Sedimentary Signatures Research Articles

Possible Indication of the Impact of the Storegga Slide Tsunami on the German North Sea Coast around 8150 cal BP

The Storegga slide tsunami (SST) at ca. 8100 ± 100–250 cal BP is known to be the largest tsunami that affected the North Sea during the entire Holocene. Geological traces of tsunami landfall were discovered along the coasts of Norway, Scotland, England, Denmark, the Faroes and Shetland Islands. So far, the German North Sea coast has been considered as being well protected due to the wide continental shelf and predominant shallow water depths, both assumed to dissipate tsunami wave energy significantly, thus hindering SST propagation dynamics. The objective of our research was to clarify if the SST reached the German Bight and if corresponding sediment markers can be found. Our research was based on the in-depth investigation of a 5 m long section of the research core Garding-2 from Eiderstedt Peninsula near Garding in North Frisia known from a previous study. For this, we newly recovered sediment core Garding-2A at exactly the same coring location as core Garding-2. Additionally, high-resolution Direct Push sensing data were collected to gain undisturbed stratigraphic information. Multi-proxy analyses of sediment material (grain size, geochemical, geochronological and microfaunal data) were carried out to reconstruct palaeoenvironmental and palaeogeographical conditions. We identified a high-energy event layer with sedimentological (e.g., erosional unconformity, rip-up clasts, fining-upward), microfaunal (e.g., strongly mixed foraminiferal assemblage) and other features typical of tsunami influence and identical in age with the SST, dated to ca. 8.15 ka cal BP. The event layer was deposited at or maximum ca. 1–1.5 m below the local contemporary relative sea level and several tens of kilometers inland from the coastline within the palaeo-Eider estuarine system beyond the reach of storm surges. Tsunami facies and geochronological data correspond well with SST signatures identified on the nearby island of Rømø. SST candidate deposits identified at Garding represent the southernmost indications of this event in the southeastern North Sea. They give evidence, for the first time, of high-energy tsunami landfall along the German North Sea coast and tsunami impact related to the Storegga slide. SST deposits seem to have been subsequently reworked and redeposited over centuries until the site was affected by the Holocene marine transgression around 7 ka cal BP (7.3–6.5 ka cal BP). Moreover, the transgression initiated energetically and ecologically stable shallow marine conditions within an Eider-related tidal channel, lasting several millennia. It is suggested that the SST was not essentially weakened across the shallow continental shelf of the North Sea, but rather caused tsunami run-up of several meters (Rømø Island) or largely intruded estuarine systems tens of kilometers inland (North Frisia, this study). We, therefore, assume that the southern North Sea coast was generally affected by the SST but sedimentary signals have not yet been identified or have been misinterpreted. Our findings suggest that the German North Sea coast is not protected from tsunami events, as assumed so far, but that tsunamis are also a phenomenon in this region.

Detangling past and modern zinc anthropogenic source contributions in an urbanized coastal river by combining elemental, isotope and speciation approaches

The accumulation of trace metals in the environmental compartments of coastal rivers is a global and complex environmental issue, requiring multiple tools to constrain the various anthropogenic sources and biogeochemical processes affecting the water quality of these environments. The Valao fluvio-estuarine system (Rio de Janeiro, Brazil) presents a challenging case of a coastal river contaminated by both modern and historical anthropogenic metal sources, located in the land and in the intra-estuary, continuously mixed by tidal cycles. This study employed a combination of spatial distribution analysis of trace metals including gadolinium (Gd), zinc (Zn) isotopic analyses, and X-ray absorption spectroscopy (XAS) to distinguish between these sources. The concentrations of metals in both dissolved (water samples) and surficial sediment compartments (Suspended Particulate Matter and sediment samples) display an overall enrichment trend from upstream to downstream. Multivariate statistical analysis allows to discriminate geogenic elements derived from watershed geology (Ti, K, and Mg) vs anthropogenic contaminants from urban runoff and domestic sewage discharges (Cu, Cr, Pb, Zn, and Gd); and legacy metal contaminants (Zn and Cd) remobilized from ancient metallurgical wastes and transported upstream in the estuary during tidal cycles. The anthropogenic Gd concentration in the dissolved compartment increases along the watercourse, highlighting continuous ongoing sewage discharge. Zinc solid speciation also indicates that Zn contribution from legacy metallurgy waste is primarily associated with sulfide-Zn and Zn-phyllosilicate in the outlet estuary, while in upstream sediments of fluvio-estuarine system, Zn is found bound to organic matter. Zinc isotope systematically reveals a progressive downstream shift to heavier isotope compositions. Upstream, the relatively pristine site and the urbanized section of the river exhibit a relatively uniform δ66/64Zn value (+0.20 ± 0.07 ‰) in suspended particulate matter (SPM) and surficial sediments. These results indicate that domestic sewage discharges contribute to Zn enrichment in sediments of the Valao fluvio-estuarine system but without modifying its isotope signature in sediments. The sediment of the downstream estuarine section shows a heavier δ66/64Zn value (+0.48 ± 0.08 ‰), indicating the strong influence of the intra-estuarine source identified as the historical metallurgic contamination. An integrated view of the geochemical tracers allows thus inferring that the untreated sewage and legacy metallurgical contamination are the primary sources of anthropogenic Zn contamination. It highlights the progressive mixing along the estuarine gradient under tidal dynamics. The influence of the former source continuously expands from the headland towards the estuary.

Characterization of biotic and abiotic signatures of modern lake sediments of western India, and its palaeo-environmental implications

A multi-proxy study of biotic and abiotic components was conducted on surface sediment samples from six lakes/wetlands located along the western transitional boundary of the contemporary Indian Summer Monsoon (ISM) in the Indian Subcontinent. The primary goal is to assess the suitability of various proxies as representatives of modern vegetation, environmental and climatic conditions. The collected data indicate significant variations in the composition and density of pollen in response to climate-induced and anthropogenic ecological changes throughout the northwest India transect. The palynological studies from eastern Rajasthan shows high forest elements in comparison to western Haryana and western Uttar Pradesh. In addition, the palynological data was juxtaposed with other biotic proxies such as diatom and isotopic studies, along with geochemical proxies and paleomagnetic data of the surface lake sediments. The presence of marker pollen taxa including Cerealia type Poaceae, Chenopodiaceae, and Brassicaceae, allows for distinct recognition of anthropogenic activities throughout the whole transect. The diversity and distribution of diatoms also support the palynological data in response to climate-induced and anthropogenic ecological changes. Furthermore, grain size, geochemistry (TOC/TN ratio with stable carbon isotope), and magnetic susceptibility data offer crucial insights about the sediment's depositional settings and general mineralogical composition. Stable carbon isotope data shows C3 dominance in relatively humid areas and C4 dominance in semi-arid areas, suggesting climate-driven control over sediment organic matter composition. Canonical correspondence analysis (CCA) indicates that biotic variables (pollen, diatom, stable isotopic composition) are significantly controlled by modern precipitation and temperature. Redundancy analysis reveals a significant influence of current average temperature and precipitation on major element oxide variations in surface lake sediments. Therefore, we propose using palynological, stable carbon isotope, diatom data, along with grain size, environmental magnetism, and geochemistry, to establish a multiproxy modern analogue for quantitative palaeoclimatic reconstructions. As a result, this study provides the first modern analogues from a climate-sensitive region that separates the area under ISM influence from an area with meager precipitation in western India.

The characteristics of modern flood deposits in the lower reaches of a small watershed and the significance of paleo-flood identification

The mountainous region of central Shandong Province in eastern China is renowned for its high frequency of rainstorms, which often result in devastating flood disasters and have profoundly affected the evolution of local ancient civilizations. To identify ancient flood disaster events, recognizing sediment signatures via multiple indices is important. Here, we investigated the 2018 flood deposits in the Danhe River Basin and sampled short core DH2, on which the grain size, total organic matter (TOM) content, carbonate content, magnetic susceptibility (MS) and pollen were measured. The fine grain size of the flood sedimentary layer reveals that the flood energy in the alluvial plain area is usually weak. The pollen species and concentration and the tree pollen content in the flood layer are significantly greater than those in the soil layer, suggesting that the flood sediment mainly originates from the mountainous areas in the upper reaches of the river, which provides more forest vegetation information. The MS of flood deposits is lower than that of the soil layer, which is mainly related to the intensity of pedogenesis. The research results indicate that the flood sediments in the downstream floodplain areas of small watersheds are predominantly composed of fine-grained components, with characteristics of high loss on ignition, low magnetic susceptibility, high pollen abundance and diverse species. These findings establish a multi-index identification system for paleoflood sedimentation, which has important reference significance for the study of paleoflood sedimentology and hydrology.

Sedimentary signatures of large earthquakes along the submerged Enriquillo–Plantain Garden transpressional plate boundary, northern Caribbean

Abstract The Enriquillo–Plantain Garden fault (EPGF), the southern branch of the northern Caribbean left-lateral transpressional plate boundary, has ruptured in two devastating earthquakes along the Haiti southern peninsula: the Mw 7.0, 2010 Haiti and the Mw 7.2, 2021 Nippes earthquakes. In Jamaica, the 1692 Port Royal and 1907 Great Kingston earthquakes caused widespread damage and loss of life. No large earthquakes are known from the 200-km-long Jamaica Passage segment of this plate boundary. To address these hazards, a National Science Foundation Rapid Response survey was conducted to map the EPGF in the Jamaica Passage south of Kingston, Jamaica, and east of the island of Jamaica. From the R/V Pelican we collected >50 high-resolution seismic profiles and 47 gravity cores. Event deposits (EDs) were identified from lithology, physical properties, and geochemistry and were dated in 13 cores. A robust 14C chronology was obtained for the Holocene. A Bayesian age model using OxCal 4.4 calibration was applied. Out of 58 EDs that were recognized, 50 have ages that overlap within their 95% confidence ranges. This allowed for their grouping in multiple basins located as much as 150 km apart. The significant age overlap suggests that EDs along the Enriquillo–Plantain Garden plate boundary resulted from large and potentially dangerous earthquakes. Most of these earthquakes may derive from the EPGF but also from thrust faulting at this strain-partitioned transpressional boundary. The recent increase in Coulomb stress on the EPGF from the Mw 7.2 Nippes earthquake in southwestern Haiti and the discoveries reported here enhance the significance for hazard in the Jamaica Passage.

Effect of Soil Tillage Systems and Crop Seasonality on the Sediment Geochemical Properties Transferred into a Headwater: A Case of Study in Tobacco Plantation

ABSTRACT The global impacts of agricultural land conversion on soil erosion and pollution, particularly in tobacco cultivation areas, are well-recognized as significant contributors to soil degradation. These areas are identified as hotspots for environmental concerns due to practices that lead to increased erosion and pollution. From this perspective, this case of study explores fine sediment samples from two areas with tobacco cultivation under different tillage systems and seasonal variations, transport into a headwater, and evaluates, on a local scale: (1) the impact of tillage systems on the geochemical signature of sediments; (2) if whether crop seasonality affects these sediment geochemical signatures. The Conventional Ridge Tillage (CRT) system involves extensive soil exposure and machinery for soil management, while the Mulch Ridge Tillage (MRT) system prioritizes soil conservation and relies on herbicides for weed control. The analytical methodology used to assess the sample element characteristics was Energy Dispersive X-ray Fluorescence (EDXRF). It was applied on the twenty fine sediments (ten of harvest and ten of inter-harvest season of tobacco) to quantitatively assess their inorganic composition. Additionally, Pearson correlation analysis, Hierarchical Cluster Analysis (HCA), and Principal Component Analysis (PCA) were applied on the EDXRF data to highlight the similarities and, thus, providing information to assess the complex data clustering patterns. As a result, the sediment compositions from the two studied soil systems are not similar. The PCA showed that the CRT sediments are characterized by the P, S, K, Ca, and Mn content, presenting a geochemical signature related to manure and fertilizer compared to the MRT, which is correlated with Al, Ti, Fe, Cu, and Zn contents, exhibiting a geochemical signature characterized by the natural soil composition. Therefore, the sediment geochemical signatures might be affected by two phases in the study area: a) tillage system characteristics and b) seasonal soil erosion. These findings underscore the importance of managing soil nutrients to mitigate soil pollution and nutrient exportation to aquatic systems. Moreover, the results emphasize the recommendations for sustainable agricultural practices in tobacco-growing areas to protect environmental quality.

Deciphering the uranium isotopic signature of coastal water and sediments from Tokyo Bay using a multi-collector inductively coupled plasma mass spectrometer

We have measured 236U/238U and 235U/238U values in JMS-1 (geochemical reference material of Tokyo Bay sediments) and coastal seawater using a multi-collector inductively coupled plasma mass spectrometer (MC-ICP-MS) equipped with both the retarding potential quadrupole lens and desolvating nebuliser system. For the accurate measurement of 236U/238U values (e.g., in the range of 10−9), mass spectrometric interferences on 236U isotope from both the peak tailing of 238U and polyatomic ion of 235UH were carefully corrected. With the sequential extraction experiments for JMS-1, whose U isotopic signatures were characteristic of isotopically-depleted U with industrial uses, authigenic U was extracted into a soluble fraction, and lithogenic U and anthropogenic U were gathered in an insoluble fraction. The anthropogenic U is likely to have been provided in insoluble forms and have deposited on the bay floor. Absence in differences of 236U/238U and 235U/238U values for seawater observed between inside and outside Tokyo Bay implies the negligibly small contribution of the anthropogenic U to U in the seawater. The data obtained here demonstrate the effective reduction of the interferences on 236U and the versatility of the isotopic signatures of U as an effective tracer for environmental circulation of U in nature.

Isotopically light Mo in sediments of methane seepage controlled by the benthic Fe–Mn redox shuttle process

Methane seepage has been extensively observed in various continental margin settings. It has profound effects on the marine redox environment and the molybdenum (Mo) cycles in marine sediments. Therefore, there has been much recent attention on the redox-sensitive behavior of Mo in methane seepage environments. However, the characteristics of the Mo isotope composition in the cold-seep system remain poorly understood. In this study, we performed geochemical analyses, including Mo content and isotope composition, on sediment samples (core QDN-MS6) from the “Haima” cold-seep deposit area in the South China Sea. The analysis reveals a significant concentration of authigenic pyrite in the mid-section of QDN-MS6 core (373–403 cm). Moreover, the δ34S value in this interval is notably elevated with high total sulfur/total organic carbon ratio. Additionally, the sediments in the mid-section exhibits substantial enrichment in Mo (enrichment factors of Mo ranging from 5.29 to 39.32). This implies that the sediments in the mid-section are influenced by sulfate-driven anaerobic oxidation of methane. Most notably, the sediments in the mid-section displayed distinct low δ98Mo values (with an average of −0.7‰). After careful consideration, we ruled out the influence of organic matter, an oxic environment, a weakly sulfidic environment, and incomplete removal of thiopolybdate as contributing factors. Based on δ56Fe-Fe/Al ratios, (Mo–U) enrichment factors, and As enrichment factors, we propose that the “benthic Fe-Mn redox shuttle process” is the primary cause of the observed light δ98Mo signatures in sediments. This newly identified mechanism sheds light on Mo isotope cycling in methane seepage environments and enhances our understanding of the Mo isotope cycling process.

Mineralogical signature of Khor Um Safi stream sediments, Central Eastern Desert, Egypt

Mineralogical signature of Khor Um Safi stream sediments, Central Eastern Desert, Egypt

A multi-tiered approach to assess fecal pollution in an urban watershed: Bacterial and viral indicators and sediment microbial communities

Development of effective pollution mitigation strategies require an understanding of the pollution sources and factors influencing fecal pollution loading. Fecal contamination of Turkey Creek in Gulfport, Mississippi, one of the nation's most endangered creeks, was studied through a multi-tiered approach. Over a period of approximately two years, four stations across the watershed were analyzed for nutrients, enumeration of E. coli, male-specific coliphages and bioinformatic analysis of sediment microbial communities. The results demonstrated that two stations, one adjacent to a lift station and one just upstream from the wastewater-treatment plant, were the most impacted. The station adjacent to land containing a few livestock was the least impaired. While genotyping of male-specific coliphage viruses generally revealed a mixed viral signature (human and other animals), fecal contamination at the station near the wastewater treatment plant exhibited predominant impact by municipal sewage. Fecal indicator loadings were positively associated with antecedent rainfall for three of four stations. No associations were noted between fecal indicator loadings and any of the nutrients. Taxonomic signatures of creek sediment were unique to each sample station, but the sediment microbial community did overlap somewhat following major rain events. No presence of Escherichia coli (E. coli) or enterococci were found in the sediment. At some of the stations it was evident that rainfall was not always the primary driver of fecal transport. Repeated monitoring and analysis of a variety of parameters presented in this study determined that point and non-point sources of fecal pollution varied spatially in association with treated and/or untreated sewage.

Transport and preservation of calcareous and organic-walled dinoflagellate cysts off Cape Blanc (NW africa) in relation to nepheloid layers

Our understanding of dinoflagellates' present-day and past ecology is limited due to the scarcity of data on the transport of dinoflagellate cysts in oceanic environments. Previous studies have shown that lateral transport affects the source-to-sink trajectory of cysts in the very productive region off Cape Blanc (NW Africa). Unsolved questions remain, such as: how far these cysts can be advected, whether the cyst sources vary over time and whether lateral transport is a permanent feature or restricted to individual events. To fill these gaps and assess the role of nepheloid layers on the lateral transport and preservation of dinoflagellate cysts, new data on dinoflagellate cyst distributions in the water column and sediments along a land-sea transect were obtained.Samples were collected in November 2018 along a shelf break-offshore transect during intense upwelling, notably, within and between the nepheloid layers. The composition and abundance of cysts with organic walls in the water column and surface sediments were studied. Moreover, the distribution of calcareous cysts was also analysed in the water samples, using non-destructive acid-free preparation methods. The records were dominated by empty cysts, but no clear indications that these originated from local resuspension of older sediments were observed. Clustering, principal component analysis and redundant discriminant analysis were used to compare cyst assemblages in the water column and surface sediments, and environmental conditions in the upper water column. The strong similarity in species composition of water samples collected in the active upwelling region to those collected from the more onshore parts of the Benthic Nepheloid Layer (BNL), upper Intermediate Nepheloid Layer (INL) (∼1000 m depth) and lower INL (∼2200 m depth) indicated that lateral transport of cysts within these NLs occurred until about ∼110 km from the shelf break. Cyst assemblages from above and below these NLs showed significantly different taxa composition reinforcing the role of NLs in the lateral advection of cysts. In the more offshore stations, vertically similar cyst assemblages were observed in the same station, independent of the sample depth, within or between the NLs, which supported that at these stations vertical transport was the dominant process influencing cyst assemblages. Consequently, the cyst signal in sediments off Cape Blanc may be affected both by horizontal transport of allochthonous cysts and vertical deposition of locally-produced cysts, particularly in the more offshore stations (>2000 m depth). Despite lateral transport and possible species-specific preservation effects, horizontal distributions of most cyst taxa in the water column and the surface sediments could be explained to a great extent by the main environmental gradients in the upper water column. This agrees with observations made in other regions, and reinforces that dinoflagellate cysts as good proxies to reconstruct past environmental conditions in offshore environments. New data on dinoflagellate cyst distribution, transport and accumulation patterns in deep environments off Cape Blanc may be useful for interpreting past environmental signals in the region. This is particularly relevant regarding calcareous cysts, as information on their distribution and ecology is very scarce. The present work contributes to a better understanding of the dispersal patterns of dinoflagellate cysts in the deep ocean, highlighting the significant role played by nepheloid layers in this process and thus on the dinoflagellate cyst signature in deep-sea sediments.

A process-based geochemical framework for carbonate sediments during marine diagenesis

A significant proportion of marine calcium carbonate sediments are comprised of metastable minerals that are susceptible to diagenetic alterations during burial. These reactions can reset the geochemical signature of sediments and pore fluids and influence elemental cycling in the ocean. However, the timing and mechanisms by which these reactions take place are poorly constrained. This study uses cores drilled on the slope of the Great Bahama Bank to provide quantitative constraints on important diagenetic reactions; namely respiration-driven dissolution, authigenic carbonate mineral formation, and conversion of aragonite to low Mg calcite (LMC). We perform detailed mineralogical characterization using newly acquired, high resolution X-ray diffraction (XRD) data and over 1000 reanalyzed XRD scans, characterize sediments texturally and elementally using electron microprobe data, calculate pore fluid saturation state with respect to aragonite using a Pitzer ion interaction approach, and use pore fluid chemistry and experimental distribution coefficients to predict authigenic carbonate compositions. These data suggest that aerobic organic matter oxidation, enabled by the advection of oxygenated seawater throughout the upper ∼ 30 m interval of sediment, causes undersaturation and thus dissolution of biogenic high Mg calcite (HMC) and aragonite. Deeper, anaerobic organic matter oxidation takes over and causes supersaturation, promoting authigenic precipitation in the form of HMC, which in turn decreases pore fluid Mg/Ca and promotes aragonite conversion to LMC. One novel aspect of this study is the identification of three types of calcites using the newly acquired XRD and electron microprobe data. Based on their unique crystallographic characteristics and chemical compositions, these types of calcites are interpreted to represent pelagic biogenic LMC, bank-derived biogenic HMC, and authigenic HMC precipitated from pore fluids. Notably, the composition of the authigenic calcite matches that predicted to precipitate from pore fluids using an empirical Mg partition coefficient in calcite. Calcites that form authigenically and from aragonite via replacement are suggested to recrystallize with burial as evidenced by the decrease in Mg content and micro-strain. This process-based geochemical framework assigns diagenetic processes to a specific depth window within the sediment column and paves the way for a mechanistic understanding of carbonate diagenesis, one that is rooted in thermodynamic and kinetic bases.

Petrogenesis of submarine volcanic arc rocks from Andaman subduction zone, Northeast Indian Ocean: Constraints from slab components and mantle wedge characteristics

The present study provides new petrological and geochemical data of the dredged rocks from submarine volcanoes along the Andaman arc and describes the petrogenetic evolution of the arc system in terms of mantle wedge characteristics, nature and quantitative input of subducted slab components, and fractionation processes of precursor magma. The studied rocks include basaltic andesite, andesite, dacite and rhyolite. These volcanic rocks exhibit LILE, LREE enrichments and HFSE depletion, corroborating their generation through subduction processes. High abundances of Th/Nd, La/Sm(N), LREE/HFSE than LILE/HFSE, LILE/LREE suggest a substantial contribution of sediments from the subducting slab over slab-dehydrated aqueous fluids to the mantle wedge. The 87Sr/86Sr-Ba/La mixing model suggests 0.6–0.8% addition of slab fluid (90:10 AOC: sediment fluid) to account for the fluid signature, whereas the 143Nd/144Nd-La/Sm(N) mixing model envisages ∼3–4% addition of sediment melt to the mantle source, reconciling the sediment signature in Andaman submarine volcanic rocks. The presence of N-MORB type mantle is attributed to the absence and/or inefficient convection of asthenospheric material from the Andaman back-arc basin to the mantle wedge. This ineffective convection can be equated with the flat subduction of the Indian Plate, caused by the convergence of the aseismic Ninety East Ridge. The non-modal batch-melting model suggests that 13–24% partial melting of the spinel lherzolite mantle beneath the Andaman submarine volcanic arc formed the parent magma. The crystallization model invokes up to 60–70% of fractionation of olivine, plagioclase, clinopyroxene, orthopyroxene, sanidine and magnetite in all the rock types with subordinate proportions of amphibole, biotite, apatite, ilmenite, and sanidine in rhyolites. The basaltic andesites, andesites and dacites do not show upper crustal input, while rhyolites indicate crustal contamination from an upper crust and/or arc crust.

The microbial lipid signature in sediments and chimneys within a back-arc basin hydrothermal system south of the Antarctic Polar Front

The impact of hydrothermal systems on surrounding sedimentary microbial communities is not well understood and previous work has been limited to high temperature vent sites at slow or ultraslow spreading oceanic centres. To build on the current understanding of hydrothermal systems, we explore for the first time the organic geochemistry of the only known back-arc basin hydrothermal system outside the Pacific Ocean: the East Scotia Ridge (ESR), which belongs to the South Georgia and South Sandwich Islands Marine Protected Area. Lipid biomarkers contained in sediments and hydrothermal sulphides along two hydrothermal vent fields north and south of the ESR, respectively, revealed the impact of hydrothermal activity, including both high temperature and low temperature diffusive venting, on sedimentary microbial communities. In the vent field north of the ESR, elevated ring indices of glycerol dialkyl glycerol tetraethers (GDGTs) and proportions of monoalkyl glycerol tetraethers (GMGTs), and a high ratio of total fatty acids (FAs; free plus polar lipids) to putative phytoplankton biomarkers in sediments suggest that high-temperature hydrothermalism has a local impact on surrounding sediments through the input of plume dwelling archaea and bacteria. This impact seems to be restricted to the periphery of the vent source, in agreement with the limited dataset available from slow or ultraslow spreading centres. Likewise, elevated FA to phytoplankton biomarker ratios within a diffusive hydrothermal field south of the ESR suggest an additional input of bacterial biomass relative to background sediments. Our results indicate that low temperature diffusive venting might have a higher impact than previously thought, being locally important in supporting the food chain in deep-sea environments. The distribution of tetraether lipids suggests that a higher proportion of thermophilic archaea thrive in the interior of sulphide chimneys, whereas total FA concentrations and distributions suggest that most bacteria inhabit the exterior chimney layers, where temperature is cooler than the innermost layer in contact with the hydrothermal fluid. Furthermore, differences in total FA concentrations suggest that chimney wall thickness is a control on bacterial abundance through the availability of a higher or lower diversity (and volume) of microhabitats. Our results also indicate that bacteria adapt to increasing temperatures by decreasing their degree of unsaturation. By comparison to GDGT data from other settings, it seems that overall ring indices in hydrothermal deposits are governed by growth temperature, although they might also reflect ecological factors. Our results suggest that hydrothermalism shapes microbial communities within chimneys and surrounding sediments following broadly similar patterns regardless of the type of spreading centre they are located at.

Potassium isotopic signatures of modern offshore detrital sediments from different climatic regimes and the implications

Potassium isotopic signatures of modern offshore detrital sediments from different climatic regimes and the implications

Non-pollen palynomorph assemblages in mid- to late Holocene wetland deposits and their palaeoenvironments of deposition: Microfossil signatures in sediment sequences of the Yangtze Delta coastal lowlands, East China

Fluvial processes such as sediment deposition within drainage channels and seasonal overbank flooding, and fluvial events such as occasional high intensity floods all leave particular sedimentary signatures in terms of their lithology and also in their contained microfossil assemblages, which represent different environments of deposition. Over several thousand years the Yangtze River in eastern China has developed a coastal lowland plain around its delta that is mainly composed of stacked fluvial sediment facies, but also includes many marine or estuarine layers in some areas, as well as deposits of limnic and semi-terrestrial pool, marsh and mire origin, some of which are highly organic. The fluvial facies are dominantly clastic sequences of sands, silts and clays that reflect a range of deposition from quiet water to high energy conditions and in varying water depths, mainly governed by fluvial input from the Yangtze and the many other, smaller, rivers and streams of the deltaic lowland. The limnic and marshland sediments reflect autochthonous deposition in a range of freshwater wetland types of varying water depth, from lake through marsh/fen to surface peatland. Allied to lithological and pollen data, non-pollen palynomorph spore assemblages and abundances within these complex sedimentary sequences, particularly from algal communities, provide signatures of floodplain wetland depositional history and hydrodynamic patterns. We have used groupings of these microfossil data to characterise the sedimentary facies of the lower Yangtze coastal plain and to reconstruct hydrological history across the area at a range of spatial scales. Fluctuations in the relative taxa abundances are good indicators of changes in water levels at the site scale from surface waterlogging through reedswamp and fen to deeper open water. While some changes seem to be site specific, the data show flooding and increased water depths that correlate with known phases of climatic deterioration.

Changes in rock magnetic properties of sediments along the Carlsberg Ridge: Inferences on active/extinct vent fields

Hydrothermal vents at Mid Ocean Ridges (MOR) are known to leave metalliferous, bacterial, temperature-induced signatures in sediments. Knowledge of active/extinct vents along the Carlsberg Ridge (CR) is sparse; further conventional methods to distinguish relevant areas are tedious/expensive. We show that basic rock magnetic measurements, including magnetic susceptibility and laboratory-induced remanent magnetizations, can help to characterize sediment samples near and away from hydrothermally activity/extinct areas at the CR. Eight spade cores from the Carlsberg ridge (of which three are in the vicinity of the Tianxiu hydrothermal field and one from the ridge flank) collected on board R.V. Sindhu Sadhana during 77th and 83rd cruises are investigated for the present study. Two spade cores consist of top 2 cm and six core lengths ranged between 22 and 38 cm. Coarse fraction and magnetic minerals were separated and studied under a binocular microscope and scanning electron microscope (SEM). Magnetic susceptibility (χlf) of sediments ranges between 1.3 and 37.1 × 10−8 m3 kg−1 with higher values for ridge valley and lower values for ridge flank. Ridge flank sediments are associated with low χlf, Saturation Isothermal Remanent Magnetization (SIRM), Hard Isothermal Remanent Magnetization (HIRM) and high χARM/SIRM, which are taken as base values. Sediments in the vicinity of the Tianxiu hydrothermal vent field are associated with high χlf, SIRM, HIRM, and low Anhysteretic remanent magnetic susceptibility (χARM)/SIRM, coarse Stable Single Domain (SSD) and fine SSD & Mixture grains with magnetite as the dominant mineral. Similar signatures are observed in two more spade cores ∼250 km south of the Tianxiu vent field, suggesting new active/relict site/sites in the vicinity. Signatures like that of flank sediments are also observed in two cores from the ridge valley indicating, the absence of hydrothermal activity in the vicinity. In the marine environment, identifying/locating metalliferous hydrothermal sediment/sites along extensive MOR is expensive and time-consuming; rock magnetic could be a non-destructive method to shortlist the areas for detailed studies.

In-depth characterization of sediment contamination in stormwater infiltration basins

Abstract Managing stormwater in infiltration-based systems enables the interception of runoff suspended solids. Accumulated particles form a layer of stormwater sediments, the contamination of which presents a critical challenge for maintenance operations but is still insufficiently understood. This study therefore aims to characterize the main contamination patterns of stormwater sediments. Sediments were sampled from 18 infiltration basins encompassing a diversity of catchments. Eighty-five substances, including metals and six families of organic micropollutants, were targeted, almost all of which were consistently quantified. A significant accumulation relative to baseline levels was ascertained in all sites. The geochemical signature of stormwater sediments was relatively close to that of road dust, but different from continental and marine sediments, revealing the contribution of urban-specific sources of contaminants. Common emission and transfer dynamics were inferred from strong correlations between metals; same observations were made for alkylphenols and the group formed by polycyclic aromatic hydrocarbons, polychlorinated biphenyls, dioxins, and furans. The predominant land use was generally insufficient to explain the inter-site variability of sediment contamination, which could still be understood from an in-depth study of each catchment and the identification of site-specific emission sources. These results constitute a milestone toward stormwater sediment reuse as a resource.

Spatial, seasonal and climatic drivers of suspended sediment atop Great Bahama Bank

ABSTRACTSuspension is the key mechanism by which fine‐grained sediment (≤125 μm) is winnowed and transported across shallow‐water carbonate platforms into adjacent deep waters. Unlike sliding and saltation, which deliver sedimentary structures via bedload, the sedimentological signature of suspended sediment is more cryptic. This study focuses on suspended sediment, and its drivers – wind, waves and tides – to better constrain the processes responsible for the transport of fine‐grained sediments. By building forward from remote sensing algorithms developed for deep‐waters, sediment suspension in the shallow water column can be mapped from satellite. By applying machine learning to Moderate Resolution Imaging Spectroradiometer data for Great Bahama Bank, this study demonstrates how the drivers of sediment suspension change over 18 years across this 100 000 km2 carbonate platform. Through time, both seasonal patterns of suspension, as well as those induced by El Niño‐Southern Oscillation and, more subtly, the Atlantic Meridional Overturning Circulation were tracked. El Niño‐Southern Oscillation modulates wind‐induced currents, while Atlantic Meridional Overturning Circulation affects local sea level. Across space, this study shows how the eastern margin of Great Bahama Bank, which is traditionally considered to be wind‐dominated, primarily owes its suspended sediment to tidal currents focused between islands. Sediment suspension across the leeward margin of Great Bahama Bank, meanwhile, can be attributed to wind‐induced currents and waves. The authors consider this work a step towards delivering a quantitative, reproducible, process‐based understanding of sediment suspension atop carbonate platforms using Earth observation data.

Evolution of the alpine Critical Zone since the Last Glacial Period using Li isotopes from lake sediments

Comprehending and predicting the way humans affect the Earth's Critical Zone remains a challenge. An understanding of the past changes resulting from human and non-human influences in the dynamics of the Critical Zone is crucial. Here, we use a retrospective approach to address this question based on a new lithium (Li) isotope record from the Late Glacial Period to the present from a pre-Alpine lake sediment sequence (Lake La Thuile, France). Coupled with the lake sediment archive, the investigation of present-day soils in the lake catchment suggests that lake sediments are not necessarily recording the erosoin of topsoil in the catchment. Our findings indicate that soil particles can be sorted during transportation to the lake, with finer particles being preferentially mobilized, highlighting the influence of fine particle transport on the Li isotope signature of soils and lake sediments. Characterized by low Li isotope signatures, changes in weathering signatures in lake sediments can be amplified by the combined effect of soil development and selective transport. In the La Thuile catchment, soil development was limited during the Late Glacial Period, whereas it became a dominant process during the Holocene climatic optimum together with enhanced selective transport of fine particles. Human activities since 3,000–4,000 yr cal BP induced a strong perturbation hindering both soil formation and selective transport by reinforcing erosion rates. After a period of topsoil destruction caused by intense deforestation and agriculture, lake Li isotopes record the evolution of soil profiles associated with changes in agricultural practices.