Biological interactions between microorganisms in the sea     

M. Aubert  M.J. Gauthier 《Marine Chemistry》1977,5(4-6)

Marine ecosystems, like terrestrial biological communities, are generally considered to depend, regarding their structure and functioning, upon the trophic and sexual relationships between organisms, either “horizontally”, between individuals at the same level, or “vertically”, all the way down the various levels of the food chains. Nevertheless, the functioning of biosystems is mostly governed by their structure, i.e., the qualitative and quantitative distribution of individuals within biocenoses, as well as the relationships with one another and with the environment. Therefore, it is vital to get to know how these connections work in order to outline the main causes of microbiological equilibrium in the sea. Actually, the major problem remains that of communication between individuals in biocenoses. This is a general problem as far as life is concerned, but it proves especially acute when it comes to microbial life because of its importance in the oceanic cycles.Data available in the literature, together with the results of our own studies in this field, led us to the assumption that some of the dissolved organic substances present in seawater might well be responsible for the control of the relationships between species. These substances would be active at various degrees of concentration, after they have been released into the medium by certain species. This theory, already adumbrated by Lucas (1938, 1947, 1955), Nigrelli (1958) and Fontaine (1970) concerning direct relationships between marine species or groups of organisms, was resumed and generalized by M. Aubert (1971) who called these substances “telemediators”.Such chemical communication plays a major role in a variety of fields including sexual behaviour, nutrition and predation, as well as defense mechanisms, mobility and migration.Remote connection of two organisms through a chemical mediation involves a sequence of actions and reactions which raises a number of problems of biochemical microecology. The organism that produces the telemediator must synthesize it — either spontaneously or in an induced way — and release it into the medium, during its active growth or after cell lysis. Next, the mediator is conveyed to the remote receiving organism, which it should reach without being degraded or chemically modified (or after such a modification. Its concentration must remain equal to or higher than its activity threshold. The receptor detects it, with or without absorption, and reacts by modifying its own metabolism or behaviour. This may go as far as causing the receptor the receptor to die. In even more complex situations, another mediator will be synthesized and released into the medium.Theoretical as it may be, such a pattern is a useful guide to explain the microbial interactions in a marine environment. It involves a number of complex microecological phenomena, some phases of which begin to be known. One specific problem is chemoreception in microorganisms, hence chemotaxis. Telemediator activity threshold and turnover in the natural environment must also be investigated.One should also take account of the physical context in which the phenomena take place. For instance, it is a known fact that an important fraction of the bacterial flora in the sea is adsorbed on solid or particulate substrates. Thus, the relationships with which they are concerned are much more probable in a sphere of a few fractions of a millimeter: this emphasizes the significance of the biochemical processes which cause the microorganisms to colonize substrates and to compete with one another in so doing. Another point of interest is how they modify the substrate until they are replaced by higher organisms.In the microbial field, communication between species has been described at various levels. Horizontally, it can take place between different bacteria or between various species of algae. Vertically, it may involve bacteria and planktonic algae, bacteria and protozoa, or algae and zooplanktonic organisms.Besides, the communication may be “positive”, if the mediator enhances the growth of the receiving organism — then, it is used as a source of carbon or nitrogen, or as a growth factor — or “negative” whenever the mediator is toxic (antibiotic, antiseptic or toxin) or induces a lethal metabolic modification in the receiver.In fact, there are various telemediation mechanisms, which correspond to increasing degrees of complexity in the biological systems: a primary mechanism, in which the mediator is synthetized by a species and controls (or modifies) the metabolism of another species in one step, and a secondary mechanism, where the mediator is synthetized by a species, and modifies the metabolism of another species; the latter, in turn, releases a primary mediator which controls the functions of a third species. This might be a longer sequence, involving a higher number of species.If the mechanism becomes cyclic, feedback may occur: as far as we know, such feedback may be either positive or negative ecologically, depending on whether it speeds up or slows down a biological process.A conception of a marine universe whose equilibrium would be controlled by the interaction of organisms within a more or less dense biotic network, with meshes made up of the relationship functions as a whole, is highly suggestive of an homology with cybernetic structures. Then, each marine organism can be considered as a separate functional unit characterized by some particular properties, its functions, which govern its activity. These units are involved in the functioning of complex and varying systems in which they intervene locally to channel up the flow of energy and matter to a given extent and in a given direction.The analogy is still more pronounced as there are feedbacks, which can control various sectors of the system. In a series of studies based on biological systems regulated by various chemical mediators, authors were able to demonstrate that the introduction of varied chemical pollutants into the marine environment entails modifications in the structure of the biological components of seawater and results in either the modification or the destruction of the mediating metabolites or “signals”. The result could be a more or less pronounced ecological drift, that varies according to the activity of the pollutant.  相似文献   

Detrital clay grain coats in estuarine clastic deposits: origin and spatial distribution within a modern sedimentary system,the Gironde Estuary (south‐west France)     

Maxime Virolle  Benjamin Brigaud  Raphaël Bourillot  Hugues Fnis  Eric Portier  Thibault Duteil  Julius Nouet  Patricia Patrier  Daniel Beaufort 《Sedimentology》2019,66(3):859-894

Porosity and permeability may be preserved in deep sandstone reservoirs by clay coating (mainly chlorite) which limits quartz overgrowths. Chloritization around quartz grains results mainly from mineralogical transformations of pre‐existing clays. It is fundamental to study those clay precursors to better understand and predict the location and distribution of clay coatings in subsurface sandstones for petroleum or geothermal prospecting. This paper reports a high‐resolution analysis of the composition, distribution and fabric of clays along a modern estuary, the Gironde (south‐west France). The scale of the study ranges from thin sections, through sand bar bodies, up to the entire estuary. Results show that clays are detrital and deposited at the same time as sand grains despite strong hydrodynamic conditions. Clays bind to medium‐grained sands forming detrital clay grain coats. On average, 26% of detrital sand grains are coated along the entire length of the estuary. Coat thickness varies from 1 μm to more than 200 μm, and coat coverage exceeds 30% in some samples. The turbidity maximum zone position (surface water turbidity from 1 to 10 g l^?1) in the estuary, which is controlled by seasonal variations in hydrodynamic processes, significantly impacts the location of the maximum clay content and the abundance of coated grains in sandy facies along the estuary. Flocculation in the water column results in the accumulation of suspended matter and contributes to the high turbidity in the estuary. Exopolymeric substances produced by diatoms are observed both in the field and by cryo‐scanning electron microscopy, suggesting that they may play a major role in binding detrital clay around sand grains. Finally, tidal bars and heterolithic point bars in the estuary funnel and estuarine channels are prime sedimentological targets for finding clay coatings and potentially good reservoir quality in deeply buried sandstones.  相似文献   

The magnetic structure of convection-driven numerical dynamos   总被引：1，自引：1，他引：0  

Julien Aubert  Jonathan Aurnou  Johannes Wicht 《Geophysical Journal International》2008,172(3):945-956

The generation of a magnetic field in numerical simulations of the geodynamo is an intrinsically 3-D and time-dependent phenomenon. The concept of magnetic field lines and the frozen-flux approximation can provide insight into such systems, but a suitable visualization method is required. This paper presents results obtained using the Dynamical Magnetic Field line Imaging (DMFI) technique, which is a representation of magnetic field lines accounting for their local magnetic energy, together with an algorithm for the time evolution of their anchor points. The DMFI illustrations are consistent with previously published dynamo mechanisms, and allow further investigation of spatially and temporally complex systems. We highlight three types of magnetic structures: (i) magnetic cyclones and (ii) magnetic anticyclones are expelled by, but corotate with axial flow vortices; (iii) magnetic upwellings are amplified by stretching and advection within flow upwellings, and show structural similarity with helical plumes found in rotating hydrodynamic experiments. While magnetic anticyclones are responsible for the regeneration of a stable axial dipole, here we show that excursions and reversals of the dipole axis are caused by the emergence of magnetic upwellings, which amplify and transport a generally multipolar magnetic field from the inner to the outer boundary of the models. Geomagnetic observations suggest the presence of magnetic structures similar to those found in our models; thus, we discuss how our results may pertain to Earth's core dynamo processes. In order to make DMFI a standard tool for numerical dynamo studies, a public software package is available upon request to the authors (supplementary material is available at: http://www.ipgp.jussieu.fr/~aubert/DMFI.html ).  相似文献   

Investigation of Transport Processes inside Karst Aquifer by Means of STATIS   总被引：1，自引：0，他引：1  

by M. Fournier  A. Motelay-Massei  N. Massei  M. Aubert  M. Bakalowicz  and J.P. Dupont 《Ground water》2009,47(3):391-400

Environmental data sets are often multidimensional and consequently display complex structure. This article shows the limitations of principal component analysis (PCA) for the study of such three-dimensional (3D) data sets. These limitations can be resolved by the use of the statistical tool STATIS. The inlet (a swallow hole) and the outlet (a spring) of a karst system of the Western Paris basin were sampled during three rain events of various intensities. These 3D geochemical data sets (variables × sites × dates) for a karst system were analyzed by STATIS method to identify hydrological processes. STATIS proceeds in three steps (interstructure, compromise, and intrastructure), which allows us to focus the analysis of hydrologic systems at different temporal and spatial scales. Compromise plane shows that suspended matter and flood are not simultaneous and highlights a rapid flow, characterized by turbidity and phosphate, which represents a point source contamination, and a ground water flow contaminated by nitrate. Intrastructure plane allows us to compare hydrochemical variations between the swallow hole and the spring lead. By this way, hydrological processes such as direct transfer and resuspension of intrakarstic sediments before and after the flood were identified what cannot be realized by comparison of inlet and outlet breakthrough curves. Finally, results obtained from the same data set by STATIS and a coupled study using PCA and normalized hysteresis curves were compared. This comparison shows the efficiency of STATIS at the identification of transport processes and vulnerability of karst system and its potential for hydrological applications.  相似文献   

ERORUN-STAFOR: A collaborative observatory for the multidisciplinary study of the critical zone processes in a tropical volcanic watershed including a Tropical Montane Cloud Forest     

Alix Toulier  Jean-Lambert Join  Pierre Staménoff  Yoan Benoit  Geneviève Lebeau  Maxime Gautier  Caroline Gorge  Eric Gayer  Emmanuel Cordier  Victor Kbidi  Guillaume Payen  Magali David  Sophie Ferreira  François Bonnardot  Julien Bonnier  Stéphane Martel  Jimmy Gonthier  Emilie Roulleau  Jean-Pierre Cammas  Dominique Strasberg  Olivier Flores  Fabrice R. Fontaine  Thomas Giambelluca  Claudine Ah-Peng 《水文研究》2024,38(2):e15061

Tropical volcanic islands are biodiversity hotspots where the Critical Zone (CZ) still remains poorly studied. In such steep topographic environments associated with extreme climatic events (cyclones), deployment and maintenance of monitoring equipment is highly challenging. While a few Critical Zone Observatories (CZOS) are located in tropical volcanic regions, none of them includes a Tropical Montane Cloud Forest (TMCF) at the watershed scale. We present here the dataset of the first observatory from the French network of critical zone observatories (OZCAR) located in an insular tropical and volcanic context, integrating a ‘Tropical Montane Cloud Forest’: The ERORUN-STAFOR observatory. This collaborative observatory is located in the northern part of La Réunion island (Indian Ocean) within the 45.0 km² watershed of Rivière des Pluies (i.e., Rainfall river) which hosts the TMCF of Plaines des Fougères, one of the best preserved natural habitats in La Réunion Island. Since 2014, the ERORUN-STAFOR monitoring in collaboration with local partners collected a multidisciplinary dataset with a constant improvement of the instrumentation over time. At the watershed scale and in its vicinity, the ERORUN-STAFOR observatory includes 10 measurement stations covering the upstream, midstream and downstream part of the watershed. The stations record a total of 48 different variables through continuous (sensors) or periodic (sampling) monitoring. The dataset consists of continuous time series variables related to (i) meteorology, including precipitation, air temperature, relative humidity, wind speed and direction, net radiation, atmospheric pressure, cloud water flux, irradiance, leaf wetness and soil temperature, (ii) hydrology, including water level and temperature, discharge and electrical conductivity (EC) of stream, (iii) hydrogeology, including (ground)water level, water temperature and EC in two piezometers and one horizontally drilled groundwater gallery completed by soil moisture measurements under the canopy. The dataset is completed by periodic time series variables related to (iv) hydrogeochemistry, including field parameters and water analysis results. The periodic sampling survey provides chemical and isotopic compositions of rainfall, groundwater, and stream water at different locations of this watershed. The ERORUN-STAFOR monitoring dataset extends from 2014 to 2022 with an acquisition frequency from 10 min to hourly for the sensor variables and from weekly to monthly frequency for the sampling. Despite the frequent maintenance of the monitoring sites, several data gaps exist due to the remote location of some sites and instrument destruction by cyclones. Preliminary results show that the Rivière des Pluies watershed is characterized by high annual precipitation (>3000 mm y⁻¹) and a fast hydrologic response to precipitation (≈2 h basin lag time). The long-term evolution of the deep groundwater recharge is mainly driven by the occurrence of cyclone events with a seasonal groundwater response. The water chemical results support existing hydrogeological conceptual models suggesting a deep infiltration of the upstream infiltrated rainfall. The TMCF of Plaine des Fougères shows a high water storage capacity (>2000% for the Bryophytes) that makes this one a significant input of water to groundwater recharge which still needs to be quantified. This observatory is a unique research site in an insular volcanic tropical environment offering three windows of observation for the study of critical zone processes through upstream-midstream-downstream measurements sites. This high-resolution dataset is valuable to assess the response of volcanic tropical watersheds and aquifers at both event and long-term scales (i.e., global change). It will also provide insights in the hydrogeological conceptual model of volcanic islands, including the significant role of the TMCFs in the recharge processes as well as the watershed hydrosedimentary responses to extreme climatic events and their respective evolution under changing climatic conditions. All data sets are available at https://doi.org/10.5281/zenodo.7983138 .  相似文献   

Magnetite‐out and pyrrhotite‐in temperatures in shales and slates     

Charles Aubourg  Mike Jackson  Maxime Ducoux  Mohannad Mansour 《地学学报》2019,31(6):534-539

Clay‐rich basins have undergone varying degrees of magnetic transformation during burial, affecting their ability to retain accurate records of Earth's dynamic magnetic field. We propose to bracket the magnetite‐out and pyrrhotite‐in temperatures in shales and slates from Taiwan and the Pyrenees by using a combination of low‐temperature magnetic transitions and geothermometers. For T_burial < 340°C, the magnetic assemblage is dominated by magnetite. Gradually with increasing burial temperature, the concentration of magnetite decreases to a few ppmv. We observe the magnetite‐out isograd at T_burial ~350°C. At T_burial >60°C and T_burial >340°C respectively, fine‐grained and coarse‐grained pyrrhotite develop. In the course of burial, a clay‐rich basin gradually loses its capability to retain a record of Earth's magnetic field. It is only during basin uplift, that coarse pyrrhotite might acquire a thermo remanent magnetization. Our results point out therefore highly contrasted magnetic properties and palaeomagnetic records between deeply buried basins and exhumed ones.  相似文献   

Non‐Destructive or Noninvasive? The Potential Effect of X‐Ray Fluorescence Spectrometers on Luminescence Age Estimates of Archaeological Samples     

Jillian Huntley  Kira E. Westaway  Damian B. Gore  Maxime Aubert  June Ross  Michael J. Morwood 《Geoarchaeology》2016,31(6):592-602

The non‐destructive nature of X‐ray fluorescence (XRF) spectrometers is a principal reason for an increase in their use in archaeological science over the last 15 years, especially for analyzing museum‐curated artifacts and in situ site fabrics. Here, we show that low‐power XRF spectrometry can be detrimental for luminescence dating (surface applications such as mud‐wasp nest dating in particular). We investigated the effects of irradiation by X‐rays emitted from handheld and benchtop spectrometers on optically stimulated luminescence (OSL) signals. Measurements were taken using a portable OSL (pOSL) unit on the following unprepared archaeological materials: sedimentary quartz grains, pottery, a mud‐wasp nest, stone tools, and a rock flake with anthropogenically applied pigment and natural pigmentation (iron oxides). We observed an increase in luminescence compared to initial background counts for all materials tested, which could lead to overestimation of age determinations in some situations. Our experiment provides a reminder of the potential effects of X‐ray radiation, and the need for thorough documentation of all recording and analytical techniques applied to archaeological materials.  相似文献   

On the limits of using combined U-series/ESR method to date fossil teeth from two Early Pleistocene archaeological sites of the Orce area (Guadix-Baza basin,Spain)     

Mathieu Duval  Christophe Falguères  Jean-Jacques Bahain  Rainer Grün  Qingfeng Shao  Maxime Aubert  Jean-Michel Dolo  Jordi Agustí  Bienvenido Martínez-Navarro  Paul Palmqvist  Isidro Toro-Moyano 《Quaternary Research》2012,77(3):482-491

The combined U-series/electron spin resonance (ESR) dating method was applied to nine teeth from two Early Pleistocene archaeological sites located in the Orce area (Guadix-Baza Basin, Southern Spain): Fuente Nueva-3 (FN-3) and Barranco León (BL). The combination of biostratigraphy and magnetostratigraphy places both sites between the Olduvai and Jaramillo subchrons (1.78–1.07 Ma).Our results highlight the difficulty of dating such old sites and point out the limits of the combined U-series/ESR dating method based on the US model. We identified several sources of uncertainties that may lead to inaccurate age estimates. Seven samples could not be dated because the dental tissues had (²³⁰Th/²³⁴U) activity ratios higher than equilibrium, indicating that uranium had probably leached from these tissues. It was however possible to calculate numerical estimates for two of the teeth, both from FN-3. One yielded a Middle Pleistocene age that seems to be strongly underestimated; the other provided an age of 1.19 ± 0.21 Ma, in agreement with data obtained from independent methods. The latter result gives encouragement that there are samples that can be used for routine dating of old sites.  相似文献   

Ensemble-Based Seismic and Production Data Assimilation Using Selection Kalman Model     

Conjard  Maxime  Grana  Dario 《Mathematical Geosciences》2021,53(7):1445-1468

Data assimilation in reservoir modeling often involves model variables that are multimodal, such as porosity and permeability. Well established data assimilation methods such as ensemble Kalman filter and ensemble smoother approaches, are based on Gaussian assumptions that are not applicable to multimodal random variables. The selection ensemble smoother is introduced as an alternative to traditional ensemble methods. In the proposed method, the prior distribution of the model variables, for example the porosity field, is a selection-Gaussian distribution, which allows modeling of the multimodal behavior of the posterior ensemble. The proposed approach is applied for validation on a two-dimensional synthetic channelized reservoir. In the application, an unknown reservoir model of porosity and permeability is estimated from the measured data. Seismic and production data are assumed to be repeatedly measured in time and the reservoir model is updated every time new data are assimilated. The example shows that the selection ensemble Kalman model improves the characterisation of the bimodality of the model parameters compared to the results of the ensemble smoother.

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Tinted windows: The presence of the UV absorbing compounds called mycosporine-like amino acids embedded in the frustules of marine diatoms     

Anitra E. Ingalls  Kenia Whitehead  Maxime C. Bridoux 《Geochimica et cosmochimica acta》2010,74(1):104-115

Diatom frustule-bound organic compounds presumably play an important role in biomineralization and constitute an important pool of organic matter preserved in diatom frustule-rich sediments. In this study, detailed analysis of diatom frustule-bound organic matter in opal-rich Southern Ocean plankton and sediments revealed for the first time the presence of low molecular weight, UV light absorbing compounds called mycosporine-like amino acids (MAAs). Chemically cleaned diatom frustule-derived biosilica was dissolved in HF, releasing bound or entrapped organic compounds that were subsequently characterized using liquid chromatography with UV-Vis and electrospray ionization mass spectrometry (LC/PDA/ESI-MS). Palythine ([M+H]⁺ = 245), porphyra-334 ([M+H]⁺ = 347) and shinorine ([M+H]⁺ = 333) were the most abundant MAAs detected in HF digests of plankton and sediment. Traces of asterina ([M+H]⁺ = 289), palythinol ([M+H]⁺ = 303) and palythinic acid ([M+H]⁺ = 329) were also detected. MAAs in cleaned HF digested frustules were up to two orders of magnitude more abundant than methanol extractable MAAs. MAAs are substituted with acid hydrolysable amino acid residues. Our results suggest that MAAs, and not proteins, could be responsible for the high proportion of the amino acids glycine and threonine found in hydrolysates of HF digested diatom-rich environmental samples. Total MAAs accounted for 3-27% of the carbon and 2-18% of total nitrogen in the frustules undergoing various chemical cleaning treatments. This is the first report of MAAs in close association with a mineral phase and we hypothesize that the mineral matrix could stabilize these compounds, thereby enhancing photoprotection against the harmful effects of UV light. The presence of frustule-bound MAAs in sediment cores further suggests the possibility that they could be used in compound-specific isotope analysis of diatom-bound organic matter and as indicators of past solar irradiance.  相似文献