Organic Matter Of Terrestrial Origin Research Articles

Holocene organic matter composition in relation to relative sea level stands and associated morphometric changes of a lagoonal system

Garzón Lagoon is a temperate shallow coastal lagoon influenced by sea level variation. A study on the isotopic composition of Holocene sedimentary organic matter was performed. Although the system was subject to significant changes in sea level, leading to important changes in the lagoon morphometry during the Holocene, the composition of the organic matter was rather surprisingly constant, being dominated by particulate organic matter of marine origin, and to a lesser extent of terrestrial origin. By ∼5000 yr BP, the sea level was +5 m amsl, and the lagoon displayed the largest morphometric dimensions. Once the sea level decreased towards 3000 yr BP and present times, the lagoon area progressively decreased. Even though we inferred significant changes in morphometry, the composition of the organic matter remained relatively constant, as the lagoon was always connected to the ocean, a condition that remains today, at least intermittently during storms or heavy rains. Only after the 1960s, a slight change in the organic matter composition was detected, consisting of a decrease in particulate organic matter of terrestrial origin.

Responses of a Submerged Macrophyte Potamogeton crispus and Epiphytic Biofilm to Humic-Substance Enrichment Coupled with Brownification in Freshwater Habitats

Brownification denotes increasing water color, partly caused by increasing dissolved organic matter of terrestrial origin in freshwater. Brownification has become a wide-spread environmental problem because water color alters the physicochemical environment and biological communities in aquatic ecosystems. However, our understanding of its ecological effects on aquatic macrophytes is limited. Here, an indoor mesocosm experiment with a common submerged macrophyte, Potamogeton crispus, along an increasing gradient of brownification was conducted over a period of 42 days. Results showed that P. crispus was able to overcome low degrees of brownification owing to the plasticity in morphological and physiological traits and P. crispus growth even benefitted from the concomitant nutrients along with brownification. However, the macrophyte growth was negatively affected by a 10-fold increase in water color beyond its current level. Additionally, collapse in antioxidant systems and potent photosynthesis inhibition implied that P. crispus could not adapt to the low-light stress generated under the high degree of brownification. Epiphytic bacteria are more sensitive to brownification than their hosts. Any degree of brownification initially caused a decrease in microbial diversity of epiphytic biofilm, whereafter the concomitant nutrients under brownification favored the growth of epiphytic microorganisms. The shading effect of a large number of epiphytic biofilms under brownification may further aggravate the low-light stress on macrophytes. Overall, the study provides new insights into the comprehensive effects and underlying mechanisms of brownification on macrophytes.

Degradation pathways for organic matter of terrestrial origin are widespread and expressed in Arctic Ocean microbiomes

BackgroundThe Arctic Ocean receives massive freshwater input and a correspondingly large amount of humic-rich organic matter of terrestrial origin. Global warming, permafrost melt, and a changing hydrological cycle will contribute to an intensification of terrestrial organic matter release to the Arctic Ocean. Although considered recalcitrant to degradation due to complex aromatic structures, humic substances can serve as substrate for microbial growth in terrestrial environments. However, the capacity of marine microbiomes to process aromatic-rich humic substances, and how this processing may contribute to carbon and nutrient cycling in a changing Arctic Ocean, is relatively unexplored. Here, we used a combination of metagenomics and metatranscriptomics to assess the prevalence and diversity of metabolic pathways and bacterial taxa involved in aromatic compound degradation in the salinity-stratified summer waters of the Canada Basin in the western Arctic Ocean.ResultsCommunity-scale meta-omics profiling revealed that 22 complete pathways for processing aromatic compounds were present and expressed in the Canada Basin, including those for aromatic ring fission and upstream funneling pathways to access diverse aromatic compounds of terrestrial origin. A phylogenetically diverse set of functional marker genes and transcripts were associated with fluorescent dissolved organic matter, a component of which is of terrestrial origin. Pathways were common throughout global ocean microbiomes but were more abundant in the Canada Basin. Genome-resolved analyses identified 12 clades of Alphaproteobacteria, including Rhodospirillales, as central contributors to aromatic compound processing. These genomes were mostly restricted in their biogeographical distribution to the Arctic Ocean and were enriched in aromatic compound processing genes compared to their closest relatives from other oceans.ConclusionOverall, the detection of a phylogenetically diverse set of genes and transcripts implicated in aromatic compound processing supports the view that Arctic Ocean microbiomes have the capacity to metabolize humic substances of terrestrial origin. In addition, the demonstration that bacterial genomes replete with aromatic compound degradation genes exhibit a limited distribution outside of the Arctic Ocean suggests that processing humic substances is an adaptive trait of the Arctic Ocean microbiome. Future increases in terrestrial organic matter input to the Arctic Ocean may increase the prominence of aromatic compound processing bacteria and their contribution to Arctic carbon and nutrient cycles.6hGoymMH-pRJKwnwbycG8JVideo

Seasonal dissolved copper speciation in the Strait of Georgia, British Columbia, Canada

The Strait of Georgia (SoG) is a semi-enclosed, urban basin with seasonally dependent estuarine water circulation, dominantly influenced by Northeast Pacific waters and the Fraser River. To establish a baseline and understand the fate and potential toxicity of Cu in the SoG, we determined seasonal and spatial depth profiles of dissolved Cu (dCu) speciation, leading to estimates of the free hydrated copper (Cu2+) concentrations, as a proxy for Cu toxicity. The concentration of dCu was largely controlled by conservative mixing of the ocean and freshwater endmembers in the SoG. In all samples, ligand concentrations exceeded dCu, by a ratio greater than 1.5, resulting in the complexation of 99.98% of the dCu by strong binding organic ligands. The concentrations of Cu2+ were less than 10-13.2 M, significantly lower than the well-established Cu toxicity threshold (10-12 M Cu2+) for microorganisms. Our results indicate that ambient Cu-binding ligands effectively buffer Cu2+ concentrations within the Strait of Georgia, posing no threat to marine life. In almost 90% of the samples, the ligands were best classified as a single ligand class, with a logKCuL,Cu2+cond between 12.5 and 14.1. The concentrations of these single class ligands were greatest in warm, low salinity, nutrient depleted waters, suggesting that either terrestrially sourced ligands dominate dCu speciation in the SoG, or freshwater sources in the SoG establish the conditions that promote the production of Cu binding ligands in its surface waters. The remaining 10% of the samples were from the euphotic zone, where we detected a stronger ligand class, L1, of logKCuL1,Cu2+cond between 13.5 and 14.3, and a weaker ligand class, L2, of logKCuL2,Cu2+cond between 11.5 and 12.3. In these surface samples, logKCuL1,Cu2+cond and logKCuL2,Cu2+cond were positively correlated with temperature, while L2 concentrations were positively correlated with chromophoric dissolved organic matter of terrestrial origin. This study is the first to perform hierarchal clustering of a trace metal speciation dataset and enabled the distinction of 6 clusters across season, depth, and region of the SoG, highlighting the influence of freshwater and open ocean ligand sources, conservative mixing dynamics, and particulate Cu concentrations on dCu speciation within estuarine basins.

Structure and seasonal variability in fish food webs in a small macrotidal estuary (Canche estuary, Eastern English Channel) based on stable carbon and nitrogen isotope analysis

Estuaries are highly important nursery habitats for a range of fish species because they provide refuge and food, especially for juveniles. However, the importance of specific salinity zones and adjacent shallow marine habitats (subtidal and surf zones) for fish feeding is not well understood, particularly in small macrotidal estuaries. Using the example of the Canche estuary, which is considered a reference for small macrotidal estuaries in France, we investigated the structure and seasonal variability in fish food webs based on stable carbon and nitrogen isotope analysis. Our results provide a new vision of the Canche estuary, which has been considered a major feeding ground for all marine fish that spend time there. Based on δ13C results, our results revealed that organic matter of terrestrial origin has little influence on functioning of the Canche food web, except for flounders in the upstream area of the estuary. Conversely, microphytobenthos and marine particulate organic matter contribute most to the food web of fish in the estuary. Our study also revealed that some fish species visit the estuary for reasons other than feeding, such as to avoid predation or because they are carried by the tide. This work confirmed the suitability of using stable isotopes to trace fish fidelity to feeding grounds less than 10 km apart.

Palynofacies, Organic Thermal Maturation and Source Rock Evaluation of Nanka and Ogwashi Formations in Updip Niger Delta Basin, Southeastern Nigeria

ABSTRACT The oil and gas prospects in the Nigerian inland basins necessitated the palynofacies characterization, thermal maturation and source rock evaluation of the Nanka and Ogwashi formations of the Niger delta basin. The Nanka Formation has dominant terrestrial microflora, brown structured phytoclasts and amorphous organic matter, opaque debris accompanied by dinoflagellate cysts. The Ogwashi Formation has maximum terrestrial microflora, medium to large brown structured phytoclasts, opaque debris with abundance of dark brown amorphous organic matter and a few marine taxa. Palynofacies constituents of the Nanka Formation reflect Kerogen Type II / III which are Gas / Oil prone shown by abundance of marine species, amorphous organic matter in conjunction with terrestrial phytoclasts and non-marine palynomorphs assemblage. The spore/pollen colour range from light brown to dark brown which suggest oil generation to production of wet gas. This corresponds to thermal alteration index (TAI) 2+ to 3+ and vitrinite reflectance index (%Ro) 0.5% to 1.3%. Palynofacies of the Ogwashi Formation has Kerogen Type III (gas prone) linked with overwhelming abundant terrestrial phytoclasts palynomorphs and large amorphous organic matter of terrestrial origin. Spore/pollen thermal alteration colour ranges from light medium brown to dark brown indicative of mature oil generation and transition to dry gas phase. The thermal alteration index and vitrinite reflectance index (%Ro) values of the Ogwashi Formation is consistent with that of the Nanka Formation.

Organic matter deposition in the Ghadames Basin (Libya) during the Late Devonian—A multidisciplinary approach

The organic-rich deposits of Late Devonian age are the second most important petroleum source rocks in the Ghadames Basin (Libya). From available stratigraphy, the peak of organic matter deposition, corresponding to a level of radioactive shales easily recognized in gamma ray logs, occurred at the Frasnian-Famennian transition. The present study was focused on samples from borehole D1–26, located in the central part of the Ghadames Basin, belonging to the Aouinet Ouenine III and IV formations (Frasnian to Famennian). The mineral and organic content of the rocks were analyzed in order to determine the origin of organic matter accumulation and estimate if the organic matter enrichment could be related to the well-known Upper Kellwasser event. The results indicate that during the Frasnian, the planktonic primary productivity was moderate, but anoxic conditions reaching the euphotic zone were frequent and allowed efficient preservation of the organic matter. At the Frasnian-Famennian transition, the deposition of the radioactive shales level can be related to a eustatic rise, which allowed incursion of nutrient-rich water in the basin, leading to increase in primary productivity and photic zone anoxia. During the Famennian, the conditions changed, associated with a relative sea level fall and/or a progradation of detrital sediments originating from the south. Photic zone anoxia was only episodic and plankton-derived organic matter was poorly preserved. Nevertheless, the important influx of organic matter of terrestrial origin allowed significant enrichment of the sediment in organic matter. Several indications suggest the radioactive shales interval could be coeval with the Upper Kellwasser level, nevertheless further stratigraphic work is needed to confirm this hypothesis.

Oxidation products of α- and β-amyrins: potential tracers of abiotic degradation of vascular-plant organic matter in aquatic environments

Environmental contextHow can we know what happens to organic matter in aquatic environments? Although several compounds exist that can be used to trace the origin and state of organic matter, not many are sufficiently stable and specific to trace degradation processes, but α- and β-amyrins can fulfil that role. Such knowledge will help us better understand and better quantify carbon fluxes in riverine and marine environments. AbstractIn order to fulfil the current need for stable and specific tracers to monitor vascular-plant organic matter degradation in aquatic environments, α-amyrin (urs-12-en-3β-ol) and β-amyrin (olean-12-en-3β-ol) were oxidised in vitro and their abiotic degradation products quantified in environmental samples from the Rhône River in France. Although they appear inert to photooxidation, they are clearly affected by autoxidation and the tracer potential of the resulting products was confirmed. Autoxidation of α- and β-amyrins produces urs or olean-12-en-3-one, 3β-hydroxy-urs or olean-12-en-11-one, urs or olean-12-en-3β,11α-diol and urs or olean-12-en-3,11-dione. 3β-Hydroxy-urs-12-en-11-one and 3β-hydroxy-olean-12-en-11-one, the main oxidation products detected, were selected as autoxidation tracers. These compounds, specific to autoxidation, were detected in dry leaves of Smilax aspera and in suspended particulate matter samples collected in the Rhône River and evidenced the importance of autoxidation in the degradation of organic matter of terrestrial origin.

The effect of water balance of a man‐made lacustrine ecosystem on the food web: does flushing affect the carbon signature of plankton and benthos?

AbstractReservoir ecosystems may be supported by considerable input of organic matter originating from the catchment. Thus, the current proportion of allochthonous and autochthonous organic matter available to reservoir biota will be affected by changes in the flushing rate. In a medium‐sized submontane reservoir, we examined reaction of the δ13C isotopic signature of fine (10–50 µm) and coarse (>50 µm) fractions of the seston, and of benthic invertebrates, to the reservoir flushing rate. The δ13C signatures of samples varied, and spatially δ13C increased significantly down‐reservoir in all instances, becoming less similar to the carbon signature of organic matter of terrestrial origin. Two distinct trends in the correlation between δ13C and flushing rate were identified as follows: (1) fine seston tended to become more 13C‐depleted and therefore similar to the carbon signature of terrestrial organic matter; and (2) the 13C signature of coarse seston became enriched with increasing flushing, and also tended to become closer to values of terrestrial organic matter. Benthic assemblages did not display any clear association with flushing rates. Such reactions in different components of the food web to allochthonous carbon input and the rate of reservoir flushing may be a common feature of other comparable Central European reservoirs and an important characteristic of their carbon cycles. Copyright © 2015 John Wiley & Sons, Ltd.

The role of solid bitumen in the development of porosity in shale oil reservoir rocks of the Upper Cretaceous in Colombia

The La Luna Formation (Turonian–Santonian age) has been traditionally considered as one of the main hydrocarbon source rocks in the Middle Magdalena Valley Basin (MMV) in Colombia. At present this formation is also considered as an organic matter-rich reservoir of shale oil type (unconventional petroleum system) of interest due to its significant resources of recoverable oil. Given the interest in this formation, and the need to increase the knowledge of its physico-chemical characteristics, a series of petrographic, geochemical (TOC content and Rock-Eval pyrolysis) and textural analyses (picnometry and mercury intrusion porosimetry, MIP) were carried out to investigate two of its members: Galembo and Salada that were sampled from a core well perforated at the center of the basin. The organic fraction of both members, Galembo and Salada, is made up mainly of a kerogen of Type II typical of a marine paleoenvironment, solid bitumen and hydrocarbons. The content in organic matter of terrestrial origin is very scarce-to-null. These rocks have a degree of maturity that corresponds to the oil window, and their high hydrogen content in combination with a relatively high carbon content makes them excellent source rocks. The uneven distribution of the various types of organic matter along the Galembo and Salada Members, particularly of the solid bitumen that is concentrated at the lower levels of both members has resulted in large variations in porosity, pore size distribution and modal pore throat characteristics even with small variations (centimetric) in depth. The sedimentary levels in which kerogen is the predominant type of organic matter have a pore size distribution in the range of mesopores and macropores of small size, whereas the solid bitumen-rich levels show a predominance of pores of small pore size with a modal pore throat diameter below 10nm. The preliminary adsorption data obtained for all these samples (to be published in a study that will follow this), indicate that they contain some micropores, which is significant in the case of levels with a high content in solid bitumen.

Reaction of lake environment on the climatic cooling – Transition from the Eemian Interglacial to Early Vistulian on the basis of Solniki palaeolake sediments (NE Poland)

Results of Cladocera and organic matter analyses from the Eemian lake deposits in Solniki (NE Poland) are presented. We focused on the reaction of the lake's environment to progressive cooling reflected in the changes of the organic matter and the Cladocera community. Approximately 3-m of sediments accumulated from the optimum of the Eemian Interglacial (E5) to the Early Vistulian (EV2) were analyzed. Results of analyses of organic matter correlated with Cladocera data enabled a reconstruction of varying environmental conditions and geneses of organic matter. The organic carbon content is closely related to climatic conditions. The lowest values are recorded in the coldest periods during the ending of the Eemian Interglacial and the Herning stadial of the Early Vistulian. The highest ones occur unexpectedly in the Eemian post-optimum: at the end of the spruce phase and at the beginning of the pine phase.During the Eemian optimum (E5), biodiversity of Cladocera species was maximal (17), but the frequency of specimens was low. At the end of the optimum (E5), an improvement of living conditions, more optimal for various ecological groups of Cladocera took place. Algae remained a significant component of organic matter. The early Eemian post-optimum (E6) is characterized as a period of the high number of zooplankton species, the highest frequency as well as biodiversity. At that time, probably a higher water level and an optimal temperature formed very favorable conditions for the fauna development. During this period, maximal values of TOC, TN and the slight increase of C/N ratio suggest a higher primary productivity with a small supply of organic matter of terrestrial origin. Coexistence of two species of the family Bosminidae and maximum values of δ15N suggest a high trophy (β-mesotrophy). High resolution and detailed analyses of the lake sediments accumulated during the pollen zone E7, allowed to identity a few minor environmental fluctuations recorded in varied Cladocera frequency, TOC and C/N ratio. In the final period of the Eemian Interglacial and in the Early Vistulian (Herning stadial), a drastic reduction in frequency of Cladocera and the features of OM (the lowest amounts of TOC and TN, and the highest value of C/N) reflect the decline of lake conditions and a lack of both primary production and aquatic vegetation in the lake. During the Amersfoort interstadial a renewed bioproduction and slightly supply of terrestrial plants in organic matter as well as revitalize zooplankton took place.

Activity concentrations and distribution of radionuclides in surface and core sediments of the Neretva Channel (Adriatic Sea, Croatia)

The activity concentrations and the distribution of manmade 137 Cs and naturally occurring radionuclides 40 K, 238 U and 232 Th in surface and core sediments of the semi enclosed, river-dominated marine environment of the Neretva Channel were investigated in relation to the sedimentological characteristics and the content of the total organic carbon (TOC). The activity concentrations of radionuclides were determined by gamma spectrometry. Distinct interrelations between sediment properties and spatial distribution of radionuclides were established. The highest accumulation of 137 Cs was found close to the river mouth, in the region of intensive deposition of organic matter of terrestrial origin. This finding implies that the river-borne organic material and its deposition processes should be considered as the most important factor controlling distribution of 137 Cs in this transitional land-sea environment. The sediment accumulation rates, estimated from distribution of 137 Cs in core sediments, were approximately 6 mm y -1 in front of the Neretva River mouth and 4 mm y -1 in the channel area. The spatial distribution of natural 40 K and 232 Th radionuclides indicates their distinct association with fine-grained sediments. The interrelation of 238 U with fine-grained particles was somewhat weaker but still present. The results obtained indicate that the accumulation pattern of natural radionuclides in the Neretva Channel sediments is mainly governed by the deposition of fine-grained material. This study scrutinizes the baseline level for occurring radionuclides and should be used for monitoring and assessing the radionuclide pollution record in the investigated transitional land-sea environment of the Adriatic.

Increasing iron concentrations in surface waters – a factor behind brownification?

Abstract. Browning of inland waters has been noted over large parts of the Northern hemisphere and is a phenomenon with both ecological and societal consequences. The increase in water color is generally ascribed to increasing concentrations of dissolved organic matter of terrestrial origin. However, oftentimes the increase in water color is larger than that of organic matter, implying that changes in the concentration of organic matter alone cannot explain the enhanced water color. Water color is known to be affected also by the quality of organic matter and the prevalence of iron. Here we investigated trends in water color, organic matter and iron between 1972 and 2010 in 30 rivers draining into the Swedish coast (data from the national Swedish monitoring program), and performed a laboratory iron addition experiment to natural waters, to evaluate the role of iron and organic matter in determining water color. By comparing the effect of iron additions on water color in the experiment, to variation in water color and iron concentration in the monitoring data, we show that iron can explain a significant share of the variation in water color (on average 25 %), especially in the rivers in the north of Sweden (up to 74 %). Furthermore, positive trends for iron are seen in 27 of 30 rivers (21–468 %) and the increase in iron is larger than that of organic matter, indicating that iron and organic matter concentrations are controlled by similar but not identical processes. We speculate that increasing iron concentrations can be caused by changes in redox conditions, that mean that more anoxic water with high concentrations of soluble FeII are feeding into the surface waters. More studies are needed about why iron is increasing so strongly, since both causes and consequences are partly different from those of increasing organic matter content.

Utility of dissolved barium in distinguishing North American from Eurasian runoff in the Arctic Ocean

Dissolved barium has been shown to have the potential to distinguish Eurasian from North American (NA) river runoff. As part of the ARK-XXII/2 Polarstern expedition in summer 2007, Ba was analyzed in the Barents, Kara, Laptev seas, and the Eurasian Basins as well as the Makarov Basin up to the Alpha and Mendeleyev Ridges. By combining salinity, δ18O and initial phosphate corrected for mineralization with oxygen (PO4*) or N/P ratios we identified the water mass fractions of meteoric water, sea ice meltwater, and marine waters of Atlantic as well as Pacific origin in the upper water column. In all basins inside the lower halocline layer and the Arctic intermediate waters we find Ba concentrations close to those of the Fram Strait branch of the lower halocline (41–45nM), reflecting the composition of the incoming Atlantic water. A layer of upper halocline water (UHW) with higher Ba concentrations (45–55nM) is identified in the Makarov Basin. Atop of the UHW, the Surface Mixed Layer (SML), including the summer and winter mixed layers, has high concentrations of Ba (58–67nM). In the SML of the investigated area of the central Arctic the meteoric fraction can be identified by assuming a conservative behavior of Ba to be primarily of Eurasian river origin. However, in productive coastal regions biological removal compromises the use of Ba to distinguish between Eurasian and NA rivers. As a consequence, the NA river water fraction is underestimated in productive surface waters or waters that have passed a productive region, whereas this fraction is overestimated in subsurface waters containing remineralised Ba, particularly when these waters have passed productive shelf regions. Especially in the Laptev Sea and small regions in the Barents Sea, Ba concentrations are low in surface waters. In the Laptev Sea exceptionally high Ba concentrations in shelf bottom waters indicate that Ba is removed from surface waters to deep waters by biological activity enhanced by increasing ice-free conditions as well as by scavenging by organic matter of terrestrial origin. We interpret high Ba concentrations in the UHW of the Makarov Basin to result from enrichment by remineralisation in bottom waters on the shelf of the Chukchi Sea and therefore the calculated NA runoff is an artefact. We conclude that no NA runoff can be demonstrated unequivocally anywhere during our expedition with the set of tracers considered here. Small contributions of NA runoff may have been masked by Ba depletion and could only be resolved by supportive tracers on the uptake history. We thus suggest that Ba has to be used with care as it can put limits but not yield quantitative water mass distributions. Only if the extra Ba inputs exceed the cumulative biological uptake the signal can be unequivocally attributed to NA runoff.

Human lakeshore development alters the structure and trophic basis of littoral food webs

Summary 1. Shoreline development and the associated loss of littoral habitats represent a pervasive alteration of the ecological integrity of lakes and have been identified as major drivers for the loss of littoral biodiversity world-wide. Little is known about the effects of shoreline development on the structure of, and energy transfer in, littoral food webs, even though this information is urgently needed for management and mitigation measures. 2. We measured macroinvertebrate biomass and analysed potential food resources using stable isotopes (δ13C, δ15N) and mixing models to compare the complexity and the trophic base of littoral food webs between undeveloped and developed shorelines in three North German lowland lakes. 3. The lower diversity of littoral habitats found at developed shorelines was associated with lower diversity of food resources and consumers. Consequently, the number of trophic links in food webs at developed shorelines was up to one order of magnitude lower as compared with undeveloped shorelines. 4. Mixing model analysis showed that consumer biomass at undeveloped shorelines was mainly derived from fine particulate organic matter (FPOM) and coarse particulate organic matter of terrestrial origin (CPOM). The contribution of CPOM to consumer biomass was twofold lower at developed shorelines, and consumer biomass was mainly derived from FPOM and suspended particulate organic matter. 5.Synthesis and application. Shoreline development impacts the flow of organic matter within littoral food webs primarily through the reduction in littoral habitat diversity. These effects are exacerbated by clearcutting of the riparian vegetation, which disrupts cross-boundary couplings between the riparian and the littoral zone. Lakeshore conservation should focus on preserving the structural integrity of the littoral zone, while restoration of coarse woody debris, reed and root habitats can be a cost-efficient measure to improve degraded lakeshores. The local effects of shoreline development demonstrated in this study might lead to whole-lake effects, but future studies are needed to derive thresholds at which shoreline development has consequences for the structure and functioning of the entire ecosystem.

Hydrology in the Sea of Marmara during the last 23 ka: Implications for timing of Black Sea connections and sapropel deposition

[1] Sediments deposited under lacustrine and marine conditions in the Sea of Marmara hold a Late Quaternary record for water exchange between the Black Sea and the Mediterranean Sea. Here we report a multiproxy data set based on oxygen and strontium isotope results obtained from carbonate shells, major and trace elements, and specific organic biomarker measurements, as well as a micropaleontological study from a 14C-dated sediment core retrieved from the Sea of Marmara. Pronounced changes occurred in δ18O and 87Sr/86Sr values at the fresh and marine water transition, providing additional information in relation to micropaleontological data. Organic biomarker concentrations documented the marine origin of the sapropelic layer while changes in n-alkane concentrations clearly indicated an enhanced contribution for organic matter of terrestrial origin before and after the event. When compared with the Black Sea record, the results suggest that the Black Sea was outflowing to the Sea of Marmara from the Last Glacial Maximum until the warmer Bølling-Allerød. The first marine incursion in the Sea of Marmara occurred at 14.7 cal ka B.P. However, salinification of the basin was gradual, indicating that Black Sea freshwaters were still contributing to the Marmara seawater budget. After the Younger Dryas (which is associated with a high input of organic matter of terrestrial origin) both basins were disconnected, resulting in a salinity increase in the Sea of Marmara. The deposition of organic-rich sapropel that followed was mainly related to enhanced primary productivity characterized by a reorganization of the phytoplankton population.

Across margin export of organic matter by cascading events traced by stable isotopes, northwestern Mediterranean Sea

We present a 1‐yr (2005‐2006) record of organic carbon (OC) and total nitrogen (TN) contents and their isotopic ratios (Δ13COC and Δ15N) in sinking particles from the western Gulf of Lions. Maximum OC and TN fluxes recorded in January 2006 and March‐April 2006 were associated with negative near‐bottom temperature anomalies. This reveals large inputs of resuspended organic matter from the shelf basinwards to depths ≫1500 m by dense shelf‐water cascading. The first pulse of organic matter had low Δ13COC (‐25.5‰) and N:C (0.08) and high Δ15N (6.6‰) values, indicative of the arrival of organic matter of terrestrial origin. In contrast, the second pulse had high Δ13COC (‐21.9‰) and N:C (0.15) and extremely low Δ15N (0.0‰) values, indicative of the transfer of organic matter with higher marine contribution. Though downslope export of organic matter from the adjacent shelf predominated, particles escaping from surface waters remained an important source of organic matter during low‐energy and low‐flux periods and especially during summer conditions, with significant contribution of N2 fixation to organic matter export. Overall, our results suggest the export of organic matter from different sources to the deep Mediterranean basin, which in turn might alter within a couple of months the quality of the sedimentary organic matter deposited on the sea floor and thus the dynamics of the deep ecosystems.

Spatial and temporal patterns of benthic macrofaunal communities on the deep continental margin in the Gulf of Guinea

Abstract Density, taxonomic composition at higher taxon level and vertical distribution of benthic macrofaunal communities and sediment characteristics (pore water, nitrogen, organic carbon, sulfur, C/N ratio, n -alcohol biomarkers) were examined at three deep sites on the Congo–Gabon continental margin. This study was part of the multidisciplinary BIOZAIRE project that aimed at studying the deep benthic ecosystems in the Gulf of Guinea. Sampling of macrofaunal communities and of sediment was conducted during three cruises (January 2001, December 2001 and December 2003) at two downslope sites (4000 m depth), one located near the Congo submarine channel (15 km in the south) and the other one far from the channel (150 km in the South). The third area located 8 km north of the Congo channel in the surroundings of a giant pockmark at 3160 m depth was sampled during one cruise in December 2003. At these three locations the macrofaunal communities presented relatively high densities (327–987 ind. 0.25 m −2 ) compared with macrofaunal communities at similar depths; that is due to high levels of food input related to the Congo river and submarine system activities that affect the whole study area. The communities were different from each other in terms of taxonomic composition at higher taxon level (phylum, class, order for all the groups except for the polychaetes classified into families). The polychaetes dominated the communities and were responsible for the increase in densities observed at both deep sites (4000 m) between January 2001 and December 2003 whereas the tanaidaceans, the isopods and the bivalves were the other most abundant taxa responsible for the spatial differences between these sites. The community at 3150 m differed from the two deep communities by higher abundances in bivalves, nemerteans and holothuroids. The composition of the polychaete community also differed among sites. In the vicinity of the Congo channel, the expected positive effect of the additional organic matter transported through the turbiditic currents on to the surrounding benthic communities was not observed, as the increase in densities during the study period was higher at the site located away from the Congo channel than near the channel (80% vs 30%). That may be due to the low food value of the organic matter of terrestrial origin carried through the turbidites, and/or to the disturbance caused by these turbidites. Conversely, far from the channel the macrofaunal communities benefit from organic matter of higher energetic value originating mainly from marine sources, but also from continental sources, carried by the Congo plume or by near-bed currents across or along the continental slope. Spatial and temporal variability in trophic and physical characteristics of the sediment habitat at both deep sites also affected the vertical distribution of the macrofaunal communities. The activities of the very active Congo system structure the deep macrofaunal communities on a large area in terms of densities, composition and vertical distribution. The food input is enhanced at regional scale as well as the heterogeneity of the sediment characteristics, mainly in terms of organic matter quality (marine vs terrigenous). In turn, the densities are enhanced as well as the regional diversity of the macrofaunal communities in terms of taxonomic composition and distribution.

Muddy-bottom meiofauna responses to metal concentrations and organic enrichment in New Caledonia South-West Lagoon

The New Caledonia South-West Lagoon is subject to both major terrigenous and urban inputs associated with the development of the Nouméa city, which may affect its functioning. Environmental parameters, sediment biochemical characteristics, metal concentrations and benthic meiofauna were assessed to better characterize and unravel the effects of these two potential disturbances in muddy sediments. Seventeen stations were sampled along disturbance gradients within four bays located around the city of Nouméa and subject to different levels of anthropogenic and terrigenous inputs. Two cruises were carried out during July (dry season) and December 2002 (beginning of the rainy season). Spatial changes were much more important than temporal ones. Temporal changes were restricted to the biochemical characteristics of superficial sediment and more specifically to its labile organic fraction. Two groups of metals were identified based on their spatial distribution. The first was composed of Cr, Mn, Co and Ni, which mainly originate from the erosion of soils and mining activities. The second was composed of Zn, Cu and Pb, which mainly originate from urban activities. All sampled bays could be considered as potentially contaminated by one or more metals. Total meiofauna density correlated negatively with bulk descriptors of organic matter (during the December cruise) and positively with EHAA/THAA ratio (during both cruises). It did not correlate with Ni, Mn, Cr and Co but did correlate negatively with Cu and Pb during the December cruise. Our results suggest that the density of meiofauna in the South-West Lagoon is positively affected by the qualitative and negatively affected by the quantitative characteristics of sedimentary organic matter. This pattern differs drastically from what is usually observed in temperate ecosystems. This discrepancy may result from the importance of the inputs of refractory organic matter of terrestrial origin in the South-West Lagoon. Metals originating from soil erosion and mining have apparently no effect on total meiofauna, whereas some metals originating from urban activities may have a negative effect on total meiofauna at least during the beginning of the rainy season.

Search for EPR markers of the history and origin of the insoluble organic matter in extraterrestrial and terrestrial rocks

The insoluble organic matter (IOM) of three carbonaceous meteorites (Orgueil, Murchison and Tagish Lake meteorites) and three samples of cherts (microcrystalline SiO 2 rock) containing microfossils with age ranging between 45 million years and 3.5 billion years is studied by electron paramagnetic resonance (EPR). The age of the meteorites is that of the solar system (4.6 billion years). The purpose of this work was to determine the EPR parameters, which allow us to discriminate between biogenic and extra terrestrial origin for the organic matter. Such indicators should be relevant for the controversy regarding the biogenicity of the organic matter in the oldest cheroot (3.5 billion years) and in Martian meteorites containing microbe-like microstructures. The organic matter of meteorites contains a high concentration of diradicaloid moieties characterised by a diamagnetic ground state S=0 and a thermally accessible triplet state S=1. The three meteorites exhibit the same singlet–triplet gap (ST gap) Δ E≈0.1 eV. To the best of our knowledge, such diradicaloids are unknown in insoluble organic matter of terrestrial origin. We have also shown that the EPR linewidth of insoluble organic matter in cherts and coals decrease logarithmically with the age of the organic matter. We conclude from this result that the organic matter in the oldest cherts (3.5 billion years) has the same age as their SiO 2 matrix, and is not due to a latter contamination by bacteria, as was recently found in meteoritic samples.