Abstract: Rapid magnetic variations on Earth are intimately linked with solar activity and this is one of the main topics in Space Weather research. Modelling and forecasting these phenomena are vital in our technological society. The Service of Rapid Magnetic Variations provides lists of these remarkable magnetic events in a continuous way in what constitutes a long geophysical series that began in the late 19th century. Although the aim of this Service remains unchanged, methods have changed with time. Here, we describe the recent evolution of the Service, its database and the latest works carried out to improve the products delivered to the scientific society.

Abstract: Different approaches to map seismic rupture in space and time often lead to incoherent results for the same event. Building on earlier work by our team, we ‘time-reverse’ and ‘backpropagate’ seismic surface wave recordings to study the focusing of the time-reversed field at the seismic source. Currently used source-imaging methods relying on seismic recordings neglect the information carried by surface waves, and mostly focus on the P-wave arrival alone. Our new method combines seismic time reversal approach with a surface wave ray-tracing algorithm based on a generalized spherical-harmonic parametrization of surface wave phase velocity, accounting for azimuthal anisotropy. It is applied to surface wave signal filtered within narrow-frequency bands, so that the inherently 3-D problem of simulating surface wave propagation is separated into a suite of 2-D problems, each of relatively limited computational cost. We validate our method through a number of synthetic tests, then apply it to the great 2004 Sumatra–Andaman earthquake, characterized by the extremely large extent of the ruptured fault. Many studies have estimated its rupture characteristics from seismological data (e.g. Lomax, Ni et al., Guilbert et al., Ishii et al., Krüger & Ohrnberger, Jaffe et al.) and geodetic data (e.g. Banerjee et al., Catherine et al., Vigny et al., Hashimoto et al., Bletery et al.). Applying our technique to recordings from only 89 stations of the Global Seismographic Network (GSN) and bandpass filtering the corresponding surface wave signal around 80-to-120, 50-to-110 and 40-to-90 s, we reproduce the findings of earlier studies, including in particular the northward direction of rupture propagation, its approximate spatial extent and duration, and the locations of the areas where most energy appears to be released.

Abstract: Reliably recording very low ambient concentrations of gaseous elemental mercury (GEM) in remote regions is often required, for example in the context of evaluating how effective the Minamata Convention is in reducing global Hg emissions. However, sampling over extended periods of time at sites that are difficult to access can be very challenging. In order to establish what role inexpensive and easy-to-use passive air samplers may play in this regard, we deployed a sampler using a Radiello diffusive barrier and activated carbon sorbent for periods of up to three years and with sampling periods ranging from one to three months in some of the most extreme, remote and challenging global environments: at Concordia station on the Antarctic plateau, on Amsterdam Island in the remote Southern Indian Ocean and at several sites on the tropical island of La Réunion. The ability to reliably record the GEM concentrations at these sites was strongly influenced by the size of the sequestered amount of mercury relative to the extent and variability of the contamination of field blank samples. In some cases, acceptably low and consistent field blank contamination could only be achieved by storing samplers in sealed glass jars during transport and storage. The size of the sequestered amount is easily increased by extending deployment times, and the experience of the current study suggests that deployment periods in excess of two months are advisable. Sampling in Antarctica was compromised by the extreme low temperatures, which caused unknown sampling rates, hoar frost accumulation, material failure and potential failure of storage seals. While good agreement with GEM concentrations measured with an active sampler was noted on Amsterdam Island, the passive sampler derived levels at the Maïdo Observatory in La Réunion were notably higher than concentrations measured simultaneously with a Tekran vapour analyzer, which was possibly related to sampling rates being temporarily elevated at the very beginning of deployment at low GEM concentrations.

Abstract: Assessment methods have been developed to estimate a preliminary conservation status for species and subsequently to facilitate the building of Red Lists. Such pre-assessment methods could be particularly useful in the French Overseas Territories (FOTs) where Red Lists tend to be out-dated or absent and where a high number of endemic species face detrimental anthropogenic pressures. We first aimed to conduct a preliminary assessment (hereafter, pre-assessment) of the conservation status of endemic plants from Guadeloupe, Martinique, Réunion, Mayotte, French sub-Antarctic islands, New Caledonia, and Scattered Islands. We then compared the various methods used in conducting the pre-assessment and discussed ways to adapt these methods to small territories. We compiled occurrence data of endemic species identified thanks to a previous taxonomic work and pre-assessed their conservation status under Red List criteria A and B and the use of a Random Forest algorithm. We then measured the accuracy, specificity, and sensitivity of each method based on existing Red Lists. The Random Forest algorithm and a method based on range-size performed best at correctly attributing conservation status. Using these pre-assessment methods, we estimated that up to 60% of the endemic flora of the FOTs is potentially threatened. Range restriction but also anthropogenic pressures were key factors that explained these risks. Pre-assessment methods are useful tools to get a first measure of species conservation status. These methods should be adapted to the territories considered and their conservation issues in order to reach a good performance.

Abstract: Combined effects of multiple, climate change-associated stressors are of mounting concern, especially in Arctic ecosystems. Elevated mercury (Hg) exposure in Arctic animals could affect behavioral responses to changes in foraging landscapes caused by climate change, generating interactive effects on behavior and population resilience. We investigated this hypothesis in little auks (Alle alle), a keystone Arctic seabird. We compiled behavioral data for 44 birds across 5 years using accelerometers while also quantifying blood Hg and environmental conditions. Warm sea surface temperature (SST) and low sea ice coverage reshaped time activity budgets (TABs) and diving patterns, causing decreased resting, increased flight, and longer dives. Mercury contamination was not associated with TABs. However, highly contaminated birds lengthened interdive breaks when making long dives, suggesting Hg-induced physiological limitations. As dive durations increased with warm SST, subtle toxicological effects threaten to increasingly constrain diving and foraging efficiency as climate change progresses, with ecosystem-wide repercussions.