Ultra-high resolution environmental and climatic reconstruction using oxygen and carbon isotopes of diatom frustules

[eng] Calcareous microfossils are not always present in marine or lacustrine sediments owing to unfavourable ecological or post-depositional conditions. These non-carbonated sediments sometimes contain abundant biogenic silica, rendering them suitable for studies of stable isotopes. For this reason, considerable progress has been made in the study of biogenic silica using isotopes in recent years. Diatom isotopes are increasingly being used for palaeoenvironmental reconstructions in lacustrine sedimentary records. Tropical proxy records offer valuable insights into past climate and environmental changes of the Earth and into possible future climate change scenarios. Research into tropical regions has therefore become a key issue among palaeoclimatologists. Influenced by the tropical circulation in the north, and by the mid-latitude westerlies in the south, the Central Andes are an ideal site to study past variations of atmospheric circulation systems. Thus, the Andean Altiplano has become a key region for the study of late Quaternary climate change in South America. Sedimentary records of high-altitude Andean Altiplano lakes usually preserve an excellent centennial- to millennial-scale record of effective moisture fluctuations and source changes during the Late Glacial and Holocene despite the fact that the interpretation is not always straightforward. Oxygen and carbon isotope analyses in carbonates (δ18Ocarbonate and δ13Ccarbonate) and δ13Cbulk have been successfully used to reconstruct the hydrological responses to climate change in different Andean lacustrine systems to date. No attempt, however, has been made to use δ18Odiatom and δ13Cdiatom despite the fact that they are usually the best preserved fossils in the sedimentary record of the Andean Altiplano lakes. For this reason, the aims of the PhD Thesis are twofold: a) to explore the possibilities that the study of δ18Odiatom and δ13Cdiatom can offer in palaeoenvironmental reconstructions, and b) to carry out high- and ultra-high resolution environmental and climate reconstructions in the Andean Altiplano during the Late Glacial- Early Holocene transition using these stable isotopes. The thesis focuses on new and poorly documented fields where δ18Odiatom and δ13Cdiatom can successfully be applied to lacustrine sediments. It shows how stable isotopes from diatom silica may be used a) to highlight the importance of reconstructing the different evolutionary stages of lake ontogeny given that climate derived palaeohydrological signals can be distorted by changes in lake morphology b) as a main proxy in ultra-high resolution moisture balance reconstructions forced by fluctuations in the intensity of the ENSO and solar activities c) to reveal the major biogeochemical processes that give rise to the formation of rhythmites, and finally d) to reconstruct the regional environmental evolution at centennial-to-millenial time scales.[spa] La tesis está basada en la reconstrucción ambiental y climática a muy alta resolución mediante los sedimentos laminados y ricos en diatomeas de un lago tropical situado en los Andes Centrales. Para la reconstrucción se ha utilizado la novedosa técnica del análisis de isótopos estables (δ18Odiat y δ13Cdiat) de la sílice de las diatomeas. Los principales resultados y conclusiones son: Diversos factores ambientales pueden influir en los valores de δ18Odiat. Los registros de δ18Odiat en sistemas lacustres cerrados no pueden ser simplemente interpretados en términos de seco o húmedo, sino que es imperativo entender la hidrología y geomorfología de cada sistema antes de hacer una interpretación de tipo estrictamente climático como se había hecho hasta la fecha. Por su parte, los análisis de δ13Cdiat han demostrado que esta técnica es una herramienta válida para realizar reconstrucciones del ciclo del carbono en los lagos, así como para dar un mejor punto de vista del ciclo del carbono a nivel global. La unidad sedimentaria laminada del Lago Chungará está formada por ritmitas multianuales compuestas por láminas de color blanco y verde. Estás láminas son ricas en diatomeas y son el resultado de diferentes procesos lacustres. Las láminas de claras se formaron como consecuencia de «blooms» extraordinarios de muy corta duración (días o semanas). Las láminas oscuras se depositaron a lo largo de diversos años bajo diferentes condiciones de la columna de agua y por tanto representan las condiciones de base del lago. Los valores de δ18Odiat muestran que los «blooms» extraordinarios fueron más intensos con condiciones de bajo nivel del lago, mientras que la formación de láminas oscuras se vio especialmente inducida por subidas del nivel. Al mismo tiempo, los valores de δ13Cdiat indican que la disponibilidad de carbono fue superior durante los «blooms» extraordinarios de diatomeas. La combinación de los dos registros ha destacado les complejas relaciones entre los procesos limnológicos, los procesos de la cuenca de drenaje, la hidrología y los forzamientos climáticos. El registro de isotopía expone claramente que, según la escala temporal, un tipo de proceso puede dominar sobre los otros en la interpretación de la isotopía

Reconciling North Atlantic climate modes: revised monthly indices for the East Atlantic and the Scandinavian patterns beyond the 20th century

Climate variability in the North Atlantic sector is commonly ascribed to the North Atlantic Oscillation. However, recent studies have shown that taking into account the second and third mode of variability (namely the East Atlantic – EA – and the Scandinavian – SCA – patterns) greatly improves our understanding of their controlling mechanisms, as well as their impact on climate. The most commonly used EA and SCA indices span the period from 1950 to present, which is too short, for example, to calibrate palaeoclimate records or assess their variability over multi-decadal scales. To tackle this, here, we create new EOF-based (empirical orthogonal function) monthly EA and SCA indices covering the period from 1851 to present, and compare them with their equivalent instrumental indices. We also review and discuss the value of these new records and provide insights into the reasons why different sources of data may give slightly different time series. Furthermore, we demonstrate that using these patterns to explain climate variability beyond the winter season needs to be done carefully due to their non-stationary behaviour. The datasets are available at 10.1594/PANGAEA.892769

ESTADÍSTICAS DE DEMANDA TURÍSTICA EN LA REGIÓN DE MURCIA

     The survey confirms an evident statistic deficit concerning the tourist demand in the Region of Murcia. However, Regional Tourist law envisages the fulfiment of a Regional Statistic Plan not yet designed, but which will have to be used in order to improve this situation. The present situation stems from the lack of an statistic regional service in the State Tourism Office. The reason for this lack is probably the scanty budget of this organization. Not only the official institutions but also the business companies lack enough information about the matter in question, although some important surveys are worth standing out because of their accurancy, but they have a problem related to their lack of contituity in the time. Next, we deal thoroughly with the statistic system on tourism which have been introduced by the European Community, the Spanish Government and some Autonomous Communities, such as Andalucia & Galicia.     El estudio constata un evidente déficit estadístico en materia de demanda turística en la Región de Murcia. No obstante, la Ley Regional de Turismo prevé la realización de un Plan Regional de Estadísticas que debe aprovecharse para corregir esta situación. La situación actual deriva de la ausencia de un servicio regional de Estadísticas en la propia Dirección General de Turismo cuya causa parece ser el exiguo presupuesto de este organismo. No sólo los organismos oficiales sino también asociaciones empresariales carecen de información suficiente sobre la materia, aunque son de destacar importantes estudios, elaborados con rigor pero que presentan el problema de su falta de continuidad en el tiempo. Se estudian a continuación los sistemas estadísticos sobre turismo que se han implantado por la UE, el Estado español y algunas Comunidades Autónomas, como Andalucía y Galicia, concluyendo en la conveniencia de adoptar la metodología andaluza (ECTA, IEA), debidamente depurada y adaptada a las necesidades regionales

Influencia de la adición de taninos enológicos en el color del vino

Los taninos son importantes componentes de la calidad del vino, ya que contribuyen tanto a la percepción en boca como a la estabilización del color con el tiempo. A su vez, el color es sin lugar a dudas uno de los aspectos organolépticos más importantes de un vino. Es por ello que la adición de taninos enológicos para mejorar las características de los vinos tintos es una práctica muy extendida en bodegas durante la elaboración de vinos tintos. Sin embargo, son muy pocos los estudios realizados en este campo y así mismo existe controversia en las opiniones de diferentes autores en cuanto a si esta adición es efectiva o no. El objetivo de este proyecto es determinar la influencia de la adición de taninos enológicos de Quebracho y de uva en el color del vino tinto. Para ello se elaboraron vinos a partir de uvas de las variedades tempranillo y garnacha procedentes de la D.O. Rioja. De cada vino se prepararon dos controles, dos muestras con tanino de Quebracho añadido en la fase pre-fermentativa y dos muestras con tanino de Quebracho y tanino de uva añadidos en la fase pre-fermentativa y post-fermentativa respectivamente. Se realizaron análisis de color y de compuestos fenólicos: intensidad de color, índice de polifenoles totales y concentración de taninos y antocianos totales en distintas etapas de la vinificación: al finalizar la fermentación alcohólica, al finalizar la fermentación maloláctica y tras la adición de SO2. Los datos fueron estudiados mediante análisis de varianza (ANOVA). Los resultados indican que la adición combinada de tanino de Quebracho y tanino de uva afecta positivamente a la intensidad del color. No obstante la adición única de tanino de Quebracho en las cantidades recomendadas por el fabricante no contribuye a la mejora de la intensidad de color. Esto sugiere que adición de taninos enológicos puede estar en muchos casos injustificada

Dinámica de los sistemas dunares costeros ante el Cambio Global: La necesidad de una gestión sostenible

El desarrollo y evolución de los sistemas arenosos costeros está gobernado por un frágil equilibrio dinámico entre la interacción de múltiples factores ambientales, y por ello estos sistemas naturales son altamente sensibles a las perturbaciones humanas. Estas alteraciones se acentúan en el contexto actual de Cambio Global. Los cambios en los vientos, en el oleaje, en la intensidad de las tormentas, en la disponibilidad de arena y en la vegetación juegan un papel crucial en el complejo desarrollo de las dunas, tanto por retener la arena que forma las dunas, como para protegerlas físicamente de la erosión. Actualmente, muchos de los ecosistemas dunares se encuentran degradados sobre todo por el déficit de aportes sedimentarios y la presión sobre la cubierta vegetal, fenómenos siempre muy relacionados con el impacto antrópico. El desarrollo natural de los sistemas dunares, incluida su vegetación, contribuye de forma significativa a amortiguar los efectos destructivos de los eventos climáticos extremos, incrementados durante el actual periodo de Cambio Global. Así, las dunas costeras suponen un patrimonio natural muy valioso que debe ser conservado. Aquí presentamos un trabajo de revisión sobre el estado del arte y una síntesis de factores y procesos de cara a un nuevo enfoque en la gestión costera. Al mismo tiempo, en este artículo se defiende una gestión que no interrumpa los procesos geomorfológicos que intervienen en el desarrollo natural del ecosistema dunar, y que son el soporte principal de su biodiversidad. Se demuestra que, a medio y largo plazo, una gestión respetuosa con la dinámica geológica dunar favorece tanto el mantenimiento de la biodiversidad como la conservación del paisaje costero y sus servicios ecosistémicos

Climatic and lacustrine morphometric controls of diatom paleoproductivity in a tropical Andean lake

15 páginas, 6 figuras, 1 tablaThe coupling of lake dynamics with catchment biogeochemistry is considered the key element controlling primary production in mountain lakes at time scales of a few decades to millennia, yet little is known on the impacts of the morphometry of lakes throughout their ontogeny. As Lake Chungará (Central Andean Altiplano, northern Chile) experienced long-term lake-level fluctuations that strongly modified its area:volume ratio, it is an ideal system for exploring the relative roles that long-term climatic shifts and lake morphometry play on biosiliceous lacustrine productivity. In this paper, we review previous data on the percent contents of total organic carbon, total inorganic carbon, total nitrogen, total biogenic silica, isotopic composition of organic matter, carbonates, and diatom frustules, as well as data on the abundance of the chlorophycean Botryococcus braunii in this lake for the period 12,400–1300 cal yr BP. We also include new data on organic carbon and biogenic silica mass accumulation rates and the diatom assemblage composition of an offshore core dated using 14C and U/Th. Biosiliceous productivity in Lake Chungará was influenced by shifts in allochthonous nutrient inputs related to variability in precipitation. Humid phases dated at approx. 12,400 to 10,000 and 9600 to 7400 cal yr BP coincide with periods of elevated productivity, whereas decreases in productivity were recorded during arid phases dated at approx. 10,000 to 9600 and 7400 to 3550 cal yr BP (Andean mid-Holocene Aridity Period). However, morphometry-related in–lake controls led to a lack of a linear response of productivity to precipitation variability. During the late Glacial to early Holocene, lowstands facilitated complete water column mixing, prompting episodic massive blooms of a large centric diatom, Cyclostephanos cf. andinus. Thus, moderate productivity could be maintained, regardless of aridity, by this phenomenon of morphometric eutrophy during the early history of the lake. The subsequent net increase in lake level introduced modifications in the area of the epilimnion sediments versus the total volume of the epilimnion, preventing complete overturn. Surpassing a certain depth threshold at approx. 8300 cal yr BP caused cessation of the morphometric eutrophy conditions associated with Cyclostephanos cf. andinus superblooms. After 7300 cal yr BP, the lake experienced a decrease in biosiliceous productivity and a change of state that involved a stronger dependence on precipitation variability, with a lesser contribution of diatoms to the total primary productivity. Our results show that the interpretation of lacustrine paleoproductivity records as paleoclimatic archives needs to take into account the effects of changes in the epilimnion sediment area to epilimnion volume ratio in association with lake ontogenyThe Spanish Ministry of Science and Innovation funded this research through the projects ANDESTER (BTE2001-3225), Complementary Action (BTE2001-5257-E), LAVOLTER (CGL2004-00683/BTE), GEOBILA (CGL2007-60932/BTE) and CONSOLIDER-Ingenio 2010 GRACCIE (CSD2007-00067)Peer reviewe

Diatom-inferred ecological responses of an oceanic lake system to volcanism and anthropogenic perturbations since 1290 CE

The impacts of natural- and human-induced processes on lake ecosystems in remote oceanic islands remain to be fully elucidated. These lakes are excellent candidates to analyze the importance of anthropogenic vs. natural forces driving lacustrine long-term ecological evolution from previous pristine pre-colonized conditions. Disentangling the effects of both is particularly relevant in highly active volcanic areas, where catastrophic eruptions can act as an atypical natural driver altering the lake's long-term ecological trajectories. In this paper we study past ecological changes occurring in Lake Azul (São Miguel island), a crater lake from the remote Azorean archipelago, to address which were the main causes of its long-term trophic history. We analyzed diatom assemblages, sedimentology, and bulk organic matter of sediments deposited since ca. 1290 CE, when a huge local eruption occurred. This episode drove the evolution of Lake Azul through six distinct phases, commencing with a restart of ecological succession after tephra deposition disrupted biogeochemical cycling. The alteration was so profound that the lake underwent a state of oligotrophic conditions for approx. 650 yr. Nutrients were sourced by fish-induced internal recycling and the overflow of the near Lake Verde during this period, rather than by allochthonous nutrient inputs modulated by climate variability and/or vegetation cover changes in the watershed after the official Portuguese colonization. It was only after recent artificial fertilization when the system overcame the volcanic-induced long-term resilience. This over-fertilization and a reduction in water turnover exacerbated the recent symptoms of eutrophication after 1990 CE. Contrary to other studies, Lake Azul constitutes an uncommon case of long-term resilience to trophic change induced by a cataclysmic volcanic eruption. It brings new insights into the fate of lake ecosystems which might be affected by similar events in the future

Recent global warming induces the coupling of dissimilar long-term sedimentary signatures in two adjacent volcanic lakes (Azores Archipelago, Portugal)

Paleoclimatological information derived from the study of lacustrine sedimentary records is not only biased by taphonomical processes but also by potential differences in the expression of climate variability in the sediments due to site-specific factors. Using a multiproxy approach (the elemental and isotopic compositions of organic matter, diatom assemblages, and marker pigments of algae and cyanobacteria), we study the different environmental signatures recorded since the Little Ice Age (LIA) in the sediments of two volcanic lakes located within the same caldera on S~ao Miguel Island (Azores Archipelago). Lake Santiago is a crater lake whose eutrophic status in the last stage of the LIA was linked to external nutrient inputs associated with this humid period. Its post-LIA evolution was forced by changes in the thermal structure of the water, which determined its degree of mixing and therefore nutrient availability through recycling from the hypolimnion. In contrast, the decadal to centennial limnological evolution of Lake Azul, a caldera lake 2.5 km from Lake Santiago, shows geochemical and micropaleontological signatures disconnected from climate variability until 1980/1990 CE due to its greater exposure to the fallout of tephra after a catastrophic eruption in c. 1290 CE. Only after 1980/1990 CE did a global warming scenario induce a common ecological restructuring of both lakes, involving the replacement of turbulence-loving algal taxa by species adapted to strengthening water column stratification. Nevertheless, this shift was relatively gradual in Lake Azul but more sudden in Lake Santiago, indicating that the local site-specific components still had an effect on the expression of climate change in the sediments. Despite the short history of anthropogenic pressure (compared to their continental counterparts) and the large atmospheric patterns operating over the Azores Archipelago, the sedimentary records of these two adjacent oceanic volcanic lakes reacted quite differently to climate changes

The recent volcanism of Flores Island (Azores): Stratigraphy and eruptive history of Funda Volcanic System

Monogenetic volcanoes occur in many different geotectonic settings and are usually small and short-lived. They can experience a variety of eruptive styles, even during the same eruption. In monogenetic volcanic fields, volcanism usually migrates to different locations over time, making volcanic hazard assessment very challenging. The eruptive history of a volcanic region, including the size, style, and location of previous eruptions, provides valuable information to help predict the behaviour of future volcanic events and their associated hazards. Here, we reconstruct for the first time the eruptive history of the Funda Volcanic System (FVS), one of the most recent (~3 ka) monogenetic eruptive centres of Flores Island (Azores), based on a detailed tephrostratigraphic work coupled with geochemical analysis of glass shards and radiocarbon dating. We identified at least three volcanic events at FVS spaced by time intervals of ~100 yr. The first event (3430 cal yr BP) was a small Strombolian eruption, the second event (3330 cal yr BP) started as a violent Strombolian eruption and may have ended as phreatomagmatic, and the third event (3250 cal yr BP) was exclusively phreatomagmatic. Our results demonstrate that volcanism at the FVS was more prolonged and recurrent than previously reported. Moreover, we show that the FVS experienced different eruptive styles in a short timeframe, ranging from small basaltic eruptions to violent explosive phreatomagmatic events. Such diversity of eruptive styles results in different volcanic products, which have different hazard implications. Our new results contribute to the knowledge of the recent volcanic activity of Flores Island, and we anticipate them to be of paramount importance for future volcanic hazard assessment studies