TOC Accumulation Research Articles

Carbon accumulation features in different functional zones of cities in the steppe zone.

This article presents findings on the study of content, profile distribution, and reserves of various carbon forms (organic carbon (TOC) and inorganic carbon (IC)) in Urbic Technosols and Ekranic Technosols within the residential zone of the city, alongside zonal Calcic Chernozems in the recreational zone of Rostov-on-Don, Aksai, and Bataysk. It was revealed that the TOC content in the upper horizons of Urbic Technosols is significantly lower than in the chernozem horizons of fallow areas, registering at 2.59 ± 0.79% and 3.25 ± 0.94%, respectively. IC exhibits an inverse trend, with maximum content observed in the upper horizons of Ekranic Technosols. Down the soil profile, disparities in TOC and IC contents are mitigated. This specificity in TOC accumulation and profile distribution signifies a "bipartite" profile alteration in buried chernozems, affecting solely the upper stratum rather than the entire soil profile. The presence of woody vegetation in the dry-steppe zone positively influences TOC accumulation. Calcic Chernozems beneath woody vegetation showcase the highest TOC reserves within the 30-cm layer (10.61 ± 1.45kg/m2). Calcic Chernozems of fallow areas under natural steppe vegetation contain 8.94 ± 1.75kg/m2, Technosols of the residential zone 8.44 ± 2.47kg/m2. For Technosols of the residential zone, a weakening of the dependence of TOC and IC content on the depth of the soil horizon is observed.

Changing the land use from degraded pasture into integrated farming systems enhance soil carbon stocks in the Cerrado biome

Integrated agricultural production systems can increase soil organic carbon stocks over time and contribute to the mitigation of climate change. The present study aimed to evaluate soil carbon stocks, accumulation rates (TOC), total nitrogen (TN), and the quality of soil organic matter (SOM) after the transition of a low-productivity pasture into agrosilvopastoral systems in the Cerrado biome. We evaluated an 11-year-old experiment, and the treatments studied were: Eucalyptus + buffel grass; Eucalyptus + cowpea; Eucalyptus + pigeon pea; eucalyptus + buffel grass + cowpea; Eucalyptus + buffel grass + pigeon pea; Eucalyptus in monoculture (with a 20 × 3 m tree arrangement and no cultivation between rows but with a history of forage and grain crop production); and a low-productivity pasture as additional treatment and reference to the soil condition previously the land-use change. In this study, TOC and TN stocks and accumulation, labile (LC) and non-labile carbon (NLC), and SOM humic fractions were evaluated at 0-10, 10-20, 20-40, and 0-40 cm depth layers. Integrated farming systems have increased TOC and TN, NLC, carbon contents and stocks in SOM chemical fractions in all depths and TOC and TN accumulation of 5.22 Mg ha-1 year-1 and 0.23 Mg ha-1 year-1, respectively, at the 0-40 cm depth layer. The integration of Eucalyptus with legumes or buffel grass increased the LC content in the surface layer of the soil. The transition from low-productivity pasture into integrated farming systems can promote the recovery of SOM and soil quality. Hence, our results suggest that agrosilvopastoral systems can be used as sustainable farming systems in the Cerrado biome.

Altitudinal Variation on Metabolites, Elements, and Antioxidant Activities of Medicinal Plant Asarum.

Asarum (Asarum sieboldii Miq. f. seoulense (Nakai) C. Y. Cheng et C. S. Yang) is a medicinal plant that contains asarinin and sesamin, which possess extensive medicinal value. The adaptation and distribution of Asarum's plant growth are significantly affected by altitude. Although most studies on Asarum have concentrated on its pharmacological activities, little is known about its growth and metabolites with respect to altitude. In this study, the physiology, ionomics, and metabolomics were investigated and conducted on the leaves and roots of Asarum along an altitude gradient, and the content of its medicinal components was determined. The results showed that soil pH and temperature both decreased along the altitude, which restricts the growth of Asarum. The accumulation of TOC, Cu, Mg, and other mineral elements enhanced the photosynthetic capacity and leaf plasticity of Asarum in high-altitude areas. A metabolomics analysis revealed that, at high altitude, nitrogen metabolism in leaves was enhanced, while carbon metabolism in roots was enhanced. Furthermore, the metabolic pathways of some phenolic substances, including syringic acid, vanillic acid, and ferulic acid, were altered to enhance the metabolism of organic acids. The study uncovered the growth and metabolic responses of Asarum to varying altitudes, providing a theoretical foundation for the utilization and cultivation of Asarum.

Succession of Microbial Communities in Waste Soils of an Iron Mine in Eastern China

The reclamation of mine dump is largely centered on the role played by microorganisms. However, the succession of microbial community structure and function in ecological restoration of the mine soils is still poorly understood. In this study, soil samples with different stacking time were collected from the dump of an iron mine in China and the physicochemical characteristics and microbial communities of these samples were comparatively investigated. The results showed that the fresh bare samples had the lowest pH, highest ion concentration, and were the most deficient in nutrients while the acidity and ion concentration of old bare samples decreased significantly, and the nutritional conditions improved remarkably. Vegetated samples had the weakest acidity, lowest ion concentration, and the highest nutrient concentration. In the fresh mine soils, the iron/sulfur-oxidizers such as Acidiferrobacter and Sulfobacillus were dominant, resulting in the strongest acidity. Bacteria from genera Acidibacter, Metallibacterium, and phyla Cyanobacteria, WPS-2 were abundant in the old bare samples, which contributed to the pH increase and TOC accumulation respectively. Acidobacteriota predominated in the vegetated samples and promoted nutrient enrichment and plant growth significantly. The microbial diversity and evenness of the three types of soils increased gradually, with more complex microbial networks, suggesting that the microbial community became more mature with time and microorganisms co-evolved with the mine soils.

Late Cretaceous astrochronology, organic carbon evolution, and paleoclimate inferences for the subtropical western South Atlantic, Espírito Santo Basin

Cyclostratigraphy has revealed the quasi-periodic nature that globally distributed sedimentary successions present through the Phanerozoic. This is mainly the case of the strong eccentricity-related greenhouse climate of the Cretaceous period, a time interval in which the long-eccentricity 405-kyr cycle has been routinely used to constrain high-resolution astronomical time scales. Despite the importance of the South Atlantic opening to the evolution of the Cretaceous climate and carbon cycle, few investigations have applied the modern cyclostratigraphic analysis to explore the eventual orbital pacing of the Cretaceous South Atlantic successions. We use geophysical and geochemical data analysis from the Petrobras well ES-1 (offshore Espírito Santo Basin to develop a floating and anchored astronomical time scale (ATS) and infer the relation between sedimentation rate and TOC accumulation. Additionally, we estimate the net primary productivity (NPP) during intervals of high TOC accumulation. Our results show a pervasive orbitally-driven forcing imprint according to the Milankovitch spectral peak ratio as predicted to Cretaceous times, with a prominent occurrence of a 405-kyr long-eccentricity cycle, being used to constrain the elapsed time. An abrupt shift in the GR data likely associated with the Cretaceous – Paleogene boundary was used to anchor our floating ATS. The evolutionary Average Spectral Misfit (eASM) and Correlation Coefficient (COCO/eCOCO) tests demonstrate that the sedimentation rate can have contrasting effects over the organic matter burial, which is likely related to the large-scale paleogeographic configuration. Our study exemplifies that orbitally-driven sedimentation can be used to build high-resolution chronology for Brazilian marginal basins.

Chemical composition of cover crops and soil organic matter pools in no‐tillage systems in the Cerrado

AbstractIn no‐tillage systems (NTS), cover crops are recommended to increase the productivity of agricultural systems. Furthermore, a greater diversity of cover crops in NTS favours an increase in soil carbon (C) stocks. However, there are scarce published data on the relationship between the chemical composition of cover crops and the accumulation of labile and stable fractions of SOM. We evaluated the relationship between the chemical composition of cover crops and SOM fractions, C stocks and maize yield. Hemicellulose, cellulose and lignin contents were determined for Urochloa ruziziensis, Canavalia brasiliensis, Cajanus cajan and Sorghum bicolor, cultivated in the off‐season of maize. Canavalia brasiliensis had high N (20.96 g kg−1) and hemicellulose (185.67 g kg−1) contents, lower lignin content (39.50 g kg−1) and high dry matter yield (3,251 kg ha−1). All these characteristics resulted in a better SOM quality. Urochloa ruziziensis, with higher hemicellulose and lower lignin contents, and low lignin/N ratio, was associated with accumulation of TOC (19.95 and 18.33 g kg−1 in 0‐ to 10‐cm and 10‐ to 20‐cm layers, respectively) and mineral‐associated organic C (on average, 16.68 g kg−1) in the soil. Cover plants with N:lignin ratio lower than 2.0 are fundamental for soil C sequestration. In conclusion, it is recommended the adoption of Urochloa ruziziensis and Canavalia brasiliensis as cover plants improve maize production, soil organic matter quality and C sequestration in the Cerrado region.

The excursion of Nitrogen and Carbon isotope in the Lower Cambrian of Tarim Basin: Implication for the transformation of anaerobic and euxinic settling

The Nitrogen (N) along with Carbon (C) isotopes, Rear earth elements (REEs) and trace elements (TEs) were detected in the lower Cambrian Yuertusi formation, Northwest Tarim Basin. Two sections of obvious isotopic and elemental cycles have been investigated, which reflects the sedimentary transformation from lower euxinic to upper anaerobic setting. The extreme negative excursion of kerogen δ13C emerged in the bottom layer silica shales. The lowest value of kerogen δ13C is up to -37‰, which is similar with the global “Base” excursion in the bottom of lower Cambrian. It could be inferred the deposition of Yuertusi formation might be occurred after the Neoproterozoic glacial. Consequently, the kerogen δ13C of upper Yuertusi formation mostly exceeded -32‰, which could inferred the rapid rise of atmosphere and oceanic temperature. Based on the typical theory of isotope fraction, the δ13C of bitumen should be lower than that of kerogen. The bitumen δ13C in the upper Yuertusi formation varies from -34‰ ∼ 31.5‰, which is lighter than the δ13C of kerogen. Nevertheless, the δ13C of bitumen in the bottom layer silica shales is heavier than the δ13C of kerogen. This phenomenon has been noticed by previous researchers. The nadir negative excursion of bulk δ15N occurred in the bottom of Yuertusi formation, which has been indicated the sedimentary environment of Euxinic photic zone. The assimilation of bioavailable nutrient N (either in form of NH4 + or NO3-) may have contributed to the persistently low δ15C values. Ammonium may have served as the dominant nutrient N source for this period. The recycled NH4+ can be used directly or was sometimes oxidized to nitrate and then quantitatively used by phytoplankton to fuel primary productivity, which finally resulted into accumulation of high TOC and negative excursion of carbon isotope in the bottom of Yuertusi formation. It could be alternative interpretation for the depositional conditions of TOC-rich shales around Ediacaran-Cambrian boundary.

Accumulation of organic matter in a mesotidal Mediterranean lagoon (Boughrara, Tunisia)

In the frame of the COZOMED project, concentrations of organic matter (TOC, DOC, POC) were monitored during two seasonal field campaigns (autumn, October 2016 and spring, April 2017) in the Boughrara Lagon, Tunisia. Results indicate strong influence of the seawater exchange and circulation, on the organic matter accumulation inside the lagoon, visible through a significant correlation between TOC and salinity in both seasons. Two times higher concentration of TOC (up to 5.5 mg/l) was recorded in autumn, when high salinity water (46 psμ) was present in the lagoon. POC made a relatively small percentage of TOC in autumn samples when high accumulation of TOC, especially its DOC fraction can be related to remineralization processes and zooplankton-mediated release of DOC. Indeed, PCA analysis identified DOC as the most significant factor influencing the observed variability in autumn samples, and correlated to NH4+ (p < 0.05) in surface waters, while POC was significantly (p < 0.05) correlated to chlorophyll a. During spring, organic matter in the lagoon was depth-dependent and under the high influence of salinity and temperature, and in the surface correlated to NO3-. Satellite data on lagoon water optical properties appear to support changes in measured organic matter concentrations indicating different optical properties of the water inside the lagoon during spring and autumn seasons. The ocean color remote sensing, with properly validated and tested robust algorithms, accommodating optically shallow waters, can provide valuable tools for monitoring and timely detection of possibly detrimental changes inside the lagoon.

Effect of temperature on tertiary nitrogen removal from municipal wastewater in a PHBV/PLA-supported denitrification system.

In this study, a poly(3-hydroxybutyrate-co-3-hydroxyvalerate)/poly(lactic acid) (PHBV/PLA)-supported denitrification system was built to remove nitrogen from municipal wastewater treatment plant secondary effluent, and the influence of operating temperature on nitrogen removal was further investigated. Results indicated that a PHBV/PLA-supported denitrification system could effectively fulfill the tertiary nitrogen removal. The nitrogen removal efficiency gradually declined with the operating temperature decreasing, and the denitrification rate at 30°C was 5 times higher than that at 10°C. Meanwhile, it was found that a slight TOC accumulation only occurred at 30°C (with an average of 2.03mg/L) and was avoided at 10~20°C. The reason for effluent TOC variation was further explained through the consumption and generation pathways of TOC in this system. Furthermore, the temperature coefficient was about 0.02919, indicating that the PHBV/PLA-supported denitrification system was a little sensitive to temperature. A better knowledge of the effect of operating temperature will be significant for the practical application of the solid-phase denitrification system.

Effects of nitrogen fertilization rate on tocopherols, tocotrienols and γ-oryzanol contents and enzymatic antioxidant activities in rice grains.

Tocopherols (Toc), tocotrienols (T3) and γ-oryzanol (GO), major bioactive compounds of rice, are known to possess potent antioxidant activity. In this study, the objective was to determine the effects of nitrogen fertilization rate on contents of Toc, T3 and GO, and activities of enzymatic antioxidants in rice grains. Experiments were conducted on five different levels of nitrogen fertilization. Among the different treatments, grains of 2N (two-fold of the recommended amount of nitrogen fertilizer) treatment showed the highest total Toc, total T3, α-T3, β-Toc, γ-Toc and γ-T3 levels, whereas 0N (no treatment) group had the highest GO content. Increasing nitrogen fertilization significantly reduced the rice grain catalase and ascorbate peroxidase, but not the superoxide dismutase activities. Under 0N and 0.5N (low N fertilization) treatments, malondialdehyde and H2O2 contents in rice grains were significantly higher than that of other treatments. These results suggest that a two-fold increase in nitrogen fertilization favor the accumulation of Toc and T3 but not GO in rice grains.

Predominance of phytoplankton-derived dissolved and particulate organic carbon in a highly eutrophic tropical coastal embayment (Guanabara Bay, Rio de Janeiro, Brazil)

We investigate the carbon dynamics in Guanabara Bay, an eutrophic tropical coastal embayment surrounded by the megacity of Rio de Janeiro (southeast coast of Brazil). Nine sampling campaigns were conducted for dissolved, particulate and total organic carbon (DOC, POC and TOC), dissolved inorganic carbon (DIC), partial pressure of CO2 (pCO2), chlorophyll a (Chl a), pheo-pigments and ancillary parameters. Highest DOC, POC and Chl a concentrations were found in confined-shallow regions of the bay during the summer period with strong pCO2 undersaturation, and DOC reached 82 mg L−1, POC 152 mg L−1, and Chl a 800 μg L−1. Spatially and temporally, POC and DOC concentrations varied positively with total pigments, and negatively with DIC. Strong linear correlations between these parameters indicate that the production of TOC translates to an equivalent uptake in DIC, with 85% of the POC and about 50% of the DOC being of phytoplanktonic origin. Despite the shallow depths of the bay, surface waters were enriched in POC and DOC relative to bottom waters in periods of high thermohaline stratification. The seasonal accumulation of phytoplankton-derived TOC in the surface waters reached about 105 g C m−2 year−1, representing between 8 and 40% of the net primary production. The calculated turnover time of organic carbon was 117 and 34 days during winter and summer, respectively. Our results indicate that eutrophication of coastal bays in the tropics can generate large stocks of planktonic biomass and detrital organic carbon which are permanently being produced and partially degraded and buried in sediments.

Strengthen effects of dominant strains on aerobic digestion and stabilization of the residual sludge

In order to strengthen the aerobic digestion of residual sludge, shorten the time of sludge stabilization and further reduce operating costs, 3 dominant strains identified as Pseudomonas sp. L3, Acinetobacter sp. L16 and Bacillus sp. L19 were isolated from long-term aerobic digestion sludge. Results showed that the sludge stabilization time were reduced by 3–4days compared with the control when the dominant strains were added to the process of sludge aerobic digestion. The addition of dominant strains accelerated the accumulation of TOC, nitrate nitrogen and ammonia nitrogen in the digestive solution at different levels, and it was beneficial to the dissolution of phosphorus. Controlling DO 3–5mg/L, pH 6.5, the strains of Pseudomonas sp. L3 and Bacillus sp. L19 were combined dosing with the dosage of 2% in the process of sludge aerobic digestion, compared with the control, digestion rates of TOC and MLSS were increased about 19% and 16%, respectively.

Land‐use related changes to sedimentary organic matter in tidal creeks of the northern Gulf of Mexico

AbstractEffects of land use on hydrology, organic matter sources, and processing may be proportionately greater in tidal creeks than large estuaries, yet tidal creek systems have been undervalued in assessments of emerging effects of anthropogenic land use. Through sampling of dated sediment cores, we identified indicators of historical land use change (past 150 yr) in a microtidal northern Gulf of Mexico tidal creek system in the early stages of urbanization. We found that tidal creeks differed from open water sites, and urbanized sites differed from less altered sites, primarily due to changes in carbon sources indicated by differences in sediment stable carbon isotope (δ13C) values, and concentrations of fecal indicator bacterium Clostridium perfringens. Total organic carbon (%TOC) and carbon : nitrogen (C : N) increased twofold in tidal creeks during upstream urbanization in the early 20th century, which led to elevated mid‐century sediment TOC accumulation rates (5–10 mg C cm−2 yr−1), followed by decreases in TOC accumulation in tidal creeks and open waters since the 1960s (0.4–1.8 mg C cm−2 yr−1). C. perfringens and nitrogen stable isotope values (δ15N) were, respectively, 1.8 and 1.5 times higher at wastewater‐influenced sites than at other sites, increasing through time or remaining high at wastewater‐influenced sites from approximately the 1950s‐present, when human populations quadrupled. Hence, urbanization altered estuarine inputs from upland C sources and increased inputs from human‐derived N and microbes. These findings suggest that tidal creeks are more sensitive archives of land‐use change than open water systems due to their proximity and greater connectivity to the watershed.

Soil physical properties of agriculturally reclaimed area after lignite mine: A case study from central Poland

For the assessment of the extent of post-mine land degradation, arranging management practices for sustainable land use, and evaluation of reclamation success research on soil physical properties plays a significant role. The aim of this study was to quantify and interpret the effects of varied agricultural reclamation methods in order to assess which of the treatments yielded higher soil quality with respect to its physical state. Basic physical and chemical parameters (texture, particle and bulk density, total porosity, total organic carbon and pH), soil water characteristic curves, water and air permeability, structure of the soil damaged by mining in the area of internal dumping ground PĿtnów (Central Poland) were therefore measured. The soil samples were taken from the following 5 different variants of over 30-year-long reclamation: black fallow (BF), monoculture of winter wheat (WW), monoculture of winter wheat with a single application in 1992 of lignite dust (WW+L), monoculture of alfalfa with orchard grass in the proportion of 90/10% (A+G), and spontaneous succession (SS). We collected from each treatment: 12 soil cores for soil water and air properties; 6-kg composite bulk samples for basic physical and chemical properties of soil; 1 undisturbed soil block for structure analysis. The reclamation methods applied on the post-mining grounds influenced in a diverse manner the physical state of the 0⿿10cm layer of the developed technogenic soil. Bulk density values generally decreased with the increase of number of factors potentially loosening the soil structure. The studied plots had sandy loam or loamy sand texture which determined their overall air and water properties. The soils were characterized by high macroporosity and favourable content of water available for plants. Less beneficial conditions of the soil were associated with air and water permeability. The present studies indicated that spontaneous succession, with the highest typological diversity of vegetation, contributed to the most preferred soil physical state. Remaining variants of reclamation (including black fallow without vegetation) also provided sufficient air and water relations in the soils. However, it should be emphasised that plants play an important role in TOC accumulation and ensuring relative stability of soil structure. Therefore rehabilitation of post-mining grounds involving vegetation is recommended.

A novel eye drop of alpha tocopherol to prevent ocular oxidant damage: improve the stability and ocular efficacy

The aim of this study was to design novel mixed micelles as an ophthalmic delivery system for alpha-tocopherol (TOC) to prevent its degradation and improve ocular efficacy. The nonionic polymers, Polyoxyl 15 Hydroxystearate (Solutol® HS15) and Pluronic® F127, were discovered to be the most effective agents for retaining the activity and solubilization of TOC, respectively. Prepared by a thin-film hydration method, HS15/Pluronic® F127 yielded good encapsulation percentages of TOC, with a 27.7% drug loading efficiency. Incorporation of cetalkonium chloride (CKC) into HS15/Pluronic® F127 mixed micelles made the zeta potential of the micelles +17 mV, potentially prolonging the residence time of formulations on ocular surfaces. The optimized micelle preparation remained stable when diluted in a synthetic tear solution. It is known that the antioxidant ability of TOC in typical formulations reduces to around 85% of its initial value after 1 month when stored at 4 or 25 °C under an air atmosphere, which limits ophthalmic applications to less than 1 month. However, encapsulated TOC in investigated micelles remained stable for at least 6 months when sealed with N2. Finally, the cationic micelles were well tolerated after multiple administrations in rabbits, and they improved ocular accumulation of TOC. Taken together, these data suggest that the optimized micelle preparations described in this study may be suitable drug carriers for the treatment of ocular oxidant damage.

Soil and vegetation transformation in abandoned vineyards of the Tokaj Nagy-Hill, Hungary

Two chronosequences, one south (S-sequence) and one southwest (SW-sequence) with differing times since their abandonment (193, 142, 101, 63, 39 and 14years), were studied on Tokaj Nagy-Hill. The sites were investigated in respect of vegetation characteristics, soil physico-chemical characteristics, total organic carbon stocks (TOC stocks), accumulation rates of total organic carbon (TOC accumulation rates), and soil profiles, which were classified according to the World Reference Base (WRB) 2007. The S-sequence was 25–35% sloped and strongly eroded, and the SW-sequence was 17–25% sloped and moderately eroded.Vegetation development at the S-sequence resulted in shrub-grassland mosaics, supplemented by protected herb species and forest development at the earliest abandonment. The SW-sequence was predominantly covered by forest vegetation, and trees were absent at the 63 and 14year old abandonment sites.Soils of the S-sequence show shallow remnants of loess cover with redeposited soil materials containing 15–65% skeletal volcanic rock of weathering products coated by secondary calcium carbonates. The SW-sequence profiles are developed on deep loess or loess derivatives. The calcium-carbonate content was higher in profiles of the S-sequence (18.1±10.4%) than in the SW-sequence (6.7±2.7%); consequently, the pH of the topsoil was higher in the S-sequence, and correlated significantly negatively with the age of abandonment in both sequences (r=−0.893; p=0.01 in S, and r=−0.739; p=0.05 in SW). TOC stocks of the top 6cm soil layers were higher in the S slope (1.82±0.71kgm−2) than in the SW-sequence (0.95±0.49kgm−2), and correlated significantly positively with the duration of abandonment. When calculated for the whole profile, TOC stocks were similar in both S- and SW-sequences (S: 8.21±3.31kgm−2; SW: 8.24±6.01kgm−2). The TOC accumulation rates of the top 6cm soil layers exhibited 18.9±10.0g C m−2y−1 in the S and 7.0±4.2g C m−2y−1 in the SW-sequence.Sites with the same age of abandonment showed different vegetation and soil features in both chronosequences, indicating that time is not the most decisive factor in soil transformation processes after abandonment of viticulture on Tokaj Nagy-Hill. Additional directing factors were slope steepness and exposition.

Productivity patterns and N-fixation associated with Pliocene-Holocene sapropels: paleoceanographic and paleoecological significance

Abstract. We have studied a suite of 35 sapropel sequences from a transect of four ODP sites across the Eastern Mediterranean to explore for paleoproductivity patterns and provide new insights on ecological changes during their deposition. Paleoproductivity variations were identified using TOC and Babio mass accumulation rates and δ15Ntotal and δ13Corg values. Elevated Ba/Al and TOC mass accumulation rates record periods of basin-wide amplified productivity. Our data further support that sapropels were formed by cyclic increases in primary production of marine organic matter largely sustained by N-fixing bacteria. This productivity increase was triggered by climate factors leading to increased fluvial discharge and amplified nutrient input that also favored the establishment of N-fixing bacteria. Enhanced productivity led to depletion of deepwater dissolved oxygen and consequently improved organic matter preservation. Primary production was more intense during the middle to Late Pleistocene compared to Pliocene equivalents, coinciding with increasing total sedimentation rates. δ15N values are dramatically lower in the sapropels than in TOC-poor background sediments, indicating a major contribution from nitrogen-fixing bacteria to the higher productivity during sapropel deposition. Additionally, different degrees of denitrification occurred as a consequence of water column oxygenation which in turns evolved from stagnant anoxic bottom waters during Pliocene sapropels to oxygen depleted and sluggish circulation in late Quaternary layers. These differences between sapropel layers provide new evidences for the general evolution of the Eastern Mediterranean basin during the last 3 Mys in terms of paleoceanographic conditions and the intensity of climate variability leading to sapropel deposition.

Diagenetic control of nitrogen isotope ratios in Holocene sapropels and recent sediments from the Eastern Mediterranean Sea

Abstract. The enhanced accumulation of organic matter in Eastern Mediterranean sapropels and their unusually low δ15N values have been attributed to either enhanced nutrient availability which led to elevated primary production and carbon sequestration or to enhanced organic matter preservation under anoxic conditions. In order to evaluate these two hypothesis we have determined Ba/Al ratios, amino acid composition, N and organic C concentrations and δ15N in sinking particles, surface sediments, eight spatially distributed core records of the youngest sapropel S1 (10–6 ka) and older sapropels (S5, S6) from two locations. These data suggest that (i) temporal and spatial variations in δ15N of sedimentary N are driven by different degrees of diagenesis at different sites rather than by changes in N-sources or primary productivity and (ii) present day TOC export production would suffice to create a sapropel like S1 under conditions of deep-water anoxia. This implies that both enhanced TOC accumulation and δ15N depletion in sapropels were due to the absence of oxygen in deep waters. Thus preservation plays a major role for the accumulation of organic-rich sediments casting doubt on the need of enhanced primary production for sapropel formation.

The sources and accumulation rate of sedimentary organic matter in the Pearl River Estuary and adjacent coastal area, Southern China

In this study, the contents, sources and accumulation rate of sedimentary organic matter (OM) in the Pearl River Estuary (PRE) and adjacent coastal area were investigated. The stable carbon isotopic composition (δ 13C) is a reliable geochemical proxy and was used to indicate the OM origin here. Nevertheless, the organic carbon and nitrogen molar ratios (TOC/TN) and the stable nitrogen isotopic composition (δ 15N) were affected by diagenesis and could be the supplementary indicators. The sources of OM were estimated based on the two end-member model. The results showed that in the estuary, sedimentary OM originated from terrestrial and aquatic mixing origins, whereas, OM in coastal sediments was dominantly algae-derived. The accumulation rate of sedimentary OM was analyzed based on 210Pb dating. Due to the sampling sites and the distinct hydraulic environments, the accumulation rates of TOC, aquatic and terrestrial OC were obviously higher in the estuary than in coastal area. TOC accumulation rates were 18–27 mg cm −2 y −1 in the estuary, and 0.84–3.6 mg cm −2 y −1 in coastal area. Aquatic OC accumulation rates were 7.9–11.3, 0.8–1.3, and 2.6–3.1 mg cm −2 y −1, and terrestrial OC accumulation rates were 9.7–16.3, 0.02–0.14, 0.16–0.42 mg cm −2 y −1 in cores 2, 5, 6, respectively. It could be seen from the high accumulation rate of organic matter in the estuary that, when nutrients increased in the river, phytoplankton biomass and productivity would also have increased. As a result, phytoplankton sinking and organic matter sedimentation usually increased with primary productivity, resulting in the observed accumulation rate of aquatic OC in the estuary. Furthermore, terrestrial OC accumulation rates in the estuary and coastal area showed an increasing trend with the age.

Organic geochemical changes in Pliocene sediments of ODP Site 1083 (Benguela Upwelling System)

The intensification of the Northern Hemisphere Glaciation (INHG) was a major event in the development of the current climate state, and as one of the most productive regions in the world's oceans, the behaviour of the Benguela Upwelling System (BUS) following the INHG is of wide interest. To investigate post-INHG changes in productivity and organic matter accumulation, total organic carbon and biomarker accumulation rates were determined for sediments from ODP Site 1083 and compared to alkenone-derived sea surface temperatures and nitrogen isotopic compositions. These data indicate that the interval between 2.6 and 2.4 Ma was characterized by dramatic changes in upwelling intensity and organic carbon export on the northern edge of the modern BUS. The upwelling is reflected by significant changes in alkenone-derived SST estimates between glacial and interglacial intervals, with a total variability of 16 °C. The studied interval is also characterized by large changes in organic matter export as reflected by changes in TOC and biomarker accumulation rates, which show maxima during OIS 98 and during the transition from OIS 97 to 96. Intervals of elevated TOC are also characterized by elevated concentrations of sedimentary microbial biomarkers and lower %CaCO 3, suggesting that enhanced delivery of labile organic matter to the seafloor resulted in enhanced remineralisation with released CO 2 being consumed by CaCO 3 dissolution. However, in apparent contrast to recent Pleistocene sediments at the same site, organic matter export after the INHG was not solely driven by upwelling intensity. Of the three Pliocene glacial–interglacial cycles examined (OIS 101 to 96), each is unique with respect to the timing and magnitude of changes in organic matter accumulation. Each is also characterized by different algal assemblages as inferred from biomarker distributions, with OIS 97 and 96 particularly dominated by diatoms. We suggest that these differences reflect the important but evolving role of Southern Ocean waters in the Pliocene BUS: nutrient depletion of SO waters occurred during parts of Pliocene glacial intervals such that even intense upwelling did not persistently result in enhanced organic matter accumulation rates.