Records of vegetation and South Asian summer monsoon dynamics in the Bay of Bengal during the current and last interglacial periods
While it is accepted that the tropical hydrological cycle has intensified during past interglacial periods due to changes in insolation, greenhouse gases, and ice volume, variations in the intensity and spatial distribution of rainfall in the South Asian monsoon domain, as well as the respective influence of these forcings during past warm periods, remain uncertain. Here, we present a pollen record from the Bay of Bengal (IODP Site U1446, located off the Mahanadi river exit, outside the influence of the Bengal fan) that allows reconstruction of vegetation changes in the core monsoon zone of India during two warm periods, the current and last interglacial periods. We compare the data with numerical model simulations (HadCM3 and LOVECLIM1.3) to assess the influence of different forcing mechanisms on the response of summer monsoon rainfall during past interglacials characterized by different levels of warming (Clément et al., 2024). We also present a pollen record from cores (SO93) taken at 16°N from the Ganges-Brahmaputra-Meghna (G-B-M) river-fed Bengal fan, covering the current interglacial period.Results from IODP Site U1446 show tropical forest expansion between 11.7-5 ka and 127-120 ka, defining two Indian humid periods, with the last interglacial showing the strongest monsoon activity, consistent with salinity reconstructions. During the last five millennia of both interglacial periods, moist tropical forest largely declined in favor of savanna marking a significant decrease in summer monsoon rainfall. Although the pollen assemblages from sites SO93 and U1446 show substantial differences in Holocene vegetation cover between the basins, the maximum expansion of the evergreen component of the tropical forest is recorded contemporaneously in both sequences. This suggests a similar Holocene evolution of the summer monsoon from central to northern India. The model-data comparison highlights boreal summer insolation as the primary driver of vegetation dynamics and monsoon intensity during interglacial periods, with CO2 and ice-sheets having a limited effect. These results also show that vegetation remains unaffected by pre-industrial CO2 variations above 250 ppmv, a threshold value that characterizes most interglacials of the last million years.Clément, C., Martinez, P., Yin, Q., Clemens, S., Thirumalai, K., Prasad, S., Anupama, K., Su, Q., Lyu, A., Grémare, A., Desprat, S., 2024. Greening of India and revival of the South Asian summer monsoon in a warmer world. Commun. Earth Environ. 5, 685.
(pp. 9895, 18/03/2025)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, ELI, UCLouvain, UL, CRPG, INSU - CNRS, UL, CNRS, IFP, MEAE, CNRS, UCLouvain, Bordeaux INP, WHOI
Fault segmentation, geometry and recent activity in the epicentral area of the 1956 Mw 7.5 Amorgos earthquake (Greece)
The Amorgos-Santorini region (Hellenic Volcanic Arc, Greece), suffered the most powerful earthquake in the Mediterranean in the 20th century (1956, Mw ~7.5). This event caused casualties, severe damage and a large tsunami. The epicentral area is offshore and is characterized by several basins bounded by submarine faults accommodating back-arc extension and the Anatolian extrusion. Recently, the Amorgos fault was identified as the causative fault of the 1956 Amorgos earthquake. However, the characteristics of this fault, such as its detailed geometry, segmentation and kinematics remain unclear and debated. Using new high-resolution bathymetric data and sediment cores, we present a detailed mapping of this fault and its neighbors.The Amorgos fault is composed of three segments separated by relay zones. Taking into account the onshore geology, where E-W striking late Miocene normal faults are mapped, the segmentation could be controlled by structural heritage. Offshore, all but the southernmost segments of the Amorgos fault exhibit cumulative scarps of at least 700 m in relief. The segments strike NE-SW, except for the northern one that displays a curved structure in its middle, at 60° with respect to the main fault (E-W striking).The central segment, where evidences of the 1956 earthquake rupture were found, is composed of several secondary faults that offset young geomorphic features at the seafloor (such as mass-wasting scars) with purely normal kinematics. In comparison, the curved northern segment shows fewer secondary faults, none of them offsetting the numerous mass-wasting scars observed along its trace. We also find here secondary NE-SW faults that are crosscutting its cumulative scarps, and are offsetting the Last Glacial Maximum wave-cut platform by up to 5 meters, testifying for their recent activity. These observations question the role of the northern E-W striking segment in the accommodation of the present-day stress regime (NW-SE extension), that may be now inactive, or activated as a strike-slip fault, although we do not observe markers laterally offset. We discuss how the geometry and segmentation of the Amorgos fault can impact the rupture propagation, especially in relation to the 1956 earthquake and morphology of the nearby faults.
(pp. https://doi.org/10.5194/egusphere-egu25-16612, 15/03/2025)
GEOAZUR 7329, INSU - CNRS, UniCA, CNRS, IRD [Occitanie], IRD, UniCA, GEGENA, URCA, Inrap, MSH-URCA, URCA, IPGP - UMR_7154, INSU - CNRS, IGN, UR, IPG Paris, CNRS, UPCité, NKUA, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, LGENS, INSU - CNRS, CNRS, ENS-PSL, PSL
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
Evolution of the Asian summer monsoon and regional karst ecological environment since the middle ages in Southwest China
The frequent droughts and floods, closely associated with the Asian summer monsoon (ASM), has profoundly affected the ecological environment and economy in East Asia. While changes in the ASM are closely related to precipitation patterns, the specific mechanism still requires further investigation. This study utilized stalagmite records from the Feilong Cave in southwest China to reconstruct the evolution of the ASM since the Medieval Warm Period (MWP). The results indicated that the ASM strengthened during the MWP and weakened during the Little Ice Age (LIA), with changes in monsoon intensity primarily driven by solar activity and variations in tropical ocean-atmosphere circulation. Different phase combinations of the Atlantic Multidecadal Oscillation, and the Pacific Decadal Oscillation also influenced on the variations of the ASM. During the MWP, with warming of the northern hemisphere landmasses, the ASM intensified, enhancing the long-range transport of moisture from the southwest (Indian summer monsoon), leading to northward shifts of the rain belt in the eastern monsoon region in China and increased precipitation in northern China. Conversely, during the LIA, cooling of the northern hemisphere landmasses led to a weakening of the ASM and reduced southwest moisture transport, resulting in southward shifts of the rain belt in the eastern monsoon China and increased precipitation in southern China. Additionally, the abnormal southward shift of the Western Pacific Subtropical High led to prolonged retention of the rain belt in southern China, causing an increase in monsoonal rainfall in southern China. Comparison with monsoonal Chinese terrestrial proxy records reveals an antiphase relationship between northern and southern parts of the eastern China. During the MWP, the counterparts showed a "wet north-dry south" pattern, while during the LIA, a "wet south-dry north" pattern emerged. Furthermore, proxy records suggest that human activities exacerbated the deterioration of karst ecological environment in southwest China since the Middle Ages.
(Scientific Reports. vol. 15, n° 2045-2322, 08/03/2025)
IGBMC, INSERM, CNRS, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, IGEC, Xjtu, NTU
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
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
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
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