The dynamics of winter sea ice and icefoot play a fundamental role in structuring intertidal ecosystems in subarctic environments. However, ongoing climate warming is rapidly altering ice regimes across northern shorelines. In the St. Lawrence Marine Estuary (Canada), reduced formation of stable icefoot increasingly exposes benthic habitats to winter-related disturbances. We investigated how such disturbance influences eelgrass (Zostera marina L.) meadows and associated benthic communities over a winter season (2024-2025). We used a sampling design that explicitly compared areas with no change (Stable state), strong cover reduction (Abraded), and bare sediment (Reference), as identified from aerial survey imagery. Substantial losses in eelgrass cover (~20%) were observed, with Abraded areas showing reduced taxa richness but comparable biomass to Stable areas. Our results revealed that persistent small mussel aggregates, still attached to remnant eelgrass rhizomes in Abraded areas, played a key role in maintaining biomass and community structure. Mussels acted as secondary foundation species, formed biogenic habitat and partially compensated for eelgrass loss by maintaining refuges and colonization surfaces for associated fauna. These findings suggest that resistance to winter disturbance depends not only on the severity of habitat loss but also on the persistence of interacting foundation species and their capacity for functional replacement. Reduced coastal protection by icefoot increases intertidal exposure to physical and physiological stressors, progressively altering subarctic benthic assemblages and shifting communities toward alternative states, potentially closer to boreal conditions. Such changes warrant greater attention regarding their consequences for ecosystem functioning and the services they provide to humans.

Coastal hazards affect many Arctic communities by threatening the integrity of low-lying infrastructures, yet coastal flooding remains poorly constrained at high latitudes because local observations of waves and water levels are scarce. Here, we map coastal flood-prone areas in the community of Ausuittuq (Grise Fiord, Nunavut), Canada’s northernmost community located in Jones Sound, a semi-enclosed basin. The study uses a community-based approach that combines coastal topographic surveys, hydrodynamic observations, wave runup measurements, and historical hindcasts. A site-specific empirical wave runup equation is developed from beach slope and offshore wave conditions, and total water levels (TWL) are reconstructed from wave and water-level hindcasts (1979-2017). Extreme TWL events are identified from annual maxima, and flood scenarios are mapped for five return periods under present-day conditions and two 2100 relative sea-level scenarios adapted to the region. Results show that extreme TWLs in Ausuittuq are controlled primarily by tides and wave runup rather than storm surge, and that numerous infrastructures are exposed to coastal flooding under all scenarios. Under present-day conditions, the 10-year event floods 40,159m 2 of land, exposing multiple homes to flooding. Under the median RCP~8.5 scenario, projected relative sea-level fall due to postglacial isostatic uplift reduces flood extent, but does not eliminate hazard, whereas the enhanced RCP~8.5 scenario increases exposure, reaching 45,400m 2 of flooded area, 1282~m of affected road, and 15 exposed homes for the 10-year event. These results show that even in a fetch-limited High Arctic environment, wave runup can generate significant coastal flood exposure and should be integrated into community-scale hazard assessments.

This study is the first of a two-part paper that summarizes the development of a prototype coastal hazard prediction system providing short-term (+48 h) forecasts of the total water level (TWL) at 50 m resolution for the province of Quebec, Eastern Canada. In this first part, the implementation of the offshore wave model component of the system, which is a regional 1 km-resolution WAVEWATCH III™ (WW3) configuration for the Estuary and Gulf of St. Lawrence (EGSL), is presented and discussed. The configuration is forced by high resolution atmosphere, ocean and sea ice forecasts provided by Environment and Climate Change Canada (ECCC) and includes a state-of-the-art parameterization of wave propagation and attenuation in sea ice that has been tuned with observations from the EGSL. Performances are assessed against wave data collected over a 2-year period during which the forecasting system was running operationally, and against historical storm data using a model hindcast. Results demonstrate reasonable forecast skills both for normal and extreme wave conditions during ice-free periods with errors ranging from 15 % to 31 % of the mean wave height. However, when sea ice is present, performances are drastically reduced, primarily due to inaccuracies in the predicted ice fields at spatial scales over which wave energy typically dissipates in sea ice.

Reconstructing the dynamical retreat pattern of former ice margins is essential to better understand the long-term evolution of ice-sheets and their sensitivity to climate change. Here we present a geomorphological map of ice-marginal landforms from Anticosti Island together with 31 cosmogenic nuclide surface exposure and 24 radiocarbon ages, that suggest close ties between regional deglaciation patterns and climate. These results reveal that the Laurentide Ice Sheet stabilized on Anticosti Island between similar to 15.5 and similar to 14.4 ka, before subsequently resuming its retreat toward the Qu & eacute;bec North Shore and into the Gulf of St. Lawrence. Moraine ages highlight a strong sensitivity of the LIS to temperature changes in the Northern Hemisphere, as the documented ice-margin stabilizations coincide with the end of Heinrich Stadial 1, a period after the Last Glacial Maximum characterized by cold winters but warming summers. In turn, ice sheet recession in the area coincided with the onset of the B & oslash;lling-Aller & oslash;d (similar to 14.6 ka), marked by relatively warmer atmosphere temperature year-round across the Northern Hemisphere. These results provide evidence for the synchronicity of the ice margin along the southeastern Laurentide Ice Sheet in response to abrupt cold periods and allow further discussion of the regional implications for deglaciation of the Laurentian Channel in the context of a large calving bay formation in the former Gulf of St. Lawrence.

The ecosystem services and functions of seagrass meadows are indisputable, and knowledge about their coverage is critical for coastal managers worldwide. In this study, the surface area coverage of the foundation species Zostera marina L. (eelgrass) was investigated in four contrasting subregions of the Estuary and Gulf of St. Lawrence (EGSL), eastern Canada. The meadows in all subregions mainly occupy intertidal zones. Our analysis covered broad spatial (meters to kilometers) and temporal (annual to decadal) scales and revealed unprecedented insights at a local and regional context. We processed surface reflectance products of the Landsat archive through the Google Earth Engine cloud computing platform. The processing scheme only considered emerged areas of intertidal zones from imagery acquired at the lowest tide levels because of inherent limitations imposed by water clarity and the poor radiometric quality for water applications of the early Landsat sensors. The polygons classified as eelgrass encompassed at least 25 % coverage of eelgrass for each patch, and the classification scheme showed a very good agreement with coastal ecosystem habitats maps generated by photointerpretation and field validation for the period between 2015 and 2019, with an overall accuracy of approximately 94 %. From the 40year period analyzed (1984-2023), the meadows' surface area dramatically increased 10- (from approx. 0.3 to 2.5 km2) to 21-fold (from approx. 0.8 to 16.7 km2). The percentage of the intertidal area occupied by eelgrass meadows varied by subregion, ranging between 17 % and 82 %. In some subregions, meadows expanded landward. Some meadows experienced relatively shortterm losses (interannual scale) in three subregions, although these losses differed in their timing. We propose several hypotheses involving hydrodynamic, sedimentological, drift ice and climatic processes that could explain long- and short-term variability of the meadow coverage. However, this complex relationship remains to be investigated. Overall, while showing suitable habitats for eelgrass colonization, this study also revealed the EGSL tidal flats as potentially important areas of biodiversity, carbon storage, and coastal protection against erosion.

Decision-making in a coastal socio-ecological system involves managing a site-specific complexity arising not only from the interaction between hydrodynamic and morphological conditions, but also from the interactions between human structures and ecological systems, as well as the conflicting needs and interests of local actors. In addition, the projections of climate change impacts on coastal systems have a degree of uncertainty, which in-creases the general unpredictability of coastal dynamic behaviour, and adds a layer of complexity to the decision -making process. Scientific knowledge can help reduce some of the inherent uncertainties, and is essential when it comes to making sound decisions on the choice of appropriate coastal defence measures (CDMs) that are adapted to specific coastal environments and improve the resilience of coastal communities. This paper is based on a meta-analysis of 355 CDMs case studies drawn from 301 publications. From these published case studies, the objectives were to analyze the geographical and physical contexts in which CDMs monitoring was carried out and, based on the findings, to recommend areas of improvement necessary to help make sound decisions in any type of coastal environment. The meta-analysis showed that study sites are not evenly distributed around the world. Most originate from Europe (n = 106), the USA (n = 151) and Australia (n = 30), while few studies have been carried out in Africa and Asia where dense population resides in high-risk zones. Also noticeable is the absence of sites in high latitude climates where ice plays a major role in the erosion process. Five basic variables (coastal type, sediment type, wave characteristics, tidal range, and currents or sediment transport characteristics) are used in publications to characterize study sites according to their physical components. However, only 13 of the 355 sites included a complete characterization using the 5 variables, of which coastal and sediment types are the most frequently identified (77.2% and 72.7% respectively). In general, CDMs are studied in the context of unconsolidated low shore (59.4%) and in sandy environments (74.6%). Information on tidal range, wave climate, and currents, or sediment transport characteristics, is much scarcer. Since 1990, 3 of the 10 CDMs identified in the studies have received more attention than the others; these are beach nourishments, seawalls and break-waters, with respective cumulative study sites of 164, 67 and 50. The geomorphological effects of CDMs are the most studied (55.1%), followed by ecological (31.2%), hydrodynamic (9.1%), and social (4.6%). Overall, this meta-analysis helped identify knowledge gaps regarding geographical and physical contexts in which CDMs monitoring was held. It also gave an indication of the kind of improvement necessary for global-scale adaptation planning, and for a better decision-making process to reduce coastal risks in the most vulnerable coastal com-munities. Finally, the analysis shows that 4.4% of the studies on defence measures include monitoring of their effects on the coastal zone. A conceptual scheme is proposed for the evaluation of adaptation solutions based on the global monitoring of coastal zones to measure coastal change trajectories in the context of climate change.

Des images LiDAR à haute résolution dévoilent des modelés d’érosion glaciaire inédits qui nuancent fortement les interprétations publiées antérieurement concernant l’histoire glaciaire de l’île d’Anticosti. Sculptées dans le roc, ces formes d’érosion glaciaire sont très diversifiées : lacs de surcreusement glaciaire, drumlins rocheux, cannelures géantes, mégaqueues-de-rat, dalles de roc déplacées par les glaciers. Bien que pour la plupart discrètes, ces formes d’érosion glaciaire sont présentes partout sur l’île. Toutefois, c’est dans les basses terres de l’est et de l’ouest que l’empreinte glaciaire est la plus forte. Dans les basses terres de l’est, l’écoulement glaciaire vers le sud-ouest, observé partout sur l’île, a été suivi par un écoulement vers le sud-est. Ces 2 écoulements avaient leur source sur le Bouclier canadien (inlandsis laurentidien). Un écoulement tardif vers le nord a été observé dans la moitié nord du plateau central (au nord de la rivière Jupiter). Cet écoulement vers le nord est attribué à la calotte glaciaire régionale qui a occupé le plateau central durant la déglaciation.

As land use intensifies, many coastal waters are becoming enriched with otherwise limiting nutrients, leading to eutrophication. While the extreme effects of eutrophication on benthic communities are well documented, there is still a lack of knowledge about how nutrient enrichment alters biogeochemical interactions occurring at the sediment-water interface. Using ex-situ experiments, this study explores the consequences of nutrient enrichment on sediment characteristics, macrofauna community and benthic fluxes. The quantity of sedimentary organic matter and porewater concentration of NH4+, NOx and PO(4)(3-)increased in enriched treatments. These changes did not affect the macrobenthic community structure. However, macroinfauna buried less deep and increased their ventilation activity. As consequences, nutrient efflux increased, thereby favouring eutrophication processes. These effects were reduced in presence of seagrass, thus illustrating the buffering capacity of seagrass in the context of environmental changes, and particularly, of eutrophication. Overall, this study highlights that the functional consequences of nutrient enrichment involve interconnected processes that are variable in space and time.

ABSTRACTDeltas are at the transition between fluvial and marine sedimentary environments where sediment density flows are often triggered during high river discharge events, forming submarine channels and sediment waves. On wave‐influenced deltas, longshore currents are particularly efficient at transporting sediment alongshore, reducing the likelihood of sediment density flows from occurring at river mouths. This study describes four deltaic sedimentary systems at different stages of their evolution on a formerly glaciated continental inner shelf of eastern Canada in order to better understand the distribution of sediment density flows on wave‐influenced deltas. Three types of settings are recognized as being prone to sediment density flows: (i) in the early stages of wave‐influence and on large deltas, converging longshore currents can lead to offshelf sediment transport; (ii) on wave‐influenced to wave‐dominated deltas, a sandy spit can re‐route the river mouth and sediment density flows form where the spit intersects the delta lip; (iii) in advanced stages of wave‐dominated deltas and during their demise, rocky headlands are exposed and can intersect the slope, where off‐shelf sediment transport occurs. These types of sediment density flows were all characterized by debris flows or surge‐type turbidity currents which have limited offshore run‐out. More rarely, hyperpycnal flows form at the river mouths, especially where the river incises glaciomarine clays prone to landsliding in the river, which increases fine‐grained fluvial suspended sediment concentration. Overall, these results highlight the predominance of fluvial‐dominated deltas during a phase of relative sea‐level fall combined with high sediment supply. However, as soon as sediment supply diminishes, wave action remobilizes sediment alongshore modifying the distribution and types of sediment density flows occurring on wave‐influenced deltas.

Intertidal vegetation provides important ecological functions, such as food and shelter for wildlife and ecological services with increased coastline protection from erosion. In cold temperate and subarctic environments, the short growing season has a significant impact on the phenological response of the different vegetation types, which must be considered for their mapping using satellite remote sensing technologies. This study focuses on the effect of the phenology of vegetation in the intertidal ecosystems on remote sensing outputs. The studied sites were dominated by eelgrass (Zostera marina L.), saltmarsh cordgrass (Spartina alterniflora), creeping saltbush (Atriplex prostrata), macroalgae (Ascophyllum nodosum, and Fucus vesiculosus) attached to scattered boulders. In situ data were collected on ten occasions from May through October 2019 and included biophysical properties (e.g., leaf area index) and hyperspectral reflectance spectra (Rrs(λ)). The results indicate that even when substantial vegetation growth is observed, the variation in Rrs(λ) is not significant at the beginning of the growing season, limiting the spectral separability using multispectral imagery. The spectral separability between vegetation types was maximum at the beginning of the season (early June) when the vegetation had not reached its maximum growth. Seasonal time series of the normalized difference vegetation index (NDVI) values were derived from multispectral sensors (Sentinel-2 multispectral instrument (MSI) and PlanetScope) and were validated using in situ-derived NDVI. The results indicate that the phenology of intertidal vegetation can be monitored by satellite if the number of observations obtained at a low tide is sufficient, which helps to discriminate plant species and, therefore, the mapping of vegetation. The optimal period for vegetation mapping was September for the study area.

The decision-making process of the coastal defence measures (CDMs) is complex and filled with uncertainties due to site-specific interactions between hydrodynamic and geomorphological conditions, which have repercussions on the ecological and social aspects of coastal communities. Scientific knowledge of the effects of CDMs contributes to the reduction in inherent uncertainties and facilitates the decision-making and design processes. The goal of this article is to present an algorithm designed to evaluate and hierarchize CDMs in relation to different coastal environments. Drawn from 411 published scientific case studies, a total of 1709 authors’ observation statements regarding the effects of CDMs on the study sites’ environmental features (type of coast, type of substrate, tidal range, and wave climate) were entered in a database, categorized, and weighted according to a qualitative scale. The algorithm processes the information by establishing a correspondence between user-selected environment features and those stocked in the database, and it evaluates user-selected CDMs in relation to the specified coastal characteristics by identifying, collating, and rating the effects as observed in similar contexts. The result is a tool able to process, structure, and concretize scientific knowledge regarding CDMs and their effects on coastal systems. It is complementary to existing tools currently used in the decision-making and design processes of the CDMs. The results present the hierarchization of CDMs according to a multilevel aggregated structure, which can be used in different ways by coastal managers, decision-makers, and engineers. The algorithm, based on standardized coastal characteristics, can be applied to any shoreline worldwide.

Coastal socio-ecological systems are complex adaptive systems with nonlinear changing properties and multi-scale dynamics. They are influenced by unpredictable coastal hazards accentuated by the effects of climate change, and they can quickly be altered if critical thresholds are crossed. Additional pressures come from coastal activities and development, both of which attracting stakeholders with different perspectives and interests. While coastal defence measures (CDMs) have been implemented to mitigate coastal hazards for centuries, a lack of knowledge and tools available to make informed decision has led to coastal managers favouring the choice of seawalls or rock armours with little consideration for socio-ecological systems features, and stakeholders' priorities. Though it is not currently widely applied in coastal zone management, multicriteria decision analysis (MCDA) is a tool that can be useful to facilitate decision making. PROMETHEE, an outranking method, was chosen to support the multicriteria decision analysis for the evaluation of CDMs in the context of four study sites characterized by distinct environmental features. The aim was to determine the relevance and benefits of a MCDA by integrating coastal zone stakeholders in a participatory decision-making process in order to select CDMs that are better adapted to the whole socio-ecological system. First, in a series of five workshops, stakeholders were asked to identify and weigh criteria that were relevant to their local conditions. Second and third, CDMs were evaluated in relation to each criterion within the local context, then, hierarchized. Initial results show that vegetation came first in three of the four sites, while rock armour ranked first in the fourth site. A post-evaluation of the participatory process indicated that the weighting phase is an effective way to integrate local knowledge into the decision-making process, but the identification of criteria could be streamlined by the presentation of a predefined list from which participants could make a selection. This would ensure criteria that are standardized, and in a format that is compatible with the MCDA. Coupled with a participatory process MCDA proved to be a flexible methodology that can synthetize multiple aspects of the problem, and contribute in a meaningful way to the coastal engineering and management decision-making process.

This article focuses on the quantification of retreat rates, geomorphological processes, and hydroclimatic and environmental drivers responsible for the erosion of an unconsolidated fine-sediment cliff along the north shore of the Gulf of St. Lawrence (Quebec, Canada). Annual monitoring using field markers over a period of twenty years, coupled with photo interpretation and historical archive analysis, indicates an average annual erosion rate of 2.2 m per year between 1948 and 2017. An acceleration in retreat occurred during the last 70 years, leading to a maximum between 1997 and 2017 (3.4 m per year) and 2000–2020 (3.3 m per year). Daily observations based on six monitoring cameras installed along the cliff between 2008 and 2012 allowed the identification of mechanisms and geomorphological processes responsible for cliff retreat. Data analysis reveals seasonal activity peaks during winter and spring, which account for 75% of total erosional events. On an annual basis, cryogenic processes represent 68% of the erosion events observed and subaerial and hydrogeological processes account for 73%. Small-scale processes, such as gelifraction, solifluction, suffosion, debris collapse, and thermoabrasion, as well as mass movement events, such as slides and mudflows, induced rapid cliff retreat. Lithostratigraphy and cliff height exert an important control on erosion rates and retreat modes, which are described by three main drivers (hydrogeologic, cryogenic, and hydrodynamic processes). Critical conditions promoting high erosion rates include the absence of an ice-foot in winter, the absence of snow cover on the cliff face allowing unrestricted solar radiation, the repetition of winter warm spells, snow melting and sediment thawing, and high rainfall conditions (>30 mm or SPI > 2). The relationships between hydroclimatic forcing and retreat rates are difficult to establish without taking into account the quantification of the geomorphological processes involved. The absence of quantitative data on the relative contribution of geomorphological processes can constitute a major obstacle in modeling the retreat of cliffs with regard to climate change.

Les côtes de la Gaspésie, et plus globalement du Québec maritime, sont particulièrement exposées à l'érosion et la submersion côtières. En raison de l'importance historique du Saint-Laurent comme voie de navigation et de l'établissement des populations le long de son littoral, les enjeux relatifs au patrimoine (ressources archéologiques, bâti, monuments et lieux de mémoire) y sont particulièrement sensibles. L'étude présentée a comporté trois volets. Le premier a permis de dresser l'état d'une douzaine de sites archéologiques côtiers connus situés dans les zones à risque, tandis que le deuxième évaluait le potentiel archéologique de secteurs exposés aux aléas côtiers, où cinq nouveaux sites d'intérêt ont été identifiés. Le troisième volet s'intéressait au patrimoine bâti menacé par ces aléas : 39 bâtiments ou sites patrimoniaux menacés ont ainsi été répertoriés. Une revue des modes de gestion des ressources patrimoniales exposées aux aléas côtiers est proposée en conclusion.

Coastal ecosystems are recognized as important providers of ecosystem services such as carbon storage, increased fish productivity, and wave energy reduction. In a context of climate change, coastal ecosystems are exposed to erosion and subject to coastal squeeze, even as they provide natural coastal protection against extreme weather. While civil engineering solutions often take centre stage in mitigating coastal erosion and protecting infrastructure from storms and sea level rise, we seek to explore the social dimension of adaptive management of socio-ecological systems and more specifically the role of knowledge and learning. Using an ecosystem services (ES) framework, we provide a first evaluation of local stakeholders' perceptions of coastal habitats in maritime Quebec. The findings demonstrate the importance of a social approach for coastal ES valuation, in particular in addressing the complex question of cultural ES. A better understanding of the links between coastal stakeholders and their natural environment can help decision-makers and practitioners design conservation management and coastal adaptation measures mainstreaming the role of coastal habitats. Nevertheless, a change towards a socio-ecological perspective will require long-lasting processes that build on social capacities, such as flexible institutions and multilevel governance systems.

Shoreline armoring has repercussions on coastal processes, including reducing the width and height of sandy beaches, which affect coastal ecosystems and ecosystem services. This project, consisting of two parts, was carried out in the Canadian province of Quebec, on the coasts of the St. Lawrence Estuary and Gulf, which cover the territory of 21 coastal Regional County Municipalities (RCM). The objectives were to characterise shoreline armoring in Eastern Quebec, to determine the role played by coastal managers, coastal citizens, and coastal engineers in the coastal defence decision-making process, and to identify possible actions to be taken by each stakeholder to improve coastal engineering development. First, over 3300 km of shoreline were segmented and characterised, allowing the mapping of what proportion of the shoreline was covered by artificial structures. In 2017, coastal defence measures (CDM) occupied about 10% of the shoreline, and 97.6% of them were reflective rigid structures. The second part of the project involved three different consultations carried out in 2017 and 2018 with 300 coastal managers, 494 coastal residents and 51 professionals from environmental and engineering firms to assess their knowledge of CDM types and functions, and to discuss about the decision process leading to the CDM identification. Results of the consultations show a significant change in the type of desired solutions compared to previous studies where rigid structures were clearly preferred. But despite a greater prioritization of soft techniques by professionals from municipalities, ministries' managers and coastal citizens, the rigid structures continue to be the type of solution mostly implemented along Quebec's coasts. This difference can be explained by a number of factors: a lack of specialized knowledge; a lack of funding; a lack of collaborative process; and regulations that are too restrictive for innovative CDM. In addition to an increase of funding for preventive CDM, for long term CDM monitoring and maintenance, for case studies and pilot projects, the main solutions proposed were interdisciplinary projects based on consultation, adjustment of environmental regulations, and development of a tool that would enable decision-makers to evaluate each option in a particular context, so as to identify the most appropriate solutions and make better decisions for the long term.

Sea ice plays an important role in subpolar seagrass meadows. It protects meadows against wave action and extreme temperatures. On the other hand, sea ice destroys seagrass leaves and removes plots of sediments and organics debris, leaving long-lasting ice-made tidal pools of various shapes and sizes within the meadow. The present study aimed at investigating the effect of sea ice on benthic community structure and biogeochemical processes in a subpolar seagrass meadow. Vegetated areas (V), artificially-created (aTP), and natural (nTP) tidal pools were sampled from April to October 2018 in a seagrass meadow located at Manicouagan Peninsula (Québec; 49°5′36″N, 68°12′44″W). aTP and nTP showed similar sediment characteristics with coarser sediment and lower particulate organic carbon and total nitrogen content but also lower NOx and higher NH4+ and PO43− porewater concentrations as compared to V. Benthic macrofauna communities showed a strong seasonality with very reduced total density, biomass and species richness during wintertime (from December to April) relatively to summertime (from June to September). Benthic macrofauna communities were also more diversified and abundant in V than in aTP and nTP. Species assemblages in aTP and nTP represented a subset of species assemblages in V with any species found exclusively in tidal pools. However, total biomass was similar among treatments, suggesting that tidal pools sheltered larger individuals than vegetated areas. These results underline the importance of considering the spatial heterogeneity of seagrass meadows when assessing the functioning of these ecosystems.