Early Diagenesis Of Organic Matter Research Articles

Occurrence, Diversity, and Genomes of "Candidatus Patescibacteria" along the Early Diagenesis of Marine Sediments.

The phylum "Candidatus Patescibacteria" (or Candidate Phyla Radiation [CPR]) accounts for roughly one-quarter of microbial diversity on Earth, but the presence and diversity of these bacteria in marine sediments have been rarely charted. Here, we investigate the abundance, diversity, and metabolic capacities of CPR bacteria in three sediment sites (Mohns Ridge, North Pond, and Costa Rica Margin) with samples covering a wide range of redox zones formed during the early diagenesis of organic matter. Through metagenome sequencing, we found that all investigated sediment horizons contain "Ca. Patescibacteria" (0.4 to 28% of the total communities), which are affiliated with the classes "Ca. Paceibacteria," "Ca. Gracilibacteria," "Ca. Microgenomatia," "Ca. Saccharimonadia," "Ca. ABY1," and "Ca. WWE3." However, only a subset of the diversity of marine sediment "Ca. Patescibacteria," especially the classes "Ca. Paceibacteria" and "Ca. Gracilibacteria," can be captured by 16S rRNA gene amplicon sequencing with commonly used universal primers. We recovered 11 metagenome-assembled genomes (MAGs) of CPR from these sediments, most of which are novel at the family or genus level in the "Ca. Paceibacteria" class and are missed by the amplicon sequencing. While individual MAGs are confined to specific anoxic niches, the lack of capacities to utilize the prevailing terminal electron acceptors indicates that they may not be directly selected by the local redox conditions. These CPR bacteria lack essential biosynthesis pathways and may use a truncated glycolysis pathway to conserve energy as fermentative organotrophs. Our findings suggest that marine sediments harbor some novel yet widespread CPR bacteria during the early diagenesis of organic matter, which needs to be considered in population dynamics assessments in this vast environment. IMPORTANCE Ultrasmall-celled "Ca. Patescibacteria" have been estimated to account for one-quarter of the total microbial diversity on Earth, the parasitic lifestyle of which may exert a profound control on the overall microbial population size of the local ecosystems. However, their diversity and metabolic functions in marine sediments, one of the largest yet understudied ecosystems on Earth, remain virtually uncharacterized. By applying cultivation-independent approaches to a range of sediment redox zones, we reveal that "Ca. Patescibacteria" members are rare but widespread regardless of the prevailing geochemical conditions. These bacteria are affiliated with novel branches of "Ca. Patescibacteria" and have been largely missed in marker gene-based surveys. They do not have respiration capacity but may conserve energy by fermenting organic compounds from their episymbiotic hosts. Our findings suggest that these novel "Ca. Patescibacteria" are among the previously overlooked microbes in diverse marine sediments.

The hysteresis of asphaltene-trapped saturated hydrocarbons during thermal evolution

Asphaltene-trapped (adsorbed or occluded) biomarkers are considered a valid source of information for crude oil with severe secondary alterations. However, thermal stress might change asphaltene-trapped hydrocarbons to some extent. Therefore, it is indispensable to investigate the thermal evolution behavior of asphaltene-trapped biomarkers. In this study, low-maturity bitumen from the Kuangshanliang area of the Sichuan Basin (China) was selected as a sample. The thermal evolution behavior of free and asphaltene-trapped saturated biomarkers was investigated by thermal simulation experiments. The results revealed, in addition to normal biomarkers, also a series of even carbon number n-alk-(1)-enes in asphaltene-occluded hydrocarbons. All of them were hardly influenced by secondary alterations. Moreover, due to the restriction of macromolecular structure, the thermal evolution of asphaltene-trapped biomarkers lags behind that of free biomarkers. Most biomarker parameters of occluded hydrocarbons changed little with increasing maturity. In particular, the distributions of occluded terpanes or steranes retained the characteristics of early diagenesis of organic matter, even if they suffered from strong thermal alteration.

Sulfate reduction and its important role in organic carbon mineralization in sediments of the Pearl River Estuary

The sulfate reduction process plays an important role in the early diagenesis of organic matter in the estuarine and coastal sediments. In this study, the sulfate reduction rates (SRR) were determined by the 35SO42− radioactive tracer method, and the SO42−, CH4, Cl− of sediment porewater and total organic carbon (TOC), temperature, and redox potential (Eh) of sediment were determined simultaneously at three stations (QA, HQ, and GS) in different sedimentary environments of the Pearl River Estuary to study the sulfate reduction process and its important role in organic matter mineralization. The results show that SRR was mainly controlled by the content and availability of organic matter in sediments of the Pearl River Estuary. The consumption of sulfate mainly included the organic matter mineralization on the upper sediments and the anaerobic oxidation of methane (AOM) driven by sulfate in the sulfate-methane transition zone (SMT), which formed two peaks in the SRR profile, respectively (stations HQ and GS). Affected by physical disturbance, there was only one SRR peak formed above the SMT at station QA. The results of flux calculations for AOM and sulfate reduction show that the contributions of AOM to total sulfate reduction were 7.04 %, 5.46 %, and 42.0 % at stations QA, HQ, and GS, respectively, which were also controlled by the content and availability of organic matter in sediments. The depths of SMT in sediments of stations QA, HQ, and GS were 25, 30, and 213 cm, respectively, which were controlled by the input of organic matter and sulfate concentration in sediments. The calculation results show that total fluxes of sulfate reduction were 22.7, 35.3, and 3.9 mmol m−2 d-l at stations QA, HQ, and GS, respectively, and the rates of organic carbon mineralization by sulfate reduction were 45.4, 70.6, and 7.8 mmol m−2 d-l. In the estuarine mouth (station GS) with relatively weak hydrodynamic force and deep water, the burying efficiency of organic matter in sediment was higher than that in the brackish coast (station HQ); whereas the burial efficiency of organic matter in sediment cannot be comprehensively estimate in the upper estuary (station QA) due to the existence of the fluid mud layer. These findings contribute to a comprehensive understanding of the biogeochemical cycling process of sulfate and methane in sediments of the Pearl River Estuary.

Modeling Small Scale Impacts of Multi-Purpose Platforms: An Ecosystem Approach

Aquaculture and marine renewable energy are two expanding sectors of the Blue Economy in Europe. Assessing the long-term environmental impacts in terms of eutrophication and noise is a priority for both the EU Water Framework Directive and the Marine Strategy Framework Directive, and cumulative impacts will be important for the Maritime Spatial Planning under the Integrated Maritime Policy. With the constant expansion of aquaculture production, it is expected that farms might be established further offshore in more remote areas, as high-energy conditions offer an opportunity to generate more power locally using Marine Renewable Energy (MRE) devices. A proposed solution is the co-location of MRE devices and aquaculture systems using Multi-Purpose Platforms (MPPs) comprising offshore wind turbines (OWTs) that will provide energy for farm operations as well as potentially shelter the farm. Disentangling the impacts, conflicts and synergies of MPP elements on the surrounding marine ecosystem is challenging. Here we created a high-resolution spatiotemporal Ecospace model of the West of Scotland, in order to assess impacts of a simple MPP configuration on the surrounding ecosystem and how these impacts can cascade through the food web. The model evaluated the following specific ecosystem responses: (i) top-down control pathways due to distribution changes among top-predators (harbor porpoise, gadoids and seabirds) driven by attraction to the farming sites and/or repulsion/killing due to OWT operations; (ii) bottom-up control pathways due to salmon farm activity providing increasing benthic enrichment predicated by a fish farm particle dispersal model, and sediment nutrient fluxes to the water column by early diagenesis of organic matter (recycled production). Weak responses of the food-web were found for top-down changes, whilst the results showed high sensitivity to increasing changes of bottom-up drivers that cascaded through the food-web from primary producers and detritus to pelagic and benthic consumers, respectively. We assessed the sensitivity of the model to each of these impacts and the cumulative effects on the ecosystem, discuss the capabilities and limitations of the Ecospace modeling approach as a potential tool for marine spatial planning and the impact that these results could have for the Blue Economy and the EU’s New Green Deal.

Impacts of redox conditions on dissolved organic matter (DOM) quality in marine sediments off the River Rhône, Western Mediterranean Sea

Sedimentary dissolved organic matter (DOM) is an important pool of intermediates produced and consumed during early diagenesis of organic matter in the anoxic subseafloor. Rapid degradation of organic matter in the coastal sediment results in stratification of redox zones. However, to date little is known about the selectivity with respect to organic matter of the initial microbially mediated anaerobic degradation processes under contrasting redox conditions and how these affect the composition of DOM. In order to study the effect of sulfate reducing vs. methanogenic conditions on DOM quality and degradation, sediments (0–18 cm) from the Rhône River Delta were incubated, with redox conditions being controlled by sulfate amendment. The progress of incubation was monitored by H2, CH4, sulfate, DIC, DOC and acetate production. DOM composition was determined by 3D Fluorescence Spectroscopy, i.e., Excitation Emission Matrix Spectroscopy (EEMs), and ultra-high-resolution Fourier Transform Ion Cyclotron Resonance Mass Spectrometry (FT-ICR-MS). Parallel factor analysis (PARAFAC) of EEMs was used to distinguish different groups of DOM (humic-like and protein-like compounds) to evaluate composition, conjugation and size of DOM. Prior to incubation, humic-like sedimentary DOM predominated; nearly half of the molecular formulae (>5000) identified by FT-ICR-MS were CHO and one third were CHNO compounds. During incubation, protein-like DOM and CHNO formulae with 3 and 4 N atoms formulae were rare under both sulfate reducing and methanogenic conditions. Incubation under sulfate reducing conditions resulted in rapid release and net accumulation of dissolved organic carbon (DOC). Protein-like DOM was rapidly cycled and humic-like DOM accumulated. Consistently, CHNO formulae with 3 and 4 N atoms decreased faster, whereas formulae with one N and oxygen-rich unsaturated compounds became more concentrated. In contrast, during incubation under methanogenic conditions, there was no net accumulation of DOC; blue-shift of humic-like peaks suggest the transformation possibly associated with loss of oxygen-bearing functional groups in conjugated structures of humic substances. This interpretation is consistent with the relative decrease of oxygenation and carbon number in the pool of aromatic and highly unsaturated compounds observed by FT-ICR-MS analysis. Approximately 90% of molecular formulae that were lost under methanogenic conditions were accumulated under sulfate reducing conditions. Our results suggest that under sulfate reducing conditions degradation of organic matter results in the accumulation of highly oxidized DOM, while protein-like compounds are selectively consumed. When the redox regime changes to methanogenic conditions, microbes apparently utilize the humic-like and oxygen-rich compounds of the oxidized DOM pool that accumulated under sulfate reducing conditions. Consequently, redox regimes and the associated biogeochemical processes influence rate and fractions of DOM released by and consumed in the deep biosphere, which could ultimately shape the composition of the preserved sedimentary organic matter and the DOM released to the ocean.

Behavior of dioxin like PCBs and PBDEs during early diagenesis of organic matter in settling material and bottom sediments from the sewage impacted Buenos Aires' coastal area, Argentina.

Settling particles (SPs) and sediments collected in the Buenos Aires sewer area were analyzed for dioxin like polychlorinated biphenyls (dlPCBs) and polybrominated diphenyl ethers (PBDEs) to follow early diagenetic changes during transport and deposition of organic matter. SP showed a temporal trend of higher total organic carbon (TOC) and fresher dlPCBs and PBDEs signatures during warm-rainy months related to more efficient washout of residues. TOC-normalized sediment trap concentrations suggest a diagenetic magnification of dlPCBs during cold-dry months due to enhanced decomposition of TOC, whereas most labile PBDEs appear to follow TOC decay. The diagenetic behavior of individual congeners along seasonal changes (cold/warm) and during deposition (bottom sediment/SP) shows the selective preservation of heavier, more persistent congeners with a positive relationship with sediment half-lives. The 3-4 times diagenetic magnification of heavier congeners observed in bottom sediments would be a prevailing long-term pathway for dlPCBs and PBDEs bioaccumulation in detritus feeding organisms.

Pore water nutrient characteristics and the fluxes across the sediment in the Pearl River estuary and adjacent waters, China

Spatio-temporal distribution of pore water nutrients and the fluxes at the sediment-water interface (SWI) were investigated to probe into the geochemical behavior of nutrients associated with early diagenesis of organic matter (OM), and to study the accumulation and transformation processes of nutrients at the SWI, as well as to discuss the impact of riverine inputs on nutrients in the Pearl River estuary (PRE) and adjacent offshore areas. Nutrient concentrations decreased from the upper to the lower reaches of the estuary, suggesting that there was a high input of anthropogenic nutrients and the estuary was acting as a nutrient sink. Dissolved inorganic nitrogen (DIN: the sum of NH4–N, NO3–N and NO2–N) concentrations in the water column and the pore water were higher in the estuary than at offshore areas due to the riverine discharge and the high accumulation rate in the estuary. NO3–N concentration was the highest of the three forms of DIN in the overlying water and showed a sharp decrease from the surficial sediment with increasing sediment depth, indicating that there was strong denitrification at the SWI. NH4–N, mainly deriving from the anaerobic degradation of OM, was the main form of DIN in the pore water and increased with depth. Negative NO3–N fluxes (into the sediment) and positive NH4–N fluxes (from the sediment) were commonly observed from incubation experiments, indicating the denitrification occurred at the SWI. DIN flux suggested that the sediment was a sink of DIN in spring, however, the sediment was the source of DIN in summer and winter. Nutrients dominantly diffused out of the sediment, suggesting that the sediment was the source of nutrients in spring at adjacent offshore areas. The fluxes directed that PO4–P mainly diffused into the sediment while SiO4–Si mainly diffused out of the sediment.

Long-Term, Low-Temperature Simulation of Early Diagenesis of Organic Matter from Algae: Significance for Immature Oil

Algae are good sources of immature oil. A long-term (more than 5 years), low-temperature (80°C) simulation of early diagenesis of organic matter from algae was carried out. In the very early stage of the simulation, different quantities of immature oil were generated after 26 to 56 days. After one year, algae showed obvious fluorescence, and the intensity was maintained during the remainder of the simulation. From the earlier stages of the simulation to the later stages, the asphaltene fractions of the soluble extracts decreased and the polar fractions increased. Asphaltene and polar compounds play important roles in the formation of immature oil, especially under briny environments. Finally, the changes in hydrocarbons during the simulation are discussed and the algae-originated phytenes and C20 bicyclic terpanes are suggested as biomarkers for immature oil.

Early diagenetic transformation of terpenoids from conifers in the aromatic hydrocarbon fraction: A long term, low temperature maturation experiment

An artificial maturation experiment at 80°C was conducted for >5years to investigate the early diagenetic transformations of organic matter (OM), mainly terpenoids, in conifers. The diagenetic products of aromatic hydrocarbons were determined in the earlier and later stages of maturation, namely, after >1year and after ∼5.5years. The OM in contemporary coniferous plants (Cedrus deodara and Platycladus orientalis) was also characterized for comparison. The results reveal that during the early diagenesis of OM from conifers, biological terpenoids were transformed into diagenetic aromatic terpenoids and common polycyclic aromatic hydrocarbons. Some polar terpenoids, such as dehydroabietate aldehydes and abietatetraenoic acid, were detected and identified. Information on these biological and evolutionary terpenoids may improve the understanding of their diagenetic pathways. The experimental data also show that the diagenesis of dehydrogenated and aromatic terpenoids and polycyclic aromatic hydrocarbons is affected by different experimental inorganic conditions. High salinity is favourable to diagenesis in aromatic fractions. Meanwhile, heavy metals such as lead and iron may delay and interrupt the transformation of terpenoids, respectively.

Feeding strategies of deep-sea sub-Arctic macrofauna of the Faroe-Shetland Channel: Combining natural stable isotopes and enrichment techniques

The response of a sub-arctic, deep-sea macrofaunal community to a simulated food sedimentation event was studied by means of a stable isotope “pulse-chase” experiment. A food pulse was simulated by adding 500 mg C m −2 of 13C-labelled diatoms, Chaetoceros radicans, to sediment cores retrieved from 1080 m in the Faroe-Shetland Channel. Carbon uptake by specific macrofaunal groups was quantified after 3 and 6 days of incubation. The carbon uptake of the dominant taxon (Polychaeta) was quantified at the genus-, and where possible, species-level, representing a data resolution that is rare in deep-sea tracer studies. The macrofaunal community reacted rapidly to the diatom addition, with 47% and 70% of the animals illustrating 13C-enrichment after 3 and 6 days, respectively. Approximately 95% of C uptake was located in the upper 2 cm due to the particularly shallow vertical distribution of the macrofaunal community and the nonexistent tracer subduction by burrowing species. Polychaetes of the families Ampharetidae and Cirratulidae were among the most heavily labelled with above background enrichment reaching 1300‰. Approximately 0.8 and 2.0 mg C m −2 were processed by the macrofauna after 3 and 6 days, representing 0.2% and 0.4% of the added carbon, respectively. It was not possible to differentiate sub-surface deposit-feeding polychaetes from predator/scavenger- and omnivorous polychaetes using their natural δ 15N signatures. However, the combination of natural abundance δ 15N data and 13C-labelling experiments proved to be useful for elucidating trophic relations in deep-sea food webs. This study confirms that macrofauna play an active role in the short-term carbon cycling at bathyal depths even at sub-zero temperatures and highlights the need for detailed knowledge of the community structure in understanding carbon processing patterns and early diagenesis of organic matter in marine sediments.

Long-term, low temperature simulation of early diagenetic alterations of organic matter from conifers: Aliphatic hydrocarbons

Early diagenetic alterations of organic matter from conifers were simulated at low temperature of 80°C for five and a half years. Their diagenetic products of aliphatic hydrocarbons were identified and quantified. The results reveal that in the early sedimentation of organic matter from conifers, n-alkanes have developed; natural terpenoids have transformed into diagenetic terpenoids, in which some seldom reported evolutionary intermediates—two cadinatetraenes, three norabietatetraenes and one abietatetraene—were detected and identified. The diagenetic pathways for cadalane-type sesquiterpenoids and abietane-type diterpenoids are proposed. The experimental data also show that the diagenesis of aliphatic hydrocarbons is influenced by different inorganic environments. The influences can be concluded as follows: high salinity is propitious to generate and expulse aliphatic hydrocarbons; iron may promote the increase of alkanes, but interrupt the alterations of terpenoids; gypsum, when not coexisting with metal, may slow the degradation from long chain alkanes to short ones; and heavy metal probably delays the early diagenesis of both alkanes and terpenoids. These influences observed under low temperature may enrich studies on early diagenesis of organic matter from higher plants.

Influence of in situ biological activity on the vertical profile of pre-emergence herbicides in sediment

The in situ effect of biological activity on herbicide degradation was studied in sediment. Early diagenesis indicators of organic matter (OM) was selected to provide information on the presence and the kinetics of the various biotic and abiotic processes involved in the degradation of fresh organic matter, the vector of herbicides in sediment. Two tandem-coring samples were taken in the Malause reservoir, one in the hyperoxic zone (Tarn confluence, MT core) and the other in the central part, under the exclusive influence of the Garonne River (MG core), after having crossed a zone where the high intensity of abiotic processes is proven. At each site, analysis of the vertical profile of the herbicides was coupled with compounds associated with early diagenesis of OM. The MT core proved nearly seven times more contaminated than the MG core. DEA played a minor role in sediment contamination. Biological activity only seems to influence herbicide degradation indirectly. Neither oxygen concentration nor the level of labile carbon indicated any correlation between the consumption of fresh organic matter and substrate degradation. Herbicide transformation thus does not seem to depend on the consortia studied but on physicochemical parameters such as hydrolysis, leading to the long half-life of herbicides in sediment and hence their long-term presence in the aquatic environment.

Natural gas geochemistry of sediments drilled on the 2005 Gulf of Mexico JIP cruise

In April and May 2005, cores were acquired and sub-sampled for gases in lease blocks Atwater Valley 13 and 14 and Keathley Canyon 151 during deep subseafloor drilling conducted as part of the JIP study of gas hydrates in the northern Gulf of Mexico. Sample types included sediment headspace gas, free gas derived from sediment gas exsolution, and gas exsolution from controlled degassing of pressurized cores. The gases measured both onboard and in shore-based labs were nitrogen, oxygen, hydrogen sulfide, carbon dioxide, and the hydrocarbons methane through hexane. The presence of seafloor mounds, seismic anomalies, a shallow sulfate–methane interface, and similar gas compositions and isotopic compositions near the seafloor and at depth suggest an upward flux of methane at both sites. Sediment gases at the Atwater Valley sites, where seafloor mounds and adjacent sediments were cored, strongly suggest a microbial source of methane, with very little thermogenic gas input. Sediment gas from all cores contained from about 96 to 99.9% methane, with the balance composed primarily of carbon dioxide. Methane to ethane ratios were greater than 1000, and often over 10,000. Gases from cores at Keathley Canyon were similar to those at Atwater Valley, however, deeper cores from Keathley Canyon contained more ethane, propane, and butane suggesting mixing with minor concentrations thermogenic gas. The isotopic composition of methane, ethane, and carbon dioxide were measured, and δ 13C values range from −84.3 to −71.5‰, −65.2 to −46.8‰, and −23.5 to −3.0‰, respectively, all consistent with microbial gas sources, early diagenesis of organic matter and perhaps biodegradation of petroleum. The presence of deep microbial gas at these sites here and elsewhere highlights a potentially significant, predominantly microbial gas source in the northern Gulf of Mexico.

Biochemical composition and early diagenesis of organic matter in coastal sediments of the NW Adriatic Sea influenced by riverine inputs

River inputs influence trophodynamic and biogeochemical processes of adjacent continental shelves. In order to provide new insights on the influence of continental inputs on the benthic trophic state and early diagenesis of sediment organic matter we collected surface sediments in the NW Adriatic Sea at three stations located at increasing distance from the Po River. Sediment samples were collected in four periods characterized by different river outflows and analysed for chloropigment content (chlorophyll-a and phaeopygments), protein, carbohydrate and lipid concentrations, prokaryote abundance and aminopeptidase activity. Sediments of the NW Adriatic Sea displayed high organic loads, tightly coupled with the outflow dynamics of the Po River. A major flooding event was responsible of an enhanced accumulation of organic material on the sea bottom. The resulting increased nutrient load in the sediment impaired organic matter degradation processes. The results of the present study suggest that the enhanced trophic state of marine coastal sediments subjected to riverine inputs are related not only to the increased nutrient inputs, but that they may be amplified by impaired degradation processes.

Anomalous Trace Elements Contents in the Spetsugli Germanium Deposit (Pavlovka Brown Coal Deposit) Southern Primorye: Communication 1. Antimony

The first data are presented on large-scale Sb accumulation (up to 1175 ppm on a whole coal basis) in the Spetsugli (Special Coals) germanium deposit (Pavlovka brown coal deposit). The distribution of anomalous Sb contents is considered in the coal-bearing molasse section. The close correlation between Ge and Sb abundances in coals together with SEM data indicate an organic mode of Sb occurrence. Such a significant Sb accumulation was caused by the filtration of volcanogenic metalliferous solutions in molasse rocks during early diagenesis of organic matter in the Late Miocene. Extremely high contents and organic mode of Sb occurrence make it possible to consider Ge-bearing coals of the Pavlovka deposit not only as a complex raw material suitable for the extraction of Sb, but also as a potential source of ecological hazard.

Early diagenesis of organic matter from sediments of the eastern subtropical Atlantic: evidence from stable nitrogen and carbon isotopes

Stable isotopes of sedimentary nitrogen and organic carbon are widely used as proxy variables for biogeochemical parameters and processes in the water column. In order to investigate alterations of the primary isotopic signal by sedimentary diagenetic processes, we determined concentrations and isotopic compositions of inorganic nitrogen (IN), organic nitrogen (ON), total nitrogen (TN), and total organic carbon (TOC) on one short core recovered from sediments of the eastern subtropical Atlantic, between the Canary Islands and the Moroccan coast. Changes with depth in concentration and isotopic composition of the different fractions were related to early diagenetic conditions indicated by pore water concentrations of oxygen, nitrate, and ammonium. Additionally, the nature of the organic matter was investigated by Rock-Eval pyrolysis and microscopic analysis. A decrease in ON during aerobic organic matter degradation is accompanied by an increase of the 15N/ 14N ratio. Changes in the isotopic composition of ON can be described by Rayleigh fractionation kinetics which are probably related to microbial metabolism. The influence of IN depleted in 15N on the bulk sedimentary (TN) isotope signal increases due to organic matter degradation, compensating partly the isotopic changes in ON. In anoxic sediments, fixation of ammonium between clay lattices results in a decrease of stable nitrogen isotope ratio of IN and TN. Changes in the carbon isotopic composition of TOC have to be explained by Rayleigh fractionation in combination with different remineralization kinetics of organic compounds with different isotopic composition. We have found no evidence for preferential preservation of terrestrial organic carbon. Instead, both TOC and refractory organic carbon are dominated by marine organic matter. Refractory organic carbon is depleted in 13C compared to TOC.

Early Diagenesis of Organic Matter from Higher Plants in a Malagasy Peaty Marsh. Application to Environmental Reconstruction During the Sub-Atlantic

The purposes of the present work were to examinate the morphological features and chemical composition of organic matter (OM) from a peaty marsh, in order to derive information on biological sources and on the changes in depositional conditions that occurred during the last 2300 years. The studied site, Tritrivakely, is a maar (a former volcanic crater lake) about 600 m wide and 50 m deep, located on Ankaratra Plateau. The maar is presently occupied by a peaty marsh with abundant Cyperaceae. The waterbody is shallow, fluctuating from 0 to 2 m. The study was concerned with the uppermost meter of peat which has accumulated for 2300 years B.P. in the maar. The Cyperaceae living in the marsh were also studied for comparison.

Chemical plumes from low‐temperature hydrothermal venting on the eastern flank of the Juan de Fuca Ridge

We report evidence for chemical anomalies in the water column from low‐temperature ridge‐flank hydrothermal venting. During cruises in 1992 and 1994, samples were taken from the water column for trace metals, nutrients, dissolved gases, and particles near each of three basaltic outcrops overlying 3.5 m. y. old crust on the eastern flank of the Juan de Fuca Ridge in Cascadia Basin. The water column above one of these outcrops, Baby Bare, which rises about 70 m above a flat turbidite plain, was the most thoroughly sampled. Thermal, chemical (Mn, Fe, δ(3He)%, CH4, and O2), and particulate anomalies in the water column confirm the existence of (1) early diagenesis of organic matter in seafloor sediment which produces a flux of dissolved metals and nutrients to bottom seawater, (2) hydrothermal emissions which are both focused (spring‐like) and diffuse, and (3) resuspension of sediment by turbulent flow of tidal currents about a topographical high. On the basis of data from the water column and thermal and chemical pore water data from 46 piston and gravity sediment cores near and on Baby Bare (FlankFlux 90 and 92), we constrain the composition of seawater in basement and thus the composition of spring‐like water. Given this composition, no measurable dissolved silica or phosphate hydrothermal anomalies are expected in the water column.

Magnetic properties of sediments in a Polish lake: evidence of a relation between the rock-magnetic record and environmental changes in Late Pleistocene and Holocene sediments

A study of mineral magnetic parameters was carried out on a Late Pleistocene and Holocene sedimentary sequence (of nearly 18 m) from Lake Bledowo (central Poland). Sediments of Lake Bledowo have already been analysed for bulk sediment mineralogy and biogenic materials. The mineral magnetic stratigraphy confirms the major changes in palaeo-environmental conditions that have been deduced from other methods. The most important mineral magnetic change results from the authigenetic formation of ferrimagnetic greigite, Fe3S4, during the beginning of lacustrine conditions (± 12 000 yr BP). Our data also indicate a detrital origin of overlying ferrimagnetic iron oxides. It is suggested that they originate from brown soils developed on the boulder clay constituting the west side of the lake shore. Variations of ferrimagnetic iron oxide size are related to the early diagenetic processes in the sediment. Larger particles are present in periods with early diagenesis of organic matter in anoxic conditions. This indicates the dissolution of fine magnetic particles by iron-oxide-reducing bacteria and results in homogeneous magnetic grain sizes, despite their origin from soils, characterized by a multimodal grain-size distribution.

Multifractal characterization of microbially induced magnesian calcite formation in Recent tidal flat sediments

Structures resulting from biogenic carbonate cementation of microbial mats in Recent siliciclastic tidal flat sediments of the North Sea are analyzed quantitatively by a novel combination of scanning electron microscopy and energy-dispersive X-ray spectrometry (SEM/EDX) imaging and subsequent multifractal analysis. Evaluation of calcium distribution patterns and their links to sediment-intrinsic mineralization processes show that the applied geometrical technique is an efficient tool for detecting microscopic variations in elemental distributions and related minerals within sedimentary matrices. Two main conclusions can be drawn: (i) magnesian calcite is a rapidly formed product of the early diagenesis of organic matter in Recent bioactive marine sediments; and (ii) multifractal spectra are measures for the spatial inhomogeneity of authigenic calcification processes acting on the sedimentary structure. This implies that elemental distribution patterns in a sedimentary system are scale-independent phenomena. Processes causing such patterns have occurred over certain periods with varying rates and on different scales. The detection of multifractal measures also opens a way towards a systematic survey of dynamic processes occurring in sedimentary structures.