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Persistence of Gondwanan woods in Myanmar through the Paleogene
No full textInternational audienceBackground and Aims: Many plant taxa of the tropical forests of South and Southeast Asia have been proposed to have Gondwanan ancestors. One significant event contributing to this origin is the African-Indian-Southeast Asian Floristic Interchange, with first events occurring during the late Cretaceous-early Eocene, before the onset of land connections between India and Asia. As the timing and mechanisms of these dispersals remain unclear, we aim to better document the dynamics of this interchange. The Burma Terrane of Myanmar, once a separate tectonic block, but now part of Southeast Asia, accreted to India in the early Paleogene, making it an ideal location to study floristic exchanges. Methods: We section and describe ten fossil wood specimens, analyzing their anatomy to determine affinities with extant taxa and their biogeographical history. Key results: We present six taxa from the late middle Eocene and lower Oligocene of Myanmar‒ including new species and a new genus ‒ from the families Fabaceae, Moraceae, Myrtaceae, Meliaceae, and Malvaceae. These findings document an extended Gondwanan distribution and biogeographical history of paleotropical lineages. Conclusions: These taxa likely dispersed during the early Paleogene from Africa to India and Myanmar, forming what we refer to as the Indo-Myanmar Paleogene floristic province. This province, which had Gondwanan affinities, persisted at least until the early Oligocene, time of suggested land connection with Asia, and served as a ‘holding pen’ for the further dispersal of some taxa into Southeast Asia, such as the Dipterocarps. However, other taxa, such as those documented in this study, did not disperse further and eventually disappeared during the Neogene. The mechanisms behind these dispersal barriers and the reasons for the eventual disappearance of these taxa from the region are still to be investigated, and could be related to the late Cenozoic changes in monsoonal climate of South Asia
AIKON : A Modular Computer Vision Platform for Historical Corpora
No full textWe present AIKON, a modular platform designed to foster historians’ collaborations on custom document corpora, and support their workflow by leveraging computer vision processes. Among the many tools that have emerged in recent years to empower historians with AI tools, AIKON stands out by: (i) providing a comprehensive environment, supporting the historians’ workflow from corpus construction to results validation and visualization; (ii) following a modular and scalable design, that makes it easy to customize the platform and to develop new modules
Tropical Cirrus Lifetime Estimated From Superpressure Balloon‐Borne Lidar Observations
No full textInternational audienceTropical tropopause layer (TTL) cirrus clouds play a key role in the Earth climate system. Yet the relative role of the various processes shaping them remains poorly known. Characterizing the temporal evolution of cloudy structures from observations is essential to address this issue but represents a challenge. Indeed, space‐ and airborne platforms move fast and mainly provide instantaneous snapshots. In boreal winter 2021–2022, two balloon‐borne lidars flew over the Equatorial Pacific Ocean, slowly drifting above the clouds. We use those unique nighttime observations to quantify the distribution of TTL cloud lifetime above this homogeneous region. This distribution is strongly asymmetric: half of the clouds live less than 1 hr, but their mean lifetime is about 6 hr. The few long‐lived clouds ( hr) dominate the cloud cover. Those results compare reasonably well with TTL cirrus lifetimes in the ERA5 reanalysis, although the modeled TTL cloud cover is largely underestimated
Surface soil phytolith assemblages in different vegetational zones of the Nilgiri Biogeographical Region, Western Ghats, India: implications for palaeoclimatic interpretation
No full textInternational audienceIn the present study, we analyzed surface soil phytolith assemblages from 70 sites across seven vegetation types spanning an altitudinal range of 300–2400 m in the Nilgiri Biogeographic Region (NBR), Western Ghats, India. A total of 29 morphotypes were identified, dominated by BILOBATE, SADDLE, RONDEL, ELONGATE, BLOCKY, and POLYHEDRAL forms. Lowland seasonally-dry tropical forests (STDFs) were characterized by high proportions of C4 grass indicators, mid-elevation moist and wet forests exhibited mixed C3-C4 signatures, while upper montane forests and grasslands contained phytolith assemblages indicating relative grass dominance, although absolute grass cover was underestimated and woody signals overrepresented. Discriminant analysis achieved a moderate classification accuracy of ∼55 %, indicating a possible overlap between vegetation types and transitional communities. Principal Component Analysis indicated that elevation and mean annual precipitation as primary controls on phytolith composition. Morphometric analysis of BILOBATE phytoliths revealed decreasing dimensions (length and shank length) with elevation and strong positive correlations with mean annual temperature, highlighting temperature as a key driver of silica deposition. Overall, this first phytolith-based vegetation study in the NBR establishes a modern reference framework for interpreting the fossil record. Our findings demonstrate both the potential and limitations of phytolith assemblages and morphometrics for reconstructing past vegetation and climate in NBR and similar tropical montane ecosystems
Towards systematic searches for LISA white dwarf binaries with multiband photometry
No full textInternational audienceContext. Ultra-compact double white dwarfs (DWDs) represent key targets for multi-messenger astrophysics, as they may be observed both through gravitational waves and the electromagnetic (EM) spectrum. The future Laser Interferometer Space Antenna (LISA) will detect thousands of these systems, and they are predicted to be the most numerous science targets of the mission.Aims. We develop a strategy to identify LISA source candidates in multiband photometric surveys.Methods. We constructed a synthetic EM catalogue of white dwarf (WD) detections based on a population synthesis code combined with a semi-analytical model of the Milky Way and a consistent cooling model for the evolution. We compared sources in the LISA band with other WD observations in magnitude-colour and colour-colour plots.Results. From a full sky survey with u ≤ 24.5, we find that 57% of the sources in the LISA band occupy a specific region in colour-colour diagrams. Inside this area, we find that ∼63% (6.5 × 104) of EM observations are LISA candidates, ∼31% (3.2 × 104) are DWDs slightly outside the LISA frequency range, and only a small contamination comes from single WDs and wider binaries.Conclusions. We find that the colour distributions of close DWDs represent a powerful tool to distinguish potential LISA sources from the broader WD population. This is an avenue to select candidates for further follow-up and identification
Urban morphology at 60m resolution over Europe using Geoclimate and OpenStreetMap
No full textInternational audienceModeling the climate of urban areas requires a realistic urban model. But to be able to reproduce the climate of a specific city, the urban canopy model has to take into account its particularities such as the materials that make up the city, its geographical extend or the different morphologies of the urban canyon encountered in the city. Even a perfect urban canopy model needs a good representation of the city to be realistic.OpenStreetMap is a complete, worldwide, open and collaborative database using multiple conventional and crowd-sourced data.To take advantage of such database, Geoclimate tool has been used to retrieve the urban morphology over the whole Europe at the block scale. In addition to building, road and vegetations fractions, Geoclimate is able to retrieve the wall density and the building height in every city.Different metrics were used to evaluate the richness of this European database. Then the data, originally in vector format has been rasterized at a 60m resolution and formatted to be used with Town Energy Balance (TEB) urban canopy model. The benefit of using such database in numerical weather prediction model such as MESONH over a well used state-of-the art land cover database such as ECOCLIMAP-SG is presented
Unexpected latest Pleistocene W-dipping reverse fault-slip in the Maritimes Alps (SE France )- Insights from passage offset in Mescla Cave
No full textInternational audienceWe investigate the late Quaternary fault reactivation within Mescla Cave, offering the first dated offset in the southwestern Alps (SW France). While our dataset is limited to one outcrop, the observed W-dipping reverse slip displacing cave passage represents an outlier among the scarce young Quaternary tectonic structures expected in this seismically active region. Using the 230 Th/U method, we dated fractured flowstones that predate the slip and stalagmite growth on the fault plane, bracketing the reactivation time frame from 51.6 ± 2.4 ka to 11.7 ± 1.3 ka. We interpret the detected displacement (23 cm) as secondary faulting associated with a larger, possibly distributed deformation along an unrecognised primary structure. Despite limited structural data containing only one strain, our findings highlight the geochronological value of caves in preserving deformation otherwise erased by erosion and provide new insights and questions into the active tectonics of the Maritimes Alps
CYCLOPs: a Unified Framework for Surface Flux-Driven Cyclones Outside the Tropics
No full textInternational audienceCyclonic storms resembling tropical cyclones are sometimes observed well outside the tropics. These include medicanes, polar lows, subtropical cyclones, Kona storms, and possibly some cases of Australian East Coast cyclones. Their structural similarity to tropical cyclones lies in their tight, nearly axisymmetric inner cores, eyes, and spiral bands. Previous studies of these phenomena suggest that they are partly and sometimes wholly driven by surface enthalpy fluxes, as with tropical cyclones. Here we show, through a series of case studies, that many of these non-tropical cyclones have morphologies and structures that resemble each other and also closely match those of tropical transitioning cyclones, with the important distinction that the potential intensity that supports them is not present in the pre-storm environment but rather is locally generated in the course of their development. We therefore propose to call these storms CYClones from Locally Originating Potential intensity (CYCLOPs). Like their tropical cousins, the rapid development and strong winds of cyclops pose a significant threat and forecast challenge for islands and coastal regions
The effect of micas on the strength of experimental granitoid fault gouge
No full textInternational audienceSheet silicates play an important role in shaping crustal rheology and shear localization at shallow depths through their low strength. However, their effect at deeper levels (>3 km) remains unclear. We conducted hydrothermal ring shear experiments on three simulated gouges with similar quartz content but varying mica types and contents. Applied temperatures T ranged from 20 to 650 • C, with sliding velocities V between 0.03 and 1 μm/s, and an effective normal stress and pore water pressure of 100 MPa. Shear strains up to 30 were attained.At 1 μm/s and 20 • C, granitoids exhibit a higher friction coefficient (μ = 0.81) than the muscovite-rich (μ = 0.47) and biotite-rich gouges (μ = 0.44). With increasing T at a fixed V of 1 μm/s, μ of granitoids decreases to 0.61 at 650 • C, whereas muscovite-and biotite-rich gouges strengthen (μ = 0.56-0.69) until T reaches 200-450 • C. At 650 • C, weakening is observed in granitoid and muscovite-rich gouges as V decreases, while biotite-rich gouge shows no change. Granitoids are weaker than the mica-rich gouges once V decreases to 0.03 μm/s and T reaches 650 • C. All gouges at 650 • C exhibit μm-wide principal slip zones, featuring microstructures consistent with dissolution-precipitation creep (DPC). These include truncated grain contacts, mineral precipitates, submicrometer grain size and low porosity. Muscovite breakdown and biotite formation occurs in muscovite-rich gouge as they weaken. Our results imply that mica enrichment in granitoid faults can lead to a weaker upper crust and stronger middle crusts as they weaken less than granitoids. The onset of DPC may trigger a frictional-viscous transition at greenschist facies depths.</div
Sedimentary record of submarine gravity‐flow events in the southern Ryukyu forearc during the last 200 000 years: archive of mega‐earthquakes and tsunamis
No full textInternational audienceDespite high convergence velocity, the southern Ryukyu subduction has relatively low and sparse instrumental seismicity, in contrast with the Yaeyama Islands, hit by huge tsunamis over the last few thousand years. This study explores the potential of deep marine sediments to record past large earthquakes and tsunamis. During the MD214/EAGER cruise (2018), four sediment cores (12 to 23 m long) were collected in the forearc area (south of Yaeyama Islands), which is an efficient trap for gravity-flow deposits. The chrono-stratigraphic framework is established with radiocarbon dating, δ 18 O stratigraphy, U-series data and tephra analysis including major/trace elements and Hf-Pb-Sr-Nd isotopes. In the basin floor, bulk sedimentation rates locally exceed 60 cm/ka, while hemipelagic sedimentation rates range from 3 to 8 cm/ka, similar to values derived from U-series data in recent sediments of the boxcores. Twenty-four gravity-flow deposits were identified over the last 20 000 years, a frequency consistent with the past tsunamis recorded in the coastal sediments over the last thousand years, emphasising their interest as archives of earthquakes and major tsunamis. At a regional scale, bulk sedimentation rates fall under 10 cm/ka for 48 large-scale gravity-flow deposits over the last 200 000 years. With average recurrence periods about 3500-4000 years, these regional events could be triggered by subduction large earthquakes (M > 7). Finally, four exceptionally large submarine gravity-flow events (mega-deposits) of unclear origin have been documented over the last 200 000 years. This work provides an 1 See Acknowledgements for the List of other participants of EAGER Cruise