2002 / José Antonio Luque; Ramón Juliá
Lake sediment response to land-use and climate change during the last 1000 years in the oligotrophic Lake Sanabria (northwest of Iberian Peninsula)
Resumen
High-resolution sequential analysis of the upper 380 mm of a sediment core from Lake Sanabria, an oligotrophic freshwater lake in the granitic zone of the NW Iberian Peninsula, shows four lacustrine sedimentary episodes, some of which have been interpreted as the Little Ice Age (LIA). Radiometric dating of the core (C-14 Accelerator Mass Spectrometry (AMS)) gives an age of 875 AD for the oldest sedimentary episode. Subsequent variations are attributed to human influence on the catchment of Lake Sanabria: agricultural activity of the San Martín de Castañeda monastery during the Middle Ages, the breached Vega de Tera dam in January 1959, or the designation of Lake Sanabria as a natural park in 1978.
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2003 / José Antonio Luque
El Lago de Sanabria: un sensor de las oscilaciones climáticas del Atlántico Norte durante los últimos 6.000 años
Resumen
Conclusión 1) El Lago de Sanabria se encuentra situado en la vertiente Atlántica de la península Ibérica, región geográfica sometida al régimen climático de la NAO (North Atlantic Oscillation). Así, el régimen de precipitaciones en el lago se encuentra fuertemente condicionado por las fases negativas o positivas de esta oscilación climática del Atlántico Norte. La elevada tasa de renovación del agua del sistema limnológico del Lago de Sanabria determina que dicho lago sea muy SENSIBLE al RÉGIMEN DE PRECIPITACIONES de la región y, en consecuencia, a los CAMBIOS CLIMÁTICOS.
Conclusión 2) El Lago de Sanabria es un lago oligotrófico situado en una cuenca hidrográfica con substrato cristalino (rocas plutónicas y metamórficas). Estas características determinan la ausencia de Carbono (C) de origen inorgánico en el sistema deposicional del lago, es decir, todo el C presente en el sedimento se encuentra asociado a la materia orgánica. Así lo demuestra el estudio paleolimnológico realizado; los valores del Loss on ignition (LOI), determinados en el sedimento, presentan una elevada correlación positiva con los valores del Total Organic Carbon (TOC).
El resto de conclusiones de esta Tesis Doctoral y los capítulos de resultados se pueden consultar en TESISENRED.NET
2004 / Castor Muñoz Sobrino; Pablo Ramil-Rego; Luis Gómez-Orellana
Vegetation of the Lago de Sanabria area (NW Iberia) since the end of the Pleistocene: a palaeoecological reconstruction on the basis of two new pollen sequences
Resumen
Various pollen sequences from lacustrine deposits close to Lago de Sanabria (NW Iberia) have for several decades been a key source of information for palaeoenvironmental reconstructions of SW Europe, though their interpretation has been the subject of some controversy. Here we present two new pollen sequences obtained from this area, and a new palaeoenvironmental reconstruction of the region.
The available pollen data reach back to before 18,000 b.p., a period of very harsh climate with seasonal (non continuous) sedimentation and a landscape characterised by herbaceous formations dominated by Gramineae and Artemisia, and scrub formations dominated by Ericaceae and Cistaceae. Subsequently sedimentation became continuous, and various regional forest expansions are apparent. At a local level, the first forest expansion began about 12,000 b.p., when Betula pollen reached 70% followed by peaks in Pinus sylvestris-type (>80%) and Quercus robur-type (40%).
The Younger Dryas saw a retreat of woodland formations in the area around the lake, with broadleaved deciduous woodland (largely oak) retreating at mid and low altitudes, but with pine woodland persisting in more sheltered sites. The climatic improvement in the Early Holocene favoured re-expansion of woodland, dominated by Pinus sylvestris-type at higher and Quercus robur and Q. pyrenaica at lower altitudes, until anthropogenic deforestation commenced around 4,000 b.p. The disappearance of natural pine woodlands in this region is probably largely attributable to human interference.
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2006 / Ramon Julià; José Antonio Luque
Climatic changes vs. catastrophic events in lacustrine systems: A geochemical approach
Resumen
A geochemical study of oligotrophic Lake Sanabria (NW Iberian Peninsula) allows us to distinguish the geochemical response of a lacustrine system to catastrophic events and climatic events. The main major elements analysed were: K, Na, Mg, Ca, Ti, Al, Fe, Mn, P and S. The organic matter content in the sediment of Lake Sanabria is determined by the rainfall regime of the region. Periods when sediments were enriched in Ti, Mg, K, and Al are indicative of relatively wet paleoenvironmental conditions, whereas intervals when sediments were enriched in S and P (associated with organic matter) are indicative of dry conditions. A factor analysis of the geochemical data shows a progressive temporal displacements from organic rich conditions (relatively high values of S and P) to inorganic rich conditions (relatively high values of Ti, Mg, K, Al, and Na).
Maximal inorganic content occurred at the beginning of two discrete sedimentary levels: the LOL2 (cal. 1160–1230 yr AD) and the LOL1 (cal. 1510–1680 yr AD) horizons. The LOL2 and LOL1 horizons constitute two discrete events related to climatic changes during the beginning and end of the Little Ice Age, respectively. In contrast, the geochemical analysis provides evidence that the samples associated with the 1959 catastrophic event that occurred in the catchment area of Lake Sanabria do not follow the long-term geochemical evolution paths of the climate driven system. r 2006 Elsevier Ltd and INQUA. All rights reserved.
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2008 / Ramón Julià; J.A. Luque; S. Riera; J.A. Alejandro
Climatic and land use changes on the NW of Iberian Peninsula recorded in a 1,500-year record from Lake Sanabria
Resumen
This multi-proxy paleoenvironmental study from Lake Sanabria (NW Iberian Peninsula), based on pollen, diatom, and sedimentology, provides evidences of climatic oscillations attributed to the Late Roman and Medieval Warm Periods as well as the Little Ice Age (LIA). From 440 to 950 AD, the climate was characterized by mild temperatures and a Mediterranean rainfall regime, although climatic cold periods were recorded at ca. 530 and 700.
Evidence from pollen indicators of land-use suggests that grazing and farming were widespread activities. This period corresponds to the end of the Roman Warm Period and the Medieval Warm Period. The onset of new climate conditions occurred between 950 and 1100 AD, as minimum values of organic matter, arboreal pollen, diatom concentration, total nitrogen (TN), and grain size indicate low temperatures and a more regular rainfall regime. This period corresponds to the LIA and ended at 1590 AD, when lake productivity tended to recover to previous values in spite of the occurrence of cool events. Total organic carbon, TN, and diatom content covary with the temperature index for the NW Iberia, suggesting that Lake Sanabria was mainly controlled by climate before the industrial period. Since 1920 AD, lake productivity has been mainly influenced by human activity.
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2011 / Margarita Jambrina; Mayte Rico; Ana Moreno; Blas Valero
La secuencia sedimentaria del Lago de Sanabria (Zamora, Noroeste de España)
El Lago de Sanabria (42º07’30”N, 06º43’00”O; 1000 m s.n.m.) en la provincia de Zamora, es el mayor lago de origen glacial de la Península Ibérica. En este trabajo se describen los resultados del análisis sedimentológico, de susceptibilidad magnética y composicional (carbono orgánico total) de cinco sondeos largos tipo Kullenberg y 10 sondeos cortos de gravedad.
El modelo cronológico se basa en 13 dataciones de 14C AMS. La edad basal del sondeo más largo es de 26.000 años antes del presente (BP) lo que indica que la extensión máxima del glaciar del valle del Tera ocurrió antes del Último Máximo Glacial a escala global. Durante una fase de lago proglacial (Unidad 7: 26 – 14,3 mil años BP) se depositaron facies clásticas de arenas gruesas y limos grises. Facies de limos con mayor contenido orgánico depositados en un ambiente glaciolacustre (Unidad 6, 14,3 – 13,1 mil años BP), representan el comienzo de la última deglaciación.
Un aumento en el aporte clástico y la sedimentación de facies de limos arenosos (Unidad 5: 13,1 – 12,2 mil años BP) se corresponde probablemente con una fase fría durante la deglaciación. Finalmente, la sedimentación durante el Holoceno (unidades 4 a 1) está dominada por limos orgánicos con intercalaciones finas de arenas.
Algunas conclusiones importantes de este trabajo:
Los sondeos del Lago de Sanabria permiten reconstruir la secuencia de eventos durante la deglaciación y el Holoceno. La presencia de depósitos proglaciales en la cubeta oriental del Lago de Sanabria demuestra que la máxima extensión del glaciar del Tera ocurrió con anterioridad a los 26.000 años BP. Los glaciares habrían desaparecido de la cuenca de Sanabria en torno a los 14,3 mil años, aunque entre los 13 y los 11 mil años tuvo lugar una fase de avance glaciar posiblemente asociada al Dryas Reciente. Durante el Holoceno temprano y los últimos 1500 años ocurrieron dos periodos de mayor aporte de sedimentos clásticos al lago.
Durante el periodo (26 – 14,3 mil años BP) el glaciar del Tera se había retirado desde su morrena frontal favoreciendo la formación de un lago proglacial en la cubeta actual del Lago de Sanabria. Esta cronología demuestra que la máxima extensión del glaciar ocurrió con anterioridad a 26 mil años BP, es decir antes del último máximo glacial global (en torno a 20 mil años BP). Esta cronología es coherente con las fechas de máxima extensión glaciar establecidas en el Pirineo y en la Cordillera Cantábrica y aporta las primeras evidencias de una deglaciación temprana en la zona de Sanabria.
La sedimentación de limos orgánicos a partir de 14,3 mil años BP marcaría la deglaciación completa de la cuenca y el establecimiento de una dinámica sedimentaria lacustre no influenciada directamente por aportes glaciares. Sin embargo, el depósito de facies arenosas y limosas proglaciares entre 13 – 11,9 mil años BP sugiere una nueva fase de avance glaciar.
El contenido en carbono total del sedimentos se ha mantenido muy constante en el intervalo de variación 5-10%, com medidas ocasionales en torno al 15%, en los periodos en los que se mantuvo la dinámica lacustre. Se detectan importantes variaciones entre las muestras próximas a la entrada del Tera (muestra 4A) y los sondeos realizados en la cubeta oriental, en torno al punto de máxima profundidad (muestra 3A). En este punto se extrajeron testigos de sedimento de casi 9m de extensión, cuya zona basal fue datada en una edad aproximada de 25.900 (+- 200) años de antigüedad.
Se reconoce una capa de arenas y limos de unos 8-10 cm de espesor localizada a una profundidad de unos 10-12 cm de la interfase sedimento– agua. Esta capa es el resultado del depósito súbito del material arrastrado durante la avenida catastrófica producida por la rotura de la presa de Vega de Tera en el año 1959. Los sondeos tomados en la cubeta occidental sólo registran la sedimentación desde el Holoceno medio. La mayor tasa de sedimentación en esta cubeta es debida a la mayor influencia de los aportes del río Tera.
Consultar el trabajo completo:
- Geogaceta Nº 50-2 Editorial: Universidad de Huelva
NOTICIAS SOBRE ESTUDIOS DE PALEO-CLIMATOLOGÍA EN EL LAGO DE SANABRIA
La lengua blanca del glaciar
26.000 años de clima en el lago
2012 / Violeta Burriel Abadía
Magnetismo ambiental, indicador de la variabilidad climática en el entorno del Lago de Sanabria últimos 26.000 años
Resumen
Las técnicas del paleomagnetismo ambiental y de la mineralogía magnética realizadas en los sedimentos de un sondeo del Lago de Sanabria, localizado en la provincia de Zamora (noroeste de España) y en las distintas litologías de su área fuente, con su posterior comparación con otros parámetros paleoambientales, han permitido reconstruir la evolución climática del entorno del lago para los últimos 26.000 años, evaluándose las técnicas del paleomagnetismo como indicadoras de los cambios climáticos.
Se ha observado una etapa proglacial hasta los 14.250 años BP, con un periodo de avance y retroceso del glaciar hasta los 12.400 años BP, posteriormente el glaciar retrocedió por completo, con dos intervalos de erosión de los suelos, desde 12.400 hasta 9.000 años BP y desde 3.000 años BP hasta la actualidad. Se han identificado dos procesos de transformación de los minerales magnéticos, uno pedogénico y otro diagenético en el lago.
El resto de contenidos de esta Tesis Doctoral se puede consultar en ZAGUAN
2013 / Laura Rodríguez-Rodríguez; Montserrat Jiménez-Sánchez; María Jose Domínguez-Cuesta; Vincent Rinterknecht; Raimon Pallàs; Régis Braucher; Didier Bourlès; Blas Valero-Garcés
New exposure ages for the Last Glacial Cycle in the Sanabria Lake region (northwestern Spain)
Resumen
The Sanabria Lake region is located in the Trevinca Massif, a mid-latitude mountain area up to 2128 m asl in the northwest corner of the Iberian Peninsula (42oN 6oW). An ice cap glaciation took place during the Last Glacial Cycle in this massif, with an equilibrium line altitude of 1687 m for the Tera glacial outlet at its local maximum (Cowton et al., 2009). A well preserved glacial sequence occurs on an area of 45 km2 around the present Sanabria Lake (1000 m asl) and is composed by lateral and end moraines in close relationship with glaciolacustrine deposits.
This sequence shows the ice snout oscillations of the former Tera glacier during the Last Glacial Cycle and offers a good opportunity to compare radiocarbon and OSL- based chronological models with new cosmogenic isotope dates. The new dataset of 10Be exposure ages presented here for the Sanabria Lake moraines is based on measurements conducted on 23 boulders and is compared with previous radiocarbon and OSL data conducted on ice related deposits (Pérez-Alberti et al., 2011; Rodríguez-Rodríguez et al., 2011).
Our results are coherent with the available deglaciation radiocarbon chronology, and support a last deglaciation origin for the whole set of end moraines that are downstream the Sanabria Lake (19.2 – 15.7 10Be ka). Discrepancies between results of the different dating methods concern the timing of the local glacial maximum, with the cosmogenic exposure method always yielding the youngest minimum ages. As proposed to explain similar observations made elsewhere (Palacios et al., 2012), reconciling the ages from different dating methods would imply the occurrence of two glacial advances close enough in extent to generate an overlapping polygenic moraine.
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2014 / Laura Rodríguez-Rodríguez; Montserrat Jiménez-Sánchez; María José Domínguez-Cuesta; Vincent Rinterknecht; Raimon Pallàs; Didier Bourlès; Blas Valero-Garcés
A multiple dating-method approach applied to the Sanabria Lake moraine complex (NW Iberian Peninsula, SW Europe)
Resumen
New evidence in the NW region of the Iberian Peninsula (w42N 6W) of a glacial advance coeval with the global Last Glacial Maximum (LGM) of the Marine Isotope Stage 2 has been identified through a dataset of exposure ages based on 23 10Be concentration measurements carried out on boulder samples taken from a set of latero-frontal moraines. Results span the interval 19.2e15.4 10Be ka, matching the last deglaciation period when Iberia experienced the coldest and driest conditions of the last 25 ka, and are consistent with Lateglacial chronologies established in other mountain regions from SW Europe.
The extent of the LGM stade identified in this work is similar to the local maximum ice extent stade recorded and dated as prior to 33 ka using radiocarbon and optically stimulated luminescence. This work showcases how multiple-dating approaches and detailed geomorphological mapping are required to reconstruct realistic palaeoglacier evolution models.
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2015 / A. Hernández; R.M. Trigo; S. Pla‑Rabes; B.Valero‑Garcés; S. Jerez; M. Rico‑Herrero; J.C. Vega; M. Jambrina‑Enríquez; S. Giralt
Sensitivity of two Iberian lakes to North Atlantic atmospheric circulation modes
Resumen
The North Atlantic Oscillation (NAO) exerts a major influence on the climate of the North Atlantic region. However, other atmospheric circulation modes (ACMs), such as the East Atlantic (EA) and Scandinavian (SCAND) patterns, also play significant roles. The dynamics of lakes on the Iberian Peninsula are greatly controlled by climatic parameters, but their relationship with these various ACMs has not been investigated in detail. In this paper, we analyze monthly meteorological and limnological long-term datasets (1950–2011 and 1992–2011, respectively) from two lakes on the northern and central Iberian Peninsula (Sanabria and Las Madres) to develop an understanding of the seasonal sensitivity of these freshwater systems to the NAO, EA and SCAND circulation modes. The limnological variability within Lake Sanabria is primarily controlled by fluctuations in the seasonal precipitation and wind, and the primary ACMs associated with the winter limnological processes are the NAO and the SCAND modes, whereas only the EA mode appears to weakly influence processes during the summer. However, Lake Las Madres is affected by precipitation, wind and, to a lesser extent, temperature, whereas the ACMs have less influence. Therefore, we aim to show that the lakes of the Iberian Peninsula are sensitive to these ACMs. The results presented here indicate that the lake dynamics, in some cases, have a higher sensitivity to variations in the ACMs than single local meteorological variables. However, certain local features, such as geography, lake morphology and anthropic influences, are crucial to properly record the signals of these ACMs.
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2016 / G. Sánchez-López; A. Hernández; S. Pla-Rabes; R.M. Trigo; M. Toro; I. Granados; A. Saez; P. Masque: J.J. Pueyo; M.J. Rubio-Inglés; S. Giralt
Climate reconstruction for the last two millennia in central Iberia: The role of East Atlantic (EA), North Atlantic Oscillation (NAO) and their interplay over the Iberian Peninsula
Resumen
A multi-proxy characterization of the uppermost sedimentary infill of an Iberian alpine lake (Cimera, 2140 m a.s.l.) was performed to establish the climatic and environmental conditions for the Iberian Central Range (ICR) over the last two millennia. This multi-proxy characterization was used to reconstruct the intense runoff events, lake productivity and soil erosion in the lake catchment and interpret these factors in terms of temperature and precipitation variability.
The Roman Period (RP; 200 BCE e 500 CE) beginning was characterized by an alternation between cold and warm periods as indicated by shortlived oscillations of intense runoff conditions and soil erosion, although warm conditions dominated the end of the period and the Early Middle Age (EMA; 500e900 CE) onset in the ICR. A noticeable decrease in intense runoff events and a progressive decrease in soil erosion during the late EMA indicated a shift to colder temperatures. In terms of precipitation, both the RP and EMA climate periods displayed a transition from dry to wet conditions that led to a decrease in lake productivity. The Medieval Climate Anomaly (MCA; 900e1300 CE) was characterized by warm and dry conditions with frequent intense runoff episodes and increases in lake productivity and soil erosion, whereas the Little Ice Age (LIA; 1300 e1850 CE) showed the opposite characteristics.
The Industrial Era (1850e2012 CE) presented an increase in lake productivity that likely demonstrates the influence of global warming. The spatio-temporal integration of the Cimera record with other Iberian reconstructions has been used to identify the main climate drivers over this region. During the RP and EMA, NeS and EeW humidity gradients were dominant, whereas during the MCA and LIA, these gradients were not evident. These differences could be ascribed to interactions between the North Atlantic Oscillation (NAO) and East Atlantic (EA) phases. During the RP, the general warm conditions and the EeW humidity gradient indicate a dominant interplay between a negative NAO phase and a positive EA phase (NAO eEAþ), whereas the opposite conditions during the EMA indicate a NAOþ eEA interaction. The dominant warm and arid conditions during the MCA and the cold and wet conditions during the LIA indicate the interplay of the NAOþ eEAþ and NAO eEA, respectively. Furthermore, the higher solar irradiance during the RP and MCA may support the predominance of the EAþ phase, whereas the opposite scenario during the EMA and LIA may support the predominance of the EA phase, which would favour the occurrence of frequent and persistent blocking events in the Atlantic region during these periods.
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2017 / Margarita Jambrina; Clemente Recio; José Carlos Vega; Blas Valero-Garcés
Tracking climate change in oligotrophic mountain lakes: Recent hydrology and productivity synergies in Lago de Sanabria (NW Iberian Peninsula)
Resumen
Mountain lakes are particularly sensitive to global change as their oligotrophic conditions may be rapidly altered after reaching an ecological threshold, due to increasing human impact and climate change.
Sanabria Lake, the largest mountain lake in the Iberian Peninsula and with a recent history of increased human impact in its watershed, provides an opportunity to investigate recent trends in an oligotrophic, hydrologically-open mountain lake, and their relationship with climate, hydrological variability and human pressure. We conducted the first systematic and detailed survey of stable isotope compositions of Sanabria Lake and Tera River together with limnological analyses during 2009–2011. δ18O lake water and δD lake water seasonal fluctuations are strongly linked to river discharges, and follow the monthly mean isotopic composition of precipitation, which is controlled by NAO dynamics. δ13CPOM and δ13CDIC revealed higher contribution of allochthonous organic matter in winter and spring due to higher river inflow and lower primary productivity.
Increased phytoplankton biomass in late summer correlated significantly with higher pH and Chl-a, and higher nutrient input and lower river inflow. However, the small δ13CPOM seasonal amplitude underlines the stability of the oligotrophic conditions and the isotopic variation in POM and DIC reflect small seasonal fluctuations mostly as a consequence of strong through flow.
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