Land-derived Organic Matter Research Articles

Ostracod Assemblages in the East Siberian Sea: A Comparative Study of River-Influenced and River-Isolated Shelf Ecosystems

The East Siberian Sea (ESS) is one of the least studied seas in terms of ostracod fauna. Ostracods are sensitive organisms to environmental changes, and detailed information on their ecology is still required. To fill this knowledge gap, we studied 33 meiobenthic dredge samples collected from the western part of the ESS and the Chaun Bay together with 17 grab samples taken from the eastern part of the sea. Quantitative analyses of the ostracod assemblages demonstrate that the river-influenced western part of the ESS is inhabited by low diverse and impoverished fauna consisting of the taxa which are able to adapt to different environmental conditions. In the isolated Chaun Bay sheltered from significant riverine influence, the ostracod assemblages contain species that prefer more stable conditions. The predominance of living specimens over dead ones and individual valves points to strong carbonate dissolution that is more pronounced in the western ESS than in the Chaun Bay. The formation of such conditions might be related to the high content of dissolved carbon dioxide resulting from bacterial remineralization of in situ produced and land-derived organic matter in the bottom sediments and low pH near the seabed. Numerous ferromanganese crusts were found on the ostracod valve surfaces and inside the shells from the Chaun Bay.

Organic Geochemical Evaluation of the Black Shale interbeds Within the Lithological Succession of the Al Aziziyah Formation, NW Libya

The samples under investigation represent the black shale in interbeds within the Al Aziziyah Formation, located in the NW part of Libya and were analysed using geochemical techniques method and a variety of organic geochemical parameters. The aim of this study is to assess the type of organic matter, thermal maturity, and environment of deposition, based on biomarker distributions and Rock-Eval pyrolysis. The Gas chromatograms of the saturated hydrocarbon fractions of the study samples display a smooth high-end member distribution of the n- n-alkanes extending beyond nC34. The sample displayed evidence of biodegradation as suggested by the presence of the loss of some of the lower molecular weight n-alkanes. The predominance of high molecular weight n-alkane in the study sample suggests a significant input of higher land plant organic matter into these sediments. Geochemical (Rock-Eval, Tmax. values ranging from 416-4390C typical of immature range). Another related feature of these rocks extracted is the presence of a high relative abundance of gammacerane, indicating an anoxic marine hypersaline source depositional environment. The relatively high abundance of common land-plant-derived biomarkers, such as oleananes, is a clear indication of major terrigenous input to the source of these extractable organic matters. The high abundance of C24 tetracyclic terpanes could be associated with higher land-plant, algae, or microbial sources, thereby suggesting a mixed source input. TOC valued < 0.5 wt.%, in the analyzed samples can be considered as a poor source rock generative potential. Based on this study, it can be said that the interbedded shales of the Al Aziziyah Formation seem to have received substantial amounts of land-derived organic matter that has been transported into an open marine subtidal depositional setting had prevailed and was deposited in a photosynthetic-organisms dominated environment (thereby suggesting a mixed source input).

Implications of Organic Matter Input, Sedimentary Environmental Conditions, and Gas Generation Potential of the Organic-Rich Shale in the Onshore Jiza-Qamar Basin, Yemen.

The Jiza-Qamar Basin is one of the most important exploration sedimentary basins in Yemen. For over a decade, the exploration of hydrocarbons has been occurring in this basin. Late Cretaceous age rocks are the most occurring organic-rich sediments in this basin, including coals, coaly shales, and shales. The studied organic-rich shale beds are from the Late Cretaceous Mukalla Formation and associated with coal seams. These organic-rich shales can serve as source rocks for hydrocarbon generation potential. The current study investigates the geochemical characteristics, including assessing the organic matter (OM) input, sedimentary environmental conditions, and hydrocarbon generation potential of the organic-rich shale within the Mukalla Formation from three well locations in the onshore Jiza-Qamar Basin using organic geochemistry, biomarker, and carbon isotope measurements. The studied shale samples have high OM content with total organic carbon values between 0.74 and 19.48 wt %. Furthermore, they contain mainly hydrogen-poor Types III and IV kerogen, indicating the presence of the gas-prone source rock. The presence of these types of kerogen indicates the abundance of vitrinite and inertinite macerals, as established by microscopic investigation. However, the studied organic-rich shales had biomarker features, including high Ph/Ph ratio between 3.82 and 7.46, high Tm/Ts ratio of more than 7, and high C29 regular steranes compared to C27 and C28 regular steranes. Apart from the biomarker results, the studied Mukalla shales are characterized by the abundance of land-derived OM that deposited in fluvial to fluvial deltaic environments under highly oxic conditions. The finding of the considerable concentration of terrigenous OM is probably confirmed by the bulk carbon isotope and maceral composition data. The maturity indicators show that the examined organic-rich shale samples in the studied wells exhibit low VR values of up to 0.71%, and thereby, they have not been yet reached the high maturity for gas generation. This low maturity level in the studied wells is probably attributed to shallow burial depth, exhibiting depth of up to 2835 m. Therefore, the substantial gas exploration operations from the organic-rich shale source rock system of the Late Cretaceous Mukalla Formation can be recommended in the deeper stratigraphic succession in the offshore Jiza-Qamar Basin.

Dominance of land-derived organic matter in highly productive Bandon Bay, Thailand

Bandon Bay is Thailand's productive area for mariculture of many economically important species including oysters and clams. High primary productivity in this shallow bay leads to organic matter (OM) production in the water column and its export to underlying sediments and adjacent areas. However, the understanding of the source and fate of OM in Bandon Bay is still scarce. To address this knowledge gap, we investigated organic carbon (OC) and total nitrogen (TN) elemental contents, C/N elemental ratios, and stable carbon (δ13C) and nitrogen isotopic (δ15N) compositions in surface sediments, sediment cores, and suspended particulate matter (SPM) collected from Bandon Bay and surrounding river systems during the wet season in 2019. δ13C values in bay sediments indicate a major contribution of from terrigenous sources. During low tide, river-associated high-δ15N input of SPM from freshwater phytoplankton input to the bay was evident. The OM source apportionment was further made using a four-end-member mixing model showing more than 70% of sediment organic matter to be of terrestrial origin (freshwater phytoplankton and land soils) most likely brought to the bay via Tapi-Phumduang River. In addition, tidal cycles, and prevailing circulation in the bay cause mixing of OM in the bay with marine OM from the Gulf of Thailand. All these processes work together to bring about dispersal, dilution, and transformation of OM in Bandon Bay, which maintain high organic content in the sediment and supply nutrients essential for high shellfish production in Bandon Bay.

Benthic Foraminifera and Productivity Regimes in the Kveithola Trough (Barents Sea)—Ecological Implications in a Changing Arctic and Actuopaleontological Meaning

The rapid response of benthic foraminifera to organic carbon flux to the seafloor makes them promising bioindicators for evaluating the organic carbon stored in marine sediments. Fjords have been described as hotspots for carbon burial, potentially playing a key role within the carbon cycle as climate regulators over multiple timescales. Nevertheless, little is known about organic carbon-rich sediments in Arctic open shelves and their role in global carbon sequestration. To this aim, four sites have been sampled along a W-E transect across the Kveithola Trough located in the NW Barents Sea. Living (stained) benthic foraminiferal density, biodiversity and vertical distribution in the sediment were analysed together with the biogeochemical and sedimentological data. We identified two main depositional environments based on the relationship between benthic foraminiferal assemblages and carbon content in the sediments: (1) an oligotrophic land-derived organic matter region located in the outer part of the trough influenced by the warm and saline Atlantic Water; and (2) a stressed eutrophic environment, with high-content of metabolizable organic matter in the inner part of the trough, which comprises the main drift and the Northern flank of the trough. The freshness and good nutritional quality of the organic matter detected in the inner region could be the result of the better preservation of the organic matter itself, basically driven by the rapid burial of fine-grained organic-rich sediments enhanced by the cold and less saline Arctic Water coming from the Barents Sea. We conclude that foraminifera provide a tool to describe the Kveithola depositional environment as a carbon burial hotspot in a changing Arctic area subjected to a pulse of fresh food intended as biopolymeric carbon.

Novel Application of a Compound-Specific Stable Isotope (CSSI) Tracking Technique Demonstrates Connectivity Between Terrestrial and Deep-Sea Ecosystems via Submarine Canyons

Studies have shown the importance of submarine canyons as conduits of land-derived organic carbon beyond the coastal shelf into the deep-sea where a single obvious river source can be identified. When there is more than one river source, identifying which rivers contribute to canyon sediment organic matter is technically challenging. Here, we compare two contrasting submarine canyons: the Hokitika Canyon, a long, narrow, and gently sloping canyon on the west coast of New Zealand; and the Kaikōura Canyon, a high productivity, short, steep canyon close to shore on the east coast of New Zealand. Both canyons have multiple potential river sources, so we applied a compound specific stable isotope (CSSI) tracking technique to identify and apportion the soil contribution from each river at locations along the length of each canyon axis. We found that land-derived carbon contributed between 74 to 100 % of the total organic carbon in the sediment of the Hokitika Canyon as far as 200 km from shore and to depths of 2000 m. However, less than 50% of the land-derived organic carbon came from the largest river closest to the canyon head. We hypothesise that longshore drift transported much of the sediment from that river past the Hokitika Canyon, while river inflows farther up-current supplied the bulk of the land-derived organic carbon. In contrast, land-derived carbon contributed less than 50% of the total organic carbon in Kaikōura Canyon sediments with land-derived organic sediment contribution decreasing steeply to less than 15% at about 24 km from shore in 1500 m water depth. Most of the land-derived organic matter (ca. 80%) came from the river with the largest suspended sediment yield, despite another (smaller) river discharging closer to the canyon head. We hypothesise that this difference in carbon source is partly due to the comparatively short and steep, and therefore dynamic, nature of Kaikoura Canyon resulting in efficient sediment through-put. The efficiency with which organic matter is captured and transferred to the deep-sea by canyons demonstrates the potential for such systems to act as natural carbon sinks driven by both geologically episodic and more regular oceanographic processes.

Influences of tropical monsoon climatology on the delivery and dispersal of organic carbon over the Upper Gulf of Thailand

Organic carbon cycling in SE Asia is data-sparse and poorly studied, although high sediment yield and organic carbon intensity occur in the tropical region. In the present study, we evaluated the role of tropical monsoon pertaining to fluvial discharge, sediment load, coastal current and water stratification on seasonal organic carbon dynamics during four sampling campaigns in the Upper Gulf of Thailand (UGoT). This study demonstrates that particulate organic carbon (POC) is closely correlated with the river influx of suspended sediment, which is generally regulated by the local rainfall. Higher POC is found near the large estuarine section (Chao Phraya River, CHAO) during southwest monsoon period and the small estuarine section (Mae Klong River, MK) during November 2013 when tropical cyclones impacted. POC in the estuarine sections is more significantly influenced by the seasonal shift compared with the coastal sections. Land-derived organic matter prevails in the small estuarine and coastal sections, while marine-derived organic matter dominates in the estuarine sections impacted by CHAO and MK. Anthropogenic inputs and dam regulation also influences the river export of organic matter during the high precipitation periods. Total organic carbon (TOC) however displays less significant seasonal monsoon variations than POC. Further, TOC tends to accumulate in the sub-silt fraction of sediments, which mainly occurs in the small estuarine and eastern coastal sections and is more obviously influenced by marine-derived factors. TOC in sediment of the CHAO and MK influenced sections however displays more seasonal variations with prevailing river input evidenced by coarser sediment and higher C/N ratios. Moreover, the almost year round water stratification across the region acts as the barrier in retaining organic carbon in the estuaries and their vicinities from dispersal into the lower portion of Gulf of Thailand. High sedimentation rate (~1.1 cm·yr−1) further facilitates the organic carbon burial in the study area. The delivery, dispersal and burial of organic carbon are closely associated with the climate-controlled precipitation, and thus the tropical monsoon climatology under the global warming in particular is an important factor influencing the organic carbon in the UGoT.

Aliphatic Hydrocarbons in Recent Dated Sediment Cores of Imo River, SE Nigeria: Environmental/Historical Implications

Four recent sediment cores (0-30 cm long) from Afam (AF), Mangrove (MG), Estuary (ES) and illegal Petroleum refinery (PT) sites of the Imo River, Southeastern Nigeria were analyzed to characterize the sources and distribution of organic matter (OM), as well as examine their historical trends of deposition and assess human-induced changes in the last ca. 5 decades using biomarker approach. Radionuclides 210Pb and 137Cs were used to assign approximate dates to each section of the cores. Evaluation of proxy parameters such as carbon preference index (CPI, 2.01 - 2.19), carbon number maximum (Cmax, 29, 31) and atomic C/N (16.51-31.32) for the most recent top layers (0-5 cm) revealed greater wash-in of land-derived organic matter (OM), attributable to the recent rise in water height. The bottom layer (PT1, 25-30 cm,) of the PT core deposited ca. 1964-1972 exhibited a CPI of 0.97 and pristane/phytane (Pr/Ph, 3.75), suggesting that oil bunkering/illegal refinery activity had begun in the region ca. 8 years after the first commercial discovery of oil in Nigeria in 1956. The occurrence in high abundance of heptadecane in the middle layer (ES4, 10-15 cm) of the ES almost corresponded with the period of eutrophication that blocked the waterway in the late 1980s. Measurement of a marked unresolved complex mixture at the near-top layer (AF5, 5-10 cm) of the AF indicated that the heaviest contamination by petroleum hydrocarbons occurred at ca. 1997-2005. This time frame coincided with the period of intensive bunkering and oil pipeline vandalism by Niger Delta militant groups.

Carbon export and drivers in the southeastern Levantine Basin

In this paper, we present C export data from the southeastern Levantine Basin, 50 km west of Haifa, at water depth of 1500 m. Particulate organic carbon (POC) fluxes were measured for 18 months by automated and single bottle sediment traps at the recently-deployed DeepLev observatory and compared with water column profiles of 234Th. Calculations, based on POC/234Th ratios, result in water column-integrated export of 18 mmolC m−2 d−1 at the end of summer (Dec 2017) and remineralization during spring (e.g. 14.4 mmolC m−2 d−1, Apr, 2018). Based on the sediment traps POC export in the basin was generally low (0.05–1 mmolC m−2 d−1 at the base of the photic zone during Dec 2017–May 2018). Fluxes were quite variable, and the export pattern was mainly controlled by coastal discharge or shelf-resuspension (winter peaks) rather than by marine primary production. This was demonstrated by: i) larger POC fluxes measured by deep water (1300 m) and twilight zone (280 m) traps compared to fluxes measured at the base of euphotic zone, ii) tight correlation of POC with total mass flux, iii) decrease of the POC percentage during winter peak events and iv) imbalance (large integrated deficit or excess) of water column 234Th. Both deficit and excess are evidence of lateral flux, where the first probably results from wave-induced shelf resuspension of organic-poor material, which underwent minimal remineralization and induced scavenging, while the latter derives from the conveyance of large amount of land-derived organic matter, which undergoes remineralization, therefore input of 234Th to the water column.

Cellulase activity and stable isotope signature of benthic macroinvertebrates in estuarine habitats: potential assimilation of land-derived organic matter

Cellulase activity and stable isotope signature of benthic macroinvertebrates in estuarine habitats: potential assimilation of land-derived organic matter

Chemometric Differentiation of Oil Families and Their Potential Source Rocks in the Gulf of Suez

An oil–oil and oil–source rock correlation study was carried out using chemometric methods applied to geochemical data for 123 Upper Cretaceous—Lower Miocene putative source rock and 46 crude oil samples from the Gulf of Suez Rift basin. The Gulf of Suez has many organic-rich intervals. The pre-rift source units, such as the Brown Limestone and Thebes formations, contain very good-to-excellent organic content, whereas the Miocene rocks are rated fair to good. HI and Tmax pyrolysis data indicate variable kerogen type and maturation histories where most of the analyzed samples occur along the Type II and Type II/III kerogen pathways from immature to the main stage of oil window with %Ro < 0.9. Carbon isotope ratios’ biomarker data for the bitumen samples indicate predominantly anoxic source rock depositional conditions with substantial algal/bacterial marine and a minor terrigenous organic matter. The Gulf of Suez oils exhibit a wide range of chemical composition from heavy-to-medium gravity and moderate-to-high sulfur content. These oils originated from carbonate/marl source rocks rich in lipids from phytoplankton/benthic algae and bacteria with less contribution of terrigenous organic debris, deposited under anoxic conditions with different thermal maturity histories equivalent to at least the early oil window. Chemometrics using 16 source-related biomarker and isotope ratios identifies six genetic families in the Gulf of Suez. The oil families share common characteristics where the precursor organic matter was deposited in a restricted marine environment with limited land-derived organic matter. The major factor that greatly modifies oil composition in the Gulf of Suez is thermal maturation. However, migration history and spatial and temporal organofacies’ variations of the presumed source rocks are also important. The overall geochemical similarity of the Gulf of Suez oils confirms the mixed nature of these fluids and suggests that no single source rock horizon is likely to have sourced the oil in this promising province. Based on oil–source correlation data and a decision tree chemometric model, the Brown Limestone, Esna, Thebes, and Nukhul formations are the effective source rocks for oil families III, IV, and V, whereas none of the source rock extracts has been assigned for Family I or VI oils.

Application of stable isotopic analyses for fish host–parasite systems: an evaluation tool for parasite-mediated material flow in aquatic ecosystems

Parasites potentially have important roles in aquatic ecosystems, although relatively little is known about their contributions to the complexity of food web structure. In this study, stable carbon and nitrogen isotope analyses (δ13C and δ15N) were applied for fish host–parasite systems in a shallow swamp–lake ecosystem to assess the validity of stable isotope technics to reveal the parasite-mediated trophic linkages in the food web. Forty host–parasite pairs, including seven parasite taxa (cestodes, trematodes, crustaceans, and hirudinids), found on six host fish species (cyprinids and percids) were examined. The parasites showed unusual δ15N fractionation, with an overall average of − 1.9‰, suggesting the intake of 14N-rich ammonia for amino acid synthesis and/or selective absorption of 15N-depleted amino acids in the host fluid. The isotopic signatures of fish hosts and their parasites were positively correlated, suggesting the absorption and transfer of host-derived nutrients during infection. A δ13C-based isotope mixing model showed that each host fish species exhibited unique dependencies on POM, land-derived organic matter, and macrophytes, suggesting the host-specific trophic niche of the associated parasites in the lake–swamp food web. These emphasized that parasites are potential pathways of material and energy flows in aquatic ecosystems, contributing substantially to the food web complexity. Stable isotope analyses are the useful tools to elucidate the host–parasite trophic linkages, and case-specific isotopic fractionation factors are the mandatory information for a better understanding of the parasite-mediated material flow in ecosystems.

Material cycling in coastal waters and the role of the Kiritappu Wetland in Hamanaka, Hokkaido: An analysis using the surf clam (Pseudocardium sachalinense) as an environmental indicator

Abstract The suspension feeding benthic bivalve surf clam, Pseudocardium sachalinense , which feeds on phytoplankton , benthic microalgae, and detritus in coastal waters, is one of the most important marine resources in Hamanaka, Hokkaido Prefecture, Japan. We measured stable carbon and nitrogen isotope ratios (δ 13C and δ15 N) and carbon‑nitrogen (C/N) ratios of surf clam adductor muscle and stomach contents, oceanic particulate organic matter (POM), oceanic sediments, riverine POM, and soil, as well as physical and chemical parameters such as temperature, salinity, chlorophyll-a, and nutrients in Hamanaka from April through September 2015. We also examined the food sources that support the surf clam, the possible connection between wetlands and coastal waters, and the spatial and seasonal variation. Our results showed that the isotope and C/N values of surf clams and oceanic organic matter were significantly different from those of riverine organic matter, and that there were no significant differences among different sites of coastal areas. This means that land-derived organic matter is not a direct food source for the surf clam and does not affect the coastal environment. In addition, benthic microalgae and epiphytes are considered to be the major food sources for the surf clam in all sampling seasons, since they have isotope and C/N values similar to those of the surf clam. The overall results, also with reference to previous relevant studies, imply the importance of conservation of wetlands which buffer excessive inflow of land-derived organic matter that may harm surf clams and the coastal environment.

Distribution patterns of organic pollutants and microbial processes in marine sediments across a gradient of anthropogenic impact

Marine sediments are part of the hydrological cycle and the ultimate storage compartment of land-derived organic matter, including pollutants. Since relevant microbially-driven processes occurring at benthic level may affect the quality of the overall aquatic system, the necessity for incorporating information about microbial communities functioning for ecosystem modelling is arising. The aim of this field study was to explore the links occurring between sediment contamination patterns by three selected class of organic pollutants (Polycyclic Aromatic Hydrocarbons, PAHs, Nonylphenols, NPs, Bisphenol A, BPA) and major microbial properties (Prokaryotic Biomass, PB; total living biomass, C-ATP; Prokaryotic C Production rate, PCP; Community Respiration rate, CR) across a gradient of anthropogenic pollution. Sediments were sampled from 34 sites selected along 700 km of the western coastline of the Adriatic Sea. Organic contamination was moderate (PAHs <830 ng g−1; NPs <350 ng g−1; BPA <38 ng g−1) and decreased southward. The amount of PAHs-associated carbon (C-PAHs) increased significantly with sediment organic carbon (OC), along with microbial functional rates. The negative relation between PCP/CR ratio and OC indicated the shift toward oxidative processes in response to organic pollution and potential toxicity, estimated as Toxic Equivalents (TEQs). Our outcomes showed that sediment organic contamination and benthic microbial processes can be intimately linked, with potential repercussions on CO2 emission rates and C-cycling within the detritus-based trophic web.

Assessing sedimentation in a temperate dystrophic lake in the NE Atlantic seaboard region

Organic materials deposited in lacustrine environments can be derived from both aquatic and terrestrial ecosystems, and can serve as valuable indicators of catchment and in-lake ecological changes over time. However, spatial and temporal variation in the deposition of these materials within a lake basin will influence the interpretation of these sediment deposits. In this study, materials deposited in suspended sediment traps and basin sediments in Lough Feeagh, a temperate coastal humic lake, show variations in organic matter, total organic carbon and nitrogen loads, algal pigment concentrations and diatom assemblages. Sediment trap samples from three locations along with adjacent surface sediment cores show a clear north–south (inlet to outlet) gradient. C/N ratios reflected a mixture of algal and land-derived organic matter with a major peat influence, and comparisons between sediment trap and surface sediment assemblages revealed pigment and diatom assemblages influenced by lake-basin position and water depth. While some coherency between trap and sediment samples was apparent a more complicated biological response is demonstrated along with reduced water clarity in recent years thus highlighting the implications of increased allochthonous imputs for biological and biogeochemical processes in oligo-humic aquatic systems.

Benthic foraminiferal response to environmental changes across Cenomanian/Turonian boundary (OAE2) in the northeastern Tethys, Kopet-Dagh basin

In order to evaluate Oceanic Anoxic Event 2 (OAE2) at the Cenomanian-Turonian boundary and its effects on benthic foraminifera, the Taherabad stratigraphic section in the east of Kopet-Dagh basin was studied for pattern of changes in benthic foraminiferal communities. Total Organic Carbon (TOC) concentration at the Taherabad section shows that black shale was not deposited in this succession but TOC increases up to 0.68 wt% in the three intervals of Rotalipora cushmani, Whiteinella archaeocretacea and Helvetoglobotruncana helvetica Zones. Also, Total Nitrogen (TN) values were measured in our study succession. High TOC/TN ratios (up to 18) occur in the intervals of TOC enrichment. Foraminiferal assemblages, TOC, TOC/TN and Detrital Index (DI, an index for detrital input) changes in the study section allowed us to divided study section into 4 intervals. Interval A and C are associated with low abundance and diversity of benthic assemblages coeval with lack of planktic foraminifera. Benthic assemblages are strongly dominated by shallow and deep infaunal agglutinated foraminifera including Lagenammina, Saccammina, Reophax and Tritaxia. The foraminiferal composition associated with higher TOC, TOC/TN and DI suggest an influx of fresh water to the basin in the warm-wet periods, which diminished hospitable conditions for planktic foraminifera and probably enhanced land-derived organic matter and/or primary productivity. The hyposaline cap led to development of salinity-stratified water and induce bottom water oxygen depletion. By contrast, the assemblages found in the interval B and D are more diverse and contain high abundance of planktic and calcareous benthic foraminifera. Common benthic taxa in these parts are praebuliminids, lenticulinids, gavelinellids and Valvulineria. These assemblages associated with lower TOC, TOC/TN and DI indicate decreased detrital input and more normal marine condition resulted in improved ventilation of sea-floor, which is favorable for planktic and benthic taxa.

Carbon isotope biogeochemistry of acetate in sub-seafloor sediments in the Sea of Okhotsk near Sakhalin Island, Russia

Biogeochemical processes involving acetate in sub-seafl oor sediments were investigated by examining the stable carbon isotopic relationships of acetate and other relevant carbon-bearing materials (i.e., total organic carbon (TOC) and ΣCO2) in fi ve piston cores retrieved from the Sea of Okhotsk off Sakhalin Island, Russia. The cores were classifi ed into two types on the basis of SO42– content: (I) those with sulfate-reducing sediments in which the depletion of pore-water SO42– with increasing depth was slight, and (II) those with methanogenic sediments in which SO42– concentrations were less than 2 mM more than 3 m below the seafl oor. Acetate was detected in all cores. The acetate content in methanogenic sediments (2.6–23.0 μM) was relatively higher than in the sulfate-reducing sediment (2.8–8.8 μM). In the sulfate-reducing sediments, the depth profi les of δ13Cacetate approximately parallel those of δ13CTOC, with the δ13Cacetate values (–39‰ to –33‰) depleted by about 12‰ relative to δ13CTOC (–24.5‰ to –22.3‰). These approximately parallel depth profi les suggest that the principal acetate production process in the sulfate-reducing sediments is fermentation of dissolved organic compounds. The fermentation products, however, tend to be similar or slightly enriched in 13C compared to their substrates. Therefore, the 13C depletion of acetate relative to TOC in the sulfate reduction zone suggests that some portion of the acetate was synthesized by acetogenesis in which the synthesized acetate is depleted in 13C compared with its precursor. Given the large contribution of land-derived organic matter in the studied sediments, organoautotrophic acetogenesis using the lignin-derived syringate monomer, which originates from land plants, is likely. In the methanogenic sediments, the δ13Cacetate values in sediments throughout the cores (–39‰ to –25‰) were depleted compared to δ13CTOC (–25.5‰ to –21.4‰). This suggests some acetogenic contribution to the total acetate production. The depth profi les of δ13Cacetate in methanogenic sediments did not parallel those of either δ13CTOC or δ13CΣCO2, probably because of the mixed isotopic effect from some production and consumption processes; namely fermentation, acetogenesis, and acetoclastic methanogenesis. * Institute of Biogeosciences, Japan Agency for Marine-Earth Science and Technology, 2-15 Natsushima-cho, Yokosuka 237-0061, Japan ** Research Institute for Global Change, Japan Agency for Marine-Earth Science and Technology, 2-15 Natsushima-cho, Yokosuka 237-0061, Japan *** Institute of Low Temperature Science, Hokkaido University, N19W8 Kita-ku, Sapporo, Hokkaido 060-0819, Japan **** Present address: Graduate School of Environmental Studies, Nagoya University, Furo-cho, Chikusa-ku, Nagoya 4648601, Japan a Corresponding author. Tel: +81358414250. Fax: +81358418791. e-mail: ijiri@eps.s.u-tokyo.ac.jp Present address: Department of Earth and Planetary Science, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033, Japan

Elemental and organic carbon proxies for redox conditions of the Oligocene formations in the Ropa Tectonic Window (Outer Carpathians, Poland): palaeoenvironmental implications

The Oligocene Grybow Succession is recognized as a counterpart of the anoxic Menilite Formation. Its comprehensive geochemical investigations are made in the key sections of the Ropa Tectonic Window (the Grybow Unit, Polish Outer Carpathians). The maceral assemblages, dominated by land-plant liptinite, vitrinite and intertinite, correspond to kerogen types II and III. A Tmax vs. HI diagram shows terrestrial kerogen type II with various additions of type III and algal kerogen type I. A variation in δ 13 C org. (from –25.21 to –27.38‰) may have resulted from variations in the composition of organic matter (the content of terrestrial vs. marine organic matter), controlled by depositional setting (turbidite vs. hemipelagic). The highest TOC contents are associated with an enhanced influx of land-derived organic matter. The redox-sensitive trace elements positively correlate with TOC and TS contents. Redox conditions varied between oxic and anoxic, as was concluded from TOC-TS, V/(V+Ni) and U/Th. The turbidity currents might have ventilated the bottom waters, especially more efficiently in the proximal zone of turbidite sedimentation. Moreover, oxygenated bottom waters may have also affected the concentration of trace metals, owing to migration of the redox interface downward within the sediments.

Natural and anthropogenic biomarkers in recent dated sediment cores from Refome Lake, SE Nigeria: environmental implications

Natural and anthropogenic biomarkers characteristics of two recent sediment cores collected toward the shoreline and center of Refome Lake (RS and RC; 30 cm long), southeastern Nigeria, were investigated in order to reconstruct past environmental conditions and asses humans-induced changes on the local ecosystem over the last century. Results from sediment bulk properties such as total organic carbon (TOC; 0.12–0.54%; mean—0.26 ± 0.9%), total nitrogen (TN; 0.01–0.05%; mean—0.03 ± 0.7%) and total inorganic carbon (TIC; 0.03–0.37%; mean—0.14 ± 1.0%) contents as well as TOC/TN (5–25; mean—11.55 ± 1.4) suggested slightly higher contribution from allochthonous over autochthonous organic matter (OM), lowered by low primary production and the characteristic Niger Delta sheltered basin morphology predominated by sandy lithology. Evaluation of molecular proxies such as carbon preference index (CPI(C24–C35); 1.23–1.74: mean—1.58 ± 0.4), carbon maxima (Cmax—17, 19, 26, 27, 29), long-chain/short-chain hydrocarbons (LHC/SH-C; 0.77–2.25, mean—1.52 ± 0.3) and Paq, (0.21–0.61, mean–0.45 ± 0.3) as well as C29/C27 (0.89–2.67; mean—1.53 ± 0.2) indicated an admixture slightly predominated by microbial OM (algae/bacteria) in the most recent top layer (RC1, 0–5 cm) of RC core and slightly more enhanced terrestrially derived OM in the middle layer (RS4, 15–20 cm) of RS core. The later sediment layer deposited at ca. 1947–1964 coincided with the period of greater wash-in of land-derived OM (associated with tree logging/forest clearing for foot path extension and farmland preparation authorized by the European settlers) occasioned by intense rainfall. The occurrence of gammacerane and 18α-oleanane in low levels in the lower and upper layers revealed trace contamination by petroleum hydrocarbons imported into the Nigerian economy prior to independence in 1960 and utilization of Niger Delta oil after 1960 following departure of the colonial masters (the British), respectively.

Organic matter in upper Albian marine sediments in the High-Tatric units, central western Carpathians related to Oceanic Anoxic Event 1d—Geochemistry, microfacies and palynology

A multidisciplinary study of upper Albian hemipelagic sediments related to the Oceanic Anoxic Event 1d (OAE1d) from the High-Tatric units (central western Carpathians, Polish part of the Tatra Mountains) was undertaken to characterize organic matter (OM) and to investigate its origin. Microfacies and palynological records combined with mineralogical and geochemical data from these sediments show the occurrence of both marine and land-derived OM in the limestone and marl successions whose deposition corresponds to the Parathalmanninella apenninica Zone in the late Albian. Both types of OM were strongly degraded under the oxic conditions that prevailed during the entire time of their deposition. The sedimentation of marls with low contents of total organic carbon (<0.24%), dominated by land-derived OM, occurred during the final phase of OAE1d. It was probably related to a sudden change in the circulation pattern at the margins of the Tatric–Zliechov sedimentary basin connected with a sea-level rise. The coastal upwelling along the Tatric Ridge that prevailed during the early late Albian gradually weakened or disappeared and was replaced by a downwelling current flowing from the shallow parts of the basin that transported land-derived OM from nearshore coastal plains.