In this paper, we explore the use of unsteady transit time distribution (TTD) theory to model pollutant removal in biofilters, a popular form of nature-based or “green” stormwater infrastructure (GSI). TTD theory elegantly addresses many unresolved challenges associated with predicting pollutant fate and transport in these systems, including unsteadiness in the water balance (time-varying inflows, outflows, and storage), unsteadiness in pollutant loading, time-dependent reactions and scale-up to GSI networks and urban catchments. From a solution to the unsteady age conservation equation under uniform sampling, we derive an explicit expression for solute breakthrough with or without first-order decay. The solution is calibrated and validated with breakthrough data from 17 simulated storm events (+/- bromide as a conservative tracer) at a field-scale biofilter test facility in Southern California. TTD theory closely reproduces bromide breakthrough concentrations, provided that lateral exchange with the surrounding soil is accounted for. At any given time, according to theory, more than half of water in storage is from the most recent storm, while the rest is a mixture of penultimate and earlier storms. Thus, key management endpoints, such as the treatment credit attributable to GSI, are inexorably linked to the age distribution of water stored and released by these systems.
Madagascar hosts several Paleoproterozoic sedimentary sequences that are key to unravelling the geodynamic evolution of past supercontinents on Earth. New detrital zircon U–Pb and Hf data, and a substantial new database of ~15,000 analyses are used here to compare and contrast sedimentary sequences in Madagascar, Africa and India. The Itremo Group in central Madagascar, the Sahantaha Group in northern Madagascar, the Maha Group in eastern Madagascar, and the Ambatolampy Group in central Madagascar have indistinguishable age and isotopic characteristics. These samples have maximum depositional ages > 1700 Ma, with major zircon age peaks at c. 2500 Ma, c. 2000 Ma and c. 1850 Ma. We name this the Greater Itremo Basin, which covered a vast area of Madagascar in the late Paleoproterozoic. These samples are also compared with those from the Tanzania and the Congo cratons of Africa, and the Dharwar Craton and Southern Granulite Terrane of India. We show that the Greater Itremo Basin and sedimentary sequences in the Tanzania Craton of Africa are correlatives. These also tentatively correlate with sedimentary protoliths in the Southern Granulite Terrane of India, which together formed a major intra-Nuna/Columbia sedimentary basin that we name the Itremo-Muva-Pandyan Basin. A new Paleoproterozoic plate tectonic configuration is proposed where central Madagascar is contiguous with the Tanzania Craton to the west and the Southern Granulite Terrane to the east. This model strongly supports an ancient Proterozoic origin for central Madagascar against the Tanzania Craton of East Africa.
The unsaturated zone serves as reservoir for geogenic and anthropogenic contaminants to local groundwater. Biogeochemical processes in this zone can be affected by nitrogen and water infiltration mobilizing contaminants, ultimately affecting groundwater quality. In this large-scale study, we evaluated the effects of estimated water and nitrogen inputs to the unsaturated zone of a public water supply wellhead protection (WHP) area with respect to subsurface occurrence and transport of nitrate, ammonium, arsenic, and uranium. Thirty-two coring sites were sampled and grouped by water application volume, irrigated – sprinkler (n=20), gravity (n=4) and non-irrigated land use. Unsaturated zone sediments were evaluated for the potential to mobilize arsenic and uranium in relation to nitrogen and water use. Sediment nitrate and ammonium had strong significant (p<0.05) correlation under all water application. Nitrate concentrations were lower beneath sprinkler-irrigated sites but had statistically higher ammonium concentrations than gravity-irrigated. Sediment nitrate concentrations were significantly (p<0.05) different among water application types, suggesting a strong effect of water volume on the changing nitrate concentration. Sediment arsenic presumably attenuated by iron (r=0.32 p<0.05). Uranium in sediments of unsaturated zone was negatively correlated to increase in sediment nitrate (r=-0.23 p<0.05) and ammonium (r=-0.19 p<0.05). Water application types were found to significantly influence sediment arsenic and uranium. While the groundwater arsenic and uranium concentration were below maximum contaminant levels, the highest uranium concentrations were observed in samples from WHP area. The study suggests that irrigation has an impact on unsaturated zone geochemistry with the potential to ultimately affect groundwater quality.
We developed a numerical thermodynamics laboratory called “Thermolab” to study the effects of the thermodynamic behavior of non-ideal solution models on reactive transport processes in open systems. The equations of state of internally consistent thermodynamic datasets are implemented in MATLAB functions and form the basis for calculating Gibbs energy. A linear algebraic approach is used in Thermolab to compute Gibbs energy of mixing for multi-component phases to study the impact of the non-ideality of solution models on transport processes. The Gibbs energies are benchmarked with experimental data, phase diagrams and other thermodynamic software. Constrained Gibbs minimization is exemplified with MATLAB codes and iterative refinement of composition of mixtures may be used to increase precision and accuracy. All needed transport variables such as densities, phase compositions, and chemical potentials are obtained from Gibbs energy of the stable phases after the minimization in Thermolab. We demonstrate the use of precomputed local equilibrium data obtained with Thermolab in reactive transport models. In reactive fluid flow the shape and the velocity of the reaction front vary depending on the non-linearity of the partitioning of a component in fluid and solid. We argue that non-ideality of solution models has to be taken into account and further explored in reactive transport models. Thermolab Gibbs energies can be used in Cahn-Hilliard models for non-linear diffusion and phase growth. This presents a transient process towards equilibrium and avoids computational problems arising during precomputing of equilibrium data.
In this work we employ a reduced-order basis of conservative chemical components to model reactive transport using a Lagrangian (particle tracking) method. While this practice is well-understood in the Eulerian (grid-based) context, its adaptation to a Lagrangian context requires a novel reformulation of particle transport properties. Because the number of conservative-species particles need not change during simulation, spatial resolution stays constant in time, and there is no increase in computational expense due to increasing numbers of product particles. Additionally, this treatment simplifies the interaction between equilibrium and kinetic reactions and allows the use of species-dependent transport operators at the same time. We apply this method to model a suite of simple test problems that include equilibrium and kinetic reactions, and results exhibit excellent match with base-case Eulerian results. Finally, we apply the new method to model a 2D problem concerning the mobilisation of cadmium by a CO$_2$ leak, showing the potential applicability of the proposed methodology.
SKB and several other waste management organizations have established the international SKB Task Force on Modeling of Groundwater Flow and Transport of Solutes (TF GWFTS) to support and interpret field experiments. Objectives of the task force are to develop, test and improve tools for conceptual understanding and simulating groundwater flow and transport of solutes in fractured rocks. Work is organized in collaborative modeling tasks. Task 9 focuses on realistic modeling of coupled matrix diffusion and sorption in heterogeneous crystalline rock matrix at depth, e.g. by inverse and predictive modeling of in-situ transport experiments. Posiva’s REPRO (rock matrix REtention PROperties) experimental campaign has been performed at the ONKALO rock characterization facility in Finland. The two REPRO experiments considered were the Water Phase Diffusion Experiment (WPDE), addressing matrix diffusion in gneiss around a single borehole interval (modeled in Task 9A), and the Through Diffusion Experiment, which is performed between sections of three boreholes and addressed by modeling in Task 9C. The Long-Term Diffusion and Sorption Experiment (LTDE-SD) was an in-situ radionuclide tracer test performed at the Swedish Äspö Hard Rock Laboratory at a depth of about 410 m below sea level. The experimental results indicated a possible deeper penetration of sorbing tracers into the rock matrix than expected. The shape of these tracer penetration profiles was difficult to reproduce. This experiment was modeled and interpreted in Task 9B. Task 9D is addressing the possible benefits of detailed models of the in-situ experiments in safety assessment calculations. The task is performed by upscaling of the WPDE models to conditions applicable for nuclear waste repositories. As Task 9 is now in a finalization process, a number of lessons learned from the 4 sub-tasks have been identified. These include: • field tracer experiments can provide surprises even when well designed and executed, • interaction between the experimentalists and modelers is important and mutually beneficial when investigating anomalous results, • differences in conceptual models have the greatest impact on model outcomes, • it is not trivial to go from modeling of field experiments to safety assessment modeling without making substantial simplifications.
Geological Carbon Sequestration mitigates climate change by capturing and storing carbon emissions in deep geologic formations. Dissolution trapping is one mechanism by which CO2 can be trapped in a deep formation. However, heterogeneity can significantly influenced dissolution efficiency. This work addresses the injection of CO2 in perfectly stratified saline formations under uncertainty. Monte Carlo two-phase flow compositional simulations involving the dissolution of CO2 into brine and evaporation of water into the CO2-rich phase are presented. We systematically analyzed the interplay between heterogeneity and buoyant forces, which is shown to control the migration of the CO2 plume as well as the temporal evolution of dissolution efficiency. Results show that when buoyant forces are important, vertical segregation controls the overall behavior of CO2, diminishing the influence of small-scale heterogeneity on dissolution. However, when buoyant forces are relatively small compared to the degree of heterogeneity, CO2 migrates preferentially through high permeability layers and dissolution efficiency increases with heterogeneity due to the stretching of the CO2 plume that enhances mixing. As a result, in this situation, the upscaling of permeability leads to an underestimation of the dissolution efficiency. A review of field sites shows that dissolution is heterogeneity-controlled in most real systems. Knowing that most numerical models cannot afford to represent heterogeneity at an adequate scale, results indicate that dissolution efficiency can be typically underestimated by a factor close to 1.5.
Pialassa Baiona is a shallow temperate coastal lagoon influenced by a variety of factors, including regional climate change and local anthropogenic disturbances. To better understand how these factors influenced modern organic carbon (OC) sources and accumulation, we measured OC as well as stable carbon isotopes (d13C) in 210Pb-dated sediments within a vegetated saltmarsh habitat and a human impacted habitat. Relative Sea Level (RSL) at the nearby tide gauge station data and four different Sea Surface Temperature (SST) data sets were analyzed starting from 1900 to assess the potential effect of sea ingression and warming on the coastal lagoon sedimentary process. The source contribution calculated from the MixSIAR Bayesian model revealed a mixed sedimentary organic matter (OM) composition dominated by increasing marine-derived OM after the 1950s, parallel with decreasing autochthonous saltmarsh vegetation (Juncus spp.) in the saltmarsh habitat and riverine-estuarine-derived OM in the impacted habitat. RSL rise in the area (8.7±0.5 mm yr−1 in the period 1900-2014) has been mainly driven by the land subsidence, especially during the central decades of the last century, enhancing the sea ingression in the lagoon. Annual SST anomalies present, starting from the eighties, a continuous warming tendency from 0.034±0.01 to 0.044±0.009°C yr-1. No direct effect on sedimentary properties was detected; however, RSL influenced OM sediment properties, although this effect was different between the two habitats.
The U.S. Geological Survey and Sonoma County Water Agency (SCWA) are engaged in a cooperative project to characterize the hydrogeology of southern Sonoma Valley, a groundwater basin in the northern California Coast Ranges where groundwater represents about 60% of the valley’s water supply. The basin lies near the Sonoma volcanic field and major transverse faults of the San Francisco Bay region, resulting in a complex aquifer system comprising volcanic and sedimentary rocks and unconsolidated sediments that are cut by faults and overlain to the south by recent Bay Muds of San Francisco Bay. Geologic sections were constructed using geologic maps and lithologic data from over 1,500 water wells compiled by SCWA to describe the subsurface geologic configuration relative to groundwater pumping wells. This work suggests an aquifer system extending to about 900 feet below land surface (ft bls), consisting of upper and lower aquifer units separated by an intermediate unit with lower hydraulic conductivity, overlying and partly interfingering with a complex suite of volcanic rocks. SCWA constructed a four-layer hydrostratigraphic model of the basin using spatial trends in the lithologic data. The hydrostratigraphic layers defined by SCWA include multiple mapped geologic formations because of heterogeneity and complex interfingering between stratigraphic units. Water from selected wells was analyzed for specific conductance, major and minor ions, nutrients, stable isotopes, carbon isotopes, and tritium. Well data were categorized by completed perforation interval into shallow wells (< 200 ft bls), mid-depth wells (200–500 ft bls), and deep wells (> 500 ft bls). Shallow wells typically have water types related to recent mountain-front recharge, and, near the tidal marshlands north of San Pablo Bay, have high chloride and total dissolved solid concentrations associated with modern saline-water intrusion. Mid-depth and deep wells have water with poor water-quality, likely influenced by connate water from consolidated marine sediments, or a mixture of water from consolidated sediments and thermal water. This cooperative basin characterization of subsurface geology, hydrostratigraphy, and water chemistry will enable SCWA to make strategic water management decisions in Sonoma Valley.
The Astromaterials Data System (AstroMat) is a NASA-funded project, working in close collaboration with the Johnson Space Center (JSC) to provide access to and preserve analytical data from JSC’s astromaterials collections. Meteorite data from close to 1000 peer-reviewed publications, primarily from the JSC Antarctic collections, and data from over 800 lunar publications have been ingested into AstroMat. Data can be explored at the level of reference and sample, or queried interactively through the AstroDB Search (AstroSearch). AstroSearch v 1.0 incorporated lunar and meteorite JSC collections, lunar missions, geofeatures, taxons, analyzed materials, and analysis methods searches. Working closely with domain scientists we have developed AstroSearch v 2.0. This version of the interface enhances the functionality of the original by adding search by chemistry (with comprehensive variable and unit selection), more granular analysis type refinement, and a streamlined customizable data output. The AstroDB Search is paired with the AstroDesk application, where users can login via their ORCiD and save an unlimited number of customized search queries. For researchers who need to submit, archive, and share their data with citable unique identifiers (DOIs) to comply with publisher and funding agency requirements, AstroMat offers a companion service to the AstroDB - the Astromaterials Data Repository (AstroRepo). Through its commitment to long-term data access and preservation, the Astromaterials Data Systems aims to help align cosmochemistry data with the Big-Data Era and reduce time to science for Planetary Sciences researchers by providing FAIR data for next generation scientific applications.
Nutrient pollution is considered one of America’s most widespread, costly, and challenging environmental problems. Artificial Floating Islands (AFIs), a phytoremediation technology, has been proven as an efficient, environmental-friendly, and cost-effective strategy to address this issue. However, most previous studies of AFIs were done in controlled conditions at mesocosm experiments. In addition, limited information exists on the use of AFIs as a nutrient remediation/prevention strategy in Ohio. This study aims to fill these gaps. We are currently undertaking a combination of mesocosm and natural experiment to assess the nutrient-removal efficiency of AFI systems in the Milliron Research Wetlands (at the Ohio State University Mansfield campus), and establish a performance baseline for two native aquatic plant species, Carex comosa and Eleocharis palustris. In this study, 18 AFIs, 6 planted with Carex comosa, 6 with Eleocharis palustris, and 6 have no plants, were deployed in a section of the Milliron Research Wetlands. Physical and chemical parameters are being monitored bi-weekly. The AFI systems are constructed using PVC pipes to provide buoyance, EVA foam mats as platforms, and nylon nets to cover the system. Each AFI unit has nine luffa sponges, inserted in the foam mat, to hold aquatic plant seedlings, keep the moisture of roots, and enlarge the surface area for bacterial biofilm development. Since nutrient removal from the wetland is affected by numerous natural processes, a mesocosm experiment was set up to assist the quantification of nutrient removal due specifically to the presence of AFIs. The mesocosm experiment mimics the natural experiment at the wetland and contain 12 equal-size tanks containing water pumped directly from the wetland, 3 of which have AFIs with Carex comosa, 3 have Eleocharis palustris, 3 have no plants, and 3 contain just water from the wetland. Physical and chemical measurements (as well as sample collections) are performed weekly in the tanks. Water in the tanks are exchanged bi-weekly. Preliminary results show that the AFI systems quickly developed large root systems and extensive bacterial biofilms. The effects of the associations between plant biomass, biofilm development, and changing chemical and physical conditions will be investigated as the experiment progresses.
Quantitative knowledge about the burial of sedimentary components at the seafloor has wide-ranging implications in ocean science, from global climate to continental weathering. The use of 230 Th-normalized fluxes reduces uncertainties that many prior studies faced by accounting for the effects of sediment redistribution by bottom currents and minimizing the impact of age model uncertainty. Here we employ a recently compiled global dataset of 230 Th-normalized fluxes with an updated database of seafloor surface sediment composition to derive global maps of the burial flux of calcium carbonate, biogenic opal, total organic carbon (TOC), non-biogenic material, iron, mercury, and excess barium (Baxs). The spatial patterns of burial of the major components are mainly consistent with prior work, but the new quantitative estimates allow evaluations of global deep-sea burial. Our integrated deep-sea burial fluxes are 136 Tg C/yr CaCO3, 153 Tg Si/yr opal, 20Tg C/yr TOC, 220 Mg Hg/yr, and 2.6 Tg Baxs/yr. Sedimentary Fe fluxes reflect a mixture of sources including lithogenic material, hydrothermal inputs and authigenic phases. The fluxes of some commonly used paleo-productivity proxies (TOC, biogenic opal, and Baxs) are not well-correlated geographically with satellite-based productivity estimates. Our new compilation of sedimentary fluxes provides more detailed information on burial fluxes, which should lead to improvements in the understanding of how preservation affects these paleoproxies.
Over the last century, runoff from farms and cities, along with land cover and land use changes, have drastically altered the mass balance of nutrients in aquatic systems, affecting both their ecological functioning and the living communities they support. Here we present the results of a multi-year, long-term study designed to assess the control of land-use and hydrology on nutrient fate and transport within a mixed land-use watershed in north-central Ohio. A total of 64 streams (with a mix of urban, cropland, pasture, and forest catchments) have been sampled periodically since the summer of 2008. Hydrological conditions during the study period exhibited marked seasonality, with usually dry winter seasons (average ppt: 23.5±7.4 cm) and wet spring seasons (average ppt: 34.5±8.1 cm). Runoff generation in response to precipitation events is faster in streams draining developed catchments and slowest in forested streams, where runoff is generated only by events > 10 mm/day. Hydrologic connectivity in the watershed appear to be limited, since only about 25% of precipitation inputs were translated into quick flow. There is a significant, positive correlation between runoff and nutrient concentrations (R2 values are: 0.40 for streams draining urban landscapes, 0.34 for forested streams, 0.30 for cropland, and 0.28 for pastureland). We also observed significant inter-annual and seasonal variations on both DIN (p = 0.02) and PO4 concentrations (p < 0.01). Compared to dry years, nutrient fluxes during wetter years are, on average, 16% higher in urban catchments and 47% higher in forested catchments, but 32% lower in pasture-dominated catchments. Baseflow is responsible for only between 20-30% of the annual nutrient export from the watershed.
Inland waters are recognized as a significant source of CO2 to the atmosphere; however, the global magnitude of this flux remains uncertain. In particular, CO2 concentrations and fluxes in stream systems are extremely variable at scales of 10’s to 100’s of meters, complicating monitoring and prediction efforts. Thus, models of pCO2 that capture these scales of spatial variability are necessary for the accurate prediction and monitoring of stream CO2 fluxes. Despite a strong conceptual framework for the hydrologic processes that control stream CO2, predictive models to date have been empirical, based on Strahler stream order and regressions between observed pCO2 and landscape variables. We hypothesize that models incorporating well-described hydrologic processes may lead to new insights into the magnitude of various CO2 sources and improve predictions. Here, we develop and apply a process-based stream network model of CO2 based on NHDplus flowlines and driven by groundwater inputs, hyporheic exchange, water-column metabolism, advective transport, and atmospheric exchange. Model output is compared with 151 measurements of pCO2 (424 - 9718 ppm) collected in August, 2019 across the upper East River watershed in Gothic, CO, a mountainous, high-elevation headwaters system within the Colorado River basin. We find that modeled pCO2 captures observed spatial patterns and predicts measured values with a RMSE of ~250 ppm and R2 of 0.47 (p<10-15). Additionally, our process-based model performs significantly better than a multiple linear regression model between observations and a geomorphic variables (r2=0.35, p<10-7). Estimates from an optimized stream network model give additional insight into CO2 sources, suggesting that groundwater accounts for 70-80% of evasion fluxes, hyporheic processes for 20-30%, and water-column metabolism for ~1% across the East River watershed. The ability of our model to predict pCO2 at the spatial scales of variability may provide an important next step in estimating global CO2 fluxes, and future research will test the predictive power of process-based models at regional and global scales.
Lava flows are one of the main hazards related to effusive basaltic volcanism. To minimize their impact during emplacement, we use lava flow potential distance-to-run predicted by propagation models. These models are partly based on infrared (IR) measurements of lava radiative heat fluxes by remote sensing (RS) methods (ground-based or satellite-based detectors) . These results are however subjected to important errors related to the poor knowledge of spectral emissivity (ε), commonly considered constant by these well-established techniques[2, 3]. This oversimplification is an important source of uncertainties in derived temperatures, which restrain our capacity to accurately model active lava flows. In this study, we developed new algorithms that take into account the effect of spectral emissivity for calculating radiative heat fluxes. We describe the temperature-emissivity relationship with equations established at two wavelengths of interest for RS (10.9 μm and 1.6 μm) that are retrieved from in situ measurements of spectral emissivity for basaltic magma from the 2014–2015 Holuhraun eruption. Spectral emissivity data were systematically acquired over a wide spectral range (400–8000 cm−1) covering TIR, MIR and SWIR, and up to 1473 K . Our results show that spectral emissivity varies linearly with temperature in TIR (10.9 μm), and nonlinearly in SWIR (1.6 μm). We confronted our lab-based results to the field IR data retrieved by  and found that temperature precision increases compared to data using constant emissivity value. These new insights will ultimately improve the thermo-rheological models of lava flows  in order to support hazard assessment in volcanic systems. References:  Kolzenburg et al. 2017. Bull. Volc. 79:45.  Harris, A. 2013: Cambridge University press. 728.  Rogic et al. 2019 Remote Sens., 11, 662  De Sousa Meneses et al. 2015. Infrared Physics & Technology 69.  Aufaristama et al. 2018, Remote Sens, 10,151.  Thompson and Ramsey, 2021, Bulletin of Volcanology, 83:41. Keywords: Spectral emissivity, temperature, IR spectroscopy, remote sensing, basalt
Evaporites and carbonates intercalated with volcanic beds are distributed in the Jialingjiang and Leikoupo Formations straddling the boundary of the Lower and Middle Triassic in the Sichuan Basin. High-resolution curves of 87Sr/86Sr ratios and δ34Ssulphate of marine sediments show the study section has relatively stable isotopic compositions of S and Sr except for the volcanic bed. The abrupt positive shift of 87Sr/86Sr ratios and negative shift of δ34Ssulphate occurred in the volcanic layer. The Sr isotopic curve defines a rough age range of 244 to 248 Ma. The volcanic bed is characterized by high anhydrite Th/U ratios, indicating a strong anoxic environment. The volcanic eruptions released a huge amount of CO2 and SO2, which could lower temperature first by sulphate aerosols and induce subsequent climate warming by greenhouse gases. This cooling-warming cycle has triggered the overturn of the deep anoxia seawater. The synergistic effects of degassing of gases (CO2 and SO2) and overturn of the deep anoxia seawater have caused the negative shifts of δ34Ssulphate, and anoxic event during the volcanic eruption. Meanwhile, volcanic eruptions and associated acid rain could have enhanced the continental weathering, resulting in an increasing flux of radiogenic 87Sr. Furthermore, volcanic eruptions and related environmental changes could have imposed severe stress on the full recovery of the ecosystem since the End-Permian mass extinction, which is corroborated by fossil records.
New Caledonia owns about 25% of the world’s nickel resources, and around 9% of the world’s reserves, distributed over 300,000 hectares of concessions allocated to date (18% of the total surface of the main island). Supergene weathering of ultramafic rocks have led to the genesis of lateritic nickel-rich ores of garnierite type (NiO> 1.5%) and / or iron oxi-hydroxide type (NiO <1.5%) under tropical lateritic conditions that have prevailed over 30 millions of years. These conditions have shaped the landscapes while offering Ni-rich regolith easy to exploit by open pit mining. Since 1880, nickel has been so far used as an economic driver and a societal development impetus. Since 1998, three worldwide projects have been developed, using pyrometallurgy (Ni-Si) and more recently hydrometallurgy (Ni-Fe) ore processes. However, natural erosion, anthropogenic disturbances (climate change, fires, urbanization, mining) can add up to disrupt the whole terrestrial and marine ecosystem functioning at the regional scale.This critical mined zone is covered by terrestrial ecosystems of great endemic biodiversity and adjoining a lagoon that has been listed as a UNESCO World Heritage Site in 2008. Such ecosystems are a valuable natural resource for the sustainable future for the next generations. Are mining and preserving ecosystems compatible, and for what economic and societal model? The conference reviews a collective research approach (mining, terrestrial and marine ecosystems impacts, restoration, biorecycling) to address this question. The corpus of acquired knowledge allows to propose an inclusive model of responsible mining activity, based on the “co-valorization” of both non-renewable and renewable primary resources through the development of circular economy and bio-economy principles, and applied all along the “mining ecosystem” project management. Considering i)the present day low GDP input of nickel mining in New Caledonia, the 98% dependency rate from fossil sources of energy, the CO2 emissions and the volatile Ni-market international context, this model, if followed, will reinforce the societal cohesion and develop a sustainable economy diversification, while enhancing energy transition and a better ecological efficiency.
Intensification of the Agulhas Leakage (AL) during glacial terminations has long been proposed as a necessary mechanism for reverting the Atlantic Meridional Overturning Circulation (AMOC) to its interglacial mode. However, lack of records showing the downstream evolution of AL signal and substantial temporal differences between AL intensification and resumption of deep‐water convection have cast doubt on the importance of this mechanism to the AMOC. Here, we analyze a combination of new and previously published data relating to Mg/Ca‐derived temperatures and ice volume‐corrected seawater δ18O records (δ18OIVC‐SW, as a proxy for relative changes in ocean salinity), which demonstrate propagation of AL signal via surface and thermocline waters to the western South Atlantic (Santos Basin) during Termination II and the early Last Interglacial. The saline AL waters were temporally stored in the upper subtropical South Atlantic until they were abruptly released in two stages into the North Atlantic via surface and thermocline waters at ca. 129 and 123 ka BP, respectively. Accounting for age model uncertainties, these two stages are coeval with the resumption of convection in the Labrador and Nordic seas during the Last Interglacial. We propose a mechanism whereby both active AL and a favorable ocean‐atmosphere configuration in the tropical Atlantic were required to allow flux of AL waters into the North Atlantic, where they then contributed to enhancing the AMOC during the Last Interglacial period. Our results provide a framework that connects AL strengthening to the AMOC intensifications that followed glaciations.