Results of the sensitivity experiments LOVECLIM as NetCDF files

Several abrupt climatic events during the present interglacial have been associated with catastrophic freshwater forcing, such as the events at 9.2and 8.2 ka BP (Alley et al., 1997; Barber et al., 1999; Marshall et al. 2007; Fleitmann et al. 2008). Proxy evidence suggests that similar events may have occurred during the last interglacial (e.g., Beets & Beets 2003; Beets et al., 2006), suggesting that freshwater-induced perturbations are an important mechanism for abrupt climate change in interglacial climates. In addition solar variability (Neff et al., 2001; Wang et al., 2005) and explosive volcanic eruptions (Crowley, 2000; Shindell et al., 2003; Jansen et al., 2007) can trigger centennial-scale climate events during interglacials and may thus have been responsible for a part of interglacial climate variability. We investigate the sensitivity of the present and last interglacial climates to realistic perturbations resulting from freshwater, solar or volcanic forcings. We will compare the differences between the two interglacial periods, between different climate models and evaluate the resulting using proxy archives.

Dinámica vegetal desde el tardiglaciar en la cuenca del Duero: interacciones con clima, fuego e impacto humano

La cuenca del Duero constituye un vasto territorio ibérico cuyo paisaje se encuentra actualmente muy alterado por la mano del hombre y es prácticamente imposible localizar alguna manifestación de su cubierta vegetal natural. Aunque la historia de la vegetación en los sectores central y oriental es relativamente bien conocida, en su mitad occidental los registros paleoecológicos estudiados hasta la fecha son prácticamente inexistentes. Esto hace que se desconozca la respuesta de la vegetación a las diferentes oscilaciones climáticas que se han producido desde el Último Máximo Glaciar, cuál fue el impacto de las diferentes culturas sobre el medio, cuándo se produjo una alteración profunda de la vegetación natural y cuál ha sido la historia de los incendios. Este último aspecto, el papel e importancia de los incendios, reviste un especial interés en la península Ibérica dada su situación geográfica y climática dentro de la cuenca Mediterránea, donde el fuego es un factor ecológico de primer nivel. Las distintas técnicas paleoecológicas son las más adecuadas para abordar todas estas preguntas. De este modo, los avatares de la vegetación a través del tiempo se han reconstruido mediante el análisis polínico y de macrofósiles, el impacto humano se ha trazado utilizando indicadores polínicos ligados a actividades antrópicas y esporas de hongos coprófilos, estudiándose los incendios a partir del registro de partículas microscópicas de carbón. La alta resolución temporal y taxonómica alcanzada en estos análisis, así como la amplia superficie abarcada con los yacimientos estudiados, hacen que la información obtenida sea altamente detallada y complete el conocimiento que se tiene sobre la cuenca del Duero. El Tardiglaciar se registra por primera vez en la Meseta Norte Ibérica en la secuencia de Ayoó de Vidriales, donde una vegetación esteparia prácticamente desarbolada domina durante los periodos fríos. Durante el interestadial Bølling/Allerød la expansión forestal (pinos, abedules) fue muy leve y tardía y fue interrumpida bruscamente por el Dryas Reciente. Al final del Dryas Reciente o al inicio del Holoceno se produjo una acusada y rápida expansión de los bosques. Esta dinámica sugiere que no hubo refugios glaciares importantes en esta zona de la Meseta durante el “Mystery Interval”, aparentemente el periodo más frío y seco. Los incendios fueron muy escasos, aumentando de forma muy brusca al inicio del Holoceno por el aumento de biomasa y las condiciones relativamente cálidas y secas. A partir de los registros de Ayoó y El Maíllo se consolida la importancia del gradiente oceanicidad-continentalidad en el Sistema Central y la Meseta Norte, que se manifiesta principalmente en la dominancia más prolongada de los pinares hacia el interior. Además, otra de las principales contribuciones de la presente tesis es proporcionar evidencia sobre la sucesión de distintos tipos de bosques en el noroeste de la Meseta, precisando el marco temporal en el que suceden. Así, se ha constatado que hubo un máximo desarrollo del bosque caducifolio durante el Holoceno medio en Ayoó de Vidriales y una baja incidencia del fuego que sugieren que el clima fue más húmedo que en el Holoceno inicial. El estudio de macrofósiles leñosos ha permitido detectar procesos que con el análisis polínico habrían pasado desapercibidos, como la persistencia hasta el Holoceno final de Pinus sylvestris en la sierra del Teleno y la sustitución de P. sylvestris por P. pinaster en la sierra de Francia durante el Holoceno inicial. También el estudio de los carbones procedentes de los arenales de Tierra de Pinares han proporcionado la prueba definitiva de la naturalidad de los pinares de P. pinaster. El impacto humano se detecta temprano en las secuencias del oeste de la cuenca del Duero, durante el Neolítico, aunque ha sido mucho más acusado desde la Edad del Hierro (ca 2700-2500 años cal BP). Para la detección del impacto humano temprano ha sido clave el análisis de esporas de hongos coprófilos, cuyo análisis fue incorporado en la secuencia de Ayoó de Vidriales. Una de sus principales consecuencias fue el establecimiento de comunidades de matorral (brezales, piornales) sobre amplias extensiones del occidente de la cuenca del Duero, vinculado al recrudecimiento de los regímenes de incendios. A pesar de que los incendios han sido ecológicamente importantes desde el inicio del Holoceno, los cambios introducidos por el hombre en sus regímenes sobrepasaron la resiliencia de los bosques originales, lo cual condujo a su sustitución sostenida por matorrales. ABSTRACT The Duero Basin constitutes a vast Iberian territory which is currently strongly disturbed due to human activities, so it is very difficult to find any remnant of the natural vegetation. Vegetation history for the eastern and western sectors of the Basin is relatively well-known but, in contrast, there is an almost complete lack of palaeoecological record in the western area. Consequently, there exists a profound ignorance about vegetation responses to the climatic oscillations occurred since the Last Glacial Maximum, the environmental impact of the different cultures, when a severe disturbance of the natural vegetation took place and fire history. The last question, the role and importance of fire, has a special interest in the Iberian Peninsula due to its geographic and climatic framework, the Mediterranean Basin, where fire is a major ecological factor. The diverse palaeoecological techmiques are the most suitable tools to address all these questions. Thus, vegetation shifts through time have been reconstructed using pollen and macrofossil analyses, human impact has been tracked by means of anthropogenic pollen indicators and dung fungal spores, while fire history has been studied from the quantification of microscopic charcoal particles. The high taxonomic and time resolution attained along with the extensive surface covered by the studied sites provide detailed information very useful to complete the knowledge on landscape dynamics in the Duero Basin. The Lateglacial is recorded for the first time in the Northern Iberian Plateau in the sequence from Ayoó de Vidriales, showing that almost treeless steppic vegetation dominated during the cold periods. Tree expansion (pines, birches) was late and slight during the Bølling/Allerød interstadial and was sharply interrupted by the Younger Dryas (YD) climatic reversal. By the end of the YD or the onset of the Holocene, a rapid forest expansion occurred. This forest dynamics suggests an absence of important glacial refugia for trees in this area of the Plateau during the Mystery Interval, apparently the coldest and driest period. Fires were fairly rare, increasing abruptly at the beginning of the Holocene due to the relatively warm and dry climate and the accumulation of biomass. The records from Ayoó and El Maíllo reinforce the role of the oceanicity-continentality gradient in the vegetation history of the Iberian Central Range and the Iberian Northern Plateau, reflected mainly in the longer dominance of pine forests towards inland areas. Further, another important contribution of this PhD Thesis is providing evidence on the succession of different forest types in the northestern fringe of the Plateau, specifying the chronological framework. A maximum of deciduous forest development and low fire activity have been detected in Ayoó de Vidriales during the mid-Holocene, suggesting that climate was wetter than in the early Holocene. The study of woody macrofossils has allowed detecting processes which would have remained unnoticed using pollen analysis alone, such as the persistence of Pinus sylvestris until the late Holocene in the Teleno Mountains and the early Holocene replacement of P. sylvestris with P. pinaster in the sierra de Francia range. The study of macroscopic charcoal fragments from palaeosols of the Tierra de Pinares has also provided the definitive proof of naturalness for the P. pinaster stands gorwing over this area at present. Early human impact, during the Neolithic, has been detected in the sequences from the western sector of the Duero Basin, although human disturbance has been more severe from the Iron Age onwards (ca 2700-2500 cal yr BP). The analysis of coprophilous fungi incorporated in the sequence of Ayoó de Vidriales has played a key role in recognizing that early human impact. One of the main consequences of human disturbance was the establishment of shrubland communities (heaths, brooms) over huge areas of the western Duero Basin, linked to severe and/or frequent fires. Despite fires has been ecologically important since the onset of the Holocene, human-induced changes in fire regimes have exceeded the resilience of original forests leading to a sustained replacement with shrublands.

New data on the Pleistocene of Trani (Adriatic Coast, Southern Italy)

Along the Apulian Adriatic coast, in a cliff south of Trani, a succession of three units (superimposed on one another) of marine and/or paralic environments has been recognised. The lowest unit I is characterised by calcareous/siliciclastic sands (css), micritic limestones (ml), stromatolitic and characean boundstones (scb), characean calcarenites (cc). The sedimentary environment merges from shallow marine, with low energy and temporary episodes of subaerial exposure, to lagoonal with a few exchanges with the sea. The lagoonal stromatolites (scb subunit) grew during a long period of relative stability of a high sea level in tropical climate. The unit I is truncated at the top by an erosion surface on which the unit II overlies; this consists of a basal pebble lag (bpl), silicicla - stic sands (ss), calcareous sands (cs), characean boundstones (cb), brown paleosol (bp). The sedimentary environment varies from beach to lagoon with salinity variations. Although there are indications of seismic events within the subunits cs, unit II deposition took place in a context of relative stability. The unit II is referable to a sea level highstand. Unit III, trangressive on the preceding, consists of white calcareous sands (wcs), calcareous sands and calcarenites (csc), phytoclastic calcirudite and phytohermal travertine (pcpt), mixed deposits (csl, m, k, c), sands (s) and red/brown paleosols (rbp). The sedimentation of this unit was affected by synsedimentary tectonic, attested by seismites found at several heights. Also the unit III is referable to a sea level highstand. The scientific literature has so far generally attributed to the Tyrrhenian (auct.) the deposits of Trani cliff. As part of this work some datings were performed on 10 samples, using the amino acid racemization method (AAR) applied to ostracod carapaces. Four of these samples have been rejected because they have shown in laboratory recent contamination. The numerical ages indicate that the deposits of the Trani cliff are older than MIS 5. The upper part of the unit I has been dated to 355±85 ka BP, thus allowing to assign the lowest stromatolitic subunit (scb) at the MIS 11 peak and the top of the unit I at the MIS 11-MIS 10 interval. The base of the unit II has been dated to 333±118 ka BP, thus attributing the erosion surface that bounds the units I and II to the MIS 10 lowstand and the lower part of the unit II to MIS 9.3. The upper part of the unit II has been dated to 234±35 ka BP, while three other numerical ages come from unit III: 303±35, 267±51, 247±61 ka BP. At present, the numerical ages cannot distinguish the sedimentation ages of units II and III, which are both related to the MIS 9.3- MIS 7.1 time range. However, the position of the units, superimposed one another, and their respective age, allows us to recognise a subsidence phase between MIS 11 and MIS 7, followed by an uplift phase between the MIS 7 and the present day, which led the deposits in their current position. This tectonic pattern is not in full agreement with what is described in the literature for the Apulian foreland.

Linking land cover changes in the subalpine and montane belts to changes in a torrential river.

Channel cbanges are the consequence of cbanges in sediment yield from the slopes and in the connectivity between slopes and channels bccause of distinct land use and climate inJpacts. In Ibis study, we investigated the characteristics and evolution of a short reach in the headwater of the !juez River, central-soutbem Pyrenees. Assessment of a series of sedimentar)' and geomorphic structures confirtned major cbanges to the valley boUom, mainly related to changes in the intensity of human activity. 'The oldest sedimentar)' structure is a terrace leve! located 3 10 4 m above the current alluvial plain. General deforestation, overgrazing and recwring tires in the montane belt ( 1100-1600 m a.sJ.) have led 10 increased soil erosioo and connectivity, and to tbe triggering of debris llows thal have been deposited on the fluvial tmace. Woody fragments from within the debris llows were dated using acceleraror mass spectrOmetry '"e radiocaroon tcchniques (AMS), yielding ages between 1 00 and 115 cal years BP, whicb coincides with tbe period of maximum deforestalion and human density in the Pyrenees. Depopulation and fannland abaodonment since tbe beginning of tbe 2001 oenrury has resulled in generalliJcod natural and artificial reforestation, a shrinkage of the eroded arcas aod a decline in connectivi¡y bdween slopes and the channel. 1be rnost impor1an1 consequence has been cbannel incision and oarrowing, and the development of a sedimed annour !ayer. Active sedimenl b8llSpOI1 is continui.Qg, although there has been a decrease in sed.iment yield from the slopes. Copyright O 2014 John Wiley & Soos, Ltd.

Vegetation and fire history since the last glacial maximum in an inland area of the western Mediterranean Basin (Northern Iberian Plateau, NW Spain)

We reconstructed vegetation responses to climate oscillations, fire and human activities since the last glacial maximum in inland NW Iberia, where previous paleoecological research is scarce. Extremely sparse and open vegetation composed of steppic grasslands and heathlands with scattered pioneer trees suggests very cold and dry conditions during the Oldest Dryas, unsuitable for tree survival in the surroundings of the study site. Slight woodland expansion during the Bolling/Allerod was interrupted by the Younger Dryas cooling. Pinewoods dominated for most of the early Holocene, when a marked increase in fire activity occurred. Deciduous trees expanded later reaching their maximum representation during the mid-Holocene. Enhanced fire activity and the presence of coprophilous fungi around 6400-6000 cal yr BP suggest an early human occupation around the site. However, extensive deforestation only started at 4500 calyrBP, when fire was used to clear the tree canopy. Final replacement of woodlands with heathlands, grasslands and cereal crops occurred from 2700 cal yr BP onwards due to land-use intensification. Our paleoecological record can help efforts aimed at restoring the natural vegetation by indicating which communities were dominant at the onset of heavy human impact, thus promoting the recovery of currently rare oak and alder stands.

Biomarkers and inorganic proxies in the paleoenvironmental reconstruction of mires: The importance of landscape in Las Conchas (Asturias, Northern Spain)

We determined the lipid distributions (n-alkanes, n-alkan-2-ones, n-alkanoic acids), total organic carbon (TOC), total nitrogen (TN), Ca/Mg and ash content in Las Conchas mire, a 3.2 m deep bryophyte-dominated mire in Northern Spain covering 8000 cal yr BP. Bog conditions developed in the bottom 20 cm of the profile, and good preservation of organic matter (OM) was inferred from n-alkanoic acid distribution, with the exception of the uppermost 20 cm (last ca. 200 yr). Microbial synthesis of long chain saturated fatty acids from primary OM likely produced a dominance of short chain n-alkanoic acids with a bimodal distribution, as well as the lack of correspondence between the n-alkane and n-alkanoic acid profiles in the upper 20 cm. This was accompanied by an increase in ash content, a decrease in TOC and variation in n-alkane ratios, thereby suggesting significant changes in the mire, namely drainage and transformation to a meadow, in the last ca. 200 yr. The distribution of n-alkan-2-ones indicated an increase in bacterial source from the bottom of the record to 94 cm, whereas their distribution in the upper part could be attributed mainly to plant input and/or the microbial oxidation of n-alkanes. The different n-alkane proxies showed variations, which we interpreted in terms of changes in vegetation (Sphagnum vs. non-Sphagnum dominated phases) during the last 8000 cal yr BP. C23 was the most abundant homolog throughout most of the record, thereby suggesting dominant humid conditions alternating with short drier phases. However, such humid conditions were not linked to paleoclimatic variation but rather to geomorphological characteristics: Las Conchas mire, at the base of the Cuera Range, receives continuous runoff—even during drier periods—which is not necessarily accompanied by additional mineral input to peat, producing the development of Sphagnum moss typical of waterlogged ecotopes and damp habitats. Thus, although geochemical proxies indicated an ombrotrophic regime in the mire, geomorphological characteristics may make a considerable contribution to environmental conditions.