Suchergebnisse

21 páginas, 12 figuras, 2 tablas. ; [EN]: Four distinctive depositional subenvironments of fossil travertines and stromatolites are identified in three high-altitude (3500–4000 m above sea level) lacustrine basins: El Peinado, San Francisco (Las Coladas Salar subbasin), and Las Peladas (southern Andean Altiplano, northwestern Argentina). These late Quaternary occurrences are characterized using geomorphological, sedimentological, petrographic, and stable isotopic data. Stromatolites of cyanobacterial origin only develop in shallow lacustrine margins of El Peinado basin. In the same basin, macrophytic travertines occur both near thermal spring seepage areas along the lake margin as in situ facies and in littoral lacustrine environments up to water depths of several metres as phytoclastic travertine facies. The stromatolites and macrophytic travertines have relatively heavy δ18O compositions, suggesting initial 16O-depleted waters and (or) evaporation effects through time. Their high δ13C compositions are interpreted as a reflection of intense CO2 evasion from the thermal groundwaters feeding the lakes. Similar laminated travertine facies, with no petrographic evidence for biotic origin, occur in both Las Coladas and Las Peladas basins. Neither petrographic nor isotopic data alone can differentiate between these two cases. Besides, diagenetic overprint in Las Peladas facies precludes the use of isotopic values as original isotopic signatures. However, the depositional environmental conditions defined by the geomorphological and sedimentological features are different. Laminated aragonitic crusts in Las Coladas basin formed in a shallow, saline lake and are associated with shoreline and terrace deposits cemented by aragonite. These travertine crusts represent periods of spring, 16O-rich discharge to the lake, as suggested by the lighter oxygen isotopic compositions. In contrast, travertines from Las Peladas occur as laminated calcitic and aragonitic units intercalated at the top of fining-upward sequences composed of conglomerates, sandstones, and intraclastic limestones. Sedimentological data suggest that these travertines originated in fluvial-influenced lake margins during low lake-level episodes. ; [FR]: Quatre sous-environnements distincts de déposition de 1tr2a8v3ertins et de stromatolithes fossilifères sont identifiés dans trois bassins lacustres de haute altitude (3500–4000 mètres au-dessus du niveau de la mer), soit les bassins El Peinado, Lad Coladas et Las Peladas (Altiplano andain sud, au nord-ouest de l'Argentine). Ces occurrences du Quaternaire tardif sont caractérisées au moyen de données géomorphologiques, sédimentologiques, pétrographiques et d'isotopes stables. Les stromatolithes d'origine cyanobactérienne ne se développent que dans les marges lacustres peu profondes du bassin El Peinado. Dans ce même bassin, les travertins macrophytiques se retrouvent près de régions de sources d'infiltration thermales le long de la bordure du lac, en tant que faciès in situ, et dans des environnements lacustres littoraux jusqu'à des profondeurs de plusieurs mètres, en tant que faciès de travertins phytoclastiques. Les stromatolithes et les travertins macrophytiques ont des compositions relativement élevées en δ18O, suggérant des eaux initialement pauvres en 16O et (ou) des effets de l'évaporation dans le temps. Leurs compositions élevées en δ13C sont interprétées comme le reflet d'un échappement intense de CO2 des eaux souterraines thermales qui alimentent les lacs. Des faciès semblables de travertins laminés, sans évidence pétrographique d'une origine biotique, se retrouvent dans les bassins de Las Coladas et de Las Peladas. Ni les données pétrographiques ni les données isotopiques ne peuvent seules faire la différence entre ces deux cas. De plus, la surimpression diagénétique dans le faciès Las Peladas empêche l'utilisation de valeurs isotopiques en tant que signatures isotopiques d'origine. Toutefois, les conditions environnementales de déposition définies par les caractéristiques géomorphologiques et sédimentologiques sont différentes. Des croûtes laminées d'aragonite dans le bassin de Las Coladas forment un lac salé peu profond et elles sont associées aux dépôts de rivage et de terrasse cimentés par l'aragonite. Ces croûtes de travertin représentent les périodes de printemps, de décharge riche en 16O vers le lac, tel que suggéré par les compositions isotopiques d'oxygène plus léger. Par contre, les travertins de Las Peladas se présentent comme des unités calcitiques et aragonitiques laminées intercalées au sommet de séquences à affinement vertical ascendant composées de conglomérats, de grès et de calcaires intraclastiques. Les données sédimentologiques suggèrent que ces travertins proviennent de bordures des lacs influencés par les cours d'eau au cours d'épisodes où le niveau du lac est bas. ; Financial support for fieldwork was provided by the Universidad Nacional de Catamarca, Argentina, and by the Departamento de Relaciones Internacionales (Consejo Superior de Investigaciones Científicas, Spain). This investigation was also funded by project PB97-0882-C03-02 of the Spanish government. ; Peer reviewed

15 páginas, 5 figuras, 1 tabla.-- Artículo en prensa.-- El PDF del artículo es su versión post-print. ; We present a palaeoclimatic reconstruction of the last glacial cycle in Iberia (ca. 120,000–11,600 cal yrs BP) based on multi-proxy reconstructions from lake sediments with robust chronologies, and with a particular focus on abrupt climate changes. The selected lake sequences provide an integrated approach from northern Iberia exploring temperature conditions, humidity variations and land-sea comparisons during the most relevant climate transitions of the last glacial period. Thus, we present evidence that demonstrates: (i) cold but relatively humid conditions during the transition from MIS 5 to MIS 4, which prevailed until ca. 60,000 cal yrs BP in northern Iberia; (ii) a general tendency towards greater aridity during MIS 4 and MIS 3 (ca 60,000 to 23,500 cal yrs BP) punctuated by abrupt climate changes related to Heinrich Events (HE), (iii) a complex, highly variable climate during MIS 2 (23,500 to 14,600 cal yrs BP) with the "Mystery Interval" (MI: 18,500 to 14,600 cal yrs BP) and not the global Last Glacial Maximum (LGM: 23,000 to 19,000 cal yrs BP) as the coldest and most arid period. The last glacial transition starts in synchrony with Greenland ice records at 14,600 cal yrs BP but the temperature increase was not so abrupt in the Iberian records and the highest humidity was attained during the Allerød (GI-1a to GI-1c) and not during the Bølling (GI-1e) period. The Younger Dryas event (GS-1) is discernible in northern Iberian lake records as a cold and dry interval, although Iberian vegetation records present a geographically variable signal for this interval, perhaps related to vegetation resilience. ; The funding for this study mainly derives from LIMNOCLIBER (REN2003-09130-C02-02), LIMNOCAL (CGL2006-13327-C04-01), GRACCIE-CONSOLIDER (CSD2007-00067) and DINAMO (CGL2009- 07992) projects, provided by the Spanish Inter-Ministry Commission of Science and Technology (CICYT), and the VILLARQUEMADO (P196/2005) project from the Aragón Regional Government (DGA). A. Moreno acknowledges the funding from the "Ramón y Cajal" postdoctoral program. ; Peer reviewed

Human activities during the last millennium have shaped most of the present-day landscapes. During this time, in the southern central Pyrenees several climate periods and phases of variable human disturbance have driven varied landscape responses. In previous studies of the sediment deposits in Lake Montcortès (southern central Pyrenees) several climatic shifts (including the Medieval Climate Anomaly and the Little Ice Age), as well as forest clearance by fire, agriculture and cattle raising as the main human impacts were recorded since Medieval times. In this work we use non-pollen palynomorphs (NPP) on the same sequence to reconstruct the different human activities, with a special focus on grazing, at an average resolution of around 30 years per sample. Independent NPP proxies for fire and forest clearance were found, supporting former studies. Moreover, the NPP record shows four periods of high abundance of coprophilous fungi: 1) 830–865 CE; 2) 1120–1290 CE; 3) 1530–1795 CE; and 4) 1865–1880 CE. These four periods correspond to phases of increased livestock farming, as reported in historical documents. Comparison of pollen, historical documents, and NPP records show that the impact on landscape dynamics during the last millennium have been mostly related to variable human population density controlled by historical, political and cultural changes in the Pyrenean mountains. Moreover, the use and comparison of several independent proxies have highlighted the strength of the indicator value obtained. © 2018 Elsevier B.V. ; Financial support for this research was provided by the Spanish Ministry of Science and Technology , through the projects LIMNOCLIBER ( REN2003-09130-C02-02 ), IBERLIMNO ( CGL2005-20236-E/CLI ), LIMNOCAL ( CGL2006-13327-C04-01 ), GLOBALKARST ( CGL2009-08415 ) and GRACCIE ( CSD2007-00067 ). JPC and EM were supported by a postdoctoral contract funded by CSIC and currently hold a Juan de la Cierva – Incorporación postdoctoral contract (refs. IJCI-2015-24273 and IJCI-2015-23839). ; Peer reviewed

Modern precipitation anomalies in the Altiplano, South America, are closely linked to the strength of the South American summer monsoon (SASM), which is influenced by large-scale climate features sourced in the tropics such as the Intertropical Convergence Zone (ITCZ) and El Niño-Southern Oscillation (ENSO). However, the timing, direction, and spatial extent of precipitation changes prior to the instrumental period are still largely unknown, preventing a better understanding of the long-term drivers of the SASM and their effects over the Altiplano. Here we present a detailed pollen reconstruction from a sedimentary sequence covering the period between 4500 and 1000 cal yr BP in Lago Chungará (18 ĝ S; 4570 m a.s.l.), a high-elevation lake on the southwestern margin of the Altiplano where precipitation is delivered almost exclusively during the mature phase of the SASM over the austral summer. We distinguish three well-defined centennial-scale anomalies, with dry conditions between 4100-3300 and 1600-1000 cal yr BP and a conspicuous humid interval between 2400 and 1600 cal yr BP, which resulted from the weakening and strengthening of the SASM, respectively. Comparisons with other climate reconstructions from the Altiplano, the Atacama Desert, the tropical Andes, and the southwestern Atlantic coast reveal that - unlike modern climatological controls - past precipitation anomalies at Lago Chungará were largely decoupled from north-south shifts in the ITCZ and ENSO. A regionally coherent pattern of centennial-scale SASM variations and a significant latitudinal gradient in precipitation responses suggest the contribution of an extratropical moisture source for the SASM, with significant effects on precipitation variability in the southern Altiplano. © 2019. This work is distributed under the Creative Commons Attribution 4.0 License. ; This investigation was funded by Fondecyt grant 1181829 and International Cooperation Grant PI20150081. The 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). In addition, we acknowledge funding from the Spanish government through the MEDLANT project. BV-G is grateful for the support of project CGL2016-76215-R/BTE. IAJ was supported by Fondecyt postdoctoral grant no. 3190181. AH was supported by a Beatriu de Pinós–Marie Curie COFUND contract within the framework of the FLOODES2k (2016 BP 00023) project. This research has been supported by the Gobierno Español (MEDLANT Project). ; Peer reviewed

We investigate Lake Estanya's diatom and pollen records from the Late Glacial (LG) to the Early Holocene (EH), in order to compare limnological and vegetation responses to common climate forcing. The biotic changes recognized in this study largely agree with the hydrological evolution of the lake described previously for the same period. The diatom record shows high sensitivity to fluctuations in both lake level and salinity concentration as a consequence of climate shifts. In addition vegetation results indicate that the area could have played an important role as regional vegetation refuge. Shallow lake conditions during the Last Glacial Maximum (LGM) were punctuated by relatively deeper freshwaters between 19.3 and 18.6. cal. kyr BP and at 18.0. cal. kyr BP, as recorded by diatom shifts. A subsequent increasing aridity trend, coinciding with the Mystery Interval (MI), affected the diatom accumulation rates, which dropped to its minimum values between 17.2 and 14.7. cal. kyr BP. Particularly dry and cold conditions during the LGM and MI are supported by the largest values of steppic pollen taxa of the whole sequence, which account for up to 40%. However, relatively high values of Betula during the Heinrich Event 1 suggest a plausible regional vegetation refuge. Abrupt cooling and warming episodes within the LG triggered remarkable ecological threshold crossings in the diatom communities, especially during the stadial/interstadial episodes. At this point, the vegetation reflects the onset of warm conditions during the Bølling/Allerød with the partial substitution of Betula by Marcescent and Evergreen Quercus, which probably indicates the arrival of temperate taxa to the area and the likely migration of birch to higher altitudes. The Younger Dryas Stadial shows a complex ecological response. Diatoms are very poorly preserved, but aquatic taxa reach their highest values. An increase in Marcescent Quercus during this cold stage lends further support to the hypothesis that this is a regional vegetation refuge. Low lake levels recorded during the EH affected the development and preservation of diatom communities. A delay in the onset of humid conditions for the EH is also supported by the vegetation composition, characterized by the maximum expansion of Juniperus. © 2013 Elsevier B.V. ; 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), GLOBALKARST (CGL2009-08415), GRACCIE-CONSOLIDER (CSD2007-00067), DINAMO (CGL2009-07992), DINAMO2 (CGL2012-33063); provided by the Spanish Inter-Ministry Commission of Science and Technology (CICYT); and PIRINEOSABRUPT (PM073/2007), provided by the Diputación General de Aragón. Mario Morellón Marteles and Graciela Gil-Romera hold post-doctoral contacts funded by the "JAE-Doc/CSIC" ref.- and "Juan de la Cierva" (grant ref. JCI2009) programs respectively. Ana Pérez-Sanz has been supported by a PhD Fellowship provided by the Aragon Government. We also thank Beatriz Bueno and Aída Adsuar for lab assistance. Finally, we are grateful to Antonia Andrade Olalla for helping in initial pollen analyses and to Joan Gomà for assistance in diatom taxonomic determinations. Two referee's constructive criticism and suggestions helped improved a former version of this paper. ; Peer Reviewed

The Marboré Cirque, which is located in the southern Central Pyrenees on the north face of the Monte Perdido Peak (42°40′0″N; 0.5°0″W; 3355 m), contains a wide variety of Holocene glacial and periglacial deposits, and those from the 'Little Ice Age' ('LIA') are particularly well developed. Based on geomorphological mapping, cosmogenic exposure dating and previous studies of lacustrine sediment cores, the different deposits were dated and a sequence of geomorphological and paleoenvironmental events was established as follows: (1) The Marboré Cirque was at least partially deglaciated before 12.7 kyr BP. (2) Some ice masses are likely to have persisted in the Early Holocene, although their moraines were destroyed by the advance of glaciers during the Mid Holocene and 'LIA'. (3) A glacial expansion occurred during the Mid Holocene (5.1 ± 0.1 kyr), represented by a large push moraine that enclosed a unique ice mass at the foot of the Monte Perdido Massif. (4) A melting phase occurred at approximately 3.4 ± 0.2 and 2.5 ± 0.1 kyr (Bronze/Iron Ages) after one of the most important glacial advances of the Neoglacial period. (5) Another glacial expansion occurred during the Dark Age Cold Period (1.4–1.2 kyr), followed by a melting period during the Medieval Climate Anomaly. (6) The 'LIA' represented a clear stage of glacial expansion within the Marboré Cirque. Two different pulses of glaciation were detected, separated by a short retraction. The first pulse occurred most likely during the late 17th century or early 18th century (Maunder Minimum), whereas the second occurred between 1790 and ad 1830 (Dalton Minimum). A strong deglaciation process has affected the Marboré Cirque glaciers since the middle of the 19th century. (7) A large rock avalanche occurred during the Mid Holocene, leaving a chaotic deposit that was previously considered to be a Late Glacial moraine. © The Author(s) 2014. ; This work was supported by HORDA (ref: 83/2009), funded by the Organismo Autónomo de Parques Nacionales, and by INDICA (CGL2011-27753-C02-01 and -02) and CGL2012-35858, funded by the Spanish Ministry of Economy and Competitiveness. Financial support for the Research Group on Geomorphology and Global Change was provided by the Aragón Government and the European Social Fund (ESF-FSE). ; 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

13 pages, 2 tables, 7 figures.-- This article is licensed under a Creative Commons Attribution 4.0 International License ; Human activities have profoundly altered the global nutrient cycle through Land Use and Cover Changes (LUCCs) since the industrial revolution and especially during the Great Acceleration (1950 CE). Yet, the impact of such activities on terrestrial and aquatic ecosystems above their ecological baselines are not well known, especially when considering the response of these systems to the intensity of LUCCs on nutrient cycles. Here, we used a multiproxy approach (sedimentological, geochemical and isotopic analyses, historical records, climate data, and satellite images) to evaluate the role that LUCCs have on Nitrogen (N) cycling in a coastal mediterranean watershed system of central Chile over the last two centuries. Despite long-term anthropogenic use (agriculture, cattle grazing) in the Matanzas watershed– lake system, these LUCC appear to have had little impact on nutrient and organic matter transfer since the Spanish Colonial period. In contrast, the largest changes in N dynamics occurred in the mid-1970s, driven by the replacement of native forests and grasslands by government-subsidized tree plantations of introduced Monterey pine (Pinus radiata) and eucalyptus (Eucalyptus globulus). These LUCC had major impacts on the transfer of organic matter (which increased by 9.4%) and nutrients (as revealed by an increase in total N) to Laguna Matanzas. Our study shows that the presence of anthropogenic land use/cover changes do not necessarily alter nutrient supply and N availability per se but rather it is the magnitude and intensity of such changes that produce major impact on these processes in these mediterranean watersheds ; This research was funded by grants CONICYT PIA AFB170008 to the Institute of Ecology and Biodiversity (IEB) and FONDECYT grant 1191568 (to C.L.); Doctoral grant Becas Chile 21150224; MEDLANT (Spanish Ministry of Economy and Competitiveness, grant CGL2016-76215-R). Additional funding was provided by the Laboratorio Internacional de Cambio Global (LINCGlobal PUC-CSIC) ; Peer reviewed

The final version is available at: http://www.sciencedirect.com/science/journal/00310182 ; Although the Central Ebro Basin (Northeastern Iberian Peninsula) is both the northernmost semi-arid area in Europe and one of the regions with the largest biodiversity, it has been insufficiently studied in terms of past climate variability due to the scarcity of suitable sites for palaeoenvironmental analyses. Previous studies from ephemeral saline lakes in the area, mainly based on palynological data, show abrupt and rapid arid/humid transitions throughout the last glacial cycle highlighting a complex palaeohydrological evolution. New cores from two saline lakes (La Playa and La Salineta) in the Los Monegros area provide multi-proxy records including sedimentology, geochemistry, and pollen indicators. This study, together with a detailed and comprehensive review of the main saline records from the Central Ebro Basin, enables us tos reconstruct a comprehensive picture of the palaeoclimate evolution during the last glacial cycle. One of the main results of this study is the alternation of humid and dry phases as a characteristic of the climate evolution during the Lateglacial. Additionally, the study suggests an important role of the increased flow from the Pyrenean rivers during deglaciation in the hydrological balance of the Central Ebro Basin. It is found that the Early Holocene is the wettest period over the sequence studied contrasting with the arid Middle Holocene interval, which is frequently absent as a result of intense aeolian erosive processes. Although anthropogenic activity partially masks the climate signal from the palynological data in the uppermost part of the sequences studied, there are some sedimentological evidences for a climate change during the last 2000 years resulting in a recovery of average saline lake levels in the Central Ebro Basin. ; This work was part of the project "Arid periods in the Mediterranean area since the Last Glacial Maximum" (REN 2000-1136/CLI), and LIMNOCLIBER (REN 2003-09130-C02-02), funded by the CICYT, and the project "Environmental evolution and effects of the anthropogenic impact in the lacustrine complex of Bujaraloz–Sástago" (PO23/2001), funded by the Aragon regional government (DGA). We acknowledge the Pyrenean Institute of Ecology (CSIC) for financial support. ; Peer reviewed

We present the first reconstruction of past flood events variability in the Basque Country and Western Ebro Basin (Northern Spain) integrating instrumental hydrological datasets (last 20 years), documentary archives (last 700 years) and Lake Arreo (655 m a.s.l.) sedimentary paleoflood record (last 1400 years). In this lake, allochthonous coarse and fine detrital layers (CDL and FDL respectively) intercalated within endogenic laminites were identified and interpreted as high- and moderate-energy flood events. The interplay between human activities and hydroclimate variability has controlled the deposition of these flood layers. Gauged data for the last 20 years suggest that floods are typically generated by heavy rainfall events on saturated soils after several days of continuous rainfall. These events occur mostly during the cold season (Oct–May). The reconstructed frequency of high-magnitude flood events from the lake record is coherent with the historical cold-season floods from Basque rivers. The lowest flood frequency took place during the 6–7th and 10–15th centuries, while higher flood frequency occurred during the 8–9th centuries and the last 500 years. Fluvial and lacustrine paleoflood records and documentary evidence show abrupt and large increases in extreme flood frequency during the termination of the Little Ice Age (1830–1870 CE) and mid to late 20th century, both periods of Rapid Climate Change (RCC). The significant increase in flood frequency observed during RCC suggests that a similar pattern could be expected in the near future with the ongoing global warming. ; This project has received funding from the European Union's Horizon 2020 research and innovation programme under the Marie Sklodowska-Curie grant agreement Nº 796752 (FLOODARC). Additional support has been obtained by the Spanish Ministry of Science, Innovation and Universities (MICINN) projects LIMNOCAL (CGL 2006–13327. C04-01/CLI), MEDLANT (CGL2016-76215-R), MEROMONT (CGL2017-85682-R) and EPHIMED (CGL2017-86839-C3-1-R) (co-financed with European FEDER funds). ; Peer reviewed

Human activities have profoundly altered the global nutrient cycle through Land Use and Cover Changes (LUCCs) since the industrial revolution and especially during the Great Acceleration (1950 CE). Yet, the impact of such activities on terrestrial and aquatic ecosystems above their ecological baselines are not well known, especially when considering the response of these systems to the intensity of LUCCs on nutrient cycles. Here, we used a multiproxy approach (sedimentological, geochemical and isotopic analyses, historical records, climate data, and satellite images) to evaluate the role that LUCCs have on Nitrogen (N) cycling in a coastal mediterranean watershed system of central Chile over the last two centuries. Despite long-term anthropogenic use (agriculture, cattle grazing) in the Matanzas watershed– lake system, these LUCC appear to have had little impact on nutrient and organic matter transfer since the Spanish Colonial period. In contrast, the largest changes in N dynamics occurred in the mid-1970s, driven by the replacement of native forests and grasslands by government-subsidized tree plantations of introduced Monterey pine (Pinus radiata) and eucalyptus (Eucalyptus globulus). These LUCC had major impacts on the transfer of organic matter (which increased by 9.4%) and nutrients (as revealed by an increase in total N) to Laguna Matanzas. Our study shows that the presence of anthropogenic land use/cover changes do not necessarily alter nutrient supply and N availability per se but rather it is the magnitude and intensity of such changes that produce major impact on these processes in these mediterranean watersheds. ; This research was funded by grants CONICYT PIA AFB170008 to the Institute of Ecology and Biodiversity (IEB) and FONDECYT grant 1191568 (to C.L.); Doctoral grant Becas Chile 21150224; MEDLANT (Spanish Ministry of Economy and Competitiveness, grant CGL2016-76215-R). Additional funding was provided by the Laboratorio Internacional de Cambio Global (LINCGlobal PUC-CSIC). ; Peer reviewed

Land degradation and soil erosion are key environmental problems in Mediterranean mountains characterized by a long history of human occupation and a strong variability of hydrological regimes. To assess recent trends and evaluate climatic and anthropogenic impacts in these highly human modified watersheds we apply an historical approach combining lake sediment core multi-proxy analyses and reconstructions of past land uses to El Tobar Lake watershed, located in the Iberian Range (Central Spain). Four main periods of increased sediment delivery have been identified in the 8 m long sediment sequence by their depositional and geochemical signatures. They took place around 16th, late 18th, mid 19th and early 20th centuries as a result of large land uses changes such as forest clearing, farming and grazing during periods of increasing population. In this highly human-modified watershed, positive synergies between human impact and humid periods led to increased sediment delivery periods. During the last millennium, the lake depositional and geochemical cycles recovered quickly after each sediment delivery event, showing strong resilience of the lacustrine system to watershed disturbance. Recent changes are characterized by large hydrological affections since 1967 with the construction of a canal from a nearby reservoir and a decreased in anthropic pressure in the watershed as rural areas were abandoned. The increased fresh water influx to the lake has caused large biological changes, leading to stronger meromictic conditions and higher organic matter accumulation while terrigenous inputs have decreased. Degradation processes in Iberian Range watersheds are strongly controlled by anthropic activities (land use changes, soil erosion) but modulated by climate-related hydrological changes (water availability, flood and runoff frequency). ; We want to thank D. Schnurenberger, A. Norens and M. Shapley (Limnological Research Center) for the 2004 field expedition to collect the cores, and the Regional Government (Junta de Comunidades de Castilla–La Mancha) for logistic support. Initial Core Descriptions were performed at the CoreLab (University of Minnesota). F. Burjachs kindly provided pollen data from Lake La Cruz sequence and P. González-Sampériz helped with vegetation dynamics interpretations. S. Vicente nicely provided and elaborated the data from the weather stations. A. Navas and T. Lopez provided quickly the last-minute grain-size analysis.We also thank the numerous colleagues involved in the field campaigns to recover the cores, the LRC,LLO and the University of Pittsburgh staff, and IPE-CSIC laboratory services. Authors would also like to acknowledge the helpful comments made by reviewers. This research has been supported by the GLOBALKARST (CGL2009-08415) and GRACCIE — ConsoliderCSD2007-00067 projects funded by the Spanish Ministry of Economy and Competitiveness and by the I-LINK programme(I-LINK0510) funded by the CSIC. F. Barreiro and M. Morellón hold 'JAE-PreDoc' and 'JAE-Doc' pre and postdoctoral contracts respectively, both co-funded by C.S.I.C. and the European Social Fund. ; Peer reviewed

Lake Arreo sequence (western Ebro Basin, Spain) illustrates the century-scale climatic variability and human interactions in the landscape during the last 2.5 kyr in the low lands of northern Spain. Two sediment cores from shallow-water and deep-water environments were analyzed using sedimentological, geochemical, mineralogical, biological ¿ diatoms, pollen and charcoal content ¿ and radiometric techniques for absolute dating. The shallow-water sequence indicates a rapid evolution from an alluvial-influenced wetland prior to 7th century BC to a wetland during the Ibero-Roman Humid Period (BC 630¿AD 465) and a deeper, carbonate producing lake during the Dark Ages Cold Period (AD 465¿890). The deep-water core shows the transition from a more saline lake during the arid Medieval Climate Anomaly (MCA, AD 890¿1300) to less saline, meromictic conditions, particularly since the onset of the Little Ice Age (LIA, AD 1300¿1870). During the last 2.5 kyr, arid conditions occurred prior to 1st century AD, during the MCA and late 19th¿mid 20th century while colder temperatures and relatively more humid conditions were more frequent during the Dark Ages, particularly the 7th century AD and the LIA. The evolution of the lake also reflects changes in grazing and agricultural practices since the Roman Period associated to the exploitation of nearby salt mining. Periods of intense human pressure on the lake watershed occurred during the High Middle Ages (AD 890¿1180) and the Modern Period (AD 1600¿1830). ; Financial support for this research was provided by the Spanish Inter-Ministry of Science and Technology (CICYT), through the projects LIMNOCLIBER (REN2003-09130-C02-02), IBERLIMNO (CGL2005-20236-E/CLI), LIMNOCAL (CGL2006-13327-C04-01), GLOBALKARST (CGL2009-08415) and GRACCIE (CSD2007-00067). Additional funding was provided by the Aragonese Regional Government–Caja Inmaculada, with a travel grant to GFZ (Potsdam). Provincial Council of Alava and the Basque Water Agency provided institutional permits for fieldwork. We acknowledge Sebastián Perez, Penélope González-Sampériz and Prof. Herb Wright for their valuable comments on the manuscript. ; Peer Reviewed

18 páginas, 1 tabla, 3 figuras ; This paper reviews multi-proxy paleoclimatic reconstructions with robust age-control derived from lacustrine, dendrochronological and geomorphological records and characterizes the main environmental changes that occurred in the Southern Pyrenees during the last millennium. Warmer and relatively arid conditions prevailed during the Medieval Climate Anomaly (MCA, ca. 900–1300 AD), with a significant development of xerophytes and Mediterranean vegetation and limited deciduous tree formations (mesophytes). The Little Ice Age (LIA, 1300–1800 AD) was generally colder and moister, with an expansion of deciduous taxa and cold-adapted montane conifers. Two major phases occurred within this period: (i) a transition MCA–LIA, characterized by fluctuating, moist conditions and relatively cold temperatures (ca. 1300 and 1600 AD); and (ii) a second period, characterized by the coldest and most humid conditions, coinciding with maximum (recent) glacier advances (ca. 1600–1800 AD). Glaciers retreated after the LIA when warmer and more arid conditions dominated, interrupted by a short-living cooling episode during the late 19th to early 20th centuries. Some records suggest a response to solar activity with colder and slightly moister conditions during solar minima. Centennial-scale hydrological fluctuations are in phase with reconstructions of NAO variability, which appears to be one of the main climate mechanisms influencing rainfall variations in the region during the last millennium. ; This research has been funded by the Spanish InterMinistry of Science and Technology (CICYT), through the projects LIMNOCAL (CGL2006-13327-C04-01), GLOBALKARST (REN2003-09130-C02-02), GRACCIECONSOLIDER (CSD2007-00067), DINAMO (CGL2009-645- 07992) and CRYOMONT (CGL2010-19724). Additional support was provided by the Spanish National Parks Agency through the project HORDA (083/2009). M. Morell´on is supported by a Postdoctoral fellowship funded by the Spanish Ministry of Education and Science through FECYT (Spanish Foundation for Science and Technology), A. P´erez-Sanz is supported by a pre-doctoral fellowship funded by the Regional Aragonese Government and A. Moreno acknowledges the "Ram´on y Cajal" postdoctoral program for funding. Miguel Sevilla is acknowledged for his help with Fig. 1. We thank Gerardo Benito, William Fletcher, Lourdes L´opez-Merino and anonymous referee for their helpful comments and their criticism, which led to a considerable improvement of the manuscript. ; 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