Impact of atmospheric circulation patterns on coastal dune dynamics, NW Spain

Dunes in temperate latitudes have experienced a significant stabilization in recent times, essentially as a consequence of the expansion of dense vegetation cover. Yet, the causes for this gradual stabilization as well as the causes promoting antecedent aeolian mobilization remain poorly understood. The Traba coastal dune field, located in NW Spain, was examined to explore the causes inducing aeolian activity and subsequent stabilization since 1940. Morphological changes were identified through the combination of aerial photographs and geophysical techniques. Local wind field regimes were simulated using a regional climate model to obtain the variability of the most relevant modes of atmospheric circulation in the North Atlantic and European regions; North Atlantic Oscillation (NAO), Eastern Atlantic (EA) and Scandinavian (SCAND). This allows us to identify the impact of these circulation modes over dune dynamics. Results document an episode of aeolian activity during the 1950s followed by a gradual stabilization and fixation of the dune coincident with a decrease on storm and wind intensity. Yet, aeolian sand movement remained active in small areas (blowouts), occurring mainly during the summer. NE winds associated with a negative phase of the EA explain the movement of sand within the dune field under favorable conditions of sand supply. On the other hand, sand supply to the dune field from the beach was promoted by NW winds coincident with the summer negative phase of NAO. During winter, the negative NAO favored frequent SW winds associated with the passage of intense storms, which in turn explain sand remobilization from the beach making sediment available for the NW winds to blow inland. With this work, it is proven that to understand past and future aeolian activity requires critical consideration of the variability and impact of the two principal modes of atmospheric circulation in the North Atlantic (NAO and EA). The SCAND mode explaining a lower percentage of the local wind field variability was also included to achieve higher significance levels of explained variance

8000 years of environmental evolution of barrier–lagoon systems emplaced in coastal embayments (NW Iberia)

The rocky and indented coast of NW Iberia is characterized by the presence of highly valuable and vulnerable, small and shallow barrier– lagoon systems structurally controlled. The case study was selected to analyse barrier–lagoon evolution based on detailed sedimentary architecture, chronology, geochemical and biological proxies. The main objective is to test the hypothesis of structural control and the significance at regional scale of any highenergy event recorded. This work is also aimed at identifying general patterns and conceptualizing the formation and evolution of this type of coastal systems. The results allowed us to establish a conceptual model of Holocene evolution that applies to rock-bounded barrier–lagoon systems. The initial stage (early Holocene) is characterized by freshwater peat sedimentation and ended by marine flooding. The timing of the marine flooding depends on the relation between the elevation of the basin and the relative mean sea-level position; the lower the topography, the earlier the marine inundation. Thus, the age of basin inundation ranged from 8 to 4 ka BP supporting significant structural differences. Once marine inundation occurred, all systems followed similar evolutionary patterns characterized by a phase of landward barrier migration and aeolian sedimentation towards the back-barrier (i.e. retrogradation) that extended circa 3.5 ka BP. The later phases of evolution are characterized by a general trend to the stabilization of the barriers and the infilling of the lagoons. This stabilization may be temporally interrupted by episodes of enhanced storminess or sediment scarcity. In this regard, washover deposits identified within the sedimentary architecture of the case study explored here suggest pervasive high-energy events coeval with some of the cooling events identified in the North Atlantic during the mid- to late Holocene

8000 years of environmental evolution of barrier–lagoon systems emplaced in coastal embayments (NW Iberia)

The rocky and indented coast of NW Iberia is characterized by the presence of highly valuable and vulnerable, small and shallow barrier– lagoon systems structurally controlled. The case study was selected to analyse barrier–lagoon evolution based on detailed sedimentary architecture, chronology, geochemical and biological proxies. The main objective is to test the hypothesis of structural control and the significance at regional scale of any highenergy event recorded. This work is also aimed at identifying general patterns and conceptualizing the formation and evolution of this type of coastal systems. The results allowed us to establish a conceptual model of Holocene evolution that applies to rock-bounded barrier–lagoon systems. The initial stage (early Holocene) is characterized by freshwater peat sedimentation and ended by marine flooding. The timing of the marine flooding depends on the relation between the elevation of the basin and the relative mean sea-level position; the lower the topography, the earlier the marine inundation. Thus, the age of basin inundation ranged from 8 to 4 ka BP supporting significant structural differences. Once marine inundation occurred, all systems followed similar evolutionary patterns characterized by a phase of landward barrier migration and aeolian sedimentation towards the back-barrier (i.e. retrogradation) that extended circa 3.5 ka BP. The later phases of evolution are characterized by a general trend to the stabilization of the barriers and the infilling of the lagoons. This stabilization may be temporally interrupted by episodes of enhanced storminess or sediment scarcity. In this regard, washover deposits identified within the sedimentary architecture of the case study explored here suggest pervasive high-energy events coeval with some of the cooling events identified in the North Atlantic during the mid- to late Holocene

Evolution of the southern dune sector of the Corrubedo complex

El estudio de las barreras arenosas costeras es fundamental porque éstas sirven de protección a otros ambientes con elevada importancia ecológica y productividad (marismas, lagunas costeras y estuarios). Sin embargo, estas barreras son ambientes altamente susceptibles a la erosión y se pueden ver afectadas por diferentes factores como cambios en el nivel del mar, oleaje, mareas, corrientes, disponibilidad de sedimento, pendiente y geomorfología del fondo marino, configuración de la línea de costa y la topografía heredada. En este trabajo se presenta una hipótesis de la evolución de la barrera costera de Corrubedo. Para el estudio de esta barrera costera se han utilizado diferentes metodologías, como el análisis de fotografías aéreas, georadar y sondeos. Por otra parte, se han datado distintos niveles mediante OSL y radiocarbono para reconstruir la historia sedimentaria. Se han reconocido un total de cuatro fases principales en el sector sur del complejo de Corrubedo. Estas fases se caracterizan por la alternancia de depósitos de grano fino y de grano grueso. Las dataciones de radiocarbono indican que la sedimentación comenzó con anterioridad a los 4500 años cal BP. En los registros de georadar se observan evidencias de la presencia del basamento a poca profundidad; lo que sugiere la influencia de la topografía heredada sobre la arquitectura resultante debido a: 1) reducción del espacio de acomodación y en consecuencia una reducción de la capacidad de almacenamiento y 2) la posición del basamento proporciona a la vez un substrato fijo que ancle la barrera y mantenga la línea de costa en una posición relativamente estable en el tiempoCoastal sand barriers are of high environmental significance because they provide protection for highly productive landward environments. However, they are also highly vulnerable environments as they can be affected by different factors such as sea-level changes, storm waves, tides, currents, sediment supply, seafloor slope and morphology, coastline development and inherited topography. The hypothesis for the evolution of the coastal barrier system of Corrubedo is presented in this study. The Corrubedo coastal barrier has been studied using a variety of methods, including geomorphologic analysis, GPR and coring for mapping sedimentary 3D architecture. Several samples have been dated using OSL and AMS radiocarbon methods to reconstruct the depositional history. Four major phases of sand barrier evolution have been recognized in the southern part of the Corrubedo complex. These phases are characterized by an alternation on the sedimentation between coarse and fine grained deposits. The radiocarbon ages indicate that sedimentation started sometime before 4500 years cal BP. Evidence of a shallow basement were detected in the GPR profiles in Corrubedo which suggests the influence of an antecedent topography on the resultant architecture by: 1) reducing the accommodation space and, therefore its storage capacity, and 2) providing a substratum for the anchoring of the barrier and maintaining a stable shorelin

Ocean and atmosphere teleconnections modulate east tropical Pacific productivity at late to middle Pleistocene terminations

The modern Eastern Equatorial Pacific (EEP) is a key oceanographic region for regulating the Earth's climate system, accounting for between 5–10% of global marine production whilst also representing a major source of carbon dioxide efflux to the atmosphere. Changes in ocean dynamics linked to the nutrient supply from the Southern Ocean have been suggested to have played a dominant role in regulating EEP productivity over glacial–interglacial timescales of the past 500 ka. Yet, the full extent of the climate and oceanic teleconnections and the mechanisms promoting the observed increase of productivity occurring at glacial terminations remain poorly understood. Here we present multi-proxy, micropaleontological, geochemical and sedimentological records from the easternmost EEP to infer changes in atmospheric patterns and oceanic processes potentially influencing regional primary productivity over glacial–interglacial cycles of the mid-late Pleistocene (∼0–650 ka). These proxy data support a leading role for the north–south migration of the Intertropical Convergence Zone (ITCZ) in shaping past productivity variability in the EEP. Productivity increases during glacial periods and notably peaks at major and “extra” glacial terminations (those occurring 1–2 precession cycles after some major terminations) coincident with the inferred southernmost position of the ITCZ. The comparison of our reconstructions with proxy records of climate variability suggests the intensification of related extratropical atmospheric and oceanic teleconnections during deglaciation events. These processes may have re-activated the supply of southern sourced nutrients to the EEP, potentially contributing to enhanced productivity in the EEP and thus counterbalancing the oceanic carbon dioxide outgassing at glacial terminations

The use of the Computerized Tomography (CT) as a sedimentary technique: application in oceanic cores from the Galicia Interior Basin (NW Iberian margin)

Las técnicas no destructivas de análisis de testigos están siendo muy empleadas debido a la cantidad y a la calidad de los datos que pueden ser obtenidos sin el requerimiento del uso de muestras, pudiendo estas estar disponibles para otro tipo de análisis. La Tomografía Computarizada (CT) es una técnica poco extendida en sedimentología. El uso del CT en el análisis de testigos es importante debido a la posibilidad de obtener parámetros físicos e imágenes de alta resolución de los testigos sin la necesidad de abrirlos y muestrearlos. En el presente estudio se muestran las imágenes tomográficas de los testigos recogidos en un transecto E-W a lo largo de la Cuenca Interior de Galicia, junto con los resultados obtenidos mediante análisis clásicos en los mismos testigos. El uso de estos datos junto con la descripción de las unidades sedimentarias identificadas y su composición elemental (obtenida con XRF core scanner) permiten una reconstrucción de la cuenca más detallada. Una de las aplicaciones de esta técnica es la identificación de algunas facies sedimentarias usando sólo la reconstrucción tomográfica, sin análisis clásicos previos de los testigos. Este hecho podría mejorar la calidad del tiempo de muestreo y la optimización de los recursoThe no-destructive techniques of core analyses are being more employed due to the quality and quantity of data that can be obtained without the requirement of the use of samples. These samples are then available to other kind of analyses. The Computerized Tomography (CT) is a technique few extended in sedimentology. The CT is relevant because it is possible to obtain physic parameters and high resolution images of the cores without the requirement of opening and sampling. In the present study the tomography images recorded across an E-W transect of the Galicia Interior Basin are showed, as well as the results of classical analyses from the same cores. The use of these data together with the description of the sedimentary units recognized and their elemental composition (obtained with XRF core scanner) allowed us a more detailed reconstruction of the basin. One of the applications of this technique is the identification of some sedimentary facies using only the tomography reconstruction, without the previous classical analyses of the cores. This fact could improve the quality of the sampling time and the optimization of the resource

Geoheritage as an educational resource and educational resources as heritage

El presente trabajo muestra una compilación de experiencias didácticas que emplean el patrimonio geológico como herramienta pedagógica en la enseñanza de las materias relacionadas con las Ciencias de la Tierra. El objetivo de todas ellas es acercar al alumnado al conocimiento y comprensión de los procesos que acontecen en nuestro planeta, con la finalidad de lograr un acercamiento y sensibilización hacia los mismos. Las seis propuestas seleccionadas presentan variedad en cuanto al contexto territorial de desarrollo de las actividades, a los contenidos y niveles trabajados (desde Enseñanza Secundaria hasta estudios universitarios) y a las metodologías utilizadas para la transmisión de dichos contenidos. Dentro de esta diversidad pueden distinguirse dos grupos de actividades diferentes. El primero de ellos se basa en el desarrollo de experiencias pedagógicas en localidades cuyas características geológicas resultan modélicas, únicas y/o espectaculares. Por el contrario, el segundo conjunto de actividades se centra en el trabajo de los recursos geológicos presentes en el entorno próximo del centro educativo. En ellas se explota su valor patrimonial, es decir, su potencial didáctico para abordar el estudio de la historia geológica del territorio. A través de las actividades incluidas en este compendio, se evidencia la validez de ambos tipos de aproximaciones y, al mismo tiempo, se debaten y realzan algunas de las virtudes más destacables de cada una de ellas. De esta manera, este catálogo podría resultar útil e inspirador para posibles planteamientos futuros.This manuscript presents a compilation of didactic experiences, which address the teaching of Earth Sciences through the knowledge of geological heritage. The aim of these proposals is to promote students’ comprehension of the Earth processes so that they may develop a positive attitude towards them. The six activities chosen offer a catalogue with a variety of sites, methodologies, contents and levels. Within this variety, the activities shown can be gathered into two separate groups. On the one hand, the first group collects experiences, which use geological heritage, i.e., the experiences are developed in places whose geological content is exemplary, unique and/or spectacular. On the other hand, the second group is focused on the geologic resources in the neighborhood of the school. These sites have heritage value, that is, an educational value for studying the geologic history of their territory. The activities drawn together show that both viewpoints are useful, and the benefits of each are pointed out. Consequently, this catalogue might be useful and inspiring for forthcoming attempts in this field