Several species of microalgae have developed a complex specialized metabolism yielding to the production of toxic compounds. When highly concentrated and quickly multiplying, these toxic microalgae are likely to induce negative environmental or toxicological effects, by forming Harmful Algal Blooms (HABs). During the past decade, a toxic benthic dinoflagellate belonging to the genus Ostreopsis has bloomed repetitively along the Mediterranean coastline. The causes implied in the increasing incidence of these toxic blooms have not yet been determined even if global change has been pointed out. Indeed, due to its geographical features, the Mediterranean Sea is particularly sensitive to increasing temperatures and solar irradiance that would lead to enhanced thermal stratification and therefore to alterations in ecosystem functioning. Blooms of Ostreopsis were associated to human afflictions in Italy and France, such as fever, water rhinorrhea, pharyngeal pain, dry or mildly productive cough, headache, nausea/vomiting, and bronchoconstriction. Adverse effects on benthic communities of bivalves, gastropods and echinoderms were also observed in some cases. These deleterious effects on both the humans and ecosystem health were attributed to analogs of the potent palytoxin, namely ovatoxins (a to h) produced by Ostreopsis cf. ovata. However, the specialized metabolism of O. cf. ovata has been partially identified and other metabolites involved in the toxic effects are likely to be produced by the microalgae and require additional studies. Specialized metabolites are also involved in the chemical mediation between organisms and, up to now, the influence of chemical cues on the development of several benthic organisms has rarely been investigated. Therefore, any answers coming from this field named chemical ecology will be of high added value. In this context, the overall objective of OCEAN-15 is to investigate the effects of climate change on the specialized metabolism of these microalgae in order to anticipate the potential modification of its toxic behavior as well as the subsequent ecological interactions that would alter marine ecosystems. This objective fits the societal challenge 1 listed in the ANR 2015 Work Program and more specifically its axis 2 through an interdisciplinary research on "health risks facing environmental changes" bringing useful knowledge to integrative policy in public health. The project OCEAN-15 was subdivided in four main tasks addressing several aspects of the chemical ecology of O. cf. ovata: (1) study of the specialized metabolism, (2) effects of global change on this metabolism, (3) ecological impacts of the metabolism; and (4) toxicological effects and mechanisms associated to the metabolites. A truly collaborative and multidisciplinary effort will help reaching the proposed objectives. In this project, we will combine some of the leading groups in France in the field of marine chemical ecology and metabolomics (ICN), phycotoxin chemistry and ecotoxicology (IFREMER), phytoplanktonic ecology (LOV) as well as human toxicology (ANSES). The capability and success of this consortium has already been demonstrated through the joint participation of the different partners to diverse research groups supported by the CNRS (GdR Phycotox, GdR MediatEC) as well as to international consortium (ISSHA, International Society for the Study of Harmful Algae). Thus, through this synergistic project, we are convinced to bring answers on the impact of global change on Ostreopsis cf. ovata specialized metabolism and thus allelopathy and toxicity. Any answers coming from this project would benefit to the society, as they will help further monitoring of HABs and protecting human health along the touristic Mediterranean coastline.

The Western Tropical South Pacific (WTSP) Ocean has recently been identified as a hotspot of N2 fixation and harbors among the highest rates reported in the global ocean. N2-fixing organisms have high iron (Fe) quotas relative to non-diazotrophic plankton and their success in the WTSP has been attributed to the alleviation of Fe limitation in this region. However, our knowledge on Fe sources and distribution in the WTSP remains limited. During the OUTPACE cruise in 2015, the proposed team identified a shallow (<500 m) hydrothermal Fe source in the WTSP close to the Tonga volcanic Arc, which resulted in high concentrations (4-60 nM) of dissolved Fe (DFe) up to the photic (~0-150 m) layer. Such inputs are suspected (together with high sea surface temperature ~27-29°C) to trigger diazotroph blooms in the WTSP. However, the potential impact of such hydrothermal input on plankton communities and biogeochemical cycles of biogenic elements (carbon (C), Nitrogen (N), Phosphorus (P)) remains to be studied. In this context, the main objectives of the TONGA project are: -To accurately quantify Fe (and other biogeochemically relevant compounds) input from shallow (<500 m) submarine volcanoes and associated hydrothermal vents along the Tonga volcanic arc for the photic zone in comparison with atmospheric deposition, -To study the fate of shallow hydrothermal plumes in the water column at the local and regional scales, -To investigate the bioavailability and the potential impact of such hydrothermal inputs on planktonic communities and biogeochemical cycles in the WTSP To achieve this goal, we propose a multidisciplinary approach based both on a 37-day oceanographic cruise (R/V L’Atalante, approved for 2019 by the TGIR FOF) in the WTSP and modeling work. The TONGA consortium involves 85 scientists from 19 international institutions among which hydrothermal geochemists, physical oceanographers, trace element chemists, biogeochemists, biologists and modelers. The cruise will consist of 31 short (6h) stations and two 5-day process studies stations above 2 known active shallow submarine volcanoes. Hydrothermal tracers and the full suite of physical/hydrological/biogeochemical/biological parameters will be measured together with atmospheric survey. We will also deploy drifting and fixed mooring lines, turbulence profilers and ARGO floats to determine how shallow hydrothermal venting impacts trace elements and isotopes distributions in the mixed layer (Task 1), and how physical parameters impact the plume dilution and transport (Task 2). The potential effect of those inputs on plankton communities (fertilization vs toxicity) depends on their bioavailability that will be assessed through trace metal chemistry investigations. The impacts on ecosystem functioning and biogeochemical fluxes (Task 3) will be investigated based on stocks, fluxes and plankton diversity measurements across hydrothermal gradients, and complemented by means of mixing experiments with hydrothermal fluids in trace metal clean Climate Reactors recently-developed by the proposed team. These observations will fuel several modelling approaches and vice-versa: (1) a multi-scale modelling approach will allow to better characterize the local and regional dispersion of hydrothermal nutrients in the WTSP, (2) a new Lagrangian modelling approach will be used to quantify the transport of hydrothermal Fe to the photic layer and (3) a coupled dynamical PISCES model version that includes dynamic Fe binding ligands, colloidal Fe, alongside hydrothermal input will allow to characterize the role of hydrothermal Fe on primary production and export. TONGA has been endorsed as a GEOTRACES process study and received a letter of support from the IMBER international programme. It will significantly improve understanding several fundamental processes linked to the impacts of shallow hydrothermal sources on ecosystem functioning, a question that have not been addressed so far.

Slow slip events (SSE) are transient processes releasing stress at faults without significant earthquake. Their discovery about two decades ago in subduction zones demonstrates a complex dynamics of the megathrust controlled by spatially variable friction at the plate interface. While deep SSEs occurring downdip of highly locked areas have been extensively studied, other subduction zones highlight another transient process where slip occurs at the same depths as large earthquakes and is synchronous to intense micro-seismicity. We refer to this type of transient as S5 for Synchronous Slow Slip & Seismic Swarm, which is the focus of our proposal. With recurrence time of a few years, S5 periodically induce stress perturbation at the megathrust and might be precursors to an incipient large earthquake, as observed for the 2011 Japan giant earthquake. However, most S5 are not followed by a large earthquake. A major challenge is to know whether some characteristics (e.g. seismicity increase, acceleration of slip, penetration of slip into highly locked areas) could be indicators of the nucleation phase of an incipient large earthquake. As a step required to answer this question, this project aims at (1) precisely observing S5 (2) using novel analysis methodologies to better document the slip and the seismicity during S5 and (3) developing new modelling approaches to consistently integrate the different observations to decipher the underlying physics. We selected four areas along the South America subduction zone where (1) the probability of observing S5 during the duration of the project is high (2) thanks to previous efforts and partnerships with local institutes, existing seismological and geodetic infrastructure enables to deploy a dense network at a lower cost. Two areas are located in the northern Andes in Ecuador and Peru and two are in Central Chile. At each targeted area, we will install additional continuous GNSS stations and broadband seismometers that will be recording during the 4 years of the project. In addition, we will regularly survey dense networks of GNSS benchmarks and perform a 6-months long seismological experiment with 10 additional broadband seismometers at both targeted areas in Chile. Together with existing data sets from dense seismological networks that recorded S5 in Ecuador and Peru, this observational effort will provide spatially and temporally high resolution data to apply novel methods. We will process the GNSS data and investigate new methods to separate non-tectonic contributions in GNSS time series. Then we will derive a velocity field used to perform refined modelling of the interseismic coupling to understand the environment of S5. A novelty is that we will develop a generalized full time-dependent slip inversion from GNSS time series opening the way for a kinematic imaging of slip and slip rate at the subduction interface. For the seismological data, we will (1) search for repeating earthquakes (2) search for tremors and low frequency earthquakes (3) systematically calculate focal mechanisms and source time functions for the largest events. An additional novelty of our proposal is to use Machine Learning (ML) techniques in order to speed up and to improve micro-seismicity analysis. Finally, we will integrate the geodetic and seismological results in a modelling approach where the spatial and temporal evolution of the seismicity and recurrence time for repeating earthquakes are consistent with the stress evolution induced by the slip developing through time at the plate interface. Simultaneously, forward numerical modelling of a frictionally heterogeneous fault will provide a synoptic view of the relations between friction parameters and observable slip behaviors. Finally, physical modelling will examine the physical conditions and characteristics required for an S5 to lead to a large earthquake.

Megathrust earthquakes can induce metric-scale sudden subsidence or uplift, and destabilize shelf sediments, instigating turbiditic flows and landslides. They can also generate tsunamis that can transport huge quantities of marine and coastal sediments and debris inland. Such dramatic events can cause many casualties, destroy infrastructure, and have longer-term impacts on the environment. They may considerably modify the landscape, affecting human settlement over millennia. Between large earthquakes, due to strain accumulation, land deformation induces relative sea level changes at rates much faster than those due to climate change. These events represent a major threat and must be accounted for in regional planning. Missing information on such extreme and rare events, necessary to better constrain the seismic hazard, is a major limitation. The largest earthquakes may recur only every 500 or 1000 yrs and the historical catalogs are too short to allow an estimation of earthquake recurrence intervals and of their magnitude. Existing models based on short historical records have not been successful at predicting earthquake recurrence. Paleoseismological and paleotsunami studies of the geological record are thus needed to address this issue and establish time series over thousands of years. The Lesser Antilles arc is a densely populated and highly touristic zone exposed to megathrust earthquakes. The largest historical event that occurred on 8 February 1843t destroyed the city of Pointe-à-Pitre on Guadeloupe, killing more than 1500 people. Today, a comparable earthquake might cause tens of thousands of casualties. The objective of the CARQUAKES project is to improve the catalog of large earthquakes and tsunamis in the Lesser Antilles and characterize the related hazards by applying an innovative and novel multidisciplinary approach combining several state-of-art methods of offshore and onshore paleoseismology and tsunami modeling. Offshore, we will use the marine sediments (i.e. turbidites/homogenites) as proxies for earthquake recurrence in the Lesser Antilles (Task 1). During the CASEIS marine cruise in Spring 2016, we collected 42 sedimentary cores in the eastern part of the Lesser Antilles arc, above the megathrust zone. The CARQUAKES project is in part conceived to permit the exploitation of this large dataset. Onshore, we will combine several approaches to retrieve the traces of extreme events: 1) paleoseismological and paleotsunami studies in coastal lagoons and ponds that may have preserved the evidence of earthquakes and tsunamis (Task 2); 2) Coral paleogeodesy along the reefs, where coral microatolls may record earthquakes in their skeletal growth (Task 3); and 3) Archaeology and history comprising analysis of historical descriptions of earthquakes and tsunamis in archives and investigations of several coastal archeological sites on Guadeloupe (Task 4). Tsunami and strain modeling will be performed to calculate the impact of earthquake cycle and tsunamis on the littoral zone (wave height, inundation and coastline variations) (Task 5). The CARQUAKES project brings together experts in tectonics, geomorphology, paleoseismology and paleotsunamis, sedimentology, paleo-environment, tsunami modeling, botany, palynology, archaeology, and history. Six partners are involved in the project. The project will benefit society because it will provide information essential to reduce the vulnerability of coastal populations in the Lesser Antilles islands. This will improve our knowledge of earthquake and tsunami hazards and their impact on coastline evolution, ecosystems (destruction and resilience) and human settlement.

The main aim of the MODAL project is to carry out hazard and hazard analyses associated to sediment deformations in submarine environments prone to earthquakes, fluid activities and landslides. The study zone -the Nice Slope (France) - is nested in heavily populated areas, highly exposed to geohazards. The major challenging scientific question in this project concerns the coupling between fluids and sediment deformation in submarine environments. Historically, the study area is sadly famous for the 1979 catastrophic submarine landslide which results in several casualties and infrastructural damage. Geotechnical and geophysical investigations carried out in late 2007 to the East of the 1979 landslide scar provide evidence for the possible occurrence of a new important sedimentary collapse and submarine landslide. Geophysical data acquired in the area show the presence of several seafloor morphological steps rooted to shallow sub-surface seismic reflections. Moreover, in situ piezocone measurements demonstrate the presence of several shear zones at the border of the shelf break at different depth below the seafloor. Both geophysical and geotechnical data suggest the start-up of a progressive failure mechanism and reveal the possible occurrence of future submarine landslide. The MODAL project is built according to a typical scheme for hazard and risk analysis going from the understanding of underlying physical processes (causal, predisposition and triggering factors) through the detection of revealing factors (thanks to geophysical mapping and imaging, in situ measurements and monitoring) and hazard assessment (calculation of probability of a given danger to occur during a given time period). More specifically, we propose to monitor the displacement rate field of the sediment and measure the fluid pressure to assess the probability of the slope failure, in response to gravity sliding, earthquake loading or excess pore pressure associated with rainfalls on the Nice region. The study site has been actively studied during the last decade within the framework of national and/or European projects. We have already an important set of geotechnical, geological and geophysical data which facilitate the application and validation of the proposed schemes. The MODAL project will be conducted within the framework of fundamental research, technological developments and practical field applications.