Pompe biologique

Résumé

Dans la biogéochimie des océans, la pompe biologique, qui relève du cycle du carbone océanique, est une série de processus biologiques conduisant à transporter le carbone de la zone photique vers les fonds marins. C'est un élément majeur du cycle du carbone. Grâce à cette pompe, l'océan a ainsi depuis le début de l'ère industrielle pu absorber 41 % du carbone anthropique émis par la consommation des énergies fossiles et la fabrication du ciment. Vue d'ensemble L'ampleur et la distribution à grande échelle du puits de carbone océanique commencent à être mieux quantifiées et géolocalisées (au moins pour la fin du et début du ). Mais en raison de rétroactions écologiques hautement complexes, les changements temporels historiques et futurs dans l'intensité et la géographie du phénomène de pompage océanique du carbone restent respectivement mal compris et difficilement prédictibles. En particulier, jusqu'à il y a peu, il était très difficile de distinguer les effets des chan

Source officielle

https://fr.wikipedia.org/wiki/Pompe_biologique

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Characterization of bacterial communities in Lake Geneva by comparing genetic and physiological methods

Coralie Chappelier

Over the last century, the level of atmospheric CO2 has increased to the highest concentrations on Earth within the past 800'000 years. Current predictions anticipate that the effects of greenhouse gases will lead to a rise in air temperature ranging between 1.4 and 5.8°C. Oceans and freshwater ecosystems absorb large quantities of CO2, but are sensitive to global climate change that directly influences water temperature and pH. Specifically, phytoplankton accounts for approximately 50% of the total photosynthesis on Earth, and contributes to the mobilization of CO2 through sinking or transferring fixed carbon to deeper water layers and sediments. Bacteria are among the most abundant entities in plankton and play a major role on the biological pump for the cycling of carbon and other elements. In order to understand and anticipate the response of aquatic ecosystems to climate change, we need to characterize how planktonic organisms respond and adapt to environmental change. In this project, we will merge microbial ecology and genomics with the ultimate goals of (i) characterizing current ecological niches of the operational taxonomic units highlighted in bacteria populations of Lake Geneva, (ii) identifying candidate adaptive genes responsible for adaptation of freshwater bacterial communities to contrasting freshwater habitats, (iii) projecting current bacteria distributions as a function of the expected change and (iv) identifying possible alterations in ecosystem functioning and services as a function of climate change. By doing this, we expect to contribute expanding our ability to characterize ecological niches using genetic data and sensitizing society about the importance of protecting freshwater ecosystems.

2020

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Unicellular algae play important roles in the biogeochemical cycles of numerous elements, particularly through the biomineralization capacity of certain species (e.g., coccolithophores greatly contributing to the "organic carbon pump" of the oceans), and unidentified actors of these cycles are still being discovered. This is the case of the unicellular alga Tetraselmis cordiformis (Chlorophyta) that was recently discovered to form intracellular mineral inclusions, called micropearls, which had been previously overlooked. These intracellular inclusions of hydrated amorphous calcium carbonates (ACCs) were first described in Lake Geneva (Switzerland) and are the result of a novel biomineralization process. The genus Tetraselmis includes more than 30 species that have been widely studied since the description of the type species in 1878. The present study shows that many other Tetraselmis species share this biomineralization capacity: 10 species out of the 12 tested contained micropearls, including T. chui, T. convolutae, T. levis, T. subcordiformis, T. suecica and T. tetrathele. Our results indicate that micropearls are not randomly distributed inside the Tetraselmis cells but are located preferentially under the plasma membrane and seem to form a definite pattern, which differs among species. In Tetraselmis cells, the biomineralization process seems to systematically start with a rod-shaped nucleus and results in an enrichment of the micropearls in Sr over Ca (the Sr/Ca ratio is more than 200 times higher in the micropearls than in the surrounding water or growth medium). This concentrating capacity varies among species and may be of interest for possible bioremediation techniques regarding radioactive Sr-90 water pollution. The Tetraselmis species forming micropearls live in various habitats, indicating that this novel biomineralization process takes place in different environments (marine, brackish and freshwater) and is therefore a widespread phenomenon.

COPERNICUS GESELLSCHAFT MBH2018

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Organic matter decomposition: bridging the gap between Rock-Eval pyrolysis and chemical characterization (CPMAS C-13 NMR)

Remy Jean Henry Albrecht

Organic matter (OM) is a key component of soils but information on its chemistry and behavior in soils is still incomplete. Numerous methods are commonly used to characterize and monitor OM dynamics, but only a few include the qualities required to become routine techniques i.e. simple, rapid, accurate and at low cost. Rock-Eval pyrolysis (RE pyrolysis) is a good candidate, as it provides an overview of OM properties by monitoring four components related to the main major classes of organic constituents (from A1 for the labile biological constituents to A4 for the mature refractory fraction). However, a question is still pending: do these four major classes used in the literature reflect a pertinent compositional chemical counterpart? C-13 Nuclear Magnetic Resonance Spectroscopy in the solid state (C-13 CPMAS NMR) has been used to answer this question by collecting information on structural and conformational characteristics of OM. Moreover, in order to avoid the blurring effect of pedogenesis on OM dynamics, a "less complex OM" source, i.e. compost samples, has been used. Results showed significant and high determination coefficients between classes, indices (of transformation of plant biopolymers, humificationaEuro broken vertical bar) from RE pyrolysis, and the main classes of OM characterized by C-13 NMR, e.g. A1 & A2 with labile/easily degradable components (alkyl C et O-alkyl C), A3 & A4 with humified OM (with aromatic C and phenolic C). The R index (contribution of bio-macromolecules) is correlated with phenolic and aromatic C, whereas the I index (related to immature OM) refers to labile--easily degradable components (alkyl C et O-alkyl C). The results confirm the pertinence of RE pyrolysis to monitor OM dynamics.

Springer2015

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COPERNICUS GESELLSCHAFT MBH2018