

Chromium isotope heterogeneity on a modern carbonate platform

Chromium isotope (δ53Cr) values of marine sedimentary rocks are increasingly utilised for monitoring changes in redox conditions in the Earth's ancient oceans and atmosphere. Carbonate rocks are of particular interest as they are relatively common in the sedimentary record and have been shown under laboratory conditions to be capable of recording the Cr isotope composition of precipitating fluids. However, little data from appropriate modern analogues is currently available to constrain the variability in δ53Cr values within a carbonate platform and slope system and assess the preservation potential of marine δ53Cr values during burial, lithification and diagenesis. In this paper we investigate the heterogeneity of δ53Cr values on a modern marine carbonate platform in the context of carbonate sediment deposition, mineralogy, and the influence of burial and early lithification. We present new δ53Cr values from carbonate sediments in the upper 200 m of ODP Leg 166 Site 1003 taken from the western margin of the Great Bahama Bank (GBB) and compare these data to modern carbonate sediments accumulating on the GBB platform-top. Shallow-water surface sediments record a range of heavy δ53Cr values from +0.77 to +1.07‰ while drill core samples record a larger range of δ53Cr values from +0.51 to +0.97‰. Down-core variability in δ53Cr values occurs systematically with changes in sediment composition and mineralogy, where more positive δ53Cr values occur in drill core samples that preserve proportionally more banktop-derived carbonate and less well developed diagenetic textures. These values decrease down-core where proportionally more pelagic carbonate exists, and with increasing neomorphism of primary aragonite to low-Mg calcite. The mineralogical dependence of δ53Cr values at Site 1003 appears to be related to variations in relative sea-level across the platform and the degree of lithification and diagenetic recrystallization with depth, rather than in response to changes in the δ53Cr composition of the overlying water column. As the GBB represents a reasonable modern analogue for many Phanerozoic and Precambrian carbonate successions, the preliminary framework presented here may have significant implications for the interpretation of vertical profiles of δ53Cr values in paleo-redox studies. In particular, smaller scale variability in ancient carbonate sections can be more simply explained by local variations in depositional environment and diagenetic regime rather than fluctuations in water column redox conditions.

Assessing Sedimentary Detrital Pb Isotopes as a Dust Tracer in the Pacific Ocean

AbstractMineral dust particles from different source regions typically have distinct Pb isotope ratios. Theoretically, Pb isotopic composition of terrigenous minerals isolated from open‐ocean sediments should allow for dust provenance reconstructions. However, Pb isotopes of terrigenous fractions of sediments have frequently been inconsistent with expected source region signatures. This study investigates the reason(s) for offsets between the Pb isotope values of the dust component in sediment cores and those expected from source regions with focus on changes in sediment composition, sediment age, and sediment processing for analysis. Pb isotope ratios from Pacific Ocean core‐top sediments show a general delineation of the Intertropical Convergence Zone (ITCZ). Isotope mixing models support these general trends, though similarity in Pb isotope ratios of disparate source regions makes constraining specific sources challenging. Pb isotope ratios in downcore samples varied on glacial/interglacial time scales, being less radiogenic during the last glacial maximum, suggesting either a weakened ITCZ or the addition of a new, less radiogenic, source to the system. Finally, Pb isotope ratios in some source region samples yielded different Pb isotope signatures in bulk source sample than in the insoluble terrigenous fraction of the source sample, indicating that differential mineral preservation within the terrigenous component in sediments may cause offsets from source signatures. Overall, while Pb isotopes show distinct basin‐scale variations, high‐resolution spatial reconstructions require tight age controls and consistency in analytical treatment if used to define ocean sediment source regions.

New insights from multi-proxy data from the West Antarctic continental rise: Implications for dating and interpreting Late Quaternary palaeoenvironmental records

The Antarctic Peninsula’s Pacific margin is one of the best studied sectors of the Antarctic continental margin. Since the 1990s, several research cruises have targeted the continental rise with geophysical surveys, conventional coring and deep-sea drilling. The previous studies highlighted the potential of large sediment drifts on the rise as high-resolution palaeoenvironmental archives. However, these studies also suffered from chronological difficulties arising from the lack of calcareous microfossils, with initial results from geomagnetic relative palaeointensity (RPI) dating promising a possible solution.This paper presents data from new sediment cores recovered on cruise JR298 from seven continental rise sites west of the Antarctic Peninsula and in the Bellingshausen Sea with the objectives to (i) seek calcareous foraminifera, especially at shallow drift sites, to constrain RPI-based age models, and (ii) investigate the depositional history at these locations. We present the results of chronological and multi-proxy analyses on these cores and two cores previously collected from the study area. We establish new age models for the JR298 records and compare them with published RPI-based age models. In addition, we evaluate the reliability of different palaeoproductivity proxies and infer depositional processes.Planktic foraminifera are present in various core intervals. Although their stable oxygen isotope (δ18O) ratios, tephrochronological constraints and glacial-interglacial changes in sediment composition provide age models largely consistent with the RPI chronologies, we also observe distinct differences, predominantly in the Bellingshausen Sea cores. Enrichments of solid-phase manganese together with evidence for “burn-down” of organic carbon in late glacial and peak interglacial sediments document non-steady-state diagenesis that may have altered magnetic mineralogy and, thus, RPI proxies. This process may explain discrepancies between RPI-based age models and those derived from δ18O data combined with tephrochronology. The data also indicate that organic carbon is a much less reliable productivity proxy than biogenic barium or organically-associated bromine in the investigated sediments.In agreement with previous studies, sediment facies indicate a strong control of deposition on the rise by bottom currents that interacted with detritus supplied by meltwater plumes, gravitational down-slope transport processes and pelagic settling of iceberg-rafted debris (IRD) and planktic microfossils. Bottom-current velocities underwent only minor changes over glacial-interglacial cycles at the drift crests, with down-slope deposition only rarely affecting these shallow locations. Maximum concentrations of coarse IRD at the seafloor surfaces of the shallow sites result predominantly from upward pumping caused by extensive bioturbation. This process has to be taken into account when past changes in IRD deposition are inferred from quantifying clasts >1 mm in size.