Basin-scale spatio-temporal variability and control of phytoplankton photosynthesis in the Baltic Sea: The first multiwavelength fast repetition rate fluorescence study operated on a ship-of-opportunity

This study presents the results of the first field application of a flow-through multi-wavelength Fast Repetition Rate fluorometer (FRRF) equipped with two excitation channels (458 and 593 nm). This device aims to improve the measurement of mixed cyanobacteria and algae community's photosynthetic parameters and was designed to be easily incorporated into existing ferrybox systems. We present a spatiotemporal analysis of the maximum photochemical efficiency (Fv/Fm) and functional absorption cross section (σPSII) recorded from April to August 2014 on a ship-of-opportunity commuting twice per week between Helsinki (Finland) and Travemünde (Germany). Temporal variations of Fv/Fm and σPSII differed between areas of the Baltic Sea. However, even though the Baltic Sea is characterized by several physico-chemical gradients, no gradient was observed in Fv/Fm and σPSII spatial distribution suggesting complex interactions between biotic and abiotic controls. σPSII was sensitive to phytoplankton seasonal succession and thus differed according to the wavelength used to excite photosystems II (PSII) pigments. This was particularly true in summer when high σPSII(593) values were observed later and longer than high σPSII(458) values, reflecting the role of cyanobacteria in photosynthetic light uptake measured at community scale. In contrast, Fv/Fm variations were similar after excitation at 458 nm or 593 nm suggesting that the adjustment of Fv/Fm in response to environmental factors was similar for the different groups (algae vs. cyanobacteria) present within the phytoplankton community

Contrôle de l’activité photosynthétique du phytoplancton en milieu côtier : utilisation de la fluorescence spectrale et de la fluorimétrie modulée

Dynamics of phytoplankton photosynthetic activity were characterised in a macrotidal coastal ecosystem (the Strait of Dover, eastern English Channel) and related to environmental conditions. Spatial and temporal variability of photosynthetic parameters were studied at different scales, between September 2008 and August 2010. The level of variability and controlling factors of photosynthetic parameters depend on the scale considered. In space, no gradient of photosynthetic parameters was found between coastal and offshore waters. By contrast, within the water column, variations of the maximum quantum yield (Fv/Fm), the maximum electron transport rate (ETRm) and the light saturation coefficient (Ek) in relation to the light history of cells were observed. At short time scale (from hour to the scale of a neap-spring tide cycle), considerable variations of photosynthetic parameters were observed. Light conditions, temperature and nutrient availability were the main controlling factors. At longer time scale (from fortnightly to inter-annual scales), Fv/Fm, α (the maximal light utilization efficiency) and ETRm varied without any clear seasonal cycle. By contrast, Ek followed the seasonal variations of light except during summer where its changes of Ek were small compared to the light variability. At these time scales, close interplays between shifts of phytoplankton communities and changes of light, temperature and nutrient availability controlled the variability of photosynthetic parameters.Les dynamiques de l’activité photosynthétique du phytoplancton ont été caractérisées dans un écosystème côtier macrotidal (le Détroit du Pas-de-Calais, Manche orientale) et associées aux conditions environnementales. La variabilité spatiale et temporelle des paramètres photosynthétiques a été étudiée à différentes échelles, entre Septembre 2008 et Août 2010. Le niveau de variabilité et les facteurs de contrôle des paramètres photosynthétiques dépendent de l’échelle considérée. Au niveau spatial, aucun gradient des paramètres photosynthétiques n’a été trouvé entre la côte et le large. A l’inverse, au sein de la colonne d’eau, des variations du rendement quantique maximum (Fv/Fm), du taux de transport maximum des électrons (ETRm) et du coefficient de saturation lumineuse (Ek), en lien avec l’histoire lumineuse des cellules, ont été observées. Aux courtes échelles de temps (de l’heure à l’échelle d’un cycle de marée morte-eau/vive-eau), des variations considérables des paramètres photosynthétiques ont été observées. Les conditions lumineuses et la disponibilité des nutriments étaient les principaux facteurs de contrôle. Aux plus grandes échelles de temps (de l’échelle semi-mensuelle à l’échelle pluriannuelle), Fv/Fm, α (l’efficacité maximale d’utilisation de la lumière) et ETRm variaient sans cycle saisonnier clair. Par opposition, Ek suivait le cycle saisonnier de la lumière. A ces échelles, les interactions entre les successions des communautés phytoplanctoniques et les changements de lumière, de température et de disponibilité en nutriments contrôlaient la variabilité de l’activité photosynthétique

Contrôle de l’activité photosynthétique du phytoplancton en milieu côtier : utilisation de la fluorescence spectrale et de la fluorimétrie modulée

Dynamics of phytoplankton photosynthetic activity were characterised in a macrotidal coastal ecosystem (the Strait of Dover, eastern English Channel) and related to environmental conditions. Spatial and temporal variability of photosynthetic parameters were studied at different scales, between September 2008 and August 2010. The level of variability and controlling factors of photosynthetic parameters depend on the scale considered. In space, no gradient of photosynthetic parameters was found between coastal and offshore waters. By contrast, within the water column, variations of the maximum quantum yield (Fv/Fm), the maximum electron transport rate (ETRm) and the light saturation coefficient (Ek) in relation to the light history of cells were observed. At short time scale (from hour to the scale of a neap-spring tide cycle), considerable variations of photosynthetic parameters were observed. Light conditions, temperature and nutrient availability were the main controlling factors. At longer time scale (from fortnightly to inter-annual scales), Fv/Fm, α (the maximal light utilization efficiency) and ETRm varied without any clear seasonal cycle. By contrast, Ek followed the seasonal variations of light except during summer where its changes of Ek were small compared to the light variability. At these time scales, close interplays between shifts of phytoplankton communities and changes of light, temperature and nutrient availability controlled the variability of photosynthetic parameters.Les dynamiques de l’activité photosynthétique du phytoplancton ont été caractérisées dans un écosystème côtier macrotidal (le Détroit du Pas-de-Calais, Manche orientale) et associées aux conditions environnementales. La variabilité spatiale et temporelle des paramètres photosynthétiques a été étudiée à différentes échelles, entre Septembre 2008 et Août 2010. Le niveau de variabilité et les facteurs de contrôle des paramètres photosynthétiques dépendent de l’échelle considérée. Au niveau spatial, aucun gradient des paramètres photosynthétiques n’a été trouvé entre la côte et le large. A l’inverse, au sein de la colonne d’eau, des variations du rendement quantique maximum (Fv/Fm), du taux de transport maximum des électrons (ETRm) et du coefficient de saturation lumineuse (Ek), en lien avec l’histoire lumineuse des cellules, ont été observées. Aux courtes échelles de temps (de l’heure à l’échelle d’un cycle de marée morte-eau/vive-eau), des variations considérables des paramètres photosynthétiques ont été observées. Les conditions lumineuses et la disponibilité des nutriments étaient les principaux facteurs de contrôle. Aux plus grandes échelles de temps (de l’échelle semi-mensuelle à l’échelle pluriannuelle), Fv/Fm, α (l’efficacité maximale d’utilisation de la lumière) et ETRm variaient sans cycle saisonnier clair. Par opposition, Ek suivait le cycle saisonnier de la lumière. A ces échelles, les interactions entre les successions des communautés phytoplanctoniques et les changements de lumière, de température et de disponibilité en nutriments contrôlaient la variabilité de l’activité photosynthétique

Control of phytoplankton photosynthetic activity in coastal system : use of spectral fluorescence and modulated fluorometry

Les dynamiques de l’activité photosynthétique du phytoplancton ont été caractérisées dans un écosystème côtier macrotidal (le Détroit du Pas-de-Calais, Manche orientale) et associées aux conditions environnementales. La variabilité spatiale et temporelle des paramètres photosynthétiques a été étudiée à différentes échelles, entre Septembre 2008 et Août 2010. Le niveau de variabilité et les facteurs de contrôle des paramètres photosynthétiques dépendent de l’échelle considérée. Au niveau spatial, aucun gradient des paramètres photosynthétiques n’a été trouvé entre la côte et le large. A l’inverse, au sein de la colonne d’eau, des variations du rendement quantique maximum (Fv/Fm), du taux de transport maximum des électrons (ETRm) et du coefficient de saturation lumineuse (Ek), en lien avec l’histoire lumineuse des cellules, ont été observées. Aux courtes échelles de temps (de l’heure à l’échelle d’un cycle de marée morte-eau/vive-eau), des variations considérables des paramètres photosynthétiques ont été observées. Les conditions lumineuses et la disponibilité des nutriments étaient les principaux facteurs de contrôle. Aux plus grandes échelles de temps (de l’échelle semi-mensuelle à l’échelle pluriannuelle), Fv/Fm, α (l’efficacité maximale d’utilisation de la lumière) et ETRm variaient sans cycle saisonnier clair. Par opposition, Ek suivait le cycle saisonnier de la lumière. A ces échelles, les interactions entre les successions des communautés phytoplanctoniques et les changements de lumière, de température et de disponibilité en nutriments contrôlaient la variabilité de l’activité photosynthétique.Dynamics of phytoplankton photosynthetic activity were characterised in a macrotidal coastal ecosystem (the Strait of Dover, eastern English Channel) and related to environmental conditions. Spatial and temporal variability of photosynthetic parameters were studied at different scales, between September 2008 and August 2010. The level of variability and controlling factors of photosynthetic parameters depend on the scale considered. In space, no gradient of photosynthetic parameters was found between coastal and offshore waters. By contrast, within the water column, variations of the maximum quantum yield (Fv/Fm), the maximum electron transport rate (ETRm) and the light saturation coefficient (Ek) in relation to the light history of cells were observed. At short time scale (from hour to the scale of a neap-spring tide cycle), considerable variations of photosynthetic parameters were observed. Light conditions, temperature and nutrient availability were the main controlling factors. At longer time scale (from fortnightly to inter-annual scales), Fv/Fm, α (the maximal light utilization efficiency) and ETRm varied without any clear seasonal cycle. By contrast, Ek followed the seasonal variations of light except during summer where its changes of Ek were small compared to the light variability. At these time scales, close interplays between shifts of phytoplankton communities and changes of light, temperature and nutrient availability controlled the variability of photosynthetic parameters

Augmented Focus Groups: On Leveraging the Peculiarities of Online Virtual Worlds when Conducting In-World Focus Groups

Increasingly, academic researchers and practitioners have been using online 3D virtual worlds such as Second Life (SL) to conduct focus groups. When doing so, researchers and practitioners have copied and pasted as is, in this new environment, the qualitative methodologies commonly used in real-world focus groups. However, the relevance of using standard focus group methodologies within an online virtual environment has been neither tested, nor the focus of previous research. In addition, online virtual worlds may offer new methodological opportunities that, so far, have been left unexplored. To fill in this methodological gap, the authors have moderated various focus groups in Second Life. When doing so, they tested the limitations inherent to using real-world protocols in an online virtual environment. During the course of this project, it became clear that the usual focus group protocols should be adapted to the peculiar context, if one wants to fully leverage this new medium. As a result, new online qualitative methodologies (e.g., 3D collages) were developed and tested during this research project

Utilisation des Rapid Light Curves (RLC) et des Steady State Light Curves (SSLC) pour la caractérisation in situ de l'activité photosynthétique du phytoplancton

L'utilisation des rapid light curves (RLC) et des steady state light curves (SSLC), pour la caractérisation in situ de l'activité photosynthétique du phytoplancton, à différentes échelles de temps, a été comparée. La possibilité d'utiliser les paramètres photosynthétiques des RLC pour prédire ceux de SSLC a été évaluée. Les résultats montrent que les RLC sont un bon outil pour la caractérisation de l'activité photosynthétique à différentes échelles temporelle

Electrical conductivity and temperature of the Earth's mantle inferred from Bayesian inversion of Swarm vector magnetic data

International audienceStudy of induced magnetic field is a powerful way to sound Earth internal structure. This work presents a full analysis and interpretation in terms of electrical conductivity and temperature of vector magnetic field measurements from Swarm Level1b data product from 26/11/2013 to 31/12/2019. Time series of the Gauss coefficients associated with the induced and inducing magnetic field are obtained from the data after removal of the core and lithospheric fields models and data selection. A Bayesian inversion of the induced field Gauss coefficients is then performed to obtain a new estimate of Earth's 1D mantle electrical conductivity down to 2000 km depth. This profile is fully compatible with the profiles derived from satellite and ground magnetic observatories data but does not present in the lower mantle the increase predicted by laboratory-based conductivity profile associated to classical mantle composition and temperature profile. Using the most recent database to model the electrical conductivity of all mineral mantle phases, two different methods are used to interpret Swarm data in terms of temperature for a given composition and water content. The first one is based on an interpretation of the conductivity estimates in terms of temperature by classical numerical root search. The second one consists in inferring a temperature probability density function from a Bayesian inversion of the Gauss coefficients associated to the induced magnetic field. Our results show that the later provide more reliable estimates of mantle temperatures, in relation to more physically grounded prior values. This second method provides also tighter constraints on the electrical conductivity estimates of the lower mantle

Rapid light curves (RLC) or non-sequential steady-state light curves (N-SSLC): which fluorescence-based light response curve methodology robustly characterizes phytoplankton photosynthetic activity and acclimation status?

This study is the first in situ work comparing rapid light curves (RLC) and non-sequential steady-state light curves (N-SSLC) in their efficiency to characterize phytoplankton photosynthetic activity and acclimation status. Measurements were carried out at two time scales (daily and annual) using the Pulse Amplitude Modulated fluorometry on samples taken in the coastal waters of a macrotidal ecosystem (the Strait of Dover, eastern English Channel). RLC and N-SSLC were compared under a wide range of environmental conditions and phytoplankton composition in order to define the best methodology to accurately capture short and long-term adjustments in the functioning of the photosynthetic apparatus. The relationships between the photosynthetic parameters extracted from RLC and N-SSLC were also studied to evaluate the possibility to use RLC to predict N-SSLC photosynthetic parameters and thus obtaining the acclimation status at steady state. At daily scale, the maximum electron transport rate and light saturation coefficient resulting from RLC (respectively, ETRm_RLC and Ek_RLC) were found to follow more closely short-term environmental light variations than ETRm and Ek resulting from N-SSLC (ETRm_N-SSLC and Ek_N-SSLC) did. RLC were thus able to detect rapid changes in photosynthetic activity that would have been overlooked with N-SSLC measurements. At annual scale, few differences were found between RLC and N-SSLC. Variations of ETRm and α derived from RLC and N-SSLC were very similar but absolute values were lower for RLC measurements. Because, at daily scale, RLC better capture the short-term changes in photosynthetic activity than N-SSLC do, using RLC to predict N-SSLC photosynthetic parameters and getting information about steady-state acclimation status is not possible at this time scale. However, this can be done at seasonal scale

Examen échographique de l'articulation métacarpo-phalangienne. Corrélation signes échographiques - lésions

peer reviewedThis paper is the result of an ex-vivo study on ultrasonography of the equine fetlock. Abnormal findings in equine isolated limbs have been compared to macroscopic findings after dissections and sensitivity and specificity of the technique have been calculated

On the conditions promoting Pseudo-nitzschia spp. blooms in the eastern English Channel and southern North Sea

International audienceThis study investigated the drivers of the blooms of Pseudo-nitzschia seriata and Pseudo-nitzschia delicatissima complexes in the eastern English Channel and southern North Sea. Phytoplankton data series acquired from 1992 to 2020 were analyzed with a multivariate statistical approach based on Hutchinson's niche concept. P. seriata and P. delicatissima complexes were found to be typically present year round, but they bloomed at different periods because they occupied different realized ecological niches. P. delicatissima complex occupied a more marginal niche and was less tolerant than P. seriata complex. P. delicatissima complex typically bloomed in April-May at the same time as Phaeocystis globosa while P. seriata complex blooms were more frequently observed in June during the decline of low intensity P. globosa blooms. P. delicatissima and P. seriata complexes were both favored by low-silicate environments and relatively low turbulence but they responded differently to water temperature, light, ammonium, phosphate and nitrite + nitrate conditions. Niche shifts and biotic interactions played important roles in the control of the blooms of P. delicatissima and P. seriata complexes. The two complexes occupied different sub-niches during their respective low abundance and bloom periods. The phytoplankton community structure and the number of other taxa presenting a niche overlapping the niches of P. delicatissima and P. seriata complexes also differed between these periods. P. globosa was the taxa contributing the most to the dissimilarity in community structure. P. globosa interacted positively with P. delicatissima complex and negatively with P. seriata complex