Plankton community structure in response to hydrothermal iron inputs along the Tonga-Kermadec arc

The Western Tropical South Pacific (WTSP) basin has been identified as a hotspot of atmospheric dinitrogen fixation due to the high dissolved iron ([DFe]) concentrations (up to 66 nM) in the photic layer linked with the release of shallow hydrothermal fluids along the Tonga-Kermadec arc. Yet, the effect of such hydrothermal fluids in structuring the plankton community remains poorly studied. During the TONGA cruise (November-December 2019), we collected micro- (20-200 μm) and meso-plankton (>200 μm) samples in the photic layer (0-200 m) along a west to east zonal transect crossing the Tonga volcanic arc, in particular two volcanoes associated with shallow hydrothermal vents (< 500 m) in the Lau Basin, and both sides of the arc represented by Melanesian waters and the South Pacific Gyre. Samples were analyzed by quantitative imaging (FlowCam and ZooScan) and then coupled with acoustic observations, allowing us to study the potential transfer of phytoplankton blooms to higher planktonic trophic levels. We show that micro- and meso-plankton exhibit high abundances and biomasses in the Lau Basin and, to some extent, in Melanesian waters, suggesting that shallow hydrothermal inputs sustain the planktonic food web, creating productive waters in this otherwise oligotrophic region. In terms of planktonic community structure, we identified major changes with high [DFe] inputs, promoting the development of a low diversity planktonic community dominated by diazotrophic cyanobacteria. Furthermore, in order to quantify the effect of the shallow hydrothermal vents on chlorophyll a concentrations, we used Lagrangian dispersal models. We show that chlorophyll a concentrations were significantly higher inside the Lagrangian plume, which came into contact with the two hydrothermal sites, confirming the profound impact of shallow hydrothermal vents on plankton production

Inter-comparaison des mesures de courant dans l'Atlantique Tropical

The present reports contains the results of a study designed to compare the current measurements from various sensors (ARGO floats, Drifters, Buoys sensors, ADCP) in Tropical Atlantic in order to estimate their complementarity and to analyse the seasonal cycle of surface and deep currents in the area.Ce rapport présente les résultats d'une étude visant à comparer les mesures de courant réalisées par différents capteurs (flotteurs ARGO, Drifters, Bouées fixes, ADCP) dans l'Altantique Tropical afin d'estimer leur complémentarité et d'analyser le cycle saisonnier des courants de surface et de fond dans la région

Multifrequency acoustics measurements during the PIRATA FR25 cruise in the Eastern Tropical Atlantic Ocean

International Conference AWA (ICAWA), Dakar, SEN, 17-/11/2015 - 19/11/201

Multifrequency acoustics measurements during the PIRATA FR25 cruise in the Eastern Tropical Atlantic Ocean

International Conference AWA (ICAWA), Dakar, SEN, 17-/11/2015 - 19/11/201

Multifrequency acoustics measurements during the PIRATA FR25 cruise in the Eastern tropical Atlantic Ocean [résumé]

PREFACE-PIRATA-CLIVAR Tropical Atlantic Variability Conference, Cape Town, ZAF, 25-/08/2015 - 27/08/2015Acoustic tools allow a simultaneous acquisition of quantitative and qualitative data at different spatio-temporal scales, providing information about biotic and abiotic ecosystem components. For the first time in 18 years history, a PIRATA cruise allowed to get such measurements in the Eastern tropical Atlantic, from Cabo-Verde islands to the equator and in the Gulf of Guinea. We present here first data sets acquired during the Pirata-FR25 cruise and some preliminary results. Several potential scientific analyses could be carried out using such data in the general framework of PREFACE, AWA & PIRATA programs. Such data will allow calibrating and validating ecosystem model developed in the Gulf of Guinea, taking into account the mesopelagiccompartment. The organization of the micronekton layers could be described including diel vertical migration taking into account hydrological parameters and currents vertical distributions. Lastly, such data will allow characterizing the micronekton layers according to equatorial zonal currents system as well as inside the Guinea Dome. Along the survey path several other oceanographic structures were susceptible to trigger an effect on micronektonic layers as the contrasted salinity (32 to 36 ?) within the Gulf of Guinea, oceanic fronts and Tropical instability waves

Multifrequency acoustics measurements during the PIRATA FR25 cruise in the Eastern tropical Atlantic Ocean [résumé]

PREFACE-PIRATA-CLIVAR Tropical Atlantic Variability Conference, Cape Town, ZAF, 25-/08/2015 - 27/08/2015Acoustic tools allow a simultaneous acquisition of quantitative and qualitative data at different spatio-temporal scales, providing information about biotic and abiotic ecosystem components. For the first time in 18 years history, a PIRATA cruise allowed to get such measurements in the Eastern tropical Atlantic, from Cabo-Verde islands to the equator and in the Gulf of Guinea. We present here first data sets acquired during the Pirata-FR25 cruise and some preliminary results. Several potential scientific analyses could be carried out using such data in the general framework of PREFACE, AWA & PIRATA programs. Such data will allow calibrating and validating ecosystem model developed in the Gulf of Guinea, taking into account the mesopelagiccompartment. The organization of the micronekton layers could be described including diel vertical migration taking into account hydrological parameters and currents vertical distributions. Lastly, such data will allow characterizing the micronekton layers according to equatorial zonal currents system as well as inside the Guinea Dome. Along the survey path several other oceanographic structures were susceptible to trigger an effect on micronektonic layers as the contrasted salinity (32 to 36 ?) within the Gulf of Guinea, oceanic fronts and Tropical instability waves

Manuel de l'utilisateur de Matecho : version 05

Un article relatif à une version précédente de ce manuel a été publié dans :Perrot, Y., Brehmer, P., Habasque, J., Roudaut, G., Béhagle, N., Sarre, A., and Lebourges-Dhaussy, A. 2018. Matecho: An Open-Source Tool for Processing Fisheries Acoustics Data. Acoust. Aust. 46(2): 241–248. doi:10.1007/s40857-018-0135-x.Matecho is an integrated and supervised Matlab processing chain, which allows realizing scientific echo-sounder data treatments. It allows applying, under user control, recent echo-sounder data processing methods needed to prepare and present acoustic data to their analysis and interpretation in the field of fisheries acoustics researches.Matecho est une chaîne de traitement Matlab intégrée et supervisée, qui permet de réaliser des traitements de données d'échosondeurs scientifiques. Elle permet d'appliquer, sous le contrôle de l'utilisateur, les méthodes récentes de traitement des données d'échosondeurs nécessaires à la préparation et à la présentation des données acoustiques pour leur analyse et leur interprétation dans le domaine de la recherche en acoustique des pêches

The Concept of “Pelagic metapopulation” as exemplified by the case of jack mackerel Trachurus murphyi in the South Pacific Ocean

International audienceno abstrac

Observations of plankton communities in the Senegalese upwelling system

International Conference AWA (ICAWA), Dakar, SEN, 17-/11/2015 - 19/11/201

Observations of plankton communities in the Senegalese upwelling system

International Conference AWA (ICAWA), Dakar, SEN, 17-/11/2015 - 19/11/201