Institut Pytheas

Critical measurements for understanding accretion and the dust/gas ratio in the solar nebula, where planets were forming 4.5 billion years ago, are being obtained by the GIADA (Grain Impact Analyser and Dust Accumulator) experiment on the European Space Agency's Rosetta spacecraft orbiting comet 67P/Churyumov-Gerasimenko. Between 3.6 and 3.4 astronomical units inbound, GIADA and OSIRIS (Optical, Spectroscopic, and Infrared Remote Imaging System) detected 35 outflowing grains of mass 10(-10) to 10(-7) kilograms, and 48 grains of mass 10(-5) to 10(-2) kilograms, respectively. Combined with gas data from the MIRO (Microwave Instrument for the Rosetta Orbiter) and ROSINA (Rosetta Orbiter Spectrometer for Ion and Neutral Analysis) instruments, we find a dust/gas mass ratio of 4 ± 2 averaged over the sunlit nucleus surface. A cloud of larger grains also encircles the nucleus in bound orbits from the previous perihelion. The largest orbiting clumps are meter-sized, confirming the dust/gas ratio of 3 inferred at perihelion from models of dust comae and trails.

The science guiding the EUREC 4 A campaign and its measurements is presented. EUREC 4 A comprised roughly 5 weeks of measurements in the downstream winter trades of the North Atlantic – eastward and southeastward of Barbados. Through its ability to characterize processes operating across a wide range of scales, EUREC 4 A marked a turning point in our ability to observationally study factors influencing clouds in the trades, how they will respond to warming, and their link to other components of the earth system, such as upper-ocean processes or the life cycle of particulate matter. This characterization was made possible by thousands (2500) of sondes distributed to measure circulations on meso- (200 km) and larger (500 km) scales, roughly 400 h of flight time by four heavily instrumented research aircraft; four global-class research vessels; an advanced ground-based cloud observatory; scores of autonomous observing platforms operating in the upper ocean (nearly 10 000 profiles), lower atmosphere (continuous profiling), and along the air–sea interface; a network of water stable isotopologue measurements; targeted tasking of satellite remote sensing; and modeling with a new generation of weather and climate models. In addition to providing an outline of the novel measurements and their composition into a unified and coordinated campaign, the six distinct scientific facets that EUREC 4 A explored – from North Brazil Current rings to turbulence-induced clustering of cloud droplets and its influence on warm-rain formation – are presented along with an overview of EUREC 4 A's outreach activities, environmental impact, and guidelines for scientific practice. Track data for all platforms are standardized and accessible at https://doi.org/10.25326/165 (Stevens, 2021), and a film documenting the campaign is provided as a video supplement.

5 pages, 1 figure.-- The MME-T-MEDNet databased was published in the Digital.CSIC repository. DOI: http://dx.doi.org/10.20350/digitalCSIC/8575. \nHANDLE: http://hdl.handle.net/10261/171445

Journal of Operational OceanographyVolume 12 Supplement 1 August 2019CONTENTSChapter 1: Introduction s11.1 Trends over the past decades s31.2 Anomalies and extreme events s6Chapter 2: S...

Global fossil fuel carbon dioxide (FFCO 2 ) emissions will be dictated to a great degree by the trajectory of emissions from urban areas. Conventional methods to quantify urban FFCO 2 emissions typically rely on self-reported economic/energy activity data transformed into emissions via standard emission factors. However, uncertainties in these traditional methods pose a roadblock to implementation of effective mitigation strategies, independently monitor long-term trends, and assess policy outcomes. Here, we demonstrate the applicability of the integration of a dense network of greenhouse gas sensors with a science-driven building and street-scale FFCO 2 emissions estimation through the atmospheric CO 2 inversion process. Whole-city FFCO 2 emissions agree within 3% annually. Current self-reported inventory emissions for the city of Indianapolis are 35% lower than our optimal estimate, with significant differences across activity sectors. Differences remain, however, regarding the spatial distribution of sectoral FFCO 2 emissions, underconstrained despite the inclusion of coemitted species information.

Surface ocean phosphate is commonly below the standard analytical detection limits, leading to an incomplete picture of the global variation and biogeochemical role of phosphate. A global compilation of phosphate measured using high-sensitivity methods revealed several previously unrecognized low-phosphate areas and clear regional differences. Both observational climatologies and Earth system models (ESMs) systematically overestimated surface phosphate. Furthermore, ESMs misrepresented the relationships between phosphate, phytoplankton biomass, and primary productivity. Atmospheric iron input and nitrogen fixation are known important controls on surface phosphate, but model simulations showed that differences in the iron-to-macronutrient ratio in the vertical nutrient supply and surface lateral transport are additional drivers of phosphate concentrations. Our study demonstrates the importance of accurately quantifying nutrients for understanding the regulation of ocean ecosystems and biogeochemistry now and under future climate conditions.

Context.Until recently, camera networks designed for monitoring fireballs worldwide were not fully automated, implying that in case of a meteorite fall, the recovery campaign was rarely immediate. This was an important limiting factor as the most fragile – hence precious – meteorites must be recovered rapidly to avoid their alteration. Aims.The Fireball Recovery and InterPlanetary Observation Network (FRIPON) scientific project was designed to overcome this limitation. This network comprises a fully automated camera and radio network deployed over a significant fraction of western Europe and a small fraction of Canada. As of today, it consists of 150 cameras and 25 European radio receivers and covers an area of about 1.5 × 106km2. Methods.The FRIPON network, fully operational since 2018, has been monitoring meteoroid entries since 2016, thereby allowing the characterization of their dynamical and physical properties. In addition, the level of automation of the network makes it possible to trigger a meteorite recovery campaign only a few hours after it reaches the surface of the Earth. Recovery campaigns are only organized for meteorites with final masses estimated of at least 500 g, which is about one event per year in France. No recovery campaign is organized in the case of smaller final masses on the order of 50 to 100 g, which happens about three times a year; instead, the information is delivered to the local media so that it can reach the inhabitants living in the vicinity of the fall. Results.Nearly 4000 meteoroids have been detected so far and characterized by FRIPON. The distribution of their orbits appears to be bimodal, with a cometary population and a main belt population. Sporadic meteors amount to about 55% of all meteors. A first estimate of the absolute meteoroid flux (mag < –5; meteoroid size ≥~1 cm) amounts to 1250/yr/106km2. This value is compatible with previous estimates. Finally, the first meteorite was recovered in Italy (Cavezzo, January 2020) thanks to the PRISMA network, a component of the FRIPON science project.

The present study reports on observations carried out in the Tropical North Atlantic in summer and autumn 2017, documenting Sargassum aggregations using both ship-deck observations and satellite sensor observations at three resolutions (MSI-10 m, OLCI-300 m, VIIRS-750 m and MODIS-1 km). Both datasets reported that in summer, Sargassum aggregations were mainly observed off Brazil and near the Caribbean Islands, while they accumulated near the African coast in autumn. Based on in situ observations, we propose a five-class typology allowing standardisation of the description of in situ Sargassum raft shapes and sizes. The most commonly observed Sargassum raft type was windrows, but large rafts composed of a quasi-circular patch hundreds of meters wide were also observed. Satellite imagery showed that these rafts formed larger Sargassum aggregations over a wide range of scales, with smaller aggregations (of tens of m2 area) nested within larger ones (of hundreds of km2). Match-ups between different satellite sensors and in situ observations were limited for this dataset, mainly because of high cloud cover during the periods of observation. Nevertheless, comparisons between the two datasets showed that satellite sensors successfully detected Sargassum abundance and aggregation patterns consistent with in situ observations. MODIS and VIIRS sensors were better suited to describing the Sargassum aggregation distribution and dynamics at Atlantic scale, while the new sensors, OLCI and MSI, proved their ability to detect Sargassum aggregations and to describe their (sub-) mesoscale nested structure. The high variability in raft shape, size, thickness, depth and biomass density observed in situ means that caution is called for when using satellite maps of Sargassum distribution and biomass estimation. Improvements would require additional in situ and airborne observations or very high-resolution satellite imagery.

Testing hypothesis about the biogeography of genes using large data resources such as Tara Oceans marine metagenomes and metatranscriptomes requires significant hardware resources and programming skills. The new release of the 'Ocean Gene Atlas' (OGA2) is a freely available intuitive online service to mine large and complex marine environmental genomic databases. OGA2 datasets available have been extended and now include, from the Tara Oceans portfolio: (i) eukaryotic Metagenome-Assembled-Genomes (MAGs) and Single-cell Assembled Genomes (SAGs) (10.2E+6 coding genes), (ii) version 2 of Ocean Microbial Reference Gene Catalogue (46.8E+6 non-redundant genes), (iii) 924 MetaGenomic Transcriptomes (7E+6 unigenes), (iv) 530 MAGs from an Arctic MAG catalogue (1E+6 genes) and (v) 1888 Bacterial and Archaeal Genomes (4.5E+6 genes), and an additional dataset from the Malaspina 2010 global circumnavigation: (vi) 317 Malaspina Deep Metagenome Assembled Genomes (0.9E+6 genes). Novel analyses enabled by OGA2 include phylogenetic tree inference to visualize user queries within their context of sequence homologues from both the marine environmental dataset and the RefSeq database. An Application Programming Interface (API) now allows users to query OGA2 using command-line tools, hence providing local workflow integration. Finally, gene abundance can be interactively filtered directly on map displays using any of the available environmental variables. Ocean Gene Atlas v2.0 is freely-available at: https://tara-oceans.mio.osupytheas.fr/ocean-gene-atlas/.

Context. During the period between 15 September 2014 and 4 February 2015, the Rosetta spacecraft accomplished the circular orbit phase around the nucleus of comet 67P/Churyumov-Gerasimenko (67P). The Grain Impact Analyzer and Dust Accumulator (GIADA) onboard Rosetta monitored the 67P coma dust environment for the entire period.

Providing timely information on urban greenhouse gas (GHG) emissions and their trends to stakeholders relies on reliable measurements of atmospheric concentrations and the understanding of how local emissions and atmospheric transport influence these observations. Portable Fourier transform infrared (FTIR) spectrometers were deployed at five stations in the Paris metropolitan area to provide column-averaged concentrations of CO 2 (XCO 2 ) during a field campaign in spring of 2015, as part of the Collaborative Carbon Column Observing Network (COCCON). Here, we describe and analyze the variations of XCO 2 observed at different sites and how they changed over time. We find that observations upwind and downwind of the city centre differ significantly in their XCO 2 concentrations, while the overall variability of the daily cycle is similar, i.e. increasing during night-time with a strong decrease (typically 2–3 ppm) during the afternoon. An atmospheric transport model framework (CHIMERE-CAMS) was used to simulate XCO 2 and predict the same behaviour seen in the observations, which supports key findings, e.g. that even in a densely populated region like Paris (over 12 million people), biospheric uptake of CO 2 can be of major influence on daily XCO 2 variations. Despite a general offset between modelled and observed XCO 2 , the model correctly predicts the impact of the meteorological parameters (e.g. wind direction and speed) on the concentration gradients between different stations. When analyzing local gradients of XCO 2 for upwind and downwind station pairs, those local gradients are found to be less sensitive to changes in XCO 2 boundary conditions and biogenic fluxes within the domain and we find the model–data agreement further improves. Our modelling framework indicates that the local XCO 2 gradient between the stations is dominated by the fossil fuel CO 2 signal of the Paris metropolitan area. This further highlights the potential usefulness of XCO 2 observations to help optimize future urban GHG emission estimates.

The imaging channel on the Mid-Infrared Instrument (MIRI) is equipped with four coronagraphs that provide high-contrast imaging capabilities for studying faint point sources and extended emission that would otherwise be overwhelmed by a bright point-source in its vicinity. Such targets might include stars that are orbited by exoplanets and circumstellar material, mass-loss envelopes around post-main-sequence stars, the near-nuclear environments in active galaxies, and the host galaxies of distant quasars. This paper describes the coronagraphic observing modes of MIRI, as well as performance estimates based on measurements of the MIRI flight model during cryo-vacuum testing. A brief outline of coronagraphic operations is also provided. Finally, simulated MIRI coronagraphic observations of a few astronomical targets are presented for illustration.

High-frequency (HF) coastal radars measure current velocity at the ocean surface with a 30–100 km range and 1–3 km resolution, every 0.25–1 h. HF radars are well suited to many applications, such as search and rescue (SaR), oil-spill mitigation and ecosystem management. Here we present a first organized core of 12 HF radars installed in five sites in four countries (Greece, Italy, France and Spain) within the European MED project, the Tracking Oil Spill and Coastal Awareness (TOSCA) network. Dedicated experiments tested radar capabilities to estimate transport driven by currents, which is the key feature for all the above applications. Experiments involved the deployment of drifters, i.e., floating buoys, acting as proxies for substances passively advected by currents. Using HF radars the search range is reduced by a factor of 1.6 to 5.3 after 24 h. The paper also underlines the importance of sharing common tools for HF radar data processing and the need to mitigate radio frequency interference. The effort can be regarded as an initial step toward the creation of a Mediterranean or European HF radar network, crucial for any European integrated ocean observing system (IOOS).

We performed nitrogen (N) budgets in the photic layer of three contrasting stations representing different trophic conditions in the western tropical South Pacific (WTSP) Ocean during austral summer conditions (February–March 2015). Using a Lagrangian strategy, we sampled the same water mass for the entire duration of each long-duration (5 days) station, allowing us to consider only vertical exchanges for the budgets. We quantified all major vertical N fluxes both entering (N 2 fixation, nitrate turbulent diffusion, atmospheric deposition) and leaving the photic layer (particulate N export). The three stations were characterized by a strong nitracline and contrasted deep chlorophyll maximum depths, which were lower in the oligotrophic Melanesian archipelago (MA, stations LD A and LD B) than in the ultra-oligotrophic waters of the South Pacific Gyre (SPG, station LD C). N 2 fixation rates were extremely high at both LD A (593 ± 51 µmol N m −2 d −1 ) and LD B (706 ± 302 µmol N m −2 d −1 ), and the diazotroph community was dominated by Trichodesmium . N 2 fixation rates were lower (59 ± 16 µmol N m −2 d −1 ) at LD C, and the diazotroph community was dominated by unicellular N 2 -fixing cyanobacteria (UCYN). At all stations, N 2 fixation was the major source of new N (> 90 %) before atmospheric deposition and upward nitrate fluxes induced by turbulence. N 2 fixation contributed circa 13–18 % of primary production in the MA region and 3 % in the SPG water and sustained nearly all new primary production at all stations. The e ratio ( e ratio = particulate carbon export ∕ primary production) was maximum at LD A (9.7 %) and was higher than the e ratio in most studied oligotrophic regions (< 5 %), indicating a high efficiency of the WTSP to export carbon relative to primary production. The direct export of diazotrophs assessed by qPCR of the nifH gene in sediment traps represented up to 30.6 % of the PC export at LD A, while their contribution was 5 and < 0.1 % at LD B and LD C, respectively. At the three studied stations, the sum of all N input to the photic layer exceeded the N output through organic matter export. This disequilibrium leading to N accumulation in the upper layer appears as a characteristic of the WTSP during the summer season.

Abstract. We studied a longitudinal transect in the Mediterranean Sea (MS) and along this transect, the influence of anticyclonic eddies at three long duration (LD) stations. The deep chlorophyll maximum depth, the euphotic layer depth and the top of the nitracline depth are clearly correlated outside of the eddies, and deepen from the oligotrophic western to the ultraoligotrophic eastern MS. We provide evidence that the locations of the three LD stations studied were near the axis of the eddies. Their diameters were close to 100 km and the studied areas were less than 10 km from the centre of the eddies. The positions of the LD stations are marked by an increase in the flux function and a decrease in apparent oxygen utilization (AOU) and in excess density σ), as expected for anticyclonic eddies. Integrated mean primary production measured in situ inside the three studied eddies confirms the previous conclusion that integrated primary production (IPP) about 150 mgC m−2 d−1 may appear as a lower limit for IPP during strong oligotrophic conditions. The mesoscale activity is strong enough to locally modify the very well-documented western-to-eastern gradient of trophic conditions in the MS. We proposed a new calculation for mixed layer depths (MLDs) enabling the determination of MLD to take into consideration processes occurring with time scales ranging from a few hours to several days, and also the winter MLD. Studying the main physical, chemical and dynamical characteristics of the three eddies enables us to consider that the vorticity barrier prevents any strong mixing and advection of outer water inside the eddy and explains why the depth range of eddies starts from the surface. As a first approximation, the anticyclonic eddies could be considered as closed systems dating back to the previous winter, making possible to draw first-order budgets. The daily new N-input in the photic zone is virtually identical to the N-export measured at 230 m by drifting traps. This means that the eddies are close to an equilibrium state where input is equal to loss. The annual N-input by winter convection, which is a fundamental criterion for new nutrient availability, may be extremely variable inside eddies, with W-MLD varying from 90.5 m at the western station to 396.5 m at the eastern station. W-MLDs are always deeper inside the eddies than outside where they are in keeping with climatological averages. AOU was low inside the eddies; this together with the near-identical export measured at 230 and 460 m seems to indicate that eddy cores are areas where low mineralisation of particulate organic matter occurs. "In" and "out" AOU comparisons indicate lower mineralisation inside the eddies suggesting a higher efficiency for CO2 sequestration via sedimentation of particulate organic matter. The three eddies are enriched in dissolved organic carbon (DOC). Sequestration of CO2 by vertical export of accumulated DOC therefore seems to be higher inside eddies. The relative importance of DOC transport in the biological pump is probably one of the main characteristics of low-P low chlorophyll (LPLC) areas, and it is likely to be reinforced inside anticyclonic eddies. The numerous anticyclonic eddies in the MS are likely to influence the water masses and their dispersion, and therefore have a strong impact on the biogeochemical properties at the scale of the MS.

Abstract. The overall goal of OUTPACE (Oligotrophy to UlTra-oligotrophy PACific Experiment) was to obtain a successful representation of the interactions between planktonic organisms and the cycle of biogenic elements in the western tropical South Pacific Ocean across trophic and N2 fixation gradients. Within the context of climate change, it is necessary to better quantify the ability of the oligotrophic ocean to sequester carbon through biological processes. OUTPACE was organized around three main objectives, which were (1) to perform a zonal characterization of the biogeochemistry and biological diversity of the western tropical South Pacific during austral summer conditions, (2) to study the production and fate of organic matter (including carbon export) in three contrasting trophic regimes (increasing oligotrophy) with a particular emphasis on the role of dinitrogen fixation, and (3) to obtain a representation of the main biogeochemical fluxes and dynamics of the planktonic trophic network. The international OUTPACE cruise took place between 18 February and 3 April 2015 aboard the RV L'Atalante and involved 60 scientists (30 onboard). The west–east transect covered ∼ 4000 km from the western part of the Melanesian archipelago (New Caledonia) to the western boundary of the South Pacific gyre (French Polynesia). Following an adaptive strategy, the transect initially designed along the 19° S parallel was adapted along-route to incorporate information coming from satellite measurements of sea surface temperature, chlorophyll a concentration, currents, and diazotroph quantification. After providing a general context and describing previous work done in this area, this introductory paper elucidates the objectives of OUTPACE, the implementation plan of the cruise and water mass and climatological characteristics and concludes with a general overview of the other papers that will be published in this special issue.

In this Collective Article on “New Mediterranean Biodiversity Records”, we present additional records of species found in the Mediterranean Sea. These records refer to eight different countries throughout the northern part of the basin, and include 28 species, belonging to five phyla. The findings per country include the following species: Spain: Callinectes sapidus and Chelidonura fulvipunctata; Monaco: Aplysia dactylomela; Italy: Charybdis (Charybdis) feriata, Carcharodon carcharias, Seriola fasciata, and Siganus rivulatus; Malta: Pomacanthus asfur; Croatia: Lagocephalus sceleratus and Pomadasys incisus; Montenegro: Lagocephalus sceleratus; Greece: Amathia (Zoobotryon) verticillata, Atys cf. macandrewii, Cerithium scabridum, Chama pacifica, Dendostrea cf. folium, Ergalatax junionae, Septifer cumingii, Syphonota geographica, Syrnola fasciata, Oxyurichthys petersi, Scarus ghobban, Scorpaena maderensis, Solea aegyptiaca and Upeneus pori; Turkey: Lobotes surinamensis, Ruvettus pretiosus and Ophiocten abyssicolum. In the current article, the presence of Taractes rubescens (Jordan & Evermann, 1887) is recorded for the first time in the Mediterranean from Italy. The great contribution of citizen scientists in monitoring biodiversity records is reflected herein, as 10% of the authors are citizen scientists, and contributed 37.5% of the new findings.

Context. So far, surface magnetic fields have never been detected on Mira stars. Only recently have the spectropolarimetric capabilities of measuring it via the Zeeman effect become available to us. Then, to complete the knowledge of the magnetic field and of its influence during the transition from asymptotic giant branch to planetary nebulae stages, we have undertaken a search for magnetic fields on the surface of Mira stars.

Coastal zones are ecosystems of high economic value but exposed to numerous disturbances, while they represent nurseries for many fish species, raising the issue of the preservation of their functions and services. In this context, the juvenile fish assemblages of all types of habitats present in shallow coastal zones were studied on the south-east coast of France using underwater visual censuses in warm (June-July 2014) and cold (April 2015) periods. A total of fourteen habitat types were characterized, which could be grouped into three broad categories, rocky substrates (natural and artificial), sedimentary bottoms with all levels of granulometry, and seagrass beds including Cymodocea nodosa and Posidonia oceanica meadows; the ecotones or interfaces between the three broad habitat categories were individualized as particular habitat types. The abiotic and biotic descriptors of the 14 habitat types individualized did not vary with time, except for a higher cover percentage and canopy height of macrophytes in the warm period, which increased the three-dimensional structure of some habitats. The taxonomic composition and density of juvenile fish assemblages were analyzed using both multivariate and univariate descriptors, after grouping the 57 fish species recorded into 41 well-individualized taxa. Juvenile fishes were recorded in all habitat types, with higher mean species richness and abundance during the warm than the cold period. The richest habitats in terms of both fish species richness and abundance were the natural rocky substrates and the interfaces between Posidonia beds and the other habitats. Although juvenile fish assemblage composition differed among habitat types and between periods, the most abundant fish species were Atherina sp., Sarpa salpa, Gobiidae, Symphodus spp., Pagellus spp. and several Diplodus species, which colonized 7 up to 14 different habitat types (depending on taxa) during their juvenile life. Most species settled in one or a few specific habitats but rapidly colonized adjacent habitats when growing. This study provided evidence of the role of all types of shallow coastal habitats as fish nurseries and their varying pattern of occupation in space and time by the different juvenile stages. It highlighted the importance of the mosaic of habitats and interfaces for the complete development of all juvenile life stages of fishes, and for the preservation of a high diversity of coastal fish assemblages and fisheries resources in the Mediterranean Sea.

GIADA (Grain Impact Analyzer and Dust Accumulator) on-board the Rosetta space probe is designed to measure the momentum, mass and speed of individual dust particles escaping the nucleus of comet 67P/Churyumov–Gerasimenko (hereafter 67P). From 2014 August to 2016 June, Rosetta escorted comet 67P during its journey around the Sun. Here, we focus on GIADA data taken between 2015 January and 2016 February which included 67P's perihelion passage. To better understand cometary activity and more specifically the presence of dust structures in cometary comae, we mapped the spatial distribution of dust density in 67P's coma. In this manner, we could track the evolution of high-density regions of coma dust and their connections with nucleus illumination conditions, namely tracking 67P's seasons. We also studied the link between dust particle speeds and their masses with respect to heliocentric distance, i.e. the level of cometary activity. This allowed us to derive a global and a local correlation of the dust particles’ speed distribution with respect to the H2O production rate.