Impact de la pollution lumineuse nocturne sur l’huitre creuse Crassostrea gigas : étude de la perturbation des rythmes biologiques et des conséquences physiologiques
La lumière artificielle nocturne (LAN) masque les cycles naturels lumineux utilisés par les organismes pour synchroniser leurs rythmes biologiques avec l’environnement. En perturbant ces rythmes, LAN peut avoir de graves conséquences physiologiques. LAN touche fortement les environnements côtiers du fait de l’importante et croissante densité de population humaine. Cependant, malgré cette menace grandissante, les effets de LAN sur ces écosystèmes sont peu étudiés. L’huitre Crassostrea gigas est une espèce clé des environnements côtiers susceptible d’être exposée à LAN. Ce travail évalue les effets de LAN à des intensités faibles et realistes sur le rythme journalier comportemental et l’horloge interne de l’huitre en fonction de l’intensité, de la composition spectrale et de la modalité d’exposition. Par ailleurs, est aussi étudié l’impact de LAN sur la croissance coquillère et le microbiote branchial de l’huitre. Les résultats indiquent que LAN affecte le rythme journalier comportemental de C. gigas et son horloge moléculaire dès 0.1 lx avec les effets les plus forts en lumière bleue et les moins forts en lumière verte. De plus, cette étude suggère que couper les éclairages directs en milieu de nuit mais en présence d’éclairage indirect (« skyglow ») peut aggraver certains effets néfastes. Enfin, LAN diminue la croissance coquillère et entraine une dysbiose du microbiote branchial. Ces effets sont directement corrélés à la robustesse du rythme journalier.
(20/12/2023)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
Glacial terminations and rates of sea-level rise
Glacial terminations in the late Pleistocene are notable for their high rates of sea-level rise. Occurring ~340 thousand years before the present (kyr BP), Termination IV (T-IV) stands out as a significant one, during which sea-level rise rates exceeded 4 meters per century. The underlying causes of such rapid deglaciation during T-IV, however, remain poorly understood due to limited absolute age constraints on marine records. We present new, radiometrically dated speleothem records obtained from Bàsura cave in northern Italy from 320 to 380 kyr BP. By transferring the speleothem-based chronology to the co-registered marine and terrestrial changes within the same sample set, we gain valuable insights into the dynamics of T-IV in the North Atlantic and Mediterranean regions. Our findings reveal that the maximum sea-level rise rates during T-IV were not synchronous with the major millennial-scale climate shifts, but rather linked to the initial phase of the subsequent interglacial period, characterized by abrupt warming in the North Atlantic. We will discuss our findings from T-IV in the context of other glacial terminations to shed light on the processes that control the high rates of sea level rise at glacial-interglacial transitions.
(11/12/2023)
NTU, ANU, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, IPMA, Xjtu, CEPAM, UNS, CNRS, UniCA, GEOAZUR 7329, INSU - CNRS, UniCA, CNRS, IRD [Occitanie], UniCA, HNHP, MNHN, UPVD, CNRS, UniPi, UNITO, NTU
Nonlinear Response of Fire to Precipitation in southern Africa over the Past 190,000 years
Low-latitude monsoons are known to be affected by precession through insolation forcing, but the role of tilt is still controversial, as its effect on the distribution of incoming solar radiation is small in these regions. Although modeling results suggest an influence of precession and obliquity on summer monsoons, periodic environmental changes at 23 kyr-1 frequency are observed on long marine and terrestrial sedimentary records from southern Africa whereas the 41 kyr-1 frequency is generally lacking in rainfall proxy records. Here, we present the fine-grained charcoal record from core MD96-2098 off Namibia covering the past 184,000 years. We interpret peaks in fire activity over southern Africa as reflecting large and intense fires propagating across open grassland savannas and paced by orbital changes in precipitation intensity associated with the South African monsoon. Our fire activity record shows periodic variations at frequencies of 23, 58, and 12 kyr-1. The non-primary orbital 58 and 12 kyr-1 frequencies correspond to composite frequencies resulting from a non-linear response of fire to precipitation controlled by a combination of precession and obliquity frequencies (23 and 41kyr-1). Thus, despite the lack of a direct tilt-related imprint in the spectral power, our charcoal record supports the influence of obliquity on the South African monsoon.
(11/12/2023)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
THE MONOID OF NUMBERS OF THE FORM 1 <= a^q /b^p < a
This paper is a study of the set of rational numbers of the form 1 <= a^q /b^p < a with a and b co-prime integers. The set F (a,b) of these numbers, with an appropriate binary law, is a monoid isomorphic to (N, +, 0). We identify the sequences of minimum and maximum record holders in F (a,b) and prove that the first one converges to 1 while the second one converges to a. We conclude that F (a,b) is dense in the set of the real numbers comprise between 1 and a.
(08/12/2023)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
Environmental controls on summer surf zone hazards, beach crowds, and resulting life risk at a high-energy sandy beach in southwest France
Surf beaches can be dangerous environments due to potentially powerful wave conditions and the presence of rip currents [1]. Understanding and predicting surf zone risks is therefore of paramount importance to prevent drowning incidents. However, hazard and water-user exposure at the coast, which combined give life risk, have been systematically measured separately. For the first time, the present work addressed all the components of the risk at a given beach by implementing a cross-disciplinary research in close collaboration with lifeguards at a rip-current dominated beach in southwest France. The experiment took place at La Lette Blanche beach, southwest France, during the lifeguard-patrolled summer period (July-August) 2022. This coast is exposed to high-energy ocean waves which, together with a meso-macrotidal tide regime, result in in a wealth of surf zone hazards, primarily rip currents and shore-break waves, occurring at different times and locations along the beach. During this 2-month period, beach crowd and the levels of rip current and shore-break wave hazards were estimated hourly by the lifeguards during patrolling hours (11AM-6PM). Wave, tide and weather conditions were also continuously recorded at nearby tide gage, wave buoy and weather station, providing comprehensive insight into the primary environmental controls. Results show that daily-mean rip-current hazard is increased for large, long-period and shore-normal waves, while shorebreak-wave hazard is increased for long-period waves and large tide range. Not surprisingly, beachgoer crowd increases for warm, sunny and light wind days, with the severe heat wave occurring in July 2022 significantly decreasing beach crowd. Days combining strong hazards and large beach attendance were also those associated with the largest amount of rescues at Vielle Saint-Girons, and of drowning incidents in southwest France. Warm, sunny and light sunny days, with large, long-period shore-normally incident waves and large tide range were the most risky days, with maximized beach crowd and shorebreak-wave and rip current hazards peaking at different times of the day and at different sectors of the beach. This collected dataset together with additional downing datasets and machine learning techniques [2] form the basis of the ongoing development of new beach exposure hazard/life risk alert system.
(07/12/2023)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, UR ETTIS, INRAE, UB
Chronic flooding events due to sea-level rise in French Guiana
As sea levels are rising, the number of chronic flooding events at high tide is increasing across the world coastlines. Yet, many events reported so far either lack observational evidence of flooding, or relate to coastal areas where ground subsidence or oceanic processes often enhance climate change-induced sea-level rise (SLR). Here we present observational and modelling evidence of high-tide flooding events that are unlikely to occur without SLR in French Guiana, where sea-level rise rates are close to the global average and where there is no significant ground subsidence. In particular, on 16 October 2020, a well-documented flooding event happened in Cayenne under calm weather conditions. Our probabilistic assessment of daily maximum water levels superimposed on SLR shows that this event can be modelled and is a consequence of SLR. As sea levels will continue to rise, we show that the number, severity and extent of such high-tide flooding events will increase across several urban areas of French Guiana, with an evolution depending on the topography. As concerns are growing regarding the economic impacts and adaptation challenges of high-tide chronic events across the world, our study provides new evidence that this early impact of SLR is emerging now.
(Scientific Reports. vol. 13, n° 2045-2322, pp. 21695, 07/12/2023)
BRGM, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, CNRM, INSU - CNRS, CNRS, Comue de Toulouse, NIOZ
Hurricane Irma: an unprecedented event over the last 3700 years? Geomorphological changes and sedimentological record in Codrington Lagoon, Barbuda
Abstract. Low-lying coasts and small islands, such as in the Lesser Antilles, are particularly vulnerable to hurricane-induced marine floods. In September 2017, category 5 Hurricane Irma, with winds up to 360 km h−1, hit the northern Caribbean islands and caused the destruction of 95 % of the structures on Barbuda Island. We investigated the geomorphological impacts and the sedimentological record related to the storm surge of this hurricane in Barbuda's Codrington Lagoon. Following Hurricane Irma, two wide inlets developed across the Codrington sandy barrier. One of these inlets was enlarged and was still open 4 years later. From available data, it seems that this barrier remained continuous for the last 250 years before Hurricane Irma. At a longer timescale, very high-resolution seismic exploration combined with sediment cores sampled in Codrington Lagoon were used to investigate Irma deposits and environmental changes for the last 3700 years. The evolution from a low-energy small and shallow lagoon to the modern wide and high-energy lagoon recorded by the lagoon sediment fill was related to both long-term sea level rise and subsidence. The top of the lagoon fill consists of a thick and extensive sand sheet recording an abrupt increase in energy. Given its location at the top of the cores and its very recent age, supported by short-lived radionuclide data, together with large inlets opening and barrier erosion after Irma that imply a large sand supply to the lagoon, this sand sheet was attributed to Hurricane Irma. From our cores, it appears that this deposit is unique over more than 3700 years. Both the opening of a new inlet and the thick upper sand sheet support the exceptional character of Irma at the scale of centuries to millennia. Our study reinforces the idea that Hurricane Irma was exceptional in terms of intensity and may be associated with global warming.
(Natural Hazards and Earth System Sciences. vol. 23, n° 1561-8633, pp. 3761-3788, 06/12/2023)
EDYTEM, USMB [Université de Savoie] [Université de Chambéry], CNRS, Fédération OSUG, LIENSs, INSU - CNRS, ULR, CNRS, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, IPGP - UMR_7154, INSU - CNRS, IGN, UR, IPG Paris, CNRS, UPCité
Impact of the Garonne river's quality on two model species: Japanese medaka at early life stages and Gammarus fossarum using an ex-situ exposure
(05/12/2023)
UR EABX, INRAE, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, RiverLy, INRAE
Using machine learning to predict drownings in surf beaches of southwest France
Background: Southwest France golden-sand beaches are very popular destination for bathing and other sea activities in summer. However, they are also potentially dangerous environments with increased risk of accidents in unsupervised areas, especially during the off-peak season, due to strong rip-current and shorebreak waves. Predicting and quantifying these accidents is of major importance for public communication and emergency services management. Previous work on beach risk prediction was conducted along a specific section of the coast (Gironde), using data from 2011-2017 to train a model and further predict drowning incidents based on sea and weather forecasts, which has led to the development of an alert system based on a logistic regression model used by local decision makers [1]. Methods: In this study, we further improve this model by using new statistical methods related to machine learning, a larger dataset (2011-2022) and by including spatialization in order to propose a modelling framework that could be generalized to other coasts. We estimated drowning risk as a combination of hazard (ocean conditions) and exposure (beachgoer crowd). Several machine learning models were trained and compared using 3-day weather and sea forecasts from 2011 to 2022 as predictors along with an emergency calls database used as an outcome on the same time frame. The training set covered 188 drowning events over 1988 days while the test set covered 81 events over 663 days. Results: Our results show this new modeling framework is able to predict days with the highest risk of drowning events with improved accuracy on the Gironde coast: AUC = 0.9 (95% CI 0.89 to 0.91), PPV = 0.49 (95%CI 0.41 to 0.55) and NPV = 0.96 (95%CI 0.95 to 0.99). Conclusions: This supports the development of a new alert system that will provide useful information to decision makers. However, “all models are wrong, but some are useful” [2]. While this model could still be improved, with further feature engineering and improved data for rescues, this work also addresses the issue of identifying the right criteria to define what would actually be the “best” model depending on risk management policies set by decision makers.
(05/12/2023)
UR ETTIS, INRAE, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, INSERM, CHU Bordeaux
Projet Phytosol Résidus de pesticides dans les sols français : présence, risques et persistance
À la différence de ce qui est fait pour les milieux aquatiques et l'atmosphère, la surveillance de la contamination des sols par les pesticides n'existe pas à l'échelle du territoire. Or, des travaux récents de chercheurs INRAE, en collaboration avec l'université de Bordeaux, montrent qu'un grand nombre de substances, en quantité importante, y persistent sous forme de résidus. Des résultats parus dans la revue Environmental Science & Technology.
(04/12/2023)
Info&Sols, INRAE, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, UMR ISPA, Bordeaux Sciences Agro, INRAE, LAS, INRAE