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An analytical framework is proposed to explore the structure and kinematics of iso-scalar fields. It is based on a two-point statistical analysis of the phase indicator field which is used to track a given iso-scalar volume. The displacement speed of the iso-surface, i.e. the interface velocity relative to the fluid velocity, is explicitly accounted for, thereby generalizing previous two-point equations dedicated to the phase indicator in two-phase flows. Although this framework applies to many transported quantities, we here focus on passive scalar mixing. Particular attention is paid to the effect of Reynolds (the Taylor based Reynolds number is varied from 88 to 530) and Schmidt numbers (in the range 0.1 to 1), together with the influence of flow and scalar forcing. It is first found that diffusion in the iso-surface tangential direction is predominant, emphasizing the primordial influence of curvature on the displacement speed. Second, the appropriate normalizing scales for the two-point statistics at either large, intermediate and small scales are revealed and appear to be related to the radius of gyration, the surface density and the standard deviation of mean curvature, respectively. Third, the onset of an intermediate ‘scaling range’ for the two-point statistics of the phase indicator at sufficiently large Reynolds numbers is observed. The scaling exponent complies with a fractal dimension of 8/3. A scaling range is also observed for the transfer of iso-scalar fields in scale space whose exponent can be estimated by simple scaling arguments and a recent closure of the Corrsin equation. Fourth, the effects of Reynolds and Schmidt numbers together with flow or scalar forcing on the different terms of the two-point budget are highlighted.

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The eastern part of the Bay of Seine (English Channel) is highly impacted by harbour activities and the dumping of dredged sediment by the port authorities of Le Havre (GPMH) and Rouen (GPMR). Sediment dredged by the GPMH (2–2.5 millions of m3 per year) has been disposed at the subtidal Octeville site since 1947. Since the 2000s, mainly fine sediment (80% of fine particles <63 μm) has been disposed using alternate mosaic boxes with limited thickness (0.2 to 0.6 m per box per year), preventing the accumulation of disposed sediment in some parts of the dumping site. During the period August 2016 to September 2017, an experimental study was set up to identify the spatio-temporal changes of the macrobenthos collected at ten stations on six dates: three stations where different volumes of sediments were dumped (from 41,000 to 186,000 m3), two stations located within the Octeville site but without dumping operations during the study and five stations outside the disposal site (northern and southern zones). The Taxonomic Richness, total abundance and abundances of the polychaete Owenia fusiformis show negative correlations with the volumes of deposited sediment, whereas use of the AMBI (AZTI's Marine Biotic Index) and B2OA (Benthic Opportunist Annelids Amphipods) indices does not allow us to distinguish the impacted zone. Our study shows that the impact of dumping remains local and the benthic habitats display a high degree of resilience with rapid recovery of the community after the cessation of disturbance. Recommendations on the future long-term strategy are proposed to improve assessment and minimise the impact of dumping sediment on this benthic habitat.

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Groundwater level (GWL) fluctuations can be expressed over a wide range of timescales. In particular, as aquifers act as low-pass filters, low-frequency variability (from interannual to decadal timescales) originating from large-scale climate variability usually represents a significant part of GWL variance. This is typically the case of aquifers in the Seine River basin for which extreme GWL then appear largely dependent on such low-frequency fluctuations. In addition to expected trend behaviours (e.g., progressive increase in air temperature or evapotranspiration, increase or decrease of monthly or seasonal precipitation amounts, etc.), global climate change can also affect, and have maybe already affected, the internal variability as described by climate modes like for instance the El Nino Southern Oscillation (ENSO) or the North-Atlantic Oscillation (NAO), which explain more or less directly the low-frequency variability of hydrological processes including GWL. How GWL in a large hydrosystem may respond to such changes then remains an open question, and even appears as an important issue regarding extreme GWL. Would that lead to more or to less severe extremes, with more groundwater droughts or, on the contrary, more groundwater floodings? Would this be expressed in the same way for aquifers exhibiting different GWL behaviours in terms of low-frequency variance? To tackle this issue, we implemented an empirical numerical approach that would allow to assess the sensitivity of aquifers to changes in large-scale climate variability, using the whole Seine hydrosystem as a test case. The approach consisted in i) identifying and modifying the spectral content, originating from large-scale climate variability, of the precipitation field using signal processing techniques, ii) re-injecting this modified field as input to a physically-based hydrological/hydrogeological modeling tool (the CaWaQS software) for the Seine basin. We used the Safran precipitation field over the period 1970-2018, which was initially used for model calibration and validation. GWL dataset for the Seine basin is a subset of a database of climate-sensitive (i.e. with as low anthropogenic influence as possible) GWL time series recently set up at BRGM and University of Rouen Normandy. First, the Safran reanalysis and observed GWL time series were analyzed using continuous wavelet transform (CWT) to identify the relevant spectral content reflecting climate variability: interannual (2-4yr), multiannual (5-8yr) and decadal (~15yr) variabilities. Then, Safran precipitation time series were decomposed into time scale components, or so-called wavelet details, using maximum overlap discrete wavelet transform (MODWT). For each time series of the precipitation field, the amplitude of components corresponding to previously identified interannual, multiannual and decadal variabilities was modified individually, by either increasing or decreasing it by 50%; and then all components, including the one that was amplitude-modulated, were re-agregating. This eventually led to six scenarios of changing variability of precipitation. The corresponding modified precipitation fields were re-injected into CaWaQS model, which produced modified GWL time series. First results indicated that amplitude-modifications of low-frequency spectral content in precipitation field cause variance-modifications of these same time scales in GWL, which should affect extreme levels, and this will be investigated in the next few months.

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We explore the coastal morphology along an uplifting 500 km-long coastal segment of the Central Andes, between the cities of Chala (Peru) and Arica (Chile). We use accurate DEM and field surveys to extract sequences of uplifted shorelines along the study area. In addition, we consider continental pediment surfaces that limit both the geographical and vertical extent of the marine landforms. We establish a chronology based on published dates for marine landforms and pediment surfaces. We expand this corpus with new 10Be data on uplifted shore platforms. The last 12 Ma are marked by three periods of coastal stability or subsidence dated ~12-11 Ma, ~8-7 Ma and ~5-2.5 Ma ago. The uplift that accumulated between these stability periods has been ~1000 m since 11 Ma; its rate can reach 0.25 mm/a (m/ka). For the last period of uplift only, during the last 800 ka, the forearc uplift has been accurately recorded by the carving of numerous coastal sequences. Within these sequences, we correlated the marine terraces with the sea level highstands (interglacial stages and sub-stages) up to MIS 19 (790 ka), i.e., with a resolution of ~100 ka. The uplift rate for this last period of uplift increases westward from 0.18 mm/a at the Peru-Chile border to ~0.25 mm/a in the center of the study area. It further increases northwestward, up to 0.45 mm/a, due to the influence of the Nazca Ridge. In this study, we document an unusual forearc cyclic uplift with ~4 Ma-long cycles. This periodicity corresponds to the predictions made by Menant et al. (2020) based on numerical models, and could be related to episodic tectonic underplating (subducting slab stripping) beneath the coastal forearc area.

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The southern coast of Argentina is composed of many coarse-grained coastal barriers, which are mostly concentrated at the mouth of a few large rivers that drains the Andean mountains. As the Patagonian estuaries are characterized by tidal ranges that are among the largest in the world, coastal barriers are exposed to high amplitude tide-induced sea-level changes as well as strong tidal currents. In order to better understand the influence of tides in wave-built sedimentary bodies, an in-depth analysis of the architecture of barrier systems has been realized at the mouth of the Santa Cruz estuary (50°S). Maximum tidal range is 12 m in this estuary. A great variety of morphologies compose both sides of the estuary inlet, from simple spits and barrier spits to beach ridges. Barrier spit and beach ridges characterize the southern side, whereas elongated simple spits and spit barriers isolating large tidal flats are more developed on the northern side. As a consequence of this configuration the northern system is much wider than the southern one (6 km vs 1 km). The site was investigated using ground-penetrating radar (400 MHz GSSI antenna), along with the analysis of digital elevation models and some sedimentological observations. Cross-shore and long-shore profiles, with a penetration depth up to 4 meters, show a large range of radar facies attributed to erosional surfaces, beach face progradation, along-drift elongation, hooks and spit terminus development, and washover deposits. The analysis of the radar architecture allows reconstructing the development of individual morphology, and helps to differentiate the influence of wave- and tide-related processes. The most open-sea barrier spit systems show a classic development controlled by the wave-related littoral drift entering into the estuary (onshore directed), and enhanced due to shore parallel flood currents into the inlet. In contrast, in the innermost part of the northern side, spits and barrier spits feature contrasting morphologies, structures and directions of elongation, either landward or seaward, reflecting a complex combination between wave-, tide-and fluvial dynamics on their construction. One of the spits imaged with the GPR shows an intense reflection that has been associated with the top of the tidal flat on which the spit migrates (Fig. 1). The GPR lines highlight the control of underlying substrate on spit morphologies A same morphology is thus characterized by different architectures; in Figure 1B the prograding sequence follows a transgressive sequence, while in Figure 1C the transgressive sequence cannot be observed in the architecture due to the highest elevation of the tidal flat. In the southern side of the estuary, the barriers show extensive progradational sequences with different slopes that seem to depend on the spit morphology, and therefore on the exposure to ocean swells.

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Artificial reefs (ARs) have been deployed for different purposes: to protect marine areas, to increase production in artisanal fisheries, to restore degraded ecological functionality, and to offset the negative impact of development projects. The assessment of ARs is currently based preferentially on physical, chemical, and biological data, whereas the links between these ecological initiatives and social data are rarely taken into account. In this study, ARs were investigated using the actor–network theory (ANT), a holistic approach developed in the social sciences that considers that nonhuman as well as human actors play a role in systems and networks. The findings show that the socio-ecological objectives of ARs are deeply dependent on the interests of the stakeholders active in each phase of the project: project identification, planning, implementation, monitoring, and management. Their position and interests strongly influence how the project is performed, and the objectives of the ARs also evolve in line with the type of stakeholders involved. Based on the interest of each stakeholder, this ANT analysis reveals that French ARs, called production ARs, also have ecological and social support objectives, including reducing conflict between fishermen or increasing natural marine resources diversity and biomass. The translation process steps provide a framework to understand the interest of each stakeholder involved in the AR network and how management actions are deployed to reach their key objectives. This approach could be used as a first step in the assessment process to define clear objectives. It would provide managers a more integrated approach to assess the success of current and future marine environmental management tools.

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The current development of human activities at sea (e.g. land reclamation, maritime activity and marine renewable energy) is leading to a significant increase in the number of infrastructures installed in marine settings. These artificial structures provide new hard-bottom habitats for many marine organisms and can thus modify the structure and functioning of coastal ecosystems. In order to better evaluate the nature of these modifications as well as the potential benefits and/or impacts generated, it becomes essential to develop assessment methods that can be applied to a wide variety of study sites from harbours to coastal offshore environments. In this context, our study aims to review the different methods and indicators available which are used to measure the modifications of biodiversity and ecological functioning generated by such structures. Among the methods reviewed, we highlight some that were developed specifically for artificial structures, and others intended for various primary uses but which have been successfully transposed to artificial structures. Nevertheless, we also point out the lack of reliable methods concerning some biological ecosystem components impacted by artificial structures. In this context, we require the adaptation or creation of brand-new indicators to achieve a better characterisation of the ecological impacts generated by these structures. Overall, this study highlights a very high number of existing methods, which provide stakeholders with useful tools to study the impacts of artificial structures, and identifies the need to develop integrative indicators to enhance the deployment of new artificial structures.

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Abstract. The North Atlantic coast of Morocco has been affected historically by marine submersion events resulting from both storms and tsunamis and causing human and economic losses. The development of proactive adaptation strategies requires the study of these events over centennial to millennial timescales. Using a 2.7 m sediment core sampled from the Tahaddart estuary, we have been able to reconstruct past marine submersion events on this coastal area of Morocco over the last 4000 years. The high-resolution sedimentological and geochemical analysis conducted on this core allows us to identify 14 sediment layers attributed to marine high-energy events. The core was dated with isotopic techniques (137Cs, 210Pbex, 14C) and the outcomes reveal that three sediment layers are in connection with two major historical marine submersion events. The first layer mentioned as E1 seems to fit with the great Lisbon tsunami in 1755 CE (Common Era), an event dated for the first time on the Atlantic coast of Morocco. The other two layers referred as E13 and E14 were dated between 3464 and 2837 cal BP and correlated with marine submersion deposits found on Spanish and Moroccan coasts, which confirms the existence of a major high-energy event (around 3200 BP) similar to the one in 1755 CE.

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