Mieropaleontologieal study of an holoeene eoastal peat in the Ría de Ares (A Coruña, España)

[Resumen] El análisis de polen, diatomeas y foraminíferos de un sedimento litoral en la Ría de Ares (A Coruña, España) ha permitido interpretaciones paleoambientales comparables. Se trata de un sedimento turboso con macrorrestos vegetales. El análisis micropaleontológico de este nivel y las dataciones absolutas sitúan la formación del mismo en el período Subboreal. La lectura paleoecológica obtenida a través del estudio micropaleontológico nos permite reconstituir dos paleoambientes fundamentalmente: un medio continental vegetado y un ambiente con condiciones salobres, consecuencia del aumento del nivel del mar.[Abstract] Pollen, diatoms and foraminifera from a raised marine sediment of the Ría de Ares (A Coruña, Spain) area produced comparable paleoenvironntental interpretations. It is an organic formation with peat associated with numerous vegetal rests. The micropaleontological analysis of this level and the absolute dating, place its formation in the Subboreal periodo The paleoecological reading obtained from a micropaleontological study allows us to reconstitute two basic paleoenvironments: a vegetal continental environment and an environment with salty conditions, as a consequence of the sea level increas

Contribution to he knowledge of the holocene vegetation in the NW of the Iberian Peninsula(Galicia, Spain)

[Abstract] A paleobocanic scudy ofcwo Galician sierras, Coure! siecra and Queixa-Invernadoiro sierra is presenced here. A palynological scudy ofche Laguna Lucenza was carried ouC in che Coure! sierra. Eighc radiocarbon daces were obcained, covering che lasc 9,000 years. In che Queixa-Invernadoiro sierra a palynological scudy was carried ouc in four sequences, which are supporred by four radiocarbon daces, covering approximace!y che lasc 8,000 years. The onsec ofche Holocene is characcerized by che scrong expansion ofoak woodland following a shorr phase ofbirch foresc along wich che gradual decline of pine. Oak woodland began ro expand during che Boreal reaching a maximum ac 8,3SO±80 BP. Towards 8,800 BPCorylus began roexpand, followed by Alnus (7 ,SOO BP) and Ulmus. In che Queixa sierra chere is a local colonizacion of birch, hiding che regional predominance of oak. During che Subboreal chere is a gradual decline of arboreal pollen and Castanea appears (4,07S±7S BP). There is a clear anchropogenic deforescacion during che lasc 4,000 years. In che firsc inscance chere is a deforescacion leading ro che exiscence of open zones. The presence oflarge quancicies of microscopic carbon parricles proves che exiscence of fire. Lacer che arrival of agriculcure accencuaces che disappearance of che forescs. Neverche!ess, alcicude will condicion sensibly che appearance of caxa indicacors of agriculcural processes

Post-disturbance vegetation dynamics during the Late Pleistocene and the Holocene: An example from NW Iberia

This is the post-print version of the final paper published in Global and Planetary Change. The published article is available from the link below. Changes resulting from the publishing process, such as peer review, editing, corrections, structural formatting, and other quality control mechanisms may not be reflected in this document. Changes may have been made to this work since it was submitted for publication. Copyright @ 2012 Elsevier B.V.There is a wealth of studies dealing with the reconstruction of past environmental changes and their effects on vegetation composition in NW Iberia, but none of them have focused specifically on the post-disturbance dynamics (i.e. the type of response) of the vegetation at different space and time scales. To fill this gap, we analysed the record of pollen and non-pollen palynomorphs (NPP) of a 235-cm thick colluvial sequence spanning the last ~ 13,900 years. The aims were to detect the changes in vegetation, identify the responsible drivers and determine the type of responses to disturbance. To extract this information we applied multivariate statistical techniques (constrained cluster analysis and principal components analysis on transposed matrices, PCAtr) to the local (hydro-hygrophytes and NPP) and regional (land pollen) datasets separately. In both cases the cluster analysis resulted in eight local and regional assemblage zones, while five (local types) and four (regional types) principal components were obtained by PCAtr to explain 94.1% and 96.6% of the total variance, respectively. The main drivers identified were climate change, grazing pressure, fire events and cultivation. The vegetation showed gradual, threshold and elastic responses to these drivers, at different space (local vs. regional) and time scales, revealing a complex ecological history. Regional responses to perturbations were sometimes delayed with respect to the local response. The results also showed an ecosystem resilience, such as the persistence of open Betula-dominated vegetation community for ~ 1700 years after the onset of the Holocene, and elastic responses, such as the oak woodland to the 8200 cal yr BP dry/cold event. Our results support the notion that palaeoecological research is a valuable tool to investigate ecosystem history, their responses to perturbations and their ability to buffer them. This knowledge is critical for modelling the impact of future environmental change and to help to manage the landscape more sustainably.The Spanish Governmen

An excess Ra-226 chronology for deep-sea sediments from Saanich Inlet, British Columbia

To further explore the efficacy of 226Ra(excess) dating for deep-sea sediments, previously dated varve sediments from Saanich Inlet were investigated. Ages obtained using 226Ra(excess) are comparable to the varve ages in the upper 20-25 m of the sedimentary record, but radiometric ages for those sediments older than c. 4000 yr BP are significant underestimates. This results from major changes in sedimentation within Saanich Inlet around 4000 yr BP linked to rising sea levels, with younger sediments characterised by a higher biogenic contribution resulting from the establishment of an anoxic fjord environment. The older sediments were deposited in a shallow water inlet characterised by variable Ra mass balance and non-radiogenic losses. Therefore, while 226Ra(excess) can produce reliable dates, its application may be limited where the relative significance of authigenic and allogenic input and bottom water anoxia have been variable and where closed-system behaviour is compromised

Tectonic denudation and topographic development in the Spanish Sierra Nevada

The denudation history of the rapidly uplifting western part of the Spanish Sierra Nevada was assessed using apatite fission track (AFT) ages and 10Be analyses of bedrock and fluvial sediments. Major contrasts in the denudation history are recorded within the 27 km2 Río Torrente catchment. Upland areas are characterized by low-relief, low slope angles, and locally the preservation of shallow marine sediments, which have experienced <200 m of erosion in the last 9 Myr. However, AFT age determinations from samples collected close to the marine sediments imply >2 km of denudation since circa 4 Ma. The minimum denudation rates of 0.4 mm yr−1 derived from AFT also contrast with the slow medium-term (104 years) erosion rates (0.044 ± 0.015 mm yr−1) estimated from 10Be measurements at high elevations. The local medium-long-term contrasts in denudation rates within the high Sierra Nevada indicate that much of the unroofing occurs by tectonic denudation on flat-lying detachments. In lower elevation parts of the catchment, rapid river incision coupled to rock uplift has produced ∼1.6 km of relief, implying that the rivers and adjacent hillslopes close to the edge of the orogen are sensitive to normal-fault-driven changes in base level. However, these changes are not transmitted into the low-relief slowly eroding upland areas. Thus the core of the mountain range continues to increase in elevation until the limits of crustal strength are reached and denudation is initiated along planes of structural weakness. We propose that this form of tectonic denudation provides an effective limit to relief in young orogens

Revealing the last 13,500 years of environmental history from the multiproxy record of a mountain lake (Lago Enol, northern Iberian Peninsula)

This is the author's accepted manuscript. The final publication is available at Springer via http://dx.doi.org/10.1007/s10933-009-9387-7.We present the Holocene sequence from Lago Enol (43°16′N, 4°59′W, 1,070 m a.s.l.), Cantabrian Mountains, northern Spain. A multiproxy analysis provided comprehensive information about regional humidity and temperature changes. The analysis included sedimentological descriptions, physical properties, organic carbon and carbonate content, mineralogy and geochemical composition together with biological proxies including diatom and ostracod assemblages. A detailed pollen study enabled reconstruction of variations in vegetation cover, which were interpreted in the context of climate changes and human impact. Four distinct stages were recognized for the last 13,500 years: (1) a cold and dry episode that includes the Younger Dryas event (13,500–11,600 cal. year BP); (2) a humid and warmer period characterizing the onset of the Holocene (11,600–8,700 cal. year BP); (3) a tendency toward a drier climate during the middle Holocene (8,700–4,650 cal. year BP); and (4) a return to humid conditions following landscape modification by human activity (pastoral activities, deforestation) in the late Holocene (4,650–2,200 cal. year BP). Superimposed on relatively stable landscape conditions (e.g. maintenance of well established forests), the typical environmental variability of the southern European region is observed at this site.The Spanish Inter-Ministry Commission of Science and Technology (CICYT), the Spanish National Parks agency, the European Commission, the Spanish Ministry of Science, and the European Social Fund

Recent climatic and anthropogenic imprints on lacustrine systems in the Pyrenean Mountains inferred from minerogenic and organic clastic supply (Vicdessos valley, Pyrenees, France)

High-resolution seismic profiling has been combined with geochemical analyses of both watershed samples and five lacustrine cores retrieved from two natural lacustrine basins of glacial origin: Lake Majeur and Lake Sigriou (1630 m a.s.l. and 1995 m a.s.l., respectively, Eastern French Pyrenees). Identifying specific minerogenic and organic markers of autochthonous and allochthonous supply, data allow documenting past climatic and anthropogenic pressures. Over the past century, the lacustrine sediment of Lake Majeur has been essentially composed of algae, drastically contrasting with the natural sedimentary infill of the basin, mainly resulting from soil erosion from the mid–late Holocene. Since ad 1907, the Lake Majeur has been used for hydroelectricity production. Human-induced lake-level regulations, affecting up to 37% of the lacustrine surface, have increased by fourfold the accumulation rate of the lake and favoured water enrichment. Rubidium abundance within the lacustrine sediments of the two lakes reflects the mid–late Holocene palaeohydrology. After dam construction in ad 1907, greater quantities of rubidium found in Lake Majeur sedimentary infills indicate drier climatic periods, such as from ad 1975 to ad 1982, during which water reservoirs were particularly in demand. Inversely, before the dam was built, rubidium fluctuations were correlated with wetter conditions and hydrological events were recorded as sandy layers deposited by canyon reactivation, synchronous with European climatic deterioration phases. We notably document that the Mediaeval Climate Anomaly was interrupted by some humid periods dated c. ad 940, ad 1080, ad 1100 and ad 1250. We also date the onset of the ‘Little Ice Age’ c. ad 1360 and identify that this period was wetter after c. ad 1500

Differential human impact and vegetation history in two adjacent Pyrenean valleys in the Ariège basin, southern France, from 3000 B.P. to the present

International audienceDetailed palynological studies in two adjoining French Pyrenean valleys, complemented by the study of archives, demonstrate that under similar climatic conditions, the forest history of each valley from the Bronze Age to present time was essentially determined by socio-economical constraints, possibly modified by natural characteristics such as topography. The studies show why the expansion of fagus (beech) at c. 4000 B.P. was asynchronous on the northern slope of the Pyrenees and emphasize the effects of the human impact on the recent lowering of the tree-line

Revealing the last 13,500 years of environmental history from the multiproxy record of a mountain lake (Lago Enol, northern Iberian Peninsula)

This is the author's accepted manuscript. The final publication is available at Springer via http://dx.doi.org/10.1007/s10933-009-9387-7.We present the Holocene sequence from Lago Enol (43°16′N, 4°59′W, 1,070 m a.s.l.), Cantabrian Mountains, northern Spain. A multiproxy analysis provided comprehensive information about regional humidity and temperature changes. The analysis included sedimentological descriptions, physical properties, organic carbon and carbonate content, mineralogy and geochemical composition together with biological proxies including diatom and ostracod assemblages. A detailed pollen study enabled reconstruction of variations in vegetation cover, which were interpreted in the context of climate changes and human impact. Four distinct stages were recognized for the last 13,500 years: (1) a cold and dry episode that includes the Younger Dryas event (13,500–11,600 cal. year BP); (2) a humid and warmer period characterizing the onset of the Holocene (11,600–8,700 cal. year BP); (3) a tendency toward a drier climate during the middle Holocene (8,700–4,650 cal. year BP); and (4) a return to humid conditions following landscape modification by human activity (pastoral activities, deforestation) in the late Holocene (4,650–2,200 cal. year BP). Superimposed on relatively stable landscape conditions (e.g. maintenance of well established forests), the typical environmental variability of the southern European region is observed at this site.The Spanish Inter-Ministry Commission of Science and Technology (CICYT), the Spanish National Parks agency, the European Commission, the Spanish Ministry of Science, and the European Social Fund

Paysages, productions et collectes végétales en Limousin (Massif central occidental) de la Tène finale à la fin du Moyen Âge (100 BC-1 400AD)

Entre 1996 et 2004, plusieurs sites archéologiques du Limousin ont fait l’objet d’une analyse carpologique. Bien que le nombre de sites et de structures analysés soit modeste, près de 219     000 restes carbonisés, imbibés ou minéralisés et environ 300 taxons de plantes cultivées et sauvages ont été déterminés permettant l’élaboration d’une première synthèse pour une période allant de la Tène finale au bas Moyen Âge. Ce travail intègre également la publication de plusieurs études carpologiques de nécropoles gallo-romaines ainsi que les acquis régionaux des recherches anthracologiques, palynologiques et sédimentologiques. La synthèse sur les plantes cultivées et utilitaires met en évidence une modification des productions céréalières entre la fin de l’époque gallo-romaine et le haut Moyen Âge, caractérisée par la montée en puissance du seigle (Secale cereale). Elle rend compte aussi d’un développement de l’arboriculture à partir de l’époque gallo-romaine, puis au haut Moyen Âge, notamment en contexte urbain. Des importations ont également été mises en évidence, comme le poivre (Piper nigrum) au haut-Empire.Between 1996 and 2004 palaeobotanical studies were performed in archaeological sites of Limousin. Despite the limited number of the sites and structures studied, the richness in plant macroremains and taxa strenghthened by the use of additional palaeobotanical studies as well as anthracological, palynological, sedimentological and palaeoclimatic data allows to propose a first synthesis concerning the agricultural production between the end of La Tene and the low Middle Ages. More than 219.000 remains (carbonized, waterlogged and mineralized) and circa 300 wild and cultivated plants taxa were determined. This work emphasizes a change in the cereal production between the end of the Gallo-Roman period and the High Middle Age characterized by the increase in rye (Secale cereale) cultivation. It also shows the development of arboriculture during the Gallo-Roman period and the high Middle Ages, especially in urban area. The import of an exotic spice : pepper (Piper nigrum), is demonstrated during the High Empire