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Holocene climatic changes in the Kerguelen archipelago (South Indian Ocean) based on marine and lacustrine palaeoclimatic archives
No full textInternational audienceClimatic variability in the Southern Hemisphere is largely controlled by the latitudinal position of the Southern Hemisphere Westerly Winds (SHW), whose migration influences precipitation, temperature, and Antarctic upwelling. This study presents the results of analyses of two lacustrine sediment cores from Lake Armor, located on the subantarctic Kerguelen Islands (49 • 15′S, 69 • 10′E), within the SHW belt. Lipid biomarkers (Glycerol Dialkyl Glycerol Tetraethers, n-alkanes, and their hydrogen isotopes) were used to reconstruct mean annual air temperature above freezing (MAF) and humidity conditions. These records are compared with a high-resolution diatom-based summer sea surface temperature (SST) reconstruction from marine core MD11-3353, situated 150 km southwest of Lake Armor. In the late glacial and Early Holocene, our results reveal a period of warm air temperature, comparable to current values and very warm sea surface temperature, 5°C above the current values. Around 9000 cal a BP, an abrupt transition occurred, marked by a cooling of 5°C in SST and 1.5°C in MAF, interpreted as a northward migration of the SHW and associated oceanic fronts. The Mid-to-Late Holocene period is characterized by pronounced MAF variability, including a notably warm interval between 3000 and 2000 cal a BP, when n-alkane dD suggests the prevalence of wetter conditions. Since ~250 cal a BP, a southward migration of the SHW has produced a 2.5°C rise in MAF. Our findings are overall consistent with previous studies from the Indian Ocean, but permit us to go a step further as by comparing SSTs and air temperatures. This suggests that SST is not a reliable predictor of air temperature on the Kerguelen Islands, particularly during the Early Holocene. We hence argue that Kerguelen air temperature is predominantly controlled by the position of westerly winds, as an indicator of reorganisations in air mass trajectories
Far-red light regulates phototactic behavior of benthic pennate epipelic diatoms under low irradiance
No full textInternational audienceDiatom-dominated microphytobenthic communities are exposed to steep and dynamic light gradients in intertidal sediments. The vertical migration of epipelic pennate diatoms is a key adaptive trait enabling optimal light acquisition. However, it remains unclear whether these organisms can detect and respond to long-wavelength light, especially because deeper photic layers are enriched in far-red due to attenuation of shorter wavelengths. Here, we investigated the phototactic responses of a natural microphytobenthic biofilm, primarily composed of epipelic pennate diatoms, to long-wavelength light at two low irradiance levels (5 and 20 µmol photons m⁻² s⁻¹), using a custom-built multispectral LED illuminator. Red light (660 and 680 nm) induced a strong upward vertical migration and a high effective quantum yield of photosynthesis. Far-red light (720 and 740 nm) also triggered a significant upward migratory response, although more moderate than red light. In contrast, near-infrared wavelengths (770 and 810 nm) elicited no significant migratory activity, indistinguishable from the dark controls. Phototactic migration was observed even at 5 µmol photons m⁻² s⁻¹, suggesting a high sensitivity to light at intensities potentially below the photosynthetic compensation point. Our results provide evidence that benthic pennate diatoms can behaviorally respond to long-wavelength, low-intensity light. This response, likely mediated by phytochrome-like photoreceptors, suggests the existence of a low-light, long-wavelength sensing mechanism that enables diatoms to detect fine-scale spectral gradients as cues for surface detection and vertical positioning within the sediment matrix
Shifts in Fossil Benthic Foraminiferal Community Trajectories During the Last Deglaciation Along the European Margin
No full textInternational audienceConstraining how faunal communities vary over time and space in response to environmental change has long been a major goal of paleoecologists. Among fossilized organisms, few yield a better and greater detailed record than foraminifera to understand past marine conditions. The analytical frameworks used to build palaeoenvironmental reconstructions have progressed over the years, providing new perspectives within the field. One of these proposed frameworks, Ecological Trajectory Analysis (ETA), offers the possibility to compare geometric properties of trajectories to understand temporal changes within communities. We provide here an application of ETA to the fossil record by comparing benthic foraminiferal data sets from three previously studied cores from the French Atlantic margin. The three cores are each separated by approximately 350 km and cover the last deglaciation, thus allowing a comparison of community dynamics at spatial and temporal scales. A major perturbation in fossil benthic communities was identified in ETA metrics at the onset of Heinrich Stadial 1, with a twofold departing and recovering trend of communities. The three sites along the French Atlantic margin also show spatial differences during the deglaciation, testimony to a contrasting response of benthic foraminifera to ice sheet dynamics and fluctuating fluvial discharges. In this instance, the application of ETA allows to compare multiple fossil foraminiferal records. At a broader scale, the use of trajectory metrics within one unique multivariate space of community resemblance stands out as a powerful tool to compare many other fossil records within the field of paleoecology
Interacting drivers of Holocene climate change in southwestern Africa: the influence of insolation, rainbelt dynamics and upwelling
No full textInternational audienceUnderstanding regional-scale patterns of long-term climate variability is essential for identifying the drivers of past environmental change. In southern Africa, the continent is often divided into three rainfall zones-summer, winter, and aseasonal-but this framework fails to capture the finer dynamics of transitional areas where tropical, subtropical, and temperate systems converge. This study examines Holocene climate variability along the western margin of the southern African monsoon region using a new 7300-year nitrogen isotope record from rock hyrax middens at Omanyne-4 in northern Namibia. Unlike other Namib Desert records that indicate progressive aridification through the Holocene, the Omanyne-4 sequence shows a long-term trend toward increasing humidity, consistent with insolation-driven enhancement of tropical and Indian Ocean moisture advection. Comparisons with records from northern Namibia, Botswana, and western Zambia reveal a coherent pattern of mid-to late Holocene humidification across the northwestern interior, in contrast to coastal aridification. Periods of both in-phase and antiphase variability with other regional records highlight the role of the Angola-Benguela Front and associated upwelling dynamics in modulating Namibian hydroclimate. These results delineate distinct Holocene climate response regions in northern Namibia and Botswana and demonstrate the non-linear nature of regional responses to insolation forcing and underscore the importance of coastal-inland atmospheric interactions in shaping long-term hydroclimate variability in southwestern Africa.</div
Mesozoic magmatism in the Andes of southern Ecuador and northern Peru: Tectonic insights from whole-rock chemistry and zircon petrochronology
No full textInternational audienceThe southern Ecuador–northern Peru region marks the transition between the northern and central Andes. This study reconstructs the Mesozoic magmatic history of this key region by integrating petrography, Usingle bondPb geochronology, whole-rock and zircon geochemistry, and εHf(t) and δ18O zircon isotopic data from plutonic rocks. Our results indicate that much of the Mesozoic magmatism occurred in an extensional arc setting, with magmatic reservoirs progressively incorporating more depleted, mantle material, while crustal contributions diminished through time. Magmatic reservoirs evolved both spatially and temporally, beginning with an extensive Triassic arc dominated by granitoids exhibiting strong crustal signatures at least until 220 Ma. This was followed by mildly enriched signatures associated with a stationary Jurassic to Early Cretaceous arc active between ∼190 and ∼ 126 Ma. Somewhere in between 126 and 104 Ma, the arc underwent a significant westward migration, potentially driven by slab rollback, which coincided with the opening of the Celica–Lancones Basin and the subsequent emplacement of the Late Cretaceous Celica–Lancones arc onto oceanic basement. This migration is consistent with westward shifts observed in central Ecuador and Colombia but contrasts with coeval eastward migration documented in central and southern Peru. In addition, new Usingle bondPb ages challenge current interpretations of a missing Jurassic arc in northern Peru by providing clear evidence that Jurassic magmatism extended at least as far south as 6°S
Autonomic cardiac regulation to slow-paced respiration in seated and supine positions
No full textInternational audiencePurpose: Respiratory modulation and positional control are the main two regulators of cardiac autonomic activity. Although both slow-paced breathing and supine position promote parasympathetic regulation, their interaction remains poorly documented. Here, the objective of this work is to study the interaction between these two autonomic controls. Methods: Twenty healthy volunteers (12 males, 8 females), age of 25.9 ± 3.9 years were included in this study. They were randomly subjected to 6 different slow and controlled breathing at 4.5, 5, 5.5, 6, 6.5, and 7 min/cycles for 3 min in supine or seated position after a 3 min baseline recording in spontaneous breathing. ECG was continuously monitored and RR intervals (RRI), total power (Ptot), the standard deviation of normal R-R intervals (SDNN), high frequency power (HF), the root mean square of successive R-R interval differences (RMSSD), and low frequency power (LF) were calculated to study autonomic regulation. Results: We observed (1) a similar increase in parasympathetic (RMSSD and LF) and overall autonomic (RRI, Ptot, and SDNN) activities in slow-paced breathing conditions, whatever the respiratory rate in comparison with control spontaneous breathing; (2) these autonomic parameters increased in sitting position, but in parasympathetic (RMSSD and LF) and overall autonomic (Ptot, and SDNN) activities interacted with respiratory control and were higher in seated slow-paced breathing. Conclusion: These results showed that (1) whatever the slow-paced breathing frequency, slow breathing favours parasympathetic control and slow heart rhythm; and (2) seated position favors autonomic cardiovascular interaction between respiratory modulation and positional control
Across ancient oceans: Eocene dispersal routes of Asian terrestrial mammals to Europe, Afro-Arabia and South America
No full textInternational audienceDuring the middle and late Eocene, Asian terrestrial mammals dispersed to Europe, while primates and rodents dispersed across the 500-to-2000 km wide Neotethys Ocean and the 1500-to-2000 km wide Atlantic Ocean to colonize Afro-Arabia and South America. This study explores how these mammals have achieved such remarkable and enigmatic dispersals. We present high-resolution paleogeographic models for the middle to late Eocene based on updated plate kinematic reconstructions, paleo-bathymetry and paleo-topography data. With this, we evaluate landmass configurations and connectivity that may have facilitated faunal exchanges from Asia toward Europe, Afro-Arabia, and South America and discuss dispersal mechanisms between these biogeographic provinces. Our reconstructions reveal that during the Bartonian (~40–38 Ma), an overland dispersal corridor between Asia and Balkanatolia became available to terrestrial mammals and acted as a pivotal pathway for Asian faunas dispersing toward western Europe and Afro-Arabia. We identified two Balkanatolian island-hopping routes across the Western Neotethys potentially enabling the dispersal of small-bodied Asian primates, rodents and artiodactyls to Afro-Arabia. Alternatively, these taxa may have rafted across the Central Neotethys. By ~34 Ma, Balkanatolia fully connected with Western Europe, opening a southern “Grande Coupure” route for Asian faunas. In the Atlantic, we identify long-distance rafting as the most plausible mechanism for the 40–34 Ma transoceanic dispersal of the Asian-originated primates and rodents from Afro-Arabia to South America despite the likely presence of sparse islands along the Walvis Ridge and the Rio Grande Rise
Smoked fish from Gabon: nutritional benefits vs. contaminant risks
No full textInternational audienceSmoked fish is the most common form of fish consumption in many African countries. Smoking is likely to cause changes in nutritional value and in the concentration of certain toxic elements. We assessed these changes in the Bonga shad (Ethmalosa fimbriata, Bowdich 1825). Fatty acids (26), vitamin A, trace elements (14) and polycyclic aromatic hydrocarbons (PAHs, 24) were examined in E. fimbriata at different smoking durations (fresh, 24 h, 48 h and 72 h). Composition of smoked fish revealed high inter-individual variability. Smoking did not affect total fatty acid concentrations, but it led to a 4.5-fold decrease in vitamin A and a decrease in the concentrations of Ca, Mg, Mn, Pb and Sr. Meanwhile, it increased the concentrations of PAHs (by a factor of 42), Cd, Mo and Na. Despite these changes, toxic metals (As, Cd and Pb) and PAHs levels remained within safety limits, except for the B(a)P Toxic Equivalent (TEQ) in 72 h-smoked fish. High inter-individual variability in toxic metals, PAHs and nutrients concentrations is suspected to originate from the heterogeneity of the smoking process, and to natural variation in fish. Overall, our results highlight the safety of artisanal smoked fish for human consumption when processed under certain conditions. To further enhance consumer safety, dietary recommendations would advise ensuring fish skin integrity in order to reduce flesh contamination
RECHARGE, a model of potential recharge of aquifers applied to mainland France
No full textInternational audienceCalculating aquifer recharge provides a means of estimating the renewable fraction of groundwater resources, which is often difficult to quantify. This paper introduces the RECHARGE method, developed to calculate potential groundwater recharge from precipitation infiltration, and its application across mainland France over an extended historical period.The method relies on a simple soil water budget approach to estimate effective precipitation, using meteorological data and a spatial parameter that accounts for land cover and allows the seasonal variability of evapotranspiration to be reflected. An effective precipitation infiltration ratio (EPIR) is then derived for catchments with homogeneous geological lithology, based on linear regressions involving the baseflow index and a GIS-derived parameter. Given the low interannual variability of the baseflow index, the EPIR is assumed to remain constant over time and is subsequently used to convert effective precipitation into potential recharge at the scale of all groundwater bodies in mainland France.To validate this approach, annual effective precipitation estimates were compared for 556 selected catchments, both with observed annual river flows and with outputs from the physically based SURFEX model. The calculated potential recharge was also evaluated at both annual and seasonal scales for the entire French territory, using SURFEX as a reference. Results demonstrate that the RECHARGE model can effectively estimate annual and seasonal potential aquifer recharge. It is suitable for large-scale applications without requiring detailed knowledge of aquifer properties. Future improvements are envisioned, particularly to enhance monthlyscale accuracy in mountainous regions.</p
Charge Transfer Between Ce and Fe During Cooling of an Aluminosilicate Melt: An In Situ XANES Investigation
No full textInternational audienceMultivalent elements are often incorporated to silicate glasses to enhance specific properties to the final product. However, these properties strongly depend on the redox state of the multivalent elements. While the redox behavior of glasses containing a single multivalent element is well studied, research on the in situ interaction between multiple multivalent elements is scarce. In this study, in situ XANES spectroscopy was used to investigate the high temperature redox state of both Ce and Fe in an aluminosilicate melt. The results were compared to room temperature measurements. Our findings demonstrate that, at high temperature equilibrium, Ce and Fe act independently. However, upon cooling below 900°C, a charge transfer process occurs between the two elements as described by the reaction Ce4+ + Fe2+ → Ce3+ + Fe4+. The existence of such a charge transfer, observed even in melts doped with very low Ce and Fe amounts, could suggests that both elements are not randomly distributed in the melt. The intensity of the charge transfer process depends on the CeO2/FeO ratio, with the element present in excess showing minimal change in redox state upon cooling. This explains the difference of room temperature redox state between samples