Precipitation changes in the Mediterranean basin during the Holocene from terrestrial and marine pollen records: a model–data comparison

Climate evolution of the Mediterranean region during the Holocene exhibits strong spatial and temporal variability. The spatial differentiation and temporal variability, as evident from different climate proxy datasets, has remained notoriously difficult for models to reproduce. In light of this complexity, we examine the previously described evidence for (i) opposing northern and southern precipitation regimes during the Holocene across the Mediterranean basin, and (ii) an east-to-west precipitation gradient or dipole during the early Holocene, from a wet eastern Mediterranean to dry western Mediterranean. Using quantitative climate information from marine and terrestrial pollen archives, we focus on two key time intervals, the early to mid-Holocene (8000 to 6000 cal yrs BP) and the late Holocene (4000 to 2000 yrs BP), in order to test the above mentioned hypotheses on a Mediterranean-wide scale. Palynologically derived climate information is compared with the output of regional-scale climate-model simulations for the same time intervals. Quantitative pollen-based precipitation estimates were generated along a longitudinal gradient from the Alboran (West) to the Aegean Sea (East); they are derived from terrestrial pollen records from Greece, Italy and Malta as well as from pollen records obtained from marine cores. Because seasonality represents a key parameter in Mediterranean climates, special attention was given to the reconstruction of season-specific climate information, notably summer and winter precipitation. The reconstructed climatic trends corroborate a previously described north-south partition of precipitation regimes during the Holocene. During the early Holocene, relatively wet conditions occurred in the south-central and eastern Mediterranean region, while drier conditions prevailed from 45° N northwards. These patterns reversed during the late Holocene, with a wetter northern Mediterranean region and drier conditions in the east and south. More sites from the northern part of the Mediterranean basin are needed to further substantiate these observations. With regard to the existence of a west-east precipitation dipole during the Holocene, our pollen-based climate data show that the strength of this dipole is strongly linked to the seasonal parameter reconstructed: Early Holocene summers show a clear east-to-west gradient, with summer precipitation having been highest in the central and eastern Mediterranean and lowest over the western Mediterranean. In contrast, winter precipitation signals are less spatially coherent. A general drying trend occurred from the early to the late Holocene; particularly in the central and eastern Mediterranean. However, summer precipitation in the east remained above modern values, even during the late Holocene interval. Pollen-inferred precipitation estimates were compared to regional-scale climate modelling simulations based on the HadAM3 GCM coupled to the dynamic HadSM3 and the high-resolution regional HadRM3 models. Climate model outputs and pollen-inferred precipitation estimates show remarkably good overall correspondence, although many simulated patterns are of marginal statistical significance. Nevertheless, models weakly support an east to west division in summer precipitation and there are suggestions that the eastern Mediterranean experienced wetter summer and winter conditions during the early Holocene and wetter summer conditions during the late Holocene. The extent to which summer monsoonal precipitation may have existed in the southern and eastern Mediterranean during the mid-Holocene remains an outstanding question; our model, consistent with other global models, does not suggest an extension of the African monsoon into the Mediterranean. Given the difficulty in modelling future climate change in Southern Europe, more simulations based on high resolution global models and very high resolution regional downscaling, perhaps even including transient simulations, are required to fully understand the patterns of change in winter and summer circulation patterns over the Mediterranean regio

Vegetation history and climate dynamics in Malta : a Holocene perspective

Cette thèse étudie la dynamique de la végétation Holocène pour Burmarrad dans le NW Malte et fournit une reconstruction paléoclimatique quantitative à base de pollen pour cet archipel méditerranéen situé au centre. Le record de pollen donne un nouvel aperçu l'échange végétation 7280-1730 cal BP qui correspondent bien avec other régional dossiers. La reconstruction du climat fournit également forte corrélation avec les sites du sud (en dessous de 40oN) de la Méditerranée. L'interprétation suggère un paysage initialement ouvert au début du néolithique, se développer en un dense Pistacia brousse ca. 6700 calBP. Depuis environ 4450 calBP le paysage devient de nouveau ouvert, coïncidant avec le début de l'âge du bronze sur l'archipel. Cette période coïncide avec une instabilité accrue du climat (entre 4500 et 3700 calBP) qui est suivie par une diminution progressive de la disponibilité de l'humidité de l'été à la fin de l'Holocène. Durant la période romaine début de l'occupation (1972-1730 calBP) le paysage reste généralement ouvert avec une augmentation modérée de Olea. Cette augmentation correspond à des preuves archéologiques pour la production de l'huile d'olive dans la région, avec l'augmentation des taxons cultivés des cultures et des espèces rudérales associés, ainsi que d'une hausse des cas d'incendies. Cette thèse propose également une synthèse des résultats d'un autre noyau (BM1) provenant de la même zone de chalandise, ainsi que les résultats d'une étude préliminaire de la pluie de pollen de surface moderne. L'archipel fournit des indications sur la végétation, les impacts humains et les changements climatiques dans un contexte de l'île au cours de l'Holocène.This thesis investigates the Holocene vegetation dynamics for Burmarrad in north-west Malta and provides a pollen-based quantitative palaeoclimatic reconstruction for this centrally located Mediterranean archipelago. The pollen record from this site provides new insight into the vegetation changes from 7280 to 1730 cal BP which correspond well with other regional records. The climate reconstruction for the area also provides strong correlation with southern (below 40oN) Mediterranean sites. The interpretation suggests an initially open landscape during the early Neolithic, surrounding a large palaeobay, developing into a dense Pistacia scrubland ca. 6700 cal BP. From about 4450 cal BP the landscape once again becomes open, coinciding with the start of the Bronze Age on the archipelago. This period is concurrent with increased climatic instability (between 4500 and 3700 cal BP) which is followed by a gradual decrease in summer moisture availability in the late Holocene. During the early Roman occupation period (1972 to 1730 cal BP) the landscape remains generally open with a moderate increase in Olea. This increase corresponds to archaeological evidence for olive oil production in the area, along with increases in cultivated crop taxa and associated ruderal species, as well as a rise in fire events. This thesis also provides a synthesis with the results from another core (BM1) taken from the same catchment area, as well as results of a preliminary modern surface pollen rain study. The Maltese archipelago provides important insight into vegetation, human impacts and climatic changes in an island context during the Holocene

Valleys : discovering Malta & Gozo's watercourses their value to society

Commonly referred to as the Great Reed or Giant Reed, and locally as Qasba l-Kbira, Arundo donax has become a familiar sight in the Maltese islands. This resilient plant thrives in riparian habitats and has become an invasive species in many regions of the world with Mediterranean-type climates. Usually found in dense stands along stream beds, it typically grows to a height of three to six metres and can replace all other plant species for stretches of one kilometre or more. It has become dominant in many sensitive sites throughout Malta, which are already under threat due to human influence. Negative impacts resulting from this invasion include increased fire risk, removal of nutrients, the uptake of substantial quantities of water and reduced species richness and diversity in colonised habitats.peer-reviewe

Palynological images from a central Mediterranean Island during the Holocene

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Environmental history on a central Mediterranean island

Through the PaleoMed project a number of cores have been taken from key locations on the Maltese Islands with the aim of establishing various aspects related to the archipelago's historical environment. A multi-disciplinary team have been investigating a number of bodies of evidence including sediments, charcoal and shells. Through this poster I will present the results from pollen samples extracted from a section of one of the cores. The core, taken from Burmarrad, has a section that has been carbon dated to 7200-3200BP. Preliminary results from this site, one of the largest flood plains on Malta, will provide an indication of the local vegetation during this chronological window. Pollen was extracted from sediment deposits following the classical treatment method (eg Moore et al., 1990). Furthermore, identification was undertaken through the use of pollen atlases of Europe and North Africa (Reille, 1992, 1995, 1998) and Beug (2004) along with IMBE's international pollen reference collection. Pollen percentages were calculated in TILIA and the pollen percentage diagram constructed using TGView software (Grimm 2004, 2005). Current results indicate that prior to 7000BP there was a high percentage of aquatic plants, while tree and shrub counts were low. At 6900BP a large increase in Pistacia pollen is recorded, with moderate increase in Plantago (especially lanceolata), Asphodelus, Dinaflagelates and Mirco Foraminifera. At this time there is also a reduction in Cichorioideae & Charcoal in the section. A similar increase in Pistacia at around this time has also been recorded from another core in Burmarrad (Djamali et al., 2012) and in southern Sicily (Tinner et al., 2009). The date of this increase corresponds to the first recorded settlement on the Maltese Islands (circa 5500BC) as well as the climatic optimum of forest cover in the Mediterranean region (Noti et al., 2009).peer-reviewe

Vegetation history, climate dynamics and cultural change in Malta: a Holocene perspective

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Fire as a motor of rapid environmental degradation during the earliest peopling of Malta 7500 years ago

International audienceThe Holocene colonisation of islands by humans has invariably led to deep-seated changes in landscape dynamics and ecology. In particular, burning was a management tool commonly used by prehistoric societies and it acted as a major driver of environmental change, particularly from the Neolithic onwards. To assess the role of early human impacts (e.g. livestock grazing, forest clearance and the cultivation of marginal land) in shaping "pristine" island landscapes, we here present a 350-year record of fire history and erosion from Malta, straddling the earliest peopling of the island. We show that recurrent anthro-pogenic burning related to Neolithic agro-pastoral practices began ~7500 years ago, with well-defined fire-return intervals (FRI) of 15e20 years that engendered erosion and rapid environmental degradation. As early as the Neolithic, this study implies that, in sensitive insular contexts, just a few generations of human activities could rapidly degrade natural islandscapes

Vegetation dynamics during the early to mid-Holocene transition in NW Malta, human impact versus climatic forcing

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Pollen analysis of present-day striped hyaena (Hyaena hyaena) scats from central Iran: Implications for dryland paleoecology and animal paleoethology

International audienceThe striped hyena is the largest living omnivorous scavenger in SW Asia. It generally lives in semi-arid desert steppe regions, often denning in small caves, rock shelters, and burrows close to human settlements. Bone fragments of wild and domestic animals and desiccated scats are frequently found in the hyena dens. In this study, eight striped hyena desiccated scats were subjected to pollen analysis. All scats were rich in pollen and the exine was well-preserved with no visible sign of corrosion. Pollen spectra revealed interesting information on the regional and local vegetation, as well as the foraging behavior and diet of the animal. They reflected an array of different landscapes ranging from natural/semi-natural xerophytic desert steppes, agricultural fields, and grazing pastures. Some scats contained certain pollen taxa very rarely observed in wetland sediments, indicating the high potential of hyena "copropalynology"in providing detailed information on the past floristic composition of the landscape. When comparing with archeobotanical data from the area, the hyena scat assemblages show that the general physiognomy of the landscape has remained almost unchanged since the 6th millennium B.C., with only minor changes in the composition or density of the woody components of the desert steppe. As most of the Holocene fossil coprolites in archeological and paleontological sites of SW Asia would have been left by striped hyena, the study of the modern analogs of such accumulations in extant hyena dens is helpful to correctly interpret the fossil faunal assemblages to reconstruct the paleolandscapes, land-use change, and animal paleoethology

Valleys : discovering Malta & Gozo's watercourses their value to society

Contents : 1/ Introduction -- 2/ LANFRANCO, S. & BELLIA, A. F. - Hotspot of vegetation diversity in the Maltese Islands -- 3/ FENECH, N. - The importance of Malta's valleys for birds -- 4/ BUHAGIAR, K. - Transformation of the cultural landscape in the valleys of northern Malta -- 5/ FELIX, I & PORTELLI, E. - Mapping valleys for sustainable planning and management -- 6/ DEIDUN, A., SCIBBERRAS, A. & SCIBERRAS, J. - The challenge of non-indigenous species -- 7/ GAMBIN, B. & PATISSIER, R. - Influence of environmental conditions on the Great Reed invasion -- 8/ CALLEJA, E., SAPIANO, M. & CUTAJAR, A. - Strengthening the climate resilience of Wied il-Fiddien through ecological restoration -- 9/ VELLA, S. - Rehabilitation and regeneration of Wied Għajn Żejtuna -- 10/ GlossaryAn interconnected labyrinth of valleys, referred to locally as ‘widien’, meander their way through the Maltese Islands. They vary from broad, gently sloping formations, born out of tectonic movements, to narrow, deep, and steep-sided ravines that largely result from erosion. The widien are essentially seasonal watercourses, fed by runoff during the wet season and lying dry for most of the summer. There are a few exceptions, such as Wied il-Baħrija, where spring-flow supports a trickle of freshwater all year round. These valleys provide a home for different species of fauna and communities of vegetation that are found only within watercourses and their immediate vicinity. These plant communities are known as riparian flora. There are two major types of riparian flora: hydrophytes, which are species that need to be fully or partially submerged in water, and non-submerged littoral flora, which grow mainly on the banks of the watercourses. Maltese valleys also host a number of other specialist plant species, such as those that thrive in rocky environments. Throughout history, water in valley beds has attracted human settlement and agricultural activity. Malta’s valleys have long been used as a source of irrigation and drinking water, as well as convenient waste disposal sites. Other common uses include transport routes, grazing and recreation. The publication of this book, co-financed through the LIFE IP Project Optimising the Implementation of the 2nd RBMP in the Malta River Basin District (LIFE 16 IPE MT 008)1, is intended to guide the reader to discover the Maltese islands’ watercourses and their value and contribution to society. The information provided is not only to create awareness of the rich diversity of flora and fauna but also on their vulnerability, and will hopefully raise awareness to reverse negative trends. Only through education and awareness to the greater public in hand with the authorities could such gems be preserved for future generations to enjoy.peer-reviewe