Evolutionary trajectories of Coastal Sand Barriers along the West Portuguese Coast during the Holocene

Coastal sand barriers are dynamic features with complex depositional sequences holding critical information regarding system response to disturbances at secular to millennial time scales. Here, the evolutionary trajectories of three barriers located along the Portuguese coast are reconstructed over the Middle to Late Holocene using geophysical subsurface images, modern morphology and dating of dune and beach deposits. The integration of new and available information from the documents of the selected site contrasts histories with modern barriers displaying ages ranging from hundreds to thousands of years and non-linear trajectories defined by shifts between morphological states. Younger barriers appear to represent the latest progradational state within a history of landward barrier migration, where progradational states alternated with transgressive states. Conversely, the oldest barrier shows a single phase of barrier growth, despite some minor hiatus in progradation. Barrier state shifts appear to have simultaneously occurred across systems, suggesting external drivers of regional scale linked to Holocene climate variability, namely, periods of storminess activity, while the different trajectories displayed by the three sites appear related to site-specific variables controlling exposure to waves and winds. Exposed sites showed a lower ability to absorb disturbances and a greater range of system responses, varying between transgressive and progradational states.info:eu-repo/semantics/publishedVersio

Windiness spells in SW Europe since the last glacial maximum

Dunefields have a great potential to unravel past regimes of atmospheric circulation as they record direct traces of this component of the climate system. Along the Portuguese coast, transgressive dunefields represent relict features originated by intense and frequent westerly winds that largely contrast with present conditions, clearly dominated by weaker northwesterly winds. Optical dating and subsurface stratigraphy document three age clusters indicating main episodes of dune mobilization during: the last termination (20-11.6 ka), Middle Holocene (5.6 ka), and Late Holocene (1.2-0.98 and 0.4-0.15 ka).We find reconstructed windfields to be analogous during all episodes and dominated by strong westerlies. Yet, larger grain size diameters and dune volumes documented for the last termination support amplified patterns compatible with a southward shift and intensification of the North Atlantic westerlies during winters. Conversely, dunes deposited after the Middle Holocene are compatible with more variable windfields and weakened patterns controlled by interannual shifts towards low values of the North Atlantic Oscillation (NAO).This work demonstrates that present windfield regimes in southern Europe are not compatible with past aeolian activity. Indeed, present day analogs indicate that wind intensities compatible with past aeolian activity are rare at present (sediment transport potentials below estimates in the aeolian record), but can occur if the jet stream is diverted to the south (i.e. 30 degrees N with negative NAO index) or if very deep cyclones anchor around 50 degrees N, extending their influence to the western Portuguese coast (relatively low NAO index). However, these conditions represent temporary patterns lasting around one day, while we suggest that the identified episodes of aeolian activity may represent semi-permanent conditions. (C) 2016 Elsevier B.V. All rights reserved

Coupling nearshore and aeolian processes: XBeach and duna process-based models

A new dune profile model, Duna, is developed and coupled with the existing XBeach model, in which some key improvements allow a much better behaviour of the intertidal beach and the inclusion of structural erosion or accretion through a longshore transport gradient. The model is shown to represent typical behaviour of a beach-dune system in Praia de Faro, Portugal and to be able to simulate processes on a decadal timescale. The model captures a balance between longshore gradients and cross-shore processes in the surf zone, competing effects of moderate conditions and storms in the intertidal area and between build-up by storm waves and aeolian transport on the berm. Vegetation behaviour is shown to play a key role in the development of the shape of the foredunes. The relation between progradation or recession rate and foredune height as often reported in literature is reproduced and explained.FCT Investigator program [IF/01047/2014]Portuguese Science Foundation (FCT)Portuguese Foundation for Science and Technology [28949, UID/MAR/00350/2013]FEDER FundsEuropean Union (EU)info:eu-repo/semantics/publishedVersio

Surficial sediment texture database for the south-western Iberian Atlantic margin

Assessing the impact of changes on the environment driven by natural or anthropogenic forcers includes the comparison between antecedent and post-event conditions. The latter is particularly relevant in order to better understand to which extent those changes actually impact or alter a particular environment and associated services and to determine the resilience of a system. In this regard, it becomes essential to create or provide databases to inform about baseline conditions. Here, we present a database that integrates surficial sediment samples collected and analysed for textural characterization within the framework of a series of research projects over circa 20 years. Collected samples along the south-western Atlantic margin of the Iberian Peninsula extend from estuaries and beaches to the adjacent continental shelf. For the case of the more dynamic environments, namely coastal sandy barriers, samples were repeated over time in order to capture the intrinsic variability of the system. Examples of the utility of this data set for a variety of purposes and environments are also included within this paper through three examples. Therefore, here we show the added value of the database as it can be used to assess the impact of a particular event or activity at an estuary by providing baseline conditions, evaluate the continental shelf sediment suitability for nourishment activities, or contribute to the understanding of the morphodynamics and classification of beaches. Finally, it is worth stating the importance of such databases to analyse medium- to long-term variability as the one induced by sea level rise, changes in storminess, or human activities.FCT Investigator programme [IF/01047/2014]info:eu-repo/semantics/publishedVersio

Simulating destructive and constructive morphodynamic processes in steep beaches

Short-term beach morphodynamics are typically modelled solely through storm-induced erosion, disregarding post-storm recovery. Yet, the full cycle of beach profile response is critical to simulating and understanding morphodynamics over longer temporal scales. The XBeach model is calibrated using topographic profiles from a reflective beach (Faro Beach, in S. Portugal) during and after the incidence of a fierce storm (Emma) that impacted the area in early 2018. Recovery in all three profiles showed rapid steepening of the beachface and significant recovery of eroded volumes (68–92%) within 45 days after the storm, while berm heights reached 4.5–5 m. Two calibration parameters were used (facua and bermslope), considering two sets of values, one for erosive (Hm0 ≥ 3 m) and one for accretive (Hm0 < 3 m) conditions. A correction of the runup height underestimation by the model in surfbeat mode was necessary to reproduce the measured berm elevation and morphology during recovery. Simulated profiles effectively capture storm erosion, but also berm growth and gradual recovery of the profiles, showing good skill in all three profiles and recovery phases. These experiments will be the basis to formulate event-scale simulations using schematized wave forcing that will allow to calibrate the model for longer-term changes.This research was funded by FCT (Fundação para a Ciência e a Tecnologia), Portugal, in the framework of the ENLACE project, grant number PTDC/CTA-GFI/28949/2017info:eu-repo/semantics/publishedVersio

Effectiveness assessment of risk reduction measures at coastal areas using a decision support system: Findings from Emma storm

Storms impact coastal areas often causing damages and losses at occupied areas. On a scenario of increasing human occupation at coastal zones and under climate change conditions (including sea level rise and increasing frequency of extreme sea levels), the consequences of storms arc expected to be amplified if no adaptation or further management actions are implemented. The selection of the best possible coastal management measures, considering both costs and effectiveness, will be mandatory in the future, in order to optimise resources. This work analyses the performance of risk reduction measures (beach nourishment and receptors - house and infrastructures - removal), using a decision support system comprised by a morphodynamic numerical model (XBeach) and a Bayesian network based on the source-pathway-receptor concept. The effectiveness of the risk reduction measures is then assessed by a simple index expressing the consequences to the receptors. The approach was tested at Faro Beach by evaluating its performance for a particular storm, Emma (Feb/March 2018), which fiercely impacted the southern coast of Portugal. The output results from the modelling were compared to field observations of the actual damages caused by the storm. The combined use of both measures or the solely use of the nourishment would avoid almost all observed impacts from this storm. The work is pioneer on demonstrating the use of a decision support system for coastal regions validated against observed impacts for a high-energy storm event. The methodology and the proposed index arc adaptable to any sandy coastal region and can be used to test (and improve) management options at a broad number of coastal areas worldwide, minimizing implementation costs and reducing the risk to the occupation and to the people. (C) 2018 Elsevier B.V. All rights reserved.FCT Investigator program [IF/01047/2014]European Union 7th Framework ProgrammeEuropean Union (EU) [603458]project EVREST [PTDC/MAR-EST/1031/2014]project EW-COAST [G-LISBOA-01-145-FEDER-028657]Portuguese Science and Technology Foundation (FCT)Portuguese Foundation for Science and Technology [UID/MAR/00350/2013]research group RNM-328 of the Andalusian Research Plan (PAI)info:eu-repo/semantics/publishedVersio

A new index to assess the state of dune vegetation derived from true colour images

Vegetation on coastal dunes is a key element, as it promotes the growth and stabilization of these landforms while contributing significantly to biodiversity. Physical (e.g. impact of storms), ecological (e.g. animal grazing) and human-related (e.g. farming and recreation) factors may disturb coastal dune vegetation, changing dune dynamics and eventually inducing ecogeomorphic state shifts. Therefore, understanding vegetation dynamics and state turns crucial to predict dune evolution paths. The latter must be supported by observations combined with the development of tools (e.g. indexes) able to detect eventual changes and to automatically categorize the state of the vegetation. Here, a multi-step index to characterise the dune vegetation state (DUVES) was developed and tested in Barreta Island (South Portugal), where grey dune vegetation has declined in recent years. The index was computed using classified true colour orthophotos and orthomosaics derived from UAS (Unmanned Aerial Systems) surveys. Google Earth images were used as complementary data to analyse the evolution trends. The possible sources of disturbance (i.e. human-related activities and gull occupation) were also investigated by comparing their distribution with the vegetation changes. DUVES successfully identified different states of vegetation cover that expressed its stability, perturbation or growth based on temporal changes and allowed the analysis of their evolutionary trends. The distribution of perturbation was mostly associated with gull nesting areas, increasing over time, and to a less extent to human-related activities. The observed grey dune habitat loss was due to replacement of plants typical from this habitat by ruderal species promoted by the positive feedback established between gulls and vegetation. The developed index proved to be of great utility to define dune habitat evolution and understand the associated drivers, being a tool with a wide range of applications, namely for improving future coastal management actions aimed at conserving dune habitats. Moreover, DUVES is potentially transferable due to its easy adaptability depending on the particularities of each study site or goal.info:eu-repo/semantics/publishedVersio

Spanish Pelagic Redfish (Sebastes mentella) Fishery in the NAFO Regulatory Area (Division 1F) in 2000

In early October 2000 an exploratory fishing for oceanic redfish have been conducted by one Spanish pelagic trawler in the NAFO Regulatory Area of Div. 1F. One scientific observer was on board this vessel during the whole fishing period. The seasonal and geographic distribution pattern of the fishing effort in the Spanish oceanic redfish fishery is presented. A shift in the fleet activity towards the south and west is observed between the second and third quarter, approaching the vicinity of the NAFO Convention area. In the fourth quarter no fishing activity occurred in the Irminger Sea, and the fleet activity concentrated in NAFO Div. 1F. The length distribution in NAFO Div. 1F is similar to the one recorded in the NEAFC oceanic redfish fishery by the Spanish and German fleets in the upper 500 m layer. Only 11 % of the females and 5 % of the redfish males caught in NAFO 1F were immature (juveniles). The majority of the adult females were sexually inactive, while 49 % of the adult males were at the fully ripe stage, so it could be a mating concentration

Process-based indicators to assess storm induced coastal hazards

Storms are responsible for several hazards (e.g. overwash, erosion, inundation) in coastal areas, leading to the destruction of property and loss of life in populated areas. Various indicators are used to express potential storm impact and describe the associated hazards. The most commonly used indicators include either forcing parameters (e.g. wave height, sea level) or coastal morphologies (e.g. dune height or berm width). Whereas they do not represent the processes associated with storm induced hazards in coastal areas. Alternatively, a hazard could be better characterised if process-based indicators are used instead. Process-based indicators express the result of the forcing mechanisms acting over the coastal morphology and reflect both hydrodynamic and morphological characteristics. This work discusses and synthesizes the most relevant process-based indicators for sandy shores subject to overwash, erosion and inundation promoted by storms. Those include: overwash depth, potential and extent; shoreline, berm or dune retreat; vertical erosion; and inundation depth and extent. The selection of a reduced set of process-based indicators to identify coastal hazards induced by storms in sandy coasts will facilitate comparison of different coastal behaviours for distinct storm return periods, and help to optimise coastal management plans, thereby contributing to the reduction of coastal risks.info:eu-repo/semantics/publishedVersio

Large-scale transgressive coastal dune behaviour in Europe during the Little Ice Age

The Little Ice Age is the most noted climatological event in recent history with dramatic consequences for a large part of the western European coastal landscape. A major morphological feature associated with this event is the presence of large-scale transgressive dune fields that actively advanced inland, encroaching, in some cases, human settlements and directly affecting coastal communities. Several hypotheses exist to explain the formation of such features, which purport increased storminess, sea-level changes, or human activities as the major drivers of the relatively well-documented enhanced aeolian activity during this event. However, these hypotheses do not explain entirely the whole process by which dunes are set into movement. Here, we show the temporal and spatial distribution of this event in terms of impact over the coast, focusing on the mobilization of coastal dunes and then elaborate a new conceptual model that explains the onset and evolution pathways of coastal dunes after the impact of the Little Ice Age. Our model proposes the combined effect of storms and other parameters to explain the initiation phases of the process, when sand becomes available and blown by the very strong winds associated with documented higher frequency and intensity of storms occurring during this period.Natural Environment Research Council NE/F019483/1 NERC Geophysical Equipment Facility 1082 "FCT Investigator" program IF/01047/2014info:eu-repo/semantics/publishedVersioninfo:eu-repo/semantics/publishedVersio