Géosciences Environnement Toulouse

Zenith Total Delay (ZTD) estimates derived from GNSS observations are essential for atmospheric and geodetic applications. When processed using Precise Point Positioning (PPP), ZTD time series exhibit enhanced stability compared to network-based approaches. However, occasional outliers - ranging from a few centimetres to several meters - still occur, potentially degrading product quality and impacting downstream applications. The mechanisms driving these anomalies remain poorly understood, and their characterisation is critical for improving PPP-based ZTD products. This study examines the nature, origins, and possible mitigation strategies for such outliers in order to enhance the reliability of GNSS-derived tropospheric parameters.We perform sensitivity tests using the CNES’s GINS software in PPP mode with integer ambiguity resolution, complemented by simplified PPP-like simulations, to identify the mechanisms underlying ZTD outliers. Particular attention is given to pre-processing procedures, which are critical for detecting and handling problematic observations and significantly impact ZTD accuracy. Building on this diagnostic phase, we explore parameter regularisation strategies aimed at mitigating the occurrence of ZTD outliers while preserving high processing quality. These analyses provide insights into both the origin of anomalies and practical approaches for improving the robustness of PPP-based tropospheric products.In addition, we investigate complementary post-processing screening methods based either on purely statistical approaches or on the comparison with independent atmospheric reanalysis ZTD data. Combined with the strategies described above, these methods aim to reduce ZTD outliers while preserving geophysical variability. This integrated approach enhances GNSS positioning performance and improves the reliability of long-term GNSS-derived tropospheric time series, supporting climate monitoring and other atmospheric applications.

The thermo-tectonic evolution of the Western Mediterranean realm reflects the superimposition of several orogenic phases inclusing the Pyrenean convergence, the Alpine collision and subsequent back-arc extension related to the opening of the Liguro-Provençal Basin. However, the long-wavelength geodynamic forcing driving this evolution remains debated. Most reconstructions rely either on basement-derived thermochronology or on basin-scale stratigraphic records, leading to segmented and sometimes conflicting interpretations. Here, we present a coupled thermochronological approach integrating crystalline basement massifs and their sedimentary cover to reconstruct the continuous geodynamic evolution of southeastern France within the Western Mediterranean realm from the Cretaceous to the Oligo-Miocene. We combine apatite and zircon fission-track and (U–Th)/He data from the Maures–Tanneron and Pelvoux crystalline massifs with new oxy-hydroxide (U–Th)/He constraints from karst-hosted bauxites and subalpine sedimentary systems of the Vocontian Basin. These datasets are jointly interpreted to derive regionally consistent time–temperature paths.Results reveal a coherent lithospheric-scale thermal signal characterized by (i) mid-Cretaceous oxide crystallization related to Durancian Isthmus uplift, coeval with heating of the crystalline massifs, (ii) Late Cretaceous to Paleogene heating followed by cooling of bauxites driven by flexural and tectonic burial during Pyrenean convergence, synchronous with exhumation of adjacent crystalline massifs, and (iii) Oligo-Miocene heating and cooling associated with Liguro-Provençal back-arc rifting. These thermal trends are independently supported by U-Pb calcite ages documenting brittle deformation and fluid circulation within subalpine and Vocontian basins.Basement and cover record synchronous thermal responses, while U-Pb calcite ages constrain the brittle response of sedimentary basins to the same lithospheric-scale deformation, indicating that sedimentary basins acted as passive recorders of lithospheric-scale forcing rather than isolated depocenters. This coupled approach demonstrates that long-wavelength geodynamic forcing controlled both exhumation of crystalline massifs and subsidence of adjacent basins, providing a unified thermo-tectonic framework for the Western Mediterranean realm.

Watersheds provide fundamental hydrological ecosystem services for human well-being and the environment, such as water provisioning, hydrological cycle regulation, and erosion control; however, these services face increasing anthropogenic and climatic pressures. This study assessed individual and combined impacts on the hydrological functionality of the Piuray–Ccorimarca watershed (Cusco, Peru) using a calibrated Soil and Water Assessment Tool (SWAT) model, analyzing water yield, soil water storage, and sediment transport across 20 scenarios. An ensemble of 10 Coupled Model Intercomparison Project Phase 6 (CMIP6) models with bias correction was implemented, integrated with land transformation projections contemplating urban expansion associated with airport development and forest recovery through Payment for Ecosystem Services mechanisms. The results reveal climate change as the dominant driver, generating water yield increases and soil water content improvements primarily due to evapotranspiration decoupling that increases the runoff coefficient. In contrast, land use change produces substantially smaller hydrological effects but critically intensifies sediment yield. Spatial vulnerability analysis identified eight persistently critical sub-basins (20.5% of area) where soil water content emerged as the dominant limiting factor. These findings establish a clear management hierarchy prioritizing climate adaptation over land use interventions, with differentiated strategies required for critical zones demanding structural interventions versus non-critical areas amenable to flexible conservation approaches.

The Earth's biosphere exhibits a notable diversity of forms, yet the full morphological extent and limits of life remain largely unexplored. Here, we develop a geometric complexity space for comparing all known unicellular and multicellular phyla using fractal descriptors of the density and heterogeneity of body mass and structure. By applying this approach to a large set of extant biological shapes, we show that life exploits a tiny portion of structural possibilities, clustering around linear, rounded, and densely structured forms, while consistently avoiding complex heteromorphic ones. We show that this restriction results from deep physical, metabolic, and developmental limitations, shaped over geological time by the evolution of body size and ecological lifestyle. Our findings provide a global, quantitative perspective on the long-standing interplay between chance and necessity in evolution, with implications for the expected forms of life beyond Earth.

Many of the world’s sandy coastlines experience significant seasonal and inter-annual variability, driven by both natural and anthropogenic factors. Natural influences include sea-level fluctuations, sediment imbalances typically caused by wave action, and changes in sediment sources from continental regions, while anthropogenic influences also play a role. This study focuses on the challenges of implementing a global shoreline evolution model which adapts the physics of smaller-scale local models to the much larger scales characteristic of climate models, typically on the order of 100 km. By incorporating regional dynamics and often overlooked factors such as sediment exchange, riverine inputs and sea level variations, this study aims to capture how coastal regions respond to climate-induced multi-factor stresses. Using optical satellite-derived coastlines, satellite altimetry data and model reanalysis, we test whether a simplified representation of complex processes can effectively reveal key regional patterns and sensitivities to climate drivers. • GLOBCOAST simplifies shoreline processes to capture broad global trends in coastal evolution. • The model assesses coastal sensitivity to key drivers like waves, water levels, and terrestrial runoff. • It reveals large-scale coastal variability, offering insights into global responses to climate changes.