HAL-CEA
Not a member yet
145450 research outputs found
Sort by
Emergent patterns of patchiness differ between physical and planktonic properties in the ocean
No full textInternational audienceWhile a rich history of patchiness research has explored spatial structure in the ocean, there is no consensus over the controls on biological patchiness and how physical-ecological-biogeochemical processes and patchiness relate. The prevailing thought is that physics structures biology, but this has not been tested at basin scale with consistent in situ measurements. Here we use the slope of the relationship between variance vs spatial scale to quantify patchiness and ~650,000 nearly continuous (dx ~200 m) measurements -representing the Atlantic, Pacific, and Southern Oceans -and find that patchiness of biological parameters and physical parameters are uncorrelated. We show variance slope is an emergent property with unique patterns in biogeochemical properties distinct from physical tracers, yet correlated with other biological tracers. These results provide context for decades of observations with different interpretations, suggest the use of spatial tests of biogeochemical model parameterizations, and open the way for studies into processes regulating the observed patterns.</div
Greenhouse Gas Budgets of Central and West Asia (2000–2020): A Significant Net Source to the Atmosphere
No full textInternational audienceThis study provides the first comprehensive quantification of three major greenhouse gases (GHGs, including CO 2 , CH 4 , and N 2 O) budgets for Central and West Asia (CWA) from 2000 to 2020, including contributions from fossil fuels, industry, and managed and unmanaged terrestrial ecosystems. We use bottom-up (BU: inventories and process-based models) and top-down approaches (TD: atmospheric inversions) to elucidate CWA's GHG budget and its changes. BU and TD budgets consistently show that CWA was a significant and growing GHG source during the 2010s: average net emissions were 4,175 (range: 4,055-4,301) Tg CO 2 eq yr 1 based on BU and using global warming potentials over a 100-year period (GWP100), and slightly higher net emissions of 4,293 (3,760-4,826) Tg CO 2 eq yr 1 based on TD. BU estimates show that CO 2 emissions from fossil fuel combustion and fugitive releases were the dominant source, accounting for 61% of the total budget in the 2010s, with 2,554 (2,526-2,582) Tg CO 2 eq yr 1 . Terrestrial natural ecosystems were a weak CO 2 sink and sources of CH 4 and N 2 O, which together resulted in a decadal mean net GHG emission of 220.5 (114.5-332.8) Tg CO 2 eq yr 1 . Non-CO 2 gases, primarily CH 4 , contributed significantly to the region's GHG emissions, accounting for 32% (BU) and 24% (TD) of CWA's total GHG budget under GWP100, and increasing to 57% (BU) and 49% (TD) with GWP20, highlighting CH 4 stronger warming impact over shorter timescales. Overall, CWA contributed about 8% of global net GHG emissions in the 2010s, with about 10% of global CO 2 , 7% of CH 4 , and 3% of N 2 O.</div
Hysteresis of the Antarctic Ice Sheet With a Coupled Climate-Ice-Sheet Model
No full textInternational audienceThe stability of the Antarctic ice sheet under different fixed CO 2 levels and orbital configurations is explored using a coupled climate-ice sheet model, starting from either a pre-industrial ice sheet or an ice-free, isostatically rebounded geometry. Simulations reveal a strong hysteresis effect: equilibrium ice volumes differ significantly for equivalent CO 2 levels, depending on the initial ice sheet geometry. Crucially, the albedo-melt feedback is accounted for in our coupled setting, resulting in a nonlinear response of the ice sheet to the CO 2 forcing. Critical CO 2 thresholds trigger either the complete Antarctic ice sheet loss or near-complete regrowth. The orbital configuration influences these CO 2 thresholds. These findings highlight the importance of ice sheetatmosphere interactions, notably the albedo-melt feedback, in projecting future long-term ice sheet behavior. Neglecting these feedbacks could lead to an overestimation of CO 2 thresholds for ice sheet destabilization, with implications for future long-term sea level rise under high emission scenarios.</div
Method Validation: Extraction of Microplastics from Organic Fertilisers
No full textInternational audienceIt has been demonstrated that organic fertilisers could be a source of microplastics (MPs) in agricultural soils. These organic fertilisers comprise a diverse array of matrices including organic waste and by-products. Currently, there is no established methodology for the extraction of MP from these matrices. The present article aims to validate a standardised protocol for the extraction of MPs from a diverse range of complex, organic-rich samples. The protocol has been developed to ensure a high recovery of MPs, to preserve their integrity, and to eliminate organic particles that interfere with FTIR analyses. Spiked MPs sized 315-5000 µm were subjected to a two-step process involving chemical digestion (H 2 O 2 , 30% (w/v), 53 • C) and density separation (NaI, >1.60 g•cm -3 ). This resulted in a mean extraction rate exceeding 95%, with undigested matter remaining below 5%. No evidence of fragmentation was observed. Furthermore, the chemical nature of spiked microplastics is still perfectly interpretable from the FTIR spectra despite the different chemical treatments undergone. These findings thus validate the method for the microplastic range 315-5000 µm. However, a new method for reanalysing the project's data produced contrasting results, suggesting a significant drop in recovery rates for size ranges below 250 µm. This reanalysis approach constitutes the second innovation of this protocol, and enables a more critical analysis of the results obtained in publications on microplastics.</div
Shotgun metagenomics reveals the flexibility and diversity of Arctic marine microbiomes
No full textInternational audiencePolar oceanographic regions are exposed to rapid changes in temperature, salinity, and light fields that determine microbial species distributions, but resilience to an increasingly unstable climate is unknown. To unravel microbial genomic potential of the Northern Baffin Bay’s polynya, we constructed eight metagenomes from the same latitude but targeting two sides of Pikialasorsuaq (The North Water) that differ by current systems, stratification, and temperature regimes. Samples from the surface and subsurface chlorophyll maximum (SCM) of both sides were collected 13 months apart. Details of metabolic pathways were determined for 18 bacteria and 10 microbial eukaryote metagenome-assembled genomes (MAGs). The microbial eukaryotic MAGs were associated with the dominant green algae in the Mamiellales and diatoms in the Mediophyceae, which tended to respectively dominate the eastern and western sides of Pikialasorsuaq. We show that microbial community taxonomic and functional signatures were ca. 80% similar at the latitude sampled with only 20% of genes associated with local conditions. From the metagenomes we found genes involved in osmotic regulation, antifreeze proteins, and photosystem protection, with hydrocarbon biodegradation and methane oxidation potential detected. The shared genomic compliment was consistent with adaptation to the Arctic’s extreme fluctuating conditions, with implications for their evolutionary history and the long-term survival of a pan-arctic microbiome. In particular, previously unrecognized genetic capabilities for methane bio-attenuation and hydrocarbon metabolism in eukaryotic phytoplankton suggest adaptation to dark conditions that will remain, despite climate warming, in the high latitude offshore waters of a future Arctic
Transboundary emission contribution to PM<sub>2.5</sub> concentrations in Indian cities
No full textInternational audienceTargeting urban air quality improvements in India, the National Clean Air Program (NCAP) was launched in 2019 to reduce PM 2.5 concentrations by 20%-30% in 122 initial cities over a 7 year period (2017-2024). However, considering the regional nature of air pollution nationwide and the significant emission load from rural areas, a potentially large fraction of urban PM 2.5 might originate from emissions outside of a city's boundary, i.e. transboundary emissions. Here, we couple top-down (STILT-PM 2.5 ) and bottom-up (WRF-Chem) modeling approaches with a new, nationwide, monthly-resolved, and fine-scale (5 km × 5 km) anthropogenic emission inventory to assess the impact of transboundary emissions to urban PM 2.5 concentrations across 143 cities (122 NCAP and 67 million plus -cities with population >1 million, among which 46 cities are also NCAP cities). We find that, on average, ∼85% (STILT-PM 2.5 : 82% [95% CI: 80-85%; IQR: 77%-94%] & WRF-Chem: 89% [95% CI: 87%-91%; IQR: 88%-96%]) of urban PM 2.5 across the 143 cities originates from transboundary emissions, with domestic biomass burning (32%), energy generation (16%) and industry (15%) being the leading average emission sources to the transboundary contribution. In addition, 107 of the 122 NCAP cities from both modeling approaches have annual transboundary PM 2.5 contributions exceeding 80%, indicating that an entire mitigation of within-boundary emissions alone in these cities will not achieve the most conservative targets outlined as part of NCAP. Our findings underscore the need for multi-scale, regional action planning and implementation to achieve PM 2.5 -air quality targets throughout India.</div
Mechanisms controlling the plasma membrane targeting and the nanodomain organization of the plant SPFH protein HIR2
No full textHIR2 is a plant-specific protein belonging to the superfamily of SPFH domain-containing proteins that were proposed to play scaffolding functions in membranes. HIR2 organizes in plasma membrane (PM) nanodomains that correspond to nanometric scale structures enriched in specific lipids and proteins acting as signaling/regulation hubs. So far, how PM nanodomains are formed and maintained in plant cells remains largely unknown. Combining state of the art microscopy techniques, we investigated the mechanisms governing the trafficking and the organization into nanodomains of Arabidopsis HIR2 protein. We revealed that the mono S-acylation of HIR2 either on C6 or on C7 was required for HIR2 targeting to the PM of Arabidopsis cells, independently of the conventional secretory pathway. Investigating the mechanisms implicated in the arrangement of HIR2 into nanodomains, we provided evidences that the lipid composition in sterols and very long chain fatty acids of the PM influenced HIR2 organization. HIR2 forms oligomers and we demonstrated here that the C-terminal part of HIR2 is required for self-assembly, similarly to animal SPFH proteins. Interestingly, we highlighted that the oligomerization of HIR2 is essential for its organization in nanodomains and to ensure HIR2 lateral stability in the PM. Overall, we propose that HIR2 nanodomain organization is a complex mechanism relying on different parameters including PM lipid composition and oligomerization. HIR proteins are involved in plant immunity. Here, we revealed that HIR2 nanodomain organization is required to boost the apoplastic ROS burst induced by the bacterial peptide flg22
Designing a general-purpose 8-bit (T)FHE processor abstraction
No full textInternational audienceMaking the most of TFHE programmable bootstrapping to evaluate functions or operators otherwise challenging to perform with only the native addition and multiplication of the scheme is a very active line of research. In this paper, we systematize this approach and apply it to build an 8-bit FHE processor abstraction, i.e., a software entity that works over FHE-encrypted 8-bit data and presents itself to the programmer by means of a conventional-looking assembly instruction set. In doing so, we provide several homomorphic LookUp Table (LUT) dereferencing operators based on variants of the tree-based method and show that they are the most efficient option for manipulating encryptions of 8-bit data (optimally represented as two basis 16 digits). We then systematically apply this approach over a set of around 50 instructions, including, notably, conditional assignments, divisions, or fixed-point arithmetic operations. We further test the approach on several simple algorithms, including the execution of a neuron with a sigmoid activation function with 16-bit precision. We conclude the paper by comparing our work to the FHE compilers available in the state of the art. Finally, this work reveals that a very limited set of functional bootstrapping patterns is versatile and efficient enough to achieve general-purpose FHE computations beyond the boolean circuit approach. As such, these patterns may be an appropriate target for further works on advanced software optimizations or hardware implementations
