Opérations topologiques pour la géomorphologie

National audienceLes paysages naturels résultent d'une succession d'événements géomorphologiques qu'il convient de simuler pour produires des résultats plausibles. En particulier, les changements topologiques doivent être pris en compte durant la formation de géométries complexes comme les arches, les ponts ou les tunnels naturels. Nous présentons une nouvelle approche pour simuler les évolutions géomorphologiques d'un terrain en 3D conçu comme un ensemble de volumes définis dans un modèle topologique, et décrivons un ensemble d'opérations atomiques afin de gérer les événements topologiques de manière robuste. Ces opérations somt combinées pour produire des scénarios d'évolutions plus complexes dans un modeleur basé sur les cartes généralisées, permettant de réduire le coût mémoire par rapport aux méthodes utilisant des voxels par exemple

Ocean temperature impact on ice shelf extent in the eastern Antarctic Peninsula

The recent thinning and retreat of Antarctic ice shelves has been attributed to both atmosphere and ocean warming. However, the lack of continuous, multi-year direct observations as well as limitations of climate and ice shelf models prevent a precise assessment on how the ocean forcing affects the fluctuations of a grounded and floating ice cap. Here we show that a +0.3–1.5 °C increase in subsurface ocean temperature (50–400 m) in the northeastern Antarctic Peninsula has driven to major collapse and recession of the regional ice shelf during both the instrumental period and the last 9000 years. Our projections following the representative concentration pathway 8.5 emission scenario from the Fifth Assessment Report of the Intergovernmental Panel on Climate Change reveal a +0.3 °C subsurface ocean temperature warming within the coming decades that will undoubtedly accelerate ice shelf melting, including the southernmost sector of the eastern Antarctic Peninsula.J.E. and C.E. are financially supported by the Spanish Ministerio de Economia y Competitividad (CTM2014–60451-C2–1-P) co-funded by the European Union through FEDER funds. J.-H.K. was supported by the grants funded by the Korea Polar Research Institute (KOPRI, NRF-2015M1A5A1037243 and PE19010). S.S. and J.S.S.D. are supported by the Netherlands Earth System Science Center funded by the Dutch Ministry of Education and Science (OCW). G.S. and D.S. were funded by the EMBRACE project (European Union’s FP7, Grant Number: 282672). We also acknowledge funding from the French ANR CLIMICE, ERC ICEPROXY 203441, ESF PolarClimate, HOLOCLIP 625 and FP7 Past4Future as well as the Netherlands Organisation of Scientific Research (NWO) through a VICI grant to S.S. The HOLOCLIP Project, a joint research project of ESF PolarCLIMATE programme, is funded by national contributions from Italy, France, Germany, Spain, Netherlands, Belgium and the United Kingdom. The research leading to these results has also received support from the European Union’s Seventh Framework programme (FP7/2007–2013) under Grant Agreement No. 243908, “Past4Future, Climate change – Learning from the past climate”

Sea ice diatom contributions to Holocene nutrient utilization in East Antarctica

Combined high-resolution Holocene δ30Sidiat and δ13Cdiat paleorecords are presented from theSeasonal Ice Zone, East Antarctica. Both data sets reflect periods of increased nutrient utilization by diatomsduring the Hypsithermal period (circa 7800 to 3500 calendar years (cal years) B.P.), coincident with a higherabundance of open water diatom species (Fragilariopsis kerguelensis), increased biogenic silica productivity(%BSi), and higher regional summer temperatures. The Neoglacial period (after circa 3500 cal years B.P.) isreflected by an increase in sea ice indicative species (Fragilariopsis curta and Fragilariopsis cylindrus,upto50%) along with a decrease in %BSi and δ13Cdiat(< 18‰ to 23‰). However, over this period, δ30Sidiatdata show an increasing trend, to some of the highest values in the Holocene record (average of +0.43‰).Competing hypotheses are discussed to account for the decoupling trend in utilization proxies including ironfertilization, species-dependent fractionation effects, and diatom habitats. Based on mass balance calculations,we highlight that diatom species derived from the semi-enclosed sea ice environment may have a confoundingeffect upon δ30Sidowncorecompositions of the seasonal sea ice zone. A diatom composition, with approximately28% of biogenic silica derived from the sea ice environment (diat-SI) can account for the increased averagecompo sition of δ30Sidiatduring the Neoglacial. These data highlight the significant role sea ice diatoms can playwith relation to their export in sediment records, which has implications on productivity reconstructions fromthe seasonal ice zone

The evolving SARS-CoV-2 epidemic in Africa: Insights from rapidly expanding genomic surveillance

INTRODUCTION Investment in Africa over the past year with regard to severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) sequencing has led to a massive increase in the number of sequences, which, to date, exceeds 100,000 sequences generated to track the pandemic on the continent. These sequences have profoundly affected how public health officials in Africa have navigated the COVID-19 pandemic. RATIONALE We demonstrate how the first 100,000 SARS-CoV-2 sequences from Africa have helped monitor the epidemic on the continent, how genomic surveillance expanded over the course of the pandemic, and how we adapted our sequencing methods to deal with an evolving virus. Finally, we also examine how viral lineages have spread across the continent in a phylogeographic framework to gain insights into the underlying temporal and spatial transmission dynamics for several variants of concern (VOCs). RESULTS Our results indicate that the number of countries in Africa that can sequence the virus within their own borders is growing and that this is coupled with a shorter turnaround time from the time of sampling to sequence submission. Ongoing evolution necessitated the continual updating of primer sets, and, as a result, eight primer sets were designed in tandem with viral evolution and used to ensure effective sequencing of the virus. The pandemic unfolded through multiple waves of infection that were each driven by distinct genetic lineages, with B.1-like ancestral strains associated with the first pandemic wave of infections in 2020. Successive waves on the continent were fueled by different VOCs, with Alpha and Beta cocirculating in distinct spatial patterns during the second wave and Delta and Omicron affecting the whole continent during the third and fourth waves, respectively. Phylogeographic reconstruction points toward distinct differences in viral importation and exportation patterns associated with the Alpha, Beta, Delta, and Omicron variants and subvariants, when considering both Africa versus the rest of the world and viral dissemination within the continent. Our epidemiological and phylogenetic inferences therefore underscore the heterogeneous nature of the pandemic on the continent and highlight key insights and challenges, for instance, recognizing the limitations of low testing proportions. We also highlight the early warning capacity that genomic surveillance in Africa has had for the rest of the world with the detection of new lineages and variants, the most recent being the characterization of various Omicron subvariants. CONCLUSION Sustained investment for diagnostics and genomic surveillance in Africa is needed as the virus continues to evolve. This is important not only to help combat SARS-CoV-2 on the continent but also because it can be used as a platform to help address the many emerging and reemerging infectious disease threats in Africa. In particular, capacity building for local sequencing within countries or within the continent should be prioritized because this is generally associated with shorter turnaround times, providing the most benefit to local public health authorities tasked with pandemic response and mitigation and allowing for the fastest reaction to localized outbreaks. These investments are crucial for pandemic preparedness and response and will serve the health of the continent well into the 21st century

MEP news : MNCH evidence into practice in West Africa : number 002

Library has French versionThis one-page MEP News Issue #2, takes stock of activities of the project in the last three months (October to December 2016) and focuses on the project situation analysis and participation at the Cochrane Africa Network meeting. Data collection focuses on the status of knowledge transfer and use of evidence, factoring in gender and health equity, and identification of enabling or inhibiting systemic factors in the area of maternal and child health

Thalassiosira lentiginosa size variation and associated biogenic silica burial in the Southern Ocean over the last 42 kyrs

International audienceThe diatom Fragilariopsis kerguelensis (O′Meara) Hustedt is thought to be the main carrier of biogenic silica to the Southern Ocean sea-floor, thereby attracting most investigations of diatom biometry. Thalassiosira lentiginosa (Janisch) Fryxell, a large centric diatom which is the second most abundant species in the Southern Ocean, conversely received very little attention to date. We here present the first study on modern sediments to explore the variability of the mean valve area of T. lentiginosa in relation to productivity and modern environmental conditions. Larger T. lentiginosa are observed around the Polar Front Zone with size decreasing both northward and southward as previously observed for F. kerguelensis. Such a pattern neither corresponds to the species productivity changes nor with the iron concentration in surface waters. Conversely, this pattern may be partly due to the low efficiency of Si uptake, internal transport and deposition of silicic acid under conditions which are outside of the species specific temperature range, i.e. at the lower and upper limit of the diatom ecological preferences. We also propose that T. lentiginosa mean valve area variations in four deep-sea cores across the frontal zones in the Atlantic and Indian sectors of the Southern Ocean resulted from changes in sea-surface temperatures and sea-ice presence modulating the species ability to make use nutrient stocks and controlling the length of its growing season, respectively. Our results also indicate that T. lentiginosa exported more biogenic silica to the sea-floor than F. kerguelensis over the last 42 kyrs

Topological Operations for Geomorphological Evolution

International audienceGeomorphological processes sculpt the shape of our everyday landscapes and must therefore be simulated to generate plausible digital landscapes. In particular, topological changes must be taken into account during the formation of complex geometries such as natural arches, bridges or tunnels. We present a novel approach to simulate the geomorphological evolution of a 3D terrain represented as a set of volumes stored in a topological model, and describe a set of atomic operations to handle topological events in a robust way. These operations form the basis to successfully implement more complex evolution scenarios in a modelling software based on generalized maps, which could be used to reduce the storage needed by other methods relying on voxel grids or layered data structures

Programming Topological Operations for Visual Illustrations in an Introductory Geomorphology Course

International audienceIn the context of teaching geomorphology phenomena, producing illustrations and animations can be a tedious process. We propose an experimental framework, dedicated to 3D erosion and sedimentation modeling written in C++, combined with an existing topological modeler. Using the ''generalized maps'' as the underlying 3D model, we process each case of collision between elements in the scene in order to guarantee both topological and geometrical coherence during user-defined animations. Erosion and sedimentation operations can be combined to manipulate evolution scenarios leading for example to the creation of arches, bridges, tunnels or caves. Some of these scenarios, implemented in our framework with the help of a geology teacher, are presented in this paper in order to show the technical feasibility of our project before developing new ones