Laura Sadori

Comparison of terrestrial and marine records of changing climate of the last 500,000 years

A broad correspondence between long pollen sequences and the deep-sea oxygen isotope record has been noted for some time, but there has been little effort to explore just how similar the two types of evidence are in terms of their overall structure on glacial-interglacial timescales and also how they may differ. These questions have profound importance both for how we view the stratigraphic record of changing climate in different regions and for our understanding of the climate system. Here we link the four longest European pollen records and derive a terrestrial sequence of vegetation events and a coherent stratigraphic scheme for the last 500,000 years. Comparison of the terrestrial and marine records shows good agreement, but it also reveals that the pollen sequences contain a higher degree of climate sensitivity than the oxygen isotope record. In addition, it suggests that neither an oxygen isotope record nor a Milankovitch-forced ice volume model may provide an appropriate template for fine-tuning the terrestrial record and that better chronologies will depend on an improved understanding of controls on sedimentation rates in individual sedimentary basins

The Postglacial record of environmental history from Lago di Pergusa, Sicily

Lacustrine sedimients from Lago di Pergusa in central Sicily provide a Postglacial record of environmental change in the Mediterranean. Magnetic susceptibility measurements, lithofacies characterization and pollen analysis were carried out anid integrated to obtain a better reconstruction of the past 11000 years. The chronoogy is provided by AMS radiocarbon dates on macrofossils or bulk sediment, and by a tephra correlative with a late-Holocene explosion from the Etna volcano. The transition period related to the present interglacial reafforestation, characterized by increasing humidity, started about 10700 years BP. The onset of the wettest conditions of the Postglacial occurred at about 9000 years BP and lasted until about 7200 years BP. Then a trend towards aridification began. leading to very dry conditions at about 3000 years BP. An unquestionable human impact on vegetation is found from 2800 years BP, although earlier land use cannot be excluded. As the climate had already induced change in the vegetation, the well-known human occupancy during the last three millennia did not produce strong effects on the environment.

The mid-Holocene climatic transition in the Mediterranean: Causes and consequences

In the Mediterranean there is often no clear time gap separating an early-Holocene period of nature-dominated environmental change from a human-dominated late-Holocene one. This mid-Holocene ‘mélange’ has been the subject of debates that have often been polarised between support for climatic causation and those favouring anthropogenic explanations for changes in vegetation, river flooding, wildfire regimes, etc. One way to shed light on the causes of mid-Holocene landscape changes is to focus on natural archives, such as lake and cave isotopes, the records of which can be unambiguously attributed to climatic forcing. These primary climate proxies can then be compared and contrasted with secondary or response variables, such as pollen and microcharcoal data, which can be the product of either climate changes or human activity or both, ideally using a multiproxy approach. In addition, synthesised primary palaeoclimate data can be compared with regional-scale climate modelling simulations. Both model output and proxy data suggest an east—west division in Mediterranean climate history. They indicate that the eastern Mediterranean experienced an increase in winter-season precipitation during the early Holocene, followed by an oscillatory decline after ~6 ka BP. In western parts of the Mediterranean, early-Holocene changes in precipitation were smaller in magnitude and less coherent spatially, and maximum increases occurred during the mid Holocene, around 6—3 ka BP, before declining to present-day values. Coincident with and partly stimulated by these climatic changes, complex societies developed across the Mediterranean, particularly in eastern parts of the basin during the Bronze Age. In consequence, by the mid-first millennium BC, human-induced land cover conversion, a drier and more variable climate, and changed fire regimes combined to establish typical sclerophyllous vegetation and landscapes in the circum-Mediterranean region.

Late Pleistocene and Holocene pollen stratigraphy at Lago di Vico, central Italy

A new pollen record from Lago di Vico (core V1) provides fundamental new information towards reconstruction of flora and vegetation history in central Italy during the last 90 000 years. The chronological framework is secured by seventeen AMS14C dates, one40Ar/39Ar date and tephra analyses. At the base of the pollen record, i.e. shortly after the40Ar/39Ar date 87 000±7000 B.P., three phases with significant expansion of trees are recorded in close succession. These forest phases, which stratigraphically correspond to St Germain II (and Ognon?) and precede pleniglacial steppe vegetation, are designated by the local names Etruria I, Etruria II and Etruria III. During the pleniglacial, a number of fluctuations of angiosperm mesophilous trees suggest the presence of tree refugia in the area. The lowest pollen concentration values are recorded at ca. 22 000 B.P. which corresponds with other pollen records from the region. The late-glacial is characterized by an expansion in the arboreal pollen curves that is less pronounced, however, than in other pollen profiles from Italy. The Holocene part of the profile is consistently dominated by deciduous oak pollen. No major changes in arboreal pollen composition are recorded but several marked and sudden declines of the tree pollen concentration suggest that the forest cover underwent dramatic changes. Clear evidence for human impact is recorded only when cultivated crops became important which dates to ca. 2630±95 B.P.

Circum-Mediterranean fire activity and climate changes during the mid-Holocene environmental transition (8500-2500 cal. BP)

A mid- to late-Holocene synthesis of fire activity from the Mediterranean basin explores the linkages among fire, climate variability and seasonality through several climatic and ecological transitions. Regional fire histories were created from 36 radiocarbon-dated sedimentary charcoal records, available from the Global Charcoal Database. During the mid-Holocene ‘Thermal Maximum’ around 7500—4500 cal. BP, charcoal records from the northern Mediterranean suggest an increase in fire while records from the southern Mediterranean indicate a decrease associated with wetter-than-present summers. A North—South partition between 40° and 43°N latitude is apparent in the central and western Mediterranean. Relatively abrupt changes in fire activity are observed c. 5500—5000 cal. BP. Records of Holocene fire activity appear sensitive to both orbitally forced climate changes and shorter-lived excursions which may be related to North Atlantic cold events, possibly modulated by an NAO-like climate mechanism. In cases where human—fire interactions have been documented, the regional coherency between fire occurrence and climate forcing suggests a dominant fire—climate relationship during the early—mid Holocene. The human influence on regional fire activity became increasingly important after c. 4000—3000 cal. BP. Results also suggest that: (1) teleconnections between the Mediterranean area and other climatic regions, in particular the North Atlantic and the low latitudes monsoon areas, influenced past fire activity; (2) gradual forcing, such as changes in orbital parameters, may have triggered abrupt shifts in fire activity; (3) regional fire reconstructions contradict former notions of a gradual (mid- to late-Holocene) aridification of the entire region due to climate and/or human activities and the importance of shorter-term events; (4) Mediterranean fire activity appears hightly sensitive to climate dynamics and thus could be considerably impacted by future climate changes.

PALYNOSTRATIGRAPHY OF THE LAST GLACIAL PERIOD IN THE VOLCANIC REGION OF CENTRAL ITALY

Abstract The summarized pollen records from the crater lakes of Valle di Castiglione, Lagaccione, Lago di Vico and Stracciacappa, in the Lazio region, are presented and correlated with each other. They outline the history of the vegetation during the last glacial period. The local name ‘Lazio Complex’ is used to describe seven main fluctuations of trees during the Pleniglacial. The succession of the main forest and non-forest periods of the last climatic cycle is generally similar to what is known in central and northern Europe, but the floristic composition and the vegetational configurations seem much more complex and sensitive to climatic changes. The history of Zelkova , Abies , Picea , Corylus , Ulmus , Carpinus betulus , Tilia and Fagus in central Italy is outlined.

Establishing a terrestrial chronological framework as a basis for biostratigraphical comparisons.

The palynological signature of interglacial deposits in the fragmentary European terrestrial record has often been used as the basis for determining their chronostratigraphical position and ultimately their age. This has placed emphasis on the presence/absence and abundance of certain characteristic taxa, but given the lack of continuous stratigraphies and independent chronologies, it has been difficult to assess the extent to which this strategy has produced reliable schemes. Here, an alternative approach is adopted whereby a chronological framework is developed for long and continuous pollen sequences from southern Europe. This in turn allows the emergence of a complete stratigraphical scheme of major vegetation events for the last 430 thousand years (ka) and the evaluation of the stage record of different taxa and their potential diagnostic value for biostratigraphical correlation. The comparison shows distinct similarities among some temperate stages of the terrestrial equivalent complexes of Marine Isotope Stages (MIS) 5 and 7 and also of MIS 9 and 11, but examination of combined records of taxa provides a possibility to differentiate between individual stages. A numerically-derived dichotomous key for the terrestrial stages based on the palynological records of 10 taxa is presented. Carpinus, Fagus, Abies, Pterocarya and Buxus emerge as the best ‘indicator pollen types’ because of their variable behaviour from one stage to the next, possibly a result of their late expansion within a temperate stage or reduced genetic variability. The analysis shows that the palynological signature of a temperate deposit can constrain the range of chronostratigraphical possibilities, but vegetation and palynological variability arising from local factors could result in difficulties in making a definite assignment at individual sites.

Mid-Holocene vegetation history of the central Mediterranean

This paper provides a synthesis of available palynological data from central Mediterranean lacustrine records, studying the causes of the important vegetation changes which occurred in the mid Holocene. They are illustrated by seven well-dated records, lakes Accesa, Mezzano, Vico, and Pergusa in Italy, Maliq, Voulkaria and Malo J. in the Balkans. A good tool for disentangling climate change and human impact is the combined interpretation of pollen percentage and concentration/influx data. Pollen concentration/influx drops are an indication of increased erosion in the catchment, mainly ascribable to forest reduction. There is no doubt that major synchronous changes could not have been caused by humans alone. Many southern European records show substantial differences between early- and late-Holocene vegetation, suggesting a general evolution from wetter to drier climatic conditions, in agreement with arid phases recognised by other, independent palaeoclimatic methods. Other pollen records show a different trend. The role of changing seasonality seems important for this region of the Mediterranean. Precipitation seasonality increased during the early to mid Holocene with winter precipitation attaining a maximum, and summer precipitation a minimum. At least three rapid climate events with changes in plant biomass are in evidence: an abrupt and short change around 8200 yr BP, another one centred around 6000 yr BP, and one soon after 3000 yr BP. From the beginning of the Bronze Age (c. 4400 yr BP in this region) human impact overlapped with a climate change, probably bipartite, towards dryness. Our results show that this aridification trend began around 8000 yr BP, and culminated around 4000 yr BP.

Human impact at Lago di Mezzano (central Italy) during the Bronze Age: a multidisciplinary approach

Abstract The purpose of this contribution is to disentangle climate forcing and human influence in the catchment of Lago di Mezzano through the interfingering of data obtained by means of archaeological, geomorphological, sedimentological and palynological approaches. A systematic archaeological survey has been undertaken and three submerged settlement areas with piles, pottery and metal tools have so far been found. The artifacts indicate that the site was inhabited, although not continuously, during the Bronze Age. Geomorphological investigations and observations in some trenches dug out on the lake shore indicate that great variations in the lakes size and strong changes in the catchment/lake surface area ratio occurred during the second half of the Holocene. Palynological, micro-charcoal, sedimentological and geochemical analyses carried out on long cores taken from the lake centre have indicated environmental changes due to either climatic influence or human impact. Even if human presence in the area has been detected during the whole Bronze Age period, the human populations caused a strong impact only in two periods centred around 3600 and 3200 cal. years BP when they settled along the lake shore, and around 3400 cal. years BP when they caused an increase in erosion leading to the beginning of the deposition of turbidites.

Mediterranean and north-African cultural adaptations to mid-Holocene environmental and climatic changes

In Mediterranean and north-African regions, cultural trajectories have shown trends sometimes coincident with climatic changes. The mid Holocene was a period of intense changes in climate, and in environmental and cultural systems. This paper reports pollen and charcoal studies from these areas aiming at presenting how impressive cultural changes frequently coincided with critical climate oscillations. Three of the main dry events of key relevance for climatic—cultural changes were selected to discuss this topic: c. 8200 cal. yr BP, c. 6000 cal. yr BP, and c. 4200 cal. yr BP. Five examples from on-site case studies were reported: (1) Wadi Teshuinat area (Fezzan, Libya, Central Sahara); (2) Benzù cave (Ceuta mountains, Spain, NW Africa); (3) La Vaquera Cave (Central System, Spain); (4) Terramara di Montale (Po Plain, Northern Italy); (5) Arslantepe (Eastern Anatolia, Turkey). Their archaeobotanical record helps to recognise and date human presence and activity in different territories. In these examples, anthropogenic signals and comparisons with other sites could be useful to distinguish climate signal from human impact in pollen records. Charcoals are evidence of human activity in cases which are not shown by pollen. Overexploitation of thinned plant resources, including overgrazing, accelerated the evolution towards xeric conditions during drying climatic phases. Humans enforced the aridity crisis and enhanced its signal in palaeoclimatic records. Sometimes, changing exploitation strategies and movements led to the onset of new cultures. Nevertheless, the onset and decline of a culture are very different critical phases, and different agents must have been involved in their occurrence. The Bronze Age marked the environment more than the Neolithic, probably because there is a relation between improvements in knowledge, cultural changes and the evolution of complex forms of land exploitation.