Abstract: The pre-ALPACA (Alaskan Layered Pollution And Chemical Analysis) 2019 winter campaign took place in Fairbanks, Alaska, in November–December 2019. One objective of the campaign was to study the life-cycle of surface-based temperature inversions and the associated surface energy budget changes. Several instruments, including a 4-component radiometer and sonic anemometer were deployed in the open, snow-covered University of Alaska Fairbanks (UAF) Campus Agricultural Field. A local flow from a connecting valley occurs at this site. This flow is characterized by locally elevated wind speeds (greater than 3 m s$$^{-1}$$) under clear-sky conditions and a north-westerly direction. It is notably different to the wind observed at the airport more than 3.5 km to the south-west. The surface energy budget at the UAF Field site exhibits two preferential modes. In the first mode, turbulent sensible heat and net longwave fluxes are close to 0 W m$$^{-2}$$, linked to the presence of clouds and generally low winds. In the second, the net longwave flux is around − 50 W m$$^{-2}$$and the turbulent sensible heat flux is around 15 W m$$^{-2}$$, linked to clear skies and elevated wind speeds. The development of surface-based temperature inversions at the field is hindered compared to the airport because the local flow sustains vertical mixing. In this second mode the residual of the surface energy budget is large, possibly due to horizontal temperature advection.

Abstract: Climate change is most strongly felt in the polar regions of the world, with significant impacts on the species that live there. The arrival of parasites and pathogens from more temperate areas may become a significant problem for these populations, but current observations of parasite presence often lack a historical reference of prior absence. Observations in the high Arctic of the seabird tick Ixodes uriae suggested that this species expanded poleward in the last two decades in relation to climate change. As this tick can have a direct impact on the breeding success of its seabird hosts and vectors several pathogens, including Lyme disease spirochaetes, understanding its invasion dynamics is essential for predicting its impact on polar seabird populations. Here, we use population genetic data and host serology to test the hypothesis that I. uriae recently expanded into Svalbard. Both black-legged kittiwakes (Rissa tridactyla) and thick-billed murres (Uria lomvia) were sampled for ticks and blood in Kongsfjorden, Spitsbergen. Ticks were genotyped using microsatellite markers and population genetic analyses were performed using data from 14 reference populations from across the tick's northern distribution. In contrast to predictions, the Spitsbergen population showed high genetic diversity and significant differentiation from reference populations, suggesting long-term isolation. Host serology also demonstrated a high exposure rate to Lyme disease spirochaetes (Bbsl). Targeted PCR and sequencing confirmed the presence of Borrelia garinii in a Spitsbergen tick, demonstrating the presence of Lyme disease bacteria in the high Arctic for the first time. Taken together, results contradict the notion that I. uriae has recently expanded into the high Arctic. Rather, this tick has likely been present for some time, maintaining relatively high population sizes and an endemic transmission cycle of Bbsl. Close future observations of population infestation/infection rates will now be necessary to relate epidemiological changes to ongoing climate modifications.

Abstract:

Dans un contexte de réchauffement climatique, la compréhension de l’évolution passée et future du climat dans le monde représente un enjeu majeur, dans la mesure où la calotte Antarctique peut contribuer à la hausse du niveau marin de près de 60 m. De ce fait, il est important d’appréhender et de documenter la variabilité climatique récente impactant le bilan de masse de surface antarctique, plus spécifiquement dans les régions côtières. Néanmoins, les enregistrements issus des observations instrumentales et satellitaires sont bien trop courts pour faire la distinction entre la variabilité naturelle du signal climatique et l’impact anthropique. D’où le lancement du raid scientifique ASUMA (« Improving the Accurancy of SUrface Mass balance of Antarctica »), dans le cadre de l’ANR (« Agence Nationale de la Recherche »), en Terre Adélie, zone côtière à fort taux d’accumulation caractérisée par la présence de vents catabatiques, afin de mieux connaitre l’évolution actuelle du bilan de masse. Un volet du projet est d’analyser la composition isotopique des carottes de névé dans l’objectif de fournir des informations sur le cycle hydrologique atmosphérique et la dynamique climatique. D’ailleurs, Sentia GOURSAUD (2018)  montre que, dans la région côtière de Terre Adélie, la composition isotopique ne dépend pas que de la température de surface locale mais qu’elle est aussi sous l’influence d’autres facteurs (dynamique atmosphérique, sources et transport de l’humidité, phénomènes post-déposition).

Dans ce rapport, deux sites de forages de carottes courtes du programme ASUMA ont été étudiés dans l’objectif de faire un transect le long de la pente menant au haut plateau antarctique, entre les points D47 à 1550 m d’altitude et STOP_0 à 2460m. Les mesures isotopiques effectuées ont permis de reconstruire la variabilité climatique sur les 50 dernières années grâce à une méthode analytique continue, l’analyse en flux continu ou CFA (« Continuous Flow Analysis »). Bien que cette méthode soit utilisée en laboratoire depuis quelques années, elle a été récemment développée au LSCE sur les carottes de névé.