1 página. Resumen de la comunicación presentada en European Union of Geosciences XII (Niza, Francia, 6-11 abril 2003) ; Phengitic micas from some HP setting carpholite-bearing rocks in the Alpine domain have been shown to have anomalous low-K content (0–9 to 0.55 pfu.) which may in part, be explained by a pirophilitic(illitic) substitution. Preliminary EMPA analyses show that phengitic micas from Amorgos(Greece) represent one of the most extreme cases of an interlayer deficit in this set of samples, interlayer content ranges from 0.65 to 0.55 pfu. ; Peer reviewed
47 páginas, 2 tablas, 6 figuras ; A multiproxy study of sediments cores from Zoñar Lake (37º29'00''N, 4º41'22'' W, 300 m a.s.l.) supported by 11 14C AMS dates provides the first high-resolution centennial-scale reconstruction of past humidity changes in southern Spain during the last 4000 years. Arid periods occurred prior to 2.9 cal. kyr BP and during 1.3-0.6 cal. kyr BP (Medieval Climate Anomaly). The most humid period occurred during 2.6-1.6 cal. kyr BP encompassing the late Iron Age-Iberian and Roman epochs. Two humid periods of lower intensity occurred between 0.8 – 0.6 cal kyr BP (1200 – 1400 AD) and about 400 cal. yr BP (around 1600 AD) coinciding with the onset of the Little Ice Age. Humid conditions are synchronous with a decline in solar output and seem to correspond to atmospheric patterns similar to negative NAO phases. Arid conditions show better correlation with northern Africa climate evolution suggesting a possible link to subtropical dynamics. The geographic location of Zoñar Lake and the robust chronology provides an opportunity to improve our understanding of the climate evolution in mid latitudes during the Late Holocene and to evaluate subtropical and high latitude factors in Mediterranean climate evolution. ; Financial support for this study was provided by the Spanish Ministry of Science and Education (projects LIMNOCLIBER REN 2003-09130-CO2-02, IBERLIMNO CGL2004-20236-E, CALIBRE CGL2006-13327-C04/CLI and CGL-2006-2956-BOS) and Andalusian Government (PAI group RNM-328). A. Moreno acknowledges the funding from the European Commission's Sixth Framework Program (Marie Curie Outgoing International Fellowships, proposal 021673-IBERABRUPT).We thank comments and suggestions from Herb Wright, who helped with a previous version of the manuscript, Francisco Mezquita and Javier Marco for their advice on ostracod identification and José.S. Carrión and Noemí Fuentes for pollen samples preparation. We also thank Achim Brauer for his support and dedication during the varve counting. We are also very grateful to the LRC (Minnesota, USA), and particularly to Doug Schnuremberger, Mark Shapley and Anders Noren for making possible the 2004 expedition. A.C. Stevenson and an anonymous reviewer provided constructive criticisms and suggestions. ; Peer reviewed
30 páginas, 10 figuras, 4 tablas.-- El PDF del artículo es su versión post-print. ; Lake Estanya is a small (19 ha), freshwater to brackish, monomictic lake formed by the coalescence of two karstic sinkholes with maximum water depths of 12 and 20 m, located in the Pre-Pyrenean Ranges (North-eastern Spain). The lake is hydrologically closed and the water balance is controlled mostly by groundwater input and evaporation. Three main modern depositional sub-environments can be recognized as: (i) a carbonate-producing 'littoral platform'; (ii) a steep 'talus' dominated by reworking of littoral sediments and mass-wasting processes; and (iii) an 'offshore, distal area', seasonally affected by anoxia with fine-grained, clastic sediment deposition. A seismic survey identified up to 15 m thick sedimentary infill comprising: (i) a 'basal unit', seismically transparent and restricted to the depocentres of both sub-basins; (ii) an 'intermediate unit' characterized by continuous high-amplitude reflections; and (iii) an 'upper unit' with strong parallel reflectors. Several mass-wasting deposits occur in both sub-basins. Five sediment cores were analysed using sedimentological, microscopic, geochemical and physical techniques. The chronological model for the sediment sequence is based on 17 accelerator mass spectrometry 14C dates. Five depositional environments were characterized by their respective sedimentary facies associations. The depositional history of Lake Estanya during the last ca 21 kyr comprises five stages: (i) a brackish, shallow, calcite-producing lake during full glacial times (21 to 17·3 kyr bp); (ii) a saline, permanent, relatively deep lake during the late glacial (17·3 to 11·6 kyr bp); (iii) an ephemeral, saline lake and saline mudflat complex during the transition to the Holocene (11·6 to 9·4 kyr bp); (iv) a saline lake with gypsum-rich, laminated facies and abundant microbial mats punctuated by periods of more frequent flooding episodes and clastic-dominated deposition during the Holocene (9·4 to 0·8 kyr bp); and (v) a deep, freshwater to brackish lake with high clastic input during the last 800 years. Climate-driven hydrological fluctuations are the main internal control in the evolution of the lake during the last 21 kyr, affecting water salinity, lake-level changes and water stratification. However, external factors, such as karstic processes, clastic input and the occurrence of mass-flows, are also significant. The facies model defined for Lake Estanya is an essential tool for deciphering the main factors influencing lake deposition and to evaluate the most suitable proxies for lake level, climate and environmental reconstructions, and it is applicable to modern karstic lakes and to ancient lacustrine formations. ; Financial support for research was provided by the Spanish Inter-Ministry Commission of Science and Technology (CICYT), through the projects LIMNOCLIBER (REN2003-09130-C02-02), IBERLIMNO (CGL2005-20236-E/CLI), LIMNO CAL (CGL2006-13327-C04-01) and GRACCIE (CSD2007-00067). Additional funding was provided by the Instituto de Estudios Altoaragoneses (IEA).TheAragoneseRegionalGovernment–CAJA INMACULADA partially funded XRD analyses, seismic studies and XRF analyses at University of Ca´diz, ETH-Zurich, University of Geneva andMARUM Centre (University of Bremen), respectively, by means of two travel grants. M. Morello´n is supported by a PhD contract with the CONAI+D (Aragonese Scientific Council for Research and Development), A. Moreno holds a ESF – Marie Curie programme post-doctoral contract, M. Rico holds a 'Juan de la Cierva' contract from the Spanish Government and J. P. Corella holds a CONAI+D PhD fellowship. ; Peer reviewed
18 páginas, 7 figuras, 5 tablas.-- El PDF es la versión post-print del artículo. ; The multi-proxy analysis of sediment cores recovered in karstic Lake Estanya (42°02′ N, 0°32′ E; 670 m a. s. l., NE Spain), located in the transitional area between the humid Pyrenees and the semi-arid Central Ebro Basin, provides the first high-resolution, continuous sedimentary record in the region, extending back the last 21 000 years. The integration of sedimentary facies, elemental and isotopical geochemistry and biogenic silica, together with a robust age model based on 17 AMS radiocarbon dates, enables precise reconstruction of the main hydrological and environmental changes in the region during the last deglaciation. Arid conditions, represented by shallow lake levels, predominantly saline waters and reduced organic productivity occurred throughout the last glacial maximum (21–18 cal kyrs BP) and the lateglacial, reaching their maximum intensity during the period 18–14.5 cal kyrs BP (including Heinrich event 1) and the Younger Dryas (12.9–11.6 cal kyrs BP). Less saline conditions characterized the 14.5–12.6 cal kyrs BP period, suggesting higher effective moisture during the Bölling/Allerød. The onset of more humid conditions started at 9.4 cal kyrs, indicating a delayed hydrological response to the onset of the Holocene which is also documented in several sites of the Mediterranean Basin. Higher, although fluctuating, Holocene lake levels were punctuated by a mid Holocene arid period between 4.8 and 4.0 cal kyrs BP. A major lake-level rise occurred at 1.2 cal kyrs BP, conducive to the establishment of conditions similar to the present and interrupted by a last major water level drop, occurring around 800 cal yrs BP, which coincides with the Medieval Climate Anomaly. The main hydrological stages in Lake Estanya are in phase with most Western Mediterranean and North Atlantic continental and marine records, but our results also show similarities with other Iberian and northern African reconstructions, emphasizing peculiarities of palaeohydrological evolution of the Iberian Peninsula during the last deglaciation. ; This research has been funded through the projects LIMNOCLIBER (REN2003-09130-C02-02), IBERLIMNO (CGL2005-20236-E/ CLI), LIMNOCAL (CGL2006-13327-C04-01), PALEODIVERSITAS (CGL2006-02956/BOS), GRACCIE (CSD2007-00067); provided by the Spanish Inter-Ministry Commission of Science and Technology (CICYT); and PIRINEOSABRUPT (PM073/2007), provided by the Diputación General de Aragón. Additional funding for XRD analyses (Univ. of Cádiz) and geochemical analyses (EEZ-CSIC and MARUM Centre) was provided by the Aragonese Regional Government – CAJA INMACULADA by means of 2 travel grants. M. Morellón and J.P. Corella are supported by PhD contracts with the CONAIþ D (Aragonese Scientific Council for Research and Development) and A. Moreno and M. Rico hold post-doctoral contracts funded by the ESF ('Marie Curie programme') and the Spanish Ministry of Science and Innovation ('Juan de la Cierva programme'), respectively. ; Peer reviewed
Palynological, sedimentological and geochemical analyses performed on the Villarquemado paleolake sequence (987 m a.s.l, 40°30′N; 1°18′W) reveal the vegetation dynamics and climate variability in continental Iberia over the last 13,500 cal yr BP. The Lateglacial and early Holocene periods are characterized by arid conditions with a stable landscape dominated by pinewoods and steppe until ca. 7780 cal yr BP, despite sedimentological evidence for large paleohydrological fluctuations in the paleolake. The most humid phase occurred between ca. 7780 and 5000 cal yr BP and was characterized by the maximum spread of mesophytes (e.g., Betula, Corylus, Quercus faginea type), the expansion of a mixed Mediterranean oak woodland with evergreen Quercus as dominant forest communities and more frequent higher lake level periods. The return of a dense pinewood synchronous with the depletion of mesophytes characterizes the mid-late Holocene transition (ca. 5000 cal yr BP) most likely as a consequence of an increasing aridity that coincides with the reappearance of a shallow, carbonate wetland environment. The paleohydrological and vegetation evolution shows similarities with other continental Mediterranean areas of Iberia and demonstrates a marked resilience of terrestrial vegetation and gradual responses to millennial-scale climate fluctuations. Human impact is negligible until the Ibero-Roman period (ca. 2500 cal yr BP) when a major deforestation occurred in the nearby pine forest. The last 1500 years are characterized by increasing landscape management, mainly associated with grazing practices shaping the current landscape. ; The funding for the present study derives from DINAMO (CGL-BOS 2009–07992), DINAMO2 (CGL-BOS 2012–33063), IBERIAN PALEOFLORA (CGL-BOS 2012–31717) and GRACCIE-CONSOLIDER (CSD2007-00067) projects, provided by the Spanish Inter-Ministry Commission of Science and Technology (CICYT). Josu Aranbarri acknowledges the predoctoral funding provided by the Basque Country Government (ref: FI-2010-5). Ana Moreno, Graciela Gil-Romera and Mario Morellón hold post-doctoral contracts funded by "Ramon y Cajal (ref: RYC-2008-02431)", "Juan de la Cierva (ref: JCI2009-04345)" and "JAE DOC CSIC (ref: JAEDOC-2011-026)" programms, respectively. Eduardo García-Prieto is supported by a predoctoral FPI grant (BES-2010-038593). We are very greateful to Aida Adsuar, Beatriz Bueno and Raquel López-Cantero for their assistance in core sampling and laboratory procedures. Josu Aranbarri thanks collegues from the Dipartimento di Biologia Ambientale, especially Alessandra Celant, for continuous encouragement. We would also like to thank Thomas M. Cronin, Anthony C. Stevenson and an anonymous reviewer for their valuable suggestions. ; Peer reviewed
30 páginas, 9 figuras, 3 tablas.- El PDF del artículo es su versión post-print. ; A multi-proxy study of short sediment cores recovered in small, karstic Lake Estanya (42°02′ N, 0°32′ E, 670 m.a.s.l.) in the Pre-Pyrenean Ranges (NE Spain) provides a detailed record of the complex environmental, hydrological and anthropogenic interactions occurring in the area since medieval times. The integration of sedimentary facies, elemental and isotopic geochemistry, and biological proxies (diatoms, chironomids and pollen), together with a robust chronological control, provided by AMS radiocarbon dating and 210Pb and 137Cs radiometric techniques, enabled precise reconstruction of the main phases of environmental change, associated with the Medieval Warm Period (MWP), the Little Ice Age (LIA) and the industrial era. Shallow lake levels and saline conditions with poor development of littoral environments prevailed during medieval times (1150–1300 AD). Generally higher water levels and more dilute waters occurred during the LIA (1300–1850 AD), although this period shows a complex internal paleohydrological structure and is contemporaneous with a gradual increase of farming activity. Maximum lake levels and flooding of the current littoral shelf occurred during the nineteenth century, coinciding with the maximum expansion of agriculture in the area and prior to the last cold phase of the LIA. Finally, declining lake levels during the twentieth century, coinciding with a decrease in human pressure, are associated with warmer climate conditions. A strong link with solar irradiance is suggested by the coherence between periods of more positive water balance and phases of reduced solar activity. Changes in winter precipitation and dominance of NAO negative phases would be responsible for wet LIA conditions in western Mediterranean regions. The main environmental stages recorded in Lake Estanya are consistent with Western Mediterranean continental records, and show similarities with both Central and NE Iberian reconstructions, reflecting a strong climatic control of the hydrological and anthropogenic changes during the last 800 years. ; This research was funded through the projects LIMNOCAL (CGL2006-13327-C04-01), PALEODIVERSITAS (CGL2006-02956/BOS), GRACCIE (CSD2007- 00067) supported by the Spanish Inter-Ministry Commission of Science and Technology (CICYT); and PM073/2007 provided by the Diputación General de Aragón. The Aragonese Regional Government and CAJA INMACULADA provided two travel grants for the analyses carried out at Univ. of Cádiz and EEZ-CSIC (Spain), and MARUM Centre (Univ. of Bremen, Germany). M. Morellón was supported by a PhD contract with the CONAI + D (Aragonese Scientific Council for Research and Development). ; Peer reviewed
