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Inadequacies in the representation of sub-seasonal phytoplankton dynamics in Earth system models
No full textInternational audienceSub-seasonal phytoplankton dynamics on timescales between 8 d and 3 months significantly contribute to annual fluctuations, making it essential to accurately represent this variability in ocean models to avoid distorting long-term trends. This study assesses the capability of Earth system models (ESMs) participating in the Coupled Model Intercomparison Project Phase 6 (CMIP6) to reproduce subseasonal surface ocean phytoplankton variations observed in ocean colour satellite data. Our findings reveal that, unlike sea surface temperature, all models struggle to accurately reproduce the total surface ocean phytoplankton variance and its decomposition across sub-seasonal, seasonal and multi-annual timescales. Over the historical period, some models strongly overestimate sub-seasonal variance and exaggerate its role in annual fluctuations, while others underestimate it. Our analysis suggests that underestimation of sub-seasonal variance is likely a consequence of the coarse horizontal resolution of CMIP6 models, which is insufficient to resolve mesoscale processes -a limitation potentially alleviated with higher-resolution models. Conversely, we suggest that the overestimation of sub-seasonal variance is potentially the consequence of intrinsic oscillations such as predator-prey oscillations in certain biogeochemical models. ESMs consistently show a reduction in variance at sub-seasonal and seasonal timescales during the 21st century under high-emission scenarios. The poor capability of CMIP6 models at simulating sub-seasonal chlorophyll dynamics casts doubt on their projections at these temporal scales and multi-annual timescales. This study underscores the need to enhance spatial resolution and constrain intrinsic biogeochemical oscillations to improve projections of ocean phytoplankton dynamics
Continuum, CO and Water vapour maps of the Orion Nebula. First millimetre spectral imaging with Concerto: First millimetre spectral imaging with CONCERTO
No full textInternational audienceThe millimetre spectrum of Galactic regions and galaxies is rich in continuum and molecular lines. That diversity is mostly tackled by either broad-band photometry or high resolution heterodyne spectroscopy. We aim to map the millimetre continuum emission of Galactic regions with a spectral resolution intermediate between broad-band photometry and heterodyne spectroscopy, enabling us to quickly cover large sky areas with spectroscopy. We report observations of the Orion Nebula with the CONCERTO instrument, which was installed at the APEX telescope focal plane from April 2021 to December 2023. We find that the spectrum of Orion is dominated by dust emission with an emissivity index from 1.3 to 2.0 along with the strong CO(2-1) and HO lines which are naturally separated from the continuum, thanks to CONCERTO spectral capabilities. Many regions show a strong free-free emission as well, at lower frequencies. We demonstrate the spectral capabilities of CONCERTO at intermediate spectral resolution, with a frequency coverage from 130 to 310 GHz. A sensitivity of 200 mK is achieved in one second, for one beam and a 6 GHz frequency width, over an 18 arcmin diameter field-of-view, which is within a factor 3 of the expectations. We show that we can spectrally disentangle the continuum from the CO line emission. The slope of the millimetre continuum is line-free mapped for the first time in Orion
Mantle Exhumation and Post‐Rift Magmatism at an Oblique Magma‐Poor Continental Margin
No full textInternational audienceContinental breakup is a fundamental tectonic process, which leads to seafloor spreading and the generation of oceanic crust. However, the current understanding of continental margins, based largely on 2‐D seismic transects, is inadequate to capture the spatial complexity of crustal evolution. Here we present a 3‐D seismic velocity model through a young, magma‐poor margin at the north‐eastern Gulf of Aden. Our results highlight the 45° obliquity between the strike of crustal thinning and extension direction, which is accommodated by two transfer zones during the formation of the Continent‐Ocean Transition (COT). This obliquity causes the margin to be segmented, which predates seafloor spreading. Along strike, we find a progressive eastward crustal thinning from 13 to 5 km, corresponding to a V‐shaped COT. This eastward variation is characterized by (a) an eastward increase of mantle exhumation due to detachment faulting, and (b) post‐rift magmatism emplaced onto serpentinized mantle in the west
Exploring Statistical Isotropy in Planck Data Release 4: Angular Clustering and Cosmological Parameter Variations Across the Sky
No full textInternational audienceThe origin of small deviations from statistical isotropy in the Cosmic Microwave Background (CMB) - the so-called CMB anomalies - remains an open question in modern cosmology. In this work, we test statistical isotropy in Planck Data Release 4 (PR4) by estimating the temperature and -mode power spectra across independent sky regions. We find that the directions with higher local bandpower amplitudes in intensity are clustered for multipoles between 200 and 2000 with clustering probabilities consistently below 1% for all these scales when compared to end-to-end (E2E) Planck simulations; notably, this range extends beyond that reported in Planck Data Release 3 (PR3). On the other hand, no significant clustering is observed in the polarization -modes. In a complementary analysis, we search for dipolar variations in cosmological parameters fitted using the previously computed power spectra. When combining temperature and polarization power spectra, we identify a potential anomaly in the amplitude of the primordial power spectrum, , with only 5 out of 600 simulations exhibiting a dipole amplitude as large as that observed in the data. Interestingly, the dipole direction aligns closely with the known hemispherical power asymmetry, suggesting a potential link between these anomalies. All other cosmological parameters remain consistent with expectations. Our findings highlight the need to further investigate these anomalies and understand their nature and potential implications for better understanding of the early Universe
On the presence of a fifth force at the Galactic Center
No full textInternational audienceAims: The presence of a Yukawa-like correction to Newtonian gravity is investigated at the Galactic Center, leading to a new upper limit for the intensity of such a correction. Methods: We perform a Markov Chain Monte Carlo analysis using the astrometric and spectroscopic data of star S collected at the Very Large Telescope by GRAVITY, NACO and SINFONI instruments, covering the period from to . Results: The precision of the GRAVITY instrument allows us to derive the most stringent upper limit at the Galactic Center for the intensity of the Yukawa contribution () to be for a scale length . This improves by roughly one order of magnitude all estimates obtained in previous works
The impact of diffuse Galactic emission on direction-independent gain calibration in high-redshift 21 cm observations
No full textInternational audienceThis study examines the impact of diffuse Galactic emission on sky-based direction-independent (DI) gain calibration using realistic forward simulations of Low-Frequency Array (LOFAR) observations of the high-redshift 21 cm signal of neutral hydrogen during the Epoch of Reionization (EoR). We simulated LOFAR observations between 147 - 159 MHz using a sky model that includes a point source catalogue and diffuse Galactic emission. The simulated observations were DI-gain calibrated with the point source catalogue alone, utilising the LOFAR-EoR data analysis pipeline. A full power spectrum analysis was conducted to assess the systematic bias introduced by DI-gain calibration using complete and incomplete sky models, relative to thermal noise. Additionally, the cross-coherence between observation pairs was computed to determine whether DI-gain calibration errors are coherent or incoherent in specific regions of power spectrum space as a function of integration time. We find that DI-gain calibration with an incomplete sky model that omits diffuse Galactic emission introduces a systematic bias in the power spectrum for bins 0.2 are largely incoherent and average down as noise. We conclude that missing diffuse Galactic emission in the sky model is not a significant contributor to the excess noise observed in the current LOFAR-EoR upper limit results on the 21 cm signal power spectrum
Pollution by polar pesticides and pharmaceuticals and risk assessment in surface water bodies along the French Mediterranean coast: Complementarity of target and non-target screenings
No full textInternational audienceAnthropogenic activities are the source of a wide range of organic micropollutants (OMPs) found in all water bodies. Among them, pharmaceuticals and pesticides are the most found in watercourses and their impacts on non-target organisms have already been documented. Pesticides are well monitored in the river-lagoon continuum with their integration into the European water frame directory (WFD). However, their presence may co-occur with pharmaceuticals from wastewater treatment plants discharges in watersheds. Their monitoring and risk assessment is an important knowledge gap in the WFD strategy. In this study, we used polar organic chemical integrative samplers to assess the concentrations of pharmaceuticals and pesticides (parent compounds and transformation products) in water bodies of the French Mediterranean coast and to assess environmental risk during late spring-early summer. Internal concentration of pharmaceuticals in mosquitofish was assessed to evaluate fish pharmaceutical burden. A non-target screening method was used to complementary describe OMPs cocktail in water. Twenty-nine pharmaceuticals and 12 pesticides were quantified using a targeted approach. Six pesticides and 23 pharmaceuticals were further detected using a non-target screening. Pharmaceuticals concentration and associated environmental risk were higher than pesticides ones in mixed-used watersheds, although their risk assessment was limited by the low number of ecotoxicological data available for pharmaceuticals. Six pharmaceuticals were found in fish tissue, increasing potential biological impacts for this trophic level. This study highlighted the importance of monitoring concentrations of pharmaceutical products in the environment and increasing the ecotoxicological testing effort to improve risk assessment
Combining high-contrast imaging with high-resolution spectroscopy: Actual on-sky MIRI/MRS results compared to expectations
No full textInternational audienceContext. Combining high-contrast imaging with high-resolution spectroscopy represents a powerful approach to detecting and characterizing exoplanets around nearby stars, despite the challenges posed by their faintness. Instruments like VLT/SPHERE represent the state of the art in high-contrast imaging; however, their spectral resolution (R ≈ 50) limits them to basic characterization of close companions. These instruments can observe planets with masses as low as 5–10 MJup at distances of around 10 AU from their stars. Detection limits are primarily constrained by speckle noise, which dominates over photon and detector noise at short separations around bright stars, even when advanced differential imaging techniques are used. Similarly, image stability also limits space-based high-contrast imaging capability. This speckle noise can, however, be largely mitigated by molecular mapping, a more recent method that leverages information from high-resolution spectroscopic data.Aims. Our objective is to understand and predict the effective detection limits associated with spectro-imaging data after processing with molecular mapping. This involves analyzing the propagation of fundamental noise sources, such as photon and detector noise, and comparing these predictions to real instrument data to assess performance losses due to instrument-based factors. Our goal is to identify and propose potential mitigation strategies for these additional sources of noise. Another key aim is to compare the predictions made by our analytical approach with actual observational data to validate and refine the model’s accuracy where necessary.Methods. We analyzed JWST/MIRI/MRS data using the recently developed semi-analytical and numerical tool, FastCurves, and compared the results with outputs from the end-to-end MIRI simulator. This simulator allows one to examine nonideal instrumental effects in detail. Additionally, we applied principal component analysis (PCA), a statistical method that identifies correlated patterns in the data, to help isolate systematic effects, both with and without molecular mapping.Results. Our analysis involves investigating the systematic effects introduced by the instrument, identifying their origins, and evaluating their impact on both noise and signal. We show that valuable insights are gained regarding the effects of straylight, fringes, and aliasing artifacts, each linked to different residual systematic noise terms in the data. The results are further supported by principal component analysis, which also demonstrates its effectiveness in mitigating these effects. Additionally, we explore the similarities and discrepancies between observed and modeled companion spectra from an astronomical perspective.Conclusions. We modified FastCurves to account for systematic effects and improve its modeling of MIRI/MRS noise, with its signal-to-noise predictions validated against empirical data. In high-stellar-flux regimes, systematic noise imposes an ultimate contrast limit when using molecular mapping alone. Our methodology, demonstrated with MIRI/MRS data, could greatly benefit other instruments, aiding in the planning of observational programs. For future instruments like ELT/ANDES and ELT/PCS, it could also inform and guide their development
Monitoring of geophysical deformations on a regional scale using the low-cost GNSS collaborative network CentipedeRTK
No full textInternational audienceDeveloped since 2019, the CentipedeRTK network is a permanent collaborative GNSS network whose main objective is to make RTK positioning freely available, mainly using low-cost receivers and antennas. Since its creation, the network has grown considerably, well beyond the borders of France, and now includes more than 800 base stations. The main sector using the network is agriculture, but more and more public and private organisations and individuals are also using it. The geoscience community quickly became interested in the network, first as users of RTK positioning (for sea level monitoring, drone surveys, etc.) and then for post-processing of the raw measurements from the base stations. Since mid-2022, the RENAG network data centre has therefore been archiving the data from the base stations on a daily basis with the aim of using them for geoscience applications. A first study based on data acquired in 2023 has demonstrated the value of these data for monitoring atmospheric water vapour over continental France. Here we focus on the use of data acquired by CentipedeRTK base stations located in mainland France to monitor geophysical movements on a regional scale. To this end, the daily positions of the CentipedeRTK stations estimated in PPP using GipsyX are analysed and compared with those estimated for nearby permanent stations belonging to conventional networks. There is a slight deterioration in the repeatability of the mean positions (15 to 20% depending on the component). The time series show an increase in dispersion, but a very good consistency of the variations is still observed. The discrepancies observed can be explained by the equipment of the CentipedeRTK stations, in particular their antenna, as well as by the direct environment of the stations, which is not always as optimal as that of conventional stations. These results will be used to develop a set of recommendations for CentipedeRTK contributors and will help to increase the value of the data collected by the network's base stations for geoscience applications.
First paleoenvironmental calibrations for modern pollen rain of Tajikistan and Uzbekistan: A case study of pollen - vegetation functional biogeography of Arid Central Asia
No full textInternational audienceStudying modern pollen rain in Middle Asia is crucial for understanding past climate and vegetation changes. This study presents the first dataset of pollen surface samples and vegetation plots from Tajikistan and Uzbekistan, known as the Tajikistan and Uzbekistan Surface Data Base (TUSDB), to enhance our understanding of past climate and vegetation changes in Arid Central Asia (ACA). Multivariate analysis methods, including TWINSPAN and CONISS, are used to review the primary vegetation types in Central Asia and assess pollen distribution across these types. Linear relationships, Davis indices, and R-values are applied to evaluate vegetation representativeness based on pollen abundances. Redundancy Analysis is used to compare pollen and climate parameters, and the reliability of TUSDB for local climate reconstructions is tested using transfer functions and machine learning approaches.The TWINSPAN analysis identifies vegetation types consistent with the Uzbek classification, such as desert, steppe, and cryophilous open woodlands. Nine vegetation subtypes are revealed by the pollen samples, with key contributions from trees like Juniperus spp. and Juglans regia, and non-arboreal plants like Cyperaceae and Poaceae. The study also highlights biases in pollen representation, with some tree taxa overrepresented and certain vegetation-important taxa underrepresented, which can be corrected using pollen R-values.Finally, functional trait aggregation for past pollen sequences shows similarities between modern pollen and vegetation plots. Climate reconstructions validated through transfer functions highlight the complementary role of local and global calibration datasets. These findings confirm the reliability of pollen signals for inferring Holocene climate and vegetation trends, enabling future Uzbek pollen-based reconstructions