Vegetation response in NW Mediterranean borderlands to the millennial-scale climate variability during the Last Glacial period
Deep-sea pollen records from the Western European margin indicate that regional vegetation oscillated between open forest and steppe during the Last Glacial period (ca. 115 – 11.7 kiloyears [kyrs]) in response to the millennial scale climate variability, specifically the Dansgaard-Oeschger, (D-O) cycles and Heinrich events (HE). The magnitude of the forest expansions during D-O warming events was modulated by orbital parameters. However, the vegetation response in the northwestern Mediterranean region during this period remains poorly understood due to the fragmentary nature of the available sequences. In this study, we present a new well-chronologically constrained high-resolution marine pollen record from the Gulf of Lion (MD99-2343, 40°29'N, 4°01'E), documenting the NW Mediterranean borderlands’ vegetation response during Marine Isotope Stages (MIS) 4 to 2 (~73 - 14 kyrs). Initial findings highlight that the extent of the temperate forest expansions in NW Mediterranean borderlands, i.e., the forest colonizing the Rhône and Ebro valleys, in response to D-Os warming events is modulated by precession; as previously indicated by Western European margin pollen records located in the Mediterranean region below 40°N. In Western Europe, the HEs are all characterized by steppe expansions, but the new pollen analysis documents another scenario with an increase in forest cover during HE 6 and 2. We hypothesize that local atmospheric and marine processes in the Gulf of Lion allowed the development of the temperate forest in the NW Mediterranean borderlands during HE 6 and 2, while the expansion of open and steppic environments occurred in other Western European regions.
(17/07/2024)
UB, UBM, CNRS, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, EPHE, PSL, LMJL, CNRS, Nantes univ - UFR ST, Nantes Univ
Climate and Human Evolution: Insights from Marine Records
The relationship between climate and human evolution is complex, and the causal mechanisms remain unknown. Here, we review and synthesize what is currently known about climate forcings on African landscapes, focusing mainly on the last 4 million years. We use information derived from marine sediment archives and data-numerical climate model comparisons and integration. There exists a heterogeneity in pan-African hydroclimate changes, forced by a combination of orbitally paced, low-latitude fluctuations in insolation; polar ice volume changes; tropical sea surface temperature gradients; the Walker circulation; and possibly greenhouse gases. Pan-African vegetation changes do not follow the same pattern, which is suggestive of additional influences, such as CO$_2$ and temperature. We caution against reliance on temporal correlations between global or regional climate, environmental changes, and human evolution and briefly proffer some ideas on how pan-African climate trends could help create novel conceptual frameworks to determine the causal mechanisms of associations between climate/habitat change and hominin evolution.
(Annual Review of Marine Science, n° 1941-1405, 09/07/2024)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, PACEA, UB, CNRS
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
(01/07/2024)
BRGM, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, NIOZ
Aquifer-CO2 leak project. Effect of CO2-rich water percolation in porous limestone cores: Simulation of a leakage in a shallow carbonate freshwater aquifer
Carbon capture and storage (CCS) is a promising technology for reducing greenhouse gas emissions, however, leakage of CO2 constitutes a major concern for aquifers. Despite abundant literature on petrophysical and geochemical changes at storage conditions, few studies address the impact of CO2 leakage on petrophysical and at aquifer-like pressures, flow rates and temperatures. The aim of the paper is to study and quantify at the core scale, the effects of various factors, including flow rates, fluid salinities, CO2 concentrations and limestone carbonate facies, on the petrophysical and geochemical parameters of a carbonate freshwater aquifer during an experimental CO2 leakage. To achieve this, successive CO2-rich water percolation experiments were performed at the core scale, while monitoring changes in petrophysical parameters and water chemistry. During our experiments, initial permeability increments were observed for both rock samples, followed by decreases in later experiments. Evidence of pore clogging and wormholes was also observed. It was found that the transport of particles led to significant porosity creation. The water monitoring sensors were sensible to the experimental leakage conditions, particularly electrical conductivity. The results of this study contribute to the understanding of petrophysical changes in carbonate aquifer systems by anticipating which type of aquifers are more vulnerable to dissolution and to what extent the CO2 leakage conditions modify the petrophysical parameters.
(Chemical Geology. vol. 657, n° 0009-2541, pp. 122105, 01/07/2024)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
Experimental testing of two urban stressors on freshwater biofilms
Aquatic ecosystems and their communities are exposed to numerous stressors of various natures (chemical and physical), whose impacts are often poorly documented. In urban areas, the use of biocides such as dodecyldimethylbenzylammonium chloride (DDBAC) and their subsequent release in wastewater result in their transfer to urban aquatic ecosystems. DDBAC is known to be toxic to most aquatic organisms. Artificial light at night (ALAN) is another stressor that is increasing globally, especially in urban areas. ALAN may have a negative impact on photosynthetic cycles of periphytic biofilms, which in turn may result in changes in their metabolic functioning. Moreover, studies suggest that exposure to artificial light could increase the biocidal effect of DDBAC on biofilms. The present study investigates the individual and combined effects of DDBAC and/or ALAN on the functioning and structure of photosynthetic biofilms. We exposed biofilms in artificial channels to a nominal concentration of 30 mg.L–1 of DDBAC and/or ALAN for 10 days. ALAN modified DDBAC exposure, decreasing concentrations in the water but not accumulation in biofilms. DDBAC had negative impacts on biofilm functioning and structure. Photosynthetic activity was inhibited by > 90% after 2 days of exposure, compared to the controls, and did not recover over the duration of the experiment. Biofilm composition was also impacted, with a marked decrease in green algae and the disappearance of microfauna under DDBAC exposure. The integrity of algal cells was compromised where DDBAC exposure altered the chloroplasts and chlorophyll content. Impacts on autotrophs were also observed through a shift in lipid profiles, in particular a strong decrease in glycolipid content was noted. We found no significant interactive effect of ALAN and DDBAC on the studied endpoints.
(Aquatic Toxicology. vol. 272, n° 0166-445X, pp. 106972, 01/07/2024)
UR EABX, INRAE, INRS, UB, CNRS, INRAE, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, UQAM
Giant sediment wave fields adjacent to debris-flow filled deep sea valleys: New evidence of cohesive flows transforming into dilute turbidity currents
Sediment waves are subaqueous sedimentary figures belonging to the supercritical flow domain and are of growing interest to the scientific community and industry. They are ubiquitously observed on the seafloor of world's oceans, as well as in the stratigraphic record imaged by marine seismic datasets. In this study we focus on the Cenozoic strata offshore Ivory Coast, where giant sediment waves developed at the base of slope range in height and wavelength: 10–100 m and 1–6 km, respectively. Sediment waves fields in this study developed simultaneously and adjacent to wide, rectilinear valleys, filled by mass-transport deposits. Thus, sediment waves serve as a rare example of large-scale deep-water cyclic steps formed through phase transformation (water entrainment and dilution) of laminar debris flows. The lithological nature of sediment waves can be estimated through the observation of polygonal faulting affecting the sediment waves fields, which suggest a dominant abundance of fine-grained material (clay and silt-prone). This study also shows that wide submarine valleys flanked by sediment waves do not necessarily correspond to sand-prone depositional systems, and that their potential to hold reservoir units for hydrocarbon exploration or CO2 storage should be evaluated with caution when in lower resolution datasets are used.
(Marine Geology. vol. 473, n° 0025-3227, pp. 107305, 01/07/2024)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
Pirumosphaera armandae nov. sp., a new Southern Ocean polycystine radiolarian genus and species
This paper describes a new monospecific polycystine radiolarian genus and its single species so far, Pirumosphaera armandae, found in the Southwest Pacific and Indian sectors of the Southern Ocean. The new spumellarian form is rarely found as a complete specimen, as only its first and second shells are commonly found. However, partially complete specimens suggest that the test of this species is made of four shells. The most diagnostic feature of the species is the peculiar shape of the first shell which protrudes through the second shell, a characteristic that does not conform to any other Quaternary spumellarian genus. Based on the distinct and unique relationship between the first and second shells, the species is assigned to the newly established Pirumosphaera genus.
(Revue de Micropaléontologie. vol. 83, n° 0035-1598, pp. 100773, 01/07/2024)
UQ [All campuses : Brisbane, Dutton Park Gatton, Herston, St Lucia and other locations], LEMAR, IRD, IFREMER, UBO EPE, CNRS, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
Synergies of chemodenitrification and denitrification in a saline inland lake
The interconnection between biotic and abiotic pathways involving the nitrogen and iron biogeochemical cycles has recently gained interest. While lacustrine ecosystems are considered prone to the biotic nitrate reduction (denitrification), their potential for promoting the abiotic nitrite reduction (chemodenitrification) remains unclear. In the present study, batch incubations were performed to assess the potential for chemodenitrification and denitrification in the saline inland lake Gallocanta. Sulfidic conditions are found in top sediments of the system while below (5–9 cm), it presents low organic carbon and high sulfate and ferrous iron availability. Anoxic incubations of sediment (5–9 cm) and water from the lake with nitrite revealed potential for chemodenitrification, especially when external ferrous iron was added. The obtained isotopic fractionation values for nitrite (ε15NNO2) were 6.8 and 12.3 ‰ and therefore, fell in the range of those previously reported for the nitrite reduction. The more pronounced ε15NNO2 ( 12.3 ‰) measured in the experiment containing additional ferrous iron was attributed to a higher contribution of the chemodenitrification over biotic denitrification. Incubations containing nitrate also confirmed the potential for denitrification under autotrophic conditions (low organic carbon, high ferrous iron). Higher reaction rate constants were found in the experiment containing 100 μM compared to 400 μM nitrate. The obtained ε15NNO3 values ( 8.5 and 15.1 ‰) during nitrate consumption fell in the range of those expected for the denitrification. A more pronounced ε15NNO3 ( 15.1 ‰) was determined in the experiment presenting a lower reaction rate constant (400 μM nitrate). Therefore, in Gallocanta lake, nitrite generated during nitrate reduction can be further reduced by both the abiotic and biotic pathways. These findings establish the significance of chemodenitrification in lacustrine systems and support further exploration in aquatic environments with different levels of C, N, S, and Fe. This might be especially useful in predicting nitrous oxide emissions in natural ecosystems.
(Chemosphere. vol. 359, n° 0045-6535, pp. 142292, 01/07/2024)
IPREM, UPPA, INC-CNRS, CNRS, UB, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, SU
Assessment of the impact of chemical pollution on endangered migratory fish in two major rivers of France, including spawning grounds
Water pollution is a one of the most contributors to aquatic biodiversity decline. Consequently, ecological risk assessment methods have been developed to investigate the effects of existing stresses on the environment, including the toxic effects of chemicals. One of the existing approaches to quantify toxic risks is called “Potentially Affected Fraction of species” (PAF), which estimates the potential loss of species within a group of species studied. In this study, the PAF method was applied to the Garonne catchment (southwest France) due to the limited information available on the involvement of water pollution in the decline of diadromous fish populations. This approach was used to quantify the potential toxic risk associated with chemical contamination of water for fish species. The objectives were to quantify this risk (1) in the Garonne and Dordogne rivers and (2) in the spawning grounds of two endangered anadromous fish species: the allis shad and the European sturgeon during the development period of their early life stages. Environmental pollution data was provided for 21 sites within the Garonne catchment between 2007 and 2022, and toxicity data was obtained specifically from freshwater toxicity tests on fish species. Then, for each site and each year, the potential toxic risk for a single substance (ssPAF) and for a mixture of substances (msPAF) was calculated and classified as high (>5%), moderate (>1% and <5%) or low (<1%). Potential toxic risks were mostly moderate and mainly associated with: metals > other industrial pollutants and hygiene and care products > agrochemicals. In summary, this study highlights the probable involvement of water contamination on the decline, fate and restoration of diadromous fish populations in the Garonne catchment, focusing notably on the toxic effects on early life stages, a previously understudied topic.
(Science of the Total Environment. vol. 931, n° 0048-9697, pp. 172748, 25/06/2024)
UR EABX, INRAE, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, RiverLy, INRAE
Tidal and geological controls on longshore sediment transport along the north of the Médoc coast, SW France
The north of the Médoc coast, SW France, is a sandy coast with complex environment settings including an irregular bathymetry, shallow bank, rocky outcrops, and an adjacent km-scale estuary. This coast is strongly affected by marine erosion and exhibits dramatic erosion trends, with shoreline retreats reaching locally several meters per year for decades. New coastal management scenarios for the next years, or even decades, need to be investigated. For this purpose, we may rely on the use of reduced-complexity shoreline change models. They are valuable tools to simulate past and future shoreline changes at time scales from seasons to centuries. These models usually rely on time and space integration of wave-driven longshore sediment transport, which is one of the main drivers of shoreline change along sandy coasts on the long-term. This longshore transport is computed from breaking wave conditions, which are controlled by several physical processes occurring within the nearshore area. However, the control of local environmental settings on breaking waves is usually over-simplified in reduced-complexity shoreline change models, if not neglected. This study investigates the sensitivity of the wave-driven longshore sediment transport along the north of the Médoc coast to different physical processes affecting the wave propagation. Results revealed that on a monthly scale the bathymetry and the bottom friction play a predominant role on longshore sediment transport patterns. In contrast, the contribution of tide-driven water levels is lower on this timescale, and even less for contribution of the tide-driven currents
(pp. 429-438, 25/06/2024)
BRGM, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS