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Review of physical processes and parameterizations of sea ice in a changing climate
No full textInternational audienceSea ice is a crucial component of polar climate systems, and is undergoing substantial changes in both the Arctic and the Southern Ocean due to evolving climatic conditions. The Arctic Ocean is undergoing a transition from being perennially ice-covered to be- ing only seasonally ice-covered. The shrinking and thinning of ice cover have been at- tributed to changes in atmospheric and oceanic forcing, as well as to changes in the phys- ical properties of pack ice. The Southern Ocean also shows signs of change, reflected in recent minima and amplified seasonality. As global warming persists in the coming decades, the role of sea ice in polar climate systems is poised for further transformation. How- ever, current theoretical frameworks and parameterization methods used in numerical models to simulate sea ice evolution and its interaction with the oceanic and atmospheric boundary layers are largely rooted in measurements from an earlier era characterized by thicker multiyear ice. In this review we aim to summarize the evolution of physical drivers governing the dynamics and thermodynamics of sea ice, snow, and ocean/atmosphere boundary layers. Furthermore, we describe and assess existing parameterization meth- ods of sub-grid scale processes, discuss recent observational findings, and propose essen- tial improvements
Origin, size distribution and hygroscopic properties of marine aerosols in the south-western Indian Ocean: report of 6 campaigns of shipborne observations
No full textMarine aerosol observations from 6 shipborne campaigns carried out in 2021 and 2023 in the southwest Indian Ocean are presented. A set of aerosol instruments is used to study the spatial and temporal variability of the aerosol size distribution, cloud condensation nuclei (CCN), activation diameters, and hygroscopicity (κ). Total number of aerosols (Na) shows concentration above 1500 cm -3 in polluted areas, and between 100-1500 cm -3 in the open ocean. CCN measurements (0.2 %, 0.4 % supersaturation) range from 40 to 500 cm -3 . At 0.2 % (0.4 %) supersaturation, the average activation diameter is 104 (76) nm and κ is 0.36 (0.25). Using a back-trajectory model, the aerosol data were classified into three source regions.Aerosols are hydrophobic in the continental group (κ from 0.1 to 0.13), hydrophilic in the Subtropical Indian Ocean group (κ from 0.24 to 0.4), and intermediate values are found in the Southern Indian Ocean group (κ from 0.17 to 0.22). Subtropical Indian Ocean κ increases with stronger wind speeds. Southern Indian Ocean κ decreases significantly (between 0.2 % and 0.4 % supersaturation) with stronger wind speeds, probably due to a higher concentration of organic species on the smallest particle surface. High aerosol concentration events are presented. Pollution related to air masses passing through a well-developed continental boundary layer. Nucleation triggered by clear skies between two cloudy periods. Arrival of air masses at the ship's location after a precipitation event.</p
Chronic and reactivated dengue infection in an immunocompromised host: insights from a case report
No full textInternational audienceBackground Dengue, a viral infection transmitted by mosquitoes, is a growing global health concern, particularly as its spread now puts half of the world’s population at risk. While dengue usually resolves after the primary infection, persistent or chronic cases can occur in immunocompromised individuals.Case presentation This case study reports a 43-year-old woman with lupus nephritis and end-stage kidney disease who experienced symptomatic dengue reactivation nearly three years after her initial infection. Despite low viral loads, dengue RNA was detectable in her blood multiple times between 32 and 34 months after the initial detection. Genomic analysis confirmed that the same DENV-1 strain persisted, suggesting chronic infection rather than reinfection. The patient's immunosuppressive treatments, including rituximab, likely impaired her immune response to the initial infection, contributing to viral persistence. Additionally, her profound immunosuppressive state at the time of reactivation, potentially exacerbated by coinfections, may have triggered the virus to re-emerge.Conclusion This case highlights the rare but clinically relevant possibility of chronic dengue infection in immunocompromised patients. The confirmed persistence of the same viral strain over nearly three years challenges the conventional view of dengue as a strictly acute infection. It raises concern about the potential for reintroduction and re-emergence of previously circulating strains, as well as the detrimental tissue consequences of chronic infection by the virus. These findings have important implications for clinical management, diagnostic strategies, and public health surveillance, and underscore the need for further research to better understand the mechanisms of dengue chronicity—particularly those involving viral immune evasion and host immune dysfunction
SPATIAL DISTRIBUTION OF ARCHAEOLOGICAL SITES IN LORALAI DISTRICT, BALOCHISTAN, PAKISTAN BASED ON GEOGRAPHIC INFORMATION SYSTEM (GIS)
No full textInternational audienceLoralai hosts a number of archaeological sites and is considered an important area, where a concentration of prehistoric archaeological sites was noted in previous research. For this purpose, the GIS spatial analysis methods, such as Buffer, K-means clustering and heat map, were used to understand the distribution of archaeological sites in the landscape. The initial result obtained from GIS and ground surveys in 2020, 2021, and 2022 indicated that the prehistoric people wisely resided in those places of the landscape where they found water and fertile land. The paper shows that natural factors were the reason behind the distribution of archaeological sites in the study area.</div
Estimating sound pressure levels from distributed acoustic sensing data using 20 Hz fin whale calls
No full textInternational audienceDistributed acoustic sensing (DAS) is a promising technology for underwater acoustics, but its instrumental response is still being investigated to enable quantitative measurements. We use fin whale 20 Hz calls to estimate the conversion between DAS-recorded strain and acoustic pressure. Our method is tested across three deployments on varied seafloor telecommunication cables and ocean basins. Results show that after accounting for well-established DAS response factors, a unique value for water compressibility provides a good estimate for the conversion. This work represents a significant step forward in characterizing DAS for marine monitoring and highlights potential limitations related to instrument noise floor
La ville numérique sans ses algorithmes : fabrique urbaine ordinaire, acteurs, institutions
No full textInternational audienceAs research on cities and digital technology gains prominence in urban studies, this position critically reassesses the common emphasis on the extraordinary nature of futuristic projects often associated with digital technology in urban imaginaries. Rather than viewing the city merely as a construct governed by algorithms and reduced to technical objects – such as sensors, mobile applications, or platforms its innovations, and its emblematic projects which are often short-lived or unfinished, this article encourages an exploration of how digital technology is negotiated, interpreted, and integrated into everyday life. This includes not only professional and institutional practices but also the daily urban practices of citizens. By focusing on the ordinary urban fabric, we can examine how digital technologies are transforming relationships among institutions, businesses, and residents in city production, as well as how these changes are inscribed within broader urban and territorial dynamics. This perspective also invites attention to the agency of the diverse actors engaged in urban production, acknowledging that their relationship with technology is never overdetermined.À l’heure où les travaux sur la ville et le numérique occupent une place de plus en plus importante dans la recherche urbaine, cet article de positionnement propose de faire un pas de côté par rapport aux contributions portant sur l’exceptionnalité de projets futuristes souvent associés au numérique dans les imaginaires urbains. Plutôt qu’une ville gouvernée par les algorithmes, résumée à ses objets techniques (capteurs, applications mobiles ou encore plateformes), à ses innovations et projets emblématiques, souvent éphémères ou inaboutis, nous invitons à observer la manière dont le numérique se négocie, s’interprète et s’incorpore au quotidien, dans des pratiques professionnelles, institutionnelles et dans des pratiques habitantes qui concourent à fabriquer la ville. Appréhender la fabrique urbaine ordinaire permet ainsi de comprendre comment les technologies numériques redéfinissent les rapports entre institutions, entreprises et habitants dans la construction de la ville et comment ces transformations s’inscrivent dans des dynamiques urbaines et territoriales. Ce parti pris est aussi une invitation à se concentrer sur l’agentivité des acteurs de la fabrique urbaine dans leur diversité, dont le rapport à la technologie n’est jamais surdéterminé
Using PlanetScope NDVI time series to detect the phenology of individual trees in the Sahel
No full textInternational audienceA C T New advancements in satellite technology enable more accurate observation of woody population dynamics, providing greater insights into the underlying processes that influence their change. In this study, we evaluate the use of PlanetScope NDVI time series to track the phenology of individual trees in the Sahel, where groundbased environmental surveys are scarce. Five-year NDVI time series were produced for 398 trees with known species recorded in Mali, Senegal, and Niger. Clouds and high aerosol contamination were filtered using MODIS products and focused on the dry season to minimize the influence of background NDVI directly (through crown influence) or indirectly (through adjacency effects). Each NDVI time series profile was fitted with a spline model to obtain the minimum NDVI day of year during the dry season. PlanetScope NDVI time series accurately captured the photosynthetic phenology of individual tree crowns in the Sahel, with discernable differences between individuals and species. When species were grouped based on four phenology types, deciduous and inverse deciduous species exhibited a relatively consistent phenological pattern across all sites. The phenology of semievergreen species and evergreen species, which include species with few leaves, was more heterogeneous. Intraspecies variation was relatively modest between sites, and most species maintained a similar NDVI profile, with shifts in leaf phenology events correlating with the timing of the wet season in each site. Overlap between the different phenology groups indicates that transitions between phenology types and species are not clear-cut, and even individuals of the same species can demonstrate plasticity. Furthermore, NDVI profiles were extracted for 500 randomly selected tree samples within eight 10 km 2 clip boxes distributed along the West African rainfall gradient from 9.9 • to 16.6 • latitude at -1.6 • longitude. This analysis showed a strong relationship between the phenology of woody plants and the timing and distribution of rainfall at each latitude. Green-up of woody vegetation before herbaceous vegetation was marked in the more southern Sahelo-Sudanian latitudes. Additionally, despite the prolonged dry season in the more northern semi-arid latitudes, trees retained their greenness remarkably late into the dry season. Increased air temperature and dryness as a result of climate change could impact tree function in this region and needs individual-based monitoring.</div
Immunological surveillance against cancer across mammals
No full textInternational audienceContrary to expectations based on their higher cell numbers, larger and longer-lived species do not face dramatically increased risk of cancer. This strongly suggests that evolution has fashioned natural cancer resistance mechanisms, yet our knowledge remains limited on what these mechanisms might be. The cancer immunological surveillance hypothesis, proposed by Burnet and Thomas in the 1950s, highlights immunity as a key factor determining species-specific cancer resistance. Here we address the original, evolutionary interpretation of this hypothesis by investigating the relationship between cancer mortality risk and markers of efficient antigen presentation. Our results show that the expansion of the MHC class I gene complex, as well as increased selection for diversity at these genes is associated with sharply decreasing cancer mortality risk across mammals. This suggests that the efficient presentation of diverse peptides in somatic cells is important for cancer suppression across mammals, providing pioneering evidence that supports the cancer immunosurveillance hypothesis across species
Blood donors as sentinels for genomic surveillance of West Nile virus in Germany using a sensitive amplicon-based sequencing approach
No full textInternational audienceBackground: West Nile virus (WNV) has emerged as a public health concern in Germany since its first detection in 2018, with evidence of expanding geographic spread. Genomic surveillance is critical for tracking viral evolution, identifying introductions, and monitoring local transmission. However, genome recovery from lowviremia samples such as those obtained through blood donor screening remains technically challenging. Aim: To develop and validate a sensitive amplicon-based sequencing protocol optimized for WNV lineage 2 and apply it to low-titer samples to support genomic surveillance in Germany. Methods: A novel primer scheme was designed for WNV lineage 2 and applied to 43 nucleic acid testing (NAT)-positive blood donor samples collected between 2020 and 2024. Amplicon-based sequencing performance was benchmarked against metagenomic next-generation sequencing (mNGS). Recovered genomes were subjected to phylogenomic analysis to assess viral diversity and transmission dynamics. Results: The amplicon protocol enabled genome recovery (> 70% coverage) from samples with viral loads as low as ∼10¹ RNA copies/µL, outperforming metagenomic NGS (mNGS). Of the 43 samples, 30 yielded complete or nearcomplete genomes. Six distinct WNV subclades (2A-2F), including German strains, were identified, indicating multiple introductions into Germany from Central Europe. Subclade 2F emerged as the dominant and widely distributed group. Berlin, Brandenburg, Saxony, and Saxony-Anhalt were identified as persistent transmission hubs. Conclusion: This study highlights blood donors as valuable sentinels for WNV genomic surveillance. The validated amplicon-based sequencing approach enables sensitive, scalable genome recovery from lowviremia samples, and when integrated with routine blood donor screening, provides a robust framework for early detection, transmission dynamics, and public health preparedness.</div
Temperature-dependent benefits and costs of cytoplasmic male sterility in snail Physa acuta
No full textInternational audienceCytoplasmic male sterility (CMS) originates from a mito-nuclear conflict where mitochondrial genes induce male sterility and nuclear genes restore male fertility in hermaphrodites. The first observation of CMS in animals was reported recently in the freshwater snail Physa acuta where it is associated with two extremes divergent mitotypes D and K. The D individuals are male-steriles while male fertility is restored by nuclear genes in K and are found mixed with the most common male-fertile N mitotype in natural populations (i.e. gynodioecy). We compared male and female fitness, growth rate and metabolism between the three mitotypes at two temperatures as this factor influences CMS in gynodioecious plants via alteration of mitochondrial functioning. Temperature did not affect male sterility which depended only on the mitotype and the presence of restorers. Our results provided evidence that CMS is beneficial to female fitness in the absence of restorers while it is costly in their presence, and furthermore driven by body mass, fulfilling a key theoretical condition for the long-term maintenance of gynodioecy. Fitness benefits and costs mediated by differences in body mass are enhanced at cold temperature, suggesting that the system dynamics may vary according to thermal conditions in nature