Aerosol spectral optical properties in the Paris urban area and its peri-urban and forested surroundings during summer 2022 from ACROSS surface observations
Abstract. The complex refractive index (CRI; n−ik) and the single scattering albedo (SSA) are key parameters driving the aerosol direct radiative effect. Their spatial, temporal, and spectral variabilities in anthropogenic–biogenic mixed environments are poorly understood. In this study, we retrieve the spectral CRI and SSA (370–950 nm wavelength range) from in situ surface optical measurements and the number size distribution of submicron aerosols at three sites in the greater Paris area, representative of the urban city, as well as its peri-urban and forested rural environments. Measurements were taken as part of the ACROSS (Atmospheric Chemistry of the Suburban Forest) campaign in June–July 2022 under diversified conditions: (1) two heatwaves leading to high aerosol levels, (2) an intermediate period with low aerosol concentrations, and (3) an episode of long-range-transported fire emissions. The retrieved CRI and SSA exhibit an urban-to-rural gradient, whose intensity is modulated by the weather conditions. A full campaign average CRI of 1.41−0.037i (urban), 1.52−0.038i (peri-urban), and 1.50−0.025i (rural) is retrieved. The imaginary part of the CRI (k) increases and the SSA decreases at the peri-urban and forest sites when exposed to the influence of the Paris urban plume. Values of k > 0.1 and SSA < 0.6 at 520 nm are related to a black carbon mass fraction larger than 10 %. Organic aerosols are found to contribute to more than 50 % of the aerosol mass and up to 10 % (urban), 17 % (peri-urban), and 22 % (forest) of the aerosol absorption coefficient at 370 nm. A k value of 0.022 (370 nm) was measured at the urban site for the long-range-transported fire episode.
(Atmospheric Chemistry and Physics. vol. 25, n° 1680-7316, pp. 3161-3189, 14/03/2025)
LISA (UMR_7583), INSU - CNRS, UPEC UP12, CNRS, UPCité, LATMOS, UVSQ, INSU - CNRS, SU, CNRS, LCE, AMU, INC-CNRS, CNRS, UiO, CERI EE - IMT Nord Europe, IMT Nord Europe, IMT, USD, TROPOS, INERIS, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, LSCE, UVSQ, INSU - CNRS, CNRS, DRF (CEA), CEA, CAE, LSCE, UVSQ, INSU - CNRS, CNRS, DRF (CEA), CEA, INSU - CNRS
Simulated millennial-scale climate variability driven by a convection–advection oscillator
The last glacial period, between around 115 and 12 thousand years before present, exhibited strong millennial-scale climate variability. This includes abrupt transitions between cold and warm climates, known as Dansgaard-Oeschger (D-O) cycles. D-O cycles have been linked to switches in dynamical regimes of the Atlantic Overturning Meridional Circulation (AMOC), but the exact mechanisms behind abrupt climate changes and AMOC regime shifts remain poorly understood. This paper introduces the convection-advection oscillator mechanism to explain the millennial-scale oscillations observed in a set of HadCM3 general circulation model simulations forced with snapshots of deglacial meltwater history. The oscillator can be separated into two components acting on different time scales. The fast convection component responds to changes in vertical stratification in the North Atlantic by activating or deactivating deep water formation sites. The slow advection component regulates the accumulation and depletion of salinity in the North Atlantic. This oscillator mechanism is triggered under specific background conditions and freshwater release patterns. The freshwater perturbation causes an instability that triggers a global salt reorganisation, modifying the North Atlantic stratification. For a given forcing pattern, the system oscillates if the salt transport can lead to an alternating reactivation and deactivation of the AMOC. Otherwise, the climate settles in a warm or cold steady state. This mechanism expands existing theories of millennial-scale variability and provides a general framework for understanding abrupt climate change in general circulation models.
(Climate Dynamics. vol. 63, n° 0930-7575, pp. 150, 07/03/2025)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, UOR
Garonne River Behavior Under Climate Change and the Potential Adaptation Strategies
According to the IPCC reports, the effects of climate change are well present from several decades ago, and it is expected to become even more pronounced during the remainder of the twenty-first century. The river basin system is defined as a complex of interaction between aquatic and terrestrial ecosystems. The interface between these ecosystems results in different responses of the river regime ranging from floods to low flow. The instability of alluvial valley due to geomorphological and fluvial dynamics, represents an additional challenge for the riparian societies face to climate changes. The Garonne River, the third largest French Atlantic River in terms of discharge, flows down in the Garonne Valley, the largest occupied and cultivated alluvial plain in France. This area is influenced by a wide range of Oceanic, Mediterranean, and mountainous climates. Hence, the complex Garonne River regime is influenced by the precipitation generated over the Massif Central and the French and Spanish Pyrenees Mountains. The surrounding alluvial aquifer, which forms an important part of this system, maintains a strong hydraulic connection with the river and sustains its low flow. Consequently, this aquifer is extremely sensitive to meteorological changes and hence to recharge system variation. The inhabitants in this area are strongly depending to the river and its alluvial aquifer. However, the impact of climate changes on socio-economic activities could be significant in this area. The adaptation to these changes creates additional challenges for decision-makers and becomes a major objective of the watershed policy. The trends assessment of the Garonne River's discharge over the last fifty years has shown a decrease in average annual discharges and substantial decrease in low flows. The dry periods are starting earlier and becoming more severe and longer. Upstream, the snow cover shows a decrease in thickness and duration, which has a negative impact on the river’s discharge and consequently on the groundwater recharge ratio. Groundwater measurements show a general decrease in water level. The observations show that most of the wells located close to the river have dried up during the dry periods since the alluvial aquifer drains into the river during these periods. The groundwater level reduction could have a negative impact on agriculture, wetlands, and river ecosystems. Thus, the implementation of adaptation measures has been initiated. The artificial recharge of the alluvial aquifer is considered as an adaptation strategy to address the effect of climate change and sustains the low flow of the river. In addition, this strategy will help to buffer the river temperature during the low flow periods. Several pilot sites in the Garonne Valley are under investigation for testing the artificial recharges. The first site, where artificial recharge has been tested since 2019, is located near the city of Agen, where the runoff is collected in a retention basin and is used to recharge the alluvial aquifer. Groundwater level in the wells near the retention basin have increased by about 1 m following rainfall events. The results of the groundwater modeling show (1) a similar magnitude aquifer response to the induced infiltration and (2) that the infiltrated water would take about 4 months to reach the Garonne River, which is an appropriate time to maintain the river's low flow, since recharge takes place in spring. Another site that has been tested is located near the city of Marmande, where the surface water from the Lateral Canal of the Garonne River has been used as a source to recharge the alluvial aquifer in May 2023. The infiltrated water has created a piezometric dome and the groundwater level has increased by 15 and 33 cm into two boreholes located about 40 m upstream and downstream of the infiltration site respectively. This experiment will be carried out on a larger scale, and further groundwater measurements and modeling will be carried out for this and other selected sites in the near future
(. vol. 114, pp. 235-262, 04/03/2025)
PACEA, UB, CNRS, BRGM, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, ACMG, SMEAG
Variations in the morphometric characteristics of Fragilariopsis kerguelensis in the Southwest Pacific sector of the Southern Ocean over the past 40,000 years
High-throughput measurements demonstrated the presence of two morphotypes of Fragilariopsis kerguelensis in the Atlantic sector of the Southern Ocean, the proportions of which in downcore samples may be used to reconstruct past sea-surface temperatures quantitatively. We here measured the mean length, width, area, and rectangularity in core SO136-111 to assess variations in both morphotypes in the Polar Front Zone of the western Pacific sector of the Southern Ocean over the past 40,000 years. Mean length, width, and area increased rapidly at the end of the glacial period when the Polar Front migrated southward to reach the core site, ocean temperature increased, and sea ice was no longer present. In contrast, mean rectangularity decreased at the end of the glacial period, when the proportion of the cold-water, high-rectangularity morphotype declined as the ocean warmed at the core site. Downcore patterns and quantitative values of all morphometric characteristics in the southwest Pacific sector agree well with previous studies from the Atlantic sector, suggesting the presence of a similar population of F. kerguelensis in the open Southern Ocean. Nevertheless, rectangularity-based relationships can ultimately produce unrealistic estimates of sea-surface temperatures in core SO136-111 when the proportion of the high-rectangularity morphotype is too low, indicating that these approaches are now limited to temperatures below 3-4°C.
(Marine Micropaleontology. vol. 195, n° 0377-8398, pp. 102447, 01/03/2025)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
Bivalve monitoring over French coasts: multi-decadal records of carbon and nitrogen elemental and isotopic ratios (δ13C, δ15N and C:N) as ecological indicators of global change
Recent changes in climate and environment, influenced by both global and local factors, have had profound impacts on coastal ecosystem functioning and trajectories. By examining archived samples from ongoing ecological monitoring efforts, particularly focusing on bivalves like mussels and oysters, we gain a valuable long-term perspective on how ecosystems are responding at various scales. We conducted analyses on carbon and nitrogen elemental and isotopic ratios (C:N, δ13C, δ15N) of mussel and oyster soft tissues collected annually at 33 sites along the French coast from 1981 to 2021. This extensive dataset (https://doi.org/10.17882/100583, Liénart et al., 2024a) offers a comprehensive view spanning multiple decades and ecosystems, allowing to track how coastal ecosystems and marine species record changing climate, physical-chemical environments and organic matter cycles. Additionally, these data are crucial for establishing isotope baselines for studying food webs. Ultimately, this data set provide valuable information for more effective ecosystem conservation and management strategies in our rapidly changing world.
(Earth System Science Data. vol. 17, n° 1866-3508, pp. 799-815, 01/03/2025)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, FTMC, CCEM, IFREMER, DYNECO, IFREMER, BOREA, MNHN, IRD, SU, CNRS, UA
A new species of the Thelepus cincinnatus complex from Saint-Pierre and Miquelon Archipelago (NW Atlantic) and genetic diversity of Amphitrite figulus (Dalyell, 1853) (Annelida, Terebelliformia)
During an ecological survey conducted in 2023 around the coastal waters of Saint-Pierre and Miquelon Archipelago, a sub-Arctic archipelago located about 20 km south of Newfoundland (NW Atlantic), two species of Terebelliformia were sampled. The first one is Amphitrite figulus (Dalyell, 1853) a species described from Europe but with a wide distribution across the Northern Atlantic Ocean. The second one, Thelepus recheri n. sp., is a new species characterised by the presence of a wide dorsal branchial gap and the presence of notopodia almost until the end of the body. Molecular studies were performed and two markers were sequenced and analyzed, COI and 16S. These genetic data revealed that (1) Thelepus recheri n. sp. belongs to the T. cincinnatus complex and (2) a clear population structure within A. figulus, with two populations on each side of the Atlantic separated from each other. However, our data are inconclusive in resolving whether these two clusters are two populations within the same species or two distinct species.
(Zootaxa. vol. 5588, n° 1175-5326, pp. 250-268, 14/02/2025)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, LEMAR, IRD, IFREMER, UBO EPE, CNRS, IUEM, IRD, INSU - CNRS, UBO EPE, CNRS, UMS POREA, INSU - CNRS, CNRS, INRAE, UIB
Devenir des PFAS dans un sol structuré : rôle des particules colloïdales et macropores
Les mousses anti-incendie contiennent un mélange de substances per- et polyfluoroalkylées (PFAS). Celles-ci sont persistantes dans l’environnement, et les sites d'entraînement des pompiers constituent une source de contamination pour les sols, leur biota et les eaux souterraines. Le devenir des PFAS dans les sols a été principalement étudié en utilisant des situations expérimentales modèles : sols recompactés, souvent saturés, et contaminés artificiellement avec quelques molécules. Nous avons étudié pour la première fois le devenir des PFAS dans un sol structuré en soumettant des colonnes de sol non perturbé, prélevées sur un ancien site d’entrainement des pompiers, à une série de pluies simulées. Ces expériences ont montré que (i) lorsque la longueur de la chaîne perfluorée nc était ≤ 7, la diffusion était le mécanisme limitant le transport, (ii) les particules colloïdales facilitaient la mobilité de certains fluoro-télomères et acides perfluorés avec n≥8, (iii) les conditions hydrodynamiques, liées à la structure du sol, déterminaient l’étendue du transport en phase colloïdale des PFAS. Ces résultats ont permis de préciser le modèle conceptuel du devenir des PFAS dans le sol et de proposer les mécanismes qu’il conviendrait d’étudier pour l’améliorer.
(04/02/2025)
EMMAH, AU, INRAE, GERS-LEE, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
Distribution of organic matter and diatom frustules (diversity, flux) along the western Indian continental shelf related to contrasting physicochemical settings
The western Indian continental shelf (eastern Arabian Sea) exhibits contrasting biogeochemical features. This area becomes highly productive due to summer monsoon-driven coastal upwelling in the south and winter monsoon-induced convective mixing in the north. Additionally, in the northern self, the eastern boundary of the Oxygen Minimum Zone (OMZ) persists but is absent in the south. Phytoplankton blooms are dominated by diatoms that contribute to sedimentary phytodetritus flux supplying major elements (C, N, Si) and food for benthic biota and hence important to address. Here we present the data on organic matter content, diatom frustule flux, abundance, and diversity using surface sediments (core tops collected using a multicorer) from 6 locations (11-21° N) along the shelf in a 2° interval at 200 m isobaths. The organic matter retrieved from the core top was relatively fresh (nearly 4.5 years old) as evident from 210 Pb profiles Frustule abundance and diversity (the maximum at 15° N and minimum at 19° N) varied from 0.10-18.46 ×10 4 valves g -1 and 0.79-2.32, respectively. A total of 36 diatom genera were found with two centric (Thalassiosira and Coscinodiscus), and one pennate (Nitzschia) diatoms as major contributors. The higher contribution of Thalassiosira was observed throughout the shelf dominating the south (11, 13, 15° N), whereas, in the north (17, 19, 21° N) Coscinodiscus was dominant.
The highest organic matter content (3.4%) and frustule abundance (18.46 × 10 4 valves g -1 ) were seen at 15° N despite low diatom valve flux (3.3 × 10 3 valves cm -2 yr -1 ) and could be due to the influence of OMZ, where organic matter is well preserved. Contrarily, the upwelling-influenced station in the south (at 11° N) exhibited the highest diatom valve flux (10.14 × 10 3 valves cm -2 yr -1 ) however low organic matter content (1.6 %) and frustule abundance (4.99×10 4 valves g -1 ) was attributed to faster mineralization. This study suggested that the preservation potential of organic matter varies across the shelf and is likely to control its recycling, impacting nutrient release and resources for the benthic community.
(Marine Environmental Research. vol. 204, n° 0141-1136, pp. 106940, 01/02/2025)
NIO, AcSIR, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
Source of rainfall above Mediterranean caves (Chauvet and Orgnac) and long-term trend of cave dripping oxygen isotopes based on 20 years monitoring records: Importance for speleothem-based climate reconstructions
(Quaternary Science Reviews. vol. 349, n° 0277-3791, pp. 109145, 01/02/2025)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, LSCE, UVSQ, INSU - CNRS, CNRS, DRF (CEA), CEA, GLACCIOS, LSCE, UVSQ, INSU - CNRS, CNRS, DRF (CEA), CEA, GEOTRAC, LSCE, UVSQ, INSU - CNRS, CNRS, DRF (CEA), CEA
Long-term impact of dredging and beach nourishment works on benthic communities
Dredging and rainbowing techniques are commonly used to replenish sandy beaches and protect the coast against erosion. Since 2003, such operations have been conducted every other year on Pyla Beach, Arcachon Bay (French Atlantic Coast). The evolution of macrobenthic communities subjected to regular disturbance was analyzed once in springtime at dredging and disposal sites, as well as in a control area, over 21 years. The overall benthic community was dominated by the same few species. The dredged area harbors a benthic community whose characteristics suggest the maintenance of a disturbed status, compared to the control area, whose community follows a trajectory possibly influenced by the general decrease of organic matter in the sediment. Regarding the disposal site, species richness is slowly declining. In both disturbed areas, the community was dominated by species able to recolonize rapidly (polychaetes, peracarid crustaceans), while the control area rather favored bivalves.
(Estuarine, Coastal and Shelf Science. vol. 313, pp. 109119, 01/02/2025)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS